805M20
EN325 · BS 970
805M20 (EN325) is an engineering steel (Case-Hardening family) to BS 970. It has a specified 0.2 % proof stress of 680 MPa and a typical tensile strength of about 930 MPa, with a uniform elongation of 13 %. Nominal carbon content is around 0.17 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 2004 MPa above it. It is designed for surface hardening — a hard, wear-resistant case over a tough core.
Bilinear material model — nonlinear FEA
Uniform elongation εu = 13.0% · conservative analysis limit ½εu = 6.5%
Bilinear (BISO) approximation. Elastic modulus E up to the 0.2% proof stress R_p0.2, then a single tangent slope Eₜ to the ultimate tensile strength: Eₜ = (Rₘ − R_p0.2) / (εu − R_p0.2/E − 0.002), where εu is the uniform elongation and Rₘ is a typical (nominal) UTS within the specified band. The half-εu figure is a conservative strain limit for the analysis. Treat these as guidance for first-pass models; for critical work use a measured true stress–strain curve for the actual product and condition.
Ratings — engineering judgement
Weldabilitygood
Low carbon (~0.17%) gives good weldability by all common processes; preheat rarely needed in thin sections.
Machinabilitymoderate
Soft and gummy at low carbon — sharp tooling helps surface finish.
Corrosion resistancepoor
No inherent corrosion resistance — protect by paint, galvanising or plating in exposed use.
Hardenabilitygood
Responds well to quench-and-temper (and, for the case-hardening/nitriding grades, to surface treatment).
Toughnessmoderate
Adequate toughness for general use at ambient temperature.
Indicative ratings derived from composition and family — engineering guidance, not specification values.
Physical properties
| Density | 7850 | kg/m³ |
| Elastic modulus | 210 | GPa |
| Shear modulus | 80.8 | GPa |
| Poisson's ratio | 0.30 | |
| Thermal expansion | 12.0 | ×10⁻⁶/°C |
| Thermal conductivity | 48 | W/(m·K) |
| Specific heat | 470 | J/(kg·K) |
| Magnetic | Yes |
Typical values for case-hardening steel — use the mill certificate for the specific product.
Chemical composition (wt %)
Nominal composition per BS 970 for 805M20 — confirm exact limits against the standard.
Available forms
Common applications
- Shafts, axles and spindles
- Gears, pinions and couplings
- Connecting rods and levers
- General machined components and fasteners
History
The case-hardening (carburising) and nitriding steels are made to be machined soft and then given a hard, fatigue-resistant surface over a tough core — the classic gear and pin steels. They developed alongside mass-produced automotive gearing.
- 1920Carburising Ni–Cr and Cr–Mn steels adopted for automotive gears
- 1930Nitriding steels (Al-bearing) developed for hard, distortion-free surfaces
- 1986EN 10084 harmonises the European case-hardening grades
This profile is generated from the grade's core data and family. Composition is decoded from the designation where its naming system defines it; physical properties are family-typical and ratings are indicative. Confirm critical values against the governing standard or the mill certificate. Equivalents, historical designations and hand-written expert notes are added per grade over time.