Investigations of thermal diffusivity and thermal expansion for three types of the barrel steel

Three types of barrel steel, i.e. 38HMJ, 30HN2MFA, and DUPLEX, were used for investigations of temperature characteristics of thermal diffusivity and thermal expansion in the temperature range from 50°C to 1000°C. The tests were carried out applying the Netzsch laser flash apparatus LFA 427 and the Netzsch dilatometer DIL 402 C. The results of the thermal expansion tests revealed that in steels 38HMJ and 30HN2MFA a material shrinkage occurs in the temperature range of 730-740°C. This effect does not occur in DUPLEX steel. The barrel of the rifle is covered with a layer of galvanic chromium. Contraction of the substrate leads to cracking of the protective layer of chromium. The cracking effect of the chromium layer can be caused by passing ferrite to austenite at 730°C. The results of thermal diffusivity investigations of tested materials confirmed phase transition effect only in the steels 38HMJ and 30HN2MFA. Taking into account that in DUPLEX steel material shrinkage in the tested temperature range does not occur, for that reason, this material is considered when designing the barrels of modern rifles.