Effect of the Plasma arc Welding Procedure on Mechanical Properties of DP700 Steel

Abstract

Dual Phase steels (DP) offer an attractive combination of formability and high strength, being widely used in structural parts for automotive industry. The microstructure of these steels consists in a ferritic matrix with a variable fraction of a martensitic phase of high hardness. In many applications DP steels must be welded; therefore the study of its weldability is a topic of great technological interest. The welded joints of these steels have tipically a performance between 0.60 and 0.90 in terms of tensile strength, due to martensite tempering in the heat affected zone (HAZ). There are few systematic studies on the influence of welding procedure on the microstructural evolution and mechanical properties of DP steels. Plasma Arc Welding (PAW) is a high power density and relatively low cost process, excellent for welding thin metals. The aim of this study is analyse the influence of PAW welding procedure on the microstructural evolution and mechanical properties behaviour of DP steel welded joints. For this purpose, DP700 steel sheets were welded with different heat input (HI). Macro and microstructure were characterized and Vickers microhardness profiles were determined, as well as Olsen cup and tensile tests. Tensile efficiency of the joints was between 0.72 and 0.79 and between 0.70 and 0.95 for the formability test. Increasing heat input increases the size of the subcritical zone; however, the mechanical properties are not significantly affected.