CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High-Hardness Wear-Resistant and Crack-Resistant Cladding Electrodes
Literature Overview
This 1999 publication by Li Wushen, Song Bingzhang, Feng Lingzhi, and Song Qingyi, conducted under the Hebei Provincial Major Science and Technology Research Project, was published in China Mechanical Engineering. The study represents a significant advancement in electrode-type hardfacing consumable development, addressing the long-standing engineering challenge of achieving simultaneously high hardness and good crack resistance in deposited overlay layers. The collaboration between Tianjin University (academic expertise) and Xingtai Special Roll Co. (industrial application) exemplifies the effective industry-academia partnership model for materials development.
Core Technical Challenges and Solutions
The central problem addressed in this research is the inherent contradiction between hardness and crack resistance in hardfacing alloys. High-carbon, high-chromium martensitic and austenitic systems can achieve hardness values exceeding 60 HRC, but the very features that provide hardness — retained austenite transformations, high carbon content, and hard carbide phases — also promote cracking during solidification and cooling.
Electrode Design Philosophy
The authors adopted a multi-strategy approach to resolve this contradiction:
| Strategy | Mechanism | Effect on Hardness | Effect on Crack Resistance |
|---|---|---|---|
| Flux composition optimization | Control dilution and cooling rate | Moderate | Significant improvement |
| Carbon content management | Balance carbide volume fraction | High | Requires careful control |
| Alloying with Mn, Ni | Stabilize austenite, refine grain | Moderate increase | Excellent improvement |
| Electrode coating formulation | Controlled melting sequence | Enables high hardness | Reduces hot cracking |
| Mechanical mixing in flux | Homogenize composition | Uniform hardness | Reduces segregation |
Metallurgical Design of the Electrode
The electrode development involved careful selection of the core wire composition and the flux coating formulation. The core wire was designed with a high carbon content (2.0-3.5 wt%) combined with chromium (12-18 wt%), manganese (1.0-2.0 wt%), and nickel (2.0-4.0 wt%). The flux coating served multiple functions:
- Deoxidation: Providing aluminum and silicon deoxidizers to refine the weld metal
- Alloying: Adding additional carbon and chromium through alloying elements in the flux
- Grain refinement: Controlling solidification grain structure through nucleation agents
- Cooling rate modification: Controlling the thermal cycle to promote favorable phase transformations
- Slag protection: Preventing atmospheric contamination during solidification
Performance Results
The developed electrode achieved the following performance characteristics:
| Parameter | Target | Achieved | Standard Reference |
|---|---|---|---|
| Hardness (as-welded) | ≥ 55 HRC | 58-62 HRC | GB/T 12470 |
| Hardness (after tempering 500°C) | ≥ 50 HRC | 52-56 HRC | — |
| Crack sensitivity index | ≤ 1.0 | 0.6-0.8 | Internal criterion |
| Wear resistance (vs. Q235 base) | ≥ 3× | 4-6× | Pin-on-disk test |
| Bond strength | ≥ 200 MPa | 220-280 MPa | Peel test |
The key innovation was the development of a flux formulation that incorporated fine-grained alloying powders mixed into the coating composition, ensuring that the molten metal composition remained within a narrow window that promoted crack-free solidification while still achieving high hardness through the precipitation of M₇C₃ and M₂₃C₆ type chromium carbides.
Engineering Application Context
The primary application target was special rolling mill rolls, which are subjected to extreme abrasive and adhesive wear during the hot rolling process. The roll surface must withstand:
- Temperatures up to 1,200°C during rolling operations
- Severe abrasive contact with hot steel slabs
- Thermal cycling causing repeated expansion and contraction
- High compressive and shear stresses from roll force
The developed electrode enabled field application on work rolls where conventional hardfacing electrodes suffered from spalling and premature failure. The improved crack resistance meant that the deposit could be applied with fewer passes and lower interpass temperatures, reducing production time and improving productivity.
Technical Insights and Practical Recommendations
Several important lessons emerge from this research:
- Flux composition is as critical as electrode composition: The flux is not merely a passive protective medium but an active participant in determining the final weld metal properties. Engineers should not overlook flux formulation when evaluating hardfacing consumables.
- The "crack-free" requirement does not mean "no cracks possible": Rather, it means designing the system so that any micro-cracks that form are arrested by the microstructure (e.g., through crack deflection at carbide particles or crack arrest at phase boundaries).
- Post-weld heat treatment is essential for optimizing properties: The as-welded structure contains significant retained austenite that provides toughness but limits hardness. Controlled tempering at 450-550°C transforms retained austenite to tempered martensite, increasing hardness while maintaining adequate toughness.
- Compatibility with base material must be verified: The electrode was designed for application on low-alloy steel roll shells, and proper joint qualification testing (per NB/T 47014 or equivalent) should be performed for each specific base material combination.
This research demonstrates that the seemingly contradictory requirements of high hardness and crack resistance can be reconciled through systematic metallurgical design of both the electrode core and flux coating, providing a practical solution for industrial hardfacing applications where both wear resistance and structural integrity are required.