Fatigue Properties Of Martensitic Stainless Steels With Ultra-low Carbon And High Cleanliness

With several decades development of stainless steel materials for hydraulic turbine, their comprehensive properties have been significantly improved. But water turbine unit is currently being developed towards large-scale and weight savings, which requires higher strength and higher yield-tensile ratio of stainless steel materials to meet the need of this new trend. The newly developed high yield-tensile ratio low carbon martensitic stainless steel, which was produced based on traditional clean casting stainless steel -- ASTM-CA6NM (ZG06Crl3Ni4Mo) , had got increasing in its strength and hardness while no decreasing in its toughness and plasticity by special heat-treatment processing. And its ratio of yield strength and tensile strength was 0.8 or over higher than it抯counter value 0.7 of traditional purity stainless steel materials. So it was fitting that the development trend of weight reduction. Fatigue crack of large-scale hydraulic turbine hasn't been solved well in the worldwide. For promotion engineering application of the high yield-tensile ratio stainless steel, fatigue properties and fatigue mechanisms were investigated.Main conclusion and creative work are given in the following: The microstructure and phase constituent on the high yield-tensile ratio stainless steel were analyzed. Single-phase lath martensitic microstructure was observed.Some fatigue properties on the high yield-tensile ratio stainless steel were systematically tested including fatigue strength, fatigue crack growth rate, fatigue crack propagation threshold and P-S-N curves. The results showed that the fatigue strength of the high yield-tensile ratio stainless steel was higher than that of traditional purity stainless steel materials, and the properties on the fatigue crack growth rate, fatigue crack propagation threshold and P-S-N curves were a little lower than those of...