Effect of Chemical Composition and Cooling Process on Microstructure and Mechanical Properties of Multiphase Steel and Martensite Steel

The effect of chemical composition and cooling process on microstructure and mechanical properties of specimens taken from the controlled rolled and cooled strips of vacuum melted multiphase and martensite steels were researched. The results show that the microstructure changes from ferrite plus pearlite to bainite and martensite, the strength increases and the elongation decreases with the decreasing of coiling temperature. The strength of sheet coiled at low temperature is mainly decided by the content of carbon, while both strength and elongation are improved with the increase of silicon content. The effect of two-step cooling process on microstructure and mechanical properties is complex. The advanced high strength automobile steel of same chemical composition can be manufactured by different controlled cooling processes for different strength classes.