Nitriding of high-alloyed tool steels is a special treatment which can lead to complex metallurgical reactions. Easily undesired structural modifications can occur. The produced layers can be very brittle and fail early during operation. One reason for the high brittleness of these layers is the high carbon content, which is displaced during nitriding by the incoming nitrogen and causes segregations at the grain boundaries. These investigations were carried out with the high-alloyed tool steels Böhler M390 (X190CrVMo20-4)  and Bodycote MV11K (X260CrVMo26-4) . Both steels are produced via the powder metallurgical route, i.e. the steel melt is atomized into powder, which is hot isostatic pressed into ingots and hot formed to steel bars.When plasma-nitriding with 25 % N2 in the nitriding atmosphere, a network of hard phases is formed at the grain boundaries. Characteristic for this network are high contents of carbon at the former grain boundaries and high contents of nitrogen in the large primary carbides. Different strategies can be applied to influence or avoid the network like structure. Among these are the raising of the nitriding temperature, the reduction of the nitriding time or of the nitrogen content in the nitriding-atmosphere.
|Translated title of the contribution||Nitriding of powder-metallurgical produced high-alloyed plastic mould steels|
|Number of pages||7|
|Journal||HTM - Haerterei-Technische Mitteilungen|
|Publication status||Published - Apr 2011|