Study On Microstructure And Mechanical Properties Of The 23MnNiCrMo54 Link-Chain Steel

Comparing domestic 23MnNiCrMo54 steel with 23MnNiCrMo54 steel made in Japan, We find that they have the same chemical compositions, but the link chain made of domestic 23MnNiCrMo54 steel had the drawbacks, such as non-uniform in deformation, low in fatigue life, and so on, in comparison with the link chain produced in Japan. Investigation on microstructure revealed that the domestic steel was composed of inhomogeneous microstructure, in which the carbides were irregular in morphology and non-uniformly distributed, and that the domestic steel has an apparent aggregation in alloying element-molybdenum and chromium. To make domestic 23MnNiCrMo54 steel can reach or exceed the level of the same type steel, it is required to gain fine, uniform spheroidized carbide microstructure. But, low carbon steel is different from high carbon steel, in which has obvious uneven carbon. So this phenomena make low carbon steel spheroidized difficult. In order for this, on the base of annealing at 1150 C 6h to eliminate alloy aggregation, we adopted two kinds of heat-treating processes, the heat treatment with deformation and the heat treatment without deformation.1. 23MnNiCrMo54 steel is quenched at 880 Cfor 0.5h and tempered at between 680 C and 720 C. With the temper temperature improved, the trend get bigger of ferrite's recovering and recrystallion and the precipitation amount of carbide get more. When the temper temperature rose to 720 掳C ,the carbide get aggregated. Also, under the condition of stable temper temperature and with the temper time long, the trend get bigger of ferrite's recovering and recrystallion and the precipitation amount of carbide get more. So 23MnNiCrMo54 steel is tempered at 700 C for 10h is benefit for gaining uniform ,fine carbide .2. Addition of a tempering at 500 C before the tempering at 700 C was powerful for the steel to obtain the fine and homogeneous carbides and then to show good mechanical properties.3. 23MnNiCrMo54 steel deformed and heat treated at 600 C or 650 C respectively can accelerate the precipitation of carbide and the microstructure is influenced by parameter Zener-Hollomon and strain. The microstructure was composed of the equal axial ferrite and disperse carbide at the condition of the bigger parameter Zener-Hollomon and the greater deformation. However, some Bainite in addition to the ferrite and disperse carbide presented in the samples with the smaller parameter Zener-Hollomon and the less deformation, and the amount and the size of the Bainite increased with a decrease in theparameter Zener-Hollomon and the strain.4. After this, 23MnNiCrMo54 steel is tempered at deformation temperature, not only carbides go on precipitating , but also deformation energy is free and decrease hardness of steel to require of make the link chain.