Research on High-Temperature Wear-Resistant Overlay Welding Electrodes

Literature Overview

This 2003 publication by Han Yongchuan from the China University of Mining and Technology (China Coal Economic Institute) investigates the development of overlay welding electrodes designed for combined high-temperature and wear resistance. The research addresses a critical engineering challenge in coal mining and thermal power equipment, where components are simultaneously subjected to abrasive wear and elevated operating temperatures that degrade conventional wear-resistant materials.

Technical Background and Service Requirements

High-temperature wear resistance represents a fundamentally different challenge from room-temperature wear resistance. At elevated temperatures, several degradation mechanisms reduce the effective hardness and wear resistance of materials:

Temperature Range	Dominant Degradation Mechanism	Effect on Wear Resistance
200–400 °C	Softening of carbide matrix	Moderate hardness reduction
400–600 °C	Carbide dissolution and diffusion	Significant hardness loss
600–800 °C	Oxidation + thermal fatigue	Combined degradation
> 800 °C	Phase transformation and creep	Severe property loss

The target applications include coal pulverizer mill liners, boiler furnace wear plates, ash handling equipment, and thermal power plant ducting components where temperatures reach 400–800 °C.

Electrode Design Philosophy

Metallurgical Strategy for High-Temperature Wear Resistance

The electrode design incorporates multiple mechanisms to maintain wear resistance at elevated temperatures:

Carbide reinforcement: Hard, thermally stable carbides (Cr7C3, Mo2C, W2C) that resist dissolution and coarsening at service temperatures.
Matrix strengthening: Solid solution strengthening through Mo, W, and V additions that maintain strength at elevated temperatures.
Thermal stability: Alloying elements that promote stable microstructures resistant to phase transformations during thermal cycling.
Oxidation resistance: Chromium-rich phases that form protective oxide scales.

Electrode Composition Design

Element	Content (wt%)	Function
C	3.5–5.0	Carbide formation
Cr	22–28	Oxidation resistance, carbide formation
Mo	4–8	High-temperature strength, carbide stability
W	2–5	Carbide stability, thermal stability
V	1–3	Fine carbide dispersion, high-temperature hardness
Mn	1.5–3.0	Deoxidation, solid solution strengthening
Si	0.5–1.5	Deoxidation
Fe	Balance	Matrix

Microstructural Analysis and Property Characterization

Room Temperature Properties

Property	Value	Comparison with Conventional Electrode
Hardness (HV30)	850–1050	60–80% higher
Wear rate (dry sliding)	0.05–0.12 mm³/N·m	50–70% lower
Compressive strength	2200–2800 MPa	Comparable
Elongation	2–5%	Lower (expected for high-hardness material)

High-Temperature Properties

Property	25 °C	400 °C	600 °C	800 °C
Hardness (HV30)	950	880	720	520
Retained hardness (%)	100	93	76	55
Wear rate (mm³/N·m)	0.08	0.10	0.18	0.35

The retained hardness at 600 °C of approximately 76% demonstrates the effectiveness of the carbide-strengthened design, compared to conventional high-carbon martensitic electrodes that typically retain only 40–50% of their room-temperature hardness at the same temperature.

Microstructural Evolution at Elevated Temperatures

The high-temperature wear resistance mechanism operates through multiple synergistic effects:

Primary carbides (Cr7C3, Mo2C, W2C): These large, thermally stable carbides maintain their integrity up to 800 °C and provide the primary wear resistance mechanism.
Secondary carbides (M6C, MC): Fine carbides formed during solidification provide additional strengthening but may coarsen at prolonged high-temperature exposure.
Matrix structure: The martensitic matrix provides a tough substrate that supports the hard carbide phase and resists cracking under thermal cycling.
Chromium-rich phases: Continuous Cr-rich films along grain boundaries contribute to oxidation resistance and maintain intergranular strength.

Defect Analysis and Weldability Considerations

Defect	Cause	Prevention
Hot cracking	High carbon + sulfur	Add Ca or Mg to flux for desulfurization
Cold cracking	High hardenability of deposit	Preheat to 200–300 °C; control interpass temperature
Excessive brittleness	Over-alloying with carbide formers	Balance C + Cr + Mo + W + V content
Poor weldability	High arc voltage requirements	Optimize flux composition for arc stability
Spalling from base	Thermal expansion mismatch	Use transition layer between base and overlay

Engineering Applications and Service Evaluation

The developed electrodes were tested in coal mill liner applications where the service conditions include:

Operating temperature: 350–500 °C (coal dust temperature)
Wear mechanism: Abrasive wear from coal and ash particles
Impact loading: Periodic impact from coal lumps
Service life target: 24–36 months (vs. 12–18 months for conventional electrodes)

Field trials demonstrated a 40–60% improvement in service life compared to standard high-carbon martensitic electrodes, validating the design philosophy of incorporating multiple high-temperature strengthening mechanisms.

Study Reflections and Implications

This research highlights the fundamental principle that high-temperature wear resistance cannot be achieved simply by maximizing room-temperature hardness. The material must be designed with explicit consideration for thermal degradation mechanisms, incorporating thermally stable strengthening phases and oxidation-resistant elements. The multi-element carbide system (Cr + Mo + W + V) provides synergistic benefits that no single carbide-forming element can achieve alone.

The practical engineering implication is that for applications involving simultaneous high temperature and wear, the electrode selection must consider the operating temperature as a primary design parameter, not merely an environmental factor. Conventional room-temperature wear-resistant electrodes may perform acceptably at low temperatures but will fail prematurely in high-temperature service due to matrix softening and carbide dissolution. The integrated approach of combining thermally stable carbides with oxidation-resistant alloying elements represents the current state-of-the-art in high-temperature wear-resistant overlay welding consumable design.