Gradient microstructure and microhardness in a nitrided 18CrNiMo7-6 gear steel

38th Risø International Symposium on Materials Science

Yang, R.^1,2 ; Wu, G.L.^1 ; Zhang, X.^3 ; Fu, W.T.^4 ; Huang, X.^3

College of Materials Science and Engineering, Chongqing University, Chongqing

400044, China^1

State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing

400044, China^2

Section for Materials Science and Advanced Characterization, Department of Wind Energy, Technical University of Denmark, Riso Campus, Roskilde

DK-4000, Denmark^3

State Key Laboratory of Metastable Materials Science and Technology, College of Materials Science and Engineering, Yanshan University, Qinhuangdao

066004, China^4

关键词: Backscatter electron imaging;    Gradient microstructure;    Hardness values;    Martensite structures;    Nitrogen concentrations;    Properties and microstructures;    Tempered martensite;    Vickers hardness measurements;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/219/1/012047/pdf
DOI  :  10.1088/1757-899X/219/1/012047

来源: IOP

【 摘 要 】

A commercial gear steel (18CrNiMo7-6) containing a tempered martensite structure was nitrided using a pressurized gas nitriding process under a pressure of 5 atm at 530 °C for 5 hours. The mechanical properties and microstructure of the nitrided sample were characterized by Vickers hardness measurements, X-ray diffraction, and backscatter electron imaging in a scanning electron microscope. A micro-hardness gradient was identified over a distance of 500 μm with hardness values of 900 HV at the top surface and 300 HV in the core. This micro-hardness gradient corresponds to a gradient in the microstructure that changes from a nitride compound layer at the top surface (∼ 20 μm thick) to a diffusion zone with a decreasing nitrogen concentration and precipitate density with distance from the surface, finally reaching the core matrix layer with a recovered martensite structure.