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渗碳后直接淬火的钎尾用Si-Mn-Mo-V钢渗碳层中存在大量马氏体微裂纹,这种微裂纹即使在等温淬火后亦很难消除,从而影响使用性能。但在渗碳淬火后等温淬火前经一次高温回火的,渗碳层马氏体微裂纹却能基本消除。另外,马氏体微裂纹形成的临界含碳量为0.75％,Si-Mn-Mo-V钢也不例外。这一切均进一步证明了钎尾热处理工艺:①渗碳层含碳量不应大于0.8％C。②气体渗碳油冷后经550～650℃×1h回火,然后再加热至钎尾心部Ac_3以上20～30℃保温20min,于260℃等温淬火并二次回火工艺的必要性。
There is a large amount of martensite micro-cracks in the carburized layer of Si-Mn-Mo-V steel for direct brazing after carburizing. Such micro-cracks can hardly be eliminated even after isothermal quenching, which affects the serviceability. However, carburizing quenching after isothermal quenching before a high temperature tempering, carburized martensitic micro-cracks can be basically eliminated. In addition, the critical carbon content of martensite micro-cracks is 0.75%, and Si-Mn-Mo-V steel is no exception. All this further prove the solder tail heat treatment process: ① carbon content of carburizing layer should not exceed 0.8% C. ② gas carburizing oil after 550 ~ 650 ℃ × 1h tempering, and then heated to the end of the brazing tip Ac_3 above 20 ~ 30 ℃ heat 20min, 260 ℃ isothermal quenching and secondary tempering the necessity of the process.