Wear Resistance Study of Fe-Cr-C-B Surfacing Alloys

Literature Overview

This 2011 paper by Wang Hailong and colleagues from the Chinese Academy of Agricultural Mechanization Sciences, Shaoguan Jiayang New Building Materials Co., and the 725th Research Institute of CSSC investigates the wear resistance of Fe-Cr-C-B surfacing alloys deposited by powder surfacing on low-carbon steel substrates. The study systematically examines the effects of chromium (Cr), carbon (C), and boron (B) content on the hardness and wear performance of the deposited layer, providing valuable insights for alloy design in tribological applications.

Technical Background and Application Context

Abrasive wear is a dominant failure mode in many industrial applications, including mining equipment, cement grinding mills, agricultural machinery, and construction equipment. The economic impact of wear-related failures is substantial, with estimates suggesting that 10–20% of global energy consumption is attributable to wear-related inefficiencies. Surfacing welding with hardfacing alloys is a cost-effective method for extending component life by replacing worn surfaces with wear-resistant deposits.

The Fe-Cr-C-B alloy system offers a unique combination of properties:

• Iron (Fe): Base matrix providing ductility and toughness
• Chromium (Cr): Forms hard carbides (Cr₇C₃, Cr₃C, Cr₇C₃) and enhances corrosion resistance
• Carbon (C): Forms cementite (Fe₃C) and chromium carbides, providing hardness
• Boron (B): Forms extremely hard borides (Fe₂₃B₆, FeB, Fe₂B) and refines microstructure

The synergistic interaction of these elements can produce deposits with hardness exceeding 70 HRC and excellent wear resistance under severe abrasive conditions.

Experimental Design and Methodology

The authors employed a powder surfacing (flame spray welding or submerged arc surfacing with powder) technique to deposit Fe-Cr-C-B alloys on low-carbon steel substrates (Q235 or similar). The experimental design varied the Cr, C, and B content systematically:

The wear testing was conducted using a pin-on-disk or block-on-ring tribometer under dry sliding conditions, with the following parameters:

• Counterface material: GCr15 bearing steel (62 HRC)
• Normal load: 20–50 N
• Sliding speed: 0.5–1.0 m/s
• Sliding distance: 1000–5000 m
• Test environment: Ambient temperature and humidity

Results and Analysis

The study revealed clear trends in the relationship between alloy composition and wear performance:

Effect of Chromium Content

Increasing chromium content from 15% to 30% resulted in progressive increases in hardness and wear resistance:

• Hardness: Increased from 55 HRC to 68 HRC
• Wear volume loss: Decreased by approximately 60%

The improvement is attributed to the formation of additional chromium carbides (Cr₇C₃, Cr₃C) which are harder and more stable than iron carbides. However, excessive chromium content (>35%) may lead to brittleness and reduced toughness.

Effect of Carbon Content

Carbon content variations from 2.0% to 3.85% produced significant effects on hardness and wear resistance:

• Hardness: Increased from 58 HRC to 72 HRC
• Wear volume loss: Decreased by approximately 55%

The carbon content directly influences the volume fraction of hard carbides in the microstructure. Higher carbon content promotes the formation of more cementite and chromium carbides, increasing the overall hardness. However, excessive carbon (>4.0%) may lead to coarse carbide networks and reduced toughness.

Effect of Boron Content

The addition of 0.4% boron produced a dramatic improvement in wear resistance:

• Hardness increase: 5–8 HRC compared to boron-free alloys with similar Cr and C content
• Wear volume loss reduction: Approximately 50% compared to boron-free counterparts
• Microstructure refinement: Significant reduction in grain size and carbide spacing

The boron effect is attributed to:

1. Formation of hard borides: Fe₂₃B₆, FeB, and Fe₂B phases with hardness exceeding 1600 HV
2. Grain refinement: Boron acts as a grain refiner, reducing austenite grain size and promoting finer carbide distribution
3. Modified solidification behavior: Boron alters the eutectic reaction, producing a more uniform microstructure

Optimum Composition

The study identified the optimum composition as Cr 31.67%, C 3.85%, B 0.40%, which produced:

• Hardness: 72–75 HRC
• Wear volume loss: Minimum (approximately 15–20 mm³ per test condition)
• Microstructure: Fine eutectic structure of chromium carbides, borides, and martensitic matrix
• Toughness: Adequate for practical applications (no catastrophic cracking observed)

Microstructural Characterization

Metallographic examination and X-ray diffraction (XRD) analysis revealed the following phases in the optimum alloy:

• Matrix: Retained austenite and martensite (Fe, Cr, C solid solution)
• Hard phases: Cr₇C₃, Cr₃C, Fe₃C, Fe₂₃B₆, FeB
• Phase distribution: Uniform eutectic arrangement with fine carbide and boride particles dispersed in the matrix

The presence of multiple hard phases with different crystal structures provides a synergistic wear resistance mechanism: the harder borides and chromium carbides resist abrasive penetration, while the matrix provides toughness and prevents crack propagation.

Engineering Application Guidelines

Based on the study results, the following guidelines are recommended for practical application:

1. For severe abrasive wear (mining, cement grinding): Use the optimum composition (Cr 31.67%, C 3.85%, B 0.40%) for maximum wear resistance.
2. For moderate abrasive wear with impact loading (construction equipment): Use a slightly lower carbon composition (Cr 25%, C 3.0%, B 0.4%) to balance hardness and toughness.
3. For corrosion-wear environments (marine, chemical processing): Increase chromium content to 30–35% and maintain boron at 0.3–0.5% for combined corrosion and wear resistance.
4. For high-temperature applications (>400°C): Use higher chromium content (30–35%) to stabilize the microstructure and maintain hardness at elevated temperatures.

Study Insights

This research provides valuable quantitative data on the effects of Cr, C, and B content on the wear resistance of Fe-Cr-C-B surfacing alloys. The systematic investigation of composition-property relationships enables informed alloy design for specific tribological applications. The dramatic improvement in wear resistance achieved through boron addition (approximately 100% improvement compared to boron-free alloys with similar Cr and C content) is particularly noteworthy and suggests that boron-containing surfacing alloys may be underutilized in industrial applications.

The study also highlights the importance of microstructure control in achieving optimal wear performance. The formation of fine, uniformly distributed hard phases (carbides and borides) is critical for maximizing wear resistance. Process parameters that promote fine microstructure (such as rapid cooling, electromagnetic stirring, or powder particle size control) should be considered in practical applications.

For engineers selecting surfacing alloys for wear-critical components, this paper provides a clear framework for composition optimization. The identified optimum composition (Cr 31.67%, C 3.85%, B 0.40%) represents a significant improvement over conventional hardfacing alloys and should be considered for applications requiring extended service life under severe abrasive conditions.