Introduction
D2-80 is a duplex (ferritic-austenitic) stainless steel fastener grade conforming to the D2 series in GB/T 3098.6-2023. It combines a ferritic and austenitic microstructure to deliver high strength, high yield, excellent corrosion resistance, and outstanding anti-galling (anti-seizing) performance — making it a superior alternative to conventional A2-70 austenitic stainless steel fasteners in demanding structural and environmental applications.
Compared to SUS304 (A2), D2-80 offers:
- Tensile strength ≥ 800 N/mm² (vs. 700 N/mm² for A2-70)
- Yield strength ≥ 600 N/mm² (vs. 450 N/mm² for A2-70)
- Neutral salt spray corrosion resistance approximately 2× better than 304
- Significantly superior stress corrosion and sulfuric acid corrosion resistance
- Excellent anti-galling performance — 4 repeated installation/removal cycles without seizing
D2 is an economical duplex grade — lower in nickel than 2205 (D6), with copper content controlled at approximately 0.3% for compatibility with low-copper applications such as new energy (photovoltaic) systems.
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Chemical Composition: D2 vs A2 vs D6
Reference: GB/T 3098.6-2023
| Grade | C (%) | Si (%) | Mn (%) | P (%) | S (%) | Cr (%) | Mo (%) | Ni (%) | Cu (%) | N (%) |
|---|---|---|---|---|---|---|---|---|---|---|
| A2 (austenitic) | ≤ 0.10 | ≤ 1.00 | ≤ 2.00 | ≤ 0.05 | ≤ 0.03 | 15.0–20.0 | — | 8.0–19.0 | ≤ 4.00 | — |
| D2 (duplex) | ≤ 0.04 | ≤ 1.00 | ≤ 6.00 | ≤ 0.04 | ≤ 0.03 | 19.0–24.0 | 0.10–1.00 | 1.5–5.5 | ≤ 0.30 | 0.05–0.20 |
| D6 (super duplex / 2205) | ≤ 0.03 | ≤ 1.00 | ≤ 2.00 | ≤ 0.04 | ≤ 0.015 | 21.0–23.0 | 2.5–3.5 | 4.5–6.5 | — | 0.08–0.35 |
Key compositional features of D2:
- Nitrogen (N, 0.05–0.20%): Enhances corrosion resistance, particularly against localized corrosion (pitting, crevice, and intergranular corrosion).
- Low Nickel (Ni, 1.5–5.5%): D2 is a nickel-saving duplex grade — more economical than 2205 (D6) while maintaining duplex microstructure.
- Low Copper (Cu ≤ 0.30%): Actual Cu content ~0.3%, suitable for low-copper applications including new energy and photovoltaic systems.
- Higher Chromium (Cr, 19–24%): Provides the foundation for superior corrosion resistance vs. A2 (15–20% Cr).
D2-80 Mechanical Properties
Standard vs Actual Performance (DIN 933 M8×25 Bolt)
| Grade | Tensile Strength Min (N/mm²) | Actual (N/mm²) | Yield Strength Min (N/mm²) | Actual (N/mm²) | Elongation Min | Actual |
|---|---|---|---|---|---|---|
| D2-80 (duplex) | 800 | ≥ 850 | 600 | ≥ 650 | 2.4 mm | 24.8 mm |
| A2-70 (austenitic) | 700 | ≥ 720 | 450 | ≥ 550 | 3.2 mm | ≥ 4.8 mm |
Performance vs Carbon Steel 8.8 Grade (M12×60 and M16×80)
| Size | Tensile Strength Min (N/mm²) | Actual | Yield Strength Min (N/mm²) | Actual | Elongation Min (%) | Actual (%) | Hardness (HRC) | Actual |
|---|---|---|---|---|---|---|---|---|
| M12×60 | 800 | 957 | 640 | 784 | 12 | 19.8 | 22–32 | 28–30 |
| M16×80 | 800 | 884 | 640 | 725 | 12 | 18.8 | 22–32 | 27–29 |
D2-80 meets or exceeds carbon steel Grade 8.8 performance levels in tensile strength, yield strength, elongation, and hardness.
Corrosion Performance vs SUS304
| Grade | Pitting Potential (mV) | Pitting Rate g/(m²·h) | 5% H₂SO₄ Corrosion Rate | Intergranular Corrosion (Method D) | SCC Crack Initiation | SCC Crack Propagation |
|---|---|---|---|---|---|---|
| 304 | 297 | 6.48 | 449.66 | 282.74 | 1 h | 3 h |
| D2 | 346 | 5.80 | 3.74 | 160.91 | 23 h | 92 h |
D2 demonstrates dramatically superior resistance to sulfuric acid corrosion and stress corrosion cracking (SCC) compared to 304 stainless steel.
Magnetic Properties
| Grade | D2 | S32205 | S30400 (304) | SUS304 | QN1701 | QN1803 |
|---|---|---|---|---|---|---|
| Relative Permeability | > 5.0 | > 5.0 | 0.01 | 1.022 | 1.008 | 1.005 |
Like 2205, D2 duplex steel is magnetic due to its ferritic phase content. This is a structural characteristic and has no correlation with corrosion resistance. The magnetic property is advantageous in applications such as mechanical machining and magnetic sorting equipment, and improves stability in surface treatment processes.
Food Safety & Environmental Compliance
SGS testing (Shanghai) confirms D2 meets food contact safety requirements:
| Test Item | Limit (mg/kg) | D2 Result | SUS304 Result |
|---|---|---|---|
| Arsenic (As) migration | 0.04 | ND | ND |
| Cadmium (Cd) migration | 0.02 | ND | ND |
| Lead (Pb) migration | 0.05 | ND | ND |
| Chromium (Cr) migration | 2.00 | ND | ND |
| Nickel (Ni) migration | 0.50 | ND | ND |
Both D2 and SUS304 comply with food safety migration limits. ND = Not Detected.
Anti-Galling (Anti-Seizing) Performance
| Material | Sample Size | Result after 4th Removal | Thread Condition |
|---|---|---|---|
| D2-80 (M12×65) | 10 pcs | No seizing in all samples | Minor thread surface marks only |
| 304 (M12×65) | 10 pcs | All seized at 2nd removal | Severe seizing, non-removable |
D2-80 demonstrates excellent anti-galling performance, completing 4 full installation/removal cycles without seizing — a critical advantage in maintenance-intensive applications.
Applications
- Rail Transit — metro, high-speed rail (HSR), and EMU train structural fasteners and components
- Construction & Architecture — structural bolts, anchors, and hardware for buildings and infrastructure
- Photovoltaic (Solar) — mounting fasteners for solar power stations, BIPV (building-integrated photovoltaics), and street lighting structures; low Cu content suits new energy system requirements
- Electronics & Hardware — connectors, nuts, valve cores, and precision hardware
- Marine & Coastal — structural fasteners in chloride-rich environments
Browse our marine-grade stainless steel fastener products: Marine Carriage Bolts (DIN 603), Marine Castle Nuts (DIN 935), and Marine Eye Bolts (DIN 444).
Standards reference: GB/T 3098.6-2023 | DIN 933 | SGS food safety testing
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