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1

Austenitic Stability and Strain-Induced Martensitic Transformation Behavior of Nanocrystalline FeNiCrMoC HSLA Steels

Park Jungbin, Jeon Junhyub, Seo Namhyuk, Kim Gwanghun, Son Seung Bae, Jung Jae-Gil, Lee Seok-Jae

Archives of Metallurgy and Materials

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2023

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Vol. 68, iss. 1

77--80

EN

The austenitic stability and strain-induced martensitic transformation behavior of a nanocrystalline FeNiCrMoC alloy were investigated. The alloy was fabricated by high-energy ball milling and spark plasma sintering. The phase fraction and grain size were measured using X-ray diffraction. The grain sizes of the milled powder and the sintered alloy were confirmed to be on the order of several nanometers. The variation in the austenite fraction according to compressive deformation was measured, and the austenite stability and strain-induced martensitic transformation behavior were calculated. The hardness was measured to evaluate the mechanical properties according to compression deformation, which confirmed that the hardness increased to 64.03 HRC when compressed up to 30%.

2

Tailoring the strength-ductility balance of a commercial austenitic stainless steel with combined TWIP and TRIP effects

Sohrabi Mohammad Javad, Mirzadeh Hamed, Sadeghpour Saeed, Geranmayeh Abdol Reza

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e170, 2023

EN

The sequential twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects were induced in a commercial AISI 304L stainless steel by tailoring the average austenite grain size (via thermomechanical processing of cold rolling and reversion/recrystallization annealing), leading to a combination of high yield stress and total elongation as well as a remarkable strength-ductility synergy similar to advanced high-strength steels (AHSS) for automotive industry. In fact, the refinement of grains promoted the TWIP effect at the expense of the TRIP effect due to its effect on increasing the apparent stacking fault energy; while the coarsening/growth of grains led to a pronounced TRIP effect via deformation-induced martensitic phase transformation during straining. Moreover, the TRIP/TWIP effects were characterized by the simple work-hardening analysis such as slope change and appearance of extremum points on the curves of work-hardening rate, logarithmic and parabolic segments on the curves of instantaneous work-hardening exponent, and deviations from the strain-hardening Hollomon lines. The results were supported by the interrupted tensile tests and detailed electron backscattered diffraction (EBSD) analysis, where the merit of the TWIP-TRIP steels was shown in the case of a commercial austenitic stainless steel.

3

Mechanical and thermal stability of retained austenite in plastically deformed bainite-based TRIP-aided medium-Mn steels

Kozłowska Aleksandra, Grajcar Adam, Janik Aleksandra, Radwański Krzysztof, Krupp Ulrich, Matus Krzysztof, Morawiec Mateusz

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 3

807--820

EN

Advanced medium-Mn sheet steels show an opportunity for the development of cost-effective and light-weight automotive parts with improved safety and optimized environmental performance. These steels utilize the strain-induced martensitic transformation of metastable retained austenite to improve the strength–ductility balance. The improvement of mechanical performance is related to the tailored thermal and mechanical stabilities of retained austenite. The mechanical stability of retained austenite was estimated in static tensile tests over a wide temperature range from 20 °C to 200 °C. The thermal stability of retained austenite during heating at elevated temperatures was assessed by means of dilatometry. The phase composition and microstructure evolution were investigated by means of scanning electron microscopy, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy techniques. It was shown that the retained austenite stability shows a pronounced temperature dependence and is also stimulated by the manganese addition in a 3–5% range.

4

Effect of Composition on Strain-Induced Martensite Transformation of FeMnNiC Alloys Fabricated by Powder Metallurgy

Choi Seunggyu, Jeon Junhyub, Seo Namhyuk, Moon Young Hoon, Shon In-Jin, Lee Seok-Jae

Archives of Metallurgy and Materials

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2020

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Vol. 65, iss. 3

1001--1004

EN

We investigated the austenite stability and mechanical properties in FeMnNiC alloy fabricated by spark plasma sintering. The addition of Mn, Ni, and C, which are known austenite stabilizing elements, increases its stability to a stable phase existing above 910°C in pure iron; as a result, austenitic microstructure can be observed at room temperature, depending on the amounts of Mn, Ni, and C added. Depending on austenite stability and the volume fraction of austenite at a given temperature, strain-induced martensite transformation during plastic deformation may occur. Both stability and the volume fraction of austenite can be controlled by several factors, including chemical composition, grain size, dislocation density, and so on. The present study investigated the effect of carbon addition on austenite stability in FeMnNi alloys containing different Mn and Ni contents. Microstructural features and mechanical properties were analyzed with regard to austenite stability.

5

In situ investigations of microstructural changes during tensile deformation of AISI 304L stainless steels

Singh Navjot, Nanda Tarun, Kumar B. Ravi, Das Swapan Kumar, Singh Vishal

Archives of Civil and Mechanical Engineering

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2019

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Vol. 19, no. 3

672--679

EN

The present work investigates the microstructural changes in an AISI 304L austenitic stainless steel during the early stages of tensile deformation (where austenite does not transform to strain induced martensite). In situ tensile experiments were conducted to record grain orientation changes and slip activation in the steel. The effect of grain size, neighboring grains, and annealing twins on orientation changes during deformation was investigated. Results showed that at a given strain level, grains lying in relatively softer regions and possessing higher Schmid factor values accommodated the plastic deformation initially and showed orientation changes toward the stable orientation. The relatively larger grains changed their orientations only at higher strain levels. Grain orientation changes were also influenced by size and crystallographic orientation of neighboring grains. For grains containing annealing twins, the orientation changes of twin and its grain were in different directions during deformation at a given strain level. Further, grains containing multiple twins showed delayed deformation. The study of tensile deformation behavior in this respect opens up new routes to alter and hence enhance the mechanical properties of materials by engineering their microstructure.

6

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.

7

Rozwój struktury wielofazowej stali typu C-Mn-Si-Al-Nb-Ti ze wzrostem odkształcenia plastycznego na zimno

Grajcar A., Opiela M., Griner S.

Inżynieria Materiałowa

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2011

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Vol. 32, nr 1

55-61

PL

Praca dotyczy identyfikacji składników strukturalnych oraz ich cech morfologicznych w stali o strukturze wielofazowej typu C-Mn-Si-Al z mikrododatkami Nb i Ti. Próbki pobrane z odcinków blach po obróbce cieplno-plastycznej poddano jednoosiowemu rozciąganiu zgodnie z kierunkiem walcowania. Odkształcenie realizowano do wydłużenia 5, 10 i 15% oraz do zerwania próbki. Analizowano rozwój struktury wielofazowej w miarę wzrostu odkształcenia na zimno, ze szczególnym uwzględnieniem austenitu szczątkowego i martenzytu indukowanego odkształceniem. Stwierdzono, że austenit cechuje duża stabilność mechaniczna, będąca efektem dużego rozdrobnienia ziaren fazy ? w wyniku zastosowanej obróbki cieplno-plastycznej, a także postępującej stopniowo fragmentacji austenitu szczątkowego. W początkowym etapie odkształcenia przemianie ulegają duże ziarna, zlokalizowane w osnowie ferrytycznej o znacznej gęstości dyslokacji. W miarę wzrostu odkształcenia przemianie ulega austenit, stanowiący graniczne obszary wysp bainitycznych. Częściowa przemiana austenitu szczątkowego w bainicie ziarnistym oraz w środkowej części warstwowych obszarów tej fazy, ulokowanych pomiędzy płytkami ferrytu bainitycznego, rozpoczyna się przy odkształceniu około 15%. Duża stabilność austenitu występującego pomiędzy płytkami ferrytu bainitycznego wynika z ciśnienia hydrostatycznego wprowadzanego przez twarde płytki tej fazy, podobnie jak wywieranego przez indukowany odkształceniem martenzyt drobnopłytkowy. Po zerwaniu próbki stabilne pozostają rozdrobnione, warstwowe obszary austenitu oraz drobne ziarenka w bainicie ziarnistym.

EN

The work concerns the identification of structural constituents and their morphological features of C-Mn-Si-Al steel with Nb and Ti microalloying additions. The test samples taken from the sheets after the thermomechanical processing (Tab. 1) were subjected to single-axis tension along a rolling direction. Deformation was realized to elongation of 5, 10 and 15% as well as to specimens rupture. In this way, the analysis of the evolution of multiphase structure as a function of cold plastic deformation with a special attention to retained austenite and strain-induced martensite was conducted. It was found that retained austenite was high mechanically stable, retained austenite. Large grains located in a ferritic matrix of high dislocation density are transformed in an initial stage of deformation (Fig. 2, 3). As the strain increases, the retained austenite at the boundary regions of bainitic islands transforms (Fig. 2, 4). A partially transformation of retained austenite in granular bainite and in a middle part of layer regions of this phase, located between bainitic ferrite plates, begins at the strain value of about 15% (Fig. 5). The high stability of austenite occurring between bainitic ferrite plates is due to hydrostatic pressure exerting by hard plates of this phase, similarly as caused by strain-induced fine-plate martensite. After the rupture of specimens, the high mechanical stability of layer regions of austenite and fine granules in granular bainite is maintained (Fig. 6).

8

The effect of (γ→α') phase transformation on texture development in metastable austenic steel

Ratuszek W., Kowalska J., Ryś J., Rumiński M.

Archives of Metallurgy and Materials

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2008

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Vol. 53, iss. 1

213-219

EN

The present research concerns the analysis of texture development in austenitic stainless steel AISI 301 subjected to cold-rolling at room temperature. X-ray phase analysis and magnetic investigations revealed the appearance of the α'-martensite within the structure of the steel after deformation. The volume fraction of strain induced martensite increased with increasing rollin g reduction. The texture measurements of both phases were conducted from the centre layers of the rolled strip after selected thickness reductions. Texture development in the case of steel AISI 301 was very complex since three processes proceeded simultaneously in the course of rolling, i.e. plastic deformation of the austenitic y-phase, strain induced phase transformation (γ→α') and deformation of the formed α'-martensite. The resultant deformation texture of the steel is described by the components from the textures of both phases, i.e. austenite and martensite. The rolling texture of austenite describe mainly orientations from the fibre α = <110>IIND and the major components of the martensite deformation texture are orientations from the fibres α l = <110>IIRD and = &gamma<111>IlND. Transformations of the ideal orientations of austenite and transformations of the martensite texture (α'→γT ) indicate that the martensitic transformation proceeded preferentially according to Ku r d j u m o v-S a c h s (K-S) and N i s h i y a m a-W a s s e r m a n n (N-W) orientation relationships with variant selection.

PL

Prezentowane badania dotyczą analizy rozwoju tekstury w austenitycznej stali nierdzewnej AISI 301 poddanej walcowaniu na zimno w temperaturze pokojowej. Dyfrakcyjna analiza fazowa i badania magnetyczne wykazały obecność martenzytu α' w strukturze stali po odkształceniu. Udział objętościowy martenzytu wzrastał ze stopniem odkształcenia. Pomiary tekstury obu faz przeprowadzono w warstwach środkowych walcowanych taśm po wybranych stopniach odkształcenia. Rozwój tekstury odkształcenia w stali AISI 301 jest złożony gdyż podczas walcowania zachodzą równocześnie trzy procesy, tj.: odkształcenie plastyczne austenitu, przemiana fazowa (γ→α') indukowana odkształceniem oraz odkształcenie powstałego martenzytu α'. Teksturę odkształcenia stali stanowią zatem składowe występujące zarówno w teksturze austenitu jak i w teksturze martenzytu. Teksturę walcowania austenitu opisują zasadniczo orientacje wchodzące w skład włókna α = <110>IIKN, natomiast główne składowe tekstury martenzytu stanowią orientację z włókien α l = <110>IIKW oraz γ= <111>IIKN. Transformacje idealnych orientacji austenitu oraz transformacje tekstury martenzytu (α' —> γ T ) wskazują na to, że przemiana martenzytyczna zachodzi w sposób uprzywilejowany zgodnie z relacjami Kurdjumova-S a c h s a (K-S) i N i s h i y a m y-W a s s e r in a n n a (N-W) z preferencyjnym wyborem określonych wariantów.

9

Badania mechanizmu zmian plastyczności w stali AlSi 302 ciągnionej z bardzo dużymi odkształceniami

Łuksza J., Rumiński M., Ratuszek W., Blacharski M.

Hutnik, Wiadomości Hutnicze

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2007

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Vol. 74, nr 1-2

53-58

PL

Drut ze stali austenitycznej AlSi 302 poddano procesowi ciągnienia wielostopniowego, stosując duże odkształcenie całkowite. Przeprowadzono badania własności mechanicznych drutu przed odkształceniem oraz po każdym ciągu. Wyniki tych badań uwidoczniły specyficzne zmiany plastyczności w zakresie 80÷95 % redukcji przekroju. Podjęto próbę wyjaśnienia mechanizmu zachodzenia obserwowanych zmian własności mechanicznych. Wykonano pomiary zawartości martenzytu indukowanego odkształceniem po każdym ciągu, a także przeprowadzono analizę rozwoju tekstury w austenicie i martenzycie. Dodatkowo dokonano obserwacji mikrostruktury drutu za pomocą mikroskopu świetlnego i elektronowego. Ostatecznie sformułowano wnioski dotyczące wpływu zmian składu fazowego stali oraz specyfiki rozwoju tekstury w poszczególnych fazach na obserwowane zmiany plastyczności ciągnionego drutu ze stali AlSi 302.

EN

AlSi 302 austenitic steel wire was multi - pass - drawn applying large total reduction. Mechanical testing of wire before deformation and after each pass was performed, revealing specific plasticity variations in the range of 80 - 95 % reduction. An attempt was made to clarify the mechanism of such changes of mechanical properties. The measurement of strain - induced martensite volume fraction was performed after each pass, as well as investigations of texture evolution were realized for both austenite and martensite. Additionally, the microstructure of wire was observed with application of optical and electron microscopes. Finally, the concluding remarks were formulated concering the impact of the variations of austenite and martensite volume fractions as well as texture evolution in both phases, on specific changes of plasticity of AlSi 302 steel drawn wire.