P 1125 – Enhancing technological properties of tool steels by cryogenic treatment
The aim of the project was to investigate the effects of cryogenic treatment on the microstructure, mechanical properties and wear resistance of the high-alloyed tool steels X38CrMoV5-3 (electroslag remelting (ESR)), X153CrMoV12 (powder metallurgy (PM) and melting metallurgy (MM)) and ~X190CrVMo20-4 (PM). The tempering parameters for the mechanical specimens and for the wear samples were selected on the basis of the tempering curves in such a way that a similar hardness was achieved for both the conventionally heat-treated and the cryogenically treated samples. Although a fine, martensitic microstructure and a more homogeneous distribution of secondary carbides was achieved for X38CrMoV5-3 by incorporating a cryogenic treatment in the conventional heat treatment process or an increased amount and a more homogeneous distribution of secondary carbides and nanocarbides for the steels X153CrMoV12 and ~X190CrVMo20-4 could be attributed to the cryogenic treatment, the mechanical properties and wear resistance (pin-on-abrasive paper wear test, slurrypot test and cavitation erosion test) of the investigated steels were not improved significantly by the cryogenic treatment. The wear resistance of the high-alloyed tool steels depends to a large extent on the primary carbides and the macro hardness, less on the secondary carbides or nanocarbides. An almost complete transformation of retained austenite into martensite in the small-sized samples was achieved both by cryogenic treatment and by triple tempering at high temperatures. A cryogenic treatment of tool components with large thickness would have a positive effect in terms of a uniform and complete transformation of the retained austenite over the whole cross section. This allows the user to better assess the technology of cryogenic treatment and thus to use it more specifically, whereby improved results can be achieved or costs can be saved.
Dr.-Ing. A. Schulz, Dr.-Ing. F. Nürnberger, Dipl.-Ing. T. Ümit