The Qatar 2022 FIFA World Cup Stadium roof structure required the fabrication of large G10MnMoV6-3 low-alloy steel cable nodes using lost foam casting. This paper details the critical processes, quality control measures, and metallurgical principles applied to achieve compliance with European standards (EN 10293:2015) while addressing challenges in casting thick-walled components (up to 150 mm).
1. Material Specifications and Casting Challenges
The cable node (4,600 kg mass, 2,600×650×830 mm dimensions) required precise chemical composition control and superior mechanical properties:
| Element | C | Si | Mn | P | S | Mo | V |
|---|---|---|---|---|---|---|---|
| EN 10293 | ≤0.12 | ≤0.60 | 1.2-1.8 | ≤0.025 | ≤0.020 | 0.2-0.4 | 0.05-0.10 |
| Actual | 0.088-0.091 | 0.46-0.49 | 1.29-1.36 | 0.014-0.015 | 0.006-0.008 | 0.25 | 0.068-0.070 |
The carbon equivalent (CE) was controlled using the IIW formula:
$$ CE = \mathrm{C} + \frac{\mathrm{Mn}}{6} + \frac{(\mathrm{Cr} + \mathrm{Mo} + \mathrm{V})}{5} + \frac{(\mathrm{Ni} + \mathrm{Cu})}{15} \leq 0.49 $$
| Property | Yield Strength | Tensile Strength | Elongation | Impact Energy |
|---|---|---|---|---|
| Requirement | ≥380 MPa | 500-650 MPa | ≥18% | ≥60 J |
| Achieved | 472-523 MPa | 582-619 MPa | 21.5-25.5% | 85-106 J |
2. Lost Foam Casting Process Design
The lost foam casting process for thick-section steel components requires careful control of pattern making, gating design, and thermal management:
2.1 Pattern Design Parameters
- Shrinkage allowance: 2% linear expansion
- Machining allowance: 15-20 mm
- EPS density: 28 kg/m³
- Coating thickness: 1.2-1.5 mm
The feeding system was designed using Chvorinov’s rule:
$$ t_{\text{solidification}} = k \left( \frac{V}{A} \right)^2 $$
Where k = 1.3 for G10MnMoV6-3 steel, V = casting volume, A = cooling surface area.
2.2 Process Control Points
| Parameter | Value | Control Method |
|---|---|---|
| Pouring Temperature | 1,560-1,580°C | Infrared pyrometer |
| Vacuum Pressure | 0.04-0.06 MPa | Digital vacuum gauge |
| Cooling Rate | ≤30°C/h (300-500°C) | Sand insulation |
3. Heat Treatment Optimization
The quenching-tempering process was optimized through multiple trials:
3.1 Phase Transformation Kinetics
The JMAK equation describes austenite decomposition during quenching:
$$ f = 1 – \exp(-kt^n) $$
Where f = transformed fraction, k = temperature-dependent rate constant, n = Avrami exponent (1.5 for G10MnMoV6-3).
3.2 Heat Treatment Schedule
| Stage | Temperature | Time | Cooling Medium |
|---|---|---|---|
| Austenitizing | 950±10°C | 8 h | Air |
| Quenching | 890-910°C | Immediate | Polymer solution |
| Tempering | 650±10°C | 8 h | Furnace cooling |
The Hollomon-Jaffe parameter ensures tempering consistency:
$$ HJP = T(20 + \log t) \times 10^{-3} $$
Where T = tempering temperature (K), t = time (hours). Target HJP range: 17.5-18.5.
4. Quality Assurance System
The multi-stage inspection protocol ensured compliance with EN 1559-2 and ASTM standards:
| Method | Standard | Acceptance Level |
|---|---|---|
| Radiography | ASTM E94 | Level 3 |
| Ultrasonic | BS EN 12680-1 | Class 2/3 |
| Magnetic Particle | BS EN 1369 | SM2/LM2/AM2 |
The dimensional tolerance control followed:
$$ \Delta D = 0.5 \sqrt[3]{L} + 0.1D $$
Where ΔD = tolerance (mm), L = nominal dimension (mm), D = machining allowance (mm).
5. Process Validation
Statistical process control (SPC) data from 25 production casts demonstrated:
- Chemical composition compliance: 100%
- Mechanical property pass rate: 96%
- NDT acceptance rate: 92%
The lost foam casting process achieved 98.5% dimensional accuracy in critical socket areas (CT8 per EN ISO 8062-3). Post-casting machining operations removed only 12-15 mm from nominal surfaces, confirming effective shrinkage control.
This technical approach demonstrates that lost foam casting is viable for producing large-scale steel structural components with complex geometries and stringent quality requirements, providing an efficient alternative to traditional forging methods.