Materials and Metallurgical Research. Ltd.

Ostrava, Czech Republic

Materials and Metallurgical Research. Ltd.

Ostrava, Czech Republic

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Michalek K.,VSB - Technical University of Ostrava | Gryc K.,VSB - Technical University of Ostrava | Tkadleckova M.,VSB - Technical University of Ostrava | Moravka J.,Materials and Metallurgical Research. Ltd. | And 3 more authors.
Archives of Metallurgy and Materials | Year: 2013

This work compares the experimental results of nickel concentration measurements in the intermixed zone of the continuously cast round blooms with a diameter of 525 mm using two types of submerged entry nozzles (SEN) - a straight-through nozzle and one with 5-ports. Based on determination of the system and optical interface in the blooms a detailed study of concentration profiles on the bloom surface in a small radius area, on the right side and then also on a cross-section of the blooms, was carried out. The results were further analysed using approximation models, and were to be used to verify the proposed model for predicting intermixed zones for a continuous casting machine, developed based on the results of physical and numerical modelling. © Warszawa - Krakow 2013.


Strilkova L.,Materials and Metallurgical Research Ltd. | Kubon Z.,Materials and Metallurgical Research Ltd. | Vodarek V.,VSB - Technical University of Ostrava
METAL 2010 - 19th International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2010

Two variants of P23/P91 heterogeneous welds were studied. The composition of filler material in Weld A corresponded to that of P91 steel, whilst for Weld B the low alloy filler material of P23 type composition was used. Results of creep rupture tests on the cross weld specimens are close to, or slightly below, the lower limit of the ±20% scatter band around the standardized curve for creep strength of the P23 steel. Creep rupture tests were performed at temperatures of 500, 550 and 600°C with time to rupture up to 60 000hours. Optical microscopy investigations and hardness measurements were carried out on longitudinal sections through ruptured cross weld specimens in order to reveal the effect of testing parameters (temperature, stress) on the preferred location of creep failure. It has been found that in both weld variants creep damage can develop simultaneously in several parts of the cross-weld specimens. The preferred failure locality during testing at 550 and 600°C was the partly decarburized zone of the low alloy P23 steel (or WM23). © 2010 TANGER Ltd., Ostrava.


Mohyla P.,VSB - Technical University of Ostrava | Kubon Z.,Materials and Metallurgical Research Ltd. | Cep R.,VSB - Technical University of Ostrava | Janasek A.,VSB - Technical University of Ostrava | Samardzic I.,Josip Juraj Strossmayer University of Osijek
Metalurgija | Year: 2014

The T24 steel represents the new generation of low-alloyed creep resistant steels with higher creep resistance and lower carbon content. It was designed as prospective material for membrane waterwalls of ultra super critical (USC) power plants, enabling to avoid preheating and post weld heat treatment (PWHT) during welding. However, our investigations concerning secondary hardening of vanadium containing low-alloyed steels show that non-tempered welded joints undergo a significant increase in hardness during exposure to operating temperature. The results then imply that PWHT of T24 steel welds is necessary and this idea is at present supported by the occurrence of several troubles with new installations of USC blocks in Europe.


Michalek K.,VSB - Technical University of Ostrava | Gryc K.,VSB - Technical University of Ostrava | Tkadleckova M.,VSB - Technical University of Ostrava | Moravka J.,Materials and Metallurgical Research Ltd. | And 3 more authors.
Materiali in Tehnologije | Year: 2012

This work compares the experimental results of nickel-concentration measurements in the intermixed zone of the continuously cast round blooms with a diameter of 525 mm using two types of submerged entry nozzles (SEN) - a straight-through nozzle and the one with 5-ports. Based on the determination of the system and optical interface in a bloom, a detailed study of the concentration profiles on the bloom surface in a small-radius area, on the right-hand side, and then alsoon the cross sections of the blooms was carried out. The results were further analysed using the approximation models, and were used to verify the proposed model predicting the intermixed zones for the continuous-casting machines. The developed model was based on the results of the physical and numerical modelling.


Holesinsky J.,VSB - Technical University of Ostrava | Vodarek V.,VSB - Technical University of Ostrava | Strilkova L.,Materials and Metallurgical Research Ltd. | Kubon Z.,Materials and Metallurgical Research Ltd.
METAL 2014 - 23rd International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2014

The paper deals with the study on creep behavior and minor phase evolution in two types of heterogeneous weld joints of P23 and P91 steels during long-term creep exposure at 550 °C. The filler material in Weld A corresponded to P91 steel and the filler metal in Weld B was similar to the chemical composition of P23 steel. The creep rupture tests on the cross-weld test pieces of both welds revealed that most failures occurred in the partly decarburized zones of P23 steel or WM23. The carbon redistribution and the minor phase evolution across the sharp P23/P91 interface were calculated using Thermocalc and Dictra computer packages. The experimental study on minor phase evolution using both EDX and SAED in TEM was in a good agreement with the computer simulations, except for M23C6 phase in P23 (WM23) steel. EBSD technique used to study on microstructure changes along the P23/P91 boundary confirmed the slowing down of the recovery/recrystallization processes in the partly decarburized zone of HAZ of the P23 steel thanks to the presence of undissolved particles of M6X and MX phases. Furthermore, the formation of Laves phase was proved in the partly decarburized zone of P23 steel. EBSD results also confirmed higher resistance of Weld A to softening processes in the partly decarburized zone of P23 steel compared to Weld B, which was in accordance with the results of creep rupture tests.


Roznovska G.,Materials and Metallurgical Research Ltd. | Kubon Z.,Materials and Metallurgical Research Ltd. | Holesinsky J.,VSB - Technical University of Ostrava | Vodarek V.,VSB - Technical University of Ostrava
METAL 2014 - 23rd International Conference on Metallurgy and Materials, Conference Proceedings | Year: 2014

The balance between strength and toughness of supermartensitic steels can be controlled by heat treatment parameters. Quality heat treatment usually consists of quenching and single or double tempering above the Ac1 temperature. Such a treatment results in stabilization of reverted austenite in the tempered martensite. Tempering can also be accompanied by intensive precipitation processes, especially in high alloyed grades. A detailed TEM characterisation of precipitation processes in a 13Cr6Ni2.5MoTi supermartensitic steel proved that single tempering at temperatures of 600 °C and 690 °C was accompanied by precipitation of three minor phases: MX (TiX), M23C6 and Laves phase (Fe2Mo type). Precipitation processes were more intensive at 690 °C. Volume fractions of MX and M23C6 phases were low. Laves phase precipitation was intensive and particles of this minor phase grew fast. However, thermodynamic calculations using the Thermocalc software suggest that Laves phase is not an equilibrium phase in the steel under consideration.


Vodarek V.,VSB - Technical University of Ostrava | Roznovska G.,Materials and Metallurgical Research Ltd | Holesinsky J.,VSB - Technical University of Ostrava | Maslova A.,VSB - Technical University of Ostrava | Kubon Z.,Materials and Metallurgical Research Ltd
Materials Science Forum | Year: 2014

This paper deals with the characterization of hardness, microstructure and precipitation processes in homogeneous T24 welds in the as-welded state and after laboratory PWHT at 745°C for 1 and 6 hours, respectively. Tempering of a T24 steel during quality heat treatment is accompanied by intensive precipitation of MX, M7C3 and M23C6 particles in the bainitic matrix. It was found that SAW welding resulted in a pronounced dissolution of minor phases in the base material close to the joined faces. In the as-welded state microstructure of the CGHAZ was bainitic and the maximum HV10 value in this part of the HAZ reached 382 units. The dominant strengthening mechanism in the CGHAZ was attributed to transformation strengthening due to decomposition of austenite to bainite. Also the HV10 level in the bainitic filler metal (ca 320 HV10) was very close to the maximum acceptable hardness. PWHT at 745°C for 1 hour resulted in a significant decrease of hardness in the weld metal and especially in the CGHAZ. TEM studies revealed that recovery of bainite in the CGHAZ and the weld metal was accompanied by intensive precipitation of MX, M7C3 and M23C6 minor phases. The hardness level in the CGHAZ dropped to approximately 255 HV10. Cyclical tempering (6 x 745°C/1 hour) resulted in a modest additional softening in all parts of the weldments due to more pronounced both precipitation processes and recovery of bainite. © (2014) Trans Tech Publications, Switzerland.


Mohyla P.,VSB - Technical University of Ostrava | Kubon Z.,Materials and Metallurgical Research Ltd | Cep R.,VSB - Technical University of Ostrava | Samardzic I.,Josip Juraj Strossmayer University of Osijek
Metalurgija | Year: 2014

This work is focused on testing and evaluation of creep properties of P92 base material (BM) and welded joints (WJ) as well. Up to date results of creep rupture test of P92 base metal and welds are presented in this article. Creep rupture strength (CRS) of WJ initially reaches values close to the BM, with longer times to fracture and especially at higher temperatures, creep strength of WJ decreases and the data is closer to the lower 40 % tolerance band.


Strilkova L.,MATERIALS AND METALLURGICAL RESEARCH Ltd | Holesinsky J.,VSB - Technical University of Ostrava | Maslova A.,VSB - Technical University of Ostrava | Kubon Z.,MATERIALS AND METALLURGICAL RESEARCH Ltd | Vodarek V.,VSB - Technical University of Ostrava
Materials Science Forum | Year: 2014

This paper deals with microstructural stability of P23/P91 dissimilar welds during longterm creep exposure at 500°C. Detailed TEM investigations on minor phase evolution were performed on specimens after long-term creep exposure. Microstructural changes in the decarburized layer of the P23 steel were studied using EBSD and TEM. Experimental data on minor phase evolution were compared to the results of thermodynamic (Thermocalc) and kinetic (Dictra) simulations. Evolution of minor phases in the P23/P91 welds during creep at 500°C was in a good agreement with results of microstructural modelling. Partial decarburization of the P23 occurred at the expense of dissolving M7C3 phase. Microstructure of the partly decarburized zone in the P23 steel remained bainitic in all specimens investigated. In spite of the partial decarburization in the P23 steel during long-term creep exposure at 500°C, creep failures occurred in the ICHAZ of the P23 steel. © (2014) Trans Tech Publications, Switzerland.


Strilkova L.,MATERIALS AND METALLURGICAL RESEARCH Ltd | Kubon Z.,MATERIALS AND METALLURGICAL RESEARCH Ltd | Vodarek V.,MATERIALS AND METALLURGICAL RESEARCH Ltd
Chemicke Listy | Year: 2011

The experience indicates, that in majority of cases where high temperature failure of power plant components occurs, defects predominate in the vicinity of weldments. P23/P91 dissimilar welds are perspective weld joints for applications in boilers of modern power plants. This contribution deals with studies on creep behaviour and local mechanical properties of P23/P91 dissimilar welds tested at 500, 550 and 600°C.

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