The microstructure, the phase constitution and hardness of Cr-V ledeburitic tool steel Vanadis 6 subjected to sub-zero treatment with several soaking time in nitrogen vapors have been investigated. The metallurgical aspects include reducing the amount of retained austenite and increasing carbide count, so wear resistant and dimensional stability are better as compared to conventionally heat treated material. The matrix is martensitic with certain amount of retained austenite, irrespectively to the time of sub-zero treatment. The amount of retained austenite has been significantly decreased from 20.2 vol. % to minimum 3.2 vol. % at 48 h soaking time. The microstructures have been characterized using the light microscopy, scanning electron microscopy and X-ray diffraction. The microstructure of sub-zero treated steel contains eutectic, secondary and increased count of small globular carbides. The count of small globular carbides for conventionally heat treated samples was around 48 x 103 / mm2 and for sub-zero treated samples was increased more than four times with maximum 209 x 103 / mm2 at 24 h soaking time. These particles have size of up 500 nm but 100 nm in most cases. The hardness has been increased as compared to no sub-zero treated samples from 875 ± 16 HV 10 up to 954.6 ± 14 HV 10 at holding time 48 h.Keywords: sub-zero treatment, carbides, Cr-V ledeburitic steel, retained austenite, microstructure
© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.