Resistance spot welding of dual-phase steels: Heat affected zone softening and tensile properties

Dual-phase (DP) steels offer favorable combinations of high strength and good deformability. These properties have made them a potential candidate for the fabrication of automobile body frame structures, which helps increase fuel economy by down-gauging material thickness and improving the crashworthiness of the vehicle. Resistance spot welding is extensively used in automotive manufacturing and is also a favorable method for joining DP steels. However, the main challenge in welding DP steel is to overcome the inconsistent failures encountered in the heat-affected zone and/or the fusion zone (nugget) in higher grades of DP steel spot welds. Failure in the heat affected zone of DP steel spot welds is related to the softening phenomenon which involves tempering of martensite as the temperature in this region reaches close to Ac1 line of the steel. This article documents the review of the earlier work on softening occurring at subcritical heat affected zone of spot welded DP steels and its effects on the tensile performance of the spot welds. Copyright © 2013 ASM International® All rights reserved.