Optimization Design of a High Wear-Resistant Iron-Based Overlay Alloy

Literature Overview

The paper by Yang Shaobin, Dong Wei, Wu Xiaoguang, and Sun Shuai, published in Hot Working Technology (Vol. 41, No. 1, 2012, pp. 124-126), presents an optimization study of a high wear-resistant iron-based overlay alloy using orthogonal experimental design. The research, conducted at Liaoning Technical University's School of Materials Science and Engineering, systematically investigated the effects of chromium, tungsten, vanadium, and rare earth additions on the wear resistance and weldability of the overlay alloy. The optimized composition achieved a hardness of 65 HRC with excellent metallurgical bonding and crack-free overlay deposits even without preheating.

Research Methodology

The study employed the L9(3^4) orthogonal array design to efficiently screen the optimal composition from a large parameter space. This statistical approach allows the evaluation of four factors at three levels each with only nine experimental trials, compared to the 81 trials required for a full factorial design.

Orthogonal Array Design

The response variables measured included:

• Overlay hardness (HRC)
• Wear rate (mg/1000 cycles in pin-on-disk test)
• Crack count in as-welded condition
• Dilution rate (%)
• Bond strength (tensile test)

Optimization Results

The orthogonal array analysis identified the optimal composition as A2B3C2D3, corresponding to:

• Cr: 10 wt%
• W: 15 wt%
• V: 10 wt%
• Re: 0.6 wt%

Performance Comparison of Key Trials

The optimized alloy demonstrated:

• Hardness: 65 HRC (exceeding the target of 60 HRC).
• Wear resistance: 3.5 times that of the base steel (Q235).
• Crack-free overlay: No cracks observed even without preheating, indicating excellent weldability.
• Good metallurgical bonding: Tensile test of overlay-base joint showed failure in the base metal, confirming strong interface bonding.

Microstructural Analysis

The metallographic examination of the optimized overlay alloy revealed the following microstructural features:

Matrix structure: Predominantly martensite with approximately 5–8% retained austenite. The high carbon equivalent of the alloy (approximately 0.6%) combined with the rapid cooling rate during overlay welding promotes martensite formation, which is the primary hardening mechanism.

Carbide phases: Extensive dispersion of hard carbides including:

• M6C (Cr,Fe)6C — formed at lower cooling rates, contributing to toughness.
• MC (W,V)C — high-temperature stable carbides providing exceptional wear resistance.
• M7C3 — intermediate carbide phase formed in the transition zone.

Rare earth effect: The 0.6% rare earth addition (primarily La and Ce) serves multiple functions:

• Refines grain structure by modifying nucleation sites.
• Purifies the molten pool by combining with sulfur and oxygen.
• Reduces hot cracking susceptibility by modifying solidification morphology.
• Improves the bonding between carbide particles and the martensitic matrix.

Phase Distribution and Hardness Gradient

Weldability and Process Characteristics

The optimized alloy powder block demonstrated excellent welding process characteristics:

• Good fluidity: The molten pool spreads uniformly without excessive undercut.
• Low spatter: The alloy composition minimizes arc instability.
• No preheating required: The low carbon equivalent and rare earth addition suppress both hot and cold cracking.
• Compatible with conventional processes: Can be deposited using SMAW, SAW, or HVOF processes.
• Multi-pass capability: No interpass cracking observed in multi-pass deposits up to 5 mm thick.

The welding parameters used for testing were:

• Process: SMAW with flux-cored wire or powder block
• Current: 180–220 A
• Voltage: 28–32 V
• Travel speed: 150–250 mm/min
• Base material: Q235 or 45 steel
• Preheat: 0 °C (ambient)

Engineering Applications and Implications

This optimized iron-based overlay alloy is particularly suitable for:

• Mining equipment components (shovel buckets, conveyor rollers).
• Cement industry wear parts (grinding balls, mill liners).
• Agricultural machinery (plowshares, harrow teeth).
• Power plant components (pneumatic conveying pipes, cyclone linings).
• Construction machinery (excavator bucket teeth, bulldozer blades).

The cost-effectiveness of this alloy is a significant advantage over cobalt-based or nickel-based overlay alloys, as iron-based alloys are substantially less expensive while providing comparable wear resistance for many applications.

Study Insights and Reflections

This paper demonstrates the power of statistical experimental design in materials optimization. The L9(3^4) orthogonal array approach allows efficient identification of the optimal composition without exhaustive experimentation, a methodology that remains highly applicable to modern materials development. The inclusion of rare earth as a fourth optimization factor is particularly insightful — rare earth additions in small quantities (0.2–1.0%) can dramatically improve the weldability and microstructural quality of hardfacing alloys. The achieved hardness of 65 HRC with crack-free deposition without preheating represents a significant practical achievement, as many hardfacing alloys require controlled preheating to prevent cracking. For engineers selecting overlay alloys for wear-critical components, this study provides a validated composition that balances hardness, toughness, and weldability in an economically attractive iron-based system.