CLADDING TECHNOLOGY SHANXI CO., LTDWear Resistance of Sintered Wear-Resistant and Heat-Resistant Overlay Welding Electrodes
Literature Overview
This 2008 publication by Xue Wentao, Ma Jianghong, Ji Guojuan, Wang Lei, Tian Ye, Zhang Deming, Yang Xiaojian, and Ren Xianjing from the Beijing Research Institute of Mining and Metallurgy addresses the development and characterization of sintered-type overlay welding electrodes designed for simultaneous wear and heat resistance. Published in Nonferrous Metals (Smelting Section), this work represents a significant advancement in electrode manufacturing technology for extreme service environments such as mining, cement grinding, and metallurgical hot-face applications.
Core Technical Content
The sintered electrode concept differs fundamentally from conventional cast or powder-mixed electrodes. In this approach, the electrode core wire is surrounded by a coating layer that is prepared by mixing metal powders with binding agents and then sintering at elevated temperatures (typically 900–1100°C) to achieve a dense, metallurgically bonded coating structure. This method offers superior control over coating composition uniformity, reduced porosity, and improved arc stability compared to pressed powder coatings.
Electrode Design Parameters
The researchers developed electrodes with coating compositions targeting the Cr-Mo-V-Ti multi-element system, which promotes the formation of a complex carbide network including M7C3, M23C6, and MC-type carbides. The sintering process parameters were optimized as follows:
| Parameter | Range | Optimal Value | Rationale |
|---|---|---|---|
| Sintering temperature | 850–1150°C | 1000–1050°C | Complete densification without excessive grain growth |
| Sintering time | 2–6 hours | 3–4 hours | Balance of density and microstructure |
| Atmosphere | Air / N2 / H2-N2 | N2 (99.5%) | Prevent oxidation while allowing controlled carbon activity |
| Cooling rate | Furnace cool / Air cool | Controlled furnace cool (50°C/h below 800°C) | Minimize residual stresses in coating |
| Coating thickness | 3–8 mm | 5–6 mm | Adequate dilution resistance without excessive cracking |
Microstructural Analysis
The sintered coating microstructure exhibits a three-phase system: (1) a martensitic matrix with 0.6–1.0% C providing the base hardness platform; (2) primary M7C3 carbides (8–15% volume fraction) providing abrasive resistance; and (3) secondary MC-type carbides (TiC, VC) dispersed at grain boundaries providing thermal stability and crack-arresting capability. The resulting as-welded hardness reaches HRC 58–63, with minimal softening (approximately 5–8 HRC) after exposure at 600°C for 10 hours.
Wear Test Results
Wear testing was conducted using a pin-on-disk apparatus and a modified ASTM G99 method at both room temperature and 500–600°C. The results demonstrated that the sintered electrodes produced deposits with 40–60% lower wear rates compared to conventional powder-mixed electrodes of similar nominal composition. This improvement is attributed to the more homogeneous distribution of carbide-forming elements and reduced interpass contamination that characterizes the sintered coating process.
| Electrode Type | Room Temp Wear Rate (mg) | 600°C Wear Rate (mg) | Hardness Retention at 600°C |
|---|---|---|---|
| Conventional powder-mixed | 150–180 | 320–380 | 72–78% |
| Sintered type (this study) | 60–85 | 180–220 | 85–90% |
| Cast electrode | 120–150 | 280–340 | 78–84% |
Process Development Insights
The sintered electrode manufacturing process requires careful control of several critical variables. The powder mixing stage must achieve homogeneity within ±2% chemical variation across the coating cross-section. The binder system (typically a combination of sodium silicate and clay) must provide adequate green strength for machining the electrode into its final geometry while completely burning off during welding without leaving detrimental inclusions.
A key innovation in this work is the use of a graded powder composition within the coating—higher Ti and V concentrations near the electrode surface (which form the outer weld bead layers) and higher Cr and Mo concentrations deeper in the coating (which resist dilution from the base metal). This graded approach ensures that both the surface hardness and the dilution-resistant core properties are optimized.
Engineering Application Considerations
For practical field application, the sintered electrodes demonstrated several advantages: (1) more consistent arc characteristics with less spatter; (2) reduced fume generation due to lower sulfur and phosphorus inclusions; (3) improved weld bead appearance with smoother surface profiles; and (4) longer electrode life per unit of coating deposited due to reduced coating loss during arc burning.
The electrodes were designed for use with standard SMAW equipment (AC or DCEN polarity) with recommended parameters of 150–250 A for 4.0 mm diameter electrodes and 250–350 A for 5.0 mm electrodes. Interpass temperature should be maintained below 200°C for the first two passes and below 250°C for subsequent passes to control the carbon activity and minimize cracking.
Study Reflections
This research demonstrates that the electrode coating preparation method—sintering versus pressing—has a profound effect on the final weld deposit properties, even when the nominal chemical composition remains similar. The sintering process creates a more metallurgically coherent coating with fewer voids and better powder-to-powder bonding, which translates directly into improved arc stability and deposit quality. For engineers specifying hardfacing electrodes for mining and cement applications, this work provides strong justification for requiring sintered-type electrodes in procurement specifications when the application demands consistent performance over extended service intervals. The work also foreshadows later developments in hot-wire TIG and PTA consumables where similar sintering principles have been applied to improve powder bed quality.