| Cold rolled sheet is widely used in automobiles, building materials, electrical home appliances manufacturing and plating steel plate. Nowadays, the domestic demand for cold rolled sheet presents structural relative excess, which consists of surplus plate with low quality and sufficient high quality sheet. So the microstructure accurate and quantitative performance requirements of cold rolled sheet are put forward for the further study. The microstructure and performance of plate after rolling must be achieved by heat treatment, which plays a crucial role on mechanical properties of finished product. This paper takes the production of ST44-3G C-Mn steel cold rolled sheet from the factory as the research object, in order to explore effects of isothermal heat treatment process on the microstructure and performance.The supercooled austenite continuous cooling transformation curve(CCT)of the tested steel was measured by using Gleeble–1500D thermal simulation testing machine, and effects of heating temperature and holding time on microstructure transformation type and microstructure at room temperature after isothermal heat treatment and supercooled austenite isothermal heat treatment process were studied according to proper process parameter from CCT curve at the same time. The results indicate that the microstructure of experimental steel at room temperature microstructure consists of ferrite, westergren, pearlite and troostite. The microstructure transformation type of experimental steel in isothermal heat treatment was the nucleation of ferrite, westergren generated, the eutectoid transformation of pearlite and generation of troostite. And the ferrite and austenite recrystallization has also been happened in the same process too.The steel sheet tensile strength, yield strength and elongation of corresponding process conditions were also analyzed. The mechanical properties model of sheet tensile strength, yield strength and elongation was established based on mechanical properties of isothermal heat treatment, selection of exponential function as the model forms, which was verified by mechanical performance datum of other isothermal heat treatment. The results show that three mechanical performance model of the experimental steel were with accuracy, the maximum error was 9.818%, 13.048% and18.824% respectively, and the average deviation of which was only 3.818%, 3.210%and 8.003% respectively, which can predict the mechanical properties of isothermalheat treatment. |
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