Effect of Vanadium on Microstructure and Properties of Iron-Based Tungsten Carbide Wear-Resistant Cladding Layers

Literature Overview and Research Motivation

Iron-based tungsten carbide (WC) wear-resistant cladding layers represent one of the most widely used surface engineering solutions for components subjected to severe abrasive and impact wear conditions. The addition of alloying elements to the iron-based matrix is a primary strategy for enhancing the mechanical properties and microstructural characteristics of these cladding layers. This study specifically investigates the effect of vanadium (V) as an alloying addition on the microstructure, hardness, wear resistance, and impact toughness of iron-based WC cladding layers produced by submerged arc welding (SAW).

The motivation for studying vanadium addition stems from its well-established role as a carbide-forming element in tool steels and wear-resistant alloys. Vanadium forms extremely hard and stable carbides (VC, V4C3) with lattice parameters and hardness values that are comparable to or exceed those of WC. The research question addressed is whether vanadium addition can enhance the performance of WC-based cladding layers beyond the already excellent properties provided by WC alone, or whether it introduces detrimental effects such as increased brittleness or reduced bonding strength.

Experimental Design and Methodology

Material System

The study examines a series of cladding compositions with varying vanadium content:

The cladding layers were deposited on Q235 carbon steel substrates using submerged arc welding with flux-cored wire (FCAW) technique. The welding parameters were held constant at: current 300 A, voltage 32 V, travel speed 250 mm/min, with a single pass depositing approximately 3 mm thickness.

Characterization Methods

The comprehensive characterization program included:

• Metallographic examination of cross-sections prepared according to ASTM E3 with Nital 5% etching
• Hardness testing using Vickers method (HV10) according to ASTM E92
• Wear testing using dry sliding wear according to ASTM G99 with alumina counterface
• Impact testing using Charpy V-notch method according to ASTM E23
• X-ray diffraction (XRD) for phase identification
• Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS)

Microstructural Analysis

Phase Evolution with Vanadium Addition

The XRD results reveal significant phase evolution as vanadium content increases:

The transition from WC-dominated to VC/V4C3-dominated carbide structure is the most significant microstructural change. At vanadium contents above 2 wt%, the vanadium carbides become the primary hard phase, replacing WC as the dominant reinforcing particle. This occurs because vanadium has a higher affinity for carbon than tungsten does, leading to preferential formation of vanadium carbides at the expense of tungsten carbides.

Grain Structure and Matrix Morphology

The matrix microstructure undergoes systematic changes with vanadium addition:

• Base sample: Retained austenite content of approximately 35% by volume, with acicular martensite in the balance. The retained austenite provides toughness through transformation toughening during wear.
• V1-V2 samples: Retained austenite decreases to 25-30% as vanadium stabilizes the martensitic transformation. The martensite morphology becomes finer and more acicular.
• V3-V4 samples: Retained austenite drops below 15%, resulting in predominantly martensitic microstructure. The matrix becomes increasingly brittle with reduced capacity for plastic deformation.

The carbide morphology also changes significantly. In the base sample, WC particles appear as irregularly shaped particles of 5-20 micrometers distributed throughout the matrix. With vanadium addition, the carbide morphology transitions to more equiaxed shapes with sizes of 2-10 micrometers, indicating a change in the nucleation and growth mechanism.

Mechanical Property Analysis

Hardness Evolution

The hardness results demonstrate a clear relationship between vanadium content and microhardness:

The hardness peaks at approximately 2-3 wt% vanadium, after which further addition produces diminishing returns or even slight decreases. This behavior can be attributed to the competing effects of:

• Increased carbide volume fraction and hardness (positive effect)
• Decreased retained austenite content (negative effect on toughness)
• Possible formation of softer phases at high vanadium content (negative effect)

Wear Resistance

The wear test results, expressed as wear volume loss under standardized conditions:

The wear resistance follows the same trend as hardness, with optimal performance at 2-3 wt% vanadium. The wear mechanism analysis reveals that the base sample exhibits primarily abrasive wear with plowing and cutting, while the vanadium-modified samples show a transition to adhesive-abrasive wear with reduced material removal rates.

Impact Toughness

The Charpy impact test results reveal a critical trade-off:

The significant reduction in impact toughness with vanadium addition is a major concern for applications involving impact loading. The loss of retained austenite, which provides transformation toughening, is the primary mechanism responsible for this degradation. Engineers must carefully evaluate the impact loading conditions of their applications when selecting vanadium content.

Engineering Applications and Optimization

Application-Specific Recommendations

Based on the comprehensive property analysis, the following recommendations are made for different application scenarios:

Process Considerations

The vanadium addition introduces several process considerations:

• Welding consumable selection: Vanadium-containing flux-cored wires require careful control of moisture content to prevent hydrogen cracking
• Preheat requirements: Preheating of 100-150°C recommended for vanadium-modified cladding to reduce cracking susceptibility
• Post-weld heat treatment: Optional tempering at 250-350°C can restore some toughness while maintaining hardness
• Layer thickness: Optimal layer thickness of 3-5 mm for single-pass deposits; multi-pass deposits require interpass temperature control

Study Insights and Conclusions

This study provides comprehensive evidence that vanadium addition to iron-based WC cladding layers significantly enhances hardness and wear resistance, with optimal performance achieved at 2-3 wt% vanadium content. The mechanism of improvement involves the formation of extremely hard vanadium carbides (VC and V4C3) that replace or supplement the tungsten carbides, creating a more effective reinforcement structure. However, the study also clearly demonstrates the inherent trade-off between wear resistance and impact toughness, with vanadium addition progressively reducing the retained austenite content that provides transformation toughening.

The practical implication is that vanadium-modified cladding layers should be selected based on the specific wear conditions of the application. For pure abrasive wear conditions without significant impact loading, the 2-3 wt% vanadium range provides optimal performance. For applications involving combined abrasive and impact wear, lower vanadium additions of 1-1.5 wt% offer the best compromise between competing property requirements. This study contributes valuable quantitative data to the ongoing optimization of wear-resistant cladding compositions, enabling engineers to make informed material selection decisions based on rigorous experimental evidence rather than empirical rules of thumb.