Recrystallization And Strengthening Mechanisms Of High Strength Steel By CSP

Strips made by CSP exhibit higher strength than those produced by conventional hot rolling,which means CSP shows a superiority in manufacturing high strength sheet. Therefore, thispaper carried out researches on the recrystallization behavior and microstructure evolution,aiming to provide a reference for composition and rolling parameters designment of700Mpahigh strength steel to be produced by CSP, and finally ended with a comprehensive analysis ofstrenthening mechanisms, especially focused on precipitation strengthening.Thermal simulation test was introduced to figure out softening mechanisms under diffeenttemperatures and strain rates. σ εcurve indicated that higher temperature or lower strain ratewas favorable for dynamic recrystallizaton, and the inflections in θ σcurves were helpful toobtain the initiation conditions of dynamic recrystallization. With mathematical method, theZenner-Hollomon parameter could be expressed as Z=ε&exp（329.074/RT）=3.82×10^-3σ_p^7.015，, andfurther the values of σc/σp, εc/εpat0.1s^-1were calculated to be0.83and0.37respectively, whichis consistent with the reported values for C-Mn steel.Analysis of strengthening mechanism led to a conclusion that the yield strength of the testedsteel could be over700Mpa only if refinement and precipitation strengthening mechanismsplayed important roles simultaneously. The ferrite grain size had a tight relationship withcumulative deformation, for example, the grain diameter was nearly5.6μm under reduction rateof97%, which was close to the limited size od CSP production; The precipitation amount of TiCwas controlled by carbon content, the volume fraction of TiC for the steel with0.065%C（wt） was0.0527%, much higher than0.0137%of the steel with0.195%C（wt）.