Forging heat treatment knowledge
Forging heat treatment knowledge - forgings
Forging is a double heat treatment of quenching and high temperature tempering, and its purpose is to make the workpiece have a good overall mechanical properties.
Forging treatment: After quenching high temperature tempering heat treatment method known as forging treatment. High temperature tempering refers to tempering between 500-650 ° C. Forging can make the steel performance, material to a large degree of adjustment, its strength, plasticity and toughness are better, with good comprehensive mechanical properties. Forging treatment to get tempered sorbite. Tempered sorbite is formed by tempering martensite and is magnified by more than 500 to 600 times under an optical metallographic microscope. It is characterized by the distribution of carbides in the ferrite matrix (including Cementite) pellets of the composite organization. It is also a tempering organization of martensite, a mixture of ferrite and granular carbides. At this time the ferrite has basically no carbon supersaturation, carbide is also a stable carbide. At room temperature is a balanced organization.
Second, forging application examples: 45 steel forgings
Forging is often used in medium carbon (low alloy) structural steels, also used in low alloy cast steel. In short, the mechanical requirements of high structural parts must be forging processing. (Hardening and tempering; thermal refining) metal materials one of the heat treatment process. Materials in the quenching after high temperature tempering called forging treatment. The purpose is to make the steel has a high toughness and sufficient strength, with a comprehensive excellent mechanical properties. Such as vertical shaft, screw, gear and so on. Usually after the parts in the processing, but also after the rough blank for mechanical processing.
45 steel forgings
45 steel is carbon structural steel, hot and cold processing performance are good, good mechanical properties, and the price is low, wide source, so widely used. Its biggest weakness is the high hardenability, cross-sectional size and require relatively high workpiece should not be used. 45 steel quenching temperature in A3 + (30 ~ 50) ℃, in practice, generally take the upper limit. High quenching temperature can make the workpiece heating speed, surface oxidation reduced, and can improve work efficiency. In order to homogenize the austenite of the workpiece, it is necessary to have sufficient holding time. If the actual installed capacity is large, you need to extend the insulation time. Otherwise, there may be due to uneven heating caused by the phenomenon of insufficient hardness. But the insulation time is too long, there will be thick grain, oxidative decarburization serious ills, affecting the quality of quenching. We believe that if the installed furnace is greater than the provisions of the provisions of the process, heating and heating time to be extended 1 /
Because 45 steel hardenability is low, so should use the cooling rate of 10% brine solution. After the workpiece into the water, it should be hardened, but not cold, if the workpiece in the cold water in the brine, it is possible to crack the workpiece, this is because when the workpiece cooled to about 180 ℃, the austenite quickly transformed into martensite Excessive tissue stress caused by. Therefore, when the quenching of the workpiece quickly cooled to the temperature area, it should be taken slow cooling method. As the water temperature is difficult to grasp, to be experienced operation, when the water in the workpiece jitter stop, you can air cooling (such as oil cool better). In addition, the workpiece into the water should not move static, should be in accordance with the geometric shape of the workpiece, for regular movement. Static cooling medium with static workpiece, resulting in uneven hardness, uneven stress leaving the workpiece deformation, or even cracking. 45 steel forgings after quenching hardness should reach HRC56 ~ 59, the possibility of lower cross section, but not less than HRC48, otherwise, it shows that the workpiece is not fully quenched, the organization may appear sorbite or even ferrite , This organization through the tempering, still remain in the matrix, not for the purpose of forging.
45 steel after quenching high temperature tempering, heating temperature is usually 560 ~ 600 ℃, hardness requirements for HRC22 ~ 34. Because the purpose of forgings is to get comprehensive mechanical properties, so the hardness range is wide. But the drawings have hardness requirements, it is necessary to adjust the tempered temperature according to the drawings to ensure the hardness. If some shaft parts require high strength, hardness requirements on the high; and some gears, with keyway shaft parts, but also forging after the milling, plug processing, hardness requirements on the lower. On 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, and tempering time is not, but must be back through the general workpiece tempering holding time is always More than an hour.