Isothermal quenching method of bearing steel G55SiMoV

Abstract

The invention discloses an isothermal quenching method of bearing steel G55SiMoV. The isothermal quenching method is characterized in that bainitic bearing steel G55SiMoV is subjected to isothermal quenching and a quenched microstructure is a bainite / martensite mixed microstructure. The isothermal quenching method comprises the following steps of 1, keeping a sample at an austenitizing temperature of 890 to 920 DEG C for 20 to 30 minutes, 2, carrying out quenching in a medium containing KNO3 and NaNO2, 3, cooling to a temperature of 270 to 290 DEG C and keeping the temperature for 15 to 45 minutes, and 4, cooling gradually to a temperature of 170 to 190 DEG C and carrying out tempering thermal insulation for 1 to 2 hours, wherein the steel G55SiMoV treated by the above steps has a lower bainite / martensite mixed microstructure and the content of lower bainite is in a range of 15 to 25%. A workpiece treated by the isothermal quenching method has the advantages of small deformation, good size stability, generation of a surface stress state, difficult generation of grinding cracks, and high impact toughness and fracture toughness. Therefore, the isothermal quenching method can improve steel performances greatly.

Description

Technical field: [0001] The invention belongs to the field of metal material heat treatment, and relates to a bearing steel quenching process, in particular to a G55SiMoV bearing steel bainite austempering process. Background technique: [0002] At present, domestic rolling mill bearings mostly use chromium bearing steels GCr15 and GCr15SiMn, using conventional martensitic quenching and low temperature tempering processes. The steps are: [0003] The quenching heating temperature is 850±5℃ for 20 minutes after austenitizing, and then cooling by two methods: (1) directly quench into spindle oil at 25℃ (room temperature), followed by tempering at 160℃ for 2 hours; (2) respectively Quench into an isothermal bath at 160°C, 200°C, 220°C and 240°C. The isothermal residence time is 10 minutes, 30 minutes, 60 minutes and 90 minutes, respectively, and then cooled to room temperature, followed by tempering at 160°C. 2 hours. [0004] This kind of process causes part of the subcooled austenit...

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Problems solved by technology

[0006] At present, there is still a lack of systematic research on the heat treatment process of 55SiMoV steel and its relationship with the structure and performance. Conventional quenching and low-temperature tempering processes are mostly used in bearing production, so early fractures often occur during use, which affects the full play of its performance.

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