XM-19
XM-19 (also known as Nitronic 50, UNS S20910) is a nitrogen-strengthened austenitic stainless steel, which stands out with its high strength and excellent corrosion resistance (especially chloride ion/stress corrosion resistance). The following is a systematic analysis from six dimensions:
I. Standard system (polymorphic specification)
XM – 10 corresponds to ASTM/international standards for different product forms, covering industrial and aviation scenarios:
| Product Form | Core Implementation Standard | Supplementary Explanation |
|---|---|---|
| Bars/Profiles | ASTM A276 | General structural components (shafts, bolts, etc.) |
| Forgings/Pressure – bearing Bars | ASTM A479 | High – pressure equipment (flanges, valve cores) |
| Aerospace Components | AMS 5764/5844 | High – temperature/high – stress environments (engines, aerospace vehicles) |
| International Compatibility | DIN W – Nr. 1.3964 | European engineering adaptation |
II. Name and code (international common name)
XM – 19 is a model in the ASTM system, and there are also the following identifications internationally:
- Core code: UNS S20910 (Unified Numbering System of the United States, globally 通用);
- Trade names: Nitronic 50 (AK Steel trademark, emphasizing high – nitrogen strengthening), Fermonic 50 (name of some manufacturers);
- Performance positioning: Super austenitic stainless steel (strength is twice that of conventional 300 series, corrosion resistance is close to duplex stainless steel).
III. Chemical composition (mass fraction%, precise corrosion-resistant design)
XM – 19 achieves strength, toughness and corrosion resistance through “Cr – Ni – Mn – N – Nb/V synergy”. Key elements and their functions:
| Element | Content Range | Core Function |
|---|---|---|
| C | ≤0.06 | Strictly control carbon to avoid intergranular corrosion (very low risk of carbide precipitation) |
| Mn | 4.0 – 6.0 | Solution strengthening, stabilize austenite (reduce Ni usage, control cost) |
| Cr | 20.5 – 23.5 | Form a Cr₂O₃ passivation film, resist uniform/pitting corrosion |
| Ni | 11.5 – 13.5 | Stabilize austenite, resist stress corrosion cracking (high Ni ensures toughness) |
| Mo | 1.50 – 3.00 | Enhance resistance to pitting/crevice corrosion (core in chlorine – containing environments) |
| N | 0.20 – 0.40 | Significantly increase strength (synergize with Mn), assist corrosion resistance (PREN↑) |
| Nb | 0.10 – 0.30 | Refine grains, inhibit high – temperature growth (improve thermal strength) |
| V | 0.10 – 0.30 | Dispersion strengthening (precipitate carbonitrides), further increase strength |
| Impurities P≤0.045, S≤0.030 | – | Strictly control embrittlement/heat cracking risk, ensure corrosion resistance |
IV. Mechanical properties (both toughness and solidity)
XM – 19, strengthened by nitrogen and alloying elements, has performance far exceeding that of conventional austenitic stainless steel:
| Performance Indicator | Typical Value (ASTM Requirement) | Comparative Reference (304 Stainless Steel) |
|---|---|---|
| Tensile Strength | ≥720 MPa | 304: ~515 MPa (60% lower) |
| Yield Strength | ≥450 MPa | 304: ~205 MPa (120% lower) |
| Elongation (δ₅) | ≥35% | 304: ≈40% (Plasticity is close, easy to form) |
| Hardness | 180 – 240 HB | 304: ≤217 HB (Higher strength after cold working) |
| Physical Properties | Density 8.0 g/cm³, Non – magnetic | Suitable for magnetic – free scenarios in medical and precision equipment |
V. Heat treatment requirements (solid solution as the core, optional aging)
- Solution Treatment (Mandatory):
- Temperature: 1050 – 1150°C (hold for 1 – 2 hours to ensure uniform dissolution of N, Nb/V);
- Cooling: Rapid water cooling (quenching) to obtain a single austenitic structure and maximize corrosion resistance;
- Application: Mandatory before delivery; re – solution treatment is required after welding (to prevent sensitization of thick – walled parts, avoid the 450 – 850°C range).
- Aging Treatment (Optional, for Strength Enhancement):
- Temperature: 700 – 800°C (hold for 2 – 4 hours), fine Nb/V carbonitrides precipitate, further increasing strength (yield strength can increase by 10 – 15%);
- Trade – off: Slightly reduces plasticity (elongation decreases by 5 – 8%), only for high – stress scenarios (such as aerospace components).
VI. Main application fields (high stress+strong corrosion scenario)
XM – 19 relies on the dual advantages of “strength × corrosion resistance” to dominate the following extreme environments:
- Marine Engineering:
- Seawater desalination (high – pressure pumps, membrane modules, pipelines): Resists pitting/crevice corrosion of 3 – 5% NaCl seawater (service life is more than twice that of 316L);
- Offshore platforms (mooring chains, underwater robotic arms): Resists seawater and wind – wave impact, replacing titanium alloys with a 30% cost reduction.
- Aerospace:
- Engines (turbine liners, fuel pipelines): Resists 600°C fuel gas corrosion and has high strength (reduces weight by 15 – 20%);
- Spacecraft (structural supports, fluid pipelines): Resists space radiation and is non – magnetic, compatible with electronic equipment.
- Energy and Chemical Industry:
- Acid oil and gas fields (wellhead valves, transmission pipes): Resists stress corrosion cracking caused by H₂S + Cl⁻ (complies with NACE MR0175);
- Nuclear energy (nuclear waste tanks, cooling pipelines): Resists radiation and high – temperature water corrosion, with stable long – term service.
- High – end Manufacturing:
- Food and medicine (soy sauce tanks, sterile equipment): Resists organic acids and meets hygiene regulations (replaces 904L, with a 25% cost reduction);
- Medical devices (surgical forceps, implant substrates): Non – magnetic and resistant to body fluid corrosion (superior to 316L, avoiding MRI interference).
Key Summary
- Core Competitiveness: Strength is twice that of 304/316L, corrosion resistance is close to super duplex steel, non – magnetic, and excellent in hot and cold workability (can be cold – rolled, forged, and welded).
- Limitations: Cost is 2 – 3 times higher than conventional stainless steel, and nickel – based alloys (such as Hastelloy B) are still needed in concentrated hydrochloric acid/hydrofluoric acid.
XM – 19 (UNS S20910/Nitronic 50) is a “benchmark austenitic steel for high – strength and corrosion resistance”. It breaks through the performance bottleneck of conventional stainless steel through nitrogen alloying, replaces some nickel – based/duplex steels in marine, aerospace, chemical and other fields, balances performance and cost, and becomes a “rigid demand material” for high – stress corrosion scenarios.