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1

Hot Ductility of High-Mn Steel with Niobium and Titanium

Opiela Marek, Fojt-Dymara Gabriela

Advances in Science and Technology. Research Journal

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2024

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Vol. 18, no 3

200--213

EN

The work presents the results of research on the effect of deformation parameters on hot ductility of high-Mn austenitic steel with niobium and titanium. The investigations were carried out on steel with 0.05% C, 24% Mn, 3.5% Si, 1.5% Al, 0.030% Nb and 0.075% Ti. Hot static tensile test was performed using Gleeble 3800 thermomechanical simulator. Samples were deformed in a temperature range from 1050°C to 1200°C with a strain rate of 3·10-3 s-1. The reduction in area (RA), determined in the static tensile test, was the basis for determining the hot ductility of the examined steel. Reduction in area of examined steel decreases from 88% at the temperature of 1050°C to 59% at 1200°C. High hot ductility of the investigated steel is the result of the synergy of chemical composition optimization, properly conducted modification of non-metallic inclusions and formed fine-grained microstructure of dynamically recrystallized austenite. In addition to hot ductility, parameters characterizing susceptibility of studied steel to high temperature cracking were also defined, namely: ductility recovery temperature (DRT), nil ductility temperature (NDT) and nil strength temperature (NST) were determined. The values of these temperatures are 1240°C, 1250°C and 1270°C, respectively. This means that the temperature of the beginning of plastic deformation of ingots of this steel may be equal even slightly above 1200°C. In addition, the high-temperature brittleness range (HTBR) was determined, which is equal 30°C.

2

Effect of Non-Metallic Inclusions on the Hot Ductility of High-Mn Steels

Opiela Marek, Fojt-Dymara Gabriela

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no 3

19--30

EN

The aim of the work was to determine the effect of non-metallic inclusions on the hot ductility of two newly developed high-Mn austenitic steels (27Mn-4Si-2Al and 24Mn-3Si-1.5Al-Ti). For this purpose, a hot tensile test was carried out in the temperature range from 1050°C to 1200°C with a constant strain rate of 2.5⸱10-3 s-1. The tests were performed on the Gleeble 3800 thermomechanical simulator. Hot ductility of tested steels was defined by determining the reduction in area (% RA). Examined steels demonstrate diversified hot ductility. Clearly higher hot ductility was noted for the 24Mn-3Si-1.5Al-Ti steel. The reduction in area of this steel in the temperature range from 1050°C to 1200°C decreases from approx. 90% to about 58%, while the reduction in area of the 27Mn-4Si-2Al steel, in the same temperature range, decreases from approx. 66% to about 34%. The presence of single, regular-shaped AlN particles and complex MnS-AlN-type non-metallic inclusions was revealed in the 27Mn-4Si-2Al steel. Whereas fine (Ce, La, Nd)S-type sulphides, properly modified with rare earth elements, were identified in the 24Mn-3Si-1.5Al-Ti steel. The AlN-type inclusions and complex MnS-AlN-type inclusions were not revealed in the 24Mn-3Si-1.5Al-Ti steel. This is due to the presence of Ti microaddition, the concentration of which guaranteed binding of the whole nitrogen into stable TiN-type nitrides. Sulphides, disclosed in the 24Mn-3Si-1.5Al-Ti steel, are globular or slightly elongated in the direction of plastic deformation, as confirmed by a very low value of the elongation factor equal 1.48. This creates the opportunity to produce sheets of high strength and ductility and low anisotropy of mechanical properties.

3

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.

4

Study of Hot Deformation Behavior of CuFe2 Alloy

Schindler I., Sauer M., Kawulok P., Rodak K., Hadasik E., Jabłońska M. Barbara, Rusz S., Ševčák V.

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 2

701--706

EN

Nil strength temperature of 1062°C and nil ductility temperature of 1040°C were experimentally set for CuFe2 alloy. The highest formability at approx. 1020°C is unusable due to massive grain coarsening. The local minimum of ductility around the temperature 910°C is probably due to minor formation of γ-iron. In the forming temperatures interval 650-950°C and strain rate 0.1-10 s-1 the flow stress curves were obtained and after their analysis hot deformation activation energy of 380 kJ·mol-1 was achieved. Peak stress and corresponding peak strain values were mathematically described with good accuracy by equations depending on Zener-Hollomon parameter.

5

Mechanical and Microstructural Response of Near Beta Ti Alloys to Hot Tensile Testing

Abbasi S. M., Momeni A., Daraee M., Akhondzadeh A., Mirsaeed S. G.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 2A

815--823

EN

Hot tensile tests were carried out on Timetal-125 and Timetal-LCB near beta Ti alloys at temperatures in range of 600-1000°C and constant strain rate of 0.1 s-1. At temperatures below 700-800°C, the homogenuous and total strains for Timetal-LCB were greater than those for Timetal-125. In contrast, at temperatures over 800°C, Timetal-125 showed better hot ductility. The yield point phenomena was observed in Timetal-LCB at all temperatures. Unlikely, for Timetal-125, it was observed only at temperatures over 800°C. The weaker yield point phenomena in Timetal-125 could be attributed to the negative effect of Al on the diffusion of V. At all temperatures Timetal-LCB exhibited higher strength than Timetal-125. It was found that there should be a direct relationship between the extent of yield point phenomena and strength and dynamic softening through hot tensile testing. It was observed that at temperatures beyond 800°C (beta phase field in both alloys) dynamic recrystallization can progress more in Timetal-125 than in Timetal-LCB. These results were in good agreement with the better hot ductility of Timetal-125 at high temperatures. At low temperatures, i.e. below 700-800°C, partial dynamic recrystallization occurs in beta and dynamic globularization in alpha phase. These processes progress more in Timetal-LCB than in Timetal-125.

6

Effect of strain rate on hot ductility of C-Mn-B steel

Lis A., Lis J., Kolan C., Knapiński M.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 41, nr 1-2

26-33

EN

Purpose: The aim of the paper is to determine the influence of hot deformation conditions on hot ductility and ó-ĺ curves of C-Mn-B steel. Design/methodology/approach: The force – energetic parameters of hot – working were determined in hot tensile tests performed in a temperature range of 700 to 1200°C by the use of Gleeble 3800 thermo – mechanical simulator with strain rate 0.01 s-1 and 6.5 s-1 After rupture the contractions of samples were measured. Samples were taken from columnar and equiaxed grains zone of continuously cast billet. Findings: Hot ductility curves as a measure of contraction in function of temperature of deformation for given strain rate and shape of the grains were established. At strain rate 6.5 s-1 there was no minimum of hot ductility for columnar grains and for equiaxed grains minimum of hot ductility was temperature 800 – 850°C (40%). At strain rate 0.01 s-1 and equiaxed grains minimum of the hot ductility (23%) was between 800 – 900°C and for columnar grains between 850-950°C at about 40%. Minimum of the hot ductility was usually in the vicinity of Ar3 temperature. Research limitations/implications: To determine in detail the hot ductility behaviour of C-Mn-B steel, a SEM investigations of rupture should be done. Practical implications: The obtained stress-strain curves can be useful in determination of power-force parameters of hot-rolling. Originality/value: The hot ductility behaviour of new-developed low carbon steel containing Boron microaddition was investigated.

7

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.

8

Zjawisko temperatury minimalnej plastyczności w stopach CuZn4 oraz CuNi25

Nowosielski R., Sakiewicz P., Gramatyka P.

Rudy i Metale Nieżelazne

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2005

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R. 50, nr 5

252-258

PL

Szereg badań przeprowadzanych od wielu dziesięcioleci na wielu metalach i stopach w wielu ośrodkach badawczych na całym świecie nie dał jednoznacznej odpowiedzi na pytanie o przyczynę zjawiska spadku plastyczności metali podczas przeróbki plastycznej w zakresie 0,3÷0,6 Th, znanego m.in. jako efekt temperatury minimum plastyczności (TMP). Badania nad wpływem heterogenicznych czynników na skalę tego zjawiska stały się jednym z kierunków prac prowadzonych na Wydziale Mechanicznym Technologicznym Politechniki Śląskiej. Szeroki zakres dokonanych oraz wciąż realizowanych badań, m.in. nad stopami miedzi; R. Nowosielski - mosiądze, P. Sakiewicz - miedzionikiel, W. Ozgowicz - brązy cynowe, a także badania nad stalami R. Oleksiak, ma na celu określenie wpływu różnych czynników na zakres i poziom efektu TMP. W niniejszym artykule autorzy ze względu na obszerność przeprowadzonych prac przedstawili tylko wybrane aspekty badań przeprowadzonych na mosiądzu oraz miedzioniklu.

EN

The phenomena of ductility minimum temperature (DMT), is one of the unexplained features of metals and their alloys, observed as the effect of middle temperature ductility decrease during high-temperature plastic deformation in the range of 0,3÷0,6Tm. Effect of Ductility Minimum Temperature is a common attribute of many polycrystal metals and alloys, for example copper and its alloys. This paper contain analyses of the Ductility Minimum Temperature effect in CuNi25 and CuZn4 alloys. On the basis of high temperature ductility tests in CuZn4 and CuNi25 sample has been found a relation between microstructure, grain size and effect of ductility minimum temperature (DMT). The non-homogeneous character of chemical composition concentrating in areas of grain joints and cracks at high temperature has been investigated by linear and point Cu and Ni analysis (EDS). This fact can be accepted as one of the reasons of non-homogeneous deformation and its location at DMT. The deformation in temperatures approximating to beginning of thermal activated processes provoke superimpose of many "inhomogeneities" causes local changes of physical and chemical material properties. It can be make an assumption that in micro scale we have to deal with two materials with different properties and the process of deformation locates in small space on theirs joints. The stress level increasing and provoke cracking between "hard" and "soft" places. The critical levels of stress concentration in whole volume of sample cause decrease of ductility and destruction of material.

9

Wpływ mikrostruktury miedzioniklu CuNi25 na zakres efektu temperatury minimalnej plastyczności (TMP)

Nowosielski R., Sakiewicz P., Gramatyka P.

Rudy i Metale Nieżelazne

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2005

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R. 50, nr 1

16-20

PL

Na podstawie przeprowadzonych wysokotemperaturowych prób rozciągania stwierdzono wpływ mikrostruktury, wielkości i kształtu ziarna na plastyczność oraz zakres występowania wysokotemperaturowe- go minimum plastyczności w stopie CuNi25. Badania metalograficzne potwierdziły dane literaturowe stwierdzające, że pękanie w zakresie temperatury minimalnej plastyczności (TMP), przebiega po granicach ziaren oraz najczęściej zarodkuje w obszarze łączenia się granic trzech ziaren oraz przecięcia bliźniaków z granicą ziarna. Analiza składu chemicznego w obszarach granic ziaren i pęknięć wykazuje lokalnie powstawanie obszarów nierównowagowych o zmiennym podwyższonym lub obniżonym, w stosunku do średniej, stężeniu Cu i Ni. Fakt ten może być przyjęty jako jedna z przyczyn pękania materiałów, w zakresie efektu TMP, i potwierdzenie mechanizmów niejednorodnego odkształcenia oraz jego lokalizacji.

EN

On the grounds of the ductility test at elevated temperature was found that exist relation between microstructure, shape and size of grain and effect of ductility minimum temperaturę (DMT), in single-phase cupronickel CuNi25 alloy. Metallographic research confirmed literature studies that cracks nucleate at points of meeting two or three boundaries of grains and cross-cut of twins with border of grain. The non-uniform of chemical composition concentrating in areas of grain boundaries and cracks at elevated temperature was investigated by linear and point Cu and Ni analysis (EDS). This analysis shows that locally areas of not equilibrium formation and concentrates at this places. This fact can be accepted as one of the reason of cracking and non-homogeneous deformation and its location at DMT.

10

Contribution to physical metallurgy of hot ductility behaviour of steels

Pavliska J., Jonšta Z., Mazanec K., Mazancová E.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2001

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Vol. 279, z. 72

55-58