Abrasive Wear Behavior of Fe-Cr-C Wear-Resistant Overlay Alloy

Literature Overview

This 2010 study by Wang Zhihui, He Dingyong, Jiang Jianmin, and Cui Li from the College of Material Science and Engineering, Beijing University of Technology, investigates the abrasive wear behavior of an Fe-Cr-C wear-resistant overlay alloy system. Published in The International Journal of Welding, this research was supported by the Beijing Municipal Education Commission Science and Technology Program. The study provides a systematic examination of how chromium content, carbon content, and microstructure evolution influence the abrasive wear performance of iron-based overlay alloys, which are widely used in mining, cement, and material handling industries.

Experimental Design and Alloy Matrix

The researchers designed a series of Fe-Cr-C overlay alloys with varying chromium content (10, 15, 20, 25, and 30 wt%) and carbon content (1.5, 2.5, and 3.5 wt%) to systematically evaluate the effect of composition on wear behavior. The overlay layers were deposited using submerged arc welding (SAW) with flux-cored wire electrodes on Q235 carbon steel substrates.

Microstructure Evolution with Composition

The microstructural evolution of the overlay layers was analyzed using optical microscopy and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The key observations were:

• Low Cr alloys (10–15 wt% Cr): Predominantly martensitic matrix with dispersed cementite (Fe₃C) and some chromium carbides (Fe₃(C,Cr)). The microstructure was relatively coarse with carbide networks along prior austenite grain boundaries.
• Medium Cr alloys (20–25 wt% Cr): Transition to a eutectic microstructure with chromium carbides (Cr₇C₃ and Cr₂₃C₆) dispersed in a martensitic matrix. The carbide volume fraction increased from approximately 15% to 35% with increasing Cr and C content.
• High Cr alloys (30 wt% Cr): Fully eutectic structure with a high volume fraction (40–55%) of chromium carbides in a martensitic or partially austenitic matrix. The carbide morphology changed from blocky (at lower C) to worm-like and vermicular (at higher C).

The carbon content played a critical role in determining the carbide morphology and distribution. Higher carbon content promoted the formation of Cr₇C₃ (which has a higher carbon-to-chromium ratio than Cr₂₃C₆), resulting in finer and more uniformly distributed carbide particles.

Abrasive Wear Testing Methodology and Results

Abrasive wear testing was conducted using a standard two-body abrasive wear test (ASTM G65 ring-on-disc method) with 600# SiC abrasive paper under normal loads of 10 N, 20 N, and 40 N. The wear track length was 1000 m for each test condition.

The results revealed an optimal composition window around 25 wt% Cr and 3.5 wt% C, beyond which further increases in Cr and C content led to diminishing returns and even degradation of wear resistance due to excessive carbide brittleness.

Wear Mechanism Analysis

The researchers identified three distinct wear mechanisms operating at different stages of the wear process:

1. Initial stage (0–100 m): Abrasive particles plough through the soft martensitic matrix, creating shallow grooves. The hard carbide particles resist penetration and act as obstacles, deflecting the abrasive particles. The wear rate is initially high but decreases rapidly as a compacted layer forms on the surface.
2. Steady-state stage (100–800 m): The wear surface reaches a quasi-equilibrium condition where the rate of material removal equals the rate of surface compaction. The dominant mechanism is micro-cutting around carbide particles, with the matrix material being preferentially removed. The wear rate stabilizes at a relatively constant value.
3. Final stage (800–1000 m): At higher loads or longer sliding distances, carbide particles begin to be pulled out from the matrix due to fatigue at the particle-matrix interface. The exposed matrix material is rapidly removed, leading to an increase in wear rate. This stage is characterized by micro-fracture and delamination.

The transition from steady-state to final-stage wear was found to be strongly dependent on the carbide-matrix bonding strength, which is influenced by the thermal expansion coefficient mismatch between the carbide and matrix phases. Alloys with finer, more uniformly distributed carbides (such as the 25Cr-3.5C composition) maintained steady-state wear for longer distances before carbide pull-out initiated.

Engineering Practice Recommendations

Based on the comprehensive study, the following recommendations are provided for engineering application:

• For general abrasive wear service: Fe-20Cr-2.5C composition provides an excellent balance of wear resistance and toughness, suitable for most material handling applications.
• For severe abrasive wear: Fe-25Cr-3.5C offers the highest wear resistance but requires careful consideration of the substrate compatibility and welding procedure to prevent cracking.
• The overlay thickness should be at least 4–5 mm for severe service to ensure adequate remaining thickness after significant wear.
• Post-weld cooling rate management is critical; rapid cooling (water quench equivalent) maximizes martensite formation and hardness, while slow cooling (air cool) reduces residual stresses at the expense of some hardness.
• For applications involving both abrasion and corrosion, the 20–25 wt% Cr range provides adequate chromium content for passive film formation while maintaining good wear resistance.

This study provides a valuable quantitative foundation for alloy selection in Fe-Cr-C overlay systems, demonstrating that the optimal composition depends on the specific wear mechanism and service conditions rather than simply maximizing hardness or carbide content.