Development of Iron-Based High-Temperature Wear-Resistant Alloy Overlay Welding Electrodes

Literature Overview

This paper by Xu Guojian, Gu Yuxi from Shenyang University of Technology, and Zhou Ye from Shenyang High Voltage Switchgear Co., Ltd., published in Journal of Shenyang University of Technology (Vol. 18, Issue S1, 1996), presents the development of an iron-based high-temperature wear-resistant alloy overlay welding electrode. The research demonstrates a cost-effective alternative to nickel-based overlay systems while achieving superior wear performance at elevated temperatures.

Core Technical Content

Alloy System and Microstructure

The developed electrode belongs to the Cr-Mo-B alloy system. The overlay weld deposit microstructure consists of:

Performance Characteristics

Red Hardness Analysis

Red hardness (hot hardness) is a critical property for high-temperature wear applications. The ability of this overlay to maintain HV 306.4 at 700°C indicates:

• The martensitic matrix retains sufficient hardness through solid solution strengthening by Cr and Mo
• The boride and carbide phases maintain their hardness at elevated temperatures due to their high melting points and strong atomic bonding
• The Cr content promotes the formation of a protective oxide scale that limits oxidative wear

Technical Interpretation

Alloy Design Rationale

The Cr-Mo-B system was selected based on the following considerations:

1. Iron base — Lower cost compared to Ni-Co base; good weldability with steel substrates; high dilution tolerance
2. Chromium (Cr) — Promotes martensite formation in the weld metal; forms hard carbides (Cr7C3); provides oxidation resistance
3. Molybdenum (Mo) — Enhances martensite stability and red hardness; forms very hard Mo2C carbides (HV 1800+); improves temper resistance
4. Boron (B) — Forms hard borides (Fe2B: HV 1200, CrB: HV 1600); modifies carbide morphology; enhances wear resistance

The eutectic structure formed by the combination of borides and carbides is particularly effective for wear resistance because:

• It provides a uniform distribution of hard phases throughout the matrix
• The interlocking of boride and carbide phases impedes crack propagation
• The eutectic structure is self-renewing during welding, ensuring consistent microstructure across multiple passes

Wear Mechanism Analysis

At room temperature, the primary wear mechanisms are:

• Abrasive wear — Hard carbides and borides resist micro-ploughing by abrasive particles
• Adhesive wear — High hardness of the overlay reduces material transfer to the counterface
• Fatigue wear — Eutectic structure impedes subsurface crack initiation and propagation

At elevated temperatures (up to 700°C), additional mechanisms come into play:

• Thermal softening — Mitigated by Mo-enhanced martensite and thermally stable borides/carbides
• Oxidative wear — Controlled by Cr-induced protective oxide scale
• Diffusion wear — Limited by the high stability of intermetallic compounds

Comparison with Nickel-Based Systems

Engineering Practice Integration

Field Application: Brick Machine Twin-Shaft Mixer Blades

The field validation on brick machine twin-shaft mixer blades provides valuable practical data:

• Original component: Quenched 45 steel blades with limited service life
• Modified component: Overlay welded blades using the developed Cr-Mo-B electrode
• Life improvement: More than 5 times the original service life
• Service conditions: Abrasive contact with clay/brick material, moderate temperature, high impact loading

This case study demonstrates that:

1. Iron-based overlay systems can provide substantial life extension for moderate-temperature wear applications
2. The cost of overlay welding is justified by the extended service life and reduced downtime
3. Field validation is essential to confirm laboratory performance predictions

Welding Procedure Development

For production implementation, the following welding procedure considerations are recommended:

1. Base metal preparation:

• Clean surface to remove rust, scale, and contamination
• Machining or grinding to establish proper fit-up
• Preheating to 150–250°C to reduce hydrogen cracking risk

1. Welding parameters (typical for SMAW with Cr-Mo-B electrodes):

• Current: 100–200 A (depending on electrode diameter)
• Polarity: DCEP (Direct Current Electrode Positive) for deep penetration
• Travel speed: 50–100 mm/min
• Interpass temperature: Below 250°C

1. Post-weld treatment:

• Allow controlled cooling (no rapid quenching)
• Stress relief at 550–650°C for 1–2 hours if residual stress is a concern
• Avoid excessive PWHT that may cause martensite tempering and hardness loss

Defect Prevention

Key Questions and Reflections

The study raises several important engineering considerations:

• Boron sensitivity — Borides are sensitive to oxidation and may be adversely affected by excessive oxygen in the weld atmosphere. Shielding gas purity and electrode flux quality are critical.
• Thermal cycling stability — While 700°C performance is demonstrated, long-term exposure with thermal cycling may cause boride coarsening or phase transformation. Creep-fatigue interaction data would be valuable.
• Scalability — The transition from laboratory-scale development to production-scale manufacturing requires careful process validation and quality system implementation.

Study Insights

This paper represents an excellent example of cost-conscious engineering innovation. By developing an iron-based alternative to expensive nickel-based overlay systems, the authors demonstrate that performance requirements can be met through intelligent alloy design without necessarily resorting to premium materials. The Cr-Mo-B system achieves superior room-temperature wear resistance (2–3 times improvement) and maintains good red hardness at 700°C, making it suitable for a wide range of industrial applications including steel pipe manufacturing equipment. The field validation on brick machine mixer blades, showing more than 5 times life improvement, provides compelling evidence of practical value. For engineers in the steel pipe industry, this research suggests that iron-based overlay solutions should be seriously considered for moderate-temperature wear applications before defaulting to more expensive nickel-based alternatives.