Boronizing in Arms Industry

Abstract

Comparison is made between several thermochemical treatment methods, with focus on boronizing. Boronizing has the potential to become a substitute for chromium plating or nitriding (gas nitriding) in the arms industry. This experimental study explored the chemical composition, hardness, corrosion resistance, tribological properties and toughness of several surface layers and coatings. The experimental substrates were EN 32CrMoV12-10 and EN 31CrMoV9 steels. Boronizing is intended for the gas tube and piston of a specific firearm. In the boride layer, the hardness of 1900 HV0.1 was reached. In the chromium and nitrided layers, hardness was 1100 HV0.1. In these experiments, original rifle tubes and disc samples were used. The thicknesses were as follows: the chromium layer: up to 70 μam, boride layer: 100 μam and nitride layer: 290 μam. Wear properties were compared using the Pin-on-Disc wear test. Fracture toughness according to Palmquist was the highest in the nitride case and the lowest in the chromium layer. Across all the layers, the range was from 2.5 to 9.5 MN/m3/2. Some differences were found between the boride layer with post-process heat treatment and layers without heat treatment. As a result of the research, it was found that Boronizing of the gas tube proved a suitable substitute for hard chrome plating or nitriding.