Case-Hardening Steel
Case-hardening steels — also referred to as carburising steels — are specially developed to deliver a combination of surface hardness and core toughness. These steels are typically low in carbon, with a content ranging between 0.10% and 0.25%, making them ideal for applications where components are required to resist surface wear while maintaining a ductile and impact-resistant core.
This dual-property performance is achieved through the case hardening process, which involves diffusing carbon into the surface layer of the steel and then heat treating it to create a hard outer shell. The result is a component with excellent wear resistance on the outside and toughness at its core, allowing it to withstand fatigue and shock loading over time.
Case-Hardening Steel
| EN-standard | Ovako | Comments | C | Si | Mn | Cr | Mo | Ni | Other |
|---|---|---|---|---|---|---|---|---|---|
| 16MnCr5 | 234, 4306 | For small-sized transmission components, low core hardness | 0.16 | 0.2 | 1.2 | 1.0 | |||
| 20MnCr5 | 236, 4326 | For small-sized transmission components, moderate core hardness. | 0.20 | 0.2 | 1.3 | 1.2 | |||
| 18CrMo8-5* | 225 | Steel designed for nitriding but also suitable for carburising | 0.18 | 0.3 | 0.8 | 1.8 | 0.5 | ||
| 20MoCr4 | 124 | For small-sized bearing and transmission components | 0.20 | 0.2 | 0.8 | 0.5 | 0.4 | ||
| 20NiCrMo2-2 | 152, 4548 | For small to medium-sized bearing and transmission components | 0.20 | 0.3 | 0.9 | 0.6 | 0.2 | 0.5 | |
| 16NiCrS4 | 146, 4730 | For medium-sized transmission components | 0.16 | 0.1 | 1.0 | 1.1 | 0.8 | ||
| 20NiCrMo7 | 157 | For medium-sized bearing and transmission components | 0.20 | 0.2 | 0.6 | 0.5 | 0.2 | 1.7 | |
| 18CrNiMo7-6 | 159, 4761 | For medium-sized bearing and transmission components | 0.18 | 0.2 | 0.7 | 1.7 | 0.3 | 1.6 | |
| 12NiCr14-6* | 245 | For large-sized bearing and transmission components | 0.13 | 0.3 | 0.5 | 1.5 | 0.1 | 3.3 | |
| 18NiCrMo 14-6 | 255 | For large-sized bearing and transmission components | 0.18 | 0.3 | 0.5 | 1.4 | 0.2 | 3.3 | |
| 22NiCrMo12·5* | 253 | For large-sized components requiring high core toughness. | 0.14 | 0.2 | 0.6 | 1.2 | 0.2 | 2.9 | |
| 24NiCrMo15-5* | 256 | For large-sized components requiring high core toughness | 0.24 | 0.3 | 0.7 | 1.2 | 0.3 | 3.6 | |
| 20NiMo9-7* | 158 | Steel giving reduced surface oxidation after gas carburising | 0.20 | 0.1 | 0.3 | 0.4 | 0.7 | 2.3 | |
| 30MoCrV20-7 * | 499 | Temperature resistant carburising steel | 0.30 | 0.2 | 0.3 | 1.7 | 1.8 | V | |
| 16CrMnNiMo9-5-2* | 277 | High hardenability grade. Possible to gas/air harden | 0.16 | 0.2 | 1.3 | 2.1 | 0.5 | 0.5 | V |
Case-hardening steels are most commonly used in transmission systems, automotive assemblies, and precision mechanical parts, where components are subject to constant friction, cyclic loading, and demanding performance requirements. Typical applications include gears, cams, crankshafts, pinions, shafts, and other moving parts that benefit from a hard, wear-resistant surface without compromising the material’s structural integrity.
Because of their low carbon base, these steels are easily machinable in their untreated condition. Components can be cut, turned, drilled, or milled to exact specifications before undergoing the case-hardening process. This allows manufacturers to produce complex geometries and detailed part features with accuracy and efficiency before applying heat treatment to improve surface durability.
After the carburising stage, components are typically quenched and tempered, producing a hard case depth of between 0.5 mm to 2.5 mm, depending on the steel grade, part size, and desired performance. This makes case-hardening steels particularly valuable in high-precision applications, where wear resistance must be matched by long-term stability and reliability under repeated stress.
At Midland Special Steels, we supply a wide range of case-hardening steel grades in bar and block form, available in standard and custom sizes. Our materials are suited to both traditional gas carburising and modern low-pressure carburising techniques, offering flexibility for different manufacturing processes and end-use requirements.
We understand that no two applications are the same. That’s why our experienced team works closely with customers to match the correct steel grade and supply condition to their specific needs. Whether you’re looking for a steel that offers a deeper case depth, improved core strength, or enhanced machinability, we can advise on the best solution for your project.
All of our case-hardening steels are supplied with full mill certification, material traceability, and optional services including cutting to length, centreless grinding, and heat treatment, ensuring your material is delivered ready for processing or final machining.
If you’re manufacturing components where strength alone isn’t enough — where precision, wear resistance, and mechanical balance are key — case-hardening steels offer a trusted and proven solution. Contact Midland Special Steels today to learn more about our stock range and how our materials can support your next engineering challenge.
