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1

The influence of thermo-mechanical processing on deformability and structural changes of duplex steel

Radwański K., Niewielski G., Kuc D.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

175-178

EN

Purpose: In conventional hot deformation methods of duplex steels, low values of boundary strain are obtained, resulting from the disparate behaviour of ferrite and austenite. This paper analyses the capacity for enhancing deformability of two-phase ferritic-austenitic steels of the "duplex" type via thermo mechanical processing. Design/methodology/approach: Steel specimens were subjected to cold deformation with a 70% rolling reduction. After a hot solution treatment beginning at 1350 degrees centigrade, the specimens were tensioned in the "Instron" strength-testing machine in temperatures ranging from 800 to 950 degrees centigrade at a rate of vr=15x10-3/3x10-1 mm/s in a 0.005 Pa vacuum. Structural examination was carried out using light and electron microscopy. A quantitative analysis of structural changes was performed using the "MetIIo" image analysis programme. Findings: The process parameters at which the investigated steel shows the superplastic flow effect have been determined. Practical implications: The capacity for increased deformability through combined thermo-mechanical processes, requiring a precise selection of the deformation parameters, has been indicated. Originality/value: The results obtained are vital for designing an effective thermo-mechanical processing technology for the investigated steel.

2

The impact of deformation on structural changes of the duplex steel

Niewielski G., Radwański K., Kuc D.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 23, nr 1

31-34

EN

Purpose: Despite the many years' research on the plasticity of duplex steels, it was impossible to conclusively determine the mechanisms for structure recovery during the plastic deformation. The paper will attempt to provide explanations for the changes taking place in the steel structure during the superplastic flow. Design/methodology/approach: After a solution heat treatment at 1250 degrees centigrade, the steel was subjected to cold deformation through rolling with the total 70% reduction. The specimens were tensioned in the "Instron" strength-testing machine at temperature 850 degrees centigrade at a rate of vr=15x10 to the -3 mm/s in a 0.005Pa vacuum. Structural examination was carried out using light and electron microscopy. The micro-diffraction technique was applied to provide diffraction images with Kikuchi lines. Findings: A joint operation of structure reconstruction mechanisms during the deformation of the analyzed steel with the process of sigma phase precipitation inhibiting further growth of the newly-formed grain has been determined. Practical implications: The capacity for increased deformability through combined thermo-mechanical processes, requiring a precise selection of the deformation parameters, has been indicated. Originality/value: The results obtained are vital for designing an effective thermo-mechanical processing technology for the investigated steel.

3

Superplasticity in titanium alloys

Sieniawski J., Motyka M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 24, nr 1

123-130

EN

Purpose: The paper reports characteristic of superplasticity phenomenon in titanium alloys and possibility of its applications. Design/methodology/approach: The main objective of the paper is to show features of superplastic forming of titanium alloys and current research trends aiming at widespread application of this technology. Findings: In the paper characteristic of selected superplastic titanium alloys was presented. The effect of microstructural parameters on superplasticity was considered too. Mechanical properties of superplastic deformed titanium alloys, determining criteria of their potential applications, were also addressed. Research limitations/implications: Application of superplastic forming (SPF) in industry is limited due to long time and high temperature of the forming process. In the paper directions of the studies were presented which can lead to increase in effectiveness of the process. Practical implications: SPF enables manufacturing of complex shape details in one-step technological operation. Together with diffusion bonding (DB) it offers particular advantages making possible to manufacture complicated multilayer structures. Originality/value: The paper summarizes achievements of the studies on the superplasticity of Ti alloys, emphasizes the role of microstructural parameters and methods of their modification leading to better results and economics of SPF.

4

The influence of hot-working processing on plasticity and structure of duplex steel

Niewielski G., Radwański K., Kuc D.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 6

325-332

EN

Purpose: There are numerous branches of industry where the (α + ϒ) duplex steels have not yet been sufficiently popularised due to problems with their forming, resulting from different properties of the both phases which make up the material. This paper analyses the influence of temperature and tension rate on the superplastic flow of the (α + ϒ) duplex steel. Design/methodology/approach: Steel specimens were cold deformed with a 70% rolling reduction. After a solution head treatment (1350 °C), the specimens were tensioned in temperatures ranging from 800 to 950 °C at a rate of vr=15x10 -3 ÷ 3x10 -1mm/s in a 0.005Pa vacuum. Structural examination was carried out using light, scanning and transmission electron microscopy. A quantitative analysis of structural changes was performed using the "MetIlo" image analysis programme. Findings: This paper has shown the cooperation of structure reconstruction mechanisms during deformation of the investigated steel and attempet the changes that take place in the steel structure during superplastic flow. Practical implications: The research carried out enabled the understanding of the phenomena taking place during deformation and annealing of the investigated alloy. The results will constitute the basis for modelling the structural changes. Originality/value: The results will be used to design the basis for a thermo-mechanical processing technology via rolling and inter-operational annealing of the investigated steel.

5

Microstructure evolution of CP titanium during high temperature deformation

Tan M. J., Zhu X. J.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 1

5-11

EN

Purpose: To investigate the superplasticity of commercially pure titanium alloy and microstructure evolution of the alloy during high temperature deformation. Design/methodology/approach: Uniaxial tensile tests were carried out at 600, 750 and 800°C with an initial strain rate from 10 -1 s -1 10 -4 s -1. EBSD technology was used to evaluate the microstructure of the commercially pure titanium alloy deformed at high temperature. Findings: It is found that this titanium alloy does not show good superplasticity at 600-800°C due to the rapid grain growth. Studies also show that the dynamic recrystallization took place at high temperatures. The optimum dynamic recrystallization conditions were found to be at 600°C with an initial strain rate of 0.001/s, attaining the highest volume fraction of fine grains whose average grain size is ≈ 9.7 µm at strain of 80%. This process not only decreases the average grain size of the alloy but also increase the misorientation angle of the grain boundary. Practical implications: The investigations of microstructure of the commercially pure titanium alloy as well as related phenomena during high temperature deformation are important for achieving desired mechanical behavior of the material. Originality/value: The dynamic recrystallization phenomenon of commercially pure titanium alloy as well as related mechanism is investigated.

6

Dynamic recrystallization in commercially pure titanium

Tan M. J., Zhu X. J.

Journal of Achievements in Materials and Manufacturing Engineering

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2006

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Vol. 18, nr 1-2

183--186

EN

Purpose: A study was conducted to investigate the dynamic recrystallization of commercially pure Titanium alloy during high temperature deformation in order to understand it further and enable expansion of its usage. Design/methodology/approach: Uniaxial tensile tests were carried out at 600, 750 and 800°C with different initial strain rates. Microstructure evolution during high temperature tensile testing was studied by using optical microscope and Electron Back Scattered Diffraction. Findings: It is found that this titanium alloys do not show good superplasticity at 600-800°C due to the rapid grain growth. Studies also show that the dynamic recrystallization took place at high temperatures. This process not only decreases the average grain size of the alloy but also increase the misorientation angle of the grain boundary. Practical implications: The investigations of dynamic recrystallization of commercially pure titanium alloy as well as related phenomena are important for achieving desired mechanical behavior of the material. Originality/value: The dynamic recrystallization phenomenon of commercially pure titanium alloy as well as related mechanism is investigated.