Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

Critical review of automotive steels spot welding: process, structure and properties

Experimental and numerical analysis on formation of stable austenite during the intercritical annealing of 5Mn steel

Austenite stability and deformation behavior in a cold-rolled transformation-induced plasticity steel with medium manganese content

This article reviews recent basic research on two classes of twins: growth twins and deformation twins. We focus primarily on studies that aim to understand, via experiments, modeling, or both, the causes and effects of twinning at a fundamental level. We anticipate that, by providing a broad perspective on the latest advances in twinning, this review will help set the stage for designing new metallic materials with unprecedented combinations of mechanical and physical properties.

Growth Twins and Deformation Twins in Metals

Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. The steels possess a single α′ martensite phase in hot and cold rolled states and multiphases after intercritical annealing. Many studies have focused on investigating the influences of chemical composition and annealing conditions on the microstructure, particularly the grain size and retained γ (γR), and on the tensile properties. The steels exhibit high strength and good ductility due to transformation induced plasticity occurring in γR, whose volume fraction is approximately 0·2–0·4. The present review summarises the important results of previous studies about the effects of both intercritical annealing conditions and alloying elements on the microstructure and tensile properties of medium Mn steels.

Current opinion in medium manganese steel

The purpose of the present contribution is to review the current knowledge about the relationship between the micro-structure of cold rolled intercritically annealed low alloy TRIP-aided sheet steels and their mechanical properties from a materials engineering point of view. The focus is on their production in existing industrial lines and on their application in the manufacture of passenger cars with a body-in-white which offers an improved passive safety. The review aims to make clear that although low alloy TRIP-aided sheet steel is by now starting to be an established structural material in BIW manufacturing, there is still room for the further optimization of the composition and the processing. In addition, there are still a number of problems related to their physical metallurgy that require a better fundamental understanding.

B.C. De Cooman

Papers

Structure–properties relationship in TRIP steels containing carbide-free bainite