Effect of ultra-fast cooling process on microstructure and properties of DP780 hot rolled strip
Aiming at the development of low-cost,high-performance DP780 hot rolled strip,the chemical composition of the optimized design is carried out to reduce the addition of expensive alloying elements Cr,Mo,V,etc.,and the content design of C,Si,Mn is optimized.The designed chemical composition is as follows:w(C)=0.105％,w(Si)=1.15％,w(Mn)=1.7％,w(Ti)=0.01％.Combined with the in-tegrated ultra-fast cooling system of front ultra-fast cooling+laminar cooling+rear ultra-fast cooling,a machine learning model of ultra-fast cooling heat transfer coefficient based on extreme learning machine was established,which effectively improved the control accuracy of the outlet temperature of front ultra-fast cooling and coiling temperature.Based on this,the effects of the front ultra-fast cooling outlet tem-perature and coiling temperature on the microstructure evolution and mechanical properties of DP780 hot rolled strip was investigated.The results show that the microstructure of DP780 hot rolled strip is ferrite and martensite when the coiling temperature is set at 190 ℃.The volume fraction of martensite decreases and the volume fraction of ferrite increases with the decrease of the front ultra-fast cooling outlet tem-perature.The microstructure of hot rolled strip is mainly ferrite,martensite and a small amount of bainite when the front ultra-fast cooling outlet temperature is set at 610 ℃ and the coiling temperature is 230 ℃.However,with the decrease of coiling temperature,the bainite in the microstructure gradually disappears,the volume fraction of martensite decreases,and the volume fraction of ferrite increases.The DP780 hot rolled strip with low cost and high performance was obtained by the integrated control process of hot rolling and ultra-fast cooling,with yield strength of 641 MPa,tensile strength of 1 068 MPa,elongation at break of 11.5％and strong plastic volume of 12 282 MPa·％.
DP780 hot rolled stripultra-fast cooling processfront ultra-fast cooling outlet temperaturecoiling temperaturemachine le-arnignmicrostructure and propertylow cost
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维普
