Crl15 Super Martensitic Stainless Steel Group And The Study Of Mechanical Properties

The Cr15super martensitic stainless steel which is designed on the basis of the traditional martensitic stainless steel has a lower carbon level, a higher level of nickel and molybdenum. Compared to traditional martensitic stainless steel, it not only has high strength and high hardness, but also has good plasticity, weldability and corro-sion resistance. In more recent years, the super martensitic stainless steel gets more attention and has been used widely.In this work, the microstructure and mechanical properties of Cr15super mart-ensitic stainless steel after different heat treatments were systematically studied by transmission electron microscope, X-ray diffraction analysis and the universal testing machine, and the results have been obtained:The results show that the microstructures of the steel after quenching are lath martensite and a small amount of retained austenite. The content of retained austenite was tested by X-ray diffraction analysis, the result shows that the content of austenite are7.24%and1.94%after quenching at1050℃. Respectively, with the rising of the quenching temperature, the original austenite grain size increases and the lath marten-site gradually become thicker. The austenite grains grow slowly with the rising quenching temperature from900℃to1050℃. When the quenching temperatures are higher than1050℃, the austenite grains grow rapidly.The microstructures of tested steel tempered at550～750℃after quenching at1050℃are the tempered martensites which become fine with the rising temepring temperature. The austenite content increases first and then decreases with tempering temperature rise and finally reaches the maximum value of31.19%at700℃while steel B is28.04%which tempered at650℃. TEM observations indicate that the lath martensite with a high dislocation density is very fine. Reversed austenites with strip and diamond shape are observed along the original austenitic grain boundaries and martensitic lath boundaries after tempering. There is also reversed austenite precipi-tating along the boundaries of lath martensite of steel A after tempered at600℃.The hardness of steel decreases with the rising quenching temperature. When quenching temperatures are900℃～1100℃, the hardness of the steels changes in a certain range. But when quenched at temperatures above1100℃, the HRC decreases rapidly. The tensile strength (σb) of test steels is894Mpa～1026Mpa and hardness (HRC) is26.1～30.6and elongation (δ) is15.1%～21.12%after different heat treat-ment.The steel A displays the best comprehensive mechanical properties when sam-ples is tempered at650℃after quenching at1050℃while steel B is tempered at600℃. And the properties of the steel A is better than steel B under the same heat treat-ment condition.