The selection of stainless steels may be based on corrosion resistance, fabrication characteristics, availability, mechanical properties in specific temperature ranges and product cost..
Trang 1• Machine tools should be rigid and in good condition Any factors that encourage chatter are undesirable
• Tools should be sharp Dull tools cause excessive work hardening of the cut surface and accentuate the difficulty in machining
• Low speeds of about 9 to 12 m/min (30 to 40 sfm) should be used High speeds are likely to create hot chips and to cause rapid tool breakdown
red-• Cobalt high-speed steel tools or tools with cemented carbide and ceramic inserts can be used The latter are preferred
• The liberal use of a good grade of sulfur-bearing cutting oil is beneficial but not essential
• In castings, holes should be formed by cores in the foundry, rather than by machining, whenever possible
• Coolants are recommended for surface grinding operations
Various sources provide statements in favor of both positive-rake and negative-rake tools and both dry cutting and liquid coolants Because high temperatures at the cutting edge are a large part of the problem, effective cooling seems desirable Negative-rake tools are likely to require more force and thus to produce more heat However, the thinner edge of a positive-rake tool is more vulnerable to heat Comparative machining data are presented in Table 17
Table 17 Feed forces required in lathe turning of austenitic manganese steels
Specimens were 31.7 mm (1.25 in.) diam bars, toughened by water quenching Roughing cuts 2.5 mm (0.098 in.) deep were taken using complex-carbide tools containing about 15% TiC + TaC (predominantly TiC) and about 7 to 10% Co New cutting edges were used for each positive or negative rake Cutting speed was 0.19 to 0.20 m/s (37 to 39 sfm)
Feed forces
Negative 7° rake Flat tool Positive 6° rake
Horizontal Vertical Horizontal Vertical Horizontal Vertical
Trang 2(b) Stainless steels suffer in comparison at this speed They are more machinable at higher speeds and permit certain operations, such as drilling of 6.4 mm (1
4-in.) diam holes, which are very difficult with austenitic manganese steel The type 304 stainless steel was cold finished
Machinability is increased by the embrittlement that develops with reheating between about 540 and 650 °C (1000 and
1200 °F) Although not usually practicable, such a treatment may be useful if the part can subsequently be properly toughened Milling usually is not considered practicable
Machinable Grade. A 20Mn-0.6C steel was developed specifically for improved machinability Table 18 gives the mechanical properties of this material Even though the yield strength was deliberately reduced from 360 MPa (52 ksi) to
a value between 240 and 310 MPa (35 and 45 ksi) to obtain improved machinability, the ultimate tensile strength exceeds
620 MPa (90 ksi), and elongation in small castings may reach 40% The heat treatment of this steel involves water quenching from 1040 °C (1900 °F) As-cast properties are lower but are probably adequate for many applications
Table 18 Typical room-temperature properties of machinable manganese steel
Tensile strength
Yield strength
Source: Abex Research Center
This nonmagnetic modified grade can be lathe turned, drilled, tapped, and threaded; even holes 6.4 mm (1
4 in.) in
diameter can be drilled and tapped in this metal In some machine shops, it is rated only slightly more difficult to drill than plain 1020 steel, and the quality of the tapped threads is considered very good Typical machining data for this steel are presented in Table 19 Wear resistance has been sacrificed for machinability, and this grade has significantly less abrasion resistance than do the various types in ASTM A 128
Table 19 Force requirements for single-point lathe turning of austenitic manganese steel
Feed force (a)
Trang 3Toughened 690 155 1310 295 0.76
As-cast 155-290 35-65 890-980 200-220 0.31-0.48
Machinable grade A (20% Mn)
Toughened 180-380 40-85 955-1000 215-225 0.33-0.57
Source: Abex Research Center
(a) Depth of cut, 3 mm (0.1 in.) on radius; feed, 0.16 mm/rev (0.0062 in./rev); turning speed, 1.35 m/s (265 ft/min); 6° positive-rake tool
Reference cited in this section
3 H.S Avery, Austenitic Manganese Steel, Metals Handbook, Vol 1, 8th ed., American Society for Metals,
1961
Austenitic Manganese Steels
Revised by D.K Subramanyam,* Ergenics Inc.; A.E Swansiger, ABC Rail Corporation; and H.S Avery, Consultant
References
1 E.C Bain, E.S Davenport, and W.S.N Waring, The Equilibrium Diagram of Iron-Manganese-Carbon
Alloys of Commercial Purity, Trans AIME, Vol 100, 1932, p 228
2 C.H Shih, B.L Averbach, and M Cohen, Work Hardening and Martensite Formation in Austenitic Manganese Alloys, Research Report, Massachusetts Institute of Technology, 1953
3 H.S Avery, Austenitic Manganese Steel, Metals Handbook, Vol 1, 8th ed., American Society for Metals,
1961
4 H.S Avery, Work Hardening in Relation to Abrasion Resistance, in Proceedings of the Symposium on Materials for the Mining Industry, published by Climax Molybdenum Company, 1974, p 43
5 Manganese Steel, Oliver and Boyd, for Hadfields Ltd., 1956
6 H.S Avery and H.J Chapin, Austenitic Manganese Steel Welding Electrodes, Weld J., Vol 33, 1954, p
459
7 F Borik and W.G Scholz, Gouging Abrasion Test for Materials Used in Ore and Rock Crushing, Part II,
J Mater., Vol 6 (No 3), Sept 1971, p 590
8 M Fujikura, Recent Developments of Austenitic Manganese Steels for Non-Magnetic and Cryogenic Applications in Japan, The Manganese Center, Paris 1984
9 D.J Schmatz, Structure and Properties of Austenitic Alloys Containing Aluminum and Silicon, Trans ASM, Vol 52, 1960, p 898
10 J Charles and A Berghezan, Nickel-Free Austenitic Steels for Cryogenic Applications: The Fe-23%
Mn-5% Al-0.2% C Alloys, Cryogenics, May 1981, p 278
11 R Wang and F.H Beck, New Stainless Steel Without Nickel or Chromium for Marine Applications, Met Prog., March 1983, p 72
12 J.C Benz and H.W Leavenworth, Jr., An Assessment of Fe-Mn-Al Alloys as Substitutes for Stainless
Steels, J Met., March 1985, p 36
13 W.J Jackson and M.W Hubbard, Steelmaking for Steelfounders, Steel Castings Research and Trade
Trang 416 P.H Adler, G.B Olson, and W.S Owen, Strain Hardening of Hadfield Manganese Steel, Metall Trans A,
Vol 17A, Oct 1986, p 1725
17 H.C Doepken, Tensile Properties of Wrought Austenitic Manganese Steel in the Temperature Range from
+100 °C to -196 °C, J Met., Trans AIME, Feb 1952, p 166
18 K.S Raghavan, A.S Sastri, and M.J Marcinkowski, Nature of the Work Hardening Behaviour in
Hadfield's Manganese Steel, Trans TSM-AIME, Vol 245, July 1969, p 1569
19 Y.N Dastur and W.C Leslie, Mechanism of Work Hardening in Hadfield Manganese Steel, Metall Trans A., Vol 12A, May 1981, p 749
20 B.K Zuidema, D.K Subramanyam, and W.C Leslie, The Effect of Aluminum on the Work Hardening
and Wear Resistance of Hadfield Manganese Steel, Metall Trans A, Vol 18A, Sept 1987, p 1629
21 Abex Research Center, Abex Corporation, unpublished research, 1981-1983
22 H.S Avery, Austenitic Manganese Steel, American Brakeshoe Company, 1949, condensed version in
Metals Handbook, American Society for Metals, 1948, p 526-534
23 T.E Norman, Eng Mining J., July, 1957, p 102
24 R Blickensderfer, B.W Madsen, and J.H Tylczak, Comparison of Several Types of Abrasive Wear Tests,
in Wear of Materials 1985, K.C Ludema, Ed., American Society of Mechanical Engineers, p 313
25 D.E Diesburg and F Borik, Optimizing Abrasion Resistance and Toughness in Steels and Irons for the
Mining Industry, in Proceedings of the Symposium on Materials for the Mining Industry, Climax
Molybdenum Company, 1974, p 15
26 U Bryggman, S Hogmark, and O Vingsbo, Abrasive Wear Studied in a Modified Impact Testing
Machine, Wear of Materials, 1979, p 292
27 "The Physical Properties of a Series of Steels, Part II," Special Report 23, Alloy Steels Research Committee, British Iron and Steel Institute, Sept 1946
28 Metals and Their Weldability, Vol 4, 7th ed., Welding Handbook, American Welding Society, 1982, p 195
Wrought Stainless Steels
Revised by S.D Washko and G Aggen, Allegheny Ludlum Steel, Division of Allegheny Ludlum Corporation
Introduction
STAINLESS STEELS are iron-base alloys containing at least 10.5% Cr Few stainless steels contain more than 30% Cr
or less than 50% Fe They achieve their stainless characteristics through the formation of an invisible and adherent chromium-rich oxide surface film This oxide forms and heals itself in the presence of oxygen Other elements added to improve particular characteristics include nickel, molybdenum, copper, titanium, aluminum, silicon, niobium, nitrogen, sulfur, and selenium Carbon is normally present in amounts ranging from less than 0.03% to over 1.0% in certain martensitic grades
The selection of stainless steels may be based on corrosion resistance, fabrication characteristics, availability, mechanical properties in specific temperature ranges and product cost However, corrosion resistance and mechanical properties are usually the most important factors in selecting a grade for a given application
Original discoveries and developments in stainless steel technology began in England and Germany about 1910 The commercial production and use of stainless steels in the United States began in the 1920s, with Allegheny, Armco, Carpenter, Crucible, Firth-Sterling, Jessop, Ludlum, Republic, Rustless, and U.S Steel being among the early producers
Trang 5Only modest tonnages of stainless steel were produced in the United States in the mid-1920s, but annual production has risen steadily since that time Even so, tonnage has never exceeded about 1.5% of total production for the steel industry Table 1 shows shipments of stainless steel over a recent 10-year period Production tonnages are listed only for U.S domestic production France, Italy, Japan, Sweden, the United Kingdom, and West Germany produce substantial tonnages
of steel, and data on production in these countries are also available However, other free-world countries do not make their figures public, and production statistics are not available from the U.S.S.R or other Communist nations, which makes it impossible to estimate accurately the total world production of stainless steel
Table 1 Total U.S shipments of stainless steel over the 10-year period from 1979 to 1988
The development of precipitation-hardenable stainless steels was spearheaded by the successful production of Stainless W
by U.S Steel in 1945 Since then, Armco, Allegheny-Ludlum, and Carpenter Technology have developed a series of precipitation-hardenable alloys
The problem of obtaining raw materials has been a real one, particularly in regard to nickel during the 1950s when civil wars raged in Africa and Asia, prime sources of nickel, and Cold War politics played a role because Eastern-bloc nations were also prime sources of the element This led to the development of a series of alloys (AISI 200 type) in which manganese and nitrogen are partially substituted for nickel These stainless steels are still produced today
Trang 6New refining techniques were adopted in the early 1970s that revolutionized stainless steel melting Most important was the argon-oxygen-decarburization (AOD) process The AOD and related processes, with different gas injections or partial pressure systems, permitted the ready removal of carbon without substantial loss of chromium to the slag Furthermore, low carbon contents were readily achieved in 18% Cr alloys when using high-carbon ferrochromium in furnace charges in place of the much more expensive low-carbon ferrochromium Major alloying elements could also be controlled more precisely, nitrogen became an easily controlled intentional alloying element, and sulfur could be reduced to exceptionally low levels when desired Oxygen could also be reduced to low levels and, when coupled with low sulfur, resulted in marked improvements in steel cleanliness
During the same period, continuous casting grew in popularity throughout the steel industry, particularly in the stainless steel segment The incentive for continuous casting was primarily economic Piping can be confined to the last segment to
be cast such that yield improvements of approximately 10% are commonly achieved Improvements in homogeneity are also attained
Over the years, stainless steels have become firmly established as materials for cooking utensils, fasteners cutlery, flatware, decorative architectural hardware, and equipment for use in chemical plants, dairy and food-processing plants, health and sanitation applications, petroleum and petrochemical plants, textile plants, and the pharmaceutical and transportation industries Some of these applications involve exposure to either elevated or cryogenic temperatures; austenitic stainless steels are well suited to either type of service Properties of stainless steels at elevated temperatures are discussed in the section "Elevated-Temperature Properties" of this article and more detailed information is available in the article "Elevated-Temperature Properties of Stainless Steels" in this Volume Properties at cryogenic temperatures are discussed in the section "Subzero-Temperature Properties" of this article
Modifications in composition are sometimes made to facilitate production For instance, basic compositions are altered to make it easier to produce stainless steel tubing and castings Similar modifications are made for the manufacture of stainless steel welding electrodes; here, combinations of electrode coating and wire composition are used to produce desired compositions in deposited weld metal
References
1 Metal Statistics: 1988, American Metal Market, Fairchild Publications, 1988
2 1988 Annual Statistical Report, American Iron and Steel Institute, 1989
Wrought Stainless Steels
Revised by S.D Washko and G Aggen, Allegheny Ludlum Steel, Division of Allegheny Ludlum Corporation
Classification of Stainless Steels
Stainless steels are commonly divided into five groups: martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, duplex (ferritic-austenitic) stainless steels, and precipitation-hardening stainless steels
Martensitic stainless steels are essentially alloys of chromium and carbon that possess a distorted body-centered cubic (bcc) crystal structure (martensitic) in the hardened condition They are ferromagnetic, hardenable by heat treatments, and are generally resistant to corrosion only to relatively mild environments Chromium content is generally
in the range of 10.5 to 18%, and carbon content may exceed 1.2% The chromium and carbon contents are balanced to ensure a martensitic structure after hardening Excess carbides may be present to increase wear resistance or to maintain cutting edges, as in the case of knife blades Elements such as niobium, silicon, tungsten, and vanadium may be added to modify the tempering response after hardening Small amounts of nickel may be added to improve corrosion resistance in some media and to improve toughness Sulfur or selenium is added to some grades to improve machinability
Ferritic stainless steels are essentially chromium containing alloys with bcc crystal structures Chromium content is usually in the range of 10.5 to 30% Some grades may contain molybdenum, silicon, aluminum, titanium, and niobium to confer particular characteristics Sulfur or selenium may be added, as in the case of the austenitic grades, to improve
Trang 7machinability The ferritic alloys are ferromagnetic They can have good ductility and formability, but high-temperature strengths are relatively poor compared to the austenitic grades Toughness may be somewhat limited at low temperatures and in heavy sections
Austenitic stainless steels have a face-centered cubic (fcc) structure This structure is attained through the liberal use
of austenitizing elements such as nickel, manganese, and nitrogen These steels are essentially nonmagnetic in the annealed condition and can be hardened only by cold working They usually possess excellent cryogenic properties and good high-temperature strength Chromium content generally varies from 16 to 26%; nickel, up to about 35%; and
manganese, up to 15% The 2xx series steels contain nitrogen, 4 to 15.5% Mn, and up to 7% Ni The 3xx types contain
larger amounts of nickel and up to 2% Mn Molybdenum, copper, silicon, aluminum, titanium, and niobium may be added
to confer certain characteristics such as halide pitting resistance or oxidation resistance Sulfur or selenium may be added
to certain grades to improve machinability
Duplex stainless steels have a mixed structure of bcc ferrite and fcc austenite The exact amount of each phase is a function of composition and heat treatment (see the article "Cast Stainless Steels" in this Volume) Most alloys are designed to contain about equal amounts of each phase in the annealed condition The principal alloying elements are chromium and nickel, but nitrogen, molybdenum, copper, silicon, and tungsten may be added to control structural balance and to impart certain corrosion-resistance characteristics
The corrosion resistance of duplex stainless steels is like that of austenitic stainless steels with similar alloying contents However, duplex stainless steels possess higher tensile and yield strengths and improved resistance to stress-corrosion cracking than their austenitic counterparts The toughness of duplex stainless steels is between that of austenitic and ferritic stainless steels
Precipitation-hardening stainless steels are chromium-nickel alloys containing precipitation-hardening elements such as copper, aluminum, or titanium Precipitation-hardening stainless steels may be either austenitic or martensitic in the annealed condition Those that are austenitic in the annealed condition are frequently transformable to martensite through conditioning heat treatments, sometimes with a subzero treatment In most cases, these stainless steels attain high strength by precipitation hardening of the martensitic structure
Standard Types. A list of standard types of stainless steels, similar to those originally published by the American Iron and Steel Institute (AISI), appears in Table 2 The criteria used to decide which types of stainless steel are standard types have been rather loosely defined but include tonnage produced during a specific period, availability (number of producers), and compositional limits Specification-writing organizations such as ASTM and SAE include these standard types in their specifications In referring to specific compositions, the term type is preferred over the term grade Some specifications establish a series of grades within a given type, which makes it possible to specify properties more precisely for a given nominal composition
Table 2 Compositions of standard stainless steels
Composition, %(a) Type UNS
Trang 88.0-0.045 0.03
302B S30215 0.15 2.00
2.0-3.0
19.0
17.0- 10.0
8.0-0.045 0.03
303 S30300 0.15 2.00 1.00
17.0-19.0
10.0
8.0-0.20 0.15 min
0.6 Mo (b)
303Se S30323 0.15 2.00 1.00
17.0-19.0
10.0
8.0-0.20 0.06 0.15 min Se
304 S30400 0.08 2.00 1.00
18.0-20.0
10.5
8.0-0.045 0.03
304L S30403 0.03 2.00 1.00
18.0-20.0
12.0
8.0-0.045 0.03
304LN S30453 0.03 2.00 1.00
18.0-20.0
12.0
8.0-0.045 0.03 0.10-0.16 N
302Cu S30430 0.08 2.00 1.00
17.0-19.0
10.0
8.0-0.045 0.03 3.0-4.0 Cu
304N S30451 0.08 2.00 1.00
18.0-20.0
10.5
8.0-0.045 0.03 0.10-0.16 N
305 S30500 0.12 2.00 1.00
17.0-19.0
13.0
10.5-0.045 0.03
308 S30800 0.08 2.00 1.00
19.0-21.0
12.0
10.0-0.045 0.03
309 S30900 0.20 2.00 1.00
22.0-24.0
15.0
12.0-0.045 0.03
309S S30908 0.08 2.00 1.00
22.0-24.0
15.0
12.0-0.045 0.03
Trang 9310 S31000 0.25 2.00 1.50
24.0-26.0
22.0
19.0-0.045 0.03
310S S31008 0.08 2.00 1.50
24.0-26.0
22.0
19.0-0.045 0.03
314 S31400 0.25 2.00
1.5-3.0
26.0
23.0- 22.0
19.0-0.045 0.03
316 S31600 0.08 2.00 1.00
16.0-18.0
14.0
10.0-0.045 0.03 2.0-3.0 Mo
316F S31620 0.08 2.00 1.00
16.0-18.0
14.0
10.0-0.20 0.10 min
10.0-0.045 0.03 2.0-3.0 Mo
316L S31603 0.03 2.00 1.00
16.0-18.0
14.0
10.0-0.045 0.03 2.0-3.0 Mo
316LN S31653 0.03 2.00 1.00
16.0-18.0
14.0
10.0-0.045 0.03 2.0-3.0 Mo; 0.10-0.16 N
316N S31651 0.08 2.00 1.00
16.0-18.0
14.0
10.0-0.045 0.03 2.0-3.0 Mo; 0.10-0.16 N
317 S31700 0.08 2.00 1.00
18.0-20.0
15.0
11.0-0.045 0.03 3.0-4.0 Mo
317L S31703 0.03 2.00 1.00
18.0-20.0
15.0
11.0-0.045 0.03 3.0-4.0 Mo
321 S32100 0.08 2.00 1.00
17.0-19.0
12.0
9.0-0.045 0.03 5 × %C min Ti
330 N08330 0.08 2.00
0.75-1.5
20.0
17.0- 37.0
34.0-0.04 0.03
347 S34700 0.08 2.00 1.00
17.0-19.0
13.0
9.0-0.045 0.03 8 × %C min - 1.0 max Nb
Trang 10348 S34800 0.08 2.00 1.00
17.0-19.0
13.0
9.0-0.045 0.03 0.2 Co; 8 × %C min - 1.0 max Nb;
0.10 Ta
384 S38400 0.08 2.00 1.00
15.0-17.0
19.0
Trang 11Duplex (ferritic-austenitic) type
329 S32900 0.20 1.00 0.75
23.0-28.0
5.00
Trang 13Fig 1 Family relationships for standard austenitic stainless steels
Trang 14Fig 2 Family relationships for standard ferritic stainless steels
Trang 15Fig 3 Family relationships for standard martensitic stainless steels
Nonstandard Types. In addition to the standard types, many proprietary stainless steels are used for specific applications Compositions of the more popular, nonstandard stainless steels are given in Table 3; some of the nonstandard grades are identified by AISI type numbers
Table 3 Compositions of nonstandard stainless steels
Composition, %(b) Designation (a) UNS
designation
Austenitic stainless steels
Trang 16Gall-Tough S20161 0.15
4.00-6.00
4.00
3.00- 18.00
15.00- 6.00
0.3- 18.5
Trang 17304BI S30424 0.08 2.00 0.75
18.00-20.00
15.00
17.0- 15.5
20.0- 12.0
10.00-0.030 0.015 3.00-4.00 Cu; 2.00-3.00 Mo
Type 317 LM S31725 0.03 2.00 1.00
18.0-20.0
17.5
13.5-0.045 0.030 4.0-5.0 Mo; 0.10 N
17-14-4 LN S31726 0.03 2.00 0.75
17.0-20.0
17.5
13.5-0.045 0.030 4.0-5.0 Mo; 0.10-0.20 N
Type 317 LN S31753 0.03 2.00 1.00
18.0-20.0
15.0
11.0-0.030 11.0-0.030 3.0-4.0 Mo; 0.10-0.22 N
Type 370 S37000
0.03-0.05
2.35
1.65- 1.0
0.5- 14.5
12.5- 16.5
17.0- 18.5
17.5-0.030 17.5-0.030
Trang 1819-9 DL S63198
0.28-0.35
1.50
0.75- 0.8
0.03- 21.0
33.00-0.03 0.03 5.00-6.70 Mo; 2.00-4.00 Cu
Sanicro 28 N08028 0.02 2.00 1.00
26.0-28.0
32.5
29.5-0.020 0.015 3.0-4.0 Mo; 0.6-1.4 Cu
AL-6X N08366 0.035 2.00 1.00
20.0-22.0
25.5
23.5-0.030 23.5-0.030 6.0-7.0 Mo
AL-6XN N08367 0.030 2.00 1.00
20.0-22.0
25.50
23.50-0.040 0.030 6.00-7.00 Mo; 0.18-0.25 N
JS-700 N08700 0.04 2.00 1.00
19.0-23.0
26.0
24.0-0.040 0.030 4.3-5.0 Mo; 8 × %C min to
0.5 max Nb; 0.5 Cu; 0.005 Pb; 0.035 S
Type 332 N08800 0.01 1.50 1.00
19.0-23.0
35.0
30.0-0.045 0.015 0.15-0.60 Ti; 0.15-0.60 Al
904L N08904 0.02 2.00 1.00
19.0-23.0
28.0
Trang 195.50-0.045 0.030 1.20-2.00 Mo; 0.14-0.20 N
DP-3 S31260 0.030 1.00 0.75
24.0-26.0
7.50
1.40- 19.00
18.00- 5.25
4.25-0.030 4.25-0.030 2.50-3.00 Mo
2205 S31803 0.030 2.00 1.00
21.0-23.0
6.50
4.50-0.030 0.020 2.50-3.50 Mo; 0.08-0.20 N
Trang 21Precipitation-hardening stainless steels
PH 14-4 Mo S14800 0.05 1.00 1.00
13.75-15.0
8.75
(a) XM designations in this column are ASTM designations for the listed alloy
(b) Single values are maximum values unless otherwise indicated
(c) Nominal compositions
(d) UNS designation has not been specified This designation appears in ASTM A 887 and merely indicates the form to be used
A cooperative study of ASTM and SAE resulted in the Unified Numbering System (UNS) for designation and identification of metals and alloys in commercial use in the United States In UNS listings, stainless steels are identified
by the letter S, followed by five digits A few stainless alloys are classified as nickel alloys in the UNS system (identification letter N) because of their high nickel and low iron (less than 50%) contents
Use of UNS numbers and AISI standard-type numbers ensures that a consumer can obtain suitable material time after time even from different producers or suppliers Nevertheless, some variation in fabrication and service characteristics can be expected, even with material obtained from a single producer
Wrought Stainless Steels
Revised by S.D Washko and G Aggen, Allegheny Ludlum Steel, Division of Allegheny Ludlum Corporation
Factors in Selection
The first and most important step toward successful use of a stainless steel is selection of a type that is appropriate for the application There are a large number of standard types that differ from one another in composition, corrosion resistance,
Trang 22physical properties, and mechanical properties; selection of the optimum type for a specific application is the key to satisfactory performance at minimum total cost
The characteristics and properties of individual types discussed in this article and elsewhere in this Volume provide some
of the information useful in steel selection For a more detailed discussion, the reader is referred to Design Guidelines for the Selection and Use of Stainless Steel, published by the Committee of Stainless Steel Producers and available through
AISI
A checklist of characteristics to be considered in selecting the proper type of stainless steel for a specific application includes:
• Corrosion resistance
• Resistance to oxidation and sulfidation
• Strength and ductility at ambient and service temperatures
• Suitability for intended fabrication techniques
• Suitability for intended cleaning procedures
• Stability of properties in service
• Toughness
• Resistance to abrasion and erosion
• Resistance to galling and seizing
• Surface finish and/or reflectivity
to determine, but actual environments are usually much more complex Tables 4 and 5 show resistance of standard types
to various common media
Table 4 Resistance of standard types of stainless steel to various classes of environments
Mild Oxidizing Reducing
Austenitic stainless steels
Trang 25Martensitic stainless steels
Trang 2617-7 PH x x x x x
An x notation indicates that the specific type may be considered for application in the corrosive environment
Table 5 Relative corrosion resistance of AISI stainless steels for different grade applications
Environment Grades(a)
Acids
Hydrochloric acid Stainless is not generally recommended except when solutions are very dilute and at room
temperature (pitting may occur)
Mixed acids There is usually no appreciable attack on type 304 or 316 as long as sufficient nitric acid is present
Nitric acid Type 304L and 430 and some higher-alloy stainless grades have been used
Phosphoric acid Type 304 is satisfactory for storing cold phosphoric acid up to 85% and for handling concentrations
up to 5% in some unit processes of manufacture Type 316 is more resistant and is generally used for storing and manufacture if the fluorine content is not too high Type 317 is somewhat more resistant than type 316 At concentrations ≤85%, the metal temperature should not exceed 100 °C (212 °F) with type 316 and slightly higher with type 317 Oxidizing ions inhibit attack
Sulfuric acid Type 304 can be used at room temperature for concentrations >80 to 90% Type 316 can be used in
contact with sulfuric acid ≤10% at temperatures ≤50 °C (120 °F) if the solutions are aerated; the attack is greater in air-free solutions Type 317 may be used at temperatures as high as 65 °C (150 °F) with ≤5% concentration The presence of other materials may markedly change the corrosion rate
As little as 500 to 2000 ppm of cupric ions make it possible to use type 304 in hot solutions of moderate concentration Other additives may have the opposite effect
Sulfurous acid Type 304 may be subject to pitting, particularly if some sulfuric acid is present Type 316 is usable at
moderate concentrations and temperatures
Organics
Acetic acid Acetic acid is seldom pure in chemical plants but generally includes numerous and varied minor
constituents Type 304 is used for a wide variety of equipment including stills, base heaters, holding tanks, heat exchangers, pipelines, valves, and pumps for concentrations ≤99% at temperatures ≤~50
°C (120 °F) Type 304 is also satisfactory if small amounts of turbidity or color pickup can be tolerated for room temperature storage of glacial acetic acid Types 316 and 317 have the broadest range of usefulness, especially if formic acid is also present or if solutions are unaerated Type 316 is used for fractionating equipment, for 30-99% concentrations where type 304 cannot be used, for storage vessels, pumps, and process equipment handling glacial acetic acid, which would be discolored
Trang 27by type 304 Type 316 is likewise applicable for parts having temperatures >50 °C (120 °F), for dilute vapors, and for high pressures Type 317 has somewhat greater corrosion resistance than type 316 under severely corrosive conditions None of the stainless steels has adequate corrosion resistance to glacial acetic acid at the boiling temperature or at superheated vapor temperatures
Aldehydes Type 304 is generally satisfactory
Amines Type 316 is usually preferred to type 304
Cellulose acetate Type 304 is satisfactory for low temperatures, but type 316 or type 317 is needed for high
temperatures
Formic acids Type 304 is generally acceptable at moderate temperatures, but type 316 is resistant to all
concentrations at temperatures up to boiling
Esters With regard to corrosion, esters are comparable to organic acids
Fatty acids Type 304 is resistant to fats and fatty acids ≤ ~150 °C (300 °F), but type 316 is needed at 150-260 °C
(300-500 °F), and type 317, at higher temperatures
Paint vehicles Type 316 may be needed if exact color and lack of contamination are important
Phthalic anhydride Type 316 is usually used for reactors, fractionating columns, traps, baffles, caps, and piping
Soaps Type 304 is used for parts such as spray towers, but type 316 may be preferred for spray nozzles and
flake-drying belts to minimize off-color product
Synthetic detergents Type 316 is used for preheat, piping, pumps, and reactors in catalytic hydrogenation of fatty acids to
give salts of sulfonated high-molecular alcohols
Tall oil (pulp and paper
industry)
Type 304 has only limited use in tall-oil distillation service High rosin acid streams can be handled by type 316L with a minimum molybdenum content of 2.75% Type 316 can also be used in the more corrosive high fatty acid streams at temperatures ≤245 °C (475 °F), but type 317 will probably be required at higher temperatures
Tar Tar distillation equipment is almost all type 316 because coal tar has a high chloride content; type 304
does not have adequate resistance to pitting
Urea Type 316L is generally required
Pharmaceuticals Type 316 is usually selected for all parts in contact with the product because of its inherent corrosion
resistance and greater assurance of product purity
Source: Ref 3
(a) The stainless steels mentioned may be considered for use in the indicated environments Additional information or corrosion expertise may be necessary prior to use in some environments; for example, some impurities may cause localized corrosion (such as chlorides causing pitting or
Trang 28stress-corrosion cracking of some grades)
General corrosion is often much less serious than localized forms such as stress-corrosion cracking, crevice corrosion in tight spaces or under deposits, pitting attack, and intergranular attack in sensitized material such as weld heat-affected zones (HAZ) Such localized corrosion can cause unexpected and sometimes catastrophic failure while most of the structure remains unaffected, and therefore must be considered carefully in the design and selection of the proper grade of stainless steel Corrosive attack can also be increased dramatically by seemingly minor impurities in the medium that may
be difficult to anticipate but that can have major effects, even when present in only parts-per-million concentrations; by heat transfer through the steel to or from the corrosive medium; by contact with dissimilar metallic materials; by stray electrical currents; and by many other subtle factors At elevated temperatures, attack can be accelerated significantly by seemingly minor changes in atmosphere that affect scaling, sulfidation, or carburization
Despite these complications, a suitable steel can be selected for most applications on the basis of experience, perhaps with assistance from the steel producer Laboratory corrosion data can be misleading in predicting service performance Even actual service data have limitations, because similar corrosive media may differ substantially because of slight variations
in some of the corrosion factors listed above For difficult applications, the extensive study of comparative data may be necessary, sometimes followed by pilot plant or in-service testing
More detailed information is available in the section "Corrosion Properties" in this article
Mechanical properties at service temperature are obviously important, but satisfactory performance at other temperatures must be considered also Thus, a product for arctic service must have suitable properties at subzero temperatures even though steady-state operating temperature may be much higher; room-temperature properties after extended service at elevated temperature can be important for applications such as boilers and jet engines, which are intermittently shut down
Fabrication and Cleaning. Frequently a particular stainless steel is chosen for a fabrication characteristic such as formability or weldability Even a required or preferred cleaning procedure may dictate the selection of a specific type For instance, a weldment that is to be cleaned in a medium such as nitric-hydrofluoric acid, which attacks sensitized stainless steel, should be produced from stabilized or low-carbon stainless steel even though sensitization may not affect performance under service conditions
Experience in the use of stainless steels indicates that many factors can affect their corrosion resistance Some of the more prominent factors are:
• Chemical composition of the corrosive medium, including impurities
• Physical state of the medium liquid, gaseous, solid, or combinations thereof
• Temperature
• Temperature variations
• Aeration of the medium
• Oxygen content of the medium
• Bacteria content of the medium
• Ionization of the medium
• Repeated formation and collapse of bubbles in the medium
• Relative motion of the medium with respect to the steel
• Chemical composition of the metal
• Nature and distribution of microstructural constituents
• Continuity of exposure of the metal to the medium
• Surface condition of the metal
• Stresses in the metal during exposure to the medium
• Contact of the metal with one or more dissimilar metallic materials
• Stray electric currents
• Differences in electric potential
• Marine growths such as barnacles
• Sludge deposits on the metal
Trang 29• Carbon deposits from heated organic compounds
• Dust on exposed surfaces
• Effects of welding, brazing, and soldering
Surface Finish. Other characteristics in the stainless steel selection checklist are vital for some specialized applications but of little concern for many applications Among these characteristics, surface finish is important more often than any other except corrosion resistance Stainless steels are sometimes selected because they are available in a variety of attractive finishes Surface finish selection may be made on the basis of appearance, frictional characteristics, or sanitation The effect of finish on sanitation sometimes is thought to be simpler than it actually is, and tests of several candidate finishes may be advisable The selection of finish may in turn influence the selection of the alloy because of differences in availability or durability of the various finishes for different types For example, a more corrosion-resistant stainless steel will maintain a bright finish in a corrosive environment that would dull a lower-alloy type Selection among finishes is described in more detail in this article in the section "Surface Finishing of Stainless Steel."
Reference cited in this section
3 D.J De Renzo, Ed., Corrosion Resistant Materials Handbook, Noyes Data Corporation, 1985
Wrought Stainless Steels
Revised by S.D Washko and G Aggen, Allegheny Ludlum Steel, Division of Allegheny Ludlum Corporation
Stainless steel plate is generally produced in the annealed condition and is either blast cleaned or pickled Blast cleaning
is generally followed by further cleaning in appropriate acids to remove surface contaminants such as particles of steel picked up from the mill rolls Plate can be produced with mill edge and uncropped ends
Sheet
Sheet is a flat-rolled product in coils or cut lengths at least 610 mm (24 in.) wide and less than 4.76 mm (0.1875 in.) thick Stainless steel sheet is produced in nearly all types shown in Table 2 except the free-machining and certain martensitic grades Sheet from the conventional grades is almost exclusively produced on continuous mills Hand mill production is usually confined to alloys that cannot be produced economically on continuous mills, such as certain high-temperature alloys
The steel is cast in ingots, and the ingots are rolled on a slabbing mill or a blooming mill into slabs or sheet bars The slabs or sheet bars are then conditioned prior to being hot rolled on a finishing mill Alternatively, the steel may be
Trang 30continuous cast directly into slabs that are ready for hot rolling on a finishing mill The current trend worldwide is toward greater production from continuous cast slabs
Sheet produced from slabs on continuous rolling mills is coiled directly off the mill After they are descaled, these hot bands are cold rolled to the required thickness, and coils off the cold mill are either annealed and descaled or bright annealed Belt grinding to remove surface defects is frequently required at hot bands or at an intermediate stage of processing Full coils or lengths cut from coils may then be lightly cold rolled on either dull or bright rolls to produce the required finish Sheet may be shipped in coils, or cut sheets may be produced by shearing lengths from a coil and flattening them by roller leveling or stretcher leveling
Sheet produced on hand mills from sheet bars is rolled in lengths and then annealed and descaled It may be subjected to additional operations, including cold reduction, annealing, descaling, light cold rolling for finish, or flattening
A specified minimum tensile strength, minimum yield strength, or hardness level higher than that normally obtained on sheet in the annealed condition, or a combination thereof, can be attained by controlled cold rolling
Sheet made of chromium-nickel stainless steel (often type 301) or of chromium-nickel-manganese stainless steel (often type 201) is produced in the following cold-rolled tempers:
Strip
Strip is a flat-rolled product, in coils or cut lengths, less than 610 mm (24 in.) wide and 0.13 to 4.76 mm (0.005 to 0.1875 in.) thick Cold finished material 0.13 mm (0.005 in.) thick and less than 610 mm (24 in.) wide fits the definitions of both strip and foil and may be referred to by either term
Cold-rolled stainless steel strip is manufactured from hot-rolled, annealed, and pickled strip (or from slit sheet) by rolling between polished rolls Depending on the desired thickness, various numbers of cold-rolling passes through the mill are required for effecting the necessary reduction and securing the desired surface characteristics and mechanical properties
Hot-rolled stainless steel strip is a semifinished product obtained by rolling slabs or billets and is produced for conversion to finished strip by cold rolling
hot-Heat Treatment. Strip of all types of stainless steel is usually either annealed or annealed and skin passed, depending on requirements When severe forming, bending, and drawing operations are involved, it is recommended that such requirements be indicated so that the producer will have all the information necessary to ensure that he supplies the proper type and condition When stretcher strains are objectionable in ferritic stainless steels such as type 430, they can be minimized by specifying a No 2 finish Cold-rolled strip in types 410, 414, 416, 420, 431, 440A, 440B, and 440C can be produced in the hardened and tempered condition
Strip made of chromium-nickel stainless steel (often type 301) or of chromium-nickel-manganese stainless steel (often type 201) is produced in the same cold-rolled tempers in which sheet is produced
For strip, edge condition is often important more important than it usually is for sheet Strip can be furnished with various edge specifications:
• Mill edge (as produced, condition unspecified)
• No 1 edge (edge rolled, rounded, or square)
• No 3 edge (as slit)
• No 5 edge (square edge produced by rolling or filing after slitting)
Trang 31Mill edge is the least expensive edge condition, and is adequate for many purposes No 1 edge provides improved width tolerance over mill edge plus a cold-rolled edge condition; rounded edges are preferred for applications requiring the lowest degree of stress concentration at corners No 3 and No 5 edges give progressively better width tolerance and squareness over No 1 edge
Finishes for foil are described by the finishing operations employed in their manufacture However, each finish in itself
is a category of finishes, with variations in appearance and smoothness that depend on composition, thickness, and method of manufacture Chromium-nickel and chromium-nickel-manganese stainless steels have a characteristic appearance different from that of straight chromium types for corresponding finish designations
Mechanical Properties. In general, mechanical properties of foil vary with thickness Tensile strength is increased somewhat, and ductility is lowered, by a decrease in thickness
Bar
Bar is a product supplied in straight lengths; it is either hot or cold finished and is available in various shapes, sizes, and surface finishes This category includes small shapes whose dimensions do not exceed 75 mm (3 in.) and, secnd, hot-rolled flat stock at least 3.2 mm (0.125 in.) thick and up to 250 mm (10 in.) wide
Hot-finished bar is commonly produced by hot rolling, forging, or pressing ingots to blooms or billets of intermediate size, which are subsequently hot rolled, forged, or extruded to final dimensions Whether rolling, forging, or extrusion is selected as the finishing method depends on several factors, including composition and final size
Following hot rolling or forging, hot-finished bar may be subjected to various operations, including:
• Annealing or other heat treatment
• Descaling by pickling, blast cleaning, or other methods
• Surface conditioning by grinding or rough turning
• Machine straightening
Cold-finished bar is produced from hot-finished bar or rod by additional operations such as cold rolling or cold drawing, which result in the close control of dimensions, a smooth surface finish, and higher tensile and yield strengths Sizes and shapes of cold reduced stock classified as bar are essentially the same as for hot-finished bar, except that all cold reduced flat stock less than 4.76 mm (0.1875 in.) thick and over 9.5 mm (0.375 in.) wide is classified as strip
Cold-finished round bar is commonly machine straightened; afterward, it can be centerless ground or centerless ground and polished Centerless grinding and polishing do not alter the mechanical properties of cold-finished bar and are used only to improve surface finish or provide closer tolerances Some increase in hardness, more marked at the surface and
particularly in 2xx and 3xx stainless steels, results from machine straightening The amount of increase varies chiefly with
composition, size, and amount of cold work necessary to straighten the bar
Trang 32Cold-finished bars that are square, flat, hexagonal, octagonal, or of certain special shapes are produced from hot-finished bars by cold drawing or cold rolling
When cold-finished bar is required to have high strength and hardness, it is cold drawn or heat treated, depending on composition, section size, and required properties Round sections can be subsequently centerless ground or centerless ground and polished
Free-machining wire is a bar commodity used for making parts in automatic screw machines or other types of machining equipment The principal types used are 303, 303Se, 416, 416Se, 420F, 430F, and 430FSe Free-machining wire is commonly produced with a cold drawn or centerless ground finish and with selected hardnesses, depending on the machining operation involved
Structural Shapes. Hot-rolled, bar-size structural shapes are produced in angles, channels, tees, and zees They can be purchased in various conditions:
• Hot rolled
• Hot rolled and annealed
• Hot rolled, annealed, and blast cleaned
• Hot rolled, annealed, and chemically cleaned
• Hot rolled, annealed, blast cleaned, and chemically cleaned
Wire
Wire is a coiled product derived by cold finishing hot-rolled and annealed rod Cold finishing imparts excellent dimensional accuracy, good surface smoothness, a fine finish, and specific mechanical properties Wire is produced in several tempers and finishes
Wire is customarily referred to as round wire when the contour is completely cylindrical and as shape wire when the contour is other than cylindrical For example, wires that are half round, half oval, oval, square, rectangular, hexagonal, octagonal, or triangular in cross section are all referred to as shape wire Shape wire is cold finished either by drawing or
by a combination of drawing and rolling
In the production of wire, rod (which is a coiled hot-rolled product approximately round in cross section) is drawn through the tapered hole of a die or a series of dies The smallest size of hot-rolled rod commonly made is 5.5 mm (0.218 in.) Rod smaller than this is produced by cold work, the number of dies employed depending on the finished diameter required
Round stainless steel wire is commonly produced within the approximate size range 0.08 to 15.9 mm (0.003 to 0.625 in.) Shape wire, except cold-finished flat wire, is commonly produced within the approximate size range of 1.12 to 12.7 mm (0.044 to 0.500 in.), although the particular shape governs the specific sizes that can be produced
Tempers of Wire. There are four classifications of wire temper: annealed-temper, soft-temper, intermediate-temper, and spring-temper
Annealed temper describes soft wire that has undergone no further cold drawing after the last annealing treatment Wire in this temper is made by annealing in open-fired furnaces or molten salt, and annealing ordinarily is followed by pickling that produces a clean, gray, matte finish It is also made with a bright finish by annealing in a protective atmosphere and sometimes is described as bright annealed wire
Soft-temper wire is given a single light draft following the final annealing operation and generally is produced to a defined upper limit of tensile strength or hardness Wire in this temper is produced with various dry-drawn finishes, including lime soap, lead, copper, and oxide It may also be given a bright finish produced by oil or grease drawing
Intermediate-temper wire is drawn one or more drafts after annealing as required to produce a specific minimum strength or hardness The properties of this wire can vary between the properties of soft-temper wire and properties approaching those of spring-temper wire Intermediate-temper wire is usually produced with one of the dry-drawn finishes
Trang 33Spring-temper wire is drawn several drafts as required to produce high tensile strengths
Special Wire Commodities. There are many classes of stainless steel wire that have been developed for specific components or for particular applications The unique properties of each of these individual wire commodities are developed by employing a particular combination of composition, steel quality, process heat treatment, and cold drawing practice The details of manufacture may vary slightly from one wire manufacturer to another, but the finished wire will fulfill the specified requirements
Cold-heading wire is produced in any of the various types of stainless steel In all instances, cold-heading wire is subjected to special testing and inspection to ensure satisfactory performance in cold-heading and cold-forging operations
Of the chromium-nickel group, types 305 and 302Cu are used for cold-heading wire and generally are necessary for severe upsetting Other grades commonly cold formed include 304, 316, 321, 347, and 384
Of the 4xx series, types 410, 420, 430, and 431 are used for a variety of cold-headed products Types 430 and 410 are
commonly used for severe upsetting and for recessed-head screws and bolts Types 416, 416Se, 430F, and 430FSe are intended primarily for free cutting and are not recommended for cold heading
Cold-heading wire is manufactured using a closely controlled annealing treatment that produces optimum softness and still permits a very light finishing draft after pickling The purposes of the finishing draft are to provide a lubricating coating that will aid the cold-heading operation and to produce a kink-free wire coil having more uniform dimensions
Cold-heading wire is produced with a variety of finishes, all of which have the function of providing proper lubrication in the header dies The finish or coating should be suitably adherent to prevent galling and excessively rapid die wear A copper coating, which is applied after the annealing treatment and just prior to the finishing draft, is available; the copper-coated wire is then lime coated and drawn, using soap as the drawing lubricant Coatings of lime and soap or of oxide and soap are also employed
Spring wire is drawn from annealed rod and is subjected to mill tests and inspection that ensures the quality required for extension and compression springs The types of stainless steel of which spring wire is commonly produced include 302,
304, and, for additional corrosion resistance, 316, and UNS N08020
Spring wire in large sizes can be furnished in a variety of finishes, such as dry-drawn lead, copper, lime and soap, and oxide and soap Fine sizes are usually wet drawn, although they can be dry drawn
Tensile strength ranges or minimums for types 302, 304, 305, and 316 spring wire in various sizes are given in Table 6
Table 6 Room-temperature tensile strength of stainless steel spring wire
Diameter Tensile strength
Trang 37>12.68 >0.499 Consult producer
The torsional modulus for stainless steel spring wire may range from 59 to 76 GPa (8.5 to 11 × 106 psi), depending on alloy and wire size Magnetic permeability is extremely low compared to that of carbon steel wire Springs made from stainless steel wire retain their physical and mechanical properties at temperatures up to about 315 °C (600 °F)
Rope wire is used to make rope, cable, and cord for a variety of uses, such as aircraft control cable, marine rope, elevator cable, slings, and anchor cable Because of special requirements for fatigue strength, rope wire is produced from specially selected and processed material
Rope wire is made of type 302 or type 304 unless a higher level of corrosion resistance is required, in which case type
316 is generally selected Special nonmagnetic characteristics may be required, which necessitate the selection of grades that have little or no ferrite or martensite in the microstructure and the use of special drawing practices to limit or avoid deformation-induced transformation to martensite
Tensile properties of regular rope wire are slightly lower than those of stainless steel spring wire Finishes for rope wire vary from a gray matte finish to a bright finish and include a series of bright to dark soap finishes Soap finishes afford some lubrication that facilitates laying up of rope and also to some extent aids in-service use
Weaving wire is used in the weaving of screens for many different applications in coal mines, sand-and-gravel pits,
paper mills, chemical plants, dairy plants, oil refineries, and food-processing plants Annealing and final drawing must be carefully controlled to maintain uniform temper and finish throughout each coil or spool Because weaving wire must be ductile, it is usually furnished in the annealed temper with a bright annealed finish, or in the soft temper with either a lime-soap finish or an oil- or grease-drawn finish
Most types of stainless steel are available in weaving wire; the most widely used types are 302, 304, 309, 310, 316, 410,
and 430 Annealed wire in the 3xx series commonly has a tensile strength of 655 to 860 MPa (95 to 125 ksi) and an
elongation (in 50 mm, or 2 in.) of 35 to 60% Soft-temper wire, which is commonly specified for sizes over 0.75 mm (0.030 in.), averages 860 to 1035 MPa (125 to 150 ksi) in tensile strength and exhibits 15 to 40% elongation For annealed wire in types 410 and 430, tensile strength averages 495 to 585 MPa (72 to 85 ksi), and elongation averages 17 to 23%
Armature binding wire is produced in types 302 or 304 stainless steel of a composition that is balanced to produce high tensile and yield strengths and low magnetic permeability Minimum tensile strength of 1515 MPa (220 ksi), minimum yield strength (0.2% offset) of 1170 MPa (170 ksi), and maximum permeability of 4.0 at 16 kA · m-1 (200 oersteds) are usually specified The wire must be strong enough to withstand the centrifugal forces encountered in use, yet ductile enough to withstand being bent sharply back on itself without cracking when a hook is formed to hold the armature wire during the binding operation Armature binding wire is furnished on spools and has a smooth, tightly adherent tinned coating that facilitates soldering
Slide forming wire is produced in all standard types, particularly in types 302, 304, 316, 410, and 430 It can be produced in any temper suitable for forming any of the numerous shapes made on slide-type wire forming machines
Wool wire is designed for the production of wool by shredding It is commonly furnished in an intermediate temper and produced to rigid standards so that it will perform satisfactorily in the wool-cutting operation Wool wire usually is made from type 430 and has a lime-soap finish
Reed wire is high-quality wire produced for the manufacture of dents for reeds that, once assembled, are used in weaving textiles and other products Dents are made by rolling the round reed wire into a flat section, and then machining and polishing the edges to a very smooth and accurate contour before cutting the wire into individual dents Accuracy in size and shape are necessary because of the various processes that the wire must undergo
Reed wire is usually made from type 430 in an intermediate temper that must be uniform in properties throughout each coil and each shipment The finish also must be uniform and bright
Trang 38Lashing wire is designed for lashing electric power transmission lines to support cables Lashing wire is usually made from type 430 It is furnished in the annealed temper with a bright finish and has a maximum tensile strength of 655 MPa (95 ksi) and minimum elongation of 17% in 255 mm (10 in.) It is normally furnished on coreless spools
Cotter pin wire is approximately half-round wire designed for fabricating cotter pins It is generally produced by rolling round wire between power-driven rolls, by drawing it between power-driven rolls, or by drawing it through a die
or Turk's-head roll To facilitate the spreading of the cotter pin ends, it is desirable that the flat side of the wire have a small radius rather than sharp corners at the edges
Cotter pin wire is commonly furnished in vibrated or hank-wound coils with the flat side of the wire facing inward Ordinarily it is produced in the soft temper to prevent undesirable springback in the legs of formed cotter pins Usually it
is furnished with a bright finish, but it is also available with a metallic coating
Stainless welding wire is available for many grades to provide good weldability with optimized mechanical properties and corrosion resistance of the weldment For example, the weldability of austenitic stainless steels is enhanced
by controlling unwanted residual elements or balancing the wire composition to provide a small amount of ferrite in the as-deposited weld metal Also, the composition of duplex stainless weld wire is generally controlled to produce levels of austenite and ferrite in the weld metal that will optimize mechanical properties and corrosion resistance
Stainless steel weld wire is produced in layer-level wound spools, straight lengths (both included in the American Welding Society AWS A5.9) and coated electrodes (AWS A5.4)
Semifinished Products
Blooms, billets, and slabs are hot rolled, hot forged, or hot pressed to approximate cross-sectional dimensions and generally have rounded corners Round billets are also produced, typically for extrusion or closed-die forging These semifinished products, as well as tube rounds, are produced in random lengths or are cut to specified lengths or to specified weights There are no invariable criteria for distinguishing between the terms bloom and billet, and often they are used interchangeably
Dimensions. The nominal cross-sectional dimensions of blooms, billets, and slabs are designated in inches and fractions of an inch The size ranges commonly listed as hot-rolled stainless steel blooms, billets, and slabs include square sections 100 × 100 mm (4 × 4 in.) and larger, and rectangular sections at least 10,300 mm2 (16 in.2) in cross-sectional area
Stainless Types. Blooms, billets, and slabs made of 4xx stainless steels that are highly hardenable (types 414, 420,
420F, 422, 431, 440A, 440B, and 440C) are annealed before shipment to prevent cracking Other hardenable types, such
as 403, 410, 416, and 416Se, also may be furnished in the annealed condition, depending on composition and size
Processing. In general practice, blooms, billets, and slabs are cut to length by hot shearing Hot sawing and flame cutting are also used When the end distortion or burrs normally encountered in regular mill cutting are not acceptable, ends can be prepared for subsequent operations by any method that does not leave distortion or burrs Usually, this is grinding Blooms, billets, tube rounds, and slabs are surface conditioned by grinding or turning prior to being processed
by hot rolling, hot forging, hot extruding, or hot piercing Material can be tested by ultrasonic and macroetching techniques in the as-worked condition; however, a more critical evaluation is possible after the material has been conditioned At the time an order is placed, producer and customer should come to an agreement regarding the manner in which testing or inspection is to be conducted and results interpreted
Pipe, Tubes, and Tubing
Pipe, tubes, and tubing are hollow products made either by piercing rounds or by rolling and welding strip They are used for conveying gases, liquids, and solids, and for various mechanical and structural purposes (Cylindrical forms intended for use as containers for storage and shipping purposes and products cast to tubular shape are not included in this category.) The number of terms used in describing sizes and other characteristics of stainless steel tubular products has grown with the industry, and in some cases terms may be difficult to define or to distinguish from one another For example, the terms pipe, tubes, and tubing are distinguished from one another only by general use, not by clear-cut rules Pipe is distinguished from tubes chiefly by the fact that it is commonly produced in relatively few standard sizes Tubing
Trang 39is generally made to more exacting specifications than either pipe or tubes, regarding dimensions, finish, chemical composition, and mechanical properties
Stainless steel tubular products are classified according to intended service, as described in the following paragraphs and tabular matter
Stainless Steel Tubing for General Corrosion-Resisting Service. Straight chromium (ferritic or martensitic) types are produced in the annealed or heat-treated condition, and chromium-nickel (austenitic) types are produced in the annealed or cold-worked condition Austenitic types are inherently tougher and more ductile than ferritic types for similar material conditions or tempers
ASTM specifications A 268 and A 269 apply to stainless steel tubing for general service: A 268 applies to ferritic grades, and A 269, to austenitic grades Most ferritic grades are also covered by ASME SA268, which sets forth the same material requirements as does ASTM A 268
Stainless steel pressure pipe is made from straight chromium and chromium-nickel types and is governed by the specifications:
Specifications
ASTM ASME
Description
A 312 SA312 Seamless and welded pipe
A 358 SA358 Electric fusion welded pipe for high-temperature service
A 376 SA376 Seamless pipe for high-temperature central-station service
A 409 Large-diameter welded pipe for corrosion or high-temperature service
A 790 SA790 Seamless and welded ferritic/austenitic stainless steel pipe
Stainless steel pressure tubes include boiler, superheater, condenser, and heat-exchanger tubes, which commonly are manufactured from chromium-nickel types; requirements are set forth in the specifications:
Trang 40A 249 SA249 Austenitic alloy welded tubes for boilers, superheaters, heat exchangers, and condensers
A 271 SA271 Austenitic alloy seamless still tubes for refinery service
A 498 Ferritic and austenitic alloy seamless and welded tubes with integral fins
A 688 SA688 Welded austenitic stainless steel feedwater heater tubes
A 789 SA789 Seamless and welded ferritic/austenitic stainless steel tubing
Stainless steel sanitary tubing is used extensively in the dairy and food industries, where cleanliness and exceptional corrosion resistance are important surface characteristics In many instances, even the slight amounts of corrosion that result in tarnishing or in release of a few ppm of metallic ions into the process stream are objectionable Sanitary tubing may be polished on the outside or the inside, or both, to provide smooth, easily cleanable surfaces Special finishes and close dimensional tolerances for special fittings are sometimes required ASTM A 270 is in common use for this tubing
Stainless steel mechanical tubing is produced in round, square, rectangular, and special-shape cross sections It is used for many different applications, most of which do not require the tubing to be pressurized Mechanical tubing is used for bushings; small cylinders; bearing parts; fittings; various types of hollow, cylindrical or ringlike formed parts; and structural members such as furniture frames, machinery frames, and architectural members ASTM A 511 and A 554 apply to seamless and welded mechanical tubing, respectively
Stainless steel aircraft tubing, produced from various chromium-nickel types, has many structural and hydraulic applications in aircraft construction because of its high resistance to both heat and corrosion Work-hardened tubing can
be used in high-strength applications, but it is not recommended for parts that may be exposed to certain corrosive substances or to certain combinations of corrosive static or fluctuating stress Low-carbon types or compositions stabilized by titanium or by niobium with or without tantalum are commonly used when welding is to be done without subsequent heat treatment
Aircraft tubing is made to close tolerances and with special surface finishes, special mechanical properties, and stringent requirements for testing and inspection It is used for structural components of aircraft fuselages, engine mounts, engine oil lines, landing gear components, and engine parts and is finding increasing application in parts for hydraulic, fuel-injection, exhaust, and heating systems
Aircraft structural tubing is both seamless and welded stainless steel tubing in sizes larger than those referred to as aircraft tubing It is commonly used in exhaust systems (including stacks), cross headers, collector rings, engine parts, heaters, and pressurizers Sometimes, stainless steel aircraft structural tubing is produced especially for parts that are to be machined Stabilized types are used for welded and brazed structures
Seamless and welded stainless steel aircraft structural tubing is made in sizes ranging from 1.6 to 125 mm ( 1
16 to 15 in.)
in outside diameter and from 0.25 to 6.35 mm (0.010 to 0.250 in.) in wall thickness It is ordinarily produced to the federal and Aerospace Material Specification (AMS) specifications listed below However, because the U.S government has embarked on a program of replacing military (MIL) specifications with AMS and ASTM specifications, the MIL specifications listed may no longer apply