______________________________________ structural steel gray cast iron end of useful life wear mark width v sub bvariation after after 10 minutes ______________________________________1 21 minutes 0 28 mm2 28 minutes 0 15 mm______________________________________ the comparison between example 1 and examples 2 and 3 shows that no significant difference exists with respect to the quality of the wear parts with the different coatings irrespective of whether said parts were coated at atmospheric pressure or in the under pressure a multi layer structure was applied directly to the hard metal of reversible cutting plates of the same type as in the preceding examples without a backing layer the plates were coated under pressure variation 2 the layer structure was compared with a multi layer coating structure different from the one of the invention but also applied without using a backing variation 1 ______________________________________layer structure variation 1 variation 2 0 5 u03bcm ti c sub 0 6 n sub 0 4 0 5 u03bcm ti c n o 0 8 u03bcm al sub 2 o sub 3 0 8 u03bcm aluminum boron mixed oxide0 3 u03bcm ti c n 0 2 u03bcm ti c n o 0 8 u03bcm al sub 2 o sub 3 0 8 u03bcm aluminum boron mixed oxide0 3.