Zhuojin Pipe Fitting Co., LtdDevelopment of K118 Nickel-Free Wear-Resistant Alloy Carbon Arc Surfacing Powder Blocks
Literature Overview
The paper by Ge Changlu, Shan Liyun, Kan Zhouping, and Liu Jiajun, published in "Coal Science and Technology" (1988, Vol. 16, No. 9, pp. 15-16), reports on the development of K118, a nickel-free wear-resistant alloy carbon arc surfacing powder block material. The authors are affiliated with China University of Mining and Technology and Xuzhou Mining Bureau Second Machinery Factory. The K118 material is specifically designed for carbon arc surfacing applications on equipment components subjected to severe wear, such as scraper conveyor parts in coal mining operations.
Background and Material Design Philosophy
The development of K118 was driven by the need for a cost-effective wear-resistant surfacing material for coal mining equipment. Traditional wear-resistant surfacing alloys often contain nickel, which is expensive and subject to supply constraints. The K118 formulation eliminates nickel entirely while maintaining excellent wear resistance through the use of boron carbide (B4C) and other carbide-forming elements.
The material is formulated as a powder block, which is a compacted form of the alloy powder that can be used directly in the carbon arc surfacing process. The powder block form offers advantages in terms of handling, storage, and consistent composition compared to loose powder. The carbon arc surfacing process involves melting the powder block with an electric arc generated between a carbon electrode and the workpiece, with the molten metal deposited onto the surface.
| Parameter | Description |
|---|---|
| Material Designation | K118 |
| Nickel Content | Zero (nickel-free) |
| Key Alloying Element | Boron carbide (B4C) |
| Surfacing Process | Carbon arc surfacing |
| Power Source | AC welding machine |
| Microstructure | Hypereutectic |
| Primary Application | Scraper conveyor parts |
Microstructure and Wear Mechanism
The K118 material produces a hypereutectic microstructure, characterized by a high volume fraction of hard carbide particles dispersed in a metallic matrix. The boron carbide (B4C) particles serve as the primary wear-resistant phase, providing excellent hardness and wear resistance. The hypereutectic composition ensures that the carbide particles are distributed throughout the solidified deposit, creating a uniform wear-resistant surface.
The wear resistance of the K118 surfacing layer is attributed to the combination of hard carbide particles and the metallic matrix. The B4C particles resist abrasive wear by their high hardness, while the metallic matrix provides toughness and prevents catastrophic failure. The hypereutectic structure is critical because it ensures a high volume fraction of hard phase without compromising the toughness of the deposit.
The choice of carbon arc surfacing as the deposition process is significant. Carbon arc surfacing produces a dilution-free deposit, meaning that the composition of the surfacing layer is essentially the same as the consumable material. This is advantageous for maintaining the precise alloy composition required for the hypereutectic microstructure. The AC power source provides a stable arc and uniform melting of the powder block, which contributes to consistent deposit quality.
Application and Performance Evaluation
The K118 material was specifically developed for scraper conveyor parts in coal mining operations. Scraper conveyors are critical equipment in underground coal mines, where the scraper chain and trough components are subjected to severe abrasive wear from coal and rock. The K118 surfacing layer provides a protective coating that extends the service life of these components.
The wear performance of the K118 surfacing layer was evaluated through laboratory wear testing and field trials. The results demonstrated that the K118 material provides excellent wear resistance, comparable to or exceeding nickel-containing wear-resistant alloys. The nickel-free formulation offers significant cost advantages without sacrificing performance.
The use of AC welding machines for carbon arc surfacing is noteworthy. AC power provides a self-clearing arc, which is advantageous for carbon arc processes where electrode sticking can be a problem with DC power. The AC process also produces a more uniform deposit with less directional solidification, which is beneficial for the isotropic distribution of carbide particles.
Engineering Practice and Process Considerations
The carbon arc surfacing process requires careful control of several parameters to achieve optimal deposit quality. The arc length must be maintained at a consistent distance to ensure uniform melting of the powder block and proper transfer of molten metal to the workpiece. The travel speed affects the dilution rate and the final microstructure of the deposit. The preheat temperature of the base material influences the cooling rate and the resulting microstructure.
The powder block form of the K118 material offers practical advantages in the field. The blocks can be handled and stored more easily than loose powder, and they provide consistent composition for each surfacing operation. The blocks are also less prone to segregation and contamination compared to loose powder, which ensures reproducible deposit quality.
Quality control of the K118 surfacing layer involves hardness testing, microstructural examination, and wear testing. The hardness profile across the deposit is measured to ensure uniform hardness distribution. Metallographic examination reveals the distribution and size of the carbide particles, which directly affects the wear resistance. Wear testing under simulated service conditions validates the performance of the surfacing layer.
Key Reflections and Implications
The development of K118 represents an important advancement in wear-resistant surfacing technology for the coal mining industry. The elimination of nickel from the alloy formulation addresses both cost and supply concerns, making the material more accessible for widespread industrial application. The hypereutectic microstructure with boron carbide particles provides excellent wear resistance, demonstrating that nickel is not essential for achieving high wear performance.
The choice of carbon arc surfacing as the deposition process is significant from a metallurgical perspective. The dilution-free nature of carbon arc surfacing ensures that the precise alloy composition is maintained in the deposit, which is critical for achieving the desired hypereutectic microstructure. This is in contrast to fusion welding processes where dilution from the base material can alter the deposit composition and microstructure.
The practical application of K118 on scraper conveyor parts demonstrates the economic viability of wear-resistant surfacing for coal mining equipment. The extension of component life through surfacing reduces the frequency of replacement and maintenance, resulting in significant cost savings for mining operations. The nickel-free formulation also reduces the environmental impact of the material, as nickel mining and processing have significant environmental consequences.
Summary
The research by Ge Changlu and colleagues on the K118 nickel-free wear-resistant alloy carbon arc surfacing powder block material represents a practical and innovative approach to solving wear problems in coal mining equipment. The hypereutectic microstructure with boron carbide particles provides excellent wear resistance without the need for expensive nickel alloying. The carbon arc surfacing process ensures dilution-free deposition, maintaining the precise alloy composition required for optimal performance. Engineers working on wear-resistant surfacing applications should consider nickel-free formulations such as K118 as a cost-effective and environmentally friendly alternative to traditional nickel-containing alloys.