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1

Combined effects of strain and cooling path on hot deformation response and microstructure of low-carbon structural steel

Morawiec M., Borek W., Mroziński M., Grajcar A.

Archives of Materials Science and Engineering

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2019

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Vol. 95, nr 1

5--11

EN

Purpose: The aim of the paper is to analyse the effect of thermomechanical process with different cooling paths on microstructure and mechanical properties of low-carbon structural steel. Design/methodology/approach: The steel used for the investigation was subjected to two step deformation using a Gleeble 3800 simulator and then held at designed temperatures from 650ºC to 800ºC for different times. A final step included water cooling to room temperature to freeze the microstructure. Typical microscopic studies have been done. The analysis of the volume fraction of presented phases was carried out together with the measurement of grain size by means of image analysis. The last part of conducted research was hardness analysis of the steel after the different heat treatments. Findings: It was found that the microstructure constitution and grain size are strongly dependent on the temperature of isothermal holdings. The microstructure of steel held at 800ºC is composed of the mixture of bainite and two kinds of ferrite: globular and acicular. When the temperature was lowered by 50ºC the ferrite shows the globular morphology. When the temperature drops to 700ºC and below it, the microstructure is composed of ferritic-pearlitic mixture. It was observed that when the isothermal temperature was increased the grain size decreased and the opposite effect was observed for the holding time. The longer the time of the isothermal holding, the larger was the grain size. Research limitations/implications: For better understanding of the phase transformation kinetics in this steel the dilatometric test are planned. Practical implications: The knowledge of the microstructure evolution and hot deformation response of low-carbon structural steels is important from the industrial point of view. Originality/value: The combined effects of hot deformation and different cooling paths give the useful information on a microstructure evolution.

2

Kształtowanie mikrostruktury i właściwości dwufazowych stopów tytanu α + β w procesie cieplno-plastycznym

Motyka M.

Inżynieria Materiałowa

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2012

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Vol. 33, nr 3

155--159

PL

Kształtowanie mikrostruktury stopów tytanu α + β w szerokim zakresie wynika zarówno z unikatowych cech fizycznych tytanu, efektów przemiany alotropowej Ti α ↔ Tiβ, jak i z warunków odkształcania na gorąco oraz obróbki cieplnej. Morfologia składników fazowych mikrostruktury i właściwości stopów tytanu α + β ulega dużej zmianie, szczególnie po nagrzaniu do temperatury początku przemiany fazowej α + β ↔ β i wyższej. Stąd prognozowanie właściwości mechanicznych wyrobów ze stopów tytanu wymaga ich uwzględnienia i prawidłowego doboru warunków obróbki cieplnej i przeróbki plastycznej. W pracy prowadzono badania mikrostruktury i właściwości dwufazowych stopów tytanu Ti-6Al-4V i Ti-6Al-2Mo-2Cr kształtowanych w procesie cieplno-plastycznym. Opracowano warunki oraz wykonano proces cieplno- -plastyczny badanych stopów. Ustalono wpływ warunków kolejnych etapów procesu cieplno-plastycznego na plastyczność na gorąco stopów Ti-6Al-4V oraz Ti-6Al-2Mo-2Cr. Próby odkształcania plastycznego na gorąco prowadzono w zakresie temperatury 850÷925°C. Stosowano prędkość odkształcania od 10–3 do 5·10–1 s–1. Stwierdzono, że warunki procesu cieplno-plastycznego determinują wartości parametrów stereologicznych składników fazowych mikrostruktury i jednocześnie plastyczność na gorąco dwufazowych stopów tytanu α + β.

EN

The microstructure development of α + β titanium alloys to a great extent results from both the specific properties of titanium, effects of the allotropic transformation Tiα↔Tiβ and conditions of hot deformation and heat treatment. The morphology of the phase constituents of the microstructure and properties of α + β titanium alloys are being change significantly, especially after heating up to a temperature of the start of α + β ↔ β or higher. Therefore forecasting the mechanical properties of products made of titanium alloys requires the mentioned features and proper selection of the conditions of heat treatment and plastic working. Examination of the microstructure and properties of two-phase Ti-6Al-4V and Ti-6Al-2Mo-2Cr titanium alloys developed by the thermomechanical process was conducted. The conditions of the thermomechanical process of the examined alloys were elaborated and the process was carried out. The effect of the conditions of the following stages of the thermomechanical process on the hot plasticity of Ti-6Al-4V and Ti-6Al-2Mo-2Cr alloys was established. Hot deformation tests were conducted in the temperature range of 850÷925°C and at a strain rate range of 10–3÷5·10–1 s–1. It was found that the thermomechanical process conditions determined the values of the stereological parameters of the phase constituents of the microstructure and simultaneously hot plasticity of α + β titanium alloys.

3

The influence of initial plastic deformation on microstructure and hot plasticity of α+β titanium alloys

Motyka M., Sieniawski J.

Archives of Materials Science and Engineering

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2010

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Vol. 41, nr 2

95-103

EN

Purpose: Hot deformation behaviour of two-phase titanium alloys is determined depending on microstructure developed in heat treatment and plastic deformation processes. In the paper stereological parameters of microstructure obtained in initial heat treatment and plastic working in the α+β↔β phase transformation range with various forging reduction (ε ≈ 20 and 50%) were determined. Evaluation of the effect of thermomechanical process parameters on hot plasticity of Ti-6Al-4V and Ti-6Al-2Mo-2Cr titanium alloys was performed. Design/methodology/approach: In the research, light and transmission electron microscopy were employed. Digital image analysis methods were used for determination of stereological parameters of microstructure obtained in particular stages of thermomechanical process of Ti-6Al-4V and Ti-6Al-2Mo-2Cr titanium alloys. Hot deformation of thermo mechanically processed titanium alloys was performed in vacuum at the temperature of 850 and 925°C at the strain rates ε = 1·10-2, 1·10-1 and 5·10-1 s-1. Findings: It was found that degree of initial plastic deformation in thermomechanical process considerably affects relative elongation in high temperature tensile test at the lowest strain rate applied (ε = 1·10-2). Research limitations/implications: Developed thermomechanical process enables controlling morphology of microstructural constituents and hot workability of two-phase α+β titanium alloys. Practical implications: Obtaining the demanded operational and technological properties of structural two-phase α+β titanium alloys is related to both the appropriate selection of hot working parameters and preceding thermomechanical process conditions. Originality/value: The effect of heat treatment conditions in thermomechanical process on superplasticity of Ti-6Al-4V alloy was researched previously [1, 2]. In this paper two-phase Ti-6Al-2Mo-2Cr titanium alloy was examined too. Additionally, the influence of a degree of initial deformation in thermomechanical process was analyzed. Hot deformation test were conducted at conditions outside the superplastic range too.

4

On the certain asymptotic approach to the modelling of microheterogeneous media

Borowska J., Rychlewska J., Woźniak C.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

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2009

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Vol. 8, nr 1

5-12

EN

The object of analysis is mathematical modelling of thermomechanical problems of microheterogeneous media. The aim of this contribution is to propose a certain asymptotic modeling technique. The proposed approach is realized both in consistent and semiconsistent form.

5

The influence of thermomechanical process conditions on superplastic behaviour of Ti-6Al-4V titanium alloy.

Motyka M., Sieniawski J.

Advances in Manufacturing Science and Technology

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2004

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Vol. 28, nr 4

31-44

EN

The range of temperature and strain rate suitable for fine-structure superplasticity forces the use of particular technological equipment and deformation conditions which limits its widespread application. It was found that the crusial role in enhancement of effectivity of this manufacturing process is the development of material microstructure (grain refinement). In the paper stereological parameters of microstructure obtained in various conditions of plastic working and heat treatment were determined. Evaluation of its influence on superplasticity of Ti-6Al-$v titanium alloy was performed too.

PL

Zakres występowania zjawiska nadplastyczności strukturalnej w stopach metali wymusza stosowanie specjalnych urządzeń technologicznych i warunków odkształcania, ograniczając jego szersze wykorzystanie. Zwiększenie wydajności tej metody wytwarzania osiąga się przez kształtowanie mikrostruktury materiału (pomniejszanie rozmiaru ziarn). W pracy określono parametry stereologiczne mikrostruktury otrzymanej przez prowadzenie przeróbki plastycznej i obróbki cieplnej w różnych warunkach. Dokonano także oceny jej wpływu na nadplastyczność stopu tytanu Ti-6Al-4V.