CLADDING TECHNOLOGY SHANXI CO., LTDNickel-Based High-Temperature Wear-Resistant Fluxless Cladding Electrode and Heat Treatment
Literature Overview and Research Background
Nickel-based alloy cladding systems are widely employed in high-temperature wear applications such as turbine components, cement kiln parts, thermal power plant hoppers, and chemical processing equipment operating above 500 degrees Celsius. Conventional cladding electrodes with flux coatings often produce slag inclusions, require slag removal between passes, and exhibit inconsistent microstructural quality. This literature introduces a novel fluxless (cored wire) nickel-based cladding electrode designed specifically for high-temperature wear resistance, along with a systematic heat treatment protocol to optimize the final microstructure and mechanical properties.
Electrode Composition and Design Philosophy
The fluxless electrode is manufactured as a cored wire with a nickel-based alloy shell and a flux-filled core. The shell composition is based on the Ni-Cr-Mo-Si system, with deliberate additions of boron and titanium to promote the formation of hard intermetallic phases. The core contains a proprietary mixture of silicon carbide, chromium oxide, and organic binders that serve as deoxidizers and microalloying agents during welding.
| Component | Shell Composition (wt%) | Core Composition |
|---|---|---|
| Ni (balance) | >60 | - |
| Cr | 22-26 | Cr2O3 (8-12%) |
| Mo | 6-8 | - |
| Si | 3-5 | SiC (15-20%) |
| B | 0.5-1.0 | - |
| Ti | 0.3-0.8 | TiO2 (3-5%) |
| C | 0.3-0.5 | - |
The fluxless design eliminates the need for slag removal between passes, enabling continuous multi-pass deposition with consistent microstructural quality. This is particularly advantageous for robotic welding applications where automated slag removal is impractical.
Welding Process Parameters and Microstructural Characteristics
The electrode is designed for use with gas metal arc welding (GMAW) processes with a shielding gas mixture of 98% argon plus 2% carbon dioxide. Optimal welding parameters include a current range of 200-320 A, voltage of 22-28 V, and wire feed speed of 4.5-7.0 m/min. The resulting dilution rate with nickel-based substrates is typically 15-25%, which is acceptable given the high nickel content of the deposited alloy.
The as-welded microstructure consists of a fine-grained austenitic matrix with dispersed NbC and Cr7C3 carbide particles, along with Ni3(B,N) intermetallic phases. The hardness in the as-welded condition ranges from 380-420 HV. The fine grain structure is attributed to the high nucleation density provided by the carbide particles in the core flux, which act as heterogeneous nucleation sites during solidification.
Heat Treatment Protocol
The critical innovation in this literature is the proposed heat treatment sequence that transforms the as-welded microstructure into a highly wear-resistant tempered martensitic-carbide composite:
- Solution treatment at 1050 degrees Celsius for 2 hours in vacuum or argon atmosphere
- Water quenching to room temperature to transform the austenite to martensite
- Double tempering at 580-620 degrees Celsius for 2 hours each with intermediate air cooling
| Condition | Hardness (HV) | Grain Size (um) | Carbide Volume Fraction (%) |
|---|---|---|---|
| As-welded | 380-420 | 25-35 | 12-18 |
| After Solution + Quench | 580-620 | 8-12 | 15-20 |
| After Double Tempering | 480-520 | 10-15 | 18-25 |
The double tempering process is essential for achieving uniform carbide distribution and preventing the formation of brittle continuous carbide networks. Single tempering often results in non-uniform carbide precipitation, with coarse particles at grain boundaries and finer particles within grains.
High-Temperature Performance
Elevated temperature wear tests at 600, 700, and 800 degrees Celsius demonstrate that the heat-treated cladding layer maintains hardness values of 320-380 HV at 600 degrees Celsius, compared to only 180-220 HV for conventional nickel-based cladding electrodes under the same conditions. The improved high-temperature wear resistance is attributed to the presence of stable carbide phases (NbC, Cr7C3) that retain their hardness at elevated temperatures, combined with the precipitation strengthening effect of Ni3(B,N) intermetallics that remain coherent with the matrix up to approximately 750 degrees Celsius.
Common Defects and Quality Control
The fluxless electrode system eliminates slag-related defects but introduces unique quality concerns:
- Core wire eccentricity leading to asymmetric dilution and hardness variation across the weld width
- Carbon pickup from the core flux causing excessive martensite formation and cracking susceptibility
- Incomplete core flux consumption resulting in oxide inclusions within the weld metal
Quality control measures include ultrasonic inspection of the core wire for eccentricity during manufacturing, strict control of carbon content in the core flux composition, and post-weld magnetic particle testing to detect any microcracks that may form during the quenching step.
Study Insights and Reflections
The development of a fluxless nickel-based cladding electrode represents a significant advancement in the practical applicability of nickel-based overlay systems. The elimination of slag removal not only improves productivity but also enhances process repeatability, which is critical for automated manufacturing environments. The heat treatment protocol described is particularly noteworthy for its systematic approach to carbide optimization through double tempering. From a manufacturing cost perspective, the heat treatment requirement adds complexity and expense, but the resulting performance improvement in high-temperature applications justifies the additional investment. The literature would benefit from additional data on the cyclic fatigue behavior of the heat-treated cladding layer, as many high-temperature applications involve combined thermal and mechanical cyclic loading that may challenge the interface integrity between the cladding layer and substrate.