Microstructural Evolution of Hypoeutectic, Near-Eutectic, and Hypereutectic High-Carbon Cr-Based Hard-Facing Alloys

A series of high-carbon Cr-based hard-facing alloys were successfully fabricated on a substrate of 0.45 pct C carbon steel by gas tungsten arc welding (GTAW) process using various alloy fillers with chromium and chromium carbide, CrC (Cr:C = 4:1) powders. These claddings were designed to observe hypoeutectic, near-eutectic, and hypereutectic structures with various (Cr,Fe)(23)C-6 and (Cr,Fe)(7)C-3 carbides at room temperature. According to X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and optical microscopy (OM), in 3.8 pct C cladding, the microstructure consisted of the primary carbides with outer shells (Cr,Fe)(23)C-6 surrounding (Cr,Fe)(7)C-3 cores and [alpha + (Cr,Fe)(23)C-6] eutectic structures. In 5.9 pct C cladding, the composite comprised primary (Cr,Fe)(7)C-3 as the reinforcing phase and [alpha + (Cr,Fe)(7)C-3] eutectic structures as matrix. Various morphologies of carbides were found in primary and eutectic (Cr,Fe)(7)C-3 carbides, which included bladelike and rodlike (with a hexagonal cross section). The 5.9C cladding with great amounts of primary (Cr,Fe)(7)C-3 carbides had the highest hardness (approximately HRC 63.9) of the all conditions.