The Influence of Laser Beam Welding and Plasma Arc Welding Processes on Dual Phase Steel Microstructure

Abstract

One important aspect in the application of dual phase (DP) steels in the automotive industry are their weldability and subsequent mechanical properties. Welding involves a rapid change in the temperature which alters the microstructure and the mechanical properties of the steel. Understanding the influence of welding conditions on the mechanical properties of DP 600 is useful for both the automotive industry and steel producers. Despite its importance, the weldability study of dual phase steels is still limited. In this paper the microstructural evolution and its influence on the mechanical properties of 1 mm thick zinc coated DP 600 steel are described for laser beam welding (LBW) and plasma arc welding (PAW) processes. Microstructural and mechanical characterisation were performed using optical microscopy, microhardness measurements, tensile tests and Erichsen cupping tests. The process comparison shows differences in the final mechanical properties resulting from the microstructural differences in the welding zones.

Key factors influencing mechanical performance of dual phase steel resistance spot welds

“…The higher the heat input, the higher the degree of HAZ softening is. For example, HAZ softening of DP600 during RSW is not reported in the literature, as also shown in this study, due to rapid thermal cycle of RSW and short dwell time at the peak temperatures, as well as its martensite low volume fraction; while, some softening of HAZ-DP600 is reported during arc welding 28 and laser welding. 25 Failure location of RSWs during the tensile shear test is governed primarily by their hardness profile.…”

“…Heat affected zone softening during welding of DP steels has been reported in the literature. 2,4,7,20,[25][26][27][28] The location of HAZ softening corresponds to the subcritical HAZ (i.e. the region in HAZ which experiences temperatures below A c1 critical 2 Effect of welding current and welding time t on FZ size and failure mode: arrows show critical FZ size for each grade below which IF (or partial interfacial) mode was obtained and above that PF mode was observed temperature).…”

“…Heat affected zone softening during welding of DP steels has been reported in the literature. 2,4,7,20,[25][26][27][28] The location of HAZ softening corresponds to the subcritical HAZ (i.e. the region in HAZ which experiences temperatures below A c1 critical temperature).…”