STAINLESS STEEL GRADE 310H (UNS S31009 / EN 1.4951) — COMPREHENSIVE TECHNICAL DATASHEET
Stainless Steel Grade 310H (UNS S31009 / EN 1.4951) is a high-carbon, fully austenitic heat-resistant alloy engineered specifically for long-term structural service and premium creep-rupture strength in aggressive high-temperature environments. Characterized by a nominal composition of 25% chromium and 20% nickel, this chemical configuration stabilizes the face-centered cubic (FCC) austenite matrix from cryogenic ranges up to melting temperatures, eliminating volatile phase transformations during severe thermal cycles.
The distinction between Grade 310H and its sibling variations (310 and 310S) is fundamentally defined by its narrow, elevated carbon range of 0.04% to 0.10%. Under high thermal exposure, this carbon forms a dense dispersion of fine intra-granular chromium carbides ($M_{23}C_6$) that act as physical obstacles to pin dislocations and inhibit plastic creep flow, supporting stable load-bearing profiles up to its critical continuous operational thresholds.
■ International Standard Specifications
Grade 310H is standardized across multiple manufacturing and safety codes, ensuring seamless multi-jurisdictional compliance for high-temperature process piping, boilers, and pressure vessel flanges.
| Standard Body | Standard Specification | Product Form Coverage | Designation Code |
|---|---|---|---|
| ASTM / ASME | ASTM A240 / ASME SA240 | Flat-Rolled Plates, Sheets, and Coils | Grade 310H (UNS S31009) |
| ASTM / ASME | ASTM A312 / ASME SA312 | Seamless and Welded Line Pipes | TP310H (UNS S31009) |
| ASTM / ASME | ASTM A213 / ASME SA213 | Seamless Boiler, Superheater, & Heat-Exchanger Tubes | TP310H (UNS S31009) |
| ASTM / ASME | ASTM A182 / ASME SA182 | Forged Flanges, Valves, Fittings, & High-Temp Parts | F310H (UNS S31009) |
| ASTM / ASME | ASTM A479 / ASME SA479 | Stainless Steel Bars and Structural Shapes | Grade 310H (UNS S31009) |
| Aerospace (AMS) | AMS 5521 | High-Temperature Plate, Sheet, and Strip | UNS S31009 |
| European (EN) | EN 10095 | Heat-Resisting Steels (Plates, Sheets, Bars) | X6CrNi25-20 (1.4951) |
■ Chemical Composition Limits (Weight %)
The chemistry profile of Grade 310H enforces a strict upper limit on silicon for flat-rolled products to suppress intermetallic phase transformations during extended exposures.
| Element | Standard 310 (UNS S31000) | Grade 310S (UNS S31008) | Grade 310H (UNS S31009) | EN 1.4951 |
|---|---|---|---|---|
| Carbon (C) | ≤ 0.25 | ≤ 0.08 | 0.04 – 0.10 | 0.04 – 0.08 |
| Chromium (Cr) | 24.00 – 26.00 | 24.00 – 26.00 | 24.00 – 26.00 | 24.00 – 26.00 |
| Nickel (Ni) | 19.00 – 22.00 | 19.00 – 22.00 | 19.00 – 22.00 | 19.00 – 22.00 |
| Manganese (Mn) max | 2.00 | 2.00 | 2.00 | 2.00 |
| Silicon (Si) max | 1.50 | 1.50 | 0.75 / 1.00* | 0.70 |
| Phosphorus (P) max | 0.045 | 0.045 | 0.045 | 0.035 |
| Sulfur (S) max | 0.030 | 0.030 | 0.030 | 0.015 |
| Nitrogen (N) max | — | — | — | 0.11 |
| Iron (Fe) | Balance | Balance | Balance | Balance |
* Note: Silicon is capped at 0.75% max for A240 flat-rolled items and 1.00% max for tubing/forgings.
■ Proprietary Datasheet Download
For principal materials specialists, pressure vessel calculators, and asset managers requiring finite element strain vectors, full life-assessment records, and certified chemical mill trace reports, the unified documentation must be accessed.
Alloy 310H — Advanced High-Temperature Technical Manual
Contains empirical data for finite element stress analysis, Larson-Miller parameters, and certified weld pool chemistry metrics. Corporate credentials required.
⬇ DOWNLOAD DATASHEET■ Physical and Thermophysical Variables
| Physical Constants | Metric Value | Imperial Value |
|---|---|---|
| Density (Ambient Base) | 7890 kg/m³ (EN: 7750 kg/m³) | 0.285 lb/in³ (EN: 0.280 lb/in³) |
| Melting Range Boundaries | 1354°C – 1402°C | 2470°F – 2555°F |
| Poisson's Ratio (ν at 20°C) | 0.30 | 0.30 |
| Shear Modulus (G at 20°C) | 77.0 GPa | 11.2 × 10⁶ psi |
| Specific Heat (0 – 100°C) | 502 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity (20°C) | 72.0 µΩ·cm | 30.7 µΩ·in |
| Relative Magnetic Permeability | ≤ 1.02 | ≤ 1.02 |
The continuous high-temperature property shifts across an expanding operational envelope are detailed in the index below:
| Service Temperature | Modulus of Elasticity (E) | Mean Coeff. of Thermal Expansion (α) | Thermal Conductivity (k) |
|---|---|---|---|
| 20°C / 68°F | 200 GPa / 29.0 Mpsi | — | 13.8 W/m·K |
| 100°C / 212°F | 196 GPa / 28.5 Mpsi | 15.9 × 10⁻⁶/K (0-100°C range) | 14.2 W/m·K |
| 315°C / 600°F | 180 GPa / 26.1 Mpsi (Est.) | 16.2 × 10⁻⁶/K (0-315°C range) | 16.3 W/m·K (Est.) |
| 500°C / 932°F | 165 GPa / 23.9 Mpsi (Est.) | 16.7 × 10⁻⁶/K (0-500°C range) | 18.7 W/m·K |
| 538°C / 1000°F | 162 GPa / 23.5 Mpsi (Est.) | 17.0 × 10⁻⁶/K (0-538°C range) | 19.1 W/m·K (Est.) |
| 1000°C / 1832°F | 120 GPa / 17.4 Mpsi (Est.) | 18.9 × 10⁻⁶/K (0-1000°C range) | 23.0 W/m·K (Est.) |
■ Mechanical Performance Profiles
The table below tracks code-mandated room-temperature design requirements for annealed configurations:
| Mechanical Parameter | ASTM A240 Flat-Rolled Limits | ASTM A182 Forged Limits | EN 10272 Bar Limits |
|---|---|---|---|
| Tensile Strength ($R_m$) | ≥ 515 MPa (75 ksi) | ≥ 515 MPa (75 ksi) | 510 – 750 MPa |
| Yield Strength ($R_{p0.2}$) | ≥ 205 MPa (30 ksi) | ≥ 205 MPa (30 ksi) | ≥ 200 MPa |
| Elongation ($A_5$) | ≥ 40% | ≥ 30% | ≥ 35% (Axial) / ≥ 30% (Tang) |
| Brinell Hardness (HBW) | ≤ 217 max | Not Specified | ≤ 192 max |
| Rockwell Hardness (HRB) | ≤ 95 max | Not Specified | Not Specified |
■ High-Temperature Creep and Stress-Rupture Kinetics
At temperatures exceeding 600°C, deformation is controlled by diffusion-assisted dislocation climb-glide. Coarser grain structures (ASTM No. 6 or coarser) combined with carbide structures prevent vacancy transport pathways, yielding high long-term load capacities.
| Temperature | Creep Limit (1% Strain) 1,000 h | Creep Limit (1% Strain) 10,000 h | Stress to Rupture 1,000 h | Stress to Rupture 10,000 h | Stress to Rupture 100,000 h |
|---|---|---|---|---|---|
| 600°C / 1112°F | 120 MPa | 100 MPa | 200 MPa | 140 MPa | 80 MPa |
| 700°C / 1292°F | 50 MPa | 35 MPa | 80 MPa | 45 MPa | 20 MPa |
| 800°C / 1472°F | 20 MPa | 10 MPa | 35 MPa | 20 MPa | 8 MPa |
| 900°C / 1652°F | 10 MPa | 6 MPa | 15 MPa | 10 MPa | 5 MPa |
| 1000°C / 1832°F | 5 MPa | 3 MPa | 9 MPa | 4 MPa | 2 MPa |
■ ASME Pressure-Retaining Ratings (1" Nominal Size Pipes)
The following table tracks allowable design metrics and maximum allowable working pressures (MAWP) for Schedule 40 and 80 pipe thickness boundaries:
| Operating Temperature Threshold | ASME Allowable Stress Limit | MAWP for Sch 40 (0.133" wall) | MAWP for Sch 80 (0.179" wall) |
|---|---|---|---|
| Up to 149°C (300°F) | 115.1 MPa (16,700 psi) | 15.20 MPa (2,205 psi) | 21.10 MPa (3,061 psi) |
| 204°C (400°F) | 106.9 MPa (15,500 psi) | 14.11 MPa (2,047 psi) | 19.59 MPa (2,841 psi) |
| 260°C (500°F) | 99.3 MPa (14,400 psi) | 13.11 MPa (1,902 psi) | 18.20 MPa (2,640 psi) |
■ High-Temperature Fastening Line Torque Values (Dry Assembly)
Austenitic stainless steels are specified for high-temperature structural bolting under specifications such as ASTM A193 Grade B8 paired with A194 Grade 8 heavy hex nuts to distribute mechanical expansion strain.
| Fastener Thread Size | Threads Per Inch (TPI) | Dry Assembly Torque (Inch-Pounds) | Dry Assembly Torque (Foot-Pounds) |
|---|---|---|---|
| 1/4" | 20 | 78.8 | 6.5 |
| 5/16" | 18 | 138.0 | 11.5 |
| 3/8" | 16 | 247.0 | 20.5 |
| 1/2" | 13 | 542.0 | 45.1 |
| 5/8" | 11 | 1160.0 | 96.7 |
| 3/4" | 10 | 1582.0 | 131.8 |
| 1" | 8 | 3595.0 | 299.6 |
■ Environmental Degradation and Process Media Restrictions
- Sigma Phase Embrittlement: Prolonged exposure within the 650°C to 900°C range triggers solid-state phase transformation, precipitating the hard, brittle intermetallic sigma ($\sigma$) phase. This induces intense room-temperature embrittlement during shutdowns. Remediation requires full solution annealing at 1040 – 1100°C followed by a rapid water quench every 1,000 hours of continuous service to preserve handling ductility.
- Atmosphere Gas Controls: Continuous operations remain stable in clean air up to 1150°C (2102°F). High-sulfur processing gases require critical temperature downgrades to protect against the formation of liquid nickel-sulfide eutectics ($\text{Ni-Ni}_3\text{S}_2$) along grain boundaries:
- Oxidizing with moderate sulfur ($\le 2 \text{ g/m}^3$ S): Safe service up to 1050°C (1922°F).
- Oxidizing with high sulfur ($> 2 \text{ g/m}^3$ S): De-rate maximum exposure limit to 950°C (1742°F).
- Reducing environments with high sulfur ($> 2 \text{ g/m}^3$ S): Extreme danger zone; eutectic melts within 635 – 750°C, causing catastrophic liquid metal cracking. Avoid Grade 310H.
- Weld Solidification Hot Cracking: The fully austenitic matrix lacks delta ferrite to dissolve tramp elements during solidification. Phosphorus, sulfur, and silicon can segregate to intradendritic boundaries, forming thin liquid films that tear under shrinkage strains. Welding procedures must eliminate preheating, limit interpass targets strictly below 150°C (302°F), and require narrow stringer beads.
■ Engineering Design Recommendations
- Procurement Audit: For creep-critical installations, mandate an absolute minimum carbon floor of 0.04 wt% and require a certified ASTM grain size of No. 6 or coarser. Do not accept low-carbon 310S or generic 310 plate stock, as their lack of stable intra-granular carbide distributions dramatically drops stress-rupture life profiles.
- Post-Weld Solution Treatment: The deployment of carbon-rich matching ER309H or E310-15/16 electrodes causes sensitization within the weld HAZ. To prevent micro-fissuring and restore protective scale integrity, enforce a mandatory full solution annealing cycle followed by rapid water quenching.
- Prohibition of Aqueous Exposure: Do not specify Grade 310H for applications involving continuous contact with wet, acidic, or highly reducing chemical environments. Due to its high carbon content and intentional carbide precipitation, the alloy is exceptionally sensitive to intergranular corrosion fields outside dry-gas zones.
