Review on the Resistance Spot Weldability of Medium-Mn TRIP steel

Medium Mn TRIP steels have a dual-phase matrix of ferrite and austenite containing intentionally redistributed manganese and carbon contents to obtain stable austenite at room temperature. However, regardless of similar and dissimilar weldment, coarse-grained HAZ and FZ undergo martensitic transformation during heating above the Ac3 temperature and then rapid cooling to room temperature. Then the high retained austenite content is sharply reduced, resulting in deterioration of mechanical properties with increased brittleness. Various ways to improve weldability have been proposed, and the paint-baking heat treatment process during automotive production can drastically improve the tensile properties of martensite, even when conducted at low temperature. This paper highlights the main characteristics and microstructural changes in the resistance spot welding of medium Mn TRIP steel, which is expected to be used as a next-generation automotive steel sheet. Key words: Medium Mn TRIP steel, Advanced high strength steel, Resistance spot welding, Paint-baking