Effect of Copper and Molybdenum Additions on the Microstructure and Mechanical Properties of Steel Shot

The effect of copper and molybdenum additions on the microstructure of particles produced by the atomization of an iron-carbon melt by an air-water jet using a new atomizer unit has been studied. The application of air-water atomization instead of water atomization is shown to intensify the solidification of particles with a fine microstructure. The introduction of molybdenum (up to 0.6 wt %) into a melt refines the structural constituents of the granules and decreases the fraction of the retained austenite, and the introduction of copper (up to 0.8 wt %) leads to the opposite results. The addition of copper (up to 0.6 wt %) and molybdenum (up to 0.6 wt %) to a melt results in a homogeneous microstructure consisting of fine acicular martensite and fine molybdenum carbides. Low-temperature vacuum tempering at 350 degrees C for 1 h leads to insignificant decarburization of the martensite and the precipitation hardening of the base metal due to copper alloying. The microstructure of a steel alloyed by molybdenum and copper provides an increase in the wear resistance of the steel shot by a factor of 1.5-2 and high quality of the shot (close to the best foreign analogs).