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1

Continuous cooling transformation (CCT) and continuous heating transformation (CHT) diagrams for the new bainitic steel

Pacyna J.

Inżynieria Materiałowa

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2013

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Vol. 34, nr 4

341--345

EN

The kinetics of transformations of undercooled austenite of the new bainitic steel was determined, in the hereby paper, as the CCT diagrams (Fig. 1 and 3). Investigations were performed for two values of austenitising temperature, it means: Ac3 + 50°C = 890°C and 950°C. The bainitic character of the new steel and its high hardenability was conﬁrmed, as well as the fact that an increase of the austenitising temperature to 950°C did not inﬂuence signiﬁcantly the kinetics of transformation of this steel austenite. The selected cooling processes courses were illustrated by photographs of microstructures of the tested steel samples (Fig. 2 and 4). The kinetics ofphase transformations of samples quenched from 890 and 950°C into bainite with a rate of 1100°C/h (0.305°C/s) was determined at their heating, in a form of the CHT diagrams (Fig. 5 and 8). The retained austenite start and ﬁnish temperature, as well as temperature of cementite M3C and carbides (MC type) precipitations were detennined by analysing differential curves of the numerically recorded dilatograms. The method of interpretation of differential curves was also shown. The dilatation effect (shrinkage) originated by carbides e precipitation was not found in the recorded dilatograms of tempering the investigated bainitic steel. None essential differences in the phase transformation kinetics at tempering the tested steel - after its previous quenching into bainite from 890 and 950°C - were found.

PL

W pracy określono kinetykę przemian przechłodzonego austenitu nowej stali bainitycznej W formie wykresów CTPc (rys. 1 i 3). Badania wykonano dla dwóch wartości temperatury austenityzowania, tj AC3 + 50°C = 890°C oraz 950°C. Potwierdzono bainityczny charakter nowej stali, jej wielką hartowność, jak również to, że wzrost temperatury austenityzowania do 950°C nie wpływa istotnie na zmianę kinetyki przemiany austenitu tej stali. Wybrane przebiegi chłodzenia próbek zilustrowano fotograﬁami ich mikrostruktury (rys. 2 i 4). Dla próbek zahartowanych z 890 i 950°C na bainit z szybkością 1100°C/h (0,305°C/s) określono, W postaci wykresów CTPcO kinetykę przemian fazowych przy ich nagrzewaniu (rys. 5 i 8). Wartości temperatury początków i końców przemiany austenitu szczątkowego, wydzielania cementytu M3C i węglików typu MC określono, analizując krzywe różniczkowe zarejestrowanych cyfrowo dylatogramów. Pokazano też sposób interpretacji krzywych różniczkowych. Na zarejestrowanych dylatogramach odpuszczania badanej stali bainitycznej nie stwierdzono efektu dylatacyjnego (skurczu) od wydzielania węglików e. Nie stwierdzono też istotnych różnic w kinetyce przemian fazowych przy odpuszczaniu badanej stali po jej uprzednim zahartowaniu na bainit z 890 i 950°C.

2

The influence of continuous heating rate on the austenite formation in the medium carbon TRIP steel

Kokosza A., Pacyna J., Bała P., Dziurka R.

Archives of Materials Science and Engineering

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2013

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Vol. 62, nr 1

22--27

EN

Purpose: The purpose of the hereby work was to determine the influence of heating rate on the austenite formation range and to draw the time-temperature-austenitizing diagram at continuous heating for TRIP 41MnSi6-5 steel. Design/methodology/approach: The dilatometric analysis was applied as the basic investigation method. Samples of the tested steel were heated to 1100°C with various heating rates. Changes in the relative elongation (ΔL) were recorded as a temperature function (T), during heating. On the basis of analysing such dependencies, for each heating rate the critical temperatures were determined. Findings: It was found, that during heating of the 41MnSi6-5 steel the austenite formation starts at the higher temperature the faster is the heating. It was observed, that directly before the start of the austenite formation, an unidentified (in the presented here investigations) transformation occurs in the investigated steel, causing its volume increase. Research limitations/implications: The performed investigations indicate that during heating of elements of small thickness or cross-sections - within the critical temperature range - the method of their heating to the required temperature becomes very important. At short heating times incorrectly selected the heating conditions can be the reason of significant errors of the heat treatment. Practical implications: The developed diagram: time-temperature-austenitizing, at a continuous heating (CHT), can be a useful tool supporting the proper selection of heating parameters within the critical temperature range. Originality/value: The dependence of the heating rate and the temperature range, in which austenite is formed in the tested 41MnSi6-5 steel, was found. It was observed that heating of the investigated steel with rates lower than 1°C/s has an insignificant influence on the temperature range within which the austenite formation occurs.

3

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.