Resistance Spot Welding of SUS316L Austenitic/SUS425 Ferritic Stainless Steels: Weldment Characteristics, Mechanical Properties, Phase Transformation and Solidification

Khuenkaew Khuenkaew,Kanlayasiri Kanlayasiri

doi:10.3390/met9060710

Abstract

This research examines the weldment characteristics and mechanical properties of lap joints of SUS316L/SUS425 stainless steels using resistance spot welding under variable weld currents and welding times. The weld current was varied between 7.0, 8.5, and 10.0 kA, and the welding time between 25, 38, and 50 cycles. The weldment quality characteristics under study were the depth of fusions, indentation depths, and nugget diameter, and the mechanical properties included the tensile shear force (TSF) and micro Vickers hardness. Phase transformation and solidification were characterized using scanning electron microscopy and energy dispersive X-ray spectrometry, together with Schaeffler and pseudo-binary predictive phase diagrams. The results revealed that the weldment quality was positively correlated with weld current and welding time, as were the TSF and micro hardness. The optimal welding condition was achieved under a 10.0 kA weld current and 25-cycle welding time. Under the optimal condition, the fusion zone exhibited compression-direction columnar grains consisting of austenite, ferrite, and martensite and the solidification was of ferrite plus Widmanstatten austenite.

Highlights

Resistance spot welding (RSW) is commonly used in the automotive, aviation, and manufacturing sectors because of its simplicity, automatability, ease of maintenance, and cost-effectiveness [1,2,3].in the automotive industry, dissimilar ferritic and austenitic stainless steel grades are widely utilized in exhaust pipes due to their attractive appearance, weldability, and corrosion-resistance [4].sections of the exhaust subjected to lower temperatures are made of ferritic stainless steel, while those exposed to high temperatures are made of austenitic stainless steel
The weldment quality characteristics included the depth of fusions, indentation depths, and nugget diameter and the mechanical properties under study were tensile shear force (TSF) and micro hardness
The joint appearance was generally enhanced with the increase of weld current and time, except the 8.5 kA/50-cycle, 10.0 kA/38-cycle, and 10.0 kA/50-cycle conditions, where expulsion and electrode deposit pits were observed on the SUS316L side which was attributable to the high heat input

Summary

Introduction

Resistance spot welding (RSW) is commonly used in the automotive, aviation, and manufacturing sectors because of its simplicity, automatability, ease of maintenance, and cost-effectiveness [1,2,3].in the automotive industry, dissimilar ferritic and austenitic stainless steel grades are widely utilized in exhaust pipes due to their attractive appearance, weldability, and corrosion-resistance [4].sections of the exhaust subjected to lower temperatures are made of ferritic stainless steel, while those exposed to high temperatures are made of austenitic stainless steel. In the automotive industry, dissimilar ferritic and austenitic stainless steel grades are widely utilized in exhaust pipes due to their attractive appearance, weldability, and corrosion-resistance [4]. RSW to dissimilar stainless steel grades renders the weld nugget prone to cracking due to high heat input, and the likelihood is multiplied if unsuited electrode caps are used, causing accumulative residual stress [4,5]. Solidification cracking normally develops in the welding of stainless steels with different metallurgical, physical, and mechanical properties [6], leading to excessive noise, vibration, and compromised strength [7]. Liu et al [8] investigated the RSW microstructure and mechanical performance of austenite stainless CRHS301LN and reported martensite transformation at interfacial fractures. Moshayedi and Sattari-Far [9]

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Results

Conclusion