This paper reports the changes of microstructure and properties in the fusion zone (FZ) and heat - affected zone (HAZ) in dissimilar weld between Austenitic stainless steel (304L) and low carbon steel under varying of welding parameters. The dimension of base materials was 500x250x3 (mm). The welding current ranged from 80A to 120A and travel speed were limited 100-200 mm/s and constant arc voltage of 25V. The welding joints were made by gas metal arc welding (GMAW). As the result, the microstructures and properties in three regions had significant differences and changed under vary welding process parameters.
Trang 1Influence of process parameters on microstructures and properties
of the heat - affected zone (HAZ) and fusion zone (FZ)
of the dissimilar metal welding
Le Thi Nhung 1 , Pham Mai Khanh 1 , Nguyen Duc Thang 2 , Pham Huy Tung 3
1 Hanoi University of Science and Technology,
lenhung.vl.hh@gmail.com
2 Centre for non-destructive evaluation
3 Vietnam Maritime University
Abstract
This paper reports the changes of microstructure and properties in the fusion zone (FZ) and heat - affected zone (HAZ) in dissimilar weld between Austenitic stainless steel (304L) and low carbon steel under varying of welding parameters The dimension of base materials was 500x250x3 (mm) The welding current ranged from 80A to 120A and travel speed were limited 100-200 mm/s and constant arc voltage of 25V The welding joints were made by gas metal arc welding (GMAW) As the result, the microstructures and properties in three regions had significant differences and changed under vary welding process parameters HAZ width and grain sizes in carbon steels are larger than stainless steel Besides, tensile strength and hardness were affected by welding parameters Weld joint at 100A, 120 mm/min would be give the highest tensile strength and hardness
Keywords: Dissimilar metal welding, welding parameters, HAZ, microstructures, OM
1 Introduction
Nowadays, dissimilar metal welds are used in many fields such as nuclear, power, oil and gas or shipbuilding industry,… It was widely known that dissimilar metal joints are intrinsically an uncertainty because of difference in the physical, mechanical and metallurgical properties of the base metals to be joined Besides, the intense heat applied during process produces both metallurgical and physical inhomogeneity in the various zones
of the weld leading to differential properties of the weld section Therefore, the investigation
of microstructure, solidification, phase transformation and mechanical properties during welding process is the best way to understand the essence of welding In other words, in order
to produce high quality joints, researching all factors affecting to mechanical properties is necessary
As the previous researchers, different welding regions in arc welding are classified into three zones as fusion zone (FZ), heat - affected zone (HAZ) and base metal (BM) which are influenced by heat input rate and heat transfer factors [3] FZ is the area between two pieces of base metal being melted and solidified HAZ is the area of base metal which is not melted and has had its microstructure and properties altered by the heat The change of welding parameters has different impact on weld geometry, microstructure and properties in welding zones For instance, as the heat input and welding speed both increase, the weld pool becomes more elongated, shifting from elliptical to teardrop shaped [2] Amuda [1] shows that, under welding conditions, the primary solidification structure of stainless steel changed from a predominantly ferrite structure to a matrix interspersed with increasing fraction of inter - dendrite martensite in the weld metal and grain boundary martensite in the HAZ In the carbon welding, ferrite is formed under different shapes as grain boundary ferrite, polygonal ferrite or acicular ferrite Besides, upper bainite, lower bainite or Widmanstatten can be observed [2] Other researches also represent that grains are smaller, the mechanical welding
is better
Trang 2Although the researching about cause-effect between welding parameters and microstructure has invested, the problems concern dissimilar metal welding documents are limited Based on previous study, the objective of this study was to find out the changes of microstructure and properties of welding between carbon steel and stainless steel under the varying of current and welding speed
2 Experimental materials and procedure
The base metals were 304L stainless steel and carbon steel using gas metal arc welding process The dimensions of plates were 500 x 250 x 3 mm The chemical composions
of base metals, filler show in the table below
Table 2.1 The chemical compositions
SS 304L 0,09 1,54 0,49 < 0.005 0,005 18.3 7.56 0,13 0,11 Carbon steel 0,1 0,62 0,02 0,04 0,05 0,02 0,08 0.005 0,01 Filler ER 309L 0,08 0.7 0,8 < 0.005 < 0.003 19.7 11.8 0.1 0.09
The welding parameters in the proceses were current and welding speed shown in the table 2.2 The values of these factors were selected by experimental statistic datas
Table 2.2 Experimental numbers and welding parameters
Affter welding processes, samples were cut to examine their microstructure, tensile strength and hardness The microstructure was observed by OM LEICA MDS4000M The tensile strength and the hardness were determined by WEW1000B and hardness tester ARK600, respectively
3 Results and discussion
3.1 Microstructure
Because of using filler ER 309L in welding process, austenite (γ) and ferrite (δ) were formed in fusion zone (figure 3.1a) Generally, grain morphology in FZ is equal structure and independent of process parameters
Figure 3.1 (a) Microstructure in fusion zone, V = 160 mm/min, I = 100 A
According the results of hardness test indicate that HAZ width in carbon steel is larger than stainless steel This can be expressed by the significant difference of thermal conductivity between carbon steel and stainless steel Figure 3.2 shows that HAZ width in stainless steel is very narrow and concentrates at fusion line
Trang 3Figure 3.2 Microstructure in HAZ of stainless steel, I =100A, V= 200 mm/min
By comparing microstructure in HAZ of carbon steel, grain size is much larger than its base metal This can be observed by comparing grain size in figure 3.2, figure 3.4 with figure 3.3 Moreover, it depends on welding parameters Figure 3.4 represents the change of grain size under varying of current welding It can be observed that if the current is constant, the welding speed is slower, heated metal at the high temperature is kept for a long time, grain size is larger Meanwhile, if we consider under constant welding speed, the increasing
of current welding is cause of developing of grain size (figure 3.5)
(a) Carbon steel (b) Stainless steel
Figure 3.3 Microstructure of base metal
Figure 3.4 Grain size in HAZ of carbon steel under varying of welding speed, I = 100A
(a) V = 120 mm/min, (b) V = 160 mm/min, (c) V = 200 mm/min
Figure 3.5 Grain size in HAZ of carbon steel under varying of welding current,
V = 200 mm/min (a) I = 60A, (b) I = 80A, (c) I = 200 A
Trang 43.2 Mechanical properties
The results of ultimate tensile strength and hardness test for dissimilar welding between 304L stainless steel and carbon steel were shown significant difference affected of current and welding speed Figure 3.6 was shown the estimated means of tensile strength As the results, welding parameters at 100A and 120 mm/min would be given the highest tensile strength
Figure 3.6 Tensile strength
The values of hardness are represented in the figure 3.7 As can be observed from the chart, there are small gap among regions Hardness in HAZ of carbon steel would be higher than others Besides, the hardness of sample 3 at 100A, 120 mm/min stand at the highest level compare with others
Figure 3.7 Hardness values
4 Conclusion
In this work, stainless steel and carbon steel were jointed using GMAW under varying
of current and welding speed Microstructure and mechanical properties of weld zones were investigated From this study, following conclusions can be drawn:
- The grain sizes observed in fusion zone are equal structure and independent of process parameters Meanwhile, microstructure in HAZ of stainless steel and carbon steel has
Tensile strength (KG/mm 2 )
Welding speed (mm/min)
Hardness (HV)
x (mm)
Trang 5significant difference and controlled by welding parameters HAZ width and grain sizes in carbon steels are larger than stainless steel
- Tensile strength and hardness were affected by welding parameters Weld joint at 100A, 120 mm/min would be give the highest tensile strength and hardness
References
[1] M.O.H Amuda and s.Mridha Microstructural features of AISI 430 Ferritic stainless
steel (FSS) weld produced under varying process parameters international journal of
mechanical and materials engineering (IJMME), Vol 4 (2009), No 2 160 - 166
[2] Sindo Kuo Welding metallurgy Published by John Wiley and Sons, Inc., Hoboken,
New Jersey 2003
[3] Zakaria Boumerzoug, Chemseddine Derfouf, Thierry Baudin Effect of welding in
microstructure and mechanical properties of an industrial low carbon steel
Engineering, 2010, 502-506