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The quenching temperature of 45th steel pipe is A3+(30~50) °C. In actual operation, the upper limit is generally taken. The high quenching temperature can accelerate the heating of the workpiece, reduce the surface oxidation, and improve the work efficiency. In order to homogenize the austenite of the workpiece, a sufficient holding time is required. If the actual loading capacity is large, it is necessary to extend the holding time appropriately. Otherwise, hardness may be insufficient due to uneven heating. However, if the holding time is too long, there will also be coarse grains, serious defects in oxidative decarburization, and quenching quality. We believe that if the furnace charge is greater than the process documentation, the heating and holding time needs to be extended by 1/5.
Because of the low hardenability of No. 45 steel pipes, a 10% brine solution with a high cooling rate should be used. After the workpiece enters the water, it should be hardened, but it is not cold. If the workpiece is completely cold in the brine, it may crack the workpiece. This is because when the workpiece is cooled to about 180°C, the austenite is rapidly transformed into martensite. Excessive tissue stress. Therefore, when the quenched workpiece is cooled to the temperature range, slow cooling method should be adopted. Because the temperature of the outlet water is difficult to grasp, it must be operated by experience. When the shaking of the workpiece in the water stops, the outlet water can be cooled (if oil cooling is better). In addition, the workpiece should not be moved to the water should be static, should be in accordance with the geometry of the workpiece, making regular movements. Static cooling media plus stationary workpieces result in non-uniform hardness, non-uniform stress, large deformations, and even cracking.
The quenched hardness of 45# tempered steel quenched and tempered parts should reach HRC56~59, and the possibility of large cross section is lower, but it cannot be lower than HRC48. Otherwise, it means that the workpiece has not been completely quenched, and sorbite and even ferrite may appear in the structure. Body tissue, which survives through tempering, remains in the matrix and does not achieve the goal of conditioning.
The 45-gauge steel pipe is quenched at high temperature and tempered. The heating temperature is usually 560-600°C, and the hardness requirement is HRC22-34. Because the purpose of tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide. However, if the drawing has hardness requirements, it is necessary to adjust the tempering temperature according to the drawing requirements to ensure the hardness. For example, some shaft parts require high strength and high hardness requirements; while some gears and shaft parts with keyways need to be milled and inserted after quenching and tempering, so the hardness requirements are lower. Regarding the tempering holding time, depending on the hardness requirements and the size of the workpiece, we believe that the hardness after tempering depends on the tempering temperature, which is not related to the tempering time, but it must be reversed. The general workpiece tempering holding time is always More than one hour.
Seamless steel pipe network for everyone details 45th steel pipe
The 45th steel pipe is a medium carbon structural steel. Its hot and cold processing properties are good, its mechanical properties are good, its price is low and its source is wide, so it is widely used. Its greatest weakness is its low hardenability, large cross-section dimensions and relatively high workpiece requirements.