Effect of cooling rate on the microstructure and properties of HSLA steel thick plates
For the low hardenability problem of low alloy high-strength steel,the microstructure variation of tested steel with C content of 0.04wt％were investigated,under different cooling medias and cooling rates.When the cooling rate is between 16.2-40.5 ℃/s,the microstructure lath bainite is obtained,and when the cooling rate is between 8.1-16.2 ℃/s,the mixed microstructure of lath bainite and granular bainite is obtained.The volume frac-tion of granular bainite increases continuously with the decrease of cooling rate.When the cooling rate is increased,the density of high angle grain boundaries in the microstructure significantly increases,while the density of low an-gle grain boundaries slightly increases,and the effective grain size decreases.Through the multi-scale simulation method,the simulation model of cooling process of thick plate is established,in order to calculate the temperature and microstrucre.With this simulation model,the volume fractions distribution of martensite,lath bainite and gran-ular bainite in 20-35 mm thick plates under different heat transfer coefficients have been calculated.The results show that when the heat transfer coefficient is set as 2 000 W/(m2K),the volume fraction of granular bainite in the center of 35 mm thick plate can reach about 73％,and 100％lath bainite can be obtained in the center of 20 mm and 28 mm thick plates.By improving the cooling intensity,the volume fraction of granular bainite in the center of a 35 mm thick plate can be reduced,which can improve the strength and toughness of the steel.
HSLAthick plateheat transfer coefficientcooling ratebainiteGB density
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