Research on the Relationship Between Wear Resistance and Hardness of Hardfacing Metals

Literature Overview

This paper by Wang Lianfang, Chen Bo, and Jin Xilong, published in Welding in 1991 (No. 6, pp. 6-9), presents a fundamental research study on the relationship between wear resistance and hardness of hardfacing metals. Conducted at Tsinghua University, this research challenges the common assumption that hardness is the primary determinant of wear resistance in hardfacing deposits. The study demonstrates that the relationship between these two properties is complex and non-linear, with hardness not being the decisive indicator of wear performance.

Core Scientific Findings

Challenging Conventional Wisdom

In the welding and hardfacing industry, hardness has traditionally been used as the primary criterion for selecting hardfacing consumables. The assumption is straightforward: harder deposits provide better wear resistance. This paper systematically challenges this assumption through comprehensive experimental investigation.

The research methodology involved:

• Testing multiple hardfacing alloys with varying hardness levels
• Conducting standardized wear tests under controlled conditions
• Analyzing the correlation between measured hardness and actual wear performance
• Investigating the microstructural features that influence wear mechanisms

Key Findings

The data clearly shows that beyond a certain hardness threshold, further increases in hardness do not proportionally improve wear resistance. In some cases, very hard deposits exhibit worse wear performance than moderately hard deposits due to brittleness and susceptibility to micro-cracking.

Wear Mechanism Analysis

The study identifies multiple wear mechanisms that operate simultaneously, with the dominant mechanism depending on the specific service conditions:

1. Abrasive wear: Hardness is the primary factor, but only up to a threshold. Beyond this point, toughness becomes more important.
2. Adhesive wear: Governed by the material's resistance to cold welding and friction. Hardness alone is insufficient; surface chemistry and microstructure play critical roles.
3. Fatigue wear: Repeated cyclic loading causes subsurface crack initiation and propagation. Hardness without adequate toughness leads to premature fatigue failure.
4. Erosive wear: Impact of solid particles or fluid jets. The optimal hardness for erosive wear depends on particle size, velocity, and angle of impact.
5. Corrosive wear: Combined chemical and mechanical action. Hardness is less relevant than corrosion resistance and passive film stability.

Microstructural Factors Beyond Hardness

Phase Composition and Distribution

The study emphasizes that the type, size, shape, and distribution of reinforcing phases (carbides, intermetallics) are critical for wear performance:

• Carbide type: WC and Cr7C3 provide different wear resistance characteristics
• Carbide size: Fine, uniformly distributed carbides outperform coarse, clustered carbides
• Carbide morphology: Rounded carbides resist crack propagation better than angular carbides
• Matrix-carbide interface: Strong bonding prevents carbide pullout during wear

Matrix Properties

The matrix phase properties significantly influence overall wear performance:

• Toughness: Absorbs energy from impact and prevents crack propagation
• Ductility: Allows plastic deformation to accommodate stress concentrations
• Thermal stability: Maintains properties at elevated operating temperatures
• Corrosion resistance: Prevents chemical attack that accelerates wear

Microstructural Optimization

Engineering Practice Implications

Consumable Selection Strategy

Based on this research, hardfacing consumable selection should follow a multi-criteria approach:

1. Identify the primary wear mechanism in the specific application (abrasive, adhesive, fatigue, erosive, or corrosive)
2. Select appropriate hardness range based on the wear mechanism, not simply the maximum available hardness
3. Evaluate microstructural features through metallurgical examination of the deposit
4. Consider the operating environment including temperature, chemical exposure, and loading conditions
5. Perform field trials to validate laboratory predictions under actual service conditions

Application-Specific Recommendations

Testing Protocol Development

The paper advocates for comprehensive wear testing that goes beyond simple hardness measurement:

1. Pin-on-disc testing: For general abrasive wear evaluation
2. Ball-on-disc testing: For contact stress and fatigue wear
3. Slurry wear testing: For erosive wear conditions
4. Corrosion wear testing: For combined chemical and mechanical wear
5. High-temperature wear testing: For elevated temperature applications
6. Field testing: For validation under actual service conditions

Key Reflections and Study Insights

This research is foundational for understanding the complex relationship between material properties and wear performance. The finding that hardness is not the sole determinant of wear resistance has profound implications for hardfacing consumable selection and application engineering.

The paper's methodology — combining laboratory testing with microstructural analysis — provides a framework for systematic evaluation of hardfacing materials. This approach should be adopted by all engineers involved in hardfacing material selection and qualification.

The concept of "optimal hardness" rather than "maximum hardness" represents a paradigm shift in hardfacing engineering. Engineers must understand the specific wear mechanism in their application and select materials that optimize the balance of hardness, toughness, and other relevant properties.

Practical Case Study

Consider a typical application: hardfacing the wear surfaces of a conveyor chute in a coal handling plant. The wear mechanism is primarily abrasive, with large coal particles impacting and sliding across the surface. Conventional wisdom would suggest selecting the hardest available hardfacing alloy. However, this research indicates that a moderately hard deposit (HV 500-600) with fine, uniformly distributed carbides and adequate toughness will outperform a very hard but brittle deposit (HV 800+) in this application.

The brittle hard deposit will crack and spall under the impact of coal particles, exposing the base material to rapid wear. The moderately hard deposit will deform slightly under impact, distributing the stress and maintaining surface integrity over a longer service life.

Reference Value and Outlook

This paper provides fundamental scientific insight that should inform all hardfacing engineering decisions. The complexity of the hardness-wear relationship underscores the need for comprehensive material characterization and application-specific testing in hardfacing projects.

The research methodology and findings are directly applicable to modern hardfacing challenges, including:

• Selection of hardfacing materials for oil and gas pipeline components
• Optimization of wear-resistant coatings for mining equipment
• Development of advanced hardfacing alloys for extreme service conditions
• Quality control and acceptance criteria for hardfacing operations

Future research should focus on developing predictive models that relate microstructural features to wear performance, enabling more rational material selection without extensive trial-and-error testing. The integration of computational materials science with experimental validation offers promising approaches to accelerating hardfacing material development.

This fundamental research from 1991 remains highly relevant today, demonstrating the enduring value of scientific inquiry in advancing engineering practice. Engineers who understand and apply these principles will achieve superior hardfacing performance and extended component service life.