RA330 (UNS N08330) - High-Temperature Carburization-Resistant Alloy Supplier of Round Bars, Tubes & Plates | Shanghai Hangbo Alloy Group

By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 Certified | Est. 2012

Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360

Quick Answer: What Is RA330?

RA330 (UNS N08330 / W.Nr. 1.4886) is an austenitic iron-nickel-chromium alloy with approximately 35% nickel, 19% chromium, and a deliberate silicon addition (1.0-1.5%) that delivers outstanding resistance to carburization and oxidation at temperatures up to 1100C. It is specified to ASTM B511/B512 (bar) and B535/B536 (pipe/tube) and widely used in heat treatment furnace radiant tubes, muffles, retorts, and chemical process equipment handling hydrocarbon-rich atmospheres. Shanghai Hangbo Alloy Group supplies RA330 as round bars, seamless tubes, and plates.

Industry Pain Point: Heat treatment furnace operators running endothermic gas carburizing atmospheres at 900-950C face a universal failure mode: chromia-forming alloys (Incoloy 800H, 310 stainless) suffer progressive carburization embrittlement within 12,000-18,000 hours because the Cr2O3 scale is permeable to carbon at these temperatures. RA330's elevated silicon content (1.0-1.5%) forms a SiO2 sub-layer beneath the Cr2O3 scale that acts as a carbon diffusion barrier -- extending radiant tube life to 25,000-35,000 hours, nearly doubling the replacement interval.

Key Properties at a Glance

Product Overview

RA330 occupies the upper mid-range of wrought heat-resistant alloys: above Incoloy 800H (32% Ni) in carburization resistance, below the cast HP-modified alloys (35Ni-25Cr-Nb) in cost. The alloy's distinctive value proposition rests on its silicon micro-alloying -- 1.0-1.5% Si is deliberately higher than virtually all competing wrought alloys in this class.

Silicon serves two synergistic functions:

1. Carburization barrier: During high-temperature service, silicon diffuses to the oxide-metal interface and forms a continuous, vitreous SiO2 (silica) sub-layer beneath the outer Cr2O3 scale. SiO2 is approximately 100x less permeable to interstitial carbon diffusion than Cr2O3 alone, creating a composite oxide structure that blocks carbon ingress far more effectively than chromium oxide forming alone.
2. Oxide scale adhesion: Silicon acts as a reactive element, pegging the oxide scale to the substrate metal through SiO2 "keys" that mechanically interlock with the alloy matrix. This suppresses scale spallation during thermal cycling -- the dominant failure mode in batch-type heat treatment furnaces that cycle between ambient and 950C on a daily basis.

Shanghai Hangbo Alloy Group supplies RA330 as round bars (for machined furnace components), seamless tubes (the dominant product form for radiant tubes and muffles), and plates (for fabricated retorts and boxes).

Executive Standards

Chemical Composition (wt.% per ASTM B511 - OES Verified)

Mechanical & Physical Properties

Room-Temperature (Annealed)

Elevated-Temperature (Typical)

Physical Properties

Heat Treatment

Solution Annealing: 1050-1120C (1920-2050F), minimum 1 hour per 25 mm thickness, rapid air cool or water quench. The anneal dissolves chromium carbides formed during hot working and homogenizes the silicon distribution for uniform SiO2 sub-layer formation in service.

No precipitation hardening -- RA330 is solid-solution strengthened only. No aging treatment is applied or required.

Stress Relief: 540-650C, 1-2 hours, air cool for cold-worked components.

Industry Applications

Quality Assurance (7-Stage)

1. Raw material: FeCr, Ni, FeSi analyzed by OES. Silicon source verified.
2. Melt chemistry: Si verified 1.0-1.5%; C <=0.06% internal target.
3. Hot working: IR pyrometry, reduction >=4:1.
4. Solution anneal: 1050-1120C, digital chart +/-5C.
5. Mechanical testing: tensile per heat-treatment lot.
6. NDE: 100% UT for bars >=50mm. PMI every piece.
7. EN 10204 3.1 MTC. SGS/TUV witness available.

Frequently Asked Questions

Q1: What is RA330 used for?

Heat treatment furnace radiant tubes, muffles, retorts, and baskets in carburizing/nitriding atmospheres at 900-1000C; chemical process equipment handling hydrocarbon-rich gases; incinerator components.

Q2: What is the density?

8.06 g/cm3.

Q3: What is the maximum service temperature?

~1100C in oxidizing atmospheres; ~950C in carburizing atmospheres.

Q4: Why does silicon matter in RA330?

Silicon (1.0-1.5%) forms a SiO2 sub-layer beneath the Cr2O3 scale that is ~100x less permeable to carbon, blocking carburization embrittlement.

Q5: What is the tensile strength?

>=550 MPa (>=80 ksi) annealed.

Q6: How does RA330 compare to Incoloy 800H?

RA330 has higher Ni (35% vs 32%), higher Si (1.0-1.5% vs <=1.0%), and ~2x carburization resistance. 800H has slightly better creep strength above 650C. For carburizing atmospheres, choose RA330.

Q7: What heat treatment?

Solution annealing at 1050-1120C, rapid air cool or water quench. No precipitation hardening.

Q8: Is RA330 weldable?

Yes -- GTAW/GMAW with ERNiCr-3 (Inconel 82) or ERNiCrFe-2 filler. Post-weld anneal at 1050-1120C recommended for carburizing service.

Q9: Price per kg?

$20-35/kg EXW. Contact sales@hangboalloy.com.

Q10: Product forms?

Round bars (6-300 mm), seamless tubes (OD 10-219 mm), plates (3-50 mm), forgings.

Q11: International shipping?

Yes -- FOB/CIF/DAP to 40+ countries. Stock 2-4 weeks; mill 8-12 weeks.

Q12: What standards?

ASTM B511/B512 (bar), B535/B536 (pipe/tube), B546 (plate).

Q13: Is RA330 magnetic?

Non-magnetic (FCC austenitic structure).

Q14: What is the melting point?

1370-1400C.

Q15: Can RA330 be used in thermal cycling?

Yes -- the SiO2 sub-layer improves scale adhesion and reduces spallation during cycling, extending component life in batch furnaces.

Q16: What is the typical radiant tube life comparison?

RA330: 25,000-35,000 hours in endothermic gas carburizing at 950C. Incoloy 800H: 12,000-18,000 hours under the same conditions. RA330 approximately doubles the replacement interval.

Contact Shanghai Hangbo Alloy Group