Wuhan University of Technology

Graduation Project (Dissertation)

Research on spot induction hardening process of automobile transmission gear

School： School of International Education

Major/Class： Automotive Engineering 1303

Student Name： Zhang LiMing

Mentor Name： Wang Zhou

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Abstract

Gear is the most basic and important part in the automobile transmission system, but the working condition of the gear of the automobile transmission system is rather bad, and it is easier to be damaged than other gears. Therefore, in order to better strengthen the surface of the gear, the spot induction hardening process is applied to the heat treatment of the automobile transmission gear. Spot induction hardening is a new type of hardening process. The biggest advantage of this process is that it can be subjected to local induction hardening, and the area of a hardening is very small. In this paper, according to the characteristics and principles of spot induction hardening, we design variables, changing the heating power, changing the cooling rate, changing the sensor moving speed, and doing spot induction hardening for large modulus gear tooth surface to experimental study.

First of all, the spot induction hardening process is compared with the traditional hardening process before the experimental investigation of the spot type induction hardening of the automobile transmission gear tooth surface. Analysis of the effect of spot type induction hardening process and the advantages of steel material parameters on the final material properties in induction hardening process spot, and then expounds the related theories, which lays the theoretical foundation for the experimental research on automobile transmission gear type induction hardening process.

Secondly, through the static point induction hardening test of gear, the properties of the material are studied. The variation of temperature along with the depth direction during the quenching process is obtained at different heating powers and different cooling rate. According to the austenitizing temperature, cooling rate and microstructure, the hardness of the alloy was measured by Vivtorinox hardness tester. The result of hardness in the depth of the hardened tooth surface was obtained.

Finally, the moving point induction hardening test of the automobile transmission gear is carried out under different sensor movement rate parameters. We obtain the law of temperature field under different technological parameters, and the result of the microstructure and hardness in the depth direction after hardening.

In this paper, spot induction partial hardening process is applied to the surface strengthening of automotive transmission gear teeth surface, revealing the regularity of different process parameters automobile transmission gear spot induction hardening temperature, microstructure and hardness, providing scientific basis for improving the comprehensive mechanical properties of automobile transmission gear.

Key words: Spot induction hardening; Automobile transmission gear; Temperature change; Micro-structure transformation; Complete martensite region

Content

Abstract I

Content III

Chapter 1: Introduction 1

1.1 Project background 1

1.2 Introduction of induction hardening 2

1.3 Research of induction hardening technology 3

1.3.1 Foreign development 3

1.3.2 Domestic development 5

1.4 Application status of automobile gear steel 6

1.4.1 Application status of foreign automobile gear steel 6

1.4.2 Application status of domestic automobile gear steel 7

1.5 The main propose of this paper 7

Chapter 2: Principle of spot induction hardening 9

2.1 Introduction of spot induction hardening 9

2.2 Basic principle of gear induction hardening 10

2.3 Skin effect and Curie spot effect 12

2.4 Two ways of gear induction heating 14