Zhuojin Pipe Fitting Co., LtdEffect of Low-Carbon Steel Arc Surfacing Process on Weld Mechanical Properties
Literature Overview
The paper by Wang Hailin, Lei Da, Gu Zhenzhen, Peng Daoheng, and Wang Jinfeng, published in Materials Protection (Vol. 53, Issue 12, 2020, pp. 84-87), investigates the influence of welding process parameters on the microstructure and mechanical properties of CO2 gas-shielded flux-cored arc surfacing on Q235 low-carbon steel substrate. The study addresses a gap in the literature regarding CO2 flux-cored wire surfacing on low-carbon steel, which is increasingly relevant for cost-effective surface hardening applications in automotive and general manufacturing industries.
Core Technical Findings
The study establishes optimal process parameters for achieving good weld bead formation, slag removal, and mechanical properties. The recommended parameter window is welding current 200-240 A, welding voltage 26-30 V, and surfacing speed 300 mm/min. Under these conditions, the substrate hardness remains above 175 HV, the surfacing layer hardness exceeds 520 HV, and the composite plate impact toughness maintains values above 45 J.
| Parameter | Optimal Range | Effect on Bead Formation | Effect on Mechanical Properties |
|---|---|---|---|
| Welding current | 200-240 A | Adequate penetration and fusion | Controls dilution and hardness |
| Welding voltage | 26-30 V | Stable arc and good slag removal | Influences carbon content and hardness |
| Surfacing speed | 300 mm/min | Consistent bead width and profile | Controls cooling rate and microstructure |
| Substrate hardness | >175 HV | Baseline reference | Maintained without significant softening |
| Surfacing layer hardness | >520 HV | Hardened surface achieved | Wear resistance improvement |
| Impact toughness | >45 J | Acceptable ductility | Adequate for moderate impact loading |
Process Parameter Analysis
The CO2 gas-shielded flux-cored wire arc surfacing process offers advantages over solid wire GMAW for surfacing applications due to the higher deposition rate, better wetting characteristics, and the ability to deposit materials with higher alloy content than the wire itself. The flux core provides additional alloying elements and deoxidizers that improve the surfacing layer composition.
The welding current range of 200-240 A represents a moderate thermal input that balances penetration depth with dilution control. Excessive current would increase dilution from the Q235 substrate, reducing the hardness of the surfacing layer below the target 520 HV threshold. Insufficient current would result in incomplete fusion and poor bead formation.
The voltage range of 26-30 V provides adequate arc length for stable arc behavior while maintaining good slag fluidity and removal characteristics. Higher voltages increase arc length and can lead to arc blow, particularly in the presence of magnetic fields from previous welds.
The surfacing speed of 300 mm/min is critical for controlling the cooling rate of the deposited metal. Faster speeds increase cooling rates, which can promote martensitic transformation and increase hardness but also increase the risk of cracking. Slower speeds reduce cooling rates, promoting softer microstructures with lower hardness but better toughness.
Mechanical Property Evaluation
The hardness values reported indicate a significant hardness gradient from substrate to surfacing layer, which is the desired outcome for wear-resistant surfacing applications. The substrate hardness above 175 HV suggests minimal softening in the base metal heat-affected zone, indicating controlled thermal input and limited dilution.
The surfacing layer hardness above 520 HV places the material in the range of martensitic or martensite-bainite microstructures, which provide excellent wear resistance. The impact toughness above 45 J at room temperature indicates that the surfacing layer retains adequate ductility despite the high hardness, suggesting a favorable microstructural balance.
The composite plate impact toughness above 45 J is particularly significant, as it demonstrates that the surfacing process does not compromise the toughness of the base metal. This is critical for applications where the component may experience impact loading or thermal cycling.
Engineering Practice Implications
For pipe and fitting manufacturers considering CO2 flux-cored wire surfacing for surface hardening of low-carbon steel components, this study provides a practical parameter starting point. The process is particularly suitable for:
- Surface hardening of pipe flanges and connection points subject to galling or wear.
- Repair of worn surfaces on carbon steel piping components without requiring replacement.
- Creating hardfacing layers on reducers, tees, and elbows in abrasive service.
- Cost-effective alternative to overlay welding with expensive consumables.
The parameter window identified in this study should be adapted to specific equipment configurations, wire diameters, and substrate thicknesses. Engineers should conduct qualification welds following ASME Section IX or equivalent standards before production implementation.
Key Questions and Reflections
The study raises important questions about the long-term performance of CO2 flux-cored wire surfacing layers under cyclic loading and thermal fatigue conditions. The impact toughness values reported are at room temperature, but many industrial applications involve elevated temperatures where toughness may degrade. Additionally, the corrosion resistance of the surfacing layer in aggressive environments is not addressed in this study.
The dilution effect from the Q235 substrate on the surfacing layer composition warrants further investigation. The hardness of 520 HV suggests limited dilution, but the exact dilution percentage and its effect on microstructure should be quantified for process optimization. Engineers should consider the effect of substrate preheating on dilution and residual stress, as low-carbon steel substrates are generally amenable to preheating without risk of cracking.
Study Insights and Reference Value
This study provides practical guidance for engineers implementing CO2 flux-cored wire surfacing on low-carbon steel components. The parameter window is conservative and achievable with standard equipment, making it accessible to most manufacturing facilities. The emphasis on mechanical property evaluation, particularly impact toughness, reflects a mature approach to surfacing qualification that considers not only hardness but also ductility and toughness.
For the steel pipe and fitting industry, where low-carbon steel components are ubiquitous, this research offers a cost-effective surface hardening solution that can extend component life without requiring material upgrades or component replacement. The process should be qualified according to applicable codes and standards before implementation in critical service applications.