Research On Dynamic Recrystallization Behavior Of Extra-heavy Backup Roll Forging Process

Heavy backup roll is a key part of steckel mill, because of its exceptional workenvironment, it needs high temperature resistance, fracture resistance, hardness,toughness and other aspects of performance. The fine equiaxed grains can be got byrepeated dynamic recrystallization and deformation. There is a high density ofdislocations and dislocation tangles in material, which can improve the microstructureand properties of material.In this paper, Gleebles-1500thermal simulation testing machine was used forthermal simulation compression tests of large steel support roll material45Cr4NiMoV.The constitutive model alloy strain curve is build, and the constitutive model wasobtained by Zener-Hollomon parameter method. According to the power dissipationtheory,45Cr4NiMoV steel thermal processing map was established by the use ofdynamic material model. Through the analysis of thermal processing graph, stable andunstable regions deformed region was identified, it provided a theoretical reference forthermal processing. The optimum process parameter of45Cr4NiMoV steel for hightemperature deformation was determined.The dynamic recrystallization critical strain of the alloy was discussed by Poliakand other scholars with hardening rate (θ) method, they thought the critical conditionwas considered correspondding to inflection point of lnθ-ε curve and the minimumvalue on-(lnθ)/ε-ε curve. The dynamic recrystallization critical strain model of45Cr4NiMoV was establishmented.The dynamic recrystallization kinetics behavior of45Cr4NiMoV steel wasstudied. Based on Avrami model, the dynamic recrystallization grain size evolutionmodel, feature strain model, the percentage of dynamic recrystallization model wereestablishmented. With the application of Deform-2D software, internal dynamicrecrystallization and grain size distribution of45Cr4NiMoV steel sample was received.By contrastion with the metallurgical test results, it indicated that the established model can predict the thermal deformation microstructure evolution process of45Cr4NiMoV steel. The Deform-3D software was used to predict the microstructureevolution during deformation for heavy supporting roller.