Wear Behavior of Carbonitrided and Nitrided Hot Working Steels*

Abstract

During forging the tools have to resist high thermal and mechanical loads. Therefore, forging dies are usually nitrided in order to increase the wear resistance of the surface areas. Compared to nitriding carbonitriding increases the hardness depths in shorter treatment times. Due to the (carbo-)nitriding, the surface near region gets a better hot hardness and a better wear resistance than the untreated material. In a second process step by nitriding after carbonitriding, a wear and corrosion resistant compound layer can be created at the surface. In the present work the wear behavior of carbonitrided and nitrided hot working steel ENX38CrMoV5-3 (1.2367) was investigated. The evaluation concerning abrasion and thermal fatigue in the contact of forging die and workpiece was carried out by model wear tests like the two-disc test (Amsler test), the ball-on-disc test and a cyclic induction heating and quenching. The conditions of the heating cycles were chosen close to the forging process. The surface areas were investigated after several cycles in order to gain information about the mechanisms of the surface modification. Finally, the treatment combination carbonitring/nitriding was transferred to forging dies and the wear behavior was investigated in fatigue-life experiments under application conditions.

Carbonitriding of Forging Dies

“…In the model wear tests, carbonitrided and tempered as well as carbonitrided and nitrided specimens were compared to quenched and tempered and nitrided specimens. For further description of the experimental setup, see [15].…”

“…Depending on the temperature and the material phase, transformations can take place under thermal load. The element nitrogen stabilizes the austenitic phase by lowering theA C1 temperature [15]. This means that surface areas with a higher nitrogen content will form austenite at lower temperatures than surfaces with lower nitrogen content.…”