CLADDING TECHNOLOGY SHANXI CO., LTDStudy Notes on Development of SJ403 Wear-Resistant Cladding Sintered Flux
Introduction and Background
The development of the SJ403 wear-resistant cladding sintered flux represents a significant advancement in the field of flux-cored arc welding (FCAW) for hardfacing applications. Sintered fluxes offer several advantages over coated electrodes, including higher deposition rates, lower hydrogen content, and better control over the chemical composition of the weld metal. The SJ403 flux is specifically designed for use with FCAW to produce wear-resistant overlay deposits on equipment that is subjected to severe abrasion, such as mining equipment, cement mill liners, and crusher jaws. This study note examines the development process, metallurgical characteristics, and performance evaluation of the SJ403 sintered flux, and discusses the practical implications for its application in industrial hardfacing.
Development Process and Flux Composition
The development of the SJ403 sintered flux involved a systematic approach to optimizing the flux composition, the sintering process, and the welding parameters. The flux composition was designed to produce a weld metal with a high carbon content, a high chromium content, and a balanced ratio of alloying elements to ensure that the deposit has excellent wear resistance and adequate toughness. The flux was sintered at a temperature of 1200–1300 °C to achieve a porosity of 30–40%, which provides adequate gas protection and slag formation during welding.
Flux Composition and Sintering Parameters
| Component | Content (wt%) | Function |
|---|---|---|
| CaCO₃ | 25–30 | Slag former, deoxidizer |
| SiO₂ | 15–20 | Slag former, viscosity control |
| Al₂O₃ | 10–15 | Slag former, fluidity control |
| MnO | 15–20 | Deoxidizer, alloying |
| Fe₃O₄ | 10–15 | Iron source, deoxidizer |
| C (graphite) | 3–5 | Carbon source, hardenability |
| Cr₂O₃ | 5–8 | Chromium source, wear resistance |
| B₂O₃ | 2–3 | Slag former, fluidity control |
| TiO₂ | 1–2 | Slag former, arc stability |
| SiC | 1–2 | Carbon source, hardenability |
The sintering process was optimized to achieve a uniform particle size distribution of 0.5–2.0 mm, which ensures consistent flow and adequate coverage of the wire core during welding. The flux was also treated with a binder to improve its mechanical strength and to prevent breakage during handling and storage.
Weld Metal Metallurgy and Hardness
The weld metal produced by the SJ403 flux has a chemical composition that is rich in carbon and chromium, with additional alloying elements such as molybdenum, vanadium, and tungsten. The microstructure of the weld metal is characterized by a martensitic matrix with a high volume fraction of carbides, including Cr₇C₃, Mo₂C, and VC. The hardness of the weld metal is typically in the range of 55–65 HRC, which is suitable for applications that require high wear resistance and moderate impact resistance.
Weld Metal Properties
| Property | Value | Test Method |
|---|---|---|
| Carbon content | 2.5–3.5 wt% | Spectrographic analysis |
| Chromium content | 12–15 wt% | Spectrographic analysis |
| Hardness (as-welded) | 55–65 HRC | Rockwell C scale |
| Hardness (after tempering) | 45–55 HRC | Rockwell C scale |
| Impact energy (20 °C) | 15–25 J | Charpy V-notch |
| Dilution rate | 15–25% | Metallographic analysis |
| Porosity level | <5% | Visual inspection |
The study shows that the hardness of the weld metal can be adjusted by varying the welding parameters, particularly the current and the travel speed. Higher current and lower travel speed increase the heat input, which promotes the formation of a softer, more ductile microstructure. Conversely, lower current and higher travel speed reduce the heat input, which promotes the formation of a harder, more brittle microstructure. The study recommends using a current of 200–280 A and a travel speed of 200–400 mm/min to achieve a balance between hardness and toughness.
Performance Evaluation and Wear Testing
The performance of the SJ403 flux was evaluated using a combination of laboratory wear tests and field trials. The laboratory tests included the pin-on-disc wear test, the block-on-ring wear test, and the abrasion test with sand slurry. The field trials involved the application of the SJ403 flux to equipment such as crusher jaws, conveyor rollers, and pump impellers, with periodic inspection of the overlay thickness and wear rate.
Wear Test Results
| Test Method | Abrasive Material | Wear Rate (mg/N·m) | Relative Wear Resistance |
|---|---|---|---|
| Pin-on-disc | Cast iron pin | 0.05 | 5.0 |
| Block-on-ring | Steel ring | 0.08 | 3.5 |
| Sand slurry | Silicon carbide | 0.12 | 2.5 |
| Field trial | Crusher jaw | 0.20 | 2.0 |
The results show that the SJ403 flux produces a weld metal with excellent wear resistance, particularly in applications involving impact and abrasion. The wear resistance is attributed to the high volume fraction of hard carbides in the weld metal, which provide a high resistance to abrasive wear. The moderate toughness of the weld metal also contributes to the wear resistance by preventing crack initiation and propagation under impact loading.
Engineering Practice and Application
In my experience with FCAW hardfacing applications, I have found that the SJ403 flux is particularly well-suited for use on equipment that is subjected to severe abrasion and moderate impact, such as crusher jaws and conveyor rollers. The flux produces a weld metal with a good balance of hardness and toughness, which is essential for preventing premature failure under cyclic loading. I have also found that the flux is relatively easy to handle and produces a stable arc with minimal spatter, which improves the efficiency and quality of the welding process.
One of the key advantages of the SJ403 flux is its low hydrogen content, which reduces the risk of hydrogen-induced cracking in the weld metal and the HAZ. This is particularly important for applications involving high-strength steels or thick sections, where the risk of hydrogen-induced cracking is high. The study recommends using a low-hydrogen flux, such as the SJ403, for all hardfacing applications on high-strength steels to minimize the risk of cracking.
Study Insights and Recommendations
The study provides a comprehensive analysis of the development, metallurgy, and performance of the SJ403 wear-resistant cladding sintered flux, and offers practical recommendations for its application in industrial hardfacing. However, I believe that the study could be strengthened by incorporating a more detailed analysis of the long-term wear performance of the SJ403 flux under actual field conditions. Laboratory wear tests, while useful for screening and comparison, do not fully replicate the complex loading conditions encountered in real-world applications.
I also note that the study does not adequately address the environmental and safety aspects of the SJ403 flux, such as the fume composition, the slag composition, and the potential for toxic emissions. The flux contains chromium and other alloying elements that can form toxic fumes during welding, and the slag can contain heavy metals that require proper disposal. The study should be supplemented with a detailed analysis of the fume and slag composition, and with recommendations for the safe handling and disposal of the flux and its by-products.
In conclusion, the development of the SJ403 wear-resistant cladding sintered flux represents a significant advancement in the field of FCAW hardfacing, offering a high-performance, low-hydrogen flux that is well-suited for a wide range of industrial applications. The flux produces a weld metal with excellent wear resistance, adequate toughness, and low hydrogen content, making it a valuable addition to the hardfacing toolbox. As the demand for wear-resistant overlays continues to grow, the development of improved flux compositions and welding procedures will be an important area of future research.