As a metallurgical expert with a focus on materials science, I can provide you with a comprehensive understanding of the process of tempering steel. Tempering is a heat treatment process used to increase the toughness of iron-based alloys. It is a critical step in the production of steel, especially for tools and components that require a balance of hardness and toughness.

The process of tempering involves heating the steel to a specific temperature, holding it at that temperature for a certain period, and then cooling it down slowly. This is done after the steel has been quenched, which is a process that hardens it by rapid cooling. Quenching makes the steel hard but brittle, and tempering is used to reduce this brittleness while maintaining a certain level of hardness.

The duration and temperature of the tempering process depend on several factors, including the type of steel, its initial hardness, the desired final hardness, and the specific application of the steel. Generally, the tempering temperature ranges from 150°C to 350°C (302°F to 662°F). The time that the steel is held at this temperature can vary widely, from as little as 15 minutes for some high-carbon steels to several hours for larger sections or for achieving specific properties.

The reference material you provided suggests a tempering temperature of 175°C to 350°C (347°F to 662°F) for 2 hours, resulting in a hardness of 53 HRC to 63 HRC. This range is typical for many high-carbon steels and provides a good balance between sharpness retention, grindability, and toughness. However, it's important to note that these values are not universally applicable to all types of steel. For instance, low-carbon steels may require different temperatures and times to achieve the desired properties.

The tempering process also affects the microstructure of the steel. When steel is heated to the tempering temperature, the martensitic structure, which is formed during quenching, starts to transform. This transformation involves the formation of tempered martensite, which has a more ductile structure compared to the brittle martensite. The duration of the tempering process influences the extent of this transformation and, consequently, the mechanical properties of the steel.

It's also worth mentioning that tempering can be performed multiple times to fine-tune the properties of the steel. Each tempering cycle can alter the balance of hardness and toughness, allowing for a more precise control over the steel's performance characteristics.

In conclusion, the time it takes to temper steel is not a one-size-fits-all answer. It is a complex process that depends on the specific requirements of the steel part being treated. The temperature and duration of the tempering process must be carefully controlled to achieve the desired balance of hardness, toughness, and other mechanical properties.

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To reduce the brittleness, the material is tempered, usually by heating it to 175-C350--C (347-C662--F) for 2 hours, which results in a hardness of 53-C63 HRC and a good balance between sharpness retention, grindability and toughness.read more >>