Study On Properties Of Heat Treatment Technology For New-type High-alloy 17Cr2Ni2Mo Carburizing Gear Steel

With the development of gear drive and expansion of its applications, the performance and heat treatment technology of the gear materials are brought up higher requirement. 17Cr2Ni2Mo steel is a kind of new steel which has been introduced from Germany recently, it has excellent mechanical properties and higher cost-effective. With the globalization of the manufacturing, domestic consumption of 17Cr2Ni2Mo steel is increasing every year, but its basic data of heat treatment is lacking or incomplete which can affect technology control and quality stability. So, based on requirement of the productive practice, the properties of heat treatment technology for 17Cr2Ni2Mo carburizing gear steel such as case hardenability, reference carbon content, change of core hardness and distortion characteristic etc were studied systematically in this paper.1. The hardenability of 17Cr2Ni2Mo steel was analyzed by jominy test and delamination test comparing to common carburizing gear steels 20CrNi2Mo and 20CrMnMo. The equal hardness curves of three alloy steels were drew, respectively. The results show that case hardenability is enhanced along the increase of surface carbon content, but all of three alloy steels have appropriate carbon content which make cases have optimal hardenability. The surface carbon content of 17Cr2Ni2Mo corresponding to best hardenability is between 0.75% and 0.85%,20CrNi2Mo and 20CrMnMo are 0.80%～0.85% and 0.80%～0.90%, respectively.2. The reference carbon content of 17Cr2Ni2Mo was studied by the hardenability curves, and effect factors of the reference carbon content were discussed. The reference carbon content curve of 17Cr2Ni2Mo was obtained. The results show that the carbon content corresponding to effective hardened layer depth which is not a fixed value, and it is changing with the workpiece size.3. The core hardness of different modules and section thicknesses for 17Cr2Ni2Mo gear steel were studied using tooth samples, and the core hardness of 20CrNi2Mo,20CrMnMo and 20Cr2Ni4 etc were predicted. The results show that the core hardness decrease regularly with modules and section thicknesses increasing. The results have a certain significance to select gear materials and predict the bending fatigue strength of gear materials.4. Distortion characteristics of 17Cr2Ni2Mo were tested by simulation tooth samples, and the samples were quenched with stilling cold oil, stirring cold oil, stilling hot oil and stirring hot oil, respectively, and then distortion results were analysed by contrast analysis mode. The results show that the cooling uniformity and the quenching distortion dealed with stirring hot oil are better, which is also benefits to reduce tooth distortion.Based on the above research, this paper does some on the analysis that reasonable surface carbon concentration can be got by proper controlling of carburizing process, and the optimal hardenability of the gear was obtained. When considering the different effect factors on reference carbon content simultaneously, the efficiency of carburizing can be improved. In addition, quenching deformation can be reduced by stirring hot oil mode.