Effect of Double Pulse Resistance Spot Welding Process on 15B22 Hot Stamped Boron Steel

Hwa-Teng Lee,Yuan-Chih Chang

doi:10.3390/met10101279

Abstract

Double pulse resistance spot welding process by applying a second step welding current is a new pathway to alter the mechanical properties for advanced high strength steels. Herein, the resistance spot welding (RSW) of hot stamped boron steel 15B22 by one-step and two-step welding with different welding currents is investigated. The results of the tensile–shear test, size of the weld nugget, hardness distribution, microstructure, and failure mode of different welding parameters are analyzed. The weldment of the two-step RSW with a higher heat input exhibits a lower tensile–shear load and lower fracture energy when the size of the weld nugget is large. The microstructural study reveals the appearance of a partially melted zone and sub-critical heat affected zone in the weldment where the fracture readily occurred. Thus, the two-step RSW process weakens the strength of the sample, which is attributed to the partial softening in the weldment due to the higher heat input.

Highlights

In order to reduce carbon emissions and energy consumption, the use of advanced high strength steels (AHSSs) is being employed in the automotive industry
The formula shows that the heat input significantly increases as current increases
Two-step resistance spot welding (RSW) is often applied for joint bonding of AHSS in practical application

Summary

Introduction

In order to reduce carbon emissions and energy consumption, the use of advanced high strength steels (AHSSs) is being employed in the automotive industry. These steel grades demonstrate higher mechanical properties than conventional high strength low alloys (HSLA) steels and could fulfil the requirements of the different parts of the automotive body. The difference in properties, such as the electrical resistivity or the content of the martensite, causes the spot welding performance of AHSS to be different from that of HSLA [2]. The appearance of the IF failure means the lower heat input and lower mechanical properties, which should be avoided as much as possible [3]

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Conclusion