Microstructure and properties of powder forging gear materials

Gear transmission of torque and power depends on the engagement of teeth, which is an important mechanical transmission part widely used. Its design and manufacturing level directly affect the quality of industrial products. In the process of transmission, the teeth, especially the roots, will be affected by the bending moment, and the meshing parts will also be subject to greater friction. In order to ensure the normal operation of the gear, it is required to have the characteristics of high bending fatigue strength, high contact fatigue strength, high hardness and wear resistance of the tooth surface, high strength and impact toughness of the core, good processing performance, high quality and low price of raw materials, and sufficient sources.

The main method of gear production in our country is still the traditional cutting process, which is difficult to process, complex process, low production efficiency, serious waste of raw materials, greatly increasing labor costs, and has a negative impact on the benefits of enterprises; and in the cutting process, the fiber of the tooth shape part is cut off, resulting in low strength of the gear, affecting its bearing capacity. However, the traditional P / M gear is not dense enough, its mechanical properties are poor, and its application scope is limited. Therefore, improving the relative density of P / M products is the key to manufacturing high-performance gear and realizing industrialization.

Powder forging (PF) refers to the process that the preform sintered by powder is heated and then forged into parts in closed die. It is a new material processing technology which combines traditional powder metallurgy and precision forging, with less cutting and no cutting. Powder forging (powder forging) has the advantages of both powder metallurgy and precision forging, and avoids the disadvantages of low relative density of powder metallurgy products, low mechanical properties, low utilization of raw materials in traditional forging process, large draft angle of forging die, poor surface accuracy of forgings, etc., which opens up a broad prospect for manufacturing high density, high strength, high toughness and high precision powder metallurgy parts, It has become one of the most important development directions of modern powder metallurgy technology. Powder forging technology has a great advantage in the production of high-performance P / M automobile parts with complex shapes, and the production process is reliable, which can greatly reduce the cutting process and processing amount in the production process. The utilization rate of raw materials is about 2 times of the traditional steel forging process.

In recent decades, the proportion of powder forging parts used in automobile is increasing, especially in the United States, Germany, Japan and other countries. Typical products include powder forging connecting rod, gear, bearing ring, piston and so on. Alven and imbrogno, foreign scholars, have prepared P / M gears by different processes. Among them, the density of P / M gears is the highest and the bending fatigue performance is the best, which is equivalent to that of steel forged gears with the same composition. Sonti and others have successfully prepared powder forged gear with relative density up to 99%, which has the same bending fatigue strength as steel forged gear, and its impact performance, pitting fatigue life is even better than steel forged gear.

Metaldyne company, GKN company and Toyota Motor Company are all committed to the development of powder forging technology. They have developed high-performance powder forged automobile connecting rods with different grades, mainly fe-c-cu series, and achieved commercial production, with high economic benefits. Following the trend of science and technology in 1972, China began to study the powder forging material, plasticity theory, forging process and equipment, forging products and other aspects, and achieved significant research results. However, due to the reasons of raw materials, technology and equipment, it failed to realize the production of industrial mould.

In recent years, powder forging technology, because of its significant advantages, has again been widely concerned by domestic scholars. Guo Biao et al. Carried out numerical simulation research on the mechanism of powder pressing, pressing process, densification forming and powder forging process. Wang et al. Studied the effect of Cu content on the microstructure and mechanical properties of fe-c-cu system powder forging connecting rod material, and the thermal deformation behavior of fe-c-2.5cu material.

At present, there are many researches on powder forging automobile connecting rod in China, but the research on powder forging gear is still lacking. In this paper, alloy powder is pressed, sintered and forged to obtain standard block, and its microstructure and mechanical properties are systematically analyzed. On this basis, a planetary gear is prepared by powder forging technology, aiming to develop a gear material suitable for powder forging, which provides beneficial exploration for the development of powder forging technology in China.