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1

Rozwój mikrostruktury austenitu stali typu HSLA podczas obróbki plastycznej na gorąco

Opiela M.

Hutnik, Wiadomości Hutnicze

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2018

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Vol. 85, nr 5

156--160

PL

W pracy zbadano wpływ parametrów obróbki plastycznej na gorąco na przebieg dynamicznych i statycznych procesów aktywowanych cieplnie w stali konstrukcyjnej typu HSLA (High Strength Low Alloy) zawierającej 0,17% C, 1,37% Mn oraz mikrododatki Nb, Ti, V o stężeniu – odpowiednio – 0,025%, 0,004% i 0,019%. Do wyznaczenia krzywych σ–ε oraz kinetyki rekrystalizacji austenitu odkształconego plastycznie wykorzystano symulator termomechaniczny Gleeble 3800. Próbki badano w zakresie temperatury od 900 do 1000°C z prędkością odkształcenia 3 s-1. Ujawniono strukturę austenitu pierwotnego próbek po dwuetapowym ściskaniu z wytrzymaniem izotermicznym przez czas od 0,2 do 120 s oraz wyznaczono energię aktywacji procesu odkształcenia plastycznego na gorąco badanej stali. Uzyskane wyniki badań pozwolą na opracowanie technologii blach grubych ze stali mikrostopowej typu HSLA metodą obróbki cieplno-plastycznej – walcowania ze sterowaną rekrystalizacją.

EN

The paper investigates the influence of hot-working parameters on the progression of thermally activated dynamic and static processes in HSLA (High Strength Low Alloy) constructional steel, containing 0.17% C, 1.37% Mn and microadditions of Nb, Ti, V in the amounts of 0.025 %, 0.004% and 0.019%, respectively. In order to determine the σ–ε curves and the kinetics of recrystallization of plastically deformed austenite, the Gleeble 3800 thermomechanical simulator was used. Specimens were tested in the temperature range from 900 to 1000°C, at the deformation rate of 3 s-1. Microstructure of primary austenite was revealed after two-stage compression of samples, with isothermal holding for the period of 0.2 to 120 s; the activation energy for hot working of the examined steel was determined. Obtained research results will allow to develop the technology of HSLA type microalloyed steel plates with the method of thermomechanical treatment – recrystallization controlled rolling.

2

Wpływ parametrów przetwarzania na strukturę i właściwości mechaniczne intermetalicznych taśmNi3Al po walcowaniu na zimno i statycznym wygrzewaniu

Jóźwik P., Polkowski W., Schindler I., Mikuszewski T., Bojar Z.

Hutnik, Wiadomości Hutnicze

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2017

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Vol. 84, nr 8

336--341

PL

W pracy przedstawiono wyniki badań wpływu temperatury walcowania i parametrów późniejszego statycznego wygrzewania izotermicznego taśm ze stopu na osnowie fazy międzymetalicznej Ni3Al z dodatkami stopowymi cyrkonu i boru na zakres przebudowy ich struktury i zmiany właściwości mechanicznych w następstwie procesów aktywowanych cieplnie. Proces obróbki plastycznej realizowano w temperaturze pokojowej lub po oziębianiu w ciekłym azocie. Zmiany struktury po izotermicznym wygrzewaniu w temperaturze 650°C, 700°C, 750°C i 800°C analizowano ilościowo przy użyciu skaningowej mikroskopii elektronowej sprzężonej z układem do analizy dyfrakcji elektronów wstecznie rozporoszonych (EBSD) a zmiany właściwości mechanicznych na podstawie wyników statycznej próby rozciągania taśm w temperaturze pokojowej w atmosferze powietrza. Stwierdzono, że walcowanie w zakresie kriogenicznym zwiększa, względem walcowania w temperaturze pokojowej, poziom zmagazynowanej energii odkształcenia plastycznego, przez co zwiększa liczbę zarodków rekrystalizacji, stopień rozdrobnienia ziarna po rekrystalizacji - aż do poziomu nano, jak też efektywność rekrystalizacji statycznej mierzoną udziałem granic szerokokątowych w ogólnej populacji granic ziarn. Uzyskane taśmy cechują się wysokim poziomem umocnienia granicami ziarn (granica plastyczności i doraźna wytrzymałość na rozciąganie istotnie powyżej 2GPa) przy zadowalającej podatności do odkształcenia trwałego (wydłużenie względne do zerwania w próbie rozciągania w temperaturze pokojowej w powietrzu, nawet powyżej 20%).

EN

An influence of the plastic working temperature and subsequent annealing on the structure and mechanical properties of Ni3Al-based intermetallic alloy with zirconium and boron additionis shown in the paper. The cold rolling process was conducted at room or liquid nitrogen temperature. The effects of structure rebuilding after isothermal heat treatment at 650°C, 700°C, 750°C or 800°C were observed by using a scanning electron microscopy coupled with an electron backscatter diffraction system (EBSD) and finally static tensile tests were done. It was confirmed that the value of plastic working temperature significantly affects stability of Ni3Al structure during isothermal annealing and, as a result, influences mechanical properties of investigated intermetallic strips. The higher amount of deformation energy stored in case of cold rolling of strips quenched at liquid nitrogen supports both more frequent nucleation of a new grains, confirmed by a bigger amount of nano grains and more effective recrystallization process estimated by a lower ratio of low to high angle grain boundaries participation in the structure. Finally not only better strength but also better plasticity of liquid nitrogen temperature rolled Ni3Al strips in comparison to room temperature rolled one was confirmed.

3

Numeryczny model zjawiska rekrystalizacji statycznej dla wysokowęglowej stali bainitycznej

Dembiczak T., Knapiński M., Garbarz B.

Hutnik, Wiadomości Hutnicze

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2017

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Vol. 84, nr 2

92--97

PL

W artykule przedstawiono model kinetyki rekrystalizacji statycznej oraz wyznaczono współczynniki równania opisującego wielkość ziaren zrekrystalizowanych statycznie w wysokowęglowej stali bainitycznej w funkcji temperatury, odkształcenia plastycznego, prędkości odkształcenia oraz początkowej wielkości ziarna austenitu. Ponadto w pracy dokonano porównania modelu kinetyki rekrystalizacji statycznej badanej stali z modelami dla stali o innych składach chemicznych. Prezentowane wyniki są kontynuacją badań opisanych w pracy [1], w której kinetykę rekrystalizacji statycznej opisano równaniami Avramiego o współczynnikach zależnych od parametrów wcześniej zadanego odkształcenia plastycznego.

EN

The article presents a model of the kinetics of static recrystallization and coefficients determined in the equation describing the size of statically recrystallized grains in high-carbon bainitic steel as a function of temperature, plastic strain, plastic strain rate and the initial grain size of austenite. Moreover the work compares the model of kinetics of static recrystallization of tested steel to models for steel with different chemical composition. The presented research is a continuation of tests presented in [1] in which the kinetics of static recrystallization is described with Avrami equation with coefficients depended on previously specified plastic deformation.

4

Kinetics of static recrystallization in the coarse-grained Fe–40 at.%Al–Zr–B alloy

Schindler I., Kopeček J., Kawulok P., Jabłońska M., Hadasik E., Jóźwik P., Opěla P., Hanus P., Polkowski W., Bojar Z.

Archives of Civil and Mechanical Engineering

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2017

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Vol. 17, no. 4

816--826

EN

The aim of works was to describe mathematically the kinetics of static recrystallization of the alloy type Fe–40 at.%Al–Zr–B (with 24.6 Al–0.01 B–0.18 Zr–0.01 C in wt.%) with the coarse-grained structure. The microstructure of the laboratory castings made of this extremely brittle alloy was homogenized by hot rolling of the material in the protective capsules and by the long-term annealing at 1200 °C. An initial microstructure with average grain size 0.77 ± 0.27 mm was obtained. Based on the isothermal plastic deformation tests and EBSD analysis, the static recrystallization kinetics of the prepared coarse-grained B2 iron aluminide after strain 0.20 was mathematically described. Recrystallized fraction depends on deformation/annealing temperature (900–1100 °C) as well as on annealing time. The activation energy of static recrystallization was calculated as 255 kJ mol−1. Competition between dynamic recovery and static recrystallization was proved after strain 0.35 and annealing temperature 1100 °C. Static recrystallization starts relatively easily in the studied alloy, but a very long-term annealing is quite necessary for the complete course of recrystallization. The mean size of recrystallized grains falls with the decreasing annealing temperature (0.47 ± 0.15 mm for temperature 1100 °C, and 0.22 ± 0.04 mm for 900 °C). Even at a temperature of 1200 °C the annealing after deformation should last approx. 1 min for obtaining the fully recrystallized microstructure. That is why the standard hot forming technologies should be combined by an interpass annealing in order to refine sufficiently the coarse grains.

5

Effects of Nb, Ti and V on recrystallization kinetics of austenite in HSLA steels

Opiela M.

Inżynieria Materiałowa

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2016

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Vol. 37, nr 6

289--294

EN

The work presents research results of impact of Nb, Ti and V microadditions on recrystallization kinetics and microstructure of newly elaborated steels assigned for production of forged machine parts, using the method of thermomechanical treatment. The study was performed with the use of Gleeble 3800 simulator. In order to determine recrystallization kinetics of plastically deformed austenite, discontinuous compression tests of specimens were done with a given strain at the rate of 10 s–1, in a temperature range from 900 to 1100°C, with isothermal holding of samples between successive stages of deformation for 2 to 100 s. Recrystallization kinetics of plastically deformed austenite was described using the Johnson-Mehl-Avrami equation. Performed two-stages compression tests revealed that microadditions introduced into steel considerably influence the kinetics of static recrystallization. Determined time of total recrystallization of austenite, tR, in a temperature range from 1100°C to 900°C changes from 100 to 600 s and from 300 to 800 s — for the Ti–V steel and Ti–Nb–V steel, respectively. Executed hot compression tests will contribute to establishing conditions of forging with the method of thermomechanical treatment.

PL

W pracy przedstawiono wyniki badań oddziaływania mikrododatków Nb, Ti i V na kinetykę rekrystalizacji i strukturę nowo opracowanych stali typu HSLA przeznaczonych do wytwarzania kutych elementów maszyn metodą obróbki cieplno-plastycznej.

6

Numerical investigation of the static recrystallization inhomogeneities across the plate thickness during continuous annealing

Sitko M., Madej Ł., Perzyński K., Kwiaton N., Kuziak R., Radwański K.

Computer Methods in Materials Science

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2015

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Vol. 15, No.3

371--379

EN

Analysis of static recrystallization inhomogeneities along the thickness of the cold rolled ferritic-pearlitic steel during continuous annealing process is the main goal of the present paper. The multiscale concurrent Cellular Automata Final Element (CAFE) model is used during the numerical investigation. The general concept of the CA algorithm of static recrystallization phenomenon is evaluated. The multiscale model of cold rolling based on the digital material representation (DMR) concept is used to accurately predict deformation energy distribution along the microstructure features and provide input data for the CA model. The final material morphology and recrystallization volume fractions after recrystallization in different plate locations: near the surface, in the middle of a plate, respectively, are evaluated. Finally, examples of obtained results of recrystallized microstructures are compared with the experimental data, to validate the approach.

PL

Celem niniejszej pracy jest analiza numeryczna niejednorodności rozwoju mikrostruktury na grubości pasma stali ferrytyczno-perlitycznej podczas ciągłego wyżarzania. W pracy wykorzystano bieżny model wieloskalowy na bazie metody elementów skończonych połączonej z metodą automatów komórkowych ( Cellular Automata Finał Element - CAFE). Model wieloskalowy walcowania na zimno oparto na idei cyfrowej reprezentacji materiału do dokładnego określenia energii zmagazynowanej w materiale w wyniku odkształcenia plastycznego, która zostanie wykorzystana jako jeden z parametrów początkowych modelu automatów komórkowych.Następnie przedstawiono wyniki w postaci morfologii materiału wraz z odpowiadającymi ułamkami części zrekrystalizowanej po procesie nagrzewania odpowiednio: przy powierzchni oraz w środku płyty. Uzyskane wyniki obliczeń numerycznych zostały porównane z danami eksperymentalnymi w celu walidacji modelu.

7

Identification of the static recrystallization cellular automata model parameters based on inverse analysis

Sitko M., Madej Ł., Kuziak R

Computer Methods in Materials Science

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2014

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Vol. 14, No. 4

206--214

EN

Development of the inverse algorithm for identification of the discrete cellular automata model of the static recrystallization based on the particle swarm optimization method is the main aim of the work. First, the idea of the inverse analysis approach is presented. Then subsequent modules of the algorithm are discussed, namely: direct problem model, experimental setup and optimization algorithm. The optimization part is realized by the basic variant of particle swarm optimization (PSO) method. Finally, examples of identified model parameters are presented and obtained results of recrystallized microstructures are compared with the experimental data.

PL

W artykule omówiono identyfikację parametrów modelu automatów komórkowych (Cellular Automata - CA) do symulacji rekrystalizacji statycznej z wykorzystaniem metody roju cząstek (Particle Swarm Optimization). W pierwszej części pracy przedstawiono główne założenia wykorzystanej do identyfikacji metody analizy odwrotnej. Następnie przedstawiono opracowany model automatów komórkowych, inspirowaną naturą metodę optymalizacji oraz omówiono uzyskane dane eksperymentalne. W ostatniej części przedstawione zostały wyniki przeprowadzonego procesu identyfikacji.

8

Modelling of static recrystallization kinetics by coupling crystal plasticity FEM and multiphase field calculations

Güvenci O., Henke T., Laschet G., Böttger B., Apel M., Bambach M., Hirt G.

Computer Methods in Materials Science

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2013

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Vol. 13, No. 2

368--374

EN

In multi-step hot forming processes, static recrystallization (SRX), which occurs in interpass times, influences the microstructure evolution, the flow stress and the final product properties. Static recrystallization is often simply modeled based on Johnson-Mehl-Avrami-Kolmogorov (JMAK) equations which are linked to the visco-plastic flow behavior of the material. Such semi-empirical models are not able to predict the SRX grain microstructure. In this paper, an approach for the simulation of static recrystallization of austenitic grains is presented which is based on the coupling of a crystal plasticity method with a multiphase field approach. The microstructure is modeled by a representative volume element (RVE) of a homogeneous austenitic grain structure with periodic boundary conditions. The grain microstructure is generated via a Voronoi tessellation. The deformation of the RVE, considering the evolution of grain orientations and dislocation density, is calculated using a crystal plasticity finite element (CP-FEM) formulation, whose material parameters have been calibrated using experimental flow curves of the considered 25MoCrS4 steel. The deformed grain structure (dislocation density, orientation) is transferred to the FDM grid used in the multiphase field approach by a dedicated interpolation scheme. In the phase field calculation, driving forces for static recrystallization are calculated based on the mean energy per grain and the curvature of the grain boundaries. A simplified nucleation model at the grain level is used to initiate the recrystallization process. Under these assumptions, it is possible to approximate the SRX kinetics obtained from the stress relaxation test, but the grain morphology predicted by the 2d model still differs from experimental findings.

PL

W wielostopniowych procesach obróbki plastycznej, rekrystalizacja statyczna (ang. static recrystallization - SRX) występująca w czasach przerw między odkształceniami, wpływa na rozwój mikrostruktury, naprężenie uplastyczniające oraz właściwości gotowego produktu. Statyczna rekrystalizacja jest często modelowana korzystając z równania Johnson-Mehl- Avrami-Kolmogorov (JMAK), które jest powiązane z lepkoplastycznym płynięciem materiału. Taki pół-empiryczny model nie jest w stanie przewidzieć mikrostruktury ziaren dla SRX. W niniejszym artykule przedstawiono podejście do symulacji statycznej rekrystalizacji austenitu wykorzystujące połączenie plastyczności kryształów z metodą pola wielofazowego. Mikrostruktura jest modelowana za pomocą reprezentatywnych elementów objętości (ang: Representative Volume Element - RVE) jednorodnej struktury ziaren austenitu z okresowymi warunkami brzegowymi. Mikrostruktura jest generowana za pomocą wieloboków Voronoi. Obliczenia odkształcenia RVE są prowadzone połączonymi metodami plastyczności kryształów i MES, z uwzględnieniem rozwoju orientacji ziaren oraz gęstości dyslokacji. Parametry modelu materiału wyznaczono na podstawie doświadczalnych krzywych płynięcia dla stali 25MoCrS4. Odkształcona struktura ziaren (gęstość dyslokacji, orientacja) jest przekazywana do siatki różnic skończonych w modelu pola wielofazowego stosując metodę interpolacji. W obliczeniach pola faz, siły pędne dla statycznej rekrystalizacji są obliczane na podstawie średniej energii w ziarnie i krzywizny granic ziaren. W celu zainicjowania rekrystalizacji stosowany jest uproszczony model zarodkowania na poziomie ziarna. Przy tych założeniach możliwe było oszacowanie kinetyki SRX na podstawie badań relaksacji naprężeń. Z drugiej strony przewidywana w modelu 2D morfologia ziaren wciąż odbiega od wyników doświadczalnych.

9

Thermo-mechanical processing and microstructure evolution of high-manganese austenitic TRIP-type steels

Dobrzański L. A., Borek W., Ondrula M.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 53, nr 2

59--66

EN

Purpose: The aim of the paper is to determine the influence of hot-working conditions on microstructure evolution and phase composition of new-developed high-manganese austenitic TRIP-type steels. Design/methodology/approach: The hot-working behaviour was determined in continuous and multistage compression tests performed in a temperature range of 850 to 1100°C by the use of the Gleeble 3800 thermo-mechanical simulator. The processes controlling work hardening and removing it were identified by microstructure evolution observations in different stages of compression with the amount of true strain 4x0.23. Phase composition of steels was confirmed by X-ray diffraction analysis. Findings: It was found that they have austenite microstructure with numerous annealing twins in the initial state. Continuous compression tests realized in the temperature range from 850 to 1050°C with the strain rate of 0.1, 1 and 10 s-1 enabled determination of yield stress values and values of εmax deformations - corresponding to maximum flow stress. The investigated steels are characterized by high values of flow stress from 120 to 380 MPa. Results of the multi-stage compression proved that applying the true strain 4x0.23 gives the possibility to refine the austenite microstructure. Research limitations/implications: To determine in detail the microstructure evolution during industrial rolling, the hot-working schedule should take into account real number of passes and higher strain rates. Practical implications: The obtained microstructure - hot-working conditions relationships and stress-strain curves can be useful in determination of power-force parameters of hot-rolling for sheets with fine-grained austenitic structures. Originality/value: The hot-working behaviour and microstructure evolution in various conditions of plastic deformation for new-developed high-manganese austenitic TRIP-type steels with Nb and Ti microadditions were investigated.

10

Effects of Nb, Ti and V on recrystallization kinetics of austenite in microalloyed steels

Opiela M., Ozgowicz W.

Journal of Achievements in Materials and Manufacturing Engineering

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2012

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Vol. 55, nr 2

759--771

EN

Purpose: The work presents research results of impact of Nb, Ti and V microadditions on flow stress, recrystallization kinetics and microstructure of newly elaborated steels assigned for production of forged machine parts, using the method of thermo-mechanical treatment. Design/methodology/approach: The study was performed with the use of Gleeble 3800 simulator. Stress-strain curves were determined during continuous compression test in a temperature range from 900 to 1100°C and at a strain rate of 1, 10 and 50 s-1. In order to determine recrystallization kinetics of plastically deformed austenite, discontinuous compression tests of specimens were done with a given strain at the rate of 10 s-1., in a temperature range from 900 to 1100°C, with isothermal holding of samples between successive stages of deformation for 2 to 100 s. Recrystallization kinetics of plastically deformed austenite was described using the Johnson-Mehl-Avrami equation. The observations of microstructures of thin foils were done using JEOL JEM 3010 transmission electron microscope. Findings: Basing on the analysis of the form and the course of curves obtained in the compression test, it was found that in the studied range of parameters of hot plastic deformation, the decrease of strain hardening of studied steels is caused by the process of continuous dynamic recrystallization. This is also confirmed by calculation results of activation energy of plastic deformation process. Performed two-stages compression tests revealed that microadditions introduced into steel considerably influence the kinetics of static recrystallization. Research limitations/implications: It was found that the time necessary for a total course of recrystallization of austenite is too long to be accepted in the production process of forgings. Practical implications: Executed hot compression tests will contribute to establishing conditions of forging with the method of thermo-mechanical treatment. Originality/value: Strain-stress curves and recrystallization kinetics curves of newly elaborated microalloyed steels have been determined.

11

Wpływ warunków odkształcenia plastycznego na zmiany naprężenia uplastyczniającego, stopień mięknięcia i strukturę stali mikrostopowej

Opiela M., Boruta J.

Hutnik, Wiadomości Hutnicze

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2012

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Vol. 79, nr 8

627--631

PL

W pracy przedstawiono wyniki badań dotyczących wpływu parametrów odkształcenia na odkształcalność na gorąco i kinetykę mięknięcia stali mikrostopowej zawierającej 0,28 %C, 1,41 %Mn, 0,027 %Nb, 0,028 %Ti i 0,019 %V. Ciągłe oraz przerywane próby ściskania próbek przeprowadzono z wykorzystaniem symulatora Gleeble 3800. Próbki badano w zakresie temperatury od 900 do 1100 °C z szybkością odkształcenia 1, 10 i 50 s-1. Próby ciągłego ściskania przeprowadzono w celu wyznaczenia krzywych s-e oraz energii aktywacji procesu odkształcenia plastycznego. W celu wyznaczenia kinetyki rekrystalizacji austenitu odkształconego plastycznie przeprowadzono przerywane próby ściskania z wytrzymaniem izotermicznym próbek między kolejnymi odkształceniami przez czas od 2 do 100 s.

EN

The paper presents the results of the effect of deformation parameters on the hot-deformation behavior and softening kinetics of the microalloyed steel containing 0.28 %C, 1.41 %Mn, 0.027 %Nb, 0.028 %Ti, and 0.019 %V. Continuous and double-hit comspression tests were performed using the Gleeble 3800 thermomechanical simulator. The samples were investigated at the temperature range from 900 to 1100 °C and strain rate of 1, 10 and 50 s-1. Continuous compression tests of samples were performed in order to obtain s-e curves and activation energy of plastic deformation. To determine the recrystallization kinetics of plastically deformed austenite, discontinuous compression tests of samples with applied deformation were performed with isothermal holding of specimens between successive deformations for 2 to 100 s.

12

Model mięknięcia z rekrystalizacją statyczną i zdrowieniem

Svyetlichnyy D., Nowak J., Pidvysotskyy V.

Hutnik, Wiadomości Hutnicze

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2012

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Vol. 79, nr 9

703--707

PL

W pracy został przedstawiony nowy model mięknięcia z uwzględnieniem rekrystalizacji statycznej i zdrowienia statycznego materiału po odkształceniu. Zaproponowany model składa się z dwóch części: klasycznego modelu rozwoju gęstości dyslokacji i modelu opracowanego na podstawie teorii KJMA. Wprowadzenia członu odpowiadającego za zdrowienie pozwala wytłumaczyć różnice wartości wykładnika Avramiego uzyskanego eksperymentalnie z wartościami teoretycznymi. Skuteczność nowego modelu została zweryfikowana badaniami eksperymentalnymi, których wyniki zamieszczono w artykule.

EN

In the paper a new model of material softening after deformation in view of processes of static recrystallization and static recovery is considered. As a starting point the difference of Avrami exponent obtained in experimental researches from theoretical value has served. It is suggested to consider not only static recrystallization process, but also recovery proceeding simultaneously in non-recrystallized grains. The theoretical background is presented and the equations for new model are received. Equations of transition from one model to another are included. An efficiency of new model is shown on the basis of experimental data.

13

Hot deformation and recrystallization of advanced high-manganese austenitic TWIP steels

Dobrzyński L A, Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2011

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Vol. 46, nr 1

71--78

EN

Purpose: The aim of the paper is to determine the influence of hot-rolling conditions on structure of new-developed high-manganese austenitic steels. Design/methodology/approach: Flow stresses during continuous and multi-stage compression tests were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steels were compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in different stages of hot-rolling was determined in metallographic investigations using light microscopy as well as X-ray diffraction. Findings: The steels are characterized by different microstructure in the initial state. Steel with higher Al concentration has stable microstructure of austenite with annealing twins, while steel with higher Si concentration consists of certain portion of e martensite in form of plates. The flow stresses are in the range of 200-430 MPa for the applied conditions of hot-working and are up to 40 MPa lower compared to continuous compressions. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery. On the basis of analysis of thermo-mechanical treatment carried out in continuous axisymetrical compression test and multi-stage compression test using the Gleeble 3800 simulator allowed to work out a schedule of three different variants of hot-rolling for each of investigated steels 26Mn-3Si-3Al-Nb-Ti and 27Mn-4Si-2Al-Nb-Ti. Research limitations/implications: To fully describe the hot-rolling behaviour of the new-developed steels, further investigations in wider temperature and strain rate ranges are required. Practical implications: Various conditions of hot-rolling for advanced high-manganese austenitic steels can be useful to determine influence of microstructure on mechanical properties obtained in static and dynamic tensile test. Originality/value: Microstructure evolution in various conditions of hot-rolling for advanced high-manganese austenitic steels were investigated.

14

Analiza rekrystalizacji statycznej austenitu stopowego w wysokowęglowej stali konstrukcyjnej

Dembiczak T., Knapiński M., Garbarz B.

Hutnik, Wiadomości Hutnicze

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2011

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Vol. 78, nr 9

831--834

PL

W artykule przedstawiono wstępne wyniki badań kinetyki rekrystalizacji statycznej austenitu zachodzącej w czasie przerwy między odkształceniami przy temperaturach 900÷1000 °C. Badania przeprowadzono w testach dwukrotnego ściskania płaskich próbek, przyjmując różne czasy przerwy pomiędzy kolejnymi odkształceniami. Analizując uzyskane krzywe płynięcia wyznaczono równania opisujące kinetykę rekrystalizacji austenitu stopowego.

EN

Results of preliminary studies of the static recrystallization kinetics of austenite occurring in holding time between deformations at temperature range of 900÷1000 °C were presented in the paper. Double compression of flat samples with holding time between successive strains were carried out. On the basis of flow curves equations describing the recrystallization kinetics of alloyed austenite were determined.

15

Electro-chemical monitoring of static recrystallization

Filus F., Schindler I., Fila J., Lasek S., Kubina T., Niewielski G., Kuc D., Hadasik E.

Archives of Civil and Mechanical Engineering

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2011

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Vol. 11, no 2

277-283

EN

The electro-chemical potentio-kinetic method has proved to be a sensitive technique for monitoring of static recrystallization in austenitic steel AISI 304 after its cold forming and annealing. Results obtained in this manner are in very good conformity with the results of metallographic and X-ray analysis, as well as with the measured values of hardness. Corrosion current density appeared to be a suitable criterion for evaluation of development of relaxation processes.

PL

W pracy zbadano możliwość elektrochemicznego monitorowania statycznej rekrystalizacji przy zastosowaniu metody potencjokinetycznej w austenitycznej stali AISI 304 po odkształceniu plastycznym na zimno i wyżarzaniu. Otrzymane wyniki wskazują na bardzo dobrą zgodność z wynikami badań metalograficznych i analizy rentgenowskiej oraz pomiarami twardości. Zmiany natężenia prądu korozyjnego mogą stanowić wygodne kryterium oceny przebiegu procesów relaksacyjnych.

16

Hot-working of advanced high-manganese austenitic steels

Dobrzański L. A., Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 2

507--526

EN

Purpose: The work consisted in investigation of newly elaborated high-manganese austenitic steels with Nb and Ti microadditions in variable conditions of hot-working. Design/methodology/approach: The force-energetic parameters of hot-working were determined in continuous and multi-stage compression test performed in temperature range of 850 to 1100°C using the Gleeble 3800 thermomechanical simulator. Evaluation of processes controlling work-hardening were identified by microstructure observations of the specimens compresses to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light, scanning and electron microscopy as well as X-ray diffraction. Findings: The investigated steels are characterized by high values of flow stresses from 230 to 450 MPa. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25)Mn alloys. Increase of flow stress along with decrease of compression temperature is accompanied by translation of εmax strain in the direction of higher deformation. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery and a deciding influence on a gradual microstructure refinement has statical recrystallization. The steel 27Mn-4Si-2Al-Nb-Ti has austenite microstructure with annealing twins and some fraction of ε martensite plates in the initial state. After the grain refinement due to recrystallization, the steel is characterized by uniform structure of γ phase without ε martensite plates. Research limitations/implications: To determine in detail the microstructure evolution during industrial rolling, the hot-working schedule should take into account real number of passes and higher strain rates. Practical implications: The obtained microstructure - hot-working relationships can be useful in the determination of power-force parameters of hot-rolling and to design a rolling schedule for high-manganese steel sheets with fine-grained austenitic structures. Originality/value: The hot-deformation resistance and microstructure evolution in various conditions of hot-working for the new-developed high-manganese austenitic steels were investigated.

17

Prediction of statically recrystallized microstructure during extrusion of aluminum alloys

Cvahte P., Kugler G., Rodič T.

Computer Methods in Materials Science

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2010

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Vol. 10, No. 4

294-306

EN

To predict evolution of microstructure of aluminum alloys after deformation a numerical model based on the method of cellular automata (CA) has been developed and combined with the finite element model (FEM). The main objective of the combined FEM-CA model is to enable numerical predictions of growth of grains in the subsurface layers of extruded bars that occurs after deformation before the quenching in the industrial hot extrusion production chain. The results of numerical simulations show a good agreement with the results of optical micrographs of the bars taken from the industrial experiments. The outcomes of this research demonstrate that numerical models can be successfully applied to simulate complex thermo-mechanical and metallurgical processes during hot extrusion.

PL

Aby przewidywać rozwój mikrostruktury stopów aluminium w procesie wyciskania opracowano numeryczny model wykorzystujący metodę automatów komórkowych (ang. Cellular automata - CA), który połączono z metodą elementów skończonych (ang fmite element method - FEM). Głównym celem połączonych modeli FEM-CA jest przeprowadzenie numerycznych symulacji rozrostu ziarna w warstwie przypowierzchniowej wyciskanego pręta. Taki rozrost jest obserwowany w warunkach przemysłowych po wyciskaniu przed rozpoczęciem chłodzenia wyrobu. Wyniki numerycznych symulacji wykazują dobrą zgodność z pomiarami za pomocą mikroskopii optycznej dla prętów pobranych z prób przemysłowych. Przeprowadzone badania wykazują, że modelowanie numeryczne może być z powodzeniem zastosowane do symulacji skomplikowanych zjawisk cieplno-mechanicznych i metalurgicznych podczas wyciskania na gorąco.

18

Processes forming the microstructure evolution of high-manganese austenitic steel in hot-working conditions

Dobrzański L. A., Borek W.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 2

397-407

EN

Purpose: The aim of the paper is to characterise the microstructure evolution of new-developed 27Mn-4Si-2Al-Nb-Ti high-manganese steel in various conditions of hot-working. Design/methodology/approach: Flow stresses during the multistage compression test were measured using the Gleeble 3800 thermo-mechanical simulator. To describe the hot-working behaviour, the steel was compressed to the various amount of deformation (4x0.29, 4x0.23 and 4x0.19). The microstructure evolution in successive stages of deformation was determined in metallographic investigations using light, scanning and electron microscopy as well as X-ray diffraction. Findings: The steel has austenite microstructure with annealing twins and some fraction of ĺ martensite plates in the initial state. The flow stresses are much higher in comparison with austenitic Cr-Ni and Cr-Mn steels and slightly higher compared to Fe-(15-25) Mn alloys. The flow stresses are in the range of 200-400 MPa for the applied conditions of hot-working. Making use of dynamic and metadynamic recrystallization, it is possible to refine the microstructure and to decrease the flow stress to 350 MPa during the last deformation at 850°C. Applying the true strains of 0.23 and 0.19 requires the microstructure refinement by static recrystallization. After the grain refinement due to recrystallization, the steel is characterised by uniform structure of ă phase without ĺ martensite plates. Research limitations/implications: To fully describe the hot-working behaviour of the new-developed steel, further investigations in wider temperature and strain rate ranges are required. Originality/value: The hot-deformation resistance and microstructure evolution in various conditions of hot-working for the new-developed high-manganese 27Mn-4Si-2Al-Nb-Ti austenitic steel were investigated.

19

Microstructure evolution of high-manganese steel during the thermomechanical processing

Dobrzański L. A., Grajcar A., Borek W.

Archives of Materials Science and Engineering

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2009

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Vol. 37, nr 2

69-76

EN

Purpose: The aim of the paper is to determine the influence of hot-working conditions on microstructure evolution of new-developed high-manganese austenitic steel. Design/methodology/approach: The hot-working behaviour was determined in continuous and multi-stage compression tests performed in a temperature range of 850 to 1100°C by the use of the Gleeble 3800 thermomechanical simulator. The processes controlling work hardening and removing it were identified by microstructure evolution observations in successive stages of compression with the amount of true strain 4x0.29, 4x0.23 or 4x0.19. Findings: The investigated steel is characterized by high values of flow stresses from 250 to 450 MPa. Increase of flow stress along with decrease of compression temperature is accompanied by translation of εmax strain in the direction of higher deformation. Results of the multi-stage compression proved that applying the true strain 4x0.29 gives the possibility to refine the austenite microstructure as a result of dynamic recrystallization. In case of applying the lower deformations 4x0.23 and 4x0.19, the process controlling work hardening is dynamic recovery and a deciding influence on a gradual microstructure refinement has statical recrystallization. Research limitations/implications: To determine in detail the microstructure evolution during industrial rolling, the hot-working schedule should take into account real number of passes and higher strain rates. Practical implications: The obtained σ-ε curves can be useful in determination of power-force parameters of hot-rolling and to design a rolling schedule ensuring a fine-grained microstructure of high-manganese steel products. Originality/value: The microstructure evolution in various conditions of hot-working for the new-developed high-manganese Mn-Si-Al-Nb steel was determined.

20

Structural and mechanical behaviour of TRIP-type microalloyed steel in hot-working conditions

Grajcar A.

Journal of Achievements in Materials and Manufacturing Engineering

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2008

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Vol. 30, nr 1

27-34

EN

Purpose: The aim of the paper is to investigate the influence of various deformation conditions on microstructure evolution and flow curves of TRIP-type steel. Design/methodology/approach: In order to determine the influence of MX-type interstitial phases on limiting the grain growth of primary austenite, samples were quenched in water from a temperature range, from 900 to 1200*C. Determination of processes controlling strain hardening was carried out in compression test using Gleeble 3800 simulator. The σ-ε curves were defined in a temperature range from 850 to 1150*C, for 0.1, 1 and 10s -1 of strain rate. To determine the progress of recrystallization samples were isothermally held for up to 60 s at 900 and 1000*C. Findings: Profitable impact of TiN and NbC particles on austenite grain growth limitation is present up to 1050*C. The values of flow stress are equal from 120 to 270 MPa. The steel is characterized by quite high values of deformation, εmax=0.4-0.65, corresponding to maximum stress on σ-ε curves. Beneficial grain refinement of primary austenite microstructure can be obtained due to static recrystallization. In temperature of 1000*C, t0.5 is equal 35 s and elongates to 43 s after decreasing deformation temperature to 900*C. The σ-ε curves obtained during multi-stage compression tests confirmed that a process controlling the strain hardening is a dynamical recovery. Research limitations/implications: To design hot-rolling conditions, the analysis of the primary austenite microstructure evolution during successive deformation cycles should be carried out. Practical implications: The obtained precipitation kinetics of MX-type phases and σ-ε curves are useful in determining hot-rolling conditions ensuring the fine-grained microstructure of primary austenite. Originality/value: The determined true stress-true strain curves were obtained for the TRIP-type microalloyed steel containing decreased Si concentration.