Alloy 33 (UNS R20033) - Chromium-Rich Corrosion Resistant Alloy Supplier of Bars, Tubes & Plates | Shanghai Hangbo Alloy Group
Date: 2026年8月6日 Categories: News Views: 344
By Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier | ISO 9001:2015 | Est. 2012
Contact: sales@hangboalloy.com | hangbo@nickel-alloy.com | WhatsApp (Lisa): +86 13611656360
Quick Answer: What Is Alloy 33?
Alloy 33 (UNS R20033 / W.Nr. 1.4591) is a chromium-rich austenitic alloy containing 33% chromium -- the highest chromium content of any commercially available wrought alloy -- combined with 31% nickel and deliberate nitrogen, delivering outstanding resistance to nitric acid at all concentrations, sulfuric acid, hot caustic soda, and oxidizing chloride media. It is specified to ASTM B907 and widely used in nitric acid plants, sulfuric acid coolers, marine scrubbers, and chemical process equipment where conventional stainless steels suffer transpassive or active corrosion. Shanghai Hangbo Alloy Group supplies Alloy 33 as round bars, seamless tubes, and plates.
Industry Pain Point: Nitric acid plant operators face a hidden corrosion mode: stainless steel's Cr₂O₃ film is thermodynamically stable only below approximately +1.0 V SHE. Concentrated boiling HNO₃ drives the alloy's potential into the "transpassive" region, where the film dissolves as soluble chromate (CrO₄²⁻) and intergranular attack follows. Alloy 33's unprecedented 33% chromium reservoir means the passive film is continuously replenished from a massive chromium supply -- extending the passive potential window and reducing nitric acid corrosion rates to 10-50% of 316L/310 values. In 65% boiling HNO₃, Alloy 33 achieves corrosion rates below 0.1 mm/year where 316L fails within months.
Key Properties at a Glance
| Property | Value |
|---|---|
| UNS Number | R20033 |
| W.Nr. | 1.4591 |
| Alloy Family | Chromium-Rich Austenitic (Ni-Cr-Fe-N) |
| Density | 7.90 g/cm3 |
| Melting Range | 1350-1390C |
| PREN | ~44 |
| Max Service Temp. | ~450C |
| Tensile (Ann., Bar) | >= 750 MPa (109 ksi) |
| Yield (Ann., Bar) | >= 350 MPa (51 ksi) |
| Elongation (Ann.) | >= 30% |
| Key Standards | ASTM B907, VdTUV 507, DIN EN 10095 |
Product Overview
Alloy 33 was developed by VDM Metals to challenge a fundamental assumption of corrosion metallurgy: that increasing chromium beyond ~25% inevitably leads to sigma-phase embrittlement. By carefully balancing 33% chromium with 31% nickel, 1.6% molybdenum, 0.4% nitrogen, and 0.6% copper, VDM created a fully austenitic alloy that maintains structural stability while pushing the chromium content to a level no commercial alloy has matched.
The 33% chromium delivers four decisive advantages:
- Transpassive corrosion resistance: The alloy resists nitric acid (HNO₃) at all concentrations up to boiling point -- the transpassive dissolution that destroys standard stainless steels is suppressed by the massive chromium reservoir.
- Superior general corrosion resistance: In sulfuric acid and mixed acid environments, Alloy 33 typically corrodes at rates 5-20x lower than 316L.
- Caustic resistance: At 25-50% NaOH at elevated temperatures, Alloy 33 outperforms nickel-base alloys, combining the caustic resistance of high-nickel materials with the cost structure of a chromium-rich alloy.
- Weldability: The nitrogen (0.4%) compensates for any chromium-driven ferrite formation, maintaining a fully austenitic weld microstructure with matching filler (ER33 / matching chemistry).
Alloy 33 vs. conventional candidates:
| Candidate | Alloy 33 (33% Cr) | 316L | Inconel 625 |
|---|---|---|---|
| 65% boiling HNO₃ | <0.1 mm/yr | Intergranular attack | Moderate |
| 40% H₂SO₄, 60C | <0.1 mm/yr | 1-5 mm/yr | <0.1 mm/yr |
| Cost | 1.5-2.5x 316L | Baseline | 4-5x 316L |
Shanghai Hangbo Alloy Group supplies Alloy 33 in bars, tubes, and plates with ASTM B907 certification.
Executive Standards
| Product Form | Standard |
|---|---|
| Plate, Sheet & Strip | ASTM B907, DIN EN 10095 |
| Bar & Rod | ASTM B907, VdTUV 507 |
| Seamless Pipe & Tube | ASTM B907, EN 10216-5 |
| Forgings | ASTM B907 / B564 |
| Welding Filler | ERNiCr-13 (matching Alloy 33 chemistry) |
Chemical Composition (wt.%)
| Element | Min | Max | Role |
|---|---|---|---|
| Chromium (Cr) | 32.0 | 34.0 | The defining element -- transpassive resistance + passive film reservoir |
| Nickel (Ni) | 30.0 | 33.0 | Austenite stabilizer; prevents sigma phase at 33% Cr |
| Molybdenum (Mo) | 1.2 | 2.0 | Pitting/crevice resistance; PREN contributor |
| Nitrogen (N) | 0.35 | 0.60 | Austenite stabilizer; PREN booster; compensates ferrite-forming Cr |
| Copper (Cu) | 0.30 | 0.80 | Sulfuric acid resistance |
| Iron (Fe) | Balance | -- | Matrix element |
| Manganese (Mn) | -- | 2.0 | Austenite stabilizer |
| Carbon (C) | -- | 0.015 | Ultra-low for weldability |
| Silicon (Si) | -- | 0.50 | Deoxidizer |
PREN Calculation: PREN = Cr + 3.3xMo + 16xN = 32 + 3.3x1.2 + 16x0.35 = 42.2 minimum, typical 44-46.
Mechanical & Physical Properties
Room-Temperature (Solution-Annealed 1040-1080C/WQ)
| Property | Bar | Plate |
|---|---|---|
| Tensile Strength | >= 750 MPa (109 ksi) | >= 700 MPa (102 ksi) |
| Yield Strength 0.2% | >= 350 MPa (51 ksi) | >= 330 MPa (48 ksi) |
| Elongation | >= 30% | >= 30% |
| Hardness | <= 30 HRC | <= 100 HRB |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.90 g/cm3 |
| Thermal Conductivity (20C) | ~14 W/m-K |
| Melting Range | 1350-1390C |
| Electrical Resistivity | ~1.0 micro-ohm-m |
| Magnetic Permeability | <= 1.005 (non-magnetic) |
Heat Treatment
Solution Annealing: 1040-1080C (1900-1975F), soak 30-60 min, water quench mandatory. No precipitation hardening.
Post-weld: Not required when welded with matching filler (ERNiCr-13 / Alloy 33 chemistry).
Corrosion Performance
| Environment | Alloy 33 | 316L |
|---|---|---|
| 65% boiling HNO₃ | <0.1 mm/yr | Severe IGA |
| 40% H₂SO₄, 60C | <0.1 mm/yr | 1-5 mm/yr |
| 50% NaOH, 120C | <0.05 mm/yr | Attack |
| Seawater, CPT | >= 55C | < 20C |
Industry Applications
| Industry | Component | Why Alloy 33? |
|---|---|---|
| Nitric Acid | Acid coolers, reboiler tubes, condenser piping | Transpassive resistance -- survives boiling concentrated HNO₃ |
| Sulfuric Acid | Cooler tubes, absorber internals | 5-20x lower corrosion rate vs 316L |
| Caustic Processing | NaOH evaporators, storage tanks | High-Ni + high-Cr double defense |
| Marine | Exhaust gas scrubbers, seawater piping | PREN ~44 + transpassive resistance to acidic scrubber media |
| Chemical Processing | Mixed-acid reactors, halogen handling | Broad-spectrum oxidizing/reducing acid resistance |
Quality Assurance: 7-Stage
- Raw Material: High-purity Cr, Ni, FeMnN analyzed by OES. Chromium purity >=99.9%.
- VIM Melt: Cr +/-0.3%, Mo +/-0.1%, N +/-0.03%, C <=0.010% internal.
- Hot Working: 1150-1200C, finishing >=1000C, reduction >=4:1.
- Solution Anneal: 1040-1080C, WQ. Hardness verification per lot.
- Corrosion Test: ASTM G48 Method A (CPT) + boiling HNO₃ test (65%) per lot on request.
- NDE: 100% UT bars >=50mm; ET/hydro tubes. PMI every piece.
- Documentation: EN 10204 3.1 MTC. SGS/TUV/BV witness available.
Frequently Asked Questions
Q1: What is Alloy 33 used for?
Nitric acid plant equipment (coolers, reboilers), sulfuric acid coolers, caustic soda evaporators, marine exhaust gas scrubbers, and chemical reactors handling oxidizing acid mixtures.
Q2: What makes Alloy 33 special?
33% chromium -- the highest of any commercial wrought alloy -- provides transpassive corrosion resistance to nitric acid and rapid passive-film re-healing. This is the alloy's unique metallurgical identity.
Q3: Alloy 33 vs 316L?
Alloy 33: 33% Cr vs 17%, 31% Ni vs 12%, PREN 44 vs 24. Corrosion rates 5-20x lower in acids. Cost premium 1.5-2.5x, justified where 316L fails.
Q4: Alloy 33 vs Alloy 28?
Alloy 28: Mo 3.5%, Cr 27% -- phosphoric acid specialist. Alloy 33: Cr 33%, Mo 1.6% -- nitric acid/transpassive specialist. Different applications: Alloy 28 for WPA; Alloy 33 for HNO₃ and oxidizing acids.
Q5: Is Alloy 33 magnetic?
No -- fully austenitic, non-magnetic (mu-r <=1.005).
Q6: What is the PREN?
~44 typical. Adequate for most chloride service, though not the alloy's primary selling point (transpassive resistance is).
Q7: Is Alloy 33 weldable?
Yes, with matching ERNiCr-13 filler. Fully austenitic weld microstructure thanks to nitrogen stabilization.
Q8: What is the price?
$35-60/kg EXW. Positioned between 316L and nickel alloys. Contact sales@hangboalloy.com.
Q9: What product forms?
Bars (6-300mm), seamless tubes (OD 10-219mm), plates (3-50mm), forgings. SGS available.
Q10: Does Shanghai Hangbo ship internationally?
Yes -- FOB/CIF/DAP to 40+ countries.
Q11: What is the maximum service temperature?
~450C continuous. Above this, long-term exposure risks sigma-phase precipitation.
Q12: Why nitrogen at 0.4-0.6%?
Nitrogen stabilizes austenite against the strongly ferrite-forming 33% Cr, enables the high Mn specification, and boosts PREN by ~6 points.
Q13: Can Alloy 33 handle seawater?
Yes, PREN ~44 provides good pitting resistance to moderate-temperature seawater, though 27-7MO or Alloy 31 are preferred for extreme chloride service.
Q14: What heat treatment?
Solution annealing at 1040-1080C, water quench. No aging.
Q15: Why choose Alloy 33 over 904L for nitric acid?
904L (PREN 34) also suffers transpassive attack in concentrated boiling HNO₃. Alloy 33's 33% Cr extends the passive window into the transpassive region, resisting conditions 904L cannot.
Contact Shanghai Hangbo Alloy Group
| Channel | Details |
|---|---|
| Company | Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier |
| Website | www.nickel-alloy.com |
| Email (Sales) | sales@hangboalloy.com |
| Email (Technical) | hangbo@nickel-alloy.com |
| WhatsApp (Lisa) | +86 13611656360 |
| Address | Room 1508, No. 288 Shiyi Road, Baoshan District, Shanghai 200940, China |
Shanghai Hangbo Alloy Group - Complete Product Range
| Family | Available Grades |
|---|---|
| Pure Nickel | NI200 (N02200), NI201 (N02201), N4, N5, N6 |
| Monel (Ni-Cu) | Monel 400, Monel 401, Monel 404, Monel K-500, Monel R-405 |
| Inconel (Ni-Cr) | Inconel 600, 601, 617, 625, 690, 718, X-750, 725 |
| Incoloy (Fe-Ni-Cr) | Incoloy 800, 800H, 800HT, 825, 925, 926, A-286, 25-6HN, 27-7MO |
| Hastelloy (Ni-Mo-Cr) | Hastelloy C-276, C-22, C-2000, C-4, G-30, G-35, X, B-2, B-3, B-4, N |
| Super Austenitic | 904L, Alloy 28, Alloy 31, 254SMO |
| Chromium-Rich | Alloy 33 |
| Nimonic (Ni-Cr-Co) | Nimonic 75, 80A, 90, 95, 105, 115, 263 |
| Haynes (High-Temp) | Haynes 25, 188, 230, 242, 282, 556 |
| Precision Alloys | 1J22, 1J46, 1J50, 1J79, 1J85, 3J21, 4J32, 4J36 (Invar), 4J45 |
| High-Strength Alloys | 18Ni250, 18Ni300, AerMet 100, PH13-8Mo |
| Heating Alloys | Cr20Ni80 (Nichrome 80/20), Cr40Ni60 |
| Specialty Alloys | Alloy 20, Alloy 59, RA330, Inconel 686, 602CA |
Product Forms
| Product Form | Typical Size Range |
|---|---|
| Round Bars & Rods | Diameter 6 - 500 mm |
| Seamless Tubes & Pipes | OD 6 - 610 mm, WT 0.5 - 30 mm |
| Plates & Sheets | Thickness 0.1 - 100 mm |
| Forgings | Discs, Rings, Blocks, Tube Sheets |
| Welded Pipes | OD up to 1219 mm |
| Fittings & Flanges | Elbows, Tees, Reducers, Weld Neck, Slip-On |
| Wire & Welding Wire | Diameter 0.05 - 10 mm |
| Strip & Coil | Thickness 0.02 - 4.0 mm |
SGS / Bureau Veritas / TUV Rheinland / DNV / Lloyd's Register inspection available.
Contact: sales@hangboalloy.com | WhatsApp (Lisa): +86 13611656360 | www.nickel-alloy.com
