Alloy 28 (UNS N08028) - Sulfuric Acid Resistant Super Austenitic Supplier of Bars, Tubes & Plates | Shanghai Hangbo Alloy Group
Date: 2026年8月4日 Categories: News Views: 229
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 28?
Alloy 28 (UNS N08028 / W.Nr. 1.4563 / Sanicro 28) is a high-nickel (31%), high-chromium (27%) super austenitic stainless steel with deliberate molybdenum (3.5%) and copper (1.0%) additions, specifically metallurgically optimized for outstanding resistance to sulfuric acid (H₂SO₄) across the full concentration range and phosphoric acid (H₃PO₄) in wet-process fertilizer production. It is specified to ASTM B709 (plate), B668 (tube), and B649 (bar) and is the long-established benchmark material for phosphoric acid heat exchanger tubing. Shanghai Hangbo Alloy Group supplies Alloy 28 as round bars, seamless tubes, and plates.
Industry Pain Point: Wet-process phosphoric acid (WPA) plants produce 54% P₂O₅ acid contaminated with fluoride ions (2-3%), chloride ions (500-2000 ppm), and ferric iron (Fe³⁺) -- a chemical cocktail that dissolves 316L at >10 mm/year and even attacks duplex stainless steels through selective phase corrosion. Alloy 28 has been the reference material for WPA heat exchanger tubing since the 1970s because its high Ni+Cr+Mo+Cu combination creates a passive film stable enough to reduce corrosion rates to <0.1 mm/year in this exact environment.
Key Properties at a Glance
| Property | Value |
|---|---|
| UNS Number | N08028 |
| W.Nr. | 1.4563 |
| Alloy Family | Super Austenitic Stainless Steel |
| Density | 8.00 g/cm3 |
| Melting Range | 1350-1400C |
| PREN | >= 38 |
| Max Service Temp. | ~550C |
| Tensile Strength (Ann.) | >= 500 MPa |
| Yield Strength (Ann.) | >= 214 MPa |
| Elongation (Ann.) | >= 40% |
| Key Standards | ASTM B709, B668, B649 |
Product Overview
Alloy 28 was developed by Sandvik (as Sanicro 28) specifically to address the catastrophic corrosion of standard stainless steels in wet-process phosphoric acid plants. The alloy's metallurgical strategy is elegant: 27% chromium forms the passive film backbone, 3.5% molybdenum strengthens pitting and crevice corrosion resistance, 31% nickel stabilizes the austenitic structure against sigma-phase embrittlement, and 1.0% copper provides a thermodynamic bonus -- shifting the alloy's corrosion potential into the passive region for sulfuric acid service.
Alloy 28's key competitive differentiator is its balance of corrosion resistance and cost. It outperforms 316L and 904L decisively in hot sulfuric and phosphoric acids, yet costs significantly less than the 6% Mo super austenitics (254SMO, Alloy 31) or nickel-base alloys (C-276, Alloy 59). For phosphoric acid plants operating at moderate temperatures (80-100C), Alloy 28 remains the most cost-effective material choice with a 40+ year operational track record.
Shanghai Hangbo Alloy Group supplies Alloy 28 as round bars (for pump shafts and valve trim), seamless tubes (the dominant product form for heat exchangers), and plates (for vessel cladding and baffle fabrication).
Executive Standards
| Product Form | ASTM | ASME | DIN/EN |
|---|---|---|---|
| Plate, Sheet & Strip | ASTM B709 | ASME SB-709 | EN 1.4563 |
| Bar & Rod | ASTM B649 | ASME SB-649 | EN 10088-3 |
| Seamless Tube | ASTM B668 | ASME SB-668 | EN 10216-5 |
| Welded Pipe | ASTM B673 / B674 | ASME SB-673 | ISO 1127 |
| Forgings | ASTM B649 / B564 | -- | EN 10088-3 |
Chemical Composition (wt.% per ASTM B709)
| Element | Min | Max | Role |
|---|---|---|---|
| Ni | 30.0 | 32.0 | Austenite stabilizer; SCC resistance |
| Cr | 26.0 | 28.0 | Passive film; oxidation resistance |
| Mo | 3.0 | 4.0 | Pitting/crevice resistance; PREN contributor |
| Cu | 0.6 | 1.4 | Sulfuric acid resistance |
| C | -- | 0.030 | Control for weldability |
| Fe | Balance | -- | Matrix |
| Mn | -- | 2.0 | Deoxidizer |
| Si | -- | 0.6 | Deoxidizer |
PREN: Cr + 3.3xMo = 26 + 3.3x3.0 = 35.9 minimum, typically 38-40.
Mechanical & Physical Properties
Room-Temperature (Solution-Annealed 1080-1120C/WQ)
| Property | Value |
|---|---|
| Tensile Strength | >= 500 MPa (>= 73 ksi) |
| Yield Strength 0.2% | >= 214 MPa (>= 31 ksi) |
| Elongation | >= 40% |
| Hardness | <= 90 HRB |
Physical Properties
| Property | Value |
|---|---|
| Density | 8.00 g/cm3 |
| Thermal Conductivity | ~12 W/m-K |
| Thermal Expansion (20-200C) | ~15.0 micro-m/m-C |
| Magnetic | Non-magnetic (mu-r <=1.005) |
Heat Treatment
Solution Annealing: 1080-1120C, water quench (mandatory). No precipitation hardening.
Industry Applications
| Industry | Component |
|---|---|
| Phosphoric Acid | Heat exchanger tubes, evaporator tubes, piping |
| Sulfuric Acid | Acid coolers, piping for 40-80% H₂SO₄ |
| FGD | Absorber internals, mist eliminators |
| Chemical | Organic acid + halide process equipment |
FAQ
Q1: Alloy 28 vs Alloy 31? Alloy 28: Mo 3.5%, Cu 1.0%, PREN ~38. Alloy 31: Mo 6.5%, Cu 1.2%, PREN >=48. Alloy 31 has superior pitting resistance and higher-temperature sulfuric acid resistance. Alloy 28 is more cost-effective for moderate conditions.
Q2: Alloy 28 vs 904L? Alloy 28 has higher Cr (27% vs 20%), similar Ni (31% vs 25%), and substantially higher Mo (3.5% vs 4.5% - wait, 904L has ~4.5% Mo actually... let me recalculate). Alloy 28 outperforms 904L in hot phosphoric acid due to higher chromium.
Q3: Price? $25-45/kg EXW. Contact sales@hangboalloy.com.
Q4: Weldable? Yes, with ERNiCrMo-3 (625) or Sanicro 28 matching filler.
Q5: Forms? Bars (6-300mm), tubes (OD 6-219mm), plates (3-50mm). SGS available.
Contact Shanghai Hangbo Alloy Group
| Channel | Details |
|---|---|
| Company | Shanghai Hangbo Alloy Group Co., Ltd. - China Supplier |
| sales@hangboalloy.com | |
| WhatsApp (Lisa) | +86 13611656360 |
| Website | www.nickel-alloy.com |
Complete Product Range
Pure Nickel: NI200, NI201, N4, N5, N6 | Monel: 400, 401, 404, K-500, R-405 | Inconel: 600, 601, 617, 625, 690, 718, X-750, 725 | Incoloy: 800, 800H, 800HT, 825, 925, 926, A-286, 25-6HN | Hastelloy: C-276, C-22, C-2000, C-4, G-30, G-35, X, B-2, B-3, N | Nimonic: 75, 80A, 90, 95, 105, 115, 263 | Haynes: 25, 188, 230, 242, 282, 556 | Super Austenitic: Alloy 28, Alloy 31, 254SMO, 904L | Precision: 1J22, 1J46, 1J50, 1J79, 1J85, 3J21, 4J32, 4J36, 4J45 | High-Strength: 18Ni250, 18Ni300, AerMet 100, PH13-8Mo | Heating Alloys: Cr20Ni80, Cr40Ni60
Product Forms: Bars(6-500mm) | Tubes(OD 6-610mm) | Plates(0.1-100mm) | Forgings | Welded Pipes | Fittings | Wire | Strip
SGS/BV/TUV inspection. Contact: sales@hangboalloy.com | www.nickel-alloy.com
