Defect and Diffusion Forum Vol. 395

Abstract: The growing pressure on tool performance and durability increases demands on the materials used and on the choice of optimal heat treatment. The properties of tool steels produced by conventional and powder metallurgy (1.2379, Vanadis 23) were compared after different heat treatment modes. Cryogenic treatment was performed in several batches for 4 hours at-90°C or-196°C. Cryogenic treatment was inserted between quenching and tempering. Mechanical properties were evaluated by hardness tests and three-point bending strength and wear resistance by Pin-on-disk tests. Metallographic analysis was performed using light and electron microscopy. On the basis of the results obtained both materials were subject to selected heat treatment and experimental forming tools produced which were used in operation. During operation the wear of the tools (shape change and volume loss) was assessed. Results of the laboratory tests were then compared with operation tests.

Abstract: N-Quench, which is a new surface heat treatment to infiltrate nitrogen into steel parts followed by quenching to achieve hardening, is gathering attention in the nitriding field as it affords low distortion while maintaining a higher effective case depth (ECD) compared with conventional nitriding. N-Quench is conducted mainly between 680°C and 800°C, where the two-phase region of ferrite and austenite exists in the Fe-N phase diagram. However, a few studies have reported on nitriding at temperatures higher than 800°C due to decomposition of NH₃, which is a key source of nitrogen infiltration. Our results revealed that in a conventional furnace such as resistance heating furnace, no nitrogen infiltrated the specimen at 930°C, which is the general carburizing temperature. On the other hand, in the infrared heating furnace, nitrogen infiltrated the specimen at 930°C successfully with lesser NH₃ introduction than that required by the conventional furnace. Therefore, in this study, the limit of NH₃ decomposition is assessed and possibility of extending the applicability of N-Quench, especially increasing the ECD while maintaining a low distortion, is examined.