CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High Cracking-Resistant Wear-Resistant Overlay Welding Electrodes
Literature Overview
Published in Mechanical Engineering Materials in 2009, this paper by Tang Wenbo, Guo Yungang, Wei Jianjun, and Huang Zhiquan addresses the development of overlay welding electrodes that combine high wear resistance with excellent crack resistance. The research was conducted jointly by Zhengzhou University and the Zhengzhou Institute of Mechanical Research, combining academic metallurgical expertise with industrial application requirements. The work is particularly relevant for applications where overlay welds are subjected to both abrasive wear and cyclic or impact loading.
Core Technical Points
Design Philosophy
The fundamental challenge in developing high-cracking-resistant wear-resistant overlay electrodes is the inherent contradiction between hardness and toughness. High hardness requires high carbon and alloy content, which promotes brittle phases and cracking. The authors adopted a multi-strategy approach to resolve this contradiction:
| Strategy | Mechanism | Effect |
|---|---|---|
| Controlled carbon content | Limit carbide volume fraction | Balance hardness and toughness |
| Additions of Ni and Mo | Promote austenite retention | Improve toughness without sacrificing hardness |
| Grain refinement | Smaller grains resist crack propagation | Reduce cracking susceptibility |
| Residual stress control | Optimize welding procedure | Minimize residual tensile stress |
Electrode Composition Design
| Electrode Grade | C (wt%) | Cr (wt%) | Ni (wt%) | Mo (wt%) | Hardness (HV) | Crack Resistance |
|---|---|---|---|---|---|---|
| Conventional | 1.5-2.5 | 20-30 | 0-2 | 0-1 | 600-700 | Poor |
| Developed Type I | 1.0-1.5 | 22-28 | 3-5 | 1-2 | 550-620 | Good |
| Developed Type II | 0.8-1.2 | 25-32 | 5-8 | 2-3 | 500-580 | Excellent |
The developed electrodes achieve a hardness of 500-620 HV, which is comparable to conventional high-carbon electrodes, while exhibiting significantly improved crack resistance. This is achieved through a combination of lower carbon content, higher nickel addition, and molybdenum reinforcement.
Metallurgical Mechanism
The key metallurgical insight is that nickel promotes austenite retention in the weld microstructure. Retained austenite acts as a tough phase that absorbs energy and deflects cracks. The microstructure of the developed electrodes consists of martensite, retained austenite, and dispersed carbides. The retained austenite fraction, controlled between 10-25 vol%, provides the critical toughness contribution.
| Microstructural Phase | Volume Fraction (%) | Hardness (HV) | Role |
|---|---|---|---|
| Martensite | 40-60 | 600-700 | Primary wear resistance |
| Retained austenite | 10-25 | 200-300 | Toughness and crack resistance |
| Carbides (Cr7C3, M7C3) | 15-30 | 1200-1800 | Abrasive wear resistance |
Welding Procedure Optimization
| Parameter | Recommended Value | Rationale |
|---|---|---|
| Preheat temperature | 100-200°C | Reduce cooling rate, minimize cracking |
| Interpass temperature | < 250°C | Prevent excessive grain growth |
| Current (A) | 80-130 (for 3.2 mm electrode) | Adequate penetration without excessive dilution |
| Arc voltage (V) | 22-28 | Stable arc, good fusion |
| Layer thickness | 3-5 mm per pass | Balance deposition rate and cooling rate |
Quality Assessment
The developed electrodes were evaluated through multiple testing methods:
| Test Method | Standard | Result |
|---|---|---|
| Transverse cracking test | AWS D17.1 | 0-10% cracking (vs. 30-50% for conventional) |
| Wear testing (dry sliding) | ASTM G99 | 30-40% lower wear rate than conventional |
| Impact toughness (Charpy) | ISO 148 | 5-15 J (vs. 0-5 J for conventional) |
| Hardness | ISO 6507 | 500-620 HV (uniform) |
| Dilution | Metallographic | 15-25% |
Engineering Practice Integration
These electrodes are particularly suitable for applications where overlay welds are subjected to both abrasive wear and impact loading, such as:
- Excavator bucket teeth and cutting edges
- Crusher hammers and anvils
- Mill rolls and grinding media
- Mining shovel teeth and side cuts
The improved crack resistance allows for more relaxed welding procedures, reducing the need for extensive preheating and post-weld heat treatment. This translates directly into lower production costs and higher productivity.
Field Application Case
In a mining operation, conventional overlay electrodes on excavator bucket teeth required replacement every 3-4 months due to cracking-induced spalling. After switching to the developed Type II electrodes, the service life increased to 7-9 months, representing a 2.5x improvement in service life and a significant reduction in maintenance downtime.
Key Questions and Reflections
A critical question addressed by this work is the long-term stability of retained austenite in service. Retained austenite can transform to martensite during cooling or under mechanical loading, potentially leading to increased brittleness over time. The authors suggest that the nickel content should be sufficient to stabilize retained austenite at operating temperatures, typically requiring at least 5% Ni for applications above 200°C.
Another reflection concerns the cost-benefit analysis. The developed electrodes have a higher material cost due to nickel and molybdenum additions, but the extended service life and reduced maintenance costs result in a favorable overall economics.
Study Insights and Implications
This paper demonstrates that the traditional trade-off between wear resistance and crack resistance in overlay welding can be effectively managed through rational alloy design. The combination of controlled carbon, strategic nickel addition, and molybdenum reinforcement provides a practical solution for demanding industrial applications. For engineers selecting overlay consumables, this work emphasizes that the total cost of ownership—including maintenance frequency and downtime—should be considered rather than focusing solely on material cost.