Izračunavanje otpora deformacije nisko ugljičnih čelika tijekom toplog valjanja

Deformation behaviour of low carbon steels under hot rolling service conditions is predicted utilising a combination of isothermic single step deformation test, anisothermic interrupted test and hot rolling simulation performed on torsion plastometer. The stress s0.05 at strain level e = 0.05 and the restoring factor fr are proposed to be used for the description of the strengthening / restoring process during repeated deformation.Deformacija nisko ugljičnih čelika tijekom toplog valjanja izračunava se kombinacijom jednokoračnog izotermnog testa na deformaciju, prekinutog testa i simulacije toplog valjanja izvedene na torzionom plastometru. za opis procesa jačanja/obnavljanja tijekom ponavljanja deformacije predlaže se uporaba naprezanja s0.05 na nivou deformacije e = 0.05 i faktora obnavljanja fr

Proučavanje sekundarne rekristalizacije u čeliku s orijentiranim zrnima pri dinamičkim uvjetima toplinske obradbe

The present study was made to investigate secondary recrystallization in grain-oriented steels annealed at short time temperature exposures with application of dynamical heating. The investigated GO steels for experiments were taken from one industrial line after final cold rolling reduction and subsequent box annealing. It was shown that application of short time heat treatment conditions could lead to complete abnormal grain growth in the investigated GO steel. The texture and microstructure obtained in the laboratory treated material is similar to that observed in the same GO steel taken after industrial final box-annealing. However, some “parasitic” grains were observed in the secondary recrystallized matrix of the laboratory treated GO steel. These “parasitic” grains possess the unwanted from magnetic properties point of view {111} orientation components.Ova studija istražuje sekundarnu rekristalizaciju u čelicima s orijentiranim zrnima odžarenim kratkotrajno, a pod utjecajem dinamičkog zagrijavanja. Istraživanja ZO čelika za eksperimente uzeti su iz jedne industrijske linije nakon konačnog hladnog redukcijskog valjanja i naknadnog žarenja u komori. Pokazano je, primjena uvjeta kratkotrajne toplinske obradbe mogu dovesti do potpuno nenormalnog rasta zrna u istraživanom ZO čeliku. Tekstura i dobivena mikrostruktura u laboratorijski obrađivanim materijalima, slični su onim primjećenih kod nekih ZO čelika uzetih nakon konačnog industrijskog žarenja u komori. Međutim, neka „parazitna“ zrna primjećena su tijekom sekundarne rekristalizacije laboratorijski tretiranih ZO čelika. Ova „parazitna“ zrna posjeduju nepoželjne (111) orijentirane komponente s točke gledišta magnetnih svojstava

Učinak druge faze topologije čestica pri početnoj temperaturi abnormalnog rasta zrna kod Fe – 3% Si čelika

The relations between regimes of dynamic annealing, state of secondary particles system and the onset temperature of abnormal grain growth are investigated. Two distinguish types of Fe-3%Si grain-oriented steels, after one and two stage cold rolling, were studied. The second phase particles remain unaffected in first type of steel during the heat treatment. Vice versa, the increased density of second phases was observed after annealing in the second type of the investigated materials. It is shown that start/onset of abnormal grain growth strongly depends on both volume fraction of second phase particles and annealing temperature. Texture and magnetic properties of the investigated samples are investigated within the current study.Istraživani su odnosi između režima dinamičkog žarenja, stanja sustava sekundarnih čestica i početne temperature abnormalnog rasta zrna. Analizirane su dvije različite vrste Fe-3%Si zrnato usmjerenih čelika, nakon prve i druge faze hladnog valjanja. Čestice druge faze ostaju nepromijenjene kod prve vrste čelika tijekom toplinske obrade. Obrnuto, uočena je povećana gustoća u drugoj fazi nakon žarenja kod druge vrste ispitanih materijala. Prikazano je da početak abnormalnog rasta zrna uvelike ovisi i o opsegu čestica druge faze i o temperaturi žarenja. Ova analiza istražuje teksturu i magnetska svojstva ispitanih uzoraka

Current profiles and AC losses of a superconducting strip with elliptic cross-section in perpendicular magnetic field

The case of a hard type II superconductor in the form of strip with elliptic cross-section when placed in transverse magnetic field is studied. We approach the problem in two steps, both based on the critical-state model. First we calculate numerically the penetrated current profiles that ensure complete shielding in the interior, without assuming an a priori form for the profiles. In the second step we introduce an analytical approximation that asumes that the current profiles are ellipses. Expressions linking the sample magnetization to the applied field are derived covering the whole range of applied fields. The theoretical predictions are tested by the comparison with experimental data for the imaginary part of AC susceptibility.Comment: 12 pages; 3 figure

Kvantifikacija mikrostrukture i vrednovanje mehaničkih svojstava u neorijentiranim elektro čelicima

This paper presents an original method of the estimation of average grain size in microstructure of broad grain size distribution and the parameter, describing the homogeneity of microstructure. The coefficient of microstructure homogeneity is defined. The mechanical properties of non-oriented electrical steels are predicted using new equation of grain size estimation.Ovaj rad predstavlja originalnu metodu utvrđivanja prosječne veličine zrna u mikrostrukturi prosječne veličine zrna i parametra te strukture opisivanjem njene homogenosti. Definiran je koeficijent homogenosti takve mikro-strukture. Mehanička svojstva neorijentiranih elektro čelika su predviđena novom jednadžbom za utvrđivanje veličine zrna

Novi oblik jednadžbe za izračunavanje otpora deformacije u industrijskim uvjetima toplog valjanja

A new equation for the prediction of steel deformation resistance under industrial hot rolling conditions is proposed. This new expression can be used for more accurate description of material deformation behavior at service conditions utilizing data from laboratory plastometer experiments.Predlaže se nova jednadžba za izračunavanje otpora deformacije čelika u industrijskim uvjetima toplog valjanja. Novi izraz se može koristiti za točniji opis deformacije materijala u radnim uvjetima za što se koriste podaci dobiveni laboratorijskim eksperimentima s plastometrom