The effects of Ar bombrdment on carbonitrides produced by N implantation in a low carbon steel are studied by Conversion Electron Mössbauer Spectroscopy. The results show two main features: dissolution and reprecipitation of the produced carbonitrides and modification of the thermal behaviour of the precipitates. Recently we have performed similar experiments bombarding samples of the same steel with He. The comparison of both experiments shows that the Ar post-bombardment is not only more effective in the dissolution and reprecipitation process, but also is more efficient in the carbonitride retention at 450°C.