Characterization of Loading Responses and Failure Loci of a Boron Steel Spot Weld

N. D. Raath,I. McGregor,R. Dashwood,S. Hepple,D. J. Hughes,D. Norman

doi:10.1007/s11661-018-4502-x

Abstract

Boron steel, classed as an ultra high-strength steel (UHSS), has been utilized in anti-intrusion systems in automobiles, providing high strength and weight-saving potential through gage reduction. UHSS spot welds exhibit unique hardness distributions, with a hard nugget and outlying base material, but with a soft heat-affected zone in-between these regions. This soft zone reduces the strength of the weld and makes it susceptible to failure. Due to the interaction of various weld zones that occurs during loading, there is a need to characterize the loading response of the weld for accurate failure predictions. The loading response of certain weld zones, as well as failure loci, was obtained through physical simulation of the welding process. The results showed a significant difference in mechanical behavior through the weld length. An important result is that instrumented indentation was shown to be a valid, quantitative method for verifying the accuracy with which weld microstructure has been recreated with regard to the target weld microstructure.

Highlights

DUE to environmental considerations, there has been a need to improve fuel economy and reduce emissions in the automotive industry
The purpose of this section is to establish the correlation between the yield strengths extracted through tensile testing and instrumented indentation
These two independent results are used to quantify how accurately the heat-affected zone (HAZ) microstructure has been recreated onto the tensile destructive specimens and the confidence that can be placed in the material constitutive behavior to be presented later in this work

Summary

Introduction

DUE to environmental considerations, there has been a need to improve fuel economy and reduce emissions in the automotive industry. A factor which contributes to this aim is reducing vehicle weight. Highstrength boron steel exhibits desirable characteristics and has been utilized to reduce vehicle weight and maintain passenger safety through gage reduction of load-bearing parts. Resistance spot welding (RSW) is one of the most widely used joining techniques of steel vehicle parts, with several thousand welds made on a single car. The weld and surrounding material have been exposed to a wide range of temperatures. These range from above 1300 °C at the center of the nugget, to ambient temperature at distances far away from the weld.

Methods

Results

Conclusion