National Repository of Grey Literature 31 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
MICROSTRUCTURAL INVESTIGATION AND MECHANICAL TESTING OF AN ULTRAFINE-GRAINED AUSTENITIC STAINLESS STEEL
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Karjalainen, L. P.
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (FEG SEM). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the treatment to produce an austenitic stainless steel with the grain size of about 1.4 mu m which exhibits tensile strength of around 1000 MPa while ductility remains close to 60 %. The results obtained for both thermomechanical conditions are compared and the relationship between microstructure refinement, phase content and mechanical properties is discussed.
MICROSTRUCTURAL INVESTIGATION AND MECHANICAL TESTING OF AN ULTRAFINE-GRAINED AUSTENITIC STAINLESS STEEL
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Karjalainen, L. P.
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (FEG SEM). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the treatment to produce an austenitic stainless steel with the grain size of about 1.4 mu m which exhibits tensile strength of around 1000 MPa while ductility remains close to 60 %. The results obtained for both thermomechanical conditions are compared and the relationship between microstructure refinement, phase content and mechanical properties is discussed.
LCF behaviour of 301LN steel: coarse-grained vs. UFG-bimodal structure
Man, Jiří ; Chlupová, Alice ; Kuběna, Ivo ; Kruml, Tomáš ; Man, O. ; Järvenpää, A. ; Karjalainen, L. P. ; Polák, Jaroslav
Low-cycle fatigue (LCF) behaviour of metastable austenitic 301LN steel with different grain sizes – coarse-grained (14 µm) and UFG (1.4 µm) with a grain bimodality – produced by reversion annealing (RA) was investigated. Symmetrical push-pull LCF tests were conducted on flat sheet specimens at room temperature with constant strain rate of 2×10–3 s–1 and constant total strain amplitude ranging from 0.4% to 0.8%. After completion of fatigue tests a ferritescope was adopted for quantitative assessment of volume fraction of deformation induced martensite (DIM). Microstructural changes, distribution and morphology of DIM in the volume of material were characterized at different scales by colour etching, TEM and EBSD techniques. Experimental data on microstructural changes are confronted with the stress-strain response and with the chemical heterogeneity present in the material.
Influence of surface morphology on fatigue behavior of metastable austenitic stainless steel AISI 347 at ambient temperature and 300°C
Smaga, M. ; Skorupski, R. ; Mayer, P. ; Kirsch, B. ; Aurich, J. C. ; Raid, I. ; Seewig, J. ; Man, Jiří ; Eifler, D. ; Beck, T.
The effect of surface modification by cryogenic turning on fatigue behavior of metastable austenitic stainless steel AISI 347 was investigated in stress-controlled fatigue tests at ambient temperature (AT) and 300 °C in air. Five different surface morphologies were manufactured by the variation of turning parameters. Surface and near surface morphology were comprehensively characterized by various experimental techniques. The experimental data on the cyclic deformation behavior, stress-strain response and fatigue life for all surface morphologies are reported.
APPLICATION OF ELECTRON CHANNELING CONTRAST IMAGING IN STUDY OF POLYCRYSTALLINE MATERIALS AND VISUALIZATION OF CRYSTAL LATTICE DEFECTS
Dluhoš, J. ; Sedláček, L. ; Man, Jiří
The application of electron channeling contrast imaging (ECCI) technique to the study of polycrystalline austenitic steel is presented. \n\nSpecifics of the ECCI technique for near surface defects observation are explained. Practical examples of the use of ECCI for study of dislocation structure of fatigue test samples are shown. \n\nUsage of a 'rocking beam' technique for electron channeling pattern (ECP) and selected area channeling pattern (SACP) acquisition on polycrystalline material is described.
GRAIN REFINEMENT EFFECT ON FATIGUE PROPERTIES OF AUSTENITIC STAINLESS STEEL WITH DEFORMATION INDUCED MARTENSITE FORMATION
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Škorík, Viktor ; Karjalainen, J.
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two different microstructural states of material were introduced by different annealing conditions during special thermo-mechanical treatment. Fatigue life curves were obtained and compared for both coarse-grained and ultra-fine-grained states of austenitic stainless steel. Magnetic measurements before, during and after cyclic loading were performed to reveal structural changes, i.e. formation of deformation-induced martensite. Relationship between microstructure refinement, phase composition and fatigue properties was discussed.
Propagation of Fatigue Cracks under Shear Loading Modes II, III and II+III in the Near-Threshold Region
Vojtek, Tomáš ; Man, Jiří (referee) ; Polák, Jaroslav (referee) ; Pokluda, Jaroslav (advisor)
Práce je zaměřena na šíření únavových trhlin v módech II, III a II + III v prahové oblasti v kovových materiálech. Byly provedeny experimenty pro ARMCO železo, titan, nikl a austenitickou ocel na třech druzích vzorků pro zatěžování trhliny ve smykových módech. Byl použit zvláštní způsob vytváření iniciační trhliny, který eliminoval efekt zavírání trhliny na začátku smykového zatěžování. Ve všech zkoumaných materiálech byly efektivní prahové hodnoty v módu II přibližně 1,7 krát nižší než v módu III. Měřením úhlů lokálních odklonů a natočení lomových faset s použitím stereofotogrammetrie v SEM bylo usuzováno na tendenci trhliny k vyhýbání do lokálního módu I. Nejmenší úhly byly zjištěny u ARMCO železa pro trhliny v módech II i III, středně velké úhly u titanu a niklu a největší úhly (vyhnutí do čistého módu I) byly pozorovány u austenitické oceli. Tyto rozdíly lze vysvětlit různým počtem dostupných skluzových systémů v krystalových mřížkách daných materiálů. Poměry mezi naměřenými prahovými hodnotami v módu I, II a III byly srovnány s předpověďmi teoretických modelů. Byl navržen analytický vztah pro efektivní prahové hodnoty v módu II, který byl v dobré shodě s experimentálními výsledky. Pomocí efektivních prahových hodnot bylo vyčísleno kritérium pro vyhýbání do módu I, které vedlo ke kritickému úhlu odklonu 40° souvisejícímu s přechodem z lokálního smykového módu do otevíracího módu.
PROPAGATION OF LONG FATIGUE CRACKS IN AUSTENITIC STEEL UNDER SHEAR MODES II AND III
Holáň, Libor ; Man, Jiří (referee) ; Polák, Jaroslav (referee) ; Pokluda, Jaroslav (advisor)
This work is focused on the realization of experiment allowing simultaneous loading under mode II and III in a single circular specimen. Proposed experiment allowed to minimize crack closure during the cyclic loading and obtained values of thresholds of stress intensity range can be considered to be very close to effective values. This was attained by means of an unique experimental devices and procedure of preparation of pre-crack of specimen with circumferential notch, which was made of stainless austenitic steel. The obtained values were compared with theoretical models with the support of molecular dynamics and ab-anitio calculation. Based on observation was found out, that fatigue crack propagation is controlled by decohesion model in austenitic steel. The morphology of fracture surfaces was studied by means of optical chromatographie and 3D stereophotogrammetry, which allowed a comparison of created morphology under shear modes II and III. Morphology of fracture surface formed (static and cyclic loading) by pre-crack was also studied by means of selected roughness parameters. The mechanism of deflection (kink) of crack growth under mode II was defined.
Grain refinement effect on fatigue properties of austenitic stainless steel with deformation induced martensite formation
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Škorík, Viktor ; Karjalalinen, L.P.
Fatigue properties of metastable austenitic 301LN steel with coarse and ultrafine-grained microstructures were investigated at ambient temperature and the effect of grain refinement was evaluated. Two different microstructural states of material were introduced by different annealing conditions during special thermomechanical treatment. Fatigue life curves were obtained and compared for both coarse-grained and ultrafine- grained states of austenitic stainless steel. Magnetic measurements before, during and after cyclic loading were performed to reveal structural changes, i.e. formation of deformation-induced martensite. Relationship between microstructure refinement, phase composition and fatigue properties was discussed.
Microstructural Investigation and Mechanical Testing of an Ultrafine-grained Austenitic Stainless Steel
Chlupová, Alice ; Man, Jiří ; Polák, Jaroslav ; Karjalainen, L. P.
Special thermomechanical treatment based on high degree deformation followed by reversion annealing was applied to 301LN austenitic stainless steel to achieve ultrafine-grained (UFG) structure with considerably enhanced mechanical properties. Two different conditions of the thermomechanical treatment were adopted and resulting microstructures with different grain sizes were characterised by optical and high resolution scanning electron microscopy (SEM-FEG). Hardness measurements and tensile tests were performed to characterize mechanical properties. To reveal structural changes induced during thermomechanical treatment and during tensile tests a magnetic induction method was additionally applied. Experimental study validated the ability of the above special treatment to produce austenitic stainless steel with grain size about 1.4 m which exhibits tensile strength about 1000MPa while ductility remains on level about 60 %. The results obtained for both thermomechanical conditions are compared and the relationship between microstructure refinement, phase content and mechanical properties is discussed.

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