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Steel knowledge: 45 # steel and 40Cr quenched and tempered steel heat treatment process is quenched and tempered dual heat treatment, the purpose is to make the workpiece has a good overall mechanical properties. Quenched and tempered steel has carbon quenched and tempered steel and alloy two major categories of quenched and tempered steel, whether carbon steel or alloy steel, the carbon content of the more stringent control. If the carbon content is too high, after quenching and tempering the strength of the workpiece is high, but the toughness is not enough, such as carbon content is too low, toughness increased strength and lack of strength. In order to get good quality and quality of the overall performance, the general carbon content control in the 0.30 ~ 0.50%. Quenching and tempering, requiring the entire section of the workpiece hardened, so that the workpiece was fine needle-shaped martensite-based microstructure. Through tempering at high temperature, sorbite-based microstructure was obtained. Small factories can not do metallurgical analysis of each furnace, usually only for hardness testing, that is to say, after quenching the hardness of the material must reach the quenching hardness, tempering hardness requirements according to the map to check. Workpieces quenching and tempering operations, must be strictly in accordance with the process of implementation of the document, we are just on the operation of the process to put some ideas. 1,45 steel quenched and tempered 45 steel is carbon structural steel, hot and cold processing performance are good, better mechanical properties, and low prices, wide source, so a wide range of applications. Its biggest weakness is low hardenability, large cross-section size and higher requirements of the workpiece should not be used. 45 steel quenching temperature A3 + (30 ~ 50) ℃, in practice, the upper limit is generally taken. High quenching temperature can make the workpiece heating speed, reduce the surface oxidation, and can improve work efficiency. In order to make the workpiece austenite uniform, you need enough holding time. If the actual loading capacity, you need to properly extend the holding time. Otherwise, there may be a lack of hardness due to uneven heating. However, holding time is too long, there will also be coarse grains, serious problems of oxidative decarburization, affecting the quenching quality. We believe that if the loading volume is larger than the process documentation, the heating and holding time needs to be extended by 1/5. Because of the 45 steel pipe hardenability is low, it should be used cooling rate of 10% saline solution. After the workpiece into the water, it should be hardened, but not cold, if the workpiece in the brine cold, it is possible to make the workpiece cracking, it is because when the workpiece cooled to about 180 ℃, austenite rapidly transformed into martensite Too much tissue stress. Therefore, when quenching the workpiece quickly cooled to the temperature region, we should take a slow cooling method. As the temperature of the water is difficult to grasp, it is necessary to experience the operation, when the water jitter to stop the workpiece, you can air water cooling (if oil cooling better). In addition, the workpiece should not move into the water should be static, should be in accordance with the geometry of the workpiece, for regular exercise. Quiescent cooling medium with a stationary workpiece, resulting in uneven hardness, uneven stress and make the workpiece deformation, or even cracking. 45 seamless steel pipe quenched and tempered hardness should reach HRC56 ~ 59, the possibility of a large cross section lower, but not lower than HRC48, otherwise, the workpiece is not fully quenched, the organization may appear sorbite or even Ferrite, this organization by tempering, still remain in the matrix, the purpose of quenching and tempering. 45 steel quenching high temperature tempering, heating temperature is usually 560 ~ 600 ℃, hardness requirements for HRC22 ~ 34. Because the purpose of quenching and tempering is to get comprehensive mechanical properties, so the hardness range is relatively wide. But the drawings have hardness requirements, it is necessary to adjust the tempering temperature according to the drawings to ensure the hardness. If some shaft parts require high strength, high hardness requirements; and some gears, keyway shaft parts, due to the quenching and tempering but also milling, plugging processing, the hardness requirements lower. About 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, and tempering time is not important, but must be back, the general tempering holding time is always More than an hour. 2, 40Cr seamless steel pipe quenched and tempered Cr can increase the hardenability of steel, improve the strength and tempering of steel stability, with excellent mechanical properties. Cr-steel should be used for quenched and tempered workpieces with large or important section size. However, there is a second type of Cr steel temper brittleness. 40Cr quenching and tempering quenching and tempering of the workpiece, a variety of parameters of the process card is provided, we experience in practice is: (A) 40Cr workpiece quenching should be oil-cooled, 40Cr steel hardenability better, in oil Cooling can be hardened, and the workpiece deformation, cracking tendency. However, small-scale enterprises in the case of tight oil supply, the shape of the workpiece is not complicated, you can quench in the water, did not find cracking, but the operator should be strictly controlled by the experience of water, water temperature. (B) 40Cr workpiece quenched and tempered hardness is still high, the second tempering temperature will increase 20 ~ 50 ℃, otherwise hard to reduce the hardness. (C) 40Cr workpiece after tempering, the complex shape of the oil cooling, simple cooling in water, the purpose is to avoid the second type of temper embrittlement. Quickly after tempering the workpiece after cooling, if necessary, applied to eliminate stress treatment. Affect the quality of quenched and tempered parts, the level of the operator is an important factor, at the same time, there are equipment, materials and pre-quenching and other reasons, we believe that: (a) the workpiece transferred from the furnace to the cooling tank slow, The temperature of the workpiece into the water has dropped below the critical point of Ar3, resulting in partial decomposition, the workpiece is not fully quenched organizations, not up to the hardness requirements. So pay attention to the speed of small parts coolant, large parts to be cold to master the time. (B) the amount of loading the workpiece to be reasonable to 1 to 2 is appropriate, the workpiece overlap caused by uneven heating, resulting in uneven hardness. (C) the workpiece into the water arrangement should maintain a certain distance, too close to the workpiece near the steam film rupture, resulting in the workpiece near the surface hardness is low. (D) quenching furnace, can not quench one breath, should be considered the degree of furnace temperature drop, half-way furnace re-warming, in order to quench the hardness before and after the same piece. (E) pay attention to the coolant temperature, 10% brine temperature above 60 ℃, can not be used. Coolant can not have oil, mud and other impurities, otherwise, there will be lack of hardness or uneven phenomenon. (F) unprocessed rough quenched and tempered, the hardness will not be uniform, in order to get a good quality quenched and tempered, the rough should be rough car, bar to be forged. (G) strict quality control, hardness after quenching low 1 to 3 units, you can adjust the tempering temperature to meet the hardness requirements. However, after quenching the hardness of the workpiece is too low, and some even only HRC25 ~ 35, must be re-quenching, must not be applied only in the temperature or low temperature tempering to finish drawing requirements done, otherwise, the loss of the significance of quenching and tending, and may have serious s consequence. The knowledge of steel pipe