Tempered steel

What is tempered steel?

Tempered steel is a type of steel specifically designed to achieve high strength and toughness through a special heat treatment process called tempering. This two-stage process first involves hardening the steel by heating it to around 900 °C and rapidly cooling it, followed by tempering at a lower temperature to achieve the desired mechanical properties.

Composition of tempered steel

The carbon content in tempered steels typically ranges from 0.25% to 0.60%, and they may be either unalloyed or low-alloyed. Alloyed tempered steels often contain chromium, nickel, and molybdenum, which improve the steel's hardenability and mechanical properties. For example, 42CrMo4 steel contains about 0.42% carbon, 1.1% chromium, and 0.2% molybdenum.

Properties of tempered steel

Tempered steels are characterized by high yield strength, fracture strength, and fatigue strength, as well as good toughness. These properties make them excellent materials for applications requiring high mechanical durability and reliability.

Applications of tempered steel in mechanical engineering

In mechanical engineering, tempered steels are widely used in the manufacture of various components. Common applications include thick shafts, connecting rods, levers, springs, gears, tools, screws, and nuts. These applications demand materials with high strength and toughness to withstand the stresses of operational conditions.

Heat treatment process of tempered steel

The tempering process consists of two main stages: hardening and tempering. During hardening, the steel is heated to its austenitizing temperature, around 900 °C, and then quickly cooled, for example in water or oil. After this, the steel undergoes tempering, where it's reheated to a lower temperature, typically 500–700 °C, and then cooled in a controlled manner. This process increases the steel's toughness and reduces the risk of brittleness.

Summary

Tempered steel is an essential material in mechanical engineering, offering a combination of high strength and good toughness. Its special heat treatment process enables versatile use in demanding applications where the durability and reliability of components are of utmost importance.