Carbonitrieren von Warmarbeitsstählen*

Abstract

Kurzfassung/AbstractUm den hohen Beanspruchungen bei der Warmmassivumformung zu begegnen, werden die Randbereiche der eingesetzten Werkzeuge nitriert. In vorangegangenen Untersuchungen zu nitrierten Gesenken zeigte sich, dass die Verschleißtiefe an kritischen Stellen deutlich über der Nitrierhärtetiefe lag. Eine Steigerung der Nitrierhärtetiefe ist durch Nitrierdauern von mehreren hundert Stunden in den meisten Fällen jedoch unwirtschaftlich. In order to withstand the rough operation conditions, the surfaces and boundary areas of forging dies are nitrided. In former investigations of nitrided dies it was shown that the depth of abrasive wear at the critical parts of the dies is much deeper than the nitriding depth. However, a further increase in nitriding depth is, in most cases, uneconomic since it would require treatment times of several hundreds of hours. Another possibility to increase the wear resistance and heat resistance of the boundary layer is to use carbonitriding. The diffusion of carbon and nitrogen then occurs at higher temperatures so that deeper hardening depths can be obtained in economic treatment times. Carbonitriding is typically used for components made of un-or low-alloyed steels, with carbon contents lower than 0.25 %. The aim of the carbonitriding treatment is then an improvement of the properties like hardenability, surface hardness, wear resistance, fatigue strength, and tempering resistance of the carbonitrided layer allowing replacement of more expensive high-alloy steels. On the development of carbonitriding treatments for hot working tool steels the initial situation and the focus is completely different. The high contents of alloying elements allow formation of finely distributed nitrides and carbonitrides, which are stable at the elevated temperatures during service and which can improve the wear resistance. Although carbonitriding provides a high potential to improve properties of the surface area of hot working steels, there are only few investigations with this aim. The investigations of the present work concern the development of carbonitriding treatments for the hot working tool steels X38CrMoV5-3 and 55NiCrMoV7, aiming at generating finely distributed precipitations providing wear-resistant and thermally stable surface layers. n

Carbonitriding of Forging Dies

“…Since the aim of the carbonitriding is the diffusion of nitrogen into the surface layer, the carbon potential was chosen to match the material's carbon content. The chosen carbon potential also includes the influence of the alloying elements on the equilibrium concentration [16].…”