Effect of hot gas atomization on spray forming of steel tubes using a close-coupled atomizer (CCA)

Hot gas atomization in spray forming has been used for the first time to improve the quality of spray-formed tubular deposits. This technique reduces gas consumption and produces smaller droplets than cold gas atomization. The flight velocity and cooling rate of the atomized droplets increase with increasing gas temperature. These features can further influence the quality of the spray-formed deposits. Until now, spray-formed tubes have not been used on industrial scale due to insufficient deposit quality in terms of porosity and bonding to the substrate. Using a close-coupled atomizer (CCA), qualitative improvements of the as-sprayed deposits have been previously studied. In the present study, a comparative investigation is done to find the influence of hot gas atomization on the spray forming of the bearing steel AISI 52100 (100Cr6) using a close-coupled atomizer. The spray-formed deposit with hot gas atomization (gas temperature about 300 °C) shows lower deposit surface temperature and smaller grain size in comparison to the deposit produced under cold gas atomization condition due to smaller droplet diameter and higher cooling rate of the droplets. Moreover, the as-sprayed deposits under hot gas atomization show a higher relative density at a lower deposit surface temperature, which extends the process window for the flexible production of spray-formed tubes.