Influence of post weld heat treatments on residual stress and mechanical properties of dissimilar welded joint of SS304 and SS202

A stainless steel SS304 and SS202 was welded by tungsten inert gas welding (TIG) with filler SS316L. The post weld heat treatments (PWHT) at 8500 , 9000C and 9500C for different periods of time were performed in order to improve the mechanical properties of the welded joint. The tensile strength was increased after post weld heat treatment, and maximum tensile strength i.e. 535.42 MPa was found in post heat treated welded joint at 9500C, and maximum percentage elongation i.e. 18.86% was found at 9000C. A decreasing profile of micro-hardness was found from the base metal (BM) to welded joint. This decrease profile may occur due to absence of martensite phase in heat affected zone (HAZ). The micro-hardness values were increased at the center of the welded joint, when post weld heat treatment (PWHT) applied. The maximum hardness values i.e. 260 HV was observed in heat treated welded joint at 9500C. The compressive residual stresses was found at the center of the welded joint because of thermal expansion and heat conduction in the heat affected zone. The residual stress decreases when post weld heat treatment temperature increased. The minimum compressive residual stress i.e. 17 MPa was found in heat treated welded joint at 9500C. 

After the welding operation of SS202 and SS304 with filler rod SS316L and normalizing heat treatment of butt welded joint with various temperature (850 , 900 , and 950C) the micro-hardness values were evaluated for each case. Thirty one hardness values were taken from each specimen to investigate the micro-hardness changes from the welded joint to base metal. The micro-hardness variation for each case as shown in fig.6. The micro-hardness values are less significant in affecting the mechanical properties of the material, because processing parameter and feed rate have more influencing factor over the hardness values [30]. The microhardness value near the top surface shows a comparatively smoother transition. All the major effect was detected in the middle and bottom of the weldment. Because of changing in solidification sequence and cooling rate of weldment, the grain size and micro-hardness number were changes. The microhardness number also play a very important role to recognizing the metallurgical phase [31]. Decrease in micro-hardness was observed from the base metal (BM) to weldment, due to absence of martensite phase in heat affected zone (HAZ), the microhardness profile shows the decrement from the base metal to weldment. After the normalizing heat treatment the microhardness values increases from 202 HV to 260 HV. And the maximum hardness value i.e. 260HV found in heat treated sample at 9500C as shown in fig.7.

This article is published in peer review journal and open access journal, International journal of research in engineering and innovation (IJREI) which have a high impact factor journal for more details regarding this article, please go through our journal website.

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