Duplex stainless steel two-stage cooling process

When the content of alloying elements in the steel is low, the cooling rate is slow, and the structure of ferrite and pearlite is obtained. When the cooling rate is fast, the solid solution carbon in the ferrite is higher, which is not conducive to reducing the yield strength and improving the ductility. The performance of two-phase steel can be improved by using two-stage cooling, that is, from the critical zone heating temperature to a certain temperature, and then fast cooling. Slow cooling can enrich the carbon in ferrite to unconverted austenite. Fast cooling can avoid the isothermal decomposition of untransformed austenite and ensure the desired biphase structure and properties. For example, 0.08%C-1.4%Mn steel, from 800℃; The mechanical properties of heating to water cooling are: σ0.2=365PMa, σb=700MPa, σ0.2/σb=0.52, eu=18%, et=21%. If the two-stage cooling process is used, that is, at 800 ° C; After heating, air cooling to 600℃; And then water cooling, its performance is: σ0.2=280MPa, σb=600MPa, σ0.2/σb=0.47, eu=21%, et=29%. Two-stage cooling reduces the yield strength and improves the ductility of the two-phase steel.