Oil and gas steels surface hardening investigation by anodic plasma electrolytic treatment

The paper is devoted to research of anodic plasma electrolytic method for hardening steels of various classes, widely used in the oil and gas industry (there were tested such grades of steels, like 20, 09G2S, U10, 18Kh2N4VA, 12Kh18N10T). Hardening was carried out in an electrolyte containing 8% ammonium chloride, 5% glycerol, and 3% carbamide for 3-5 min. Studies have shown that low- and medium-carbon steels form hardened surface layers up to 150-200 micrometers deep from the surface with an increase of microhardness up to 4.66 times, relative to the original structure. High-alloy steels have a smaller hardening zone (up to 70 micrometers) and a smaller increase of microhardness (up to 1.49 times). The wear resistance of treated steels is enhanced from 27.7% (for steel 12Kh18N10T) up to 86.6% (for steel 09G2S) in comparison to their initial state. The investigation of corrosion behavior of samples tested in 5% NaCl solution using potentiodynamic Tafel curves method is showed also the enhance of corrosion resistance of strengthened steels samples by anodic plasma electrolytic treatment in comparison to untreated samples.