Isothermal normalizing process of 18CrNiMo7-6 gear steel directly after warm forging

doi:10.13251/j.issn.0254-6051.2020.11.015

Abstract

Abstract: Isothermal normalizing of 18CrNiMo7-6 gear steel directly after warm forging was studied. The results show that the cooling rate, isothermal temperature and isothermal time are the key process parameters in the isothermal normalizing process utilizing residual warm forging heat. Lower cooling rate and higher isothermal temperature can effectively improve pearlite transformation in limited isothermal time, reduce the content of retained austenite and non-equilibrium microstructure such as martensite and bainite at room temperature, and therefore obtain ideal microstructure and properties. The hardness of 163-164 HBS, ferrite grain size of grade 10-11.5 and banded structure of grade 1.5 can be obtained by the process of cooling rate of 0.1 ℃/s and 1 ℃/s and isothermal temperature of 650 ℃ for 1 h. The microstructure and properties can meet the technical requirements, meanwhile it has good machinability and provides ideal microstructure for subsequent heat treatment process.

Key words: gear steel, warm forging, isothermal normalizing, hardness, microstructure

CLC Number:

TG156.4

Wang Huizhen, Zhai Yuewen, Zhou Leyu. Isothermal normalizing process of 18CrNiMo7-6 gear steel directly after warm forging[J]. Heat Treatment of Metals, 2020, 45(11): 78-82.

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