Performance Analysis And Mechanical Fatigue Determination Of 40Cr By Different Conditions Of Nitrogen/Water Spray Quenching

Heat treatment technology is one of the most important areas of advanced manufacturing technology nowadays, which could give or improve the performance of materials in usage by changing the internal microstructure of the metal or the chemical composition of the surface. Nitrogen/water atomized spray quenching process is a new heat treatment process. This technology has raised a wild attention and study for its advantages that the cooling rate is fast, uniformity, environment friendly and the controllable process.This article focus on carbon 40Cr alloy structural steel, and the object is treated with nitrogen/water atomized spray quenching, oil quenching under different process parameters and then the treated test pieces were subjected to tensile and fatigue experiments under high temperature after quenching experiments. The changes of fatigue and mechanical properties of the 40Cr steel after different nitrogen/water atomized spray quenching treatment are compared; we can get the following conclusions through the research as follows:After a nitrogen/water atomized hardening treatment, the hardness of the specimen improves significantly, and the hardness increases with the increase of water. Besides, the tensile strength of the specimen improved significantly, too. And there is proportional relationship with the changes of water volume.Nitrogen/water atomized spray quenching process can improve the fatigue limit of 40Cr steel, under the same nitrogen pressure, the dispersion degree of SN curve increases with the increase of the amount of water.The fatigue fracture under high temperature after nitrogen/water atomized spray quenching treatment include three parts:the initiation fatigue crack zone, the fatigue crack propagation zone and the final fracture zone, and the final fracture zone takes a larger proportion of the fracture area.In conclusion, after a comprehensive study of microstructure and mechanical properties of 40Cr steel after nitrogen/water treatment, it indicates that, compared with other quenching process, nitrogen/water atomized spray quenching process can control the mechanical and fatigue performance of the specimen by adjusting the amount of water, and there is a relatively wide range of the control ability.