Effect of Vanadium on Microstructure and High-Temperature Properties of Argon Arc Overlay Layer on Semi-High Speed Steel

Literature Overview and Technical Context

This study focuses on the effect of vanadium addition on the microstructure and high-temperature performance of argon arc welding (GTAW/TIG) overlay layers deposited on semi-high speed steel substrates. Semi-high speed steels, such as W6Mo5Cr4V2 and similar grades, are widely used in cutting tools, dies, and wear-resistant components where a balance of hardness, toughness, and red hardness (hot hardness) is required. When these components suffer from surface wear or damage, overlay repair welding provides an economical and effective restoration method. However, the high-temperature performance of the overlay layer is critical for maintaining cutting and wear resistance during hot working operations, making the selection of alloying elements—particularly vanadium—a key design consideration.

Experimental Framework and Process Parameters

The research employed gas tungsten arc welding (GTAW) to deposit overlay layers on semi-high speed steel substrates, with vanadium content varied from 0 to 3.0 wt% in the filler wire composition. The base filler composition was designed to match the semi-high speed steel matrix, containing approximately 0.8 wt% C, 4.0 wt% Cr, 5.0 wt% W, and 1.0 wt% Mo, with vanadium as the variable element. The welding was performed in a multi-pass configuration to achieve a minimum overlay thickness of 4 mm.

GTAW Welding Parameters

Parameter	Value	Rationale
Welding Current	150–180 A	Adequate penetration for tool steel
Arc Voltage	18–22 V	Stable arc with tungsten electrode
Travel Speed	60–80 mm/min	Controlled heat input for fine grain
Shielding Gas	100% Argon, 15–20 L/min	Prevent oxidation of reactive elements
Interpass Temperature	< 150°C	Limit grain growth in previous passes
Number of Passes	4–6	Achieve target overlay thickness
Electrode	Thoriated tungsten, 2.4 mm	Stable arc, good wetting

The low heat input characteristic of GTAW is advantageous for tool steel overlays, as it minimizes grain growth and limits the diffusion of alloying elements between passes, preserving the intended composition of each layer.

Microstructural Characterization and Vanadium Effects

The microstructural analysis revealed that vanadium plays a multifaceted role in the overlay microstructure, influencing both the matrix transformation and the carbide precipitation behavior. At the as-welded condition, the matrix consists primarily of martensite with retained austenite, and the vanadium carbide content and morphology vary significantly with vanadium addition.

Microstructural Evolution

Vanadium (wt%)	Matrix Structure	Primary Carbides	Secondary Carbides	Retained Austenite (%)	Grain Size (μm)