Electron beam surface hardening by depositing nickel-chromium based layers in air
摘要
Austenitic chromium-nickel steels are extensively used in the fabrication of parts and assemblies for oil and mining equipment due to their excellent manufacturability and corrosion resistance. However, these steels exhibit limited resistance to abrasive wear. Surface modification of steel workpieces offers a route to enhance this property. In this study, non-vacuum electron beam deposition was utilized as a surface hardening method. A commercial grade nickel-chromium based self-fluxing powder was deposited onto the steel workpieces made of austenitic stainless steel 12Kh18N9T (0.12 C–18Cr–9Ni–Ti) equivalent to AISI 321. The microstructure of the resulting coatings was characterized by optical and scanning electron microscopy. The phase composition of the materials was determined by X‑ray diffraction analysis. Abrasive wear resistance was evaluated under exposure to fixed and loosely fixed abrasive particles. The primary structural components of the modified layers included a solid solution of iron and chromium in nickel, as well as crystals of chromium borides (CrB and Cr5B3) and complex carbide ((Cr,Fe)23C6). The microhardness of the modified layers measuring up to 6 GPa was achieved. The minimum mass loss during the abrasive wear testing was observed during an electron beam deposition of the material with a specific surface energy of 3.9 kJ/cm2. The wear rate of this surface-modified alloy, when tested against fixed and loosely fixed abrasive particles, was reduced by factors of 1.2 and 2.7, respectively, compared to the untreated austenitic chromium-nickel steel. A sequential deposition of two surface layers resulted in further improvement in the tribological performance of the surface-alloyed material, exhibiting a 1.7-fold and 3.9-fold increase in wear resistance under exposure to fixed and loosely fixed abrasive particles, respectively, relative to the base material.