Investigation on Impact of Heat Input on Microstructural, Mechanical, and Intergranular Corrosion Properties of Gas Tungsten Arc-Welded Ti-Stabilized 439 Ferritic Stainless Steel

Santosh K Gupta,Awanikumar P Patil,Himanshu Vashishtha,Ramesh C Rathod,Vipin Tandon

doi:10.1007/s11665-021-06512-7

Abstract

In the present study, gas tungsten arc welding was employed to weld Ti-stabilized 439 ferritic stainless steel using 308L austenitic stainless steel filler electrode with varying heat input, i.e., low heat input (LHI) and high heat input (HHI). The optical microstructure revealed the formation of retained austenite (RA) and ferrite in the weld zone (WZ), whereas the peppery structure consisting of chromium-rich carbides were observed in the heat-affected zone for both the weldments. The volumetric fraction of RA was calculated using X-ray diffraction analysis. The RA’s content decreased, whereas grain size in WZ increased with an increase in heat input. The local misorientation and grain boundary distribution in the welded region was investigated by electron backscattered diffraction. The LHI weldment depicted the higher micro-hardness and tensile strength attributed to the higher content of RA as compared to HHI; however, the opposite trend was observed for the intergranular corrosion resistance.

Highlights

In recent years, there has been a significant increase in the demand for ferritic stainless steels (FSSs) attributed to their economic advantage and a good combination of mechanical and corrosion properties as compared to austenitic stainless steels (ASSs) (Ref 1)
The medium chromium 439 FSS is used, and the calculated value of Kfactor is 20.55, which is higher than the critical value, and no martensite is observed in the base metal (BM) in the optical microstructure
In stainless steels (SSs), the chemical composition of BM and filler electrode plays a significant role in determining the solidification mode in the weld zone (WZ), which can be determined through the WRC 1992 diagram by calculating the ratio of chromium equivalent (Creq) to nickel equivalent (Nieq) (Ref 23)

Summary

Introduction

There has been a significant increase in the demand for ferritic stainless steels (FSSs) attributed to their economic advantage and a good combination of mechanical and corrosion properties as compared to austenitic stainless steels (ASSs) (Ref 1). The FSSs suffers from sensitization during the welding resulting in an intergranular corrosion (IGC) (Ref 5). It is reported that the carbide precipitation occurs faster in FSSs due to the lower solubility of carbon compared to ASSs (Ref 6). Proper control on the addition of carbon content or by adding titanium (Ti) and/or niobium (Nb) as stabilizing elements has proved to be the most viable option to reduce the IGC without compromising its ductility and corrosion resistance of FSSs weldments (Ref 7)

Methods

Results

Conclusion