How can the heat treatment process be formulated?
45 steel quenching and tempering45 steel is a medium carbon structural steel, cold and hot processing performance is good, mechanical performance is good, and low prices, wide range of sources, so widely used. Its biggest weakness is hardenability, low cross section size and relatively high requirements of the workpiece should not be used.
Because the hardenability of 45 steel is low, the 10% brine solution should be used at a high cooling rate. The workpiece into the water, should be hardened, but not cold, if the workpiece in the brine cold, it is possible to make the workpiece cracking, this is because when the workpiece is cooled to about 180 DEG C when austenite transforms into martensite rapidly caused by excessive stress caused by. Therefore, when the quenched workpiece is cold to the temperature zone, a slow cooling method should be adopted. As the water temperature is difficult to grasp, we must rely on experience to operate, when the workpiece shaking in the water stopped, you can water out of air cold (such as oil, cold better). In addition, the workpiece into the water should be moving, not static, should be in accordance with the geometry of the workpiece, regular movement. The stationary cooling medium plus the stationary workpiece causes uneven hardness and uneven stress, causing the workpiece to become deformed and even crack.45 pieces of quenched and tempered steel after quenching hardness should reach HRC56~59, the possibility of large section low, but not less than HRC48, otherwise, the work has not been fully quenched sorbite, appear even ferrite may in the organization, the organization through tempering, is still retained in the base body, not up to quality objective.
45 steel quenching temperature at A3+ (30~50) DEG C, in practical operation, usually take the upper limit. High quenching temperature can accelerate the workpiece heating, reduce the surface oxidation, and improve the work efficiency. Adequate homogenization time is required for the homogenization of austenite in the workpiece. If the actual amount of furnace installed is large, it is necessary to extend the insulation time properly. Otherwise, there might be a lack of hardness due to uneven heating. However, when the holding time is too long, the defects of coarse grain and serious decarburization of oxidation and decarburization will also be affected, which will affect the quality of quenching. We believe that if the amount of furnace is larger than the process documents, the heating and insulation time should be extended by 1/5.
45 steel quenched after high temperature tempering, heating temperature is usually 560~600 degrees, hardness requirements of HRC22~34. Because the purpose of quenching and tempering is to obtain 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 requirements of the drawings to ensure hardness. If some shaft parts require high strength, hardness requirements are high; and some gear, with keyway of shaft parts, due to hardening and tempering, but also for milling, insert processing, hardness requirements are lower. On the tempering time, apparent hardness requirements and the workpiece dimensions, we believe that the tempering hardness depends on the tempering temperature and tempering time, little relationship, but must return through general workpiece tempering time for more than an hour.
