Abrasion resistance of surface-modified steels used for artillery weapon barrels
A barrel is one of the most tribologically and thermally loaded parts of artillery weapons. The influence of the salt bath nitrocarburizing and hard-chrome plating of three steels used for artillery barrels on their abrasion resistance is studied in this paper. The tested steels are 42CrMo4, 30CrNiMo8, and 36CrNiMo4 in the initial quenched and tempered state. The test results from the ''dry sand/rubber wheel'' method, after 700 m of wear path, showed that the hard-chrome plating of 42CrMo4 and 30CrNiMo8 steels improved their abrasion resistance. In addition, reduced abrasive wear of 42CrMo4 steel samples was also achieved by nitrocarburizing. Hard chrome-plated samples exhibited good wear resistance due to their greater hardness and bigger thickness of the compound zone in comparison with that obtained on nitrocarburized samples.
Thermo-chemical erosion in gun barrels
Abstract When a gun fires the metal temperatures at the bore may reach 1100°C in a few milliseconds and decline to half this value by the time the projectile reaches the muzzle. Although the temperature fluctuation does not penetrate very far from the surface it does create a hard and brittle surface layer commonly referred to as the heat-affected zone . The diffusion of chemical species such as CO, CO 2 , H 2 , H 2 O and N 2 into the hot surface forms a chemically-affected zone . Wear rate in guns is related to the thickness of this chemically-affected zone. From the equation of mass diffusion a simple equation of the Arrhenius type is derived relating the wear per round to the initial temperature, the maximum surface temperature, and the erosivity of the propellant. This equation is verified by trials on a vented vessel, which simulate gunfire, and also by data on the wear rates of numerous gun and propellant combinations. The erosivity of service propellants is correlated with their chemical composition and demonstrates that CO and H 2 are very erosive whereas CO 2 , H 2 O and N 2 are much less erosive.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.