Tempering is a technique for smelting steel, which means that the steel after quenching hardening or normalization is immersed at a temperature lower than the critical temperature for a period of time, and then cooled down at a certain rate to increase the toughness of the material. a processing method. According to the metallurgical principle, after quenching and normalization, it is put back to the medium temperature for immersion (aging) for a period of time, which can promote the precipitation of part of the carbides, and at the same time can eliminate part of the residual stress caused by rapid cooling, so it can improve the toughness of the material and Flexible.
The effect of tempering treatment depends on the tempering temperature, time, cooling rate and other factors. As the tempering temperature increases, the strength and hardness of the material decrease, but the ductility of the material increases.
The impact resistance of the material will be significantly reduced near 300 ℃ tempering, which is called temper brittleness. Since the precipitation of carbon atoms or alloy elements is proportional to the time, the hardness of the material will decrease with the extension of the tempering time. Since the tempering temperature is below the critical point of phase change, the strength of the material is not related to the cooling rate. However, due to tempering embrittlement, if the cooling rate of the material is too slow between 375 and 575 °C, embrittlement is likely to occur. If tempering near 300 ℃, there is also embrittlement, which is caused by the precipitation of unfavorable plate carbides, which must be paid attention to when tempering.
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