Quenched and tempered steels are carbon seamless steel and alloy quenched and tempered steel two categories, either carbon or alloy steel, the carbon content of more stringent controls. If the carbon content is too high, the strength of the workpiece after quenching may be shrill, but the toughness is not enough, as the carbon content is too low, increase the toughness and lack of strength. In order to get a good piece quenched overall performance, the overall control of the carbon content of 0.30 to 0.50%. When the tone of hardened, the entire section of the hardenability requirements of the workpiece, the workpiece was dominated by fine needle quenched martensite microstructure.
By tempering to obtain a uniform sorbite based microstructure. Small plants cannot engage each furnace metallurgical analysis, generally only for hardness testing, that is to say, hardness after quenching hardness of the material must meet hardness requirements for check in Figure tempering. No. 45 steel quenching temperature in A3 + (30 ~ 50), in practice, is usually taken ceiling. High quenching temperature can make the workpiece heating speed, reduce surface oxidation, and can achieve better efficiency. In order to homogenize the austenitic workpiece, you need sufficient holding time. If the actual installed furnace capacity, would be adapted to extend the holding time. Otherwise, there may be caused due to insufficient hardness of the uneven heating of the phenomenon. However, holding time is too long, will also appear coarse grains, oxidation and decarbonization serious ills affecting quenching quality. We believe that if installed furnace is greater than the specified process documents. Heat insulation needs to extend the fifth time. Because No. 45 steel hardenability is low, it should be 10% larger cooling rate of saline solution. The workpiece into the water, it should hardenability, but not through the cold, if the workpiece in a cold brine permeability, it is possible cracking of the workpiece, this is because when the workpiece is cooled to about 180 , causing the austenite into martensite rapidly tissue caused by excessive stress.
Therefore, when hardened workpiece rapid cooling to the temperature of the region, they should take the slow cooling method. Because the water temperature is sometimes difficult to grasp, accountable experience operating, shake the water stops when the workpiece can be air-cooled water (if oil cooler better). In addition, moving the workpiece into the water should not be static, should be in accordance with the geometry of the workpiece, as the rules of sport. Stationary cooling medium plus stationary workpiece, resulting in uneven hardness, stress uneven leaving considerable deformation of the workpiece, and even cracking.
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