Case-hardened steel is a specialised material that features a wear-resistant coating and a tough, ductile core, both of which are necessary for components that must withstand repeated loading and high friction. It is a form of steel designed primarily for sectors where surface strength, core resilience, and durability are critical to performance. This guide describes the operation of case hardening, the primary grades and standards, its benefits, the processing mode, and its applications.
What Is Case Hardening Steel?
Case-hardening steel, also known as carburising steel, is a low-carbon steel (typically 0.10-0.30% carbon) designed to be case-hardened, only its surface is made very hard, while the core remains quite soft and tough. This special mix is achieved through heat treatment, which introduces more carbon into the surface layer before it is hardened and tempered.
The outcome is a component, which can resist surface wear and impact stresses without breaking – essential in challenging mechanical and automotive conditions.
Why Case Hardening Is Important
The majority of traditional steels become brittle during hardening throughout. Case hardening addresses this drawback by forming a hard outer coating that is abrasion-resistant, while still allowing the core to remain ductile, fatigue-resistant, and tough. This renders the material perfect, in which the parts can endure high mechanical loads, shock, and cyclic stress without catastrophic failure.
How Case Hardening Works
Case hardening is performed in three major steps:
Carburising (Introduction of Carbon on Surface)
The steel is heated in an environment with a lot of carbon or gas, and the carbon will penetrate the surface.
Hardening
The part is then quenched (rapidly cooled) after carbon uptake to convert the carbon-rich surface into a martensitic hard layer.
Tempering
This makes it less brittle and still gives the desired hardness and toughness levels.
Gas, pack, or low-pressure carburising may be used, depending on requirements.
Chemical Composition & Material Grades
The case-hardening steels are mostly characterised by low carbon content, which makes them easy to carburise and machine prior to treatment. The common chemical analysis includes:
- Carbon (C): 0.10 – 0.30%
- Manganese (Mn): Strengthens and hardens.
- Silicon (Si): Increases resistance to oxidation.
- Chromium (Cr) / Nickel (Ni): This metal is added in special grades for greater core strength and durability.
Widely used industrial grades are:
- 16MnCr5: This is common in transmission pieces.
- 20MnCr5: Provides moderately core rigidity and surface hardness.
- 22NiCrMo12.5 / 24NiCrMo15: These are used in larger parts that require greater toughness.
These grades are held in both block and bar form at Midland Special Steels, with the option of bespoke dimensions to meet specific machining or fabricating requirements.
Advantages of Case Hardening Steel
The benefits of case-hardened steel are high:
- Increased Wear Resistance: A hardened surface reduces friction and extends component life.
- Superior Core Toughness: The core provides shock absorption and resistance to cracking.
- Machinability: Core machinability is enhanced by a low-carbon core, which is easy to machine prior to heat treatment.
- Precision: Allows narrow tolerances on sophisticated geometries before the hardening.
Typical Applications
Case-hardened steel is also used in the staple industries, where the most important considerations are strength and durability. Common uses are:
- Gears and pinions
- Cams and shafts
- Automotive assemblies: Crankshafts.
- Components of transmission, industrial machinery parts.
These applications have the advantage of a hardened surface that can withstand repeated friction, and the core can still withstand dynamic changes in load.
Comparison with Through-Hardening Steel
Unlike case-hardening steels, through-hardening steels are hardened throughout the grain. This method increases overall strength at the expense of fundamental ductility and shock resistance, so it is used in other applications (tools, structural components). Case hardening is still the material of choice for transporting parts in assembly that require surface durability as well as internal flexibility (Thyssenkrupp).
Standards and Specifications
Case hardening steels are usually made to meet recognised standards, such as:
- DIN EN ISO 683-3 (not yet DIN EN 10084)- Assigns case hardening grades and requirements.
- DIN EN 10132-2 – Applicable to strip and other forms.
These standards provide reliability and interchangeability to fabrication and engineering projects in the industrial sector.
Sourcing and Services
When procuring case-hardening steel, it is important to work with a reputable supplier. The Midland Special Steels range includes a wide variety of quality grades of case-hardening bars and blocks, with complete mill certification and traceability, and optional processing services such as cutting to length, centreless grinding, and heat treatments.
Their professional staff can recommend the best grade of material and supply condition depending on the application you want to use it for, whether you need deep case depths, high core strength, or machinability.
Choosing the Right Grade for Your Project
The choice of the appropriate steel grade is based on:
- Criteria of application (load, speed, wear conditions)
- Required case depth
- Balance of core strength and hardness.
- Processing technique (gas vs. low-pressure carburising)
With the help of material specialists, the performance and cost-efficiency can be improved considerably.
Conclusion
Case-hardening steel is a flexible, strong material solution that provides the optimal balance of surface hardness and core toughness. Its extensive use in the mechanical, automotive, and precision industries highlights its usefulness in applications where wear resistance, impact durability, and reliability are required.
Knowledge of case hardening, grades, and available benefits enables engineers, specifiers, and buyers to make better material selections, which, in turn, determines optimal performance and lifecycle value.
Midland Special Steels, a stockholder of case-hardening steel, is one of the UK’s most reliable stockists, consulted for available stock, personalised advice, or to browse their stock online.
