Mechanical tests of PVD coatings made on steel 310S were carried out within this study by the scratch test method. It was found that the additions of Al and Ir caused lower critical load values compared to the coating without additions. Despite the reduction of the critical load of the coating by the aluminium addition, the effect of aluminium was considered advantageous owing to the refinement of the structure causing the coating to become more plastic and reducing the number and sizes of micro-cracks. The addition of iridium results in an embrittlement of the coating structure and its poorer adhesion to the substrate. Comparison of the findings from the scratch test with the observations from an optical and a scanning microscopes was also made.