A572 Gr.55
ASTM A572
A572 Gr.55 is a structural steel (HSLA family) to ASTM A572. It has a specified 0.2 % proof stress of 380 MPa and a typical tensile strength of about 485 MPa, with a uniform elongation of 17 %. Nominal carbon content is around 0.23 %. For nonlinear FEA, a bilinear model uses E = 210 GPa up to yield and a tangent modulus of 632 MPa above it. It is a general-purpose wrought steel selected on strength, cost and availability.
Bilinear material model — nonlinear FEA
Uniform elongation εu = 17.0% · conservative analysis limit ½εu = 8.5%
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
Weldabilitymoderate
Medium carbon (~0.23%) — preheat and hydrogen-controlled consumables advisable, especially in thicker 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.
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 | 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 astm hsla steel — use the mill certificate for the specific product.
Chemical composition (wt %)
Typical composition per ASTM A572 (Nb and/or V micro-alloying).
Available forms
Common applications
- Building and bridge steelwork
- Platforms, frames and support structures
- Crane and lifting structures
- General heavy fabrication
History
The ASTM structural steels are the North-American parallel to the European S-grades — A36 the ubiquitous mild steel, the A572 HSLA grades the higher-strength micro-alloyed workhorses, and A588 the weathering grade — specified across US bridge and building codes. Grade 55 — the “Gr.” number is the minimum yield in ksi (Gr.50 ≈ 345 MPa).
- 1960ASTM A36 becomes the standard US structural carbon steel
- 1966ASTM A572 introduces the columbium/vanadium HSLA grades (42–65 ksi)
- 1968ASTM A588 weathering steel standardised for bare bridge use
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.