Development of intelligent hot forging tools with increased wear resistance by cyclic edge-zone hardening
|authors:||Golovko, O.; Puppa, J.; Nürnberger, F.; Rodman, D.; Maier, H. J.; Behrens, B.-A.|
|publication:||Proceedings of the 10th TOOL Conference, Bratislava, October 4th to 7th, 2016, pp. 291-300|
Tools used for hot forging are subjected to severe process related thermal, mechanical, tribological, and chemical loads, which usually interfere with each other. The present study aims at developing an inherent system for wear protection tools used in hot forging processes. Therefore, the chemical composition of a hot working tool steel is modified in such a way that the austenite start temperature Ac1b is decreased significantly by adding suited alloying elements. The development started with alloying concepts based on a hot working tool steel along with additional elements used to stabilize the austenite. In comparison to the initial alloy it is possible to reduce the Ac1b-temperature significantly by alloying with manganese, nickel and cobalt. For example adding a mass fraction of 3.9 % manganese and 1.8 % nickel caused a reduction of the Ac1b-temperature by 128 °C. The effect of additional alloying elements was tested regarding the mechanical properties, the wear characteristics and the cyclic hardening effect of the tool steel. An alloy with 2.0 % manganese and 1.6 % nickel was chosen for further industrial tests. Serial hot forging tests were carried out with tools in the form of a punch on an automatic multi-station press with horizontal ram movement. Tools were tested with and without nitration. The use of a nitrided punch made of the modified steel extended the tool life up to 133 %. For the process investigated the wear resistance was successfully increased by cyclic edge-zone hardening using the newly developed hot forging tool steel in combination with a nitriding treatment.