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1

Influence of the Carbon Content on the Kinetics of Phase Transformations During Continuous Heating from As-Quenched State in a Cr-Mn-Mo Model Alloys

Dziurka R., Pacyna J.

Archives of Metallurgy and Materials

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2012

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Vol. 57, iss. 4

943-950

EN

The presented work concerns the research on the kinetics of phase transformations during continuous heating from as-quenched state of three Cr-Mn-Mo model alloys with a different carbon content. The kinetics of phase transformations during continuous heating of investigated alloys was presented on the CHT (Continuous, Heating, Transformation) diagrams. The CHT diagrams were made on the grounds of dilatograms recorded for quenched samples, heated with various rates. Also the methodology of the dilatometric samples preparation and the method of the characteristic points determination was described. The investigated alloys are the model alloys. Taking into account their chemical compositions the possibility of improving their properties by means of the heat treatment can be expected. The investigations of the carbon influence on microstructures of model alloys with Cr-Mn-Mo were carried out. Broadening the knowledge on the carbon influence on the kinetics of phase transformations during continuous heating from as-quenched state, will help in designing new alloys with a better properties.

PL

Niniejsza praca zawiera badania kinetyki przemian fazowych przy nagrzewaniu ze stanu zahartowanego trzech modelowych stopów Cr-Mn-Mo o różnej zawartości węgla. Kinetyka przemian fazowych przy nagrzewaniu badanych stopów jest przedstawiona za pomocą wykresów CHT. Wykresy CHT zostały wykonane na podstawie dylatogramów nagrzewania z różnymi szybkościami uprzednio zahartowanych próbek. Ponadto w pracy zamieszczono metodologie przygotowania próbek do badań dylatometrycznych i przykłady wyznaczania punktów charakterystycznych. Badane stopy sa stopami modelowymi. Biorąc pod uwagę ich składy chemiczne istnieje możliwość poprawy ich właściwości za pomoca obróbki cieplnej. W pracy została podjęta próba zbadania wpływu węgla na mikrostrukture stopów Cr-Mn-Mo po odpuszczaniu. Niniejsze badania poszerza wiedzę na temat wpływu węgla na kinetykę przemian fazowych przy nagrzewaniu ze stanu zahartowanego, co pomoże w projektowaniu nowych stopów o lepszych własnościach.

2

The mossabauer spectroscopy studies of ε carbides precipitation

Krawczyk J., Bała P., Hanc A.

Archives of Metallurgy and Materials

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2008

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Vol. 53, iss. 3

689-693

EN

This work complements the knowledge concerning the kinetics of 6 carbide precipitation and decomposition. Investigations were performed on 120MnCrMo V8-6-4-2 steel, which was designed in 1998, in Phase Transformations Research Group of Department of Physical and Powder Metallurgy at the Faculty of Metals Engineering and Industrial Computer Science at AGH University of Science and Technology in Krakow. The samples of investigated steel were austenitized at the temperature of 900°C and hardened in oil. Next, three from four samples were tempered. Tempering consisted of heating the samples up to chosen temperatures with a heating rate of O.OSźC/s and, after reaching desired temperature, fast cooling. CEMS technique was applied for Mossbauer studies. Stabilized retained austenite by heating up to 80źC, in the result of mechanical destabilization, transforms into low-temperature tempered martensite, with the microstructure of low bainite (into the structural constituent in which 6 carbide exists). Influence of hardened steel heating temperature on 6 carbide precipitation was determined. Also the knowledge of the mechanisms of precipitation and decomposition of 6 carbide enables proper design of the heat treatment of 120MnCrMoV8-6-4-2 steel in respect to its application for hot working tools. Mossbauer spectroscopy was applied not only for quantitative analysis of 6 carbide, but also to analyze the values of hyperfine magnetic field, quadrupole splitting, isomeric shift and relation of 2 to 3 Zeeman splitting component line, what resulted in significant conclusions concerning the changes in its morphology and the level of stresses being present in it.

PL

W pracy przedstawiono wyniki pomiarów mossbauerowskich wykonanych na odpuszczonych do wybranych temperatur wczesniej zahartowanych próbkach ze stali 120MnCrMoV8-6-4-2. Pomiary wykonywano zarówno na powierzchniach szlifowanych jak i wypolerowanych po szlifowaniu. Poszczególne składowe widma mossbauerowskiego zostały zidentyfikowane i przypisane odpowiednim fazom. W pracy skupiono się na analizie skladowych pochodzących od węglika ε Do pomiarów mossbauerowskich zastosowano technikę elektronów konwersji wewnętrznej CEMS z detektorem gazowym, wypelnionym objętościowo 98% He + 2% Ar, pod ciśnieniem 0,9 at. Źródłem mossbauerowskim byl 57CoRh o aktywności 10 mCi. Zastosowanie techniki CEMS pozwoliło na badanie warstw powierzchniowych o grubości około 100 nm. Parametry widm składowych zostały wyznaczone w oparciu o program filtrujący MOSDS. Na podstawie analizy nadsubtelnego pola magnetycznego, rozszczepienia kwadrupolowego, przesunięcia izomerycznego, stosunku 2 do 3 linii sekstetu zemanowskiego oraz intensywności widma składowego pochodzącego ad węglików ε wnioskowano na temat produktów destabilizacji austenitu szczątkowego po odpuszczeniu ciągłym do 80C, o wpływie tekstury osnowy na orientację krystalograficzną wydzieleń węglika ε, zakresie temperatur występowania węglików ε w strukturze podczas ciągłego odpuszczania oraz przemianie ε - cementyt. Otrzymane wyniki pozwolą w przyszłych publikacjach na dyskusję, która uzupełni wiedzę na temat kinetyki przemian fazowych przy odpuszczaniu stali stopowych.

3

TEM studies of tempered structural steels with Ni

Krawczyk J., Bała P., Pacyna J.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 21, nr 1

59-62

EN

Purpose: The reason for writing this paper was to describe the influence of Ni addition on the microstructure of structural steels after tempering. In this investigation, four model alloys on the variable concentration of Ni and constant concentration of carbon and other elements were used. Design/methodology/approach: The alloys were melted in air and hot forged into bars 20 x 35 mm. The samples for investigations were machined after normalizing. All samples for TEM investigations were used in quenched and tempered conditions. Quenching was performed in oil at room temperature. After quenching samples were tempered at 200 degrees centigrade for 2 h. The microstructure of the investigated steels were investigated using JEM200CX transmission electron microscope. Findings: An increase of Ni content in investigated structural steels causes a decrease of epsilon carbide concentration in their microstructure after tempering at 200 degrees centigrade for 2 hours. Cementite precipitates in these steels independently on the boundaries of martensite needles boundaries and on the twin boundaries in the areas in which the precipitates of epsilon carbide dissolved. Research/limitations/implications: Presented results may be used to design new technologies of tempering of structural steels with nickel addition. Originality/value: Morphology of epsilon carbides precipitates.

4

Effect of carbon content upon the early stage of tempering of steel with Mn and V addition

Dąbrowski R., Pacyna J.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 10

585-588

EN

Purpose: In this paper the effect of carbon content on the transformations taking place at the early stage of tempering (precipitation of the ε carbide) of the model alloys with manganese and vanadium addition is evaluated. Design/methodology/approach: The alloys with specially designed chemical composition (constant content of alloying elements and varied carbon content) were investigated by means of dilatometric method. The range of temperature of the early stage tempering was established on the basis of differentiated dilatogram curves digitally recorded during heating up step of the previously hardened specimens. In order to unify the experimental conditions, only one heating rate was chosen. Findings: It was shown that carbon has a similar influence on the first stage of the tempering of the model alloys containing manganese and vanadium addition when considering a qualitative way of the effect. But when a quantitative way is taken into account, the effect of carbon content is different. Research limitations/implications: Investigations of the early stage of the tempering will be continued for its more accurate quantitative analysis. Authors are expecting that there is a relationship between an intensity of this stage of tempering and steel’s properties. Practical implications: The results of the research have strong cognitive meaning. It is possible that in the future they may be used for designing of chemical composition of steels for which presently only the low-temperature tempering is provided. Originality/value: The results contained in this paper have very high cognitive significance and in the future it may be possible to use them for elaboration of detailed heat treatment technology of new steels, which are anticipated to be subjected to low-temperature tempering only.