关键词: 齿轮钢, 渗碳, 晶粒长大, AlN

Abstract: The effects of heating temperature and holding time on the austenite grain growth behavior of SCr420H gear steel samples with different AlN precipitation states were experimentally investigated. The equilibrium precipitation and dissolution law of AlN precipitates in the experimental steel was calculated by Thermo-Calc thermodynamic calculation software， and the precipitation behavior of AlN in the experimental steel was studied by field emission transmission electron microscopy. The results show that the hot-rolled and air-cooled samples are mixed grain structure after being carburized for 0.5 h at 950-1 050 ℃， and the average austenite grain size level is below grade 5. The austenite grains of the samples after 1 210 ℃ solution-water quenching treatment do not grow up after carburizing at 950-1 000 ℃ for 0.5-6 h or at 1 050 ℃ for 0.5-2 h， the austenite grain size level is grade 9.5-10. The abnormal grain growth phenomenon occurs after 2 hours carburizing at 1 050 ℃. The sample after 1 210 ℃ solution-water quenching is isothermally treated at 700 °C for 1 h and then water-cooling so that it can be carburized at 1 050 °C for 8 h without abnormal grain growth or mixed grain structure， the average austenite grain size is 14 µm， the grain size level is grade 9.4. The growth behavior of austenite grains during carburization process is mainly controlled by the solubility and the ripening rate of the secondary phase AlN in the sample. The size of AlN precipitates in the solution-treated sample after carburization at 1 050 ℃ for 0.5 h is less than 80 nm， with an average size of 27.8 nm. 14.3% AlN particles larger than 100 nm appear in the sample after carburization at 1 050 ℃ for 2.5 h， with an average size of 64.2 nm.

Key words: Gear Steel, Carburizing, Grain Growth, AlN