Zhuojin Pipe Fitting Co., LtdOverlay Welding Process Optimization for Crankshaft Repair
Literature Overview
This research paper published in the Journal of Shenyang Ligong University (2020, Vol. 39, No. 1) by Lei Jinhong and colleagues from Shenyang Ligong University and Zhejiang Yatong Welding Materials Co., Ltd. presents a systematic investigation of overlay welding process parameters for crankshaft surface hardening. The study examines the effects of welding current and argon gas flow rate on the microhardness, wear resistance, and microstructure of overlay deposits on 20CrMnTi steel using SHQ-605 wear-resistant wire with a WSE-350 pulsed GTAW machine. This work is particularly relevant to my expertise in welding metallurgy and process optimization, as it demonstrates a rigorous experimental approach to parameter selection.
Experimental Design and Methodology
The experimental approach followed a systematic parameter study methodology:
| Parameter | Range Investigated | Optimum Value |
|---|---|---|
| Welding current | Variable | 50 A |
| Argon flow rate | Variable | 8 L/min |
| Welding process | Pulsed GTAW | — |
| Base metal | 20CrMnTi | — |
| Filler wire | SHQ-605 | — |
| Equipment | WSE-350 | — |
The characterization methods employed included:
- Microhardness testing using HV-1000 microhardness tester
- Wear testing using MDW-02 pin-on-disc wear tester
- Microstructural analysis using SEM (scanning electron microscopy)
- Friction coefficient measurement
Results and Analysis
The experimental results revealed significant parameter sensitivity:
| Performance Metric | Range Observed | Optimum Condition |
|---|---|---|
| Microhardness | 2291–3549 HV | 2837 HV at 50A, 8L/min |
| Wear rate | 2×10⁻⁷–7.33×10⁻⁷ g/N·min | 2×10⁻⁷ g/N·min at 50A, 8L/min |
| Friction coefficient | 0.2–0.8 | 0.27 at 50A, 8L/min |
The microstructural analysis revealed that the overlay weld metal consisted primarily of lath martensite, which is consistent with the high-carbon, high-alloy composition of SHQ-605 wire undergoing rapid solidification during GTAW. The overlay layer bonded well with the 20CrMnTi base metal, indicating adequate wetting and metallurgical compatibility.
Effect of Welding Current
The welding current directly controls the heat input and weld pool geometry:
- Lower current produces narrower, shallower welds with lower dilution but potentially incomplete fusion.
- Higher current produces wider, deeper welds with greater dilution and potentially excessive heat-affected zone.
- The optimum of 50 A represents a balance between adequate penetration and controlled heat input.
Effect of Argon Flow Rate
The argon flow rate provides inert gas shielding to prevent atmospheric contamination:
- Insufficient flow rate leads to oxidation and nitridation of the weld pool.
- Excessive flow rate can create turbulence that entrains air into the weld pool.
- The optimum of 8 L/min provides adequate shielding without causing flow instability.
Metallurgical Considerations
The formation of lath martensite in the overlay deposit is metallurgically significant:
- Lath martensite forms under conditions of moderate cooling rates and is generally more ductile than plate martensite.
- The high hardness values (2291–3549 HV) indicate a highly hardened microstructure, which provides excellent wear resistance.
- However, extremely high hardness values may indicate embrittlement risk, particularly in impact or cyclic loading conditions.
- The wide range of hardness values (over 1000 HV spread) suggests significant sensitivity to process parameters, which is characteristic of hardfacing overlay welds.
Engineering Practice Integration
For crankshaft repair applications, the following practical considerations emerge:
- The overlay welding approach is suitable for restoring worn bearing journals and crankpins, but dimensional accuracy must be maintained through subsequent grinding.
- The high hardness of the overlay deposit (approximately 2837 HV at optimum) provides excellent wear resistance but may be excessive for bearing surfaces where compatibility with bearing material is important.
- Post-weld stress relief is essential to prevent cracking of the hard martensitic overlay, particularly in thick sections where residual stresses are high.
- The pulsed GTAW process was selected for its precise heat input control, which is advantageous for thin overlay layers on precision components.
Study Insights
This paper demonstrates the value of systematic experimental investigation in welding process development. The researchers did not simply select parameters based on experience but conducted a structured parameter study with quantitative performance measurements. The identification of an optimum parameter combination (50A, 8L/min) with corresponding performance metrics provides actionable guidance for practitioners.
From a metallurgical perspective, I note that the extremely high hardness values observed (up to 3549 HV) are characteristic of rapidly solidified hardfacing deposits and represent a trade-off between wear resistance and toughness. In crankshaft applications, where the bearing surfaces experience cyclic loading and potential impact events, the toughness of the overlay deposit is as important as its hardness. The paper does not report impact energy or fracture toughness measurements, which would be valuable additions for a complete assessment of the overlay deposit's serviceability.
The work also highlights the importance of filler material selection—SHQ-605 is a high-alloy hardfacing wire designed specifically for severe wear applications. The compatibility between this high-alloy filler and the 20CrMnTi base metal is a critical consideration, as high dilution can reduce the hardness of the overlay deposit, while low dilution may result in poor bonding.