NITRIDE WIDTH AND MICROHARDNESS IN H-12 ION NITRIDED STEEL

The ion nitriding technique was used on an AISI H-12 tool steel aiming to correlate measurements of the nitride width, microhardness profile and fractography measurements and nitriding time. The ion nitriding conditions were 500-degrees-C and 500 V, employing a 80% H2-20% N2 gas mixture. The average width of the nitrides formed near the surface exposed to the plasma was linearly related to the nitriding time. The surface microhardness (about 15 mum into the surface) increased with time until a maximum is reached and a plateau was developed near the nitrided surface. However, when exposure time is above 27 ks the surface microhardness decreased. The hard case measurements employing fractography revealed a correlation with the microhardness measurements and nitriding time. The role of tungsten, which is contained in H-12 tool steels and absent in H-13, is discussed.