The Study Of Heat Deformation Behavior On Ti+P-IF Steel And Ti-IF Steel

IF steel is the mainly material in the modern automobile industry. The hot rolling is one of the most important links in the production process. The microstructure after hot rolling has the heredity to the subsequent cold rolling and recrystallization so that it has very great theoretical and real role to comprehend the hot deformation behavior of the IF steel in the hot rolling process.In this paper, the experiments were carried on the Gleeble-3800 hot Thermal Mechanical Simulator for the Ti+P-IF steel and Ti-IF steel. The hot deformation behavior of the two steel in single pass,double pass and the whole hot rolling process were investigated by the analysis of metallurgical structure, TEM and the stress-strain curve, The results are follows:1. The conclusions in the single pass are as follows:(1)The critical flow stress of the Ti+P-IF steel in austenite region and ferrite region islarger than that of the Ti-IF steel, and the critical flow stress in the two-phase region issmaller than the Ti-IF steel.(2)The recrystallization can occur with deformation temperature at 950℃and 0.1 s^-1 thestrain rate for the Ti-IF steel.(3)Under the same deformation condition, the second phase particle in the Ti+P-IF steelis smaller and the flow stress of the Ti+P-IF steel and the Ti-IF steel is increasing withthe increasing strain rate of deformation.2. The conclusions in the duale pass are as follows:(1)The second phase particles gather and grow up with the prolonging the holding time.The second-phase particles in the Ti-IF steel precipitate together with deformationtemperature at 800℃and precipitate dispersively with deformation temperature at900℃.(2)The flow stress of the two steel will declined if the holding time is prolonged withdeformation temperature at 800℃, but the flow stress will increase in certain holdingtime with deformation temperature at 900℃.(3)The strain resistance of the Ti+P-IF steel is larger than the Ti-IF steel withdeformation temperature at 800℃, and the strain resistance of the Ti+P-IF steel is lowerthan the Ti-IF steel with deformation temperature at 900℃. 3. The conclusions are as follows in the whole hot rolling process:(1) The flow stress will small with the low slab reheating temperature in the austenite region for the same steel, the flow stress of the Ti+P-IF steel is larger than the Ti-IF steel for the same heating temperature.(2) Hot rolling in the ferrite region:①In order to get fine and even ferrite grain at the high slab reheating temperature, the strain rate should be small in the high temperature finishing rolling. On the contrary, the strain rate should be large in the low temperature finishing rolling.②In order to get fine and even ferrite grain at the low slab reheating temperature, the strain rate should be large in the high temperature finishing rolling. On the contrary, the strain rate should be small in the low temperature finishing rolling.