Abrasive Wear Performance of WC-Mn13 Weld Overlay Composite Material

Literature Overview

This 2007 publication by Wu Hong, Peng Jianhong, Xu Yunhua, and Huo Qunying from the Xi'an University of Architecture and Technology Wear-Resistant Materials Research Institute investigates the abrasive wear performance of a composite weld overlay material combining tungsten carbide (WC) particles with austenitic manganese steel (Mn13). The study was supported by the National Natural Science Foundation of China and the 863 Program (grant 2002AA-302509), reflecting its significance in the context of China's strategic materials development. The composite concept leverages the exceptional hardness of WC (approximately 2,000-2,400 HV) with the work-hardening capability of Mn13 austenitic steel to create a synergistic wear-resistant system.

Composite Design Philosophy

The design of the WC-Mn13 composite weld overlay is based on a dual-mechanism wear resistance strategy:

1. Hardness-based resistance: WC particles provide high hardness resistance against abrasive particles, particularly effective against hard, angular abrasives such as quartz, granite, and silicon carbide.
2. Work-hardening resistance: The Mn13 austenitic matrix undergoes severe plastic deformation during impact-abrasion, transforming from soft austenite (approximately 200 HV) to work-hardened martensite (approximately 400-500 HV) with increased dislocation density and deformation twins.

This dual mechanism makes the composite particularly effective in impact-abrasion environments, such as those encountered in mining equipment, shot blasting machines, and material handling systems.

The following table presents the composition and properties of the composite system:

Microstructural Characteristics

The as-deposited microstructure of the WC-Mn13 composite overlay exhibits a three-phase system:

• Austenitic matrix: The Mn13 matrix solidifies as austenite due to the high manganese content, which stabilizes the face-centered cubic (FCC) phase. The austenite grains are typically 50-150 μm in size.
• WC particles: Tungsten carbide particles are distributed throughout the matrix. The distribution uniformity depends on the powder feed stability and weld pool fluidity. Under optimal conditions, the WC particles exhibit a relatively homogeneous distribution with a maximum clustering distance of 200-300 μm.
• Manganese carbides: Some WC particles undergo partial dissolution during welding, releasing tungsten and carbon into the matrix. This can lead to the formation of manganese carbides (Mn3C, Mn23C6) at grain boundaries, which may affect the toughness of the matrix.

A critical issue in WC-based composites is the thermal decomposition of WC during welding. At temperatures above 1,200 °C, WC can decompose according to the reaction: WC → W2C + C. The decomposition rate depends on the heating rate, temperature, and holding time. In the PTA process, the rapid heating and cooling rates limit the extent of WC decomposition, typically preserving 85-95% of the original WC particles. However, in processes with higher heat input, such as submerged arc welding, the decomposition rate can be higher, reducing the effective hardness contribution of the carbide phase.

Wear Testing Methodology and Results

The wear testing was conducted using a dry sliding abrasion test apparatus with standardized alumina (Al2O3) abrasive paper or a pin-on-disc configuration. The test parameters are summarized below:

The wear performance of the WC-Mn13 composite was compared with several reference materials:

The results demonstrate that the wear resistance of the WC-Mn13 composite improves monotonically with increasing WC content, with a 30 vol% WC fraction providing the optimal balance between wear resistance and toughness. Beyond 30 vol%, the improvement in wear resistance diminishes while the brittleness of the deposit increases, raising concerns about spalling failure under impact loading.

Failure Mechanism Analysis

Scanning electron microscopy (SEM) analysis of the worn surface reveals distinct wear mechanisms depending on the WC content:

• Low WC content (20 vol%): The worn surface shows evidence of both abrasive grooving and matrix plastic deformation. The WC particles act as hard obstacles that deflect abrasive particles, but the soft matrix between particles undergoes significant material removal through micro-ploughing.
• Optimal WC content (30 vol%): The worn surface is characterized by a dense distribution of WC particles protruding above the matrix surface, creating a protective hard surface. The matrix between particles is work-hardened and resistant to further material removal. The wear mechanism transitions from abrasive to a mixed abrasive-fatigue regime.
• High WC content (40 vol%): While the initial wear rate is low, the worn surface shows evidence of inter-particle cracking and spalling. The high volume fraction of brittle WC particles creates stress concentration sites that initiate cracks under impact-abrasion loading. The cracks propagate through the matrix, leading to large-scale material loss.

Engineering Applications and Recommendations

The WC-Mn13 composite weld overlay is particularly suited for the following applications:

• Mining equipment: Excavator buckets, conveyor rollers, crusher liners, and shovel teeth subjected to both abrasion and impact.
• Cement industry: Mill liners, kiln wear plates, and fan blades exposed to abrasive cement slurries.
• Power generation: Coal mill wear plates, fan blades, and duct linings in coal-fired power plants.
• Material handling: Chutes, hoppers, and conveyor components in aggregate processing.

For optimal performance, the following recommendations are made:

1. The WC volume fraction should be maintained at 25-35% to balance wear resistance and toughness.
2. The welding process should be selected to minimize WC decomposition; PTA with argon shielding is preferred over SAW.
3. The weld bead should be deposited in a single layer to avoid remelting of previously deposited WC particles.
4. Post-weld cooling should be controlled to promote the retention of austenite in the matrix, as the work-hardening response of austenite is superior to that of ferrite.
5. Regular hardness testing should be performed during service to monitor the work-hardening progression and predict remaining service life.

Study Insights and Outlook

This study provides a comprehensive understanding of the wear behavior of WC-Mn13 composite weld overlays and establishes clear guidelines for their optimization and application. The dual-mechanism wear resistance concept of combining hard ceramic particles with a work-hardening matrix is a powerful materials design strategy that has been validated through systematic experimental investigation.

The research contributes to the broader field of composite surface engineering by demonstrating that the mechanical properties of a composite weld overlay are not simply the weighted average of its constituents but are governed by complex interactions between the phases. The distribution, size, and volume fraction of the hard phase, combined with the deformation behavior of the matrix, determine the overall wear performance.

Future research directions should include the investigation of nano-sized WC particles for enhanced dispersion and reduced brittleness, the development of multi-component carbide systems (WC-Co-Cr) for improved bonding between the carbide and matrix phases, and the application of advanced characterization techniques such as nanoindentation mapping and in-situ X-ray diffraction to elucidate the wear mechanisms at the nanoscale. The integration of computational modeling with experimental validation will further accelerate the development of next-generation composite wear-resistant overlays tailored for specific industrial applications.