EBSD analýza fázového složení oceli TRIP při různých úrovních deformace

EBSD Analysis of Phase Compositions of TRIP Steel on Various Strain Levels

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Flat test bar made of TRIP steel was sequentially strained in tension. Eeach deformation step was made on a predefined strain level in which the phase composition was measured using EBSD; the analyses were made ex-situ exactly in the same area of 30x30 micrometer. Retained austenite (RA) was present in the form of elongated grains (plates) and roughly equiaxial ones. The RA content was initially 14.5% and decreased with imposed strain down to approximately 5% in selected strain range from 0% to 10%. This is in agreement to some extent with outcomes of both in-situ and ex-situ experiments presented by other authors, the difference beeing supposed either in data clean up or in variation in micriostructure of particular steel. Kernel average misorientation method was confirmed as useful tool to discern bainite and grainy ferrite in lightly deformed specimen. Problem arose in distinguishing between martensite and deformed ferrite at higher deformation levels because of high dislocation density and/or lattice distortion in both components. The ferrite and retained austenite fraction were analysed with sufficient accuracy; martensite fraction was established with high degree of uncertainty.

Ploché zkušební tyče z oceli TRIP byly postupně deformovány v tahu. V každém deformačním kroku bylo měřeno fázové složení pomocí metody EBSD; tyto analýzy byly prováděny ex-situ stále v jednom přesně definovaném místě o velikosti 30x30 mikrometrů. Zbytkový austenit (RA) byl přítomen ve formě zrn protáhlých (desek) a zhruba rovnoosých. Podíl RA činil zpočátku 14.5% a se vzrůstající deformací v rozsahu 0 až 10% klesl na cca 5%. Toto je v hrubém souladu s výsledky ostatních autorů, dosažených in-situ i ex-situ , přičemž pozorovaný rozdíl je patrně způsoben buďto filtrací dat nebo přirozenou variací mikrostruktury dané oceli. Byla potvrzena vhodnost metody jádrových průměrů dezorientací pro odlišení bainitického feritu od feritické matrice u lehce deformovaných vzorků. Problémy vyvstaly při rozlišování martenzitu a deformovaného bainitu při vyšších stupních deformace a to díky vysoké hustotě dislokací a/nebo distorzi mřížky obou strukturních komponent. Podíly feritu a zbytkového austenitu se podařilo stanovit s dostatečnou přesností; podíl martenzitu je však zatížen velkou chybou.

Flat test bar made of TRIP steel was sequentially strained in tension. Eeach deformation step was made on a predefined strain level in which the phase composition was measured using EBSD; the analyses were made ex-situ exactly in the same area of 30x30 micrometer. Retained austenite (RA) was present in the form of elongated grains (plates) and roughly equiaxial ones. The RA content was initially 14.5% and decreased with imposed strain down to approximately 5% in selected strain range from 0% to 10%. This is in agreement to some extent with outcomes of both in-situ and ex-situ experiments presented by other authors, the difference beeing supposed either in data clean up or in variation in micriostructure of particular steel. Kernel average misorientation method was confirmed as useful tool to discern bainite and grainy ferrite in lightly deformed specimen. Problem arose in distinguishing between martensite and deformed ferrite at higher deformation levels because of high dislocation density and/or lattice distortion in both components. The ferrite and retained austenite fraction were analysed with sufficient accuracy; martensite fraction was established with high degree of uncertainty.

Difrakce zpětně rozptýlených elektronů (EBSD), TRIP efekt, zbytkový austenit

Electron backscattering diffraction (EBSD), TRIP effect, Retained austenite

2009

02.06.2009

University of Žilina

Žilina

1335-0803

Materiálové inžinierstvo

XVI

2

11–17

7