Nanoindentation Properties of 18CrNiMo7-6 Steel after Carburizing and Quenching Determined by Continuous Stiffness Measurement Method

• Published in: Metals (Basel ) 2020-01, Vol.10 (1), p.125
• Main Authors: Zhou, Guiyuan, Guo, Jian, Zhao, Junyu, Tang, Qian, Hu, Zhaonan
• Format: Article
• Language: English
• Subjects: 18crnimo7-6 steel; Carburizing; carburizing and quenching treatment; Case hardenability; Case hardening; Compressive properties; Convexity; Dimensional analysis; Experiments; Hough transformation; indentation size effect; Load; Measurement methods; Mechanical properties; Nanoindentation; Nickel chromium molybdenum steels; Parameter modification; Quenching; Residual stress; Size effects; Stiffness; Strain rate; Stress relaxation; Yield strength; Yield stress
• ISSN: 2075-4701; 2075-4701
• DOI: 10.3390/met10010125

In this work, the nanomechanical properties involving the indentation size effect (ISE) and yield strength of a surface-modified layer of 18CrNiMo7-6 steel after case hardening were investigated via nanoindentation experiments. The experimental results showed that the hardness increased with an increase in strain rate; the contact stiffness versus indentation depth curves take the form of upper convexity due to residual compressive stress relaxation. On the basis of the Ruiz-Moreno model, a modified model considering the cutoff parameter as a function of indentation depth was proposed. This model was able to better describe the ISE of the surface-modified layer. With the Hough transform error angle of 0.1° as the critical value (h0.1° is the corresponding depth), when h > h0.1°, the yield strength calculated by the Ma model started to disperse at the depth of h0.1°. These results provide useful insight into the local mechanical properties of 18CrNiMo7-6 steel after carburizing and quenching treatment.