In the fields of mining, metallurgy, and ore transportation, components such as cutting teeth and scraper conveyors are subject to severe abrasive wear, imposing extremely high demands on surface wear resistance. To enhance the reliability of equipment, plasma cladding technology with high bonding strength, high alloying capability, and production efficiency has become the preferred process for repairing wear-resistant components. Fe-Cr-C series cladding alloys are widely used due to their excellent wear resistance and cost-effectiveness. However, hypereutectic alloys suffer from insufficient crack resistance and low toughness, while hypoeutectic alloys, although more ductile, have inferior wear resistance due to the morphology of carbides. To improve the wear resistance of hypoeutectic alloys, alloy elements such as Nb and Ti are often added to strengthen the matrix and carbides and optimize the microstructure. NbC and TiC, as hard alloy reinforcing phases, have high hardness and good thermal stability, but also have drawbacks such as low fracture toughness of TiC and poor bonding at the NbC/Fe interface. Nevertheless, these issues can be mitigated by forming composite carbides, which exhibit superior comprehensive properties compared with individual carbides. This study aims to introduce Nb and Ti elements into hypoeutectic Fe-7Cr-C series alloys using plasma cladding technology. By changing the Nb/Ti atomic ratio, it explores the influence mechanism of these elements on the microstructure and properties of (Nb,Ti)C reinforced Fe-7Cr-C-Nb-Ti series cladding layers. The primary goal is to address the issues of low hardness and poor wear resistance in hypoeutectic Fe-7Cr-C series cladding alloys to meet the higher performance requirements for wear resistance in mechanical components. In the experiment, 20 steel plates are used as the substrate. Five groups of cladding alloy powders with different Nb-to-Ti atomic ratios are prepared and cladded via plasma cladding technology. Various techniques, including thermodynamic analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness testing, and abrasive wear testing, are employed to comprehensively evaluate the microstructure and mechanical properties of the cladding alloys under different Nb/Ti ratios. The results show that as the Nb/Ti ratio increases, the microstructure of the cladding layer gradually transforms from a hypoeutectic structure (α-(Fe-Cr) + network eutectic M7C3 + (Nb,Ti)C) to a near-eutectic structure (M + A' + (Nb,Ti)C + M7C3 + NbC(script)), and finally to a hypereutectic structure (martensite, austenite matrix, a large amount of primary (Nb,Ti)C, and a small amount of secondary NbC and M23C6). During this process, the quantity of (Nb,Ti)C in the cladding layer continuously increases, with its morphology being granular in the range of Nb/Ti = 0.5∶1 to 2∶1, and transforming into dendritic and clustered shapes at Nb/Ti = 2.4∶1. Simultaneously, the amount of M7C3 gradually decreases until it disappears, with a small amount of M23C6 precipitating in the cladding layer. The microhardness and wear resistance of the cladding layer first increases and then decreases with the Nb/Ti ratio. When Nb/Ti = 2∶1, the alloy exhibits the best performance, with a microhardness of 728.4HV0.5 and the lowest wear loss (0.209 1 g). This phenomenon is attributed to the synergistic strengthening effect of the low-carbon martensite matrix and a large number of appropriately sized granular primary (Nb,Ti)C hard particles, as well as a good balance between the total amount of carbides and eutectic carbides in the alloy microstructure, which improves the wear resistance of the alloy by approximately 3.1 times compared with when Nb/Ti = 2.4∶1.
Key words
Fe-7Cr-C-Nb-Ti alloy /
plasma cladding /
Nb/Ti /
(Nb,Ti)C /
microstructure evolution /
wear resistance
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Funding
National Natural Science Foundation of China Youth Fund Project (51901141); Liaoning Provincial Department of Education Basic Research Project for Higher Education Institutions (LJKMZ20221108)
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