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Mechanical stability of retained austenite in aluminum-containing medium-Mn steel deformed at different temperatures

Kozłowska Aleksandra, Radwański Krzysztof, Matus Krzysztof, Samek Ludovic, Grajcar Adam

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

324--338

EN

The thermal and mechanical stabilities of retained austenite in aluminum-containing medium-Mn 0.16C–4.7Mn–1.6Al–0.2Si sheet steel were investigated. The strain-induced martensitic transformation in Mn TRIP steel was studied at different temperatures. Static tensile tests were carried out at the temperature ranging from − 60 to 200 °C. The tests allowed to study the influence of the temperature on austenite-to-martensite transformation kinetics. The interrupted tensile tests and corresponding X-ray measurements of retained austenite amount were performed to determine the mechanical stability of retained austenite using the Sugimoto model. The microstructure changes were investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Observed results reflected the effects of deformation temperature on the mechanical stability of retained austenite and the corresponding response of this phase to martensitic transformation. It was found that an increase in the deformation temperature resulted in the reduced intensity of the TRIP effect due to the higher mechanical stability of retained austenite. At the highest deformation temperature (200 °C), the evidence of thermally activated processes affecting the mechanical behavior was identified.

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Non-Metallic Inclusions and Hot-Working Behaviour of Advanced High-Strength Medium-Mn Steels

Grajcar A., Woźniak D., Kozłowska A.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 2A

811--820

EN

The work addresses the production of medium-Mn steels with an increased Al content. The special attention is focused on the identification of non-metallic inclusions and their modification using rare earth elements. The conditions of the thermomechanical treatment using the metallurgical Gleeble simulator and the semi-industrial hot rolling line were designed for steels containing 3 and 5% Mn. Hot-working conditions and controlled cooling strategies with the isothermal holding of steel at 400°C were selected. The effect of Mn content on the hot-working behaviour and microstructure of steel was addressed. The force-energetic parameters of hot rolling were determined. The identification of structural constituents was performed using light microscopy and scanning electron microscopy methods. The addition of rare earth elements led to the total modification of non-metallic inclusions, i.e., they replaced Mn and Al forming complex oxysulphides. The Mn content in a range between 3 and 5% does not affect the inclusion type and the hot-working behaviour. In contrast, it was found that Mn has a significant effect on a microstructure.

3

Thermomechanically Rolled Medium-Mn Steels Containing Retained Austenite

Grajcar A., Skrzypczyk P., Woźniak D.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1691--1697

EN

Chemical composition of four medium-Mn steels containing a various Mn content (3 and 5%) have been proposed in the present work. The two steels are base steels whereas the other two contain Nb microaddition. Thermomechanical rolling tests of 3.3 mm sheets have been carried out using a semi-industrial hot strip rolling line. Detailed investigations of the identification of structural constituents using light microscopy and scanning electron microscopy techniques have been performed. X-ray method has been applied to determine an amount of retained austenite and its C content. Significant microstructural parameters were revealed using an EBSD technique. It was found that the Mn addition affects strongly a microstructure type, stability of retained austenite and mechanical properties determined with a static tensile test. The steels containing 3% Mn are characterized by a good combination of strength and ductility whereas the tensile strength up to 1300 MPa is possible to obtain for the higher Mn content steels.

PL

W pracy zaprojektowano cztery składy chemiczne stali średniomanganowych zawierających 3 i 5% Mn. Dwie stale to stale bazowe, a pozostałe dwie zawierają mikrododatek Nb. Przeprowadzono próby walcowania termomechanicznego taśm o grubości 3.3 mm, stosując półprzemysłową linię walcowania na gorąco. Przeprowadzono szczegółowe badania identyfikacji składników strukturalnych z zastosowaniem mikroskopii świetlnej i skaningowej mikroskopii elektronowej. Udział austenitu szczątkowego i stężenie C w tej fazie wyznaczono metodą rentgenowska. Metoda EBSD została użyta do ilościowego wyznaczenia istotnych parametrów mikrostrukturalnych. Stwierdzono, że dodatek Mn ma silny wpływ na rodzaj otrzymanej mikrostruktury, stabilizację austenitu szczątkowego oraz własności mechaniczne wyznaczone w statycznej próbie rozciągania. Stale zawierające 3% Mn charakteryzują się dobrym połączeniem wytrzymałości i plastyczności, a stale o wyższym stężeniu Mn pozwalają uzyskać wytrzymałość na rozciąganie do 1300 MPa.

4

Microstructural Features of Strain-Induced Martensitic Transformation in Medium-Mn Steels with Metastable Retained Austenite

Grajcar A., Kilarski A., Radwański K., Swadźba R.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1673--1678

EN

The work addresses relationships between the microstructure evolution and mechanical properties of two thermomechanically processed bainitic steels containing 3 and 5% Mn. The steels contain blocky-type and interlath metastable retained austenite embeded between laths of bainitic ferrite. To monitor the transformation behaviour of retained austenite into strain-induced martensite tensile tests were interrupted at 5%, 10%, and rupture strain. The identification of retained austenite and strain-induced martensite was carried out using light microscopy (LM), scanning electron microscopy (SEM) equipped with EBSD (Electron Backscatter Diffraction) and transmission electron microscopy (TEM). The amount of retained austenite was determined by XRD. It was found that the increase of Mn addition from 3 to 5% detrimentally decreases a volume fraction of retained austenite, its carbon content, and ductility.

PL

W pracy przedstawiono zależności pomiędzy rozwojem mikrostruktury i własnościami mechanicznymi dwóch obrobionych cieplno-plastycznie stali bainitycznych zawierających 3 i 5% Mn. Stale zawierają blokowe ziarna i warstwy austenitu szczątkowego umieszczone pomiędzy listwami ferrytu bainitycznego. W celu monitorowania postępu przemiany austenitu szczątkowego w martenzyt odkształceniowy, próby rozciągania prowadzono do zerwania oraz przerywano przy odkształceniu 5 i 10%. Identyfikacji austenitu szczątkowego oraz martenzytu odkształceniowego dokonano przy użyciu mikroskopii swietlnej (LM), skaningowej mikroskopii elektronowej (SEM) z wykorzystaniem techniki EBSD (Electron Backscatter Diffraction), a także transmisyjnej mikroskopii elektronowej (TEM). Udział austenitu szczątkowego wyznaczono metodą rentgenowską. Stwierdzono, że wzrost zawartości Mn z 3 do 5% obniża udział austenitu szczątkowego, stężenie węgla w tej fazie, a także ciągliwość stali.