CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of High Crack Resistance Wear-Resistant Overlay Welding Electrodes
Overview of the Study
This literature reports on the systematic development of a new generation of flux-cored or solid overlay welding electrodes designed to simultaneously deliver high hardness (exceeding 55 HRC in the as-deposited condition) and superior crack resistance during welding on carbon and low-alloy steels. The dual requirement of wear resistance and crack resistance is notoriously difficult to achieve because the alloying additions and microstructural features that promote one property often undermine the other. The authors approach this challenge through a combined strategy of optimised alloy design, controlled flux chemistry, and process parameter refinement.
Alloy Design and Metallurgical Strategy
The core alloying philosophy is based on the formation of a fine, uniformly distributed carbide matrix within a tempered martensitic or bainitic binder phase. The key alloying elements and their roles are summarised below:
| Element | Content (wt%) | Primary Function |
|---|---|---|
| C | 2.5–3.2 | Carbide formation (Cr7C3, Cr23C6) |
| Cr | 12–16 | Carbide stabiliser, matrix hardening |
| Mo | 3–5 | Secondary hardening, temper resistance |
| V | 0.8–1.5 | Fine MC carbide dispersion |
| Ni | 1.5–3.0 | Reduced crack sensitivity, toughness enhancement |
| Mn | 1.0–2.0 | Deoxidiser, solidification control |
| Si | 0.3–0.8 | Deoxidiser, slag fluidity |
The addition of nickel is particularly noteworthy. While nickel does not directly contribute to hardness, it significantly reduces the hydrogen-induced cracking susceptibility of the deposited metal by improving the ductility of the martensitic matrix and promoting a more favourable solidification morphology. The authors report that increasing nickel content from 1.5% to 3.0% reduces the critical carbon equivalent (CE) of the electrode from 0.55% to 0.48%, which translates to a meaningful reduction in preheat requirements for thick-section applications.
Crack Resistance Mechanisms and Testing
The study employs multiple methods to evaluate crack resistance, including the following:
- Single-V Groove Restraint Test (SVRT): Performed in accordance with ASTM A949 to assess hot crack and cold crack susceptibility.
- Weld Constraint Test (WCT): Performed in accordance with ASTM A743 to measure the cracking index and threshold restraint strain.
- Hydrogen Diffusion Test: Quantification of diffusible hydrogen content in the deposited weld metal using the gas chromatography method.
The results demonstrate that the optimised electrode formulation achieves a WCT cracking index below 1.5 (classified as "very good" crack resistance) and a diffusible hydrogen content below 8 mL/100g of deposited metal, well within the limits specified by ISO 3676 for high-strength steel welding.
A critical finding is that the flux coating composition plays an equally important role as the filler metal alloy. The authors identify that a basic flux with a controlled CaF2 content of 12–18% provides the optimal balance between slag fluidity (for good bead appearance) and hydrogen absorption reduction (for crack resistance). Excessive CaF2 above 20% leads to increased hydrogen pickup, while insufficient CaF2 below 10% results in poor slag detachability and slag inclusion defects.
Process Parameter Optimisation
The study also investigates the influence of welding process parameters on crack resistance and hardness:
| Parameter | Low Value | High Value | Effect on Crack Resistance |
|---|---|---|---|
| Current (A) | 180 | 320 | Lower current reduces cooling rate, improves crack resistance |
| Travel speed (mm/min) | 150 | 450 | Lower speed increases heat input, reduces thermal gradient |
| Preheat temperature (°C) | 50 | 250 | Higher preheat significantly reduces crack tendency |
| Interpass temperature (°C) | 150 | 350 | Maintaining above 200°C is critical for multi-pass builds |
The authors recommend a preheat temperature of 150–200°C for base materials with a carbon equivalent above 0.45%, with an interpass temperature maintained above 200°C for multi-layer welds. These recommendations align with common practice in high-performance overlay welding and are consistent with the guidance provided in AWS D10.9 and ISO 15614.
Engineering Practice Implications
From a practical fabrication standpoint, the electrode formulation described in this study is particularly well-suited for overlay applications on mining equipment components such as bucket teeth, cone crushers, and conveyor rollers, where both extreme wear resistance and structural integrity are required. In my own experience, many of the high-hardness overlay electrodes available in the market suffer from unacceptable crack sensitivity, leading to high rework rates and production delays. The nickel-enhanced formulation reported here represents a meaningful improvement in this regard.
However, I would caution that the hardness-crack resistance balance achieved in laboratory conditions may not translate directly to field welding environments where contamination, inadequate preheat, and variable operator technique are common. A robust qualification procedure following NB/T 47014 or ASME IX is essential before any new electrode is introduced into production service.
Study Insights and Reflections
This work demonstrates that the traditional trade-off between hardness and crack resistance in overlay welding can be substantially mitigated through careful alloy design, particularly through strategic nickel addition and flux optimisation. The study provides valuable quantitative data on the relationship between composition, microstructure, and crack resistance that can guide both electrode manufacturers and end-user engineers. Future work should focus on extending the service life evaluation under actual operating conditions, including thermal cycling and impact loading, to fully validate the practical benefits of the new electrode formulation.