Case-hardened steel

What is case-hardening steel?

Case-hardening steel is a type of steel specifically used in applications where a hard, wear-resistant surface and a tough core are required. This is achieved through the case-hardening process, where the carbon content of the steel’s surface layer is increased by heat treatment. Typically, case-hardening steels have a low carbon content, around 0.10–0.25%.

The case-hardening process for case-hardening steel

In case hardening, the finished machine part is exposed to a carbon-rich medium at a temperature of 850–950 °C. This treatment increases the carbon content in the surface layer, which is usually 0.5–1.0 mm thick, but can be thicker. After carburizing, the part is rapidly quenched, which increases its hardness. During quenching, the carburized surface transforms into martensite, and its hardness depends on the carbon content of the layer. The result is a component with a hard surface and a softer core.

Applications of case-hardening steel in mechanical engineering

Case-hardening steels are widely used in mechanical engineering for parts that require high wear and fatigue resistance as well as toughness. Common applications include gears, shafts, camshafts, rolling elements, and various tools and fasteners. In these applications, the properties of case-hardening steel ensure long service life and reliability of the components under demanding conditions.

Grades and composition of case-hardening steel

Case-hardening steels are available in various grades, each with its own specific properties. For example, 20MnCr5 is a commonly used grade containing about 0.20% carbon, 1.3% manganese, and 1.2% chromium. Another example is 18CrNiMo7-6, which contains about 0.18% carbon, 1.7% chromium, 1.6% nickel, and 0.3% molybdenum. These alloying elements enhance the hardenability and toughness of the steel, making them suitable for demanding mechanical engineering applications.

Summary

Case-hardening steel is an essential material in mechanical engineering, especially for parts that require a hard surface and a tough core. Through the case-hardening process, these properties are achieved, making case-hardening steel an excellent choice for components subjected to wear and fatigue, such as gears and shafts. Different steel grades and alloying elements allow the properties of case-hardening steel to be tailored precisely to the needs of machine shops and machining facilities.