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Dual Stabilization Heat Treatment in a TRIP assisted Steel to realize Third Generation Advanced High Strength Steel Properties

JN Mohapatra*, D Satish Kumar, G Balachandran

Low carbon steel (0.17 wt. % C) with 1.72% Mn and 1.35% Si, micro alloyed with 0.02% Nb and 0.04% Ti was subjected to dual stabilization heat treatment that involves intercritical austenization at 790°C, 810°C and 830°C for 5 minutes for first stabilization followed by isothermal bainitic holding at 450°C for 30 seconds and water quenched to form martensite and retained austenite. The steel was reheated to 450°C for 30 seconds, where partition of carbon from martensite to retained austenite take place stabilizing the austenite second time and then water quenched. The steel showed 45% to 47% ferrite, 21%-37% bainite, 14% to 26% martensite and 3.3% to 9.5% retained austenite. The mechanical properties showed yield strength between 460 and 480 MPa, tensile strength between 960 and 1010 MPa, total elongations between 27 and 28% with tensile toughness above 27 GPa.% conforming to third generation advanced high strength steel.