Wyniki wyszukiwania - Biblioteka Nauki

1

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

100%

Grajcar A. , Opiela M. , Griner S.

|

tom 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).

2

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

100%

Sohrabi M. J. , Mirzadeh H. , Sadeghpour S. , Geranmayeh A. R.

|

tom 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

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

100%

Singh N. , Nanda T. , Kumar B. R. , Das S. K. , Singh V.

|

2019

|

tom 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.

4

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

100%

Kozłowska A. , Grajcar A. , Janik A. , Radwański K. , Krupp U. , Matus K. , Morawiec M.

|

tom 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.

5

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

80%

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

|

tom 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.