Properties of an intelligent hot-working tool steel with alloy adapted nitriding layers
Golovko A.N. Properties of an intelligent hot-working tool steel with alloy adapted nitriding layers / Golovko A.N., Behrens B.-A., Nürnberger F, Paschke H, MaierH.J., Puppa J, Rodman D // Пластична деформація металів : матеріали наук.-практ. конф. : тез. допов., 22-26 травня 2017 р., м. Дніпро. – Дніпро : [б.в.], 2017. – С. 49.
Tools used for hot forging are exposed to severe process-related loads. Increasing the hardness of the tool surface layer usually results in decreased wear. Due to cyclical contact with hot workpieces and subsequent liquid cooling the hot forging tool can be the subject of a process inherent surface rehardening. Preliminary studies revealed, that modifying the hot-working tool steel 1.2365 (DIN 32CrMoV12-28 / H10 ASTM) with manganese causes an increased surface rehardening due to the decrease of the austenite start temperature Ac1b. Tools made of this modified steel demonstrated higher wear resistance when additionally combined with a surface nitriding treatment. In order to evaluate the influence of nitriding type and parameters, samples for notch impact test were machined out of experimentally modified casted and the standard steel 1.2365. Both steels contained approximately 0.3 wt.-% C, 3 wt.-% Cr, 3 wt.-% Mo and 0.8 wt.-% V. Additionally, the modified steel contained 2 wt.-% Mn. The casted ingots were forged to rods with the ratio of 4. Experimental samples were hardened from a temperature of 1000 °С with a subsequent annealing at temperatures of 570 °С and 560 °С, each lasting 3 hours. Nitriding was carried out by a plasma nitriding treatment using different process parameters. Light microscopy revealed that the thickness of the nitride layer varied from 75 µm to 250 µm. The micro hardness depth in the surface layer was examined. Notch impact tests were carried out at temperatures of 300 °С, 500 °С and 700 °С. The influences of nitriding type and testing temperature were determined for both samples of the standard and the modified steel in longitudinal and cross direction to the billet axis. It was determined that at the temperatures of about 700 °C the impact energy is increased for the samples of the modified steel.