Study On Phase Change Behavior Or Microstructure And Properties Of Low Carbon Microalloyed Steel

In order to meet the high requirements of various industries for the steel industry,the development of low-carbon micro-alloyed high-strength steel with high strength,high toughness,high weldability and high formability has become a hot research topic nowadays.In this paper,several kinds of low-carbon micro-alloyed steels were selected,and the phase transformation was analyzed through isothermal transformation process,and the influence of hot rolling and tempering processes on the microstructure and properties of the experimental steel were studied through process simulation and hot rolling experiments,and the experimental data can be provided for industrial production.The main results obtained in this paper are as follows:(1)The isothermal transformation experiment shows that the microstructure of the steel transformed from lath bainite to martensite and ferrite with the increasing of holding temperature under undeformed condition.The microhardness of the steel decreases first and then increases with the increasing of holding temperature when the temperature is between 460?560? and 580?700?.The microstructure of the steel transformed from granular bainite to ferrite and martensite with the increasing of holding temperature under deformed condition.The microhardness of the steel decreases first and then increases when the temperature is between460?600?,and the microhardness decreases gradually when the temperature is between 600?700?.(2)Process simulation shows that the grain size of the steel decreases and its microhardness increases when the deformation temperature is lower.The microhardness of Ti,Ti-Mo and TiNb steel are 175HV,210HV,186HV and 170HV,189HV,181HV,respectively,when the deformation temperature are 900? and 1100?,respectively.The microstructure of the steel is changed from bainite to ferrite and martensite,and the microhardness increases first and then decreases with increasing of isothermal temperature.The microhardness of the steel decreases gradually with the increasing of holding time when the temperature is at 500? and 600?,and the microhardness of the steel is gradually increased when the temperature is at 700?,and the slow cooling after isothermal increase the nano-hardness of the ferrite matrix.(3)The results of hot rolling experiment show that the yield strength and tensile strength of the steel increase with the increasing of finishing rolling temperature.The yield strength and tensile strength of Ti and Ti-Nb steels decreases,and the yield strength and tensile strength of Ti-Mo steels increases with the increasing of finishing cooling temperature.(4)The results of tempering experiment show that the yield strength of Ti steel and Ti-Mo steel increase and the tensile strength decrease,and the yield strength and tensile strength of TiNb steel increase when the tempering temperature is at 600?.The yield strength and tensile strength of Ti steel decrease,and the yield strength of Ti-Mo steel increase and the tensile strength decrease,and the yield strength and tensile strength of Ti-Nb steel increase when the tempering temperature is at 700?.