Duplex stainless steel alloy elements and cooling rate

The experimental and theoretical calculations show that the critical cooling rate for obtaining the biphase structure after heating the critical zone is related to the manganese content in the steel. The critical cooling rate required to obtain the biphase structure can be estimated by the presence of alloying elements in the root steel, which provides a basis for selecting the appropriate cooling method in the production of heat-treated biphase steel.
When the chemical composition of the steel is certain, the lower cooling rate should be adopted as far as possible under the premise of ensuring the biphase structure, so that the carbon in the ferrite has sufficient time to diffuse into the austenite, thereby reducing the yield strength of the biphase steel and improving the ductility of the biphase steel. If the content of alloying elements in the steel is higher than 4, the critical cooling rate is too high, and the ferrite contains higher solidly dissolved carbon after cooling, which is not conducive to obtaining dual-phase steel with excellent performance, then the chemical composition of the steel should be changed, the content of alloying elements in the steel should be increased, thus reducing the critical cooling rate, or in the production process of dual-phase steel, the supplemental tempering process should be added to reduce the solidly dissolved carbon in the ferrite. Improve the performance of duplex steel. If the steel contains strong carbide forming elements, when estimating the critical cooling rate, the austenite hardenability and favorable influence of these elements on the critical region heating should be taken into account, and the carbide particles of V and Ti can improve the austenite hardenability and reduce the critical cooling rate through the nashing effect of the phase interface.