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Jurci P.,Paulinska 16 | Sobotova J.,Czech Technical University | Salabova P.,Prikner tepelne zpracovani kovu | Prikner O.,Prikner tepelne zpracovani kovu | And 2 more authors.
International Heat Treatment and Surface Engineering | Year: 2013

The Cr-V ledeburitic steel Vanadis 6 was vacuum austenitised, nitrogen gas quenched and double tempered under various combinations of heat treatment regimes. For selected samples, a subzero period was inserted between quenching and tempering. The results obtained infer that: (1) the as quenched microstructure consisted of martensite, retained austenite and undissolved carbides; (2) the subzero processing reduced the amount of the retained austenite and increased the tetragonality of the martensitic lattice; (3) the as quenched hardness of the steel was higher by 2-3 HRC due to subzero processing; (4) the as tempered hardness increased with increasing austenitising temperature, but it decreased slightly during the subzero period; (5) no negative impact of subzero processing on toughness was recorded; (6) the wear resistance increased with subzero period when a 100Cr6 steel was used as a counterpart. © 2013 IHTSE Partnership. Source


Sobotova J.,Czech Technical University | Salabova P.,Prikner tepelne zpracovani kovu | Prikner O.,Prikner tepelne zpracovani kovu | Sustarsic B.,Slovenian Institute of Metals And Technology | Jenko D.,Slovenian Institute of Metals And Technology
Vacuum | Year: 2015

Microstructure, phase constitution and hardness of Cr-V ledeburitic steel Vanadis 6 subjected to sub-zero treatment with a soaking time of 4 h and at a temperature of -196 °C have been examined with reference to the same material after conventional heat treatment. Microstructures have been characterized using light microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Hardness has been evaluated by Vickers method. As-annealed material consists of the ferritic matrix and of two carbide phases, namely M7C3 and MC. After the heat treatment, the matrix is martensitic with certain amount of retained austenite. Sub-zero treatment results in more complete martensitic transformation. The martensite contains areas with extremely enhanced carbon content. Sub-zero treatment refines the size of martensitic domains and increases the dislocation density inside the domains. Microstructure of sub-zero treated steel contains enhanced amount of small globular carbides, as compared to conventionally heat treated material. These particles have a size of around 100 nm in most cases. Small globular carbides are of the cementitic nature for both the no sub-zero treated steels and the sub-zero treated material. Bulk hardness manifests a moderate increase due to the sub-zero treatment. The increase in hardness is more significant when higher austenitizing temperature is used for the treatment, which is associated with more pronounced reduction of the retained austenite content. © 2014 Elsevier Ltd. Source


Sobotova J.,Czech Technical University | Adame J.,Czech Technical University | Salabova P.,Prikner tepelne zpracovani kovu | Prikner O.,Prikner tepelne zpracovani kovu | And 2 more authors.
Materiali in Tehnologije | Year: 2013

Specimens made from P/M Vanadis 6 cold-work steel were austenitized, quenched and tempered for various combinations of the parameters. The selected sets of samples, also in the sub-zero range, were treated at a temperature of -196 °C after quenching. The microstructure was investigated as a function of the austenitizing temperature and the parameters of the sub-zero processing using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. It was found that the as-quenched microstructure is composed of martensite, retained austenite and carbides. The sub-zero processing reduced the amount of retained austenite and led to an increase in the tetragonality of the martensitic lattice. As a result, the hardness of the material was higher by 2 HRc before the tempering of the samples after the sub-zero processing, but the hardness of the sub-zero-processed material after tempering is about 2.5 HRc lower than that of the non-sub-zero-processed steel. Based on the facts that the sub-zero-processed steel contained less retained austenite and an unknown amount of the expected nano-precipitates, we expected it to have a lower capability to manifest the secondary-hardening effect. Source


Jurci P.,University of Trnava | Kusy M.,University of Trnava | Domankova M.,University of Trnava | Caplovic L.,University of Trnava | And 4 more authors.
METAL 2013 - 22nd International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2013

The ledeburitic steel Vanadis 6 has been austenitized at the temperatures 1000 - 1075°C, nitrogen gas quenched and 2x tempered at the temperatures 480 - 600°C. Each tempering cycle was 2 h. Sub-zero treatment carried out via various regimes has been inserted in-between quenching and tempering, except one set of specimens. The effect of sub-zero treatment on the tempering characteristics of the material has been investigated. It has been found that the martensite after sub-zero processing differs from that of conventionally transformed in terms of substructure. The sub-zero treatment induced a multiple reduction of the volume fraction of retained austenite. This makes a difference between as-tempered microstructure of sub-zero treated and no-sub-zero treated steel, which results in different as-tempered hardness. © 2013 TANGER Ltd., Ostrava. Source


Jurci P.,Czech Technical University | Sobotovav J.,Czech Technical University | Cejp J.,Czech Technical University | Salabova P.,Prikner tepelne zpracovani kovu | Prikner O.,Prikner tepelne zpracovani kovu
METAL 2010 - 19th International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2010

The P/M Vanadis 6 cold work steel was austenitized, quenched and tempered. For selected sets of specimens, also sub-zero period was inserted between quenching and tempering. The structure, hardness and three point bending strength was investigated as a function parameters of heat treatment. The as-quenched hardness of the material raises with the use of the sub-zero period. On the other side, the use of sub-zero period results in a slight hardness decrease of the as-tempered material. Furthermore it was found that the three point bending strength decreased markedly with increased austenitizing temperature and also slightly with the use of sub-zero treatment. The lowering of bending strength with increasing austenitizing temperature can be considered as natural because of the austenitic grain growth. On the other hand, the lowering of bending strength due to the use of sub-zero processing can not be explained as simply as expected on first sight. The situation is more complex since the hardness behaves in a rather surprising way, which is discussed in the paper. © 2010 TANGER Ltd., Ostrava. Source

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