Abrasion Characteristics of CO2 Welding with High Chromium-Molybdenum Alloy Powder Spraying Composite Surfacing on Deep Loosening Plowshares

Literature Overview

This 2014 paper published in the Journal of Inner Mongolia University of Science and Technology (Vol. 33, No. 4, pp. 357–361) by Jiao Renbao, Yang Hai, Wang Guilian, and Shao Dongwei from Jiamusi University School of Mechanical Engineering investigates a novel composite surfacing process for deep loosening plowshares. The process combines CO2 gas shielded arc welding with high chromium-molybdenum alloy powder spraying (powder injection), creating a composite surfacing layer. The research was supported by the Jiamusi University Science and Technology Fund (Grant L2013-063). The classification number TG455 places this in the general surfacing technology category.

Technical Concept and Process Description

The composite surfacing process described in this paper represents a hybrid approach that combines the advantages of arc welding (strong metallurgical bond) with powder injection (precise alloy composition control and high deposition rate). The process can be described as follows:

Process Configuration

The CO2 shielding gas provides economical shielding with good arc stability, while the powder injection system introduces high-chromium-molybdenum alloy powder into the welding arc zone, where it melts and mixes with the molten weld pool. The resulting deposit combines the base metal from the arc welding with the injected alloy powder, creating a composite microstructure with enhanced wear resistance.

Microstructural Analysis

The metallographic examination revealed that the surfacing layer microstructure consists primarily of:

1. Lower bainite: The dominant phase in the matrix, formed during moderate cooling rates. Lower bainite provides a good combination of hardness and toughness, with fine carbide particles dispersed within the ferrite matrix.
2. Retained austenite: Present in variable amounts, contributing to toughness through transformation-induced plasticity during wear.
3. Carbide phases: Chromium and molybdenum carbides are present as fine particles, providing dispersion strengthening and resistance to abrasive wear.

The interfacial examination confirmed a good metallurgical bond between the surfacing layer and the base material, with no visible cracks, porosity, or incomplete fusion at the interface. This metallurgical bond is critical for ensuring that the surfacing layer remains attached during service loading.

Wear Testing Results

The wear testing was conducted using an abrasive wear tester, and the results showed a significant improvement in wear resistance:

The 2.38-fold improvement in wear resistance represents a substantial enhancement that directly translates to extended equipment service life and reduced maintenance costs in agricultural applications.

Engineering Analysis and Discussion

Why Deep Loosening Plowshares Require Special Treatment

Deep loosening plows operate under extremely severe wear conditions:

• Abrasive soil: The plowshares contact abrasive soil containing rocks, gravel, and hard particles, creating severe abrasive wear.
• Impact loading: The plowshares experience repeated impact loading as they penetrate and break up hard soil.
• High temperatures: Frictional heating during plowing can raise local temperatures significantly.
• Corrosive environment: Soil moisture and chemical constituents can cause corrosion.

Traditional plowshares, typically made from low-carbon steel or medium-carbon steel, wear through rapidly under these conditions, requiring frequent replacement. The composite surfacing approach addresses this problem by providing a wear-resistant surface layer while maintaining the structural integrity of the base material.

Advantages of the Composite Process

The CO2 welding with powder injection approach offers several advantages over alternative surfacing methods:

1. Cost-effectiveness: CO2 gas is inexpensive, and the process does not require specialized equipment beyond a standard GMAW setup with a powder injection attachment.
2. High deposition rate: Powder injection significantly increases the deposition rate compared to solid wire welding, making the process economical for large surface areas.
3. Composition control: The powder injection allows precise control of the surfacing alloy composition, independent of the base metal composition.
4. Good metallurgical bond: Unlike thermal spraying, the arc welding process creates a true metallurgical bond between the surfacing layer and the base material.
5. Field applicability: The process can be performed in field conditions with minimal equipment setup, making it suitable for on-site repair and maintenance.

Microstructural Mechanisms of Wear Resistance

The enhanced wear resistance of the composite surfacing layer can be attributed to several mechanisms:

• Hard carbide reinforcement: Fine chromium and molybdenum carbides dispersed throughout the matrix provide resistance to abrasive particle indentation and ploughing.
• Lower bainite matrix: The fine-lamellar lower bainite structure provides a tough matrix that supports the hard carbide particles and resists crack propagation.
• Retained austenite transformation: During abrasive wear, retained austenite transforms to martensite under stress, providing work hardening that increases resistance to further wear.
• Multi-phase synergy: The combination of hard carbides, tough matrix, and transformation-induced plasticity creates a synergistic wear resistance mechanism that outperforms any single-phase material.

Practical Implementation Considerations

For successful implementation of this composite surfacing process in agricultural equipment manufacturing and repair, the following considerations are important:

1. Powder quality control: The alloy powder must be consistent in composition, particle size, and flowability. Powder moisture content must be controlled to prevent porosity.
2. Welding parameter optimization: The balance between arc welding parameters and powder injection rate must be optimized to achieve the desired microstructure and wear resistance. Too high a powder injection rate can lead to incomplete melting and poor bond strength.
3. Surface preparation: The base metal surface must be thoroughly cleaned and prepared to ensure good metallurgical bonding. Rust, paint, and contaminants must be removed.
4. Layer thickness: The surfacing layer thickness should be sufficient to provide wear resistance throughout the expected service life, typically 3–5 mm for plowshare applications.
5. Quality inspection: Visual inspection, magnetic particle testing, and hardness testing should be performed on each surfacing job to ensure quality consistency.

Comparative Analysis with Alternative Processes

The CO2 welding with powder injection approach occupies a favorable position in this comparison, offering a good balance of deposition rate, cost, bond strength, and wear resistance with excellent field applicability.

This paper presents a practical and effective composite surfacing solution for agricultural equipment wear protection, demonstrating that the combination of CO2 gas shielded welding with high chromium-molybdenum alloy powder injection can achieve a 2.38-fold improvement in wear resistance with good metallurgical bonding, providing a cost-effective and field-applicable solution for extending the service life of deep loosening plowshares under severe abrasive wear conditions.