Life enhancement of hot-forging dies by plasma-nitriding

Hot-forging dies, made of AISI-H13 hot-work tool steel, were plasma-nitrided in order to improve the surface properties of the material. A diffusion layer without the white layer was formed on the material by controlling the nitriding parameters: vacuum pressure, temperature, N₂ / H₂ ratio and DC bias potential. The nitriding time was varied from 2 to 16 hours. Micro-hardness measurements were performed on the surface and through the diffusion layer for each nitrided material. Optical microscopy was performed on the as-received and nitrided materials. The surface hardness of the materials increased from 550 HV0.1 to 1300 HV0.1 after plasma-nitriding. Materials plasma-nitrided for 8-10 hours had the highest surface hardness. Surface hardness decreased after 10 hours of plasma-nitriding. Work pieces, made of AISI-1020 steel, were forged at 900°C by the plasma-nitrided dies and the lives of the dies were measured. The lives of plasma-nitrided hot-forging dies increased largely in comparison to those of the as-received dies. Highest life enhancement of the dies was achieved by 10 hours of plasma-nitriding.