| LIU Xiaokun,YAN Shidang,ZHANG Heng,SHI Lubing,LIU Zhongming,PEI Bang,HE Xu.Experimental Study on Mechanical Properties of Surface-hardened Layer of Gear Steel Based on Flat Indentation Method[J],54(7):225-234 |
| Experimental Study on Mechanical Properties of Surface-hardened Layer of Gear Steel Based on Flat Indentation Method |
| Received:June 19, 2024 Revised:October 09, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2025.07.019 |
| KeyWord:hardened layer gear steel stress-strain relationship energy density equivalence flat indentation finite element analysis |
| Author | Institution |
| LIU Xiaokun |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| YAN Shidang |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| ZHANG Heng |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| SHI Lubing |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| LIU Zhongming |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| PEI Bang |
Zhengzhou Machinery Research Institute Zhengzhou Transmission Technology Co., Ltd., Zhengzhou , China |
| HE Xu |
Chengdu Miniature Mechanical Testing Science & Technology Co.Ltd., Chengdu , China |
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| Abstract: |
| The surface of the component is modified by heat treatment or other techniques to achieve a hardened layer. Obtaining the stress-strain relationship is challenging due to the high hardness and difficulty of sampling. In order to realize the indentation test of elastic-plastic mechanical properties such as the stress-strain relationship of the surface-hardened layer of gear steel, the work aims to propose a flat indentation model based on energy density equivalence to describe the relationship between material Hollomon power law (H-law) parameters, indenter diameter, indentation work and displacement for the high-strength hardened layer material. Furthermore, a method for determining the H-law parameter of materials with flat indentation was also developed. Finite Element Analysis (FEA) was employed to determine the parameters of the flat indentation model within the range of Young's modulus E of 200 GPa, initial yield stress σy of 200 MPa, 400 MPa, …, 1 800 MPa and 2 000 MPa and strain hardening exponent n of 0.05, 0.1, …, 0.35 and 0.4. The prediction error of the flat indentation model on the stress hardening exponent was corrected. Flat indentation models with different surface roughness and surface curvatures were modeled and calculated to investigate the effect of the two types of surface morphology on indentation results. Proposed correction methods reduced the requirement of indentation surface topography and improved the robustness of the flat indentation method when the surface roughness Ra of the measured material was 0.4 μm, 0.8 μm, 1.6 μm, and 3.2 μm, and the surface radius of curvature R was 5 mm, 10 mm, 20 mm, and 50 mm, respectively. In terms of experimentation, a diamond cylindrical flat indenter with a diameter of 0.3 mm was employed to perform flat indentation tests on the base metals of four commonly used gear steels of 18CrNiMo7-6, 20Cr2Ni4A, 18Cr2Ni4WA and 20CrMnMoH. The maximum indentation displacement was approximately 60 μm, and the maximum indentation load was approximately 700 N. The initial yield stress and strain hardening exponent of the H-law parameter were obtained by inverting the loading coefficient and loading exponent of the loading section of the indentation energy-displacement curve. The Young's modulus of the H-law parameter was obtained by inverting the unloading stiffness of the unloading section of the curve. The conditional yield strength Rp0.2 and tensile strength Rm were obtained from the H-law parameter. The results of the indentation test and the results of the uniaxial tensile test were in good agreement with each other. The maximum error in the elastic modulus and tensile strength was no greater than 3%, while the maximum error in the conditional yield strength was no greater than 6%. The hardened layer heat treatment was carburizing and quenching. The treatment conditions were as follows of well gas carburizing, nitrogen-methanol atmosphere, carburizing temperature of (930±5) ℃ carburizing time of 22 h, quenching temperature of (830±5) ℃ (20CrMnMoH:(850± 5) ℃), and quenching medium of bright quenching oil. The stress-strain relationship of the four hardened layer materials was evaluated through the use of the flat indentation test method, and the results demonstrated good repeatability. In conclusion, a straightforward and precise indentation test method with broad applicability is proposed. It is capable of effectively obtaining the elastic-plastic mechanical properties of the surface-hardened layer of gear steel. |
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