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Formability of Invar 36 alloy at high temperatures

Kawulok Petr, Jurek David, Schindler Ivo, Kawulok Rostislav, Opěla Petr, Němec Josef, Kawuloková Monika, Rusz Stanislav, Sauer Michal

Journal of Metallic Materials

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2022

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Vol. 74, no. 1

15--20

EN

By using of hot tensile tests, which were performed on simulator HDS-20, the formability of Invar 36 alloy was investigated. By a special type of a tensile test, involving a continuous control heating of the tested specimens and their simultaneous load by a constant tensile force of 80 N, a nil-strength temperature of investigated alloy 1419°C was determined. By continuous uniaxial tensile tests to rupture the strength and plastic properties of the Invar 36 alloy were determined in the wide range of deformation temperatures (from 800°C to 1390°C) and mean strain rates (from 0.09 s-1 to 75 s-1). On the basis of obtained results the 3D maps were constructed, expressing the dependence of the contractual hot ultimate tensile strength, hot ductility and hot reduction of area of the Invar 36 alloy on the deformation temperature and on the mean strain rate. Based on the determined plastic properties, the nil-ductility temperature of the investigated alloy of 1390°C was also determined.

PL

Za pomocą prób rozciągania na gorąco, które przeprowadzono na symulatorze HDS-20, zbadano odkształcalność stopu Invar 36. Przy użyciu specjalnej próby rozciągania, polegającej na ciągłym sterowanym nagrzewaniu badanych próbek i równoczesnym ich obciążeniu stałą siłą rozciągającą 80 N, wyznaczono temperaturę zerowej wytrzymałości badanego stopu, która wyniosła 1419°C. Za pomocą ciągłych jednoosiowych prób rozciągania prowadzonych do zerwania określono właściwości wytrzymałościowe i plastyczne stopu Invar 36 w szerokim zakresie temperatur odkształcenia (od 800°C do 1390°C) i średnich prędkości odkształcenia (od 0,09 s-1 do 75 s-1). Na podstawie uzyskanych wyników skonstruowano mapy 3D, wyrażające zależność wytrzymałości na rozciąganie na gorąco, plastyczności na gorąco i przewężenia stopu Invar 36 od temperatury odkształcenia i średniej szybkości odkształcania. Na podstawie wyznaczonych właściwości plastycznych określono również temperaturę przejścia w stan kruchy badanego stopu wynoszącą 1390°C.

2

Study of the hot forming conditions of HSLA steel on the tensile testing machine

Kozelsky P., Melecky J., Schindler I., Cagala M.

Hutnik, Wiadomości Hutnicze

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2008

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Vol. 75, nr 8

486-488

EN

The aim of the conducted experimental work was to study the deformation behaviour in the hot state and causes that lead to failure of compactness of a microalloyed steel determined for the tube production. The results of the formability testing are presented, performed by measurements of the strength and plastic properties by means of the tensile test performed at the forming temperatures and displacement speed of the cross beam in the range of 6 to 300 mm/min. It was shown that in the case of this material it is not essentially possible to avoid a defect formation after its cooling by a change of the forming speed.

PL

Celem przeprowadzonego eksperymentu było zbadanie technologicznej plastyczności stali HSLA w warunkach przeróbki plastycznej na gorąco, jak również przyczyn pękania stali mikroskopowych stosowanych do produkcji rur. Zaprezentowano zależność wytrzymałości i właściwości plastycznych badanej stali od warunków odkształcania. Próby rozciągania prowadzono dla temperatur z zakresu przeróbki plastycznej na gorąco tej stali z prędkością w zakresie od 6 do 300 mm/min. Wykazano, że w przypadku badanej stali zmiana prędkości kształtowania nie wpływa w istotny sposób na możliwość uniknięcia defektów po operacji chłodzenia.

3

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.

4

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.

5

Numerical study to identify the material parameters of a damage model

Schwartz R., Castagne S., Habraken A.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 2

237-242

EN

In the continuous casting (CC) process, one of the reject factors is the presence of transversal cracks in the product. This type of macroscopic damage is expected to be due to the process loading in the bending and unbending area of the CC line. At this stage, the material looses a part of its ductility because of the temperature range[1] and some intergranular cracks are expected to appear. In order to study this damage, a 2D model was developed[2]. It models the intergranular crack at the mesoscopic level: the grains are meshed by solid elements and the grain boundaries are interface elements where sliding and decohesion can happen[3]. These mechanisms are predicted according a damage law relying on the creep and diffusion of voids. A representative cell is meshed according microscopic analysis telling the grain size and shape. Already validated for a microalloyed steel with C level < 0.1 wt% this model must be extended to peritectic and stainless steels. The first step is to identify the model parameters for these grades. As a preparation work, the type and the quantity of hot tensile tests required to be able to identify a single set of parameters for the damage law must be determined. So, simulations of hot tensile test of notched samples are needed. The computed stress and strain history is applied on the representative cell and the moment of rupture is determined in function of the input parameters. Thanks to inverse modelling, the parameters of the damage law are adapted in order to get one single set of parameters with only two different geometries of notch and two different strain histories.

PL

W wyniku obciążenia i gięcia materiału w procesie ciągłego odlewania pojawiają się defekty makroskopowe w formie poprzecznych pęknięć. W celu symulacji procesu pękania międzyziarnowego opracowano model 2D w mezoskali dla stali mikro skopowych, gdzie zawartość węgla nie przekracza O.1% wagi Celem niniejszej pracy jest rozszerzenie możliwości modelu w celu uwzględnienia stali perytektycznych i nierdzewnych. Aby określić parametry reologiczne dla poszczególnych materiałów przeprowadzono testy rozciągania na gorąco. W pracy wykorzystano symulacje MES z podłączoną komórką reprezentującą materiał w skali mezo. Do określenia parametrów modelu pęki nią posłużyła metoda analizy odwrotnej inverse.

6

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.