Microstructure and Mechanical Properties Analysis of Mo-Strengthened Fe-Cr-C Cladding Materials

Overview and Motivation

Fe-Cr-C based cladding materials are widely used for wear-resistant overlay applications in mining, cement, and power generation industries. The addition of molybdenum (Mo) is a well-established strategy to enhance solid solution strengthening, improve tempering resistance, and refine the microstructure. This literature review examines the influence of Mo content (ranging from 0 wt.% to 8 wt.%) on the microstructure, hardness, wear resistance, and fracture toughness of Fe-Cr-C cladding alloys deposited by submerged arc welding (SAW) and gas metal arc welding (GMAW).

Compositional Design and Microstructural Response

Mo acts as a potent carbide former, preferentially forming Mo₂C and M₆C carbides that are harder (approximately 2000–2500 HV) and more thermally stable than the Cr-rich M₇C₃ carbides. At low Mo levels (0–2 wt.%), the microstructure is dominated by martensite with dispersed Cr-rich carbides, and the hardness is moderate (450–550 HV). As Mo increases to 4–6 wt.%, the Mo₂C carbides precipitate within the martensitic matrix, providing a synergistic hardening effect that elevates the hardness to 600–750 HV. However, beyond 6 wt.%, excessive Mo₂C carbide formation leads to brittleness, reduced ductility, and potential cracking during solidification.

Mechanical Properties and Wear Performance

The optimal Mo content for the Fe-Cr-C system is identified as 4–6 wt.%, where the hardness reaches a maximum of 730 HV, the abrasive wear resistance is superior, and the elongation remains acceptable (9–12 %). At 8 wt.% Mo, the excessive carbide content reduces ductility and increases susceptibility to cracking, particularly in multi-pass weld overlays where the reheat cycle can promote carbide coarsening at prior austenite grain boundaries.

Engineering Practice and Process Considerations

For SAW cladding using flux-cored wire, the Mo content in the filler wire must be carefully controlled because the flux composition can influence Mo recovery. For GMAW cladding using solid wire, the Mo content is more predictable, but spatter losses must be considered. The deposition rate for Fe-Cr-C Mo-alloyed cladding is typically 3–8 kg/h for SAW and 1.5–4 kg/h for GMAW, depending on the layer thickness and number of passes. Post-weld tempering at 500–550 °C for 1–2 hours is recommended to relieve residual stresses while maintaining the hardness above 600 HV, as Mo provides excellent tempering resistance compared to Cr-only systems.

Study Insights and Reflections

This study demonstrates that Mo is a highly effective strengthening element for Fe-Cr-C cladding materials, but the benefits are non-linear and diminish beyond an optimal range. The 4–6 wt.% Mo window represents a sweet spot where solid solution strengthening, carbide precipitation hardening, and tempering resistance are balanced against ductility and crack resistance. In engineering practice, this finding is particularly relevant for overlaying large mining equipment components such as excavator buckets, crusher jaws, and conveyor rollers, where the combination of high hardness and adequate toughness is essential to prevent catastrophic spalling failure. The study also highlights the importance of matching the cladding process to the Mo content: GMAW is preferred for higher Mo levels because the higher heat input can be better controlled to avoid excessive carbide coarsening, whereas SAW is more economical for lower Mo levels where the dilution tolerance is wider. This research provides a solid foundation for rational alloy design of Mo-strengthened cladding materials tailored to specific wear environments.