Continuous cooling transformation behaviors of low carbon steels with two Si contents (0.50% and 1.35%) were investigated under undeformed and deformed conditions. Effects of Si contents, deformation, and cooling rates on γ transformation start temperature (Ar3), phase microstructures, and hardness were studied. The results show that, in the case of the deformation with the true strain of 0.4, the length of bainitic ferrite laths is significantly decreased in low Si steel, whereas, the M/A constituent becomes more uniform in high Si steel. An increase in cooling rates lowers the Ar3 greatly. The steel with higher level of Si exhibits higher Ar3, and higher hardness both under undeformed and deformed conditions compared with the steel with a lower Si content. Especially, the influence of Si on Ar3 is dependent on deformation. Such effects are more significant under the undeformed condition. The hardness of both steels increases with the increase of cooling rates, whereas, the deformation involved in both steels reduces the hardness.
CAI Ming-huiDING HuaZHANG Jian-suLI LongLI Xiao-binDU Lin-xiu
Ultra-fine austenite grains with size of 1～3μm were prepared in a Nb-V-Ti steel through repetitive treatment of rapid heating and quenching.A model for the growth kinetics of these ultra-fine austenite grains was successfully created through successive 2 processes,and the activation energy Q for growth was estimated to be about 693.2 kJ/mol,which directly shows the inhibition effect of microalloy elements on the growth of ultra-fine austenite grains.
Hot deformation experiments were carried out on Gleeble 1500 thermo-mechanical simulator. The bainite transformation after deformation was investigated by optical microstructure analysis. The results indicated that the deformation accelerated the bainite transformation when the deformation was carried out at high temperature and no or little ferrite was precipitated before bainite transformation; when the deformation was carried out at low temperature, the deformation hindered the bainite transformation because a lot of ferrite precipitated before bainite transformation.
DU Lin-xiu YI Hai-long DING Hua LIU Xiang-hua WANG Guo-dong
