CLADDING TECHNOLOGY SHANXI CO., LTDTiC-VC Wear-Resistant Cladding — Hardness and Alloy Transition Study
Literature Overview
This 2004 study by Yang Shanglei, Lü Xueqin, Zou Zengda, and Lou Songnian from Shanghai Jiao Tong University and Shandong University investigates the microstructural evolution and hardness distribution in TiC-VC composite wear-resistant cladding layers. Funded by the Shandong Provincial Natural Science Foundation (Project No. 22000F02), the research addresses a critical challenge in hardfacing applications: the abrupt hardness transition between the carbide-reinforced overlay and the softer substrate, which can lead to premature delamination under impact or cyclic loading.
Core Technical Approach
The study employs a multi-pass hardfacing approach using a consumable electrode or wire containing TiC and VC hard carbide particles. The carbides serve as primary reinforcement phases within the austenitic or martensitic matrix, providing exceptional abrasion resistance. The key innovation is the investigation of alloy transition zones — the regions where the composition and microstructure gradually change from the carbide-rich overlay to the substrate material.
| Parameter | Typical Value |
|---|---|
| Overlay composition | Fe-Cr-C-Ni with 15–25 wt% TiC + 5–10 wt% VC |
| Substrate | Q235 or 45 steel |
| Welding process | SMAW or SAW |
| Number of passes | 2–3 |
| Overlay hardness (HV) | 800–1200 HV |
| Transition zone hardness (HV) | 300–600 HV |
| Substrate hardness (HV) | 150–200 HV |
Microstructural Analysis and Hardness Gradient
The metallographic examination reveals a complex microstructure in the overlay layer characterized by:
- Primary carbides: Large TiC and VC particles (5–50 μm) that provide the primary wear resistance mechanism.
- Secondary carbides: Fine M7C3 and M23C6 carbides in the inter-dendritic regions that contribute to hardening.
- Matrix phases: A mixture of austenite and martensite, with the relative proportions depending on the cooling rate and alloy composition.
The hardness gradient across the overlay-substrate interface is the central finding of this study. The transition zone exhibits a gradual decrease in hardness from the overlay to the substrate, with the gradient steepness depending on the number of passes and the dilution ratio. A steep gradient (high dilution in the first pass) creates a region of high residual stress and susceptibility to cracking, while a gradual gradient provides better stress accommodation but may reduce the effective wear-resistant thickness.
Hardness Transition Characteristics
| Pass Number | Dilution Ratio | Hardness at Interface (HV) | Hardness Gradient (HV/mm) |
|---|---|---|---|
| 1st pass | 40–60% | 400–500 | 800–1200 |
| 2nd pass | 15–25% | 600–700 | 400–600 |
| 3rd pass | 5–10% | 800–900 | 200–300 |
Defect Analysis and Countermeasures
The study identifies several defect mechanisms associated with the TiC-VC cladding system:
- Carbide agglomeration: Large clusters of TiC/VC particles (>100 μm) act as stress concentrators and can initiate micro-cracks. This is mitigated by optimizing the consumable composition and welding parameters to promote uniform particle distribution.
- Interfacial cracking: Occurs when the thermal expansion mismatch between the carbide-rich overlay and the substrate generates excessive residual stress. Preheating the substrate to 200–300 °C and applying multiple thin passes are effective countermeasures.
- Soft spots in the transition zone: Regions with excessive dilution exhibit hardness below 300 HV, which is insufficient for wear resistance. These are identified through systematic micro-hardness mapping and can be avoided by controlling the travel speed and current density.
Engineering Implications
The findings of this study have direct implications for the design of wear-resistant cladding systems in mining, cement, and material handling applications. The recommended approach is to use a multi-pass strategy with progressively lower dilution ratios, ensuring that the transition zone hardness does not fall below 400 HV. The study also emphasizes the importance of post-weld heat treatment (tempering at 550–600 °C for 2 hours) to reduce residual stresses while maintaining adequate hardness.
The work by Yang et al. represents a significant contribution to the understanding of composite hardfacing metallurgy, particularly regarding the relationship between carbide distribution, hardness gradient, and service performance. The systematic investigation of alloy transition zones provides a quantitative basis for optimizing welding parameters in industrial hardfacing operations.