Austenitic XM-18 (UNS S21603) Stainless Steel Plate/Coil
Austenitic XM-18 (UNS S21603) Stainless Steel Plate/Coil: High-Strength, High-Nitrogen Corrosion Resistance
Complete technical data for XM-18 (UNS S21603) austenitic stainless steel plate and coil according to ASTM A240, including chemistry, mechanical and physical properties, international equivalents, and application guidance.
Hot rolling, cold rolling, annealing, pickling, descaling
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Austenitic XM-18 Stainless Steel Plate/Coil Introduction
XM-18 (UNS S21603) is a high-nitrogen, nickel-manganese-chromium-molybdenum austenitic stainless steel that offers a combination of high strength, excellent toughness, and superior corrosion resistance. The intentional addition of nitrogen (0.25–0.35%) increases the yield and tensile strengths without sacrificing ductility, while maintaining a fully austenitic, non-magnetic structure in the annealed condition. This alloy exhibits good resistance to pitting and crevice corrosion in chloride-containing environments, making it suitable for demanding marine, chemical processing, and oil & gas applications. Typical product forms include hot-rolled or cold-rolled plate, sheet, coil, and strip. XM-18 provides an attractive balance of mechanical properties and fabricability, often selected as a cost-effective alternative to more highly alloyed materials where high strength and moderate corrosion resistance are required.
Austenitic XM-18 Stainless Steel Plate/Coil Chemical Composition
Chemical requirements as specified in ASTM A240/A240M for grade XM-18 (UNS S21603). All values are weight percent (%). Balance is iron (Fe). The high nitrogen content is key to the alloy's strength and corrosion resistance.
| Element | Standard Value (%) | Remarks |
|---|---|---|
| Carbon, C | ≤0.03 | Max |
| Manganese, Mn | 7.50–9.00 | |
| Silicon, Si | ≤0.75 | Max |
| Phosphorus, P | ≤0.045 | Max |
| Sulfur, S | ≤0.030 | Max |
| Chromium, Cr | 17.5–20.5 | |
| Nickel, Ni | 5.0–7.0 | |
| Molybdenum, Mo | 2.00–3.00 | |
| Nitrogen, N | 0.25–0.35 | |
| Iron, Fe | Balance | Approx. 63–68% |
Austenitic XM-18 Stainless Steel Plate/Coil Physical, Thermal and Electrical Properties
Typical physical and thermal properties of UNS S21603 in the annealed condition. The values are representative for general engineering use and may vary slightly with processing history. Thermal expansion and conductivity are important for applications involving thermal cycling.
| Property | Typical Value | Unit | Test Condition / Temperature |
|---|---|---|---|
| Density (ρ) | 7.81 | g/cm³ | Room temperature |
| Elastic Modulus (E) | 193 (28 × 10³ ksi) | GPa | Tension, room temperature |
| Shear Modulus (G) | 76 | GPa | Calculated from E and ν |
| Poisson's Ratio (ν) | 0.30 | Room temperature | |
| Coefficient of Thermal Expansion (α) | 16.5 | µm/m·°C | 20–100 °C |
| Coefficient of Thermal Expansion (α) | 17.5 | µm/m·°C | 20–315 °C |
| Coefficient of Thermal Expansion (α) | 18.5 | µm/m·°C | 20–538 °C |
| Thermal Conductivity (λ) | 15.0 | W/m·K | At 100 °C |
| Thermal Conductivity (λ) | 18.5 | W/m·K | At 500 °C |
| Specific Heat Capacity (cp) | 500 | J/kg·K | 0–100 °C |
| Electrical Resistivity (ρe) | 0.72 | µΩ·m | At 20 °C |
| Magnetic Permeability | <1.005 | µ (relative) | Annealed, non-magnetic |
Austenitic XM-18 Stainless Steel Plate/Coil Mechanical Properties
Mechanical property requirements for ASTM A240 XM-18 plate, sheet and strip in the solution-annealed condition. The alloy delivers high strength and good ductility. Test parameters: room temperature, longitudinal specimen. Hardness values are indicative and not always mandatory for all product forms.
| Property | Standard Requirement | Unit | Test Condition |
|---|---|---|---|
| Tensile Strength (Rm) | ≥690 (100 ksi) | MPa | Room temperature, per ASTM A370 |
| Yield Strength (ReH, 0.2% offset) | ≥415 (60 ksi) | MPa | Room temperature, per ASTM A370 |
| Elongation (A) in 50 mm (2 in.) | ≥30 | % | Gauge length 50 mm |
| Hardness (HRB) | ≤95 | HRB | As annealed |
| Hardness (HBW) | ≤248 | HBW | As annealed |
| Bend Test (180°) | No cracks on outside surface | Bend diameter = specimen thickness (t ≤ 19 mm) |
Austenitic XM-18 Stainless Steel Plate/Coil Exact Equivalent Material Standards and Substitute Grades
| Country / Region | Standard | Grade Designation | Remarks |
|---|---|---|---|
| USA | ASTM A240 / A959 | XM-18 (UNS S21603) | Original designation; fully equivalent to itself |
| Global | UNS | S21603 | Universal Numbering System, identical chemistry |
Austenitic XM-18 Stainless Steel Plate/Coil Application Introduction
XM-18 (S21603) combines high strength, good ductility, and enhanced corrosion resistance, making it suitable for weight-sensitive, corrosive environments. Its excellent toughness even at cryogenic temperatures expands its utility. Typical processing includes forming, welding, and machining, though high nitrogen content requires slightly higher machining forces.
Product Applications: Plates and coils for pressure vessel fabrication, Sheet metal components requiring high strength and formability, Fasteners (bolts, nuts, washers) in corrosive environments, Springs and wire forms with high fatigue resistance, Shafts and pump components exposed to brackish or seawater, Heat exchanger plates and frames
Processed into products: Pump impellers and casings, Valve stems and seats, Hose clamps and marine hardware, Fastener sets for chemical flange connections, Cryogenic tank hardware (non-magnetic requirement), Load-bearing structural brackets in corrosive atmospheres
Application industries: Chemical and petrochemical processing (tanks, reactors, piping), Marine and offshore engineering (fasteners, shafts, valve bodies), Oil & gas exploration and production (downhole equipment, wellhead components), Desalination and water treatment (high-pressure components), Power generation (turbine parts, boiler components), Food and pharmaceutical equipment (where high surface finish and corrosion resistance needed)
Austenitic XM-18 Stainless Steel Plate/Coil Similar or Nearby Alternative Stainless Steels
| Country / Region | Standard | Grade | Remarks |
|---|---|---|---|
| USA | ASTM A240 / A959 | UNS S21900 (Nitronic 40) | High-nitrogen austenitic, higher Cr (18-22) and Mn (8-10), no Mo; lower strength but good corrosion resistance |
| USA | ASTM A276 / A240 | UNS S20910 (Nitronic 50 / XM-19) | Higher Ni (11.5-13.5), Mo (1.5-3.0) and N (0.10-0.30); superior strength and corrosion resistance, often used as an upgrade |
| Europe | EN 10088-1 | 1.4462 (X2CrNiMoN22-5-3) | Duplex stainless steel, not austenitic; high strength and corrosion resistance, comparable pitting resistance but magnetic |
| USA | ASTM A240 | 316L (S31603) | Standard austenitic, lower strength (~485 MPa UTS), no N addition; much lower cost, commonly used but not a strength replacement |
Notes:
Welding: XM-18 is readily weldable by GTAW, GMAW, SMAW processes. Filler metal typically ER2209 (duplex) or matching composition filler. Post-weld annealing is not always required due to low carbon; low heat input recommended to retain properties. Corrosion: Excellent resistance to chloride stress-corrosion cracking, higher than 304/316 grades. Pitting resistance equivalent number (PREN) ≈ 30–36 (calculated as %Cr + 3.3%Mo + 16%N). Heat treatment: Solution anneal at 1065–1120°C (1950–2050°F) followed by water quenching or rapid air cool. Machining: Requires heavy feed rates, sharp tools, and adequate cooling due to work hardening tendency. Data source: Properties based on published ASTM standards and industry datasheets for UNS S21603.
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