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Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel
Král, Petr ; Dvořák, Jiří ; Sklenička, Václav ; Horita, Z. ; Tokizawa, Y. ; Tang, Y. ; Kunčická, Lenka ; Kuchařová, Květa ; Kvapilová, Marie ; Svobodová, M.
The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. The as-received P92 steel was deformed by high-pressure torsion (HTP), high-pressure sliding (HPS) and rotary swaging (RS) at room temperature prior creep testing. These SPD methods imposed significantly different equivalent plastic strain in the range from 1 up to 20. Constant load creep tests in tension were performed in an argon atmosphere at 873 K and applied stress ranging from 50 to 200 MPa. The microstructure and phase composition of P92 steel were studied using a scanning electron microscope Tescan Lyra 3 and a transmission electron microscope Jeol 2100F. The results show that under the same creep loading conditions the HPT and HPS-processed P92 steel exhibited significantly faster minimum creep rates, creep fracture strain and the decrease in the value of the stress exponent of the creep rate in comparison with as-received P92 steel. However, it was revealed that the RS-processed specimens exhibited one order of magnitude lower minimum creep rate and lower ductility compared to commercial P92 steel. The creep curves for the HPT and HPS-processed states exhibited a pronounced minimum of strain rate. The pronounced minimum of strain rate disappeared when these states were annealed at 923K/500h before application of creep loading. The microstructure changes occurring during creep and different creep behaviour between as-received and deformed states are discussed.
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Výroba pouzdra objemovým tvářením za studena
Kouřil, Jakub ; Kunčická, Lenka (oponent) ; Jopek, Miroslav (vedoucí práce)
Bakalářská práce je zaměřena na výrobu součásti objemovým tvářením za studena. Předmětem práce je návrh technologie výroby pouzdra o sériovosti 6 000 000 ks/rok pomocí protlačování a pěchování. K výrobě je použita austenitická korozivzdorná ocel X5CrNi18-10. Na základě simulací byla zvolena nejvhodnější geometrická konfigurace tvářecích operací. Celý výrobní postup se skládá z první dělící, dvou tvářecích a poslední obráběcí a rádlovaní operace. Na základě vypočtené tvářecí síly o velikosti 175,6 kN a potřebného výkonu o velikosti 425 W, byl zvolen tvářecí automat CHUN ZU CBF-83S. Současně je navržen nástroj a v závěru je provedeno technicko-ekonomické zhodnocení, jehož součástí je také výpočet kusové ceny při uvažování 15% zisku, která činí 1,24 Kč.
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WE43 BIOCOMPATIBLE ALLOY AFTER SEVERE PLASTIC DEFORMATION: STRUCTURE CHARACTERIZATION
Kunčická, Lenka ; Král, Petr ; Dvořák, Jiří ; Kocich, R.
The report presents results of the analyses of biocompatible WE 43 Mg-based alloy processed by friction stir processing (FSP) at two different rotational speeds of 400 RPM, and 1200 RPM. The structures were observed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD). Observations were primarily focused on characterizations of grains and textures, supplementary testing of mechanical properties was performed via tensile tests. The results of low angle grain boundaries fractions and grain sizes showed that both the processing methods led to significant grain refinement and recrystallization, the average grain diameter within the 1200 RPM sample was less than 2 μm. Texture observations showed slight tendencies of the grains to align in the {0001}〈101̅0〉 and {0001}〈112̅0〉 preferential orientations, however, the maximum intensities were only about two times random. Supplementary tensile tests confirmed the positive effects of FSP on structures and properties of both the samples.
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