Microstructure And Performance Control Of Hot Rolled TRIP 590 Steel Produced By Simulated CSP Process

TRIP(Transformation Induced Plasticity)steel is an advanced high strength automotive steel with high strength,good plasticity,comprehensive formability and so on,which can provide powerful guarantee for automobile safety and lightweight,so it has broad application prospects in the future.However,currently hot rolled TRIP steel is mainly produced by conventional continuous casting and rolling(CCR)process at home and abroad.The disadvantage is that the thickness specification of hot rolled TRIP steel by using CCR process cannot cover the range of cold rolled products,therefore the application is greatly limited.Compared with the CCR process,the compact strip production(CSP)process holds obvious advantages in the production of thin and ultra-thin specification for steel products with low energy consumption and low cost.It is achieved that some cold rolled products can be replaced by hot rolled products produced by CSP process,which meets the development trend of green manufacturing of steel materials.But the physical metallurgy characteristics of CSP process is different from the CCR process,thus it needs to be investigated urgently.Based on this,the 0.2C-1.2Si-1.5Mn TRIP steel as the research object was studied in the paper.And the CSP process Was simulated by means of Thermecmastor-Z thermal simulation machine,which reveals the continuous cooling transformation behavior,the pro-eutectoid ferrite and bainite isothermal transformation behavior.At the same time,the effect of intermediate cooling process and coiling process on the microstructure and mechanical properties of hot rolled TRIP steel produced by simulated CSP process were further investigated by means of rolling experiments.The main results obtained are as follows:(1)The dynamic continuous cooling transformation(CCT)curve and Time-Temperature-Transformation(TTT)curve of the experimental steel were obtained.(2)The study on the effect of intermediate cooling process and coiling process on the microstructure and mechanical properties of hot rolled TRIP steel produced by simulated CSP process shows that when the intermediate cooling temperature is 680 oC,the optimal mechanical properties were obtained..And with the isothermal holding time increasing,the mechanical properties of experimental steel change slightly,which is beneficial for the CSP process.When the coiling temperature is 400 ℃,the retained austenite will decompose with the isothermal time prolonging,which makes the performance deteriorated.However,when the coiling temperature is 360 ℃,the mechanical properties of experimental steel increase with th e isothermal holding time prolonging.(3)The optimum technological parameters on simulated CSP process of 0.2C-1.2Si-1.5Mn hot-rolled TRIP steel were obtained.The optimal intermediate cooling and coiling process parameters are 680 ℃,6 s,400 oC and 15 min,respectively.Correspondingly,the proportion of ferrite,bainite and retained austenite in matrix is 46.59%,46.31%and 7.1%,respectively.What’s more,the yield strength,tensile strength,elongation and the product of strength and elongation are 519 MPa,740 MPa,29%and 21.46 GPa%,respectively,which meets the performance requirements of TRIP 590 steel.