439
1.4509 · EN 10088 / AISI · 1.4509
439 is a stainless steel (Ferritic family) to EN 10088 / AISI (1.4509). It has a specified 0.2 % proof stress of 250 MPa and a typical tensile strength of about 430 MPa, with a uniform elongation of 22 %. Nominal carbon content is around 0.03 %. For nonlinear FEA, a bilinear model uses E = 200 GPa up to yield and a tangent modulus of 830 MPa above it. As a ferritic stainless it offers useful corrosion resistance at lower cost than austenitics, though with reduced toughness and formability.
Bilinear material model — nonlinear FEA
Uniform elongation εu = 22.0% · conservative analysis limit ½εu = 11.0%
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
Weldabilitymoderate
Weldable with care; grain coarsening and loss of toughness in the HAZ are the main concerns.
Machinabilitymoderate
Soft and gummy at low carbon — sharp tooling helps surface finish.
Corrosion resistancegood
Good atmospheric and mild-chemical resistance from the chromium content; less resistant than austenitics in chlorides.
Hardenabilitylow
Limited hardenability at low carbon — surface hardening is possible but through-hardening is not.
Toughnessmoderate
Adequate toughness for general use at ambient temperature.
Indicative ratings derived from composition and family — engineering guidance, not specification values.
Physical properties
| Density | 7700 | kg/m³ |
| Elastic modulus | 200 | GPa |
| Shear modulus | 76.9 | GPa |
| Poisson's ratio | 0.30 | |
| Thermal expansion | 10.5 | ×10⁻⁶/°C |
| Thermal conductivity | 25 | W/(m·K) |
| Specific heat | 460 | J/(kg·K) |
| Magnetic | Yes |
Typical values for ferritic steel — use the mill certificate for the specific product.
Chemical composition (wt %)
Composition per EN 10088 / AISI for 439 (1.4509).
Available forms
Common applications
- Process, food and pharmaceutical equipment
- Architectural and marine hardware
- Fasteners and fittings for corrosive service
- Tanks, pipework and heat exchangers
History
The ferritic (chromium-only, nickel-free) stainless steels are the economical branch of the family — magnetic, with good atmospheric and stress-corrosion resistance but less toughness and formability than the austenitics. Modern stabilised grades widen their use in automotive exhausts and trim. A stabilised ferritic — a nickel-free, stress-corrosion-immune alternative to 304 for milder service.
- 1913Chromium stainless steels emerge (Brearley, Sheffield)
- 1970Stabilised low-interstitial ferritics (Ti/Nb) improve weldability and ductility
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.