Effect of Normalizing Cooling Method on Microstructure and Mechanical Properties of 9%Cr Ferritic Heat Resistant Steel

The 9%Cr ferritic heat resistant steel was normalized by oil cooling and water cooling, and then was tempered. The effects of normalizing cooling methods on the microstructure and mechanical properties of the test steel were studied. The results show that compared with those by water cooling, the strip width of the martensitic slats of the test steel by oil cooling was larger, the dislocation density was smaller, and the size of M₂₃C₆ carbide precipitated on the grain boundary was smaller. Compared with those by water cooling, the yield strength, tensile strength, percentage elongation after facture and impact absorption work on the upper platform of the test steel by oil cooling increased by 9.3%, 4.7%, 6.1%, 5.4%, respectively, and the tough-brittle transition temperature was reduced by 17.7 ℃; the tensile properties and impact properties were enhanced.