Ultrafast heating of advanced high strength steels

Abstract

Microstructure, texture and the tensile properties of a 70% cold rolled advanced high strength steel with microstructure of ferrite and pearlite were studied after reheating with different heating rates and subsequent quenching. Sub-size tensile samples were reheated with rates of 10, 500 and 1000°C/s to temperatures between Ac1 and Ac3 and above Ac3 and subsequently quenched without isothermal soaking and with isothermal soaking of 30 s and 60s. By following the microstructure and texture changes it was found that after reheating with 500°C and 1000°C the recrystallization was suppressed and the alpha-gamma phase transformation starts in a nonrecrystallized or partially recrystallized matrix. Significant grain refinement and increase of both tensile strength and elongation was observed in the samples after ultrafast heating and subsequent quenching without isothermal soaking. The isothermal soaking erased the grain refining effect of the ultrafast heating even if it was as short as 30s.