Zhuojin Pipe Fitting Co., LtdEffect of Arc Surfacing Process Parameters on Mechanical Properties of Low Carbon Steel
Literature Overview
This paper by Wang Hailin et al. (2020), published in Materials Protection (Vol. 53, No. 12, pp. 84-87), investigates the influence of CO2 gas-shielded flux-cored wire arc surfacing process parameters on the microstructure and mechanical properties of Q345 low carbon steel composite plates. The research is conducted at Hubei University of Automotive Technology's School of Materials Science and Engineering. The study addresses a practical gap in the literature—systematic investigation of flux-cored wire surfacing on low carbon steel substrates—and provides actionable process parameter ranges for achieving high-performance composite plates with hardness exceeding 520 HV in the surfacing layer while maintaining adequate toughness in the base material.
Core Technical Findings
The authors conducted a systematic parametric study of CO2 gas-shielded flux-cored wire arc surfacing on Q345 steel, examining the effects of welding current, voltage, and travel speed on weld bead geometry, slag removal quality, hardness distribution, and impact toughness. The optimal process window identified is:
| Process Parameter | Optimal Range | Effect on Weld Quality | Effect on Mechanical Properties |
|---|---|---|---|
| Welding current | 200–240 A | Adequate penetration and bead width | Controls dilution and hardness gradient |
| Welding voltage | 26–30 V | Good bead profile and slag removal | Influences cooling rate and microstructure |
| Travel speed | 300 mm/min (stable) | Uniform bead geometry | Controls heat input and grain size |
| Shielding gas | CO2 (100%) | Acceptable arc stability | Promotes martensitic transformation |
Key performance metrics achieved under optimal conditions:
- Base metal hardness: maintained above 175 HV (no significant softening in HAZ)
- Surfacing layer hardness: maintained above 520 HV (excellent wear resistance)
- Composite plate impact toughness: maintained above 45 J (adequate fracture resistance)
Process Parameter Analysis and Metallurgical Mechanisms
The selection of CO2 as the shielding gas for flux-cored wire surfacing on low carbon steel is significant from a metallurgical perspective. CO2 is an active gas that promotes:
- Higher arc temperature and deeper penetration
- More complete deoxidation through the formation of CO bubbles
- Promotion of martensitic transformation in the deposited metal due to its deoxidizing and carburizing effects
- Increased carbon activity in the arc, which can enrich the deposited metal in carbon and promote carbide formation
The hardness gradient between the base metal (175 HV) and the surfacing layer (520 HV) represents a difference of approximately 345 HV, which corresponds to a transition from ferrite-pearlite microstructure in the base metal to predominantly martensitic or martensite-carbide microstructure in the surfacing layer. This large hardness differential creates a concern regarding thermal mismatch stresses at the interface, which must be managed through appropriate process design.
The impact toughness requirement of 45 J at room temperature is particularly important. In many surfacing applications, achieving high hardness inevitably comes at the expense of toughness. The fact that the authors maintained impact toughness above 45 J while achieving 520 HV hardness in the surfacing layer demonstrates successful microstructural control—likely through a balanced martensite-carbide structure with controlled carbide size and distribution.
Engineering Practice Integration
For piping engineers and fabrication shops considering arc surfacing for wear protection on low carbon steel components, the following practical guidance emerges:
- Process selection criteria: CO2 gas-shielded flux-cored wire surfacing is suitable for:
- Carbon steel pipe bodies requiring localized wear protection
- Large-area surfacing where productivity is important (flux-cored wire offers higher deposition rates than solid wire)
- Applications where preheating is not desired or practical (the process works without preheat)
- Quality control considerations:
- Hardness mapping across the interface should be performed to verify the hardness gradient is acceptable
- Impact testing should be conducted at the interface region (not just in the surfacing layer) to verify adequate toughness
- Slag removal quality should be inspected—poor slag removal indicates process parameter deviation
- Standards compliance: The composite plate construction should comply with relevant standards:
- GB/T 12566 for surfacing process qualification
- ASME B31.3 requirements for composite construction in process piping
- API 5L requirements if the base pipe is line pipe
Key Questions and Reflections
The study raises several important considerations for engineering practice:
- Long-term performance: The mechanical properties reported are for the as-deposited condition. What is the effect of service exposure—thermal cycling, corrosion, mechanical loading—on the long-term stability of the hardness and toughness?
- Interface integrity: The large hardness differential (175 HV vs. 520 HV) raises concerns about interface cracking under thermal cycling. The study does not address thermal fatigue behavior of the interface.
- Dilution control: The effect of dilution on surfacing layer composition and properties is not extensively discussed. For critical applications, dilution rate should be controlled and measured.
- Multi-pass considerations: The study appears to focus on single-pass or limited-pass surfacing. Multi-pass surfacing introduces interpass temperature effects and stress accumulation that require additional consideration.
Study Insights and Implications
This paper provides a practical, well-defined process window for CO2 gas-shielded flux-cored wire arc surfacing on Q345 low carbon steel. The identified parameters (200–240 A, 26–30 V, 300 mm/min) represent a reproducible baseline that fabrication engineers can adopt with confidence for initial process development. The achievement of 520 HV hardness with 45 J impact toughness is technically significant—it demonstrates that high wear resistance and adequate fracture resistance can coexist in a surfacing layer when process parameters are properly controlled. For the piping industry, this is particularly relevant for applications involving erosion-corrosion, such as slurry handling, sand-laden fluid transport, and abrasive media processing, where localized wear protection is required on carbon steel pipe bodies. The study's emphasis on slag removal quality as a process indicator is also valuable—poor slag removal is often an early indicator of parameter drift and should be incorporated into in-process quality monitoring. Engineers should note that while these parameters provide an excellent starting point, process qualification testing specific to the actual component geometry, base material chemistry, and service conditions remains essential before production implementation.