In the production of high-strength steel wheels, casting defects such as cracks and porosity can significantly compromise structural integrity. This study proposes a pressure plugging method combined with optimized welding parameters to repair defects in 40CrMnMo steel castings. The approach integrates preheating, laser cleaning, and post-weld heat treatment to ensure defect-free repair while maintaining mechanical properties.
Material Characteristics and Weldability Analysis
The chemical composition of 40CrMnMo steel casting material is shown in Table 1. The carbon equivalent (Ceq) calculation determines weldability:
$$C_{eq} = C + \frac{1}{6}Mn + \frac{1}{5}Mo = 0.65\%$$
This high carbon equivalent indicates poor weldability, necessitating strict thermal management during repair.
| Element | C | Mn | Si | Cr | Mo |
|---|---|---|---|---|---|
| Content (wt%) | 0.41 | 1.10 | 0.26 | 1.10 | 0.26 |
Pressure Plugging Methodology
The repair process involves three critical phases:
- Laser Surface Preparation:
$$E = P \cdot \tau \cdot f$$
Where E = laser energy density (J/cm²), P = power (135W), τ = pulse width (60ns), f = scanning frequency (46kHz) - Segmented Welding Sequence:
- Defect segmentation into 5-8mm sections
- Progressive repair with J107Cr electrodes
- Thermal Management:
$$T_{preheat} = 120^\circ C \pm 10^\circ C$$
$$T_{interpass} = 105^\circ C \pm 15^\circ C$$
| Parameter | Value |
|---|---|
| Current | 245A ± 15A |
| Voltage | 27V ± 2V |
| Travel Speed | 385 mm/min |
| Heat Input | 1.00 kJ/mm |
Mechanical Performance Analysis
The mechanical properties of repaired steel castings were evaluated under varying thermal conditions:
$$ \sigma_y = 926 \text{ MPa (Yield Strength)} $$
$$ \sigma_{UTS} = 1045 \text{ MPa (Ultimate Tensile Strength)} $$
$$ \delta = 19\% \text{ (Elongation)} $$
| Condition | Impact Energy (J) | Fracture Stress (MPa) |
|---|---|---|
| Heat Input 1.00 kJ/mm | 38 | 926 |
| Heat Input 1.45 kJ/mm | 22 | 855 |
Microstructural Analysis
Post-repair metallography revealed:
- Complete elimination of casting defects
- Fine-grained microstructure in HAZ
- No evidence of secondary cracking or porosity
The repair process maintained the original steel casting’s microstructure while achieving full defect closure.
Process Optimization
Key parameters for successful steel casting repair:
- Laser cleaning energy density: 8-12 J/cm²
- Interpass temperature control: ΔT ≤ 50°C
- Post-weld heat treatment: 450°C × 3h
The relationship between preheat temperature (Tp) and critical fracture stress (σf) is expressed as:
$$ \sigma_f = 850 + 0.64T_p \quad (80^\circ C \leq T_p \leq 150^\circ C) $$
Industrial Implementation
Field applications demonstrated:
- 95% success rate in heavy-duty wheel repairs
- 30% reduction in total repair time compared to conventional methods
- Consistent compliance with ASTM E8/E8M tensile standards
This methodology proves particularly effective for large-scale steel castings where complete recasting is economically prohibitive.
Conclusion
The pressure plugging method with optimized thermal management enables effective repair of steel casting defects in high-strength wheels. By maintaining strict control of heat input (1.00 kJ/mm) and interpass temperature (105°C), the process achieves mechanical properties matching original specifications while eliminating defect propagation risks. This approach provides a cost-effective solution for extending the service life of critical steel casting components.