Post heat treatment of high temperature (HT)-CVD TiN-coated steel substrates 42CrMo4 (4140) and X155CrVMo12-1 (D2) was investigated. The desired substrate structures and hardness could be achieved by post quench hardening and tempering. The coating structure seemed unchanged under light microscopy. The support of the coating by higher substrate hardness was confirmed by higher critical loads in scratch tests. Technological experiments, such as bending tests, alternating bending tests and notched-bar tests, were performed. CVD TiN-coated/post hardened and tempered, and uncoated hardened and tempered steel 4140, reached the same bending 0.2%-yield strength, lifetime at alternating bending, and notch toughness. Bending strength and lifetime at alternating bending of CVD TiN-coated D2 were low compared to the uncoated quench-hardened state because of decarburisation during deposition. These differences disappeared after post quench hardening and tempering. TEM-investigations of the coating/substrate interface were done to explain the structure and mechanical properties of CVD-coated and post heat-treated steels.