What is the tempering temperature for carbon steel and alloy steel?

The tempering temperature of carbon steel and alloy steel needs to be determined according to the material characteristics and process requirements, as follows:

Tempering temperature of carbon steel
Low temperature tempering: The temperature range is 150-250 ℃, and the microstructure after tempering is tempered martensite. This temperature range is mainly used to reduce internal stress, decrease brittleness, maintain high hardness (58-62HRC) and wear resistance after quenching. Low temperature tempering is generally used for tools made of carbon steel (such as cutting tools, measuring tools, molds, etc.), rolling bearings, carburized parts, etc.
Medium temperature tempering: The temperature range is 350~500 ℃, and the microstructure after tempering is tempered martensite, with a hardness range of 35~50HRC. The main purpose of medium temperature tempering is to obtain high elasticity, high yield strength, while maintaining sufficient toughness, such as tempering springs, springs, and forging dies. However, it should be noted that some steels may experience temper brittleness during medium temperature tempering (250-350 ℃).
High temperature tempering: The temperature range is 500~650 ℃, and the microstructure after tempering is tempered martensite, with a hardness range of 23~35HRC. The main purpose of high-temperature tempering is to obtain comprehensive mechanical properties that have both certain strength, hardness, and good impact toughness. The heat treatment of quenching followed by high-temperature tempering is called quenching and tempering, abbreviated as quenching and tempering. Generally used for important parts made of medium carbon steel (0.3%~0.5% C), such as crankshafts, connecting rods, gears, shafts, etc.

Tempering temperature of alloy steel
Low temperature tempering: Similar to carbon steel, the low-temperature tempering temperature of alloy steel is also in the range of 150-250 ℃, mainly used to maintain high hardness and wear resistance.
Medium temperature tempering: The medium temperature tempering temperature of alloy steel may be adjusted due to different alloy elements, but it is generally within the range of 250~500 ℃. This temperature range is mainly used to obtain high elasticity and high yield strength.
High temperature tempering: For alloy steels, especially those containing medium to strong carbide forming elements, the high-temperature tempering temperature may be selected between 500~600 ℃ to achieve secondary hardening, even if the alloy steel still has high toughness when working at high temperatures. This is particularly important for tool steel. In addition, the high-temperature tempering temperature for stress relief of carbon steel and low – and medium alloy steel is usually between 600~700 ℃. Carbon steel is generally selected at 600-650 ℃, while low and medium alloy steels require higher temperatures (such as 650-700 ℃) due to the delayed recovery and recrystallization of alloying elements.