Development of K118 Wear-Resistant Alloy Carbon Arc Overlay Powder Blocks

Literature Overview

This 1988 study published in Coal Science and Technology by Ge Changlu, Shan Liliyun, Kan Zhouping, and Liu Jiajun from China University of Mining and Technology and Xuzhou Mining Bureau Second Machinery Factory presents the development of K118 wear-resistant alloy powder blocks for carbon arc overlay welding. This work is historically significant as it represents early Chinese research into developing specialized consumables for the coal mining industry, where extreme abrasion resistance is required for equipment operating in harsh underground environments. The K118 designation follows the Chinese classification system for welding consumables, where "K" denotes carbon arc welding powder (碳弧气刨堆焊粉) and "118" is the product series number.

Technical Background and Application Requirements

In coal mining operations, equipment components such as crusher jaws, conveyor rollers, shovels, and excavator buckets experience severe abrasive wear from coal, rock, and abrasive particles. The service life of these components is limited by surface wear, and traditional replacement strategies result in high costs and production downtime. Weld overlay with wear-resistant alloys offers an effective solution by rebuilding worn surfaces and restoring or even enhancing the original performance.

The K118 powder block is designed for carbon arc overlay welding (also known as carbon arc air gouging overlay or carbon electrode arc welding), a process that uses a carbon electrode to create a molten pool in which alloy powder is fed and melted onto the base metal. This process is particularly suitable for field repair applications where portability and simplicity are valued.

Material Design and Composition

The K118 alloy composition is designed to achieve high hardness and excellent abrasion resistance through the formation of hard carbide phases. The typical composition includes:

The high carbon content (3–6 wt%) combined with strong carbide-forming elements (Cr, Mo, W) results in the formation of complex carbides such as M7C3, M6C, and M23C6, which provide the primary wear resistance. The hardness of the K118 overlay layer typically achieves HRC 58–65 or HV 900–1200, significantly exceeding the hardness of typical carbon steel base materials.

Process Characteristics and Application Method

Carbon arc overlay welding with powder blocks offers several advantages for field application:

• Simplicity: The process requires only a carbon electrode holder, power source, and the powder block itself, making it highly portable.
• Versatility: Can be applied to various base materials including carbon steel, low-alloy steel, and cast iron.
• High deposition rate: The carbon arc creates a deep molten pool that allows rapid buildup of overlay material.
• Good fusion: The deep penetration of the carbon arc ensures strong metallurgical bonding with the base material.

The application process involves:

1. Surface preparation: Grinding the worn area to sound metal, removing rust, oil, and loose material.
2. Preheating: For thick sections or high-carbon base materials, preheating to 200–300 °C is recommended to prevent cracking.
3. Powder application: The K118 powder block is placed in the molten pool created by the carbon arc, or the powder is fed directly into the arc.
4. Welding: Multiple passes may be required to build up the desired overlay thickness, typically 3–10 mm depending on the application.
5. Post-weld treatment: Stress relief annealing may be required for critical applications, though many field applications rely on the inherent toughness of the overlay.

Performance Evaluation and Study Insights

The performance of the K118 overlay layer is evaluated through several methods:

• Hardness testing: Vickers or Rockwell hardness measurements confirm the achieved hardness level and uniformity across the overlay.
• Abrasion testing: Standard abrasion tests (such as ASTM G65 or dry sand-rubber wheel tests) quantify the wear resistance improvement over the base material.
• Impact testing: Charpy V-notch impact tests assess the toughness of the overlay layer, ensuring it can withstand impact loading without catastrophic fracture.
• Field trials: Practical application on mining equipment provides real-world validation of the overlay performance and service life extension.

This study reflects the practical engineering approach common in the Chinese heavy industry sector during the 1980s, where the focus was on developing cost-effective, locally producible solutions for specific industrial needs. The K118 powder block represents a successful example of materials development driven by application requirements, where the composition was optimized through iterative testing and field validation. For modern engineers, this work serves as a historical reference point, demonstrating the fundamental principles of wear-resistant alloy design that remain relevant today. The evolution from powder blocks to modern powder metallurgy consumables for thermal spray and laser cladding reflects the broader technological advancement in surface engineering, while the core metallurgical principles of carbide formation and matrix hardening remain unchanged. Engineers should recognize that understanding these foundational materials and processes provides valuable insight into the design of modern wear-resistant overlay systems, enabling more informed selection and application of contemporary technologies.