Improvement of surface properties by combined processes - A comparison: CVD plus induction hardening against carburizing plus CVD

摘要

The properties of tools and components can be improved by the combination of heat treatment and surface engineering processes due to the addition of the single process advantages and due to the utilization of process interactions. A well known and clear example is the combination CVD-coating with wear resistant films + quench hardening (through-hardening) of high alloyed tool steels for forming tools. The thin wear resistant coating (e.g. TiN) is supported by the high strength of the hardened substrate. This combination can be further improved by adding surface heat treatment processes like induction hardening or carburizing. Several low and high alloyed, structural and tool steels (AISI 4140, 52100, H13, A2, D2, etc.) have been treated by CVD TiN-coating + induction hardening respectively carburizing + CVD TiN-coating + gas quench-mg. Both combined processes resulted in surfaces with very promising properties. The results were compared concerning chemical compositions, micro-structures, hardness, residual stresses and scratch tests. Homogeneous, dense TiN-coatings with high hardness, high compressive residual stresses and good adhesion were supported by high strength substrate surfaces. An extra advantage of these combined processes compared to CVD + through-hardening were compressive residual stresses in the substrate surfaces.