Test steel is melted by a 50 kg vacuum induction furnace
forged to 60 mm slab
homogenized at 1 250 ℃ then hot-rolled to 4 mm plate and cold rolled to 1 mm sheet. The effect of austempering temperature (350 ~ 450 °C) and holding time (1 ~ 10 min) on structure and mechanical properties of 820℃ 3 min quenched test TRIP steel cold-rolled sheet has been studied. Results show that the effect of process of austempering on mechanical properties of test steel is obvious; the optimum austempering process is 820℃ 3 min +400℃ 5 min
water cooling
the tensile strength and total elongation are respectively 766 MPa and 37%
i. e. the strength-plasticity product is 28. 34 GPa
% ; a lot of Nb (CN) particles precipitation with 10 nanometer size is main factor to increase the strength of test steel.