Overlay Welding Process Research for Crankshaft Repair

Literature Overview

This research paper, published in the Journal of Shenyang Ligong University (2020, Vol. 39, Issue 1), investigates the overlay welding process parameters for crankshaft repair using a WSE-350 DC pulse argon arc welding machine with SHQ-605 wear-resistant welding wire on a 20CrMnTi steel substrate. Funded by the Liaoning Provincial Department of Education Key Project (LG201901) and the Shenyang City Young and Middle-aged Scientific and Technological Innovation Talent Support Program, this study systematically examines the effects of welding current and argon gas flow rate on overlay layer performance. The work is conducted jointly by Shenyang Ligong University and Zhejiang Yatong Welding Materials Co., Ltd., representing a strong industry-academia collaboration.

Experimental Design and Methodology

The study employs a systematic experimental approach to optimize overlay welding parameters for crankshaft repair applications. The experimental matrix focuses on two key parameters: welding current and argon shielding gas flow rate.

Testing Methods

The overlay layer properties were characterized using multiple complementary techniques:

1. Microhardness: HV-1000 microhardness tester, measuring hardness across the overlay layer depth.
2. Wear resistance: MDW-02 wear tester, measuring wear rate and friction coefficient.
3. Microstructural analysis: Scanning electron microscopy (SEM) for microstructure characterization and interface examination.

Results and Analysis

Microhardness Distribution

The overlay layer microhardness ranged from 2291 to 3549 HV across the tested parameter range. At the optimal parameters (50A, 8 L/min argon), the microhardness reached 2837 HV. This hardness level is significantly higher than the base 20CrMnTi steel (typically 200-300 HV in as-received condition), providing substantial wear resistance improvement.

Wear Performance

The optimal combination achieved a wear rate of 2×10⁻⁷ g/N·min with a friction coefficient of 0.27, representing excellent tribological performance for a wear-resistant overlay application.

Microstructural Characteristics

SEM analysis revealed that the overlay layer exhibited a lath martensite microstructure with good fusion to the 20CrMnTi substrate. The lath martensite morphology is particularly favorable for wear resistance applications because:

• Lath martensite contains higher carbon content in the lath structure, providing greater hardness.
• The lath orientation creates a tough, fine-grained structure that resists crack propagation.
• The transformation from austenite to martensite during cooling creates compressive residual stresses at the surface, further enhancing wear resistance.
• The fine grain size of lath martensite (compared to plate martensite) provides better fatigue resistance.

Parameter Optimization Analysis

The relationship between welding current, argon flow rate, and overlay performance can be understood through the following mechanisms:

Effect of Welding Current

• Higher current increases heat input, leading to wider weld beads and greater dilution with the base metal.
• Excessive heat input can cause grain coarsening at the fusion line and reduce the hardness gradient.
• Too low current results in insufficient penetration and poor fusion with the substrate.
• The optimal current of 50A represents a balance between adequate deposition rate and controlled heat input.

Effect of Argon Flow Rate

• Insufficient argon flow leads to oxidation of the molten pool, causing porosity, inclusions, and reduced hardness.
• Excessive argon flow can cause turbulence in the shielding gas stream, actually drawing in atmospheric contamination.
• The optimal flow rate of 8 L/min provides stable, laminar shielding that effectively excludes atmospheric contamination while maintaining process stability.

Integration with Engineering Practice

Application to Crankshaft Repair

Crankshaft failure is one of the most common and costly failures in internal combustion engines and industrial machinery. Common failure modes include:

• Journal bearing surface wear and scoring
• Oil hole stress cracking
• Fatigue cracking at fillet radii
• Corrosion damage in marine environments

Overlay welding is particularly effective for:

1. Restoring worn journal dimensions to specification
2. Providing a hard, wear-resistant surface layer
3. Improving fatigue resistance at critical stress locations
4. Repairing cracked surfaces after crack removal

Process Recommendations for Crankshaft Overlay Welding

Based on the findings of this study and general engineering practice:

• Pre-heat the crankshaft to 200–250°C to reduce cooling rate and prevent cracking.
• Use multiple thin passes (1-2 mm each) to control heat input and minimize distortion.
• Apply interpass temperature control (below 300°C) to prevent grain coarsening.
• Perform post-weld tempering at 550–600°C to relieve residual stresses while maintaining overlay hardness.
• Machine the overlay surface to final dimensions and verify hardness after machining.

Key Reflections

This study demonstrates the value of systematic parameter optimization in overlay welding applications. The relatively simple experimental design (two parameters, multiple levels) yielded clear and actionable results. The lath martensite microstructure achieved with SHQ-605 wire on 20CrMnTi steel is particularly noteworthy, as it provides an excellent combination of hardness, toughness, and wear resistance. For engineers involved in crankshaft repair, this research provides a validated process window that can be adapted to similar repair scenarios, with appropriate adjustments for component geometry and operational requirements.