Abstract
Ultrafast heating(UFH)at the rates of 10-300℃/s was employed as a new strategy to anneal a cold-rolled 7wt％Mn steel,followed by the immediate cooling.Severely deformed strain-induced martensite and lightly-deformed thermal martensite,both had been already enriched with C and Mn before,trans-formed to fine and coarse austenite grains during the UFH,leading to the bimodal size distribution.Com-pared with the long intercritical annealing(1A)process,the UFH processes produced larger fraction of RA grains(up to 37％)with a high density of dislocation,leading to the significant increase in yield strength by 270 MPa and the product of strength and elongation up to 55 GPa％due to the enormous work hard-ening capacity.Such a significant strengthening is first attributed to high density dislocations preserved after UFH and then to the microstructural refinement and the precipitation strengthening;whilst the sus-tainable work hardening is attributed to the successive TRIP effect during deformation,resulting from the large fraction of RA instantly formed with the bimodal size distribution during UFH.Moreover,the results on the microstructural characterization,thermodynamics calculation on the reverse transformation tem-perature and the kinetic simulations on the reverse transformation all suggest that the austenitization during UFH is displacive and involves the diffusion and partition of C.Therefore,we propose that it is a bainite-like transformation.
基金项目
国家自然科学基金(51831002)
国家自然科学基金(51861135302)
中央高校基本科研业务费专项(FRF-TP-18-002C2)
NETL
NSTL
维普
万方数据