This study investigates the application of laser cladding technology to repair surface defects in ZG230-450 (25# steel) casting components, focusing on microstructure evolution, mechanical properties, and wear resistance enhancement. The research establishes critical process parameters and material relationships through advanced characterization techniques and mathematical modeling.
1. Process Fundamentals and Microstructural Evolution
The laser cladding process for steel casting repair follows fundamental thermal dynamics governed by:
$$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T + \frac{q}{\rho c_p} $$
where T represents temperature distribution, α thermal diffusivity, q laser energy input, and ρcp volumetric heat capacity. The solidification morphology in steel casting components evolves through three distinct zones:
| Zone | Microstructure | Cooling Rate (°C/s) |
|---|---|---|
| Upper Clad | Equiaxed + Dendritic | 103-104 |
| Middle Clad | Columnar Dendritic | 102-103 |
| Interface | Planar | 101-102 |
2. Phase Transformation Kinetics
The austenite (γ) to martensite transformation in steel casting components follows Koistinen-Marburger relationship:
$$ f_m = 1 – \exp[-0.011(M_s – T_q)] $$
where fm is martensite volume fraction, Ms martensite start temperature, and Tq quenching temperature. The carbide precipitation kinetics can be expressed as:
$$ \frac{dX}{dt} = k(T)(1 – X)^n $$
where X is transformed fraction, k temperature-dependent rate constant, and n Avrami exponent.
3. Mechanical Property Enhancement
The hardness profile across steel casting repair interfaces follows exponential decay behavior:
$$ H(y) = H_c + (H_b – H_c)\left[1 – \exp\left(-\frac{y}{\lambda}\right)\right] $$
where Hc represents clad hardness (310 HV0.1), Hb base metal hardness (170 HV0.1), and λ characteristic diffusion length (≈150 μm).
4. Wear Resistance Optimization
The wear rate reduction in steel casting components follows Archard’s modified equation:
$$ \frac{V}{s} = \frac{k}{H} \sqrt{\frac{E’}{\sigma_y}} $$
where V/s is volumetric wear per unit sliding distance, k wear coefficient, H hardness, E’ composite elastic modulus, and σy yield strength. The clad layer demonstrates 2× wear resistance improvement compared with base steel casting material.
5. Process Parameter Optimization
The laser cladding quality in steel casting repair can be predicted through dimensionless number analysis:
$$ \Pi = \frac{P\alpha}{vD\rho c_p(T_m – T_0)} $$
where P is laser power, v scanning speed, D beam diameter, and Tm melting temperature. Optimal process windows occur when 0.8 ≤ Π ≤ 1.2.
6. Residual Stress Management
The thermal stress distribution in steel casting components after laser cladding follows:
$$ \sigma_{\text{res}} = \frac{E\alpha\Delta T}{1 – \nu} \left[1 – \frac{1}{(1 + \frac{h_c}{h_s})^3}\right] $$
where hc and hs represent clad and substrate thickness, respectively. Proper parameter selection reduces residual stresses by 40-60% compared with conventional welding methods.
7. Industrial Implementation
The developed laser cladding technology has been successfully applied to various steel casting components, showing remarkable improvements:
| Component Type | Service Life Extension | Cost Reduction |
|---|---|---|
| Traction Pins | 300% | 45% |
| Valve Bodies | 250% | 38% |
| Gear Housings | 180% | 32% |
This comprehensive study establishes laser cladding as a superior alternative to traditional repair methods for steel casting components, providing both theoretical foundations and practical implementation guidelines for industrial applications.