Abstract: Method of treating a workpiece comprising a titanium metal, wherein a titanium metal surface layer of the workpiece is converted to titanium nitrides. The method comprises the following steps; a) heating the workpiece to an initial nitriding temperature (Tn1) and b) subjecting said workpiece to one or more nitriding temperatures (Tn1, Tn2) for predetermined time(s) in a nitrogen containing gas under high pressure at hot isostatic pressing (HIP) conditions for converting the titanium metal surface layer to a first layer portion consisting of titanium nitrides and a second layer portion comprising a nitrogen gradient in the titanium metal. The method further comprises c) quenching the workpiece in the nitrogen containing gas under high pressure at hot isostatic pressing (HIP) conditions, in order to strengthen the titanium metal below the in step b) formed first nitride layer portion.