As critical components in coke dry quenching systems, ZG35Cr24Ni7SiN steel casting liners face extreme operational challenges including thermal cycling (950-1050°C), mechanical impact, and abrasive wear. Through comprehensive analysis of chemical composition, microstructural characteristics, and casting defects, we propose systematic improvements to enhance service life and reliability.
1. Composition-Property Relationships
The chemical composition of ZG35Cr24Ni7SiN steel casting significantly influences its high-temperature performance:
| Element | Function | Optimal Range | Impact on Performance |
|---|---|---|---|
| C | Austenite stabilizer | 0.30-0.40% | $$C_{eq} = \%C + 0.05\%N$$ Determines matrix strength and carbide formation |
| Cr | Oxidation resistance | 23-25.5% | Forms protective Cr2O3 layer: $$k_p = A\cdot e^{-Q/(RT)}$$ (Parabolic oxidation constant) |
| Ni | Austenite stabilizer | 7-8.5% | Maintains FCC structure: $$Ni_{eq} = \%Ni + 30\%C + 0.5\%Mn$$ |
| N | Strengthening | 0.20-0.28% | Enhances creep resistance: $$\dot{\epsilon} = A\sigma^n e^{-Q/(RT)}$$ |
The phase stability can be predicted using Schaeffler diagram modification:
$$Cr_{eq} = \%Cr + \%Mo + 1.5\%Si + 0.5\%Nb$$
$$Ni_{eq} = \%Ni + 30\%C + 0.5\%Mn + 30\%N$$
Maintaining Nieq/Creq > 0.5 ensures full austenitic structure.
2. Critical Defect Analysis
Common failure modes in steel casting liners include:
| Defect Type | Root Cause | Impact on Service Life |
|---|---|---|
| Thermal cracks | ΔT > 800°C/min during quenching | Reduces fatigue life by 40-60% |
| Oxidation pitting | Cr depletion < 18% at surface | Accelerates wear rate by 3-5× |
| Creep deformation | σ0.2 < 340MPa at 1000°C | Causes dimensional instability |
The thermal stress during cyclic operation can be calculated as:
$$σ_{thermal} = EαΔT/(1-ν)$$
Where E = 150-180GPa, α = 18×10-6/°C, and ν = 0.3 for this steel casting.
3. Process Optimization Strategies
Key improvements for steel casting production:
| Parameter | Original | Optimized | Benefit |
|---|---|---|---|
| Cooling rate | 50°C/min | 80-100°C/min | Grain refinement to ASTM 4-5 |
| N content | 0.22% | 0.25-0.28% | Increased yield strength by 15% |
| Post-casting HT | 1150°C/4h | 1180°C/2h + 650°C/8h | Reduces δ-ferrite < 3% |
The optimized solution treatment temperature follows:
$$T_{sol} = 850 + 25(\%Cr + \%Si) – 20(\%Ni)$$
For typical composition: Tsol = 1180-1200°C
4. Field Performance Validation
Modified steel casting liners demonstrate:
- Service life extension from 2 to 6 months
- Wear resistance improvement by 120-150%
- Thermal shock cycles increased to >5000
The improved oxidation resistance follows Wagner’s theory:
$$(Δm/A)^2 = k_p t$$
Where kp decreased from 3.2×10-12 to 1.8×10-12 g2/cm4s after optimization.
These advancements in steel casting technology significantly enhance the reliability of high-temperature industrial equipment while reducing maintenance costs by 40-60%.