45# steel heat treatment

Heat treatment process of 45# (number) steel and 40Cr steel quenched and tempered
Quenching and tempering is a double heat treatment of quenching and high temperature tempering, and its purpose is to make the workpiece have good comprehensive mechanical properties.
Quenched and tempered steel has two categories: carbon quenched and tempered steel and alloy quenched and tempered steel. Regardless of whether it is carbon steel or alloy steel, its carbon content is controlled strictly. 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 will increase and the strength will be insufficient. In order to obtain good overall performance of quenched and tempered parts, the carbon content is generally controlled at 0.30~0.50%.
When quenching and tempering, the entire section of the workpiece is required to be quenched, so that the workpiece can obtain a microstructure dominated by fine needle-shaped quenched martensite. Through high temperature tempering, a microstructure dominated by uniform tempered sorbite is obtained. It is impossible for small factories to conduct metallographic analysis for each furnace, and generally only perform hardness testing. This means that 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.
The operation of the quenching and tempering treatment of the workpiece must be carried out strictly in accordance with the process documents. We only provide some views on how to implement the process during the operation.
Carburizing treatment is generally used for heavy-duty parts with wear-resistant surfaces and impact-resistant cores, and its wear resistance is higher than quenching and tempering + surface quenching. The carbon content on the surface is 0.8-1.2%, and the core is generally 0.1-0.25% (0.35% is used in special cases). After heat treatment, the surface can obtain high hardness (HRC58-62), the core hardness is low, and impact resistance. To
If 45 steel is used for carburizing, hard and brittle martensite will appear in the core after quenching, and the advantages of carburizing will be lost. At present, the carbon content of the materials using the carburizing process is not high, and the core strength can reach a high level of 0.30%, which is rare in applications. 0.35% have never seen an example, only an introduction in the textbook. The process of quenching and tempering + high frequency surface quenching can be used, and the wear resistance is slightly worse than that of carburizing. To
The recommended heat treatment system for 45 steel specified in the GB/T699-1999 standard is normalizing at 850°C, quenching at 840°C, and tempering at 600°C. The achieved performance is yield strength ≥355MPa
The GB/T699-1999 standard stipulates that the tensile strength of 45 steel is 600MPa, the yield strength is 355MPa, the elongation is 16%, the reduction of area is 40%, and the impact energy is 39J
The unquenched hardness of No. 45 steel is less than HRC28, which is relatively soft and not wear-resistant. The hardness after quenching can (note that it is possible) greater than HRC55, and the wear resistance is better.
The hardness of 45# steel after quenching can (note that it is possible) greater than HRC55. But this is a small cross-section, a larger cross-section will reduce the hardness obtained. And the possibility of cracking in winter is also possible. Pay attention to these aspects. To
Do not use surface nitriding treatment. Although the surface hardness can be increased a lot, the base material will have a very low hardness. Although it is wear-resistant, small pits will be pressed out.

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