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

Guiyuan Zhou,Jian Guo,Junyu Zhao,Zhaonan Hu,Qian Tang

doi:10.3390/met10010125

Guiyuan Zhou, Jian Guo + Show 3 more

Open Access

https://doi.org/10.3390/met10010125

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Journal: Metals	Publication Date: Jan 15, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of South China, Chongqing University

Abstract

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.

Highlights

Gearboxes in wind turbines and cement mills require high performance to work in extremely harsh conditions for a long period of time
This maximum ofthe thestraight-line straight-linesegments segmentsunder under different error angles shown in Figure resultresult indicates that there no significant difference in the maximum depth ofdepth the straight-line segment. This indicates that is there is no significant difference in the maximum of the straight-line under the threethe strain rates, sorates, the indentation depth influenced by the by residual compressive stress segment under three strain so the indentation depth influenced the residual compressive is independent of the strain to the previous analysis,analysis, we propose that the residual stress is independent of the rate
According to the previous we propose that the compressive stress has no influence on the on elastic modulus and hardness at a depth of ~250 nm and residual compressive stress has no influence the elastic modulus and hardness at a depth of ~250 nm only a slight influence at a depth of

Summary

Introduction

Gearboxes in wind turbines and cement mills require high performance to work in extremely harsh conditions for a long period of time. The surface-modified layer plays an important role in improving resistance against the wear and fatigue of gears. In actual operation, damage is still frequent, such as tooth breakage and spalling [1,2,3]. Both the wind turbines and cement mills suffer severe and variable dynamic loads, so it is very important to investigate the damage behaviors and mechanisms of tooth surfaces under a dynamic load. Given that the mechanical properties, such as the yield strength and the hardening exponent, play an essential role in gear design, the measurement of the local mechanical properties is of great significance. It is difficult to obtain the local mechanical properties of materials around the tooth’s surface by means of a macroscopic method; the nanomechanical characterization method is of great significance and would help to enrich our understanding of the nanomechanical properties of the surface-modified

Results

Discussion

Conclusion