What Does Quenching And Tempering Mean?

1. What does tempering treatment mean?

Quenching and tempering treatment: The heat treatment method of high-temperature tempering after quenching is called quenching and tempering treatment. High-temperature tempering refers to tempering between 500-650 °C.

2. What is the purpose of conditioning?

Quenching and tempering can adjust the properties and materials of steel to a great extent, and its strength, plasticity, and toughness are good, and it has good comprehensive mechanical properties.

3. What kind of steel does quench and tempered steel belong to?

Quenched and tempered steel has two categories: carbon quenched and tempered steel and alloy quenched and tempered steel. Whether it is carbon steel or alloy steel, its carbon content is strictly controlled. If the carbon content is too high, the strength of the workpiece after quenching and tempering is high, but the toughness is not enough. If the carbon content is too low, the toughness is improved and the strength is insufficient. In order to obtain good comprehensive performance of the quenched and tempered parts, the carbon content is generally controlled at 0.30~0.50%. During quenching and tempering, the entire section of the workpiece is required to be hardened, so that the workpiece can obtain a microstructure dominated by fine needle-like quenched martensite. Through high-temperature tempering, a microstructure dominated by uniformly tempered sorbate is obtained. It is impossible for small factories to conduct a metallographic analysis for each furnace. Generally, only a hardness test is performed. That is to say, the hardness after quenching must reach the quenching hardness of the material, and the hardness after tempering is checked according to the requirements of the drawing.

4. About the quenching and tempering process of #45 steel

#45 steel is a medium carbon structural steel with good hot and cold processing properties, good mechanical properties, low price, and wide sources, so it is widely used. Its biggest weakness is low hardenability, and workpieces with large cross-sectional dimensions and relatively high requirements should not be used. The quenching temperature of #45 steel is A3+(30~50)℃. In actual operation, the upper limit is generally taken. A high quenching temperature can speed up the healing of the workpiece, reduce surface oxidation, and improve work efficiency. In order to homogenize the austenite of the workpiece, a sufficient holding time is required. If the actual furnace load is large, it is necessary to extend the holding time appropriately. Otherwise, there may be insufficient hardness due to uneven heating. However, if the holding time is too long, there will also be coarse grains and serious oxidative decarburization, which will affect the quenching quality. We believe that if the furnace loading is greater than the requirements of the process document, the heating and holding time should be extended by 1/5. Because of the low hardenability of #45 steel, a 10% salt solution with a large cooling rate should be used. After the workpiece enters the water, it should be hardened, but not cold through. If the workpiece is cooled in saltwater, it may crack the workpiece. This is because when the workpiece is cooled to about 180 ℃, the austenite rapidly transforms into martensite. 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 it is difficult to grasp the water temperature, it must be operated by experience. When the workpiece in the water stops shaking, it can be cooled by water and air (if it can be cooled by oil, it is better). In addition, the workpiece should be moved and not static when it enters the water and should be moved regularly according to the geometric shape of the workpiece. The static cooling medium and the static workpiece will cause uneven hardness and uneven stress, which will cause the workpiece to deform and even crack. The hardness of #45 steel quenched and tempered parts after quenching should reach HRC56~59, the possibility of the large cross-section is lower, but not lower than HRC48, otherwise, it means that the workpiece has not been fully quenched, and sorbate or even ferrite may appear in the structure The tissue, through tempering, still remains in the matrix and cannot achieve the purpose of tempering. The high-temperature tempering of #45 steel after quenching, the heating temperature is usually 560~600℃, and the hardness is required to be 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 requirements of the drawings to ensure the hardness. For example, some shaft parts require high strength and high hardness; while some gears and shaft parts with key grooves need to be milled and inserted after quenching and tempering, so the hardness requirements are lower. Regarding the tempering 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 holding time of the workpiece is always more than an hour.