904L Stainless Steel (UNS N08904) - Super Austenitic Sulfuric Acid Resistant Supplier of Bars, Tubes & Plates | Shanghai Hangbo Alloy Group
Date: 2026年8月4日 Categories: News Views: 220
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 904L?
904L (UNS N08904 / W.Nr. 1.4539 / Uranus B6) is a high-alloy super austenitic stainless steel with elevated nickel (25%), chromium (21%), molybdenum (4.5%), and deliberate copper (1.5%) that delivers superior resistance to sulfuric acid, phosphoric acid, and chloride pitting compared to standard 316L — at a substantially lower cost than 6% Mo alloys or nickel-base grades. It is the globally recognized benchmark for sulfuric acid piping, cooling systems, and chemical process equipment where 316L is simply inadequate. Shanghai Hangbo Alloy Group supplies 904L as round bars, seamless tubes, and plates.
Industry Pain Point: Chemical plant maintenance budgets are routinely devoured by the 18-month replacement cycle of 316L sulfuric acid piping. At 40-60% H₂SO₄ concentrations and temperatures above 40°C, 316L corrodes at 1-3 mm/year because the acid strips the passive Cr₂O₃ film. Upgrading to 904L — with its 4.5% Mo + 1.5% Cu chemistry specifically engineered for this exact environment — reduces corrosion rates to <0.1 mm/year, extending piping replacement intervals from 18 months to 10+ years. The 2-3× material cost premium over 316L is recovered within the first avoided shutdown.
Key Properties at a Glance
| Property | Value |
|---|---|
| UNS Number | N08904 |
| W.Nr. | 1.4539 |
| Alloy Family | Super Austenitic Stainless Steel |
| Density | 8.00 g/cm3 |
| Melting Range | 1300-1390C |
| PREN | >= 34 |
| Max Service Temp. | ~400C |
| Tensile Strength (Ann.) | >= 490 MPa (71 ksi) |
| Yield Strength (Ann.) | >= 220 MPa (31 ksi) |
| Elongation (Ann.) | >= 35% |
| Key Standards | ASTM B625, B649, B677 |
Product Overview
904L is the original "super austenitic" stainless steel — the first commercially successful grade to break through the performance ceiling of standard 300-series austenitics by substantially increasing the nickel, molybdenum, and copper content. Developed in the 1960s by Creusot-Loire (France) as Uranus B6, 904L remains one of the most widely specified corrosion-resistant stainless steels globally.
The alloy's performance rests on a simple metallurgical formula: take the basic 20Cr-25Ni austenitic matrix, add 4.5% molybdenum for pitting and crevice corrosion resistance in chlorides, then add 1.5% copper specifically for sulfuric acid service. The copper plays a subtle but decisive role — in sulfuric acid at intermediate concentrations (20-80%), the cathodic reaction shifts from oxygen reduction to hydrogen evolution, and the alloy's corrosion potential drifts into the active region where standard stainless steels dissolve rapidly. Copper shifts the alloy's corrosion potential more noble (positive), pushing it back into the passive region where the Cr₂O₃ film is stable.
904L's market position:
- Above 316L: 4× the molybdenum (4.5% vs 2.1%), 2× the nickel (25% vs 12%), and 1.5% copper that 316L completely lacks. 904L survives where 316L dissolves.
- Below 254SMO: 254SMO (PREN >=43, 6% Mo) offers higher pitting resistance for seawater and chloride service. 904L (PREN >=34, 4.5% Mo) is the cost-effective choice for sulfuric/phosphoric acid where extreme chloride pitting resistance is not the primary requirement.
- Below Alloy 28: Alloy 28 (PREN >=38, 3.5% Mo, 27% Cr) was specifically designed for wet-process phosphoric acid. 904L handles general sulfuric/phosphoric duties at lower cost.
Shanghai Hangbo Alloy Group supplies 904L as round bars, seamless tubes, and plates with full ASTM certification and EN 10204 3.1 MTC.
Executive Standards
| Product Form | ASTM | ASME | EN / W.Nr. |
|---|---|---|---|
| Plate, Sheet & Strip | ASTM B625 | ASME SB-625 | 1.4539 |
| Bar & Rod | ASTM B649 | ASME SB-649 | EN 10088-3 |
| Seamless Tube | ASTM B677 | ASME SB-677 | EN 10216-5 |
| Welded Pipe | ASTM B673 / B674 | ASME SB-673 | — |
| Forgings | ASTM B649 / B564 | — | — |
Chemical Composition (wt.% per ASTM B625)
| Element | Min | Max | Role |
|---|---|---|---|
| Ni | 23.0 | 28.0 | Austenite stabilizer; Cl-SCC resistance |
| Cr | 19.0 | 23.0 | Passive film; oxidation resistance |
| Mo | 4.0 | 5.0 | Pitting/crevice resistance; PREN anchor |
| Cu | 1.0 | 2.0 | Sulfuric acid specialist — noble potential shift |
| C | -- | 0.020 | Ultra-low for weldability |
| Mn | -- | 2.0 | Austenite stabilizer |
| Fe | Balance | -- | Matrix |
PREN: Cr + 3.3xMo = 19 + 3.3x4.0 = 32.2 minimum, typical 34-37.
Mechanical & Physical Properties
Room-Temperature (Solution-Annealed 1050-1100C/WQ)
| Property | Value |
|---|---|
| Tensile Strength | >= 490 MPa (71 ksi) |
| Yield Strength 0.2% | >= 220 MPa (31 ksi) |
| Elongation | >= 35% |
| Hardness | <= 90 HRB |
| Young's Modulus | ~195 GPa |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.00 g/cm3 |
| Thermal Conductivity | ~12 W/m-K |
| Thermal Expansion (20-200C) | ~15.5 micro-m/m-C |
| Electrical Resistivity | ~0.95 micro-ohm-m |
| Magnetic Permeability | <= 1.005 (non-magnetic) |
Heat Treatment
Solution Annealing: 1050-1100C (1920-2010F), water quench mandatory. No precipitation hardening.
Corrosion Performance
| Environment | 904L Corrosion Rate | 316L Corrosion Rate |
|---|---|---|
| 40% H₂SO₄, 60C | <0.1 mm/year | 2-5 mm/year |
| 10% H₂SO₄, 80C | <0.1 mm/year | >10 mm/year |
| Phosphoric Acid (tech grade), 100C | <0.1 mm/year | 1-3 mm/year |
| Seawater, 40C | Resistant | Pitting within months |
Industry Applications
| Industry | Component | Why 904L? |
|---|---|---|
| Sulfuric Acid | Piping, coolers, storage tanks | Copper alloying neutralizes active corrosion in 20-80% H₂SO₄ |
| Phosphoric Acid | Reactor vessels, heat exchangers | Survives wet-process acid with fluoride + chloride contaminants |
| Chemical Processing | Acetic/formic acid equipment, mixed-acid reactors | Broad-spectrum acid resistance at moderate cost |
| Oil & Gas | Sour gas piping, produced water handling | H₂S + chloride resistance; NACE MR0175 compliance |
| Seawater Cooling | Plate heat exchangers, condenser tubes | Adequate pitting resistance for moderate-temperature seawater |
| Pulp & Paper | Bleach plant washers, ClO₂ piping | Resists chlorine dioxide and acid-chloride mixtures |
Quality Assurance: 7-Stage
- Raw Material: Ni, Cr, Mo, Cu analyzed by OES. Copper purity verified >=99.9%.
- Melt Chemistry: Cu +/-0.05%, Mo +/-0.10%, C <=0.015% internal.
- Hot Working: 1150-1200C, finishing >=950C, reduction >=4:1.
- Solution Anneal: 1050-1100C, WQ. Hardness <=90 HRB.
- Corrosion Test: ASTM G48 Method A (pitting) or ASTM A262 Practice C (intergranular) on request per lot.
- NDE: 100% UT bars >=50mm; 100% ET/hydro tubes. PMI every piece.
- Documentation: EN 10204 3.1 MTC. SGS/TUV/BV witness available.
Frequently Asked Questions
Q1: What is 904L used for?
Sulfuric acid piping and storage (20-80% H₂SO₄), phosphoric acid reactor vessels, chemical process equipment handling organic acids, seawater cooling systems, and pulp & paper bleach plant components.
Q2: 904L vs 316L?
904L: Mo 4.5%, Ni 25%, Cu 1.5%. 316L: Mo 2.1%, Ni 12%, Cu 0%. 904L survives sulfuric/phosphoric acid where 316L dissolves. Cost premium 2-3×, justified by 10× longer service life in acid service.
Q3: 904L vs 254SMO?
254SMO: PREN >=43, Mo 6%. 904L: PREN >=34, Mo 4.5%. 254SMO for chloride pitting resistance (seawater). 904L for sulfuric/phosphoric acid at lower cost.
Q4: 904L vs Alloy 28?
Alloy 28: Cr 27%, Mo 3.5%, PREN >=38 — phosphoric acid specialist. 904L: Cr 21%, Mo 4.5%, PREN >=34 — sulfuric acid specialist. Choose based on acid type and concentration.
Q5: What is the density?
8.00 g/cm3 — same as standard stainless steel.
Q6: What is the melting point?
1300-1390C (2370-2535F).
Q7: Is 904L magnetic?
No, non-magnetic (mu-r <=1.005).
Q8: What is the price?
$15-30/kg EXW for bars. Contact sales@hangboalloy.com.
Q9: Is 904L weldable?
Yes, with ERNiCrMo-3 (625) or ER385 (904L matching) filler. Post-weld anneal recommended for maximum acid resistance.
Q10: Why does copper matter in 904L?
1.5% Cu shifts the corrosion potential more noble, preventing the alloy from entering the active dissolution region in sulfuric acid.
Q11: What product forms?
Bars (6-300mm), tubes (OD 6-219mm), plates (3-50mm), forgings, welded pipes. SGS available.
Q12: Does Shanghai Hangbo ship internationally?
Yes — FOB/CIF/DAP to 40+ countries.
Q13: What is the PREN?
PREN >=34, typical 34-37. Predictive of pitting resistance in chloride environments.
Q14: Can 904L be used for seawater?
Yes, for moderate-temperature seawater (<40C). For hot seawater or stagnant conditions where crevice corrosion risk is high, upgrade to 254SMO.
Q15: What is the solution annealing temperature?
1050-1100C (1920-2010F), water quench.
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 |
| Hastelloy (Ni-Mo-Cr) | Hastelloy C-276, C-22, C-2000, C-4, G-30, G-35, X, B-2, B-3, N |
| Super Austenitic | 904L, Alloy 28, Alloy 31, 254SMO |
| 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
