The Evolution Of The Microstructure Of High Carbon Martensitic Stainless Steel Used As A Cutlery Material During Manufacturing Process

The evolution of the microstructure, carbides and performance of 7Cr17MoV martensitic stainless steel used as a cutlery material during manufacturing process has been studied. The results are useful for guiding the production. The research contents and conclusions are as follows:Thermodynamic calculation of equilibrium precipitation in 7Cr17MoV stainless steel during solidification process was carried out by Thermo-calc software. Fe-C equilibrium phase diagrams containing 17% Cr were calculated. Element compositions in Ferrite, Austenite and carbide varied along with the solidification. M7C3 carbides precipitated from austenite first, and then transformed to M23C6 carbides. The microstructure of 7Cr17MoV stainless steel was 87% ferrite and 13% carbides.The study on electroslag remelting (ESR) of 7Cr17MoV martensitic stainless steel shows that matrix structures were changed and the morphology and distribution of carbides were improved by ESR. The removal efficiency of inclusions can be improved by optimizing slag system and slag amount.The hot compressive deformation behaviour of 7Cr17MoV stainless steel were investigated using a Gleeble-3500 hot simulator. The results show that stress increased rapidly, then increased slowly to peak, finally keep steady as strain increasing. Peak stress decreased with decreasing in strain rate and increasing in deformation tempreture. The flow stress constitutive equation was established. Microstructures were refined by the increase of deformation tempreture and cooling rate and the decrease of strain rate.By studying the effect of rolling on microstructure, carbides and performance of 7Crl7MoV stainless steel, it was found that the microstructure of the rolled and annealed steel consisted of pearlite and spheroidal carbides. After cold rolling, the aggregation of carbides was no longer evident, and the carbides appeared to be small in size and uniformly distributed, whereas carbides in hot rolled strips clearly aggregated. Decreasing the thickness of the cold rolled strips led to the decrease in the size of the carbide particles while increasing their number, which improved the particle distribution. The carbide phase, which primarily consisted of M23C6, did not change during cold rolling and annealing. The tensile strength and yield strength first decreased and then increased, and the elongation increased as the thickness of the cold rolled strips decreased. Dimples and the second phase particles were readily observed upon tensile fracture. The the second phase particles are identified to be primarily carbides and oxide inclusions.The heat treatment on 7Cr17MoV cold rolling strips was studied. The results demonstrate that the best heat treatment technology by which optimum comprehensive properties could be obtained was:quenching on 1050℃-1100℃ and holding time is greater than 15 min, then tempering on 200℃-250℃. Hardness, tensile strength, elongation, corrosion potential were greater than 55 HRC,1800 MPa,4%,-0.25 V, and self-corrosion current was less than 2.0 ×10-8 A/cm2 after heat treatment.