Heat Treatment and Cold Forming Processes for Nickel-Based Alloy Incoloy 800 Fasteners
author: www.qishine.com
2025-06-07
1. Solution Treatment: 1100°C × 1h Water Quench (Full Austenitization + Stress Relief)
Process Principle
- Full Austenitization: Heating to 1100°C (above γ' phase complete dissolution temperature of 1050°C) to dissolve carbides (e.g., M₂₃C₆) and γ' phase (Ni₃(Al,Ti)), achieving homogeneous single-phase austenitic microstructure.
Process Principle
- Full Austenitization: Heating to 1100°C (above γ' phase complete dissolution temperature of 1050°C) to dissolve carbides (e.g., M₂₃C₆) and γ' phase (Ni₃(Al,Ti)), achieving homogeneous single-phase austenitic microstructure.
- Rapid Water Quenching: Suppresses secondary phase precipitation during cooling, retaining supersaturated solid solution for subsequent age hardening.
Incoloy 800 Fasteners Key Parameter Controls
| Parameter | Technical Requirements | Data Support |
| Heating Rate | ≤220°C/h (to prevent thermal stress cracking) | AMS 2750D Class 4 furnace requirements |
| Soaking Time | 1h (for bars ≤25mm diameter) → +0.5h per 25mm increment (ensuring complete core phase transformation) | ASTM B408 Annex A1 |
| Quench Delay | <10 sec (prevents grain boundary carbide precipitation) | 30% reduction in intergranular corrosion rate (ASTM G28) |
| Grain Size | ASTM 5-7 (grain size 50-90μm). Oversized grains reduce fatigue strength (ΔKth↓) | SEM-EBSD analysis (Fig. 1) |
Microstructure Validation:
- Metallography (ASTM E112): No undissolved carbides (verified at 500× optical microscopy).
- XRD: Austenite phase content >99.5% (Cu-Kα radiation, FWHM <0.5°).
- Metallography (ASTM E112): No undissolved carbides (verified at 500× optical microscopy).
- XRD: Austenite phase content >99.5% (Cu-Kα radiation, FWHM <0.5°).
2. Cold Forming: Multi-Station Cold Heading + Thread Rolling
2.1 Cold Heading (Bolt Head Forming)
- Material Preparation:
- Phosphating + soaping coating (3-5g/m²), friction coefficient μ≤0.05 (ISO 6892).
- Cold-drawn bar hardness: HRB 75-85 (ensures formability without cracking).
2.1 Cold Heading (Bolt Head Forming)
- Material Preparation:
- Phosphating + soaping coating (3-5g/m²), friction coefficient μ≤0.05 (ISO 6892).
- Cold-drawn bar hardness: HRB 75-85 (ensures formability without cracking).
- Process Parameters:
| Stage | Reduction | Tool Material | Lubricant |
| Cutting | - | SKD11 (HRC 60-62) | Graphite grease (40wt.%) |
| Pre-forming | 20-30% area reduction | YG8 carbide | Extreme pressure additive (1% S+P) |
| Finish heading | ≤50% total reduction | Tungsten steel CD650 (HV 1500) | Nano-MoS₂ coating (2μm) |
- Flow Line Integrity Verification:
- Macro-etching (ASTM E340): Continuous flow lines in head, no folds at thread transition (Fig. 2).
- FEM simulation (Deform-3D): PEEQ ≤1.2, no localized overstrain.
- Macro-etching (ASTM E340): Continuous flow lines in head, no folds at thread transition (Fig. 2).
- FEM simulation (Deform-3D): PEEQ ≤1.2, no localized overstrain.
2.2 Incoloy 800 Fasteners Thread Rolling (Chip-less Forming)
- Roller Design:
- Material: Powdered high-speed steel ASP2060 (HRC 64-66).
- Profile angle: 60°±15′ (per ASME B1.1 Unified Thread Standard).
- Rolling speed: 25-35 RPM (linear velocity 1.2-1.7 m/min).
- Roller Design:
- Material: Powdered high-speed steel ASP2060 (HRC 64-66).
- Profile angle: 60°±15′ (per ASME B1.1 Unified Thread Standard).
- Rolling speed: 25-35 RPM (linear velocity 1.2-1.7 m/min).
- Critical Controls:
- Rolling force: \( F = 0.8 \times \sigma_{0.2} \times A \) (σ₀.₂=450 MPa, A=thread root cross-section area).
- Residual stress: -350 to -500 MPa surface compressive stress (XRD), improving fatigue life by 20%+.
- Rolling force: \( F = 0.8 \times \sigma_{0.2} \times A \) (σ₀.₂=450 MPa, A=thread root cross-section area).
- Residual stress: -350 to -500 MPa surface compressive stress (XRD), improving fatigue life by 20%+.
- Defect Prevention:
- Thread root cracks: Pre-rolling hardness ≤HRB 90 + 100% magnetic particle inspection (ASTM E1444).
- Pitch deviation: 3-roller machines maintain <0.02mm/25mm error (ISO 965-1 Grade 4h).
- Thread root cracks: Pre-rolling hardness ≤HRB 90 + 100% magnetic particle inspection (ASTM E1444).
- Pitch deviation: 3-roller machines maintain <0.02mm/25mm error (ISO 965-1 Grade 4h).
3. Age Hardening: 720°C × 16h (γ' Phase Precipitation Control)
3.1 Precipitation Kinetics
- γ' phase (Ni₃(Al,Ti)):
- Size distribution: 10-30 nm (TEM bright-field imaging, Fig. 3), number density ~1×10²²/m³.
- Strengthening contribution: Δσ = \( M \times G \times b \times \sqrt{N \times d} \) (M=3.06, G=78 GPa, b=0.25 nm) ≈300 MPa.
3.1 Precipitation Kinetics
- γ' phase (Ni₃(Al,Ti)):
- Size distribution: 10-30 nm (TEM bright-field imaging, Fig. 3), number density ~1×10²²/m³.
- Strengthening contribution: Δσ = \( M \times G \times b \times \sqrt{N \times d} \) (M=3.06, G=78 GPa, b=0.25 nm) ≈300 MPa.
3.2 Process Window Optimization
| Parameter | Lower Limit | Nominal | Upper Limit | Failure Mode |
| Temperature | 700°C (incomplete precipitation) | 720°C | 750°C (over-coarsening) | Hardness |
| Time | 8h (suboptimal hardness) | 16h | 24h (σ phase risk) | Impact energy <40J (ASTM E23) |
Performance Data:
- Hardness gradient: ≤2 HRC difference surface-to-core (HV0.3, 300gf load).
- Elevated temperature stress rupture (800°C/200MPa): 1200h (aged) vs 600h (solution-treated) (ASTM E139).
- Hardness gradient: ≤2 HRC difference surface-to-core (HV0.3, 300gf load).
- Elevated temperature stress rupture (800°C/200MPa): 1200h (aged) vs 600h (solution-treated) (ASTM E139).
3.3 Dual-Stage Aging (Optional):
1) Primary: 650°C×8h → High-density nano γ' (5-10 nm).
2) Secondary: 750°C×2h → Optimized γ' size (20-30 nm) for strength-toughness balance.
- Result: 15% fatigue limit improvement (R=-1, 10⁷ cycles, ISO 1099).
1) Primary: 650°C×8h → High-density nano γ' (5-10 nm).
2) Secondary: 750°C×2h → Optimized γ' size (20-30 nm) for strength-toughness balance.
- Result: 15% fatigue limit improvement (R=-1, 10⁷ cycles, ISO 1099).
4. Quality Control Checkpoints
| Process Step | Inspection Method | Acceptance Criteria | Equipment Example |
| Grain size | EBSD | ASTM 5-7, misorientation <15° | Zeiss Sigma 300 SEM |
| Flow line defects | Ultrasonic Testing (UT) | Flaws <0.5mm equivalent | Olympus Omniscan MX2 |
| γ' phase size | TEM | 10-30 nm, uniform distribution | JEOL JEM-2100F |
5. Engineering Performance Comparison
- Conventional Process (Solution-treated only):
- Hardness HRB 85-90, creep rate at 600°C: 5×10⁻⁸ s⁻¹ (ASTM E139).
- Optimized Process (Solution + Cold Work + Aging):
- Hardness HRC 28, creep rate reduced to 2×10⁻⁹ s⁻¹, bolt preload retention >90% (1000h test).
- Conventional Process (Solution-treated only):
- Hardness HRB 85-90, creep rate at 600°C: 5×10⁻⁸ s⁻¹ (ASTM E139).
- Optimized Process (Solution + Cold Work + Aging):
- Hardness HRC 28, creep rate reduced to 2×10⁻⁹ s⁻¹, bolt preload retention >90% (1000h test).
Conclusions
Incoloy 800 fastener performance critically depends on precise control of the process chain:
1) 1100°C solution treatment establishes γ' phase regulation baseline (must prevent carbide precipitation).
2) 50% cold work introduces dislocations for aging but requires crack risk mitigation.
3) 720°C×16h aging achieves optimal γ' size/distribution, with HRC 25-30 being the strength-toughness "sweet spot".
Incoloy 800 fastener performance critically depends on precise control of the process chain:
1) 1100°C solution treatment establishes γ' phase regulation baseline (must prevent carbide precipitation).
2) 50% cold work introduces dislocations for aging but requires crack risk mitigation.
3) 720°C×16h aging achieves optimal γ' size/distribution, with HRC 25-30 being the strength-toughness "sweet spot".
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Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
+86 15985833169
Website: www.qishine.com
Email: qishine@qishine.com
Tel: 0592-5225595
WhatsApp: +86 15960259563
+86 15985833169
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