New High-Alloy Wear-Resistant Overlay Welding Electrode

Literature Overview

This 1990 paper by Ge Changlu and Ying Pengzhan from China University of Mining and Technology, together with Qi Aiyi and Liu Guangxin from Shandong Laiwu Coal Machinery Factory, published in Coal Science and Technology, presents the development of a novel high-alloy wear-resistant overlay welding electrode designed specifically for the demanding service conditions in coal mining machinery. The electrode was developed to address the severe abrasive wear experienced by critical components such as scraper chain links, conveyor rollers, and mining bucket teeth, which operate under high-stress, high-abrasion conditions in underground coal mines. The study reflects an era of intensive materials development in China's coal industry, where equipment reliability and maintenance cost reduction were paramount concerns.

Core Technical Approach and Electrode Design

The electrode development followed a systematic approach combining thermodynamic calculations, metallurgical experimentation, and field performance testing. The authors targeted a deposit microstructure of martensite with retained austenite and dispersed carbide particles, which provides an optimal combination of hardness, toughness, and wear resistance. The base composition was designed to achieve a hardness of 50–58 HRC in the as-welded condition, with a compressive strength exceeding 1500 MPa to resist indentation by coal and rock particles.

The electrode composition was carefully balanced to achieve the desired microstructure. The carbon content was set at 0.6–0.8 wt% to promote martensite formation, while chromium was maintained at 12–15 wt% to enhance hardenability and carbide stability. Molybdenum at 2–3 wt% was added to increase solid solution strengthening and refine the grain structure. The manganese content was controlled at 1.5–2.0 wt% to provide austenite stabilization and improve weldability.

Electrode Composition and Properties

The flux coating composition was equally critical. The authors developed a basic-type flux with calcium carbonate, calcium fluoride, and iron oxide as the primary constituents, supplemented with alloying additions of chromium oxide, molybdenum metal powder, and titanium dioxide. The flux served multiple functions: it provided arc stability, slag protection, deoxidation, and alloy enrichment. The CaF₂ content was optimized at 8–10% to reduce hydrogen absorption and minimize cold cracking tendency, which is particularly important for high-carbon, high-alloy electrodes.

Microstructural Characterization

Metallographic examination of the as-welded deposit revealed a predominantly martensitic microstructure with 15–20% retained austenite and dispersed M₇C₃ and M₂₃C₆ carbide particles. The carbide particles were 2–5 μm in size and uniformly distributed throughout the martensitic matrix, contributing to wear resistance through both microstructural hardening and particle reinforcement. After tempering at 250 °C for 2 hours, the hardness decreased slightly to 48–54 HRC, but the toughness improved significantly, with a Charpy impact energy of 15–20 J at room temperature.

The dilution ratio was measured at approximately 20–25% for single-pass welding on carbon steel base material, which provided adequate alloy enrichment while maintaining a strong metallurgical bond with the substrate. Multi-pass welding with interpass temperature control below 150 °C was recommended to achieve uniform hardness throughout the deposit thickness.

Process and Standards Analysis

The electrode was qualified in accordance with GB/T 5117 (Non-cored electrode for manual metal arc welding) and GB/T 1351 (Steel — Delivery technical conditions). The welding procedure was established using the following parameters:

The authors emphasize that electrode storage and baking are critical for maintaining weld quality. The electrode must be baked at 300–350 °C for 1 hour before use and kept in a portable electrode oven during welding to prevent moisture absorption. Failure to maintain proper electrode dryness results in hydrogen-induced cracking, which is particularly detrimental for high-carbon, high-alloy deposits.

Field Performance Testing

The developed electrode was tested on scraper chain links of a D710-type single-rope mining scraper conveyor, which operates in an underground coal mine with a coal seam thickness of 2.5 m and a rock hardness index of 3–5. The overlay layer was applied to the wear surfaces of the chain links with a thickness of 5–8 mm in 3 passes. The wear life was measured at 4.2 times that of the original quenched and tempered 45 steel surface, representing a significant improvement in maintenance intervals.

A comparative wear test was also conducted using a pin-on-disk tribometer against a 100# SiC abrasive paper. The specific wear rate of the overlay layer was measured at 0.025 mm³/N·m, compared to 0.12 mm³/N·m for the base 45 steel, confirming a 4.8-fold improvement in wear resistance.

Key Questions and Reflections

One important consideration that the authors address is the balance between hardness and toughness in the overlay deposit. While high hardness is desirable for wear resistance, excessive hardness can lead to brittle fracture under impact loading, which is common in mining equipment. The retained austenite content plays a crucial role in this balance: it acts as a crack-arresting phase that enhances toughness without significantly reducing hardness. The authors recommend that the retained austenite content be maintained between 15–25% for optimal performance, which can be achieved by controlling the cooling rate and tempering temperature.

Another practical concern is the spatter rate and electrode deposition efficiency. High-alloy electrodes tend to produce more spatter than low-alloy electrodes due to the higher arc voltage and the tendency of alloyed molten metal to oxidize and form oxide inclusions that detach from the weld pool. The authors measured a deposition efficiency of 82–85% for the developed electrode, which is acceptable but lower than the 90–95% typical of low-alloy electrodes. This means that a higher current consumption is required per unit of deposited metal, which should be factored into cost calculations.

Study Insights and Implications

This 1990 study represents an important contribution to the development of wear-resistant overlay welding consumables in China's coal mining industry. The systematic approach to electrode design, combining thermodynamic calculations with metallurgical experimentation and field validation, sets a benchmark for consumable development methodology. The resulting electrode achieved a successful balance of hardness, toughness, and wear resistance that was validated through both laboratory testing and extended field service. For contemporary engineering practice, the study highlights the enduring importance of tailored consumable development for specific service conditions: a generic wear-resistant electrode cannot match the performance of one specifically designed for the particular wear mechanism, base material, and operating environment of the application. The study also underscores the value of field testing as the ultimate validation of laboratory results, and the importance of considering practical factors such as electrode handling, baking requirements, and deposition efficiency in the overall assessment of a new consumable.