时间：2015-10-08 16:24　作者：admin　点击： 次

 No. 45 steel is the name in GB, it is a kind of high-quality carbon structural steel of steel grade.
    No. 45 steel is a medium to medium carbon structural steel with good cold and hot workability, good mechanical properties, low price and wide sources, so it is widely used.
    The quenching temperature of No. 45 steel is A3+(30~50) ℃. In actual operation, the upper limit is generally taken.A higher quenching temperature can speed up the heating of the workpiece, reduce surface oxidation, and improve work efficiency.In order to homogenize the austenite of the workpiece, sufficient holding time is required.If the actual amount of furnace installed is large, the holding time needs to be extended appropriately.Otherwise, there may be insufficient hardness due to uneven heating.However, if the holding time is too long, coarse grains and serious oxidative decarburization will also occur, which will affect the quenching quality.We believe that if the furnace load is greater than the provisions of the process documents, the heating and holding time needs to be extended by 1/5.
    Because of the low hardenability of No. 45 steel, a 10% saline solution with a high cooling rate should be used.After the workpiece enters the water, it should be quenched, but not cold through. If the workpiece is cooled in salt water, it may crack the workpiece. This is caused by the rapid transformation of austenite into martensite when the workpiece is cooled to about 180°C. Caused by excessive tissue stress.Therefore, when the quenched workpiece is rapidly cooled to this temperature region, a slow cooling method should be adopted.Since the temperature of the water outlet is difficult to control, it must be operated by experience. When the shaking of the workpiece in the water stops, the water outlet and air cooling can be used (oil cooling is better).In addition, the workpiece should be moved but not static when it enters water, and should be moved regularly according to the geometric shape of the workpiece.The static cooling medium and the static workpiece result in uneven hardness, uneven stress and large deformation or even cracking of the workpiece.
    The hardness of the 45# steel quenched and tempered part after quenching should reach HRC56~59. The possibility of a large cross section is lower, but it cannot be lower than HRC48. Otherwise, it means that the workpiece has not been completely quenched, and there may be sorbite or even ferrite in the structure. Body tissue, this kind of tissue is still retained in the matrix through tempering, and cannot achieve the purpose of quenching and tempering.
    For high temperature tempering after quenching of No. 45 steel, the heating temperature is usually 560~600℃, and the hardness requirement is HRC22~34.Because the purpose of quenching and tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide.However, if the drawings have hardness requirements, the tempering temperature must be adjusted according to the drawings to ensure the hardness.For example, some shaft parts require high strength, and the hardness requirements are high; and 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 and holding time, it depends on the hardness requirements and the size of the workpiece. We believe that the hardness after tempering depends on the tempering temperature, which has little to do with the tempering time, but it must be back through. Generally, the tempering and holding time of the workpiece is always More than one hour.