1 Purpose and significance of the research Study and develop a new process for heat treatment of austempered ductile iron which can obtain excellent performance, reduce cost and energy consumption, and is easy to operate and realize, namely, room temperature oil grading austempering.
2 room temperature oil classification austempering heat treatment process test study 21 austenitizing temperature and time on the microstructure and properties of the impact of 211 austenitizing temperature test shows that increasing the austenitizing temperature can increase the amount of retained austenite, Austria The higher the austenitizing temperature, the higher the carbon content in the austenite, the stronger the austenite stability, and the more the austenite amount after the classification austempering, and vice versa. When the austenitizing temperature rises to 920, the heated structure is completely austenitized, the austenite is relatively uniform, and the carbon content is high, and fine upper bainite, a small amount of lower bainite and stable residue can be obtained. Austenite, this matrix structure is not only high in hardness but also has good toughness. Continue to increase the austenitizing temperature, the structure is obviously coarsened, the amount of retained austenite is large, the upper bainite needle is coarse and the distribution is sparse, the hardness is obviously reduced, and the toughness is also reduced.
22 grading quenching time on the organization and performance 221 mathematical calculation of the grading quenching time control grading time is essentially to control the pre-cooling temperature of the workpiece. According to the heat transfer relationship between the test piece and the quenching medium, the classification quenching time of the sample is calculated to be between 13722538s.
The experimental study of grading quenching time of 222 increases the hardness with the increase of the classification time. The impact toughness is less than 30s in the classification time. With the extension of the classification time, the impact value increases, but when the classification time continues to increase, the impact toughness is It is on a downward trend. It can also be seen from the metallographic structure that when the classification time is less than 5 s, the overall temperature of the sample is still high due to the short pre-cooling time, and the cooling rate in the furnace is small, resulting in insufficient test hardenability and pearlescence. The transformation of body organization. As the grading time increases, the overall temperature of the sample decreases before isothermal, which causes the cooling rate to increase significantly. The acicular structure in the product increases and refines, and the upper bainite structure begins to appear in the tissue. When the grading time is about 30 s. At the same time, we obtained the desired Aube organization after isothermal. The tissue has moderate hardness, good toughness and good comprehensive mechanical properties. When the grading time continues to increase, the lower bainite increases and the retained austenite decreases, so the hardness continues to rise, the toughness decreases, the grading time is too long, and the workpiece is pre-cooled below the Ms point, producing a certain amount of martensite. High hardness and low toughness. Of course, in actual production, it is also necessary to determine the classification quenching time according to the equivalent wall thickness of the workpiece.
Effect of isothermal temperature and time on microstructure and properties Isothermal is the last control process of room temperature oil grading austempering process. When studying the influence of isothermal transformation temperature on microstructure and properties, the tensile strength of the studied austempered ductile iron Four indexes of mechanical properties such as elongation, impact toughness and hardness were investigated.
3 Application of heat treatment deformation on the final gear of the tractor. The internal diameter of the gear before and after the heat treatment and the key length of the gear that affects the meshing of the gear are determined. It is found that after the temperature quenching treatment by the room temperature oil, the deformation is small, both positive and regular. The tolerances are within the tolerances, so tolerances must be reserved for machining.
4 Conclusions (1) Room temperature oil grading Austempering is a new process for the production of austempered ductile iron and high-strength toughened ductile iron without salt bath.
(2) Room temperature oil classification Austempering heat treatment Select reasonable process parameters to obtain austempered ductile iron with good comprehensive mechanical properties. The process also reduces the sensitivity to isothermal temperature and time.
(3) Under the premise of ensuring hardenability, the classification quenching time is prolonged for workpieces with large equivalent wall thickness values ​​and large structural dimensions.
2 room temperature oil classification austempering heat treatment process test study 21 austenitizing temperature and time on the microstructure and properties of the impact of 211 austenitizing temperature test shows that increasing the austenitizing temperature can increase the amount of retained austenite, Austria The higher the austenitizing temperature, the higher the carbon content in the austenite, the stronger the austenite stability, and the more the austenite amount after the classification austempering, and vice versa. When the austenitizing temperature rises to 920, the heated structure is completely austenitized, the austenite is relatively uniform, and the carbon content is high, and fine upper bainite, a small amount of lower bainite and stable residue can be obtained. Austenite, this matrix structure is not only high in hardness but also has good toughness. Continue to increase the austenitizing temperature, the structure is obviously coarsened, the amount of retained austenite is large, the upper bainite needle is coarse and the distribution is sparse, the hardness is obviously reduced, and the toughness is also reduced.
22 grading quenching time on the organization and performance 221 mathematical calculation of the grading quenching time control grading time is essentially to control the pre-cooling temperature of the workpiece. According to the heat transfer relationship between the test piece and the quenching medium, the classification quenching time of the sample is calculated to be between 13722538s.
The experimental study of grading quenching time of 222 increases the hardness with the increase of the classification time. The impact toughness is less than 30s in the classification time. With the extension of the classification time, the impact value increases, but when the classification time continues to increase, the impact toughness is It is on a downward trend. It can also be seen from the metallographic structure that when the classification time is less than 5 s, the overall temperature of the sample is still high due to the short pre-cooling time, and the cooling rate in the furnace is small, resulting in insufficient test hardenability and pearlescence. The transformation of body organization. As the grading time increases, the overall temperature of the sample decreases before isothermal, which causes the cooling rate to increase significantly. The acicular structure in the product increases and refines, and the upper bainite structure begins to appear in the tissue. When the grading time is about 30 s. At the same time, we obtained the desired Aube organization after isothermal. The tissue has moderate hardness, good toughness and good comprehensive mechanical properties. When the grading time continues to increase, the lower bainite increases and the retained austenite decreases, so the hardness continues to rise, the toughness decreases, the grading time is too long, and the workpiece is pre-cooled below the Ms point, producing a certain amount of martensite. High hardness and low toughness. Of course, in actual production, it is also necessary to determine the classification quenching time according to the equivalent wall thickness of the workpiece.
Effect of isothermal temperature and time on microstructure and properties Isothermal is the last control process of room temperature oil grading austempering process. When studying the influence of isothermal transformation temperature on microstructure and properties, the tensile strength of the studied austempered ductile iron Four indexes of mechanical properties such as elongation, impact toughness and hardness were investigated.
3 Application of heat treatment deformation on the final gear of the tractor. The internal diameter of the gear before and after the heat treatment and the key length of the gear that affects the meshing of the gear are determined. It is found that after the temperature quenching treatment by the room temperature oil, the deformation is small, both positive and regular. The tolerances are within the tolerances, so tolerances must be reserved for machining.
4 Conclusions (1) Room temperature oil grading Austempering is a new process for the production of austempered ductile iron and high-strength toughened ductile iron without salt bath.
(2) Room temperature oil classification Austempering heat treatment Select reasonable process parameters to obtain austempered ductile iron with good comprehensive mechanical properties. The process also reduces the sensitivity to isothermal temperature and time.
(3) Under the premise of ensuring hardenability, the classification quenching time is prolonged for workpieces with large equivalent wall thickness values ​​and large structural dimensions.
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