CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of HM1 Overlay Welding Electrode
Literature Overview
Published in 2005 by Liu Yaodong, Du Hui, and Nie Faming from the School of Materials Science and Engineering at Changchun University of Technology, this study documents the development and characterization of a new overlay welding electrode designated HM1. The work is situated within the field of welding technology and addresses the need for specialized consumables capable of producing overlay layers with tailored wear resistance and mechanical properties for specific industrial applications.
Electrode Design Philosophy
The HM1 electrode was developed to produce a hardfacing overlay layer suitable for components subjected to severe abrasive wear. The design follows a multi-phase hardfacing philosophy, where the weld metal is engineered to contain a high volume fraction of hard carbide particles dispersed in a ductile matrix. The electrode composition was optimized through systematic variation of alloying elements, with particular attention paid to the carbon, chromium, and tungsten content, which govern carbide type, morphology, and distribution.
The electrode is classified as a low-hydrogen, cellulosic-coated or low-hydrogen-sodium-type electrode, designed for use with DC electrode positive (DCEP) polarity. The coating serves multiple functions: it stabilizes the arc, supplies additional alloying elements to the weld pool, controls the weld metal chemistry, and provides a slag cover that promotes controlled cooling and grain refinement.
| Electrode Designation | HM1 |
|---|---|
| Polarity | DCEN (electrode negative) or DCEP depending on coating |
| Current range | 80–220 A |
| Weld metal hardness (as-welded) | 55–62 HRC |
| Carbon content | 3.5–4.5 wt% |
| Chromium content | 18–22 wt% |
| Tungsten content | 4–6 wt% |
| Applicable welding positions | Flat, horizontal, vertical-up |
Microstructural Characterization
Metallographic analysis of the HM1 overlay reveals a three-phase microstructure consisting of primary M7C3 carbides, secondary M23C6 carbides, and a martensitic matrix. The primary carbides form during solidification as large, irregularly shaped particles, while the secondary carbides precipitate during cooling through the austenite-to-martensite transformation. The martensitic matrix provides the necessary toughness to resist impact and thermal shock, while the carbide network provides the abrasion resistance.
The researchers conducted systematic studies on how welding parameters — current, voltage, travel speed, and interpass temperature — affect the microstructure and hardness of the overlay. Key findings include:
- Higher welding currents produce coarser primary carbides and slightly lower overall hardness due to increased dilution and slower cooling rates.
- Lower travel speeds result in deeper weld penetration and higher dilution, which reduces the effective alloy content in the overlay.
- Interpass temperatures above 200 °C promote carbide coarsening and reduce overlay hardness by 3–5 HRC compared to cold-pass welding.
Qualification and Application Testing
The HM1 electrode was qualified through a comprehensive test program including tensile testing of weld coupons, impact testing at room temperature and low temperature, hardness profiling across the overlay thickness, and simulated wear testing. The results demonstrated that the HM1 overlay layer achieved a consistent hardness in the range of 55–62 HRC with acceptable toughness, making it suitable for applications such as crusher jaws, excavator bucket teeth, and mill liners.
Study Insights and Reflections
The development of HM1 represents a practical approach to consumable design that balances compositional optimization with manufacturing feasibility. The study's systematic approach — varying one parameter at a time while holding others constant — provides a clear understanding of parameter effects, which is valuable for both consumable manufacturers and welding engineers selecting electrodes for specific applications. The work also highlights an important principle in hardfacing design: hardness alone is insufficient for qualification, and the combination of hardness, toughness, and carbide morphology must be considered holistically. For modern practitioners, the HM1 development methodology remains a useful template for developing new overlay consumables, particularly when targeting specific service conditions where standard electrodes do not provide adequate performance.