AISI 310 STAINLESS STEEL SERIES — TECHNICAL DATASHEET AND METALLURGICAL REPORT
The AISI 310 series comprises highly alloyed, fully austenitic stainless steels engineered for service in severe, high-temperature environments where exceptional oxidation resistance, structural stability, and creep performance are required. This grade family represents a chromium-nickel alloy system containing nominal concentrations of 25% chromium and 20% nickel.
The elevated chromium content facilitates the development of a stable, self-healing, chromium-rich oxide ($Cr_2O_3$) passive layer that acts as a physical barrier to oxygen transport. Nickel acts as the primary austenite stabilizer, retaining the face-centered cubic ($\text{FCC}$) crystal lattice from cryogenic limits up to melting, preventing phase transformations during thermal cycling, and significantly enhancing high-temperature creep strength and low-temperature impact toughness.
■ Grade Classifications and Distinctions
The alloy family is subdivided into three distinct grades based on carbon and silicon optimization to suit specific thermal, mechanical, and fabrication constraints:
- AISI 310 (UNS S31000): The standard grade containing up to 0.25% carbon. Higher carbon provides enhanced room-temperature and short-time high-temperature tensile strength, but increases sensitivity to grain boundary precipitation.
- AISI 310S (UNS S31008 / EN 1.4845): The low-carbon variant ($\le 0.08\%$ C). Optimized for weldability, minimizing the kinetics of chromium carbide precipitation to perform safely where moist corrosive condensates or post-weld aqueous exposure occur.
- AISI 310H (UNS S31009): The high-carbon modification ($0.04\% - 0.10\%$ C) with a lower silicon ceiling ($0.75\%$). Developed for load-bearing components at extreme temperatures, utilizing carbon to promote dislocation-pinning mechanisms and boost creep strength.
■ Chemical Composition Standards (wt%)
Composition limits are strictly regulated under international specifications such as ASTM A240, ASME SA240, and EN 10095 to balance oxidation resistance, high-temperature mechanical properties, and weldability.
| Element | AISI 310 (UNS S31000) | AISI 310S (UNS S31008) | AISI 310H (UNS S31009) | EN 1.4845 |
|---|---|---|---|---|
| Carbon (C) | ≤ 0.25 | ≤ 0.08 | 0.04 - 0.10 | ≤ 0.10 |
| 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 | 1.50 |
| Phosphorus (P) max | 0.045 | 0.045 | 0.045 | 0.045 |
| Sulfur (S) max | 0.030 | 0.030 | 0.030 | 0.015 |
| Molybdenum (Mo) max | 0.75 | 0.75 | — | — |
| Copper (Cu) max | 0.50 | 0.50 | — | — |
| Iron (Fe) | Balance | Balance | Balance | Balance |
■ Proprietary Datasheet Download
For design engineers, plant metallurgists, and procurement officers requiring granular structural load logs, full Larson-Miller parameters, and dynamic thermal-cycling profiles, the comprehensive manual must be accessed.
AISI 310 / 310S / 310H — Advanced High-Temperature Technical Manual
Contains empirical data for finite element analysis, long-term activation energy curves, and certified welding procedure limits. Corporate credentials required.
⬇ DOWNLOAD DATASHEET■ Physical Constants and Thermophysical Performance
| Physical Property | Metric Value | Imperial Value |
|---|---|---|
| Density (Annealed) | 7.89 g/cm³ | 0.285 lb/in³ |
| Density (Cold-Rolled 310S) | 8.03 g/cm³ | 0.290 lb/in³ |
| Melting Range | 1354 - 1402 °C | 2470 - 2555 °F |
| Specific Heat Capacity (0-100°C) | 502 J/kg·K | 0.12 BTU/lb·°F |
| Electrical Resistivity (20°C) | 78.0 μΩ·cm | 30.7 μΩ·in |
| Poisson's Ratio | 0.30 | 0.30 |
| Relative Magnetic Permeability | 1.02 (Annealed) | 1.02 (Annealed) |
The combination of low thermal conductivity and a high coefficient of thermal expansion creates severe thermal gradients during rapid heating or cooling, inducing high localized stresses. Below are the temperature-dependent variables:
| Temperature Threshold | Thermal Conductivity (W/m·K) | Mean Coeff. of Thermal Expansion (×10⁻⁶ K⁻¹) | Tension Modulus (GPa) |
|---|---|---|---|
| 25°C / 77°F | 12.7 | — | 200 |
| 100°C / 212°F | 14.1 | 15.9 (0-100°C range) | 194 |
| 300°C / 572°F | 17.3 | 16.2 (0-315°C range) | 190 |
| 500°C / 932°F | 20.1 | 17.0 (0-538°C range) | 181 |
| 700°C / 1292°F | 23.7 | 17.5 (0-649°C range) | 146 |
| 900°C / 1652°F | 26.0 | 19.1 (0-981°C range) | 132 |
■ Mechanical Strength Profiles
At room temperature, the stable austenitic matrix provides moderate strength paired with high ductility. As service temperatures escalate, it retains structurally useful properties far exceeding carbon steels.
| Mechanical Property | ASTM A240 Limits (Sheet/Plate) | EN 10095 Limits (1.4845) |
|---|---|---|
| Ultimate Tensile Strength (Rm) | ≥ 515 MPa (≥ 75 ksi) | 500 - 700 MPa |
| 0.2% Proof Strength (Rp0.2) | ≥ 205 MPa (≥ 30 ksi) | ≥ 210 MPa |
| 1.0% Proof Strength (Rp1.0) | — | ≥ 230 MPa |
| Elongation (A5) | ≥ 40% | ≥ 35% |
| Hardnell Hardness max (HBW) | 217 | 192 |
■ Long-Term Creep and Stress-Rupture Properties
The activation energy for creep deformation ($Q_c$) is 345 kJ/mol, which retards recovery climb. The table below lists average stress values required to produce 1% strain or creep rupture over extended operational blocks:
| Temperature | Stress for 1% Strain (1,000 h) | Stress for 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 | 100.0 MPa | 90.0 MPa | 170.0 MPa | 130.0 MPa | 80.0 MPa |
| 700°C / 1292°F | 45.0 MPa | 30.0 MPa | 80.0 MPa | 40.0 MPa | 18.0 MPa |
| 800°C / 1472°F | 18.0 MPa | 10.0 MPa | 35.0 MPa | 18.0 MPa | 7.0 MPa |
| 900°C / 1652°F | 10.0 MPa | 4.0 MPa | 15.0 MPa | 8.5 MPa | 3.0 MPa |
■ Fastener and Bolting Assembly Torque Specs (Dry Contact)
Austenitic stainless steels are standardly utilized for high-temperature fastening lines under specifications such as ASTM A193 Grade B8 (Class 1 & 2) paired with A194 Grade 8 heavy hex nuts.
| 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 |
■ Phase Instability and High-Temperature Corrosion Mechanics
- Sigma (σ) Phase Embrittlement: Prolonged exposure within 650°C to 950°C ($1200^\circ\text{F} - 1742^\circ\text{F}$) causes the microstructural decomposition of delta-ferrite into the hard, intermetallic sigma phase. This leads to severe room-temperature embrittlement, requiring a full solution anneal at 1100°C to 1150°C followed by a rapid water quench to restore impact values.
- Solidification Segregation: In castings and welds, the alloy solidifies via a primary austenitic sequence ($L \rightarrow L + \gamma \rightarrow \delta + \gamma$). Positive segregation pushes Cr and Ni into interdendritic liquid zones, facilitating blocky sigma nucleation at triple junctions. Quantitative microstructural auditing is achieved via electrolytic 10% oxalic acid etching.
- Sustained Environment Boundaries: Static air limits reach up to 1150°C (2100°F), dropping to 1030°C for cyclic operations. Flue gas, sulfur, or reducing agents necessitate immediate service downgrades:
- Oxidizing with low sulfur ($\le 2\text{ g/m}^3$): Safe limit is 1050°C (1922°F).
- Oxidizing with high sulfur ($> 2\text{ g/m}^3$): Downgrade maximum service limit to 950°C (1742°F) to avoid liquid-phase eutectic boundary cracking.
- Nitriding or Carburizing atmospheres: Continuous limits drop to 850°C – 950°C due to internal carbide/nitride matrix network choking.
- Weld Hot-Cracking Mitigation: Solidification as a fully austenitic weld pool creates narrow boundaries with minimal trace solubility for P and S impurities. To prevent micro-fissuring, eliminate preheating, limit interpass thresholds strictly below 150°C (300°F), employ stringer bead passes, and enforce V-prep geometries with closer tack-welding pitches.
■ Engineering Design Recommendations
- Creep vs. Fabrication Selection: Specify Grade 310H for extreme-temperature, load-bearing structures where fine, dispersed $M_{23}C_{6}$ carbides pin dislocation networks and maximize creep life. Reserve Grade 310S for heavily welded line configurations where low carbon prevents wet sensitization during cold shutdown blocks.
- Forging Verification: For critical pressure lines, prioritize hot-deformed forgings (ASTM A182 F310) over castings. Forgings utilize a minimum 3:1 reduction ratio to break up interdendritic segregation bands and seal internal porosity, boosting cyclic fatigue performance by 25% to 40%.
- Thermal Shock Warning: Due to low thermal conductivity and a high coefficient of thermal expansion, the 310 series is highly susceptible to massive localized strains during rapid cooling blocks. Do not specify these grades for applications involving regular fluid or liquid quenching.