1st Paragraph: During manufacturing of highly hardenable AHSS undesirable martensite readily forms after hot rolling, welding, etc., causing poor cold rollability, thickness inconsistency, deteriorated strip shape, weld breaks, etc. To soften the material prior to downstream processing, high temperature tempering with short heating and cooling cycles is often needed. With rapid heating and cooling, martensite from fine grain austenite has mixed lath and plate morphology while coarse grain austenite produces predominantly lath martensite. In latter case the precipitation during tempering occurs at low angle lath boundaries through fast nucleation and sluggish growth and recovery of martensite is faster. With plate martensite the precipitation occurs at high angle boundaries proceeding through coarsening of carbides. Rapid heating and soaking can lead to partial reaustenitization and formation of fresh martensite during cooling causing abnormal tempering and negating softening.
Authors: Evgueni Poliak, Olga Girina, Pavan Venkatasurya, and Damon Panahi
Keywords: Rapid Heating, Quenching, Tempering, Austenite Grains, Martensite Morphology