Experimental study on austenite-bainite ductile iron gear Li Xiaoqin1, Xia Lanting2 (1.Shanxi Electromechanical Design and Research Institute, Taiyuan 030009, China; 2. Taiyuan Heavy Machinery College, Taiyuan 030024, China) Austempered Austempered Ductile Iron It is an engineering material with excellent comprehensive performance. It not only has high strength, high hardness, high wear resistance, but also good plasticity and toughness. It can replace the manganese-based and chromium-based low-alloy steel to make gears, which can reduce the cost by about 30% and has good chip performance. Low running noise, high contact fatigue strength, strong pitting resistance, good wear and wear resistance, low sensitivity to notch, and simple production process. The original drawings of the 60,000 sets of Cummins engine gears processed by Datong Gear Factory for the Second Automobile are required to be made of Ao-Bei ductile iron. At that time, there was no manufacturer in China, and 16MnCr5 alloy steel was temporarily replaced. Our institute cooperated with Datong Gear Factory on Austria-Bein. The development of the ductile iron Cummins engine gear has achieved satisfactory results, indicating that it is an excellent material to use O-Bei ductile iron instead of steel to make gears.
1. As the heating temperature increases, the amount of austenite increases, and some of the transformation into martensite and high-carbon bainite during cooling lowers the toughness and increases the strength and hardness.
However, when the heating temperature is too high, a large amount of austenite remains in the structure, resulting in a decrease in hardness and strength, and coarse grains, delaying the start of isothermal transformation, and promoting secondary carbide precipitation.
Prolonging the austenitizing time is beneficial to the organization and uniform composition, but the time is too long and the crystal grains are coarse. In addition, the austenitizing time is also related to the original structure, wall thickness, etc. D 3) The isothermal temperature is based on the C curve, and the quenched martensite is prone to occur when the isothermal temperature is lower than the Ms line. It is generally considered that 340T: is the boundary temperature of the upper and lower bainite, and the lower bainite is formed in the range of Ms to 3401: and has good wear resistance. The effect of isothermal temperature on mechanical properties, such as. It can be seen that the tensile strength is about 300X: the maximum is reached, and the toughness is about 380X: the peak. If the isothermal temperature is too low, more quenched martensite appears, resulting in high hardness and low toughness. As the isothermal temperature increases, the amount of austenite increases, the quenched martensite decreases, and the bainite tends to be coarse, resulting in a decrease in strength and hardness and an increase in toughness. However, when the isothermal temperature exceeds 380t, the amount of austenite begins to decrease, and carbides are precipitated from austenite, which reduces the comprehensive mechanical properties of ductile iron. D 4) Isothermal time isother temperature is essential for obtaining Au-Bei tissue, such as According to the chemical composition of the ductile iron, the austenitizing state, the isothermal temperature and the wall thickness of the casting, etc. The isothermal time is too short, there is a large amount of quenched martensite in the structure, only a small amount of lower bainite and retained austenite, and the brittleness is very large. With the extension of the isothermal time, the quenched martensite is correspondingly reduced, and the lower bainite The austenite is increased, and the isothermal time is too long to obtain upper bainite having carbide precipitation.
The influence of time TVs isothermal time on mechanical properties was determined by repeated experiments. The austempering process was determined to be as follows. The as-cast mechanical properties and microstructure 4 test results and the analysis of the cast properties and microstructure of Cummins gears are shown in Table I. The mechanical properties after heat treatment are shown in Table 2. For the matrix structure after heat treatment, see C 900t910X: The grain growth of nodular cast iron tends to be much smaller than that of steel, and the higher the solidification temperature is beneficial to the homogenization of carbon in the matrix. The temperature of the isothermal transformation differs significantly from the tissue obtained. Table 2 shows that the isothermal temperature is 250t2601C, and its comprehensive mechanical properties are not ideal. When the temperature is 280T:300T: Austempered ductile iron with excellent comprehensive mechanical properties can be obtained.
Table 2 The mechanical properties of the heat treatment after heat treatment is better, the spheroidization rate is more sturdy, the more the number of balls, the smaller the ball diameter, the absence of free cementite, and the austenitization of W-ball iron is more favorable. Therefore, the austenitizing temperature can be lowered and the time is shortened, and the tensile strength of the austempered ductile iron is more than one time as compared with the ordinary ductile iron. The hardness is increased by 80%c. It can be seen from Table 2 that when the joint is lower bainite, the tensile strength is as high as 丨300N/mni2-丨6(H)N/mm2, the elongation is 丨3%, and it has good wear resistance. Sex, the f gear can also significantly reduce the noise when the substrate is woven into a two-phase mixture of lower bainite and austenite. This kind of organization has the strength of good rape. toughness. Under non-alloy conditions. The heating degree is 5 conclusion 9I0T:, the isothermal temperature is 280V301:, can obtain good comprehensive mechanical properties, is an excellent material for manufacturing gears. Aobei ductile iron can meet the technical requirements of Cummins engine gears, and can completely replace 16MnCr5 alloy steel gears.
Compared with the 6MnCr5 steel gear, the weight of the Austempered ductile iron gear is light, the cost of the blank is low, the material utilization rate is short, the heat treatment cycle is short, the deformation is small, and the cutting performance before quenching can reduce the gear production cost by about 30%.
test:. Beijing: Mechanical Industry Press, Liang Tianyi, et al. The application of quark elements in cast iron. Xi'an: Xi'an Jiaotong University Press, W92. Wang Jingde. Wu Mingxiang of the å©ä¸¨ 体 ball 黾 cast iron on the tractor planetary gear shaft. Development and application of austenite-å©ä¸¨æ°ä½“å°é‡‘çƒé“磨çƒ
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