Hangbo Alloy Group
Shanghai · Est. 2012
UNS N08330 / W.Nr. 1.4886 — Nickel-iron-chromium-silicon solid-solution alloy with outstanding thermal shock resistance, exceptional carburization protection, and proven reliability in industrial furnaces, heat treatment fixtures, and petrochemical reformer tubes.
RA330 (UNS N08330 / W.Nr. 1.4886) is a nickel-iron-chromium-silicon solid-solution alloy engineered specifically for extreme high-temperature service where both thermal shock resistance and carburization protection are critical. Developed by Rolled Alloys, RA330 bridges the performance gap between standard austenitic stainless steels like 310S and premium nickel-based superalloys, delivering exceptional service life in demanding furnace and heat treatment applications at temperatures up to 1150°C (2100°F).
What makes RA330 truly distinctive is its elevated silicon content (0.75-1.50%) combined with 34-37% nickel. The silicon forms a self-healing SiO2 subscale beneath the chromium oxide surface layer, dramatically enhancing oxidation resistance at temperatures where conventional stainless steels rapidly degrade. Meanwhile, the high nickel content prevents sigma phase embrittlement — a common failure mechanism in Fe-Cr alloys exposed to the 600-900°C temperature range for extended periods — and provides the ductility necessary to accommodate thermal cycling without cracking.
The alloy's austenitic structure is fully stable across all temperatures from cryogenic to near-melting, meaning it undergoes no detrimental phase transformations that could cause volume changes, distortion, or embrittlement during rapid heating and cooling cycles. This stability, combined with good thermal conductivity and moderate strength retention at elevated temperatures, makes RA330 the material of choice for furnace rolls, quenching fixtures, carburizing boxes, and heat treatment grids where components repeatedly cycle between ambient and 1000°C+.
RA330 also exhibits outstanding resistance to carburization in carbon-rich atmospheres. Unlike lower-nickel alloys that readily absorb carbon, forming brittle chromium carbides that deplete the matrix of corrosion-resistant chromium, RA330's high nickel content reduces carbon solubility and slows diffusion rates. In practical terms, this translates to 2-3 times longer service life than 310S in carburizing furnace applications, reducing downtime and replacement costs for heat treatment operations.
At Hangbo Alloy Group, RA330 is supplied in solution-annealed condition per ASTM B511, ASTM B535, ASTM B536, and AMS 5716. We stock round bars, seamless tubes, plates, forgings, and welding wire for immediate shipment, with full material test certificates and optional third-party inspection from SGS, TUV, or Bureau Veritas.
The chemistry of RA330 is carefully balanced to optimize high-temperature oxidation resistance, carburization protection, and structural stability. The silicon addition is the key differentiator from standard 310S — it promotes the formation of a dense, adherent SiO2 subscale that dramatically slows oxidation kinetics. Nickel is maintained at 34-37% to ensure a fully austenitic structure and prevent sigma phase formation, while chromium at 17-20% provides the primary oxidation-resistant Cr2O3 surface scale.
| Element | Min % | Max % | Role |
|---|---|---|---|
| Nickel (Ni) | 34.0 | 37.0 | Austenite stabilizer, sigma phase prevention, carburization resistance |
| Chromium (Cr) | 17.0 | 20.0 | Oxidation resistance, Cr2O3 scale formation |
| Iron (Fe) | Balance | Balance | Matrix element, cost optimization |
| Silicon (Si) | 0.75 | 1.50 | SiO2 subscale, enhanced oxidation & carburization resistance |
| Manganese (Mn) | — | 2.00 | Deoxidation, hot workability |
| Carbon (C) | — | 0.08 | Controlled to minimize carbide precipitation |
| Phosphorus (P) | — | 0.030 | Residual element, restricted |
| Sulfur (S) | — | 0.030 | Residual element, restricted for hot workability |
RA330 has a stable FCC austenitic crystal structure that remains unchanged from cryogenic temperatures to the melting point. This structural stability eliminates the volumetric changes associated with phase transformations, giving the alloy its characteristic thermal shock resistance. The thermal expansion coefficient is moderate — higher than ferritic steels but lower than many austenitic stainless grades — which helps reduce thermal stresses in components with thick-to-thin section transitions.
| Property | Value | Unit |
|---|---|---|
| Density | 8.02 | g/cm³ |
| Melting Range | 1370 - 1425 | °C |
| Specific Heat (20°C) | 460 | J/kg·K |
| Thermal Conductivity (100°C) | 12.5 | W/m·K |
| Thermal Conductivity (500°C) | 17.2 | W/m·K |
| Thermal Conductivity (800°C) | 22.0 | W/m·K |
| Electrical Resistivity (20°C) | 1.02 | μΩ·m |
| Modulus of Elasticity (20°C) | 197 | GPa |
| Coefficient of Thermal Expansion (21-538°C) | 16.0 | μm/m·°C |
| Coefficient of Thermal Expansion (21-871°C) | 17.2 | μm/m·°C |
| Curie Temperature | Non-magnetic | — |
RA330 is not age-hardenable — its strength is derived entirely from solid-solution strengthening by chromium, nickel, and silicon in the austenitic matrix. In the solution-annealed condition, the alloy exhibits moderate tensile strength with exceptional ductility, making it highly formable and resistant to cracking during fabrication. The values below represent typical properties for solution-annealed bars and plates per ASTM B511 / ASTM B536.
| Property | Value |
|---|---|
| Tensile Strength | 517 - 655 MPa (75 - 95 ksi) |
| Yield Strength (0.2% offset) | 207 - 310 MPa (30 - 45 ksi) |
| Elongation in 2 inches | 35 - 45% |
| Reduction of Area | 50 - 65% |
| Hardness | 70 - 90 HRB (130 - 185 HB) |
| Charpy V-notch Impact (room temp) | 80 - 120 J |
RA330 retains useful strength at elevated temperatures, though — as with all solid-solution alloys — mechanical properties decrease progressively with increasing temperature. The alloy is not intended for high-stress structural applications above 980°C, where creep becomes the dominant design consideration. However, for furnace fixtures, radiant tubes, and other moderate-stress applications, RA330 provides reliable performance through its full 1150°C service range. The data below represents typical short-term tensile properties at temperature.
| Temperature (°C) | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) |
|---|---|---|---|
| 21 (Room) | 585 | 260 | 40 |
| 538 (1000°F) | 450 | 185 | 42 |
| 649 (1200°F) | 380 | 160 | 45 |
| 760 (1400°F) | 270 | 120 | 52 |
| 871 (1600°F) | 170 | 83 | 60 |
| 982 (1800°F) | 97 | 48 | 68 |
| 1093 (2000°F) | 52 | 28 | 75 |
RA330 delivers outstanding oxidation resistance up to 1150°C through a dual-layer protective oxide mechanism. The chromium content (17-20%) forms a continuous Cr2O3 surface scale that provides primary oxidation protection. Beneath this layer, the elevated silicon content (0.75-1.50%) forms a dense, self-healing SiO2 subscale that acts as a diffusion barrier, dramatically slowing further oxygen ingress and chromium depletion. This silicon-enhanced protection is what allows RA330 to outperform 310S (which lacks intentional silicon addition) by a factor of 2-3x in cyclic oxidation testing at 1100°C.
The alloy performs well in air, combustion gases, flue gas environments, and mildly oxidizing process atmospheres. In sulfidizing environments, however, the nickel content can react with sulfur to form low-melting-point nickel sulfide eutectics, and RA330 is generally not recommended for service in high-sulfur reducing atmospheres above 800°C. For such conditions, cobalt-based alloys like Haynes 188 or high-chromium nickel alloys may be more suitable.
One of RA330's most valuable characteristics is its exceptional resistance to carburization — the absorption of carbon from the furnace atmosphere into the metal surface. In carburizing atmospheres at 850-1050°C, carbon diffuses into the alloy matrix and reacts with chromium to form brittle Cr23C6 carbides. This depletes the surrounding matrix of chromium, reducing oxidation resistance and causing embrittlement that leads to premature cracking and failure.
RA330's 34-37% nickel content is key to its carburization resistance. Nickel reduces both the solubility and diffusion rate of carbon in the austenite lattice, effectively slowing the carburization process. In comparative testing, RA330 exhibits approximately 50-70% less carbon pickup than 310S after 500 hours exposure to a carburizing atmosphere at 980°C. The silicon content provides additional protection by promoting the formation of a continuous oxide subscale that acts as a physical barrier to carbon ingress.
In nitriding atmospheres (ammonia-based), RA330 also performs well, though the protection mechanism differs. The nickel content does not directly inhibit nitrogen diffusion to the same extent as carbon, but the dense chromium oxide scale provides an effective barrier. For severe nitriding service, alloys with higher nickel content (Inconel 600, 601) may offer additional protection.
RA330 is typically supplied in the solution-annealed condition, which provides the optimum combination of ductility, formability, and grain structure for most applications. The standard heat treatment parameters are:
RA330 is readily weldable by all common arc welding processes. The fully austenitic structure eliminates the risk of martensite formation in the heat-affected zone, and the alloy is not susceptible to hydrogen-induced cold cracking. Key welding recommendations:
RA330's unique combination of thermal shock resistance, carburization protection, and high-temperature oxidation resistance makes it a workhorse material in demanding thermal processing industries:
RA330 occupies a strategic position between standard stainless steels and premium nickel alloys for high-temperature service:
| Property | RA330 (N08330) | 310S (S31008) | Incoloy 800H (N08810) |
|---|---|---|---|
| Ni Content | 34-37% | 19-22% | 30-35% |
| Cr Content | 17-20% | 24-26% | 19-23% |
| Si Content | 0.75-1.50% | ≤1.50% | ≤1.00% |
| Max Service Temp | 1150°C | 1100°C | 1100°C |
| Carburization Resistance | Excellent | Moderate | Good |
| Thermal Shock | Excellent | Good | Excellent |
| Sigma Phase Risk | Low | Moderate-High | Low |
| Relative Cost | $$$ | $$ | $$$$ |
The choice between these alloys depends on the specific failure mechanism in a given application. If sigma phase embrittlement is the primary concern (650-900°C long-term exposure), RA330 and 800H are both excellent choices. If carburization is the limiting factor, RA330's combination of high nickel and intentional silicon addition gives it a clear advantage. If cost is the primary driver and service conditions are less severe, 310S remains a viable option.
Hangbo Alloy Group manufactures and supplies RA330 in a comprehensive range of product forms and dimensions, all supported by EN 10204 3.1 material test certificates and available with third-party inspection:
| Standard | Description |
|---|---|
| ASTM B511 / ASME SB-511 | Bar and Rod — Nickel-Iron-Chromium-Silicon Alloy |
| ASTM B535 / ASME SB-535 | Seamless Pipe and Tube |
| ASTM B536 / ASME SB-536 | Plate, Sheet, and Strip |
| ASTM B512 / ASME SB-512 | Wire |
| ASTM B366 | Factory-Made Wrought Fittings |
| AMS 5716 | Bar, Forging, and Ring — Solution Heat Treated |
| EN 10095 | Heat Resisting Steels and Nickel Alloys |
| NACE MR0175 / ISO 15156 | Petroleum and Natural Gas — Materials for H2S Service (applicable at controlled hardness) |
Hangbo Alloy Group is a trusted manufacturer and supplier of RA330 (UNS N08330) in round bars, seamless tubes, plates, forgings, and welding wire. We provide full MTC documentation, third-party inspection (SGS/TUV/BV), and competitive mill-direct pricing. Typical lead time for standard sizes: 7-14 days. Custom forgings: 3-5 weeks.
Contact our sales team: [email protected] | Phone/WhatsApp: +86-136-1165-6360 | We respond within 10 minutes.
Get a Quote for RA330 →Common questions from engineers, procurement managers, and fabricators working with RA330 alloy.
RA330 (UNS N08330) is a nickel-iron-chromium-silicon alloy with 34-37% nickel — nearly double the nickel content of 310S (19-22%). This higher nickel provides superior resistance to sigma phase embrittlement and carburization, while the intentional silicon addition (0.75-1.50%) enhances oxidation resistance through SiO2 subscale formation. RA330 typically lasts 2-3x longer than 310S in carburizing furnace service and thermal cycling applications.
RA330 has a density of 8.02 g/cm³ at room temperature. Its melting range is 1370-1425°C (2500-2597°F), with a typical melting point around 1400°C. The coefficient of thermal expansion is 16.0 μm/m·°C (21-538°C) and 17.2 μm/m·°C (21-871°C). Thermal conductivity ranges from 12.5 W/m·K at 100°C to 22.0 W/m·K at 800°C.
Per ASTM B511: Ni 34.0-37.0%, Cr 17.0-20.0%, Fe balance (~42-48%), Si 0.75-1.50%, Mn ≤2.00%, C ≤0.08%, P ≤0.030%, S ≤0.030%. The elevated silicon is the key differentiator from 310S — it forms a dense SiO2 subscale that dramatically improves oxidation and carburization resistance at temperatures above 1000°C.
In solution-annealed condition: Tensile strength 517-655 MPa (75-95 ksi), Yield strength (0.2% offset) 207-310 MPa (30-45 ksi), Elongation 35-45%, Hardness 70-90 HRB. RA330 is not age-hardenable — its strength comes from solid-solution strengthening. At 871°C, tensile strength decreases to ~170 MPa with elongation increasing to ~60%.
RA330 is rated for continuous service up to 1150°C (2100°F) in air and oxidizing atmospheres. For intermittent service, brief excursions to 1200°C are acceptable. In carburizing atmospheres, the practical limit is typically 1095°C (2000°F). For stressed components, creep becomes the limiting factor above 980°C, and design stresses must be carefully evaluated using creep-rupture data.
RA330 resists thermal shock through three mechanisms: (1) its fully austenitic structure undergoes no phase transformations during heating/cooling, eliminating volumetric changes that cause stress; (2) the high nickel content provides excellent ductility and toughness, allowing the material to absorb thermal strain without cracking; (3) moderate thermal conductivity helps dissipate temperature gradients. This makes RA330 ideal for quenching fixtures that cycle between room temperature and 1000°C+ multiple times daily.
RA330 exhibits outstanding carburization resistance — typically absorbing 50-70% less carbon than 310S after 500 hours at 980°C in a carburizing atmosphere. The 34-37% nickel content reduces carbon solubility and diffusion rate in the austenite matrix, while the silicon-enhanced oxide subscale provides a physical barrier to carbon ingress. This makes RA330 the preferred material for carburizing furnace fixtures, grids, and baskets.
RA330 pricing varies with product form, dimensions, and nickel market conditions. Approximate price ranges (FOB Shanghai, July 2026): Round bars 6-100mm: $18-28 USD/kg; Plates 3-30mm: $20-30 USD/kg; Seamless tubes: $30-45 USD/kg; Custom forgings: $22-35 USD/kg. Prices are subject to nickel LME fluctuation. Contact Hangbo Alloy at [email protected] for a current quotation — typically responded within 10 minutes.
RA330 is readily weldable using GTAW (TIG), GMAW (MIG), or SMAW (stick). Recommended filler: ERNiCr-3 (Inconel 82) for matching or superior oxidation resistance. No preheat required. Maintain interpass temperature below 150°C. Post-weld heat treatment is generally not necessary, though stress relief at 900-950°C may be applied for severe thermal cycling service. Use dedicated stainless steel brushes to avoid iron contamination.
RA330 is supplied in the solution-annealed condition: heat to 1120-1175°C (2050-2150°F), hold for 1 hour per 25mm of thickness, then rapidly cool in air or water. This produces a uniform austenitic grain structure with maximum ductility. Stress relief (when needed after welding or cold working): 900-950°C for 1 hour per 25mm, air cool. RA330 cannot be hardened by heat treatment.
Both are excellent high-temperature alloys, with key differences: RA330 has higher silicon (0.75-1.50% vs ≤1.00%) for superior oxidation and carburization resistance, while 800H has slightly higher chromium (19-23% vs 17-20%). RA330 is generally preferred for carburizing furnace service, while 800H is often selected for petrochemical reformer tubes where creep strength at 800-950°C is critical. RA330 is typically 15-25% less expensive than 800H.
Hangbo Alloy Group supplies: Round bars (6-300mm diameter), Seamless tubes & pipes (6-219mm OD), Plates & sheets (0.5-50mm thickness), Custom forgings (flanges, rings, discs, shafts), Welding wire (0.8-5.0mm diameter), and Wire & strip (0.1-12mm wire, 0.05-3.0mm strip). All products come with full EN 10204 3.1 MTC and optional third-party inspection (SGS/TUV/BV).
Hangbo Alloy Group maintains mill-direct supply of RA330 round bars, seamless tubes, plates, forgings, and welding wire in all standard sizes. Our technical team can assist with material selection, heat treatment specification, welding procedure recommendations, and export documentation. We support customers in the heat treatment, industrial furnace, petrochemical, power generation, and glass manufacturing industries with reliable quality and fast delivery worldwide.
For quotations, material certifications, or technical consultation, contact our sales team or call +86-136-1165-6360. Email: [email protected]. We typically respond within 10 minutes during business hours.
Request a quotation for RA330 round bars, tubes, plates, or custom forgings. We stock standard sizes and accept custom orders with fast turnaround.