THE MICROSTRUCTURAL CHANGES IN THE SURFACE-LAYER OF GUN BARRELS

The white-layer formation and its microstructure were investigated in two fired gun barrels, one after 1650 rounds and the other after 500 rounds. The thickness of the white layer is independent of the number of rounds fired and is probably a function of the environment and pressure and temperature conditions. The presence of austenite and Fe3C in the white layer was confirmed, but in addition a much wider spectrum of carbides was observed within the white layer, namely Fe2C, Fe5C2 and Fe20C9. The morphology of the eutectic and carbides suggests their formation is a result of splat cooling from the liquid state. There are indications that the oxidizing process takes place concurrently with carburization. Some correlations between the white-layer formation and the wear erosion rate could be deduced.