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The Effects of Hot Deformation Parameters on the Size of Dynamically Recrystallized Austenite Grains of HSLA Steel

Gnapowski Sebastian, Opiela Marek, Kalinowska-Ozgowicz Elżbieta, Szulżyk-Cieplak Joanna

Advances in Science and Technology. Research Journal

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2020

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Vol. 14, no 2

76--84

EN

Materials scientists are seeking to produce metals with reduced weight and dimensions while maintaining the appropriate mechanical properties. There are several ways to improve the internal structure of metals, such as the ultrasound used to solidify liquid metal. The homogeneity of the grains and the uniformity of the metal structure affects its mechanical strength. This paper presents the results of investigations into the effects of hot deformation parameters in compression on the austenite grain size in the HSLA (High Strength Low Alloy) steel (0.16% C, 0.037% Nb, 0.004% Ti, 0.0098% N). The axisymmetric compression investigations were performed on cylindrical investigation specimens using a Gleeble 3800 thermomechanical simulator with the strain rate of 1÷15.9 s-1 and strain degree ε = 1.2. Before deformation, the research specimens were austenitized at TA = 1100÷1250 °C. The metallographic observations of the primary austenite grains were conducted with an optical microscope, while the structure of dynamically recrystallized austenite, inherited by martensite, was examined by using a scanning electron microscope.

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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.

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The static recrystallization kinetics acquired from stress relaxation method

Kliber J., Horsinka J., Knapiński M.

Hutnik, Wiadomości Hutnicze

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2014

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Vol. 81, nr 1

35--38

EN

Recovery can be described using the Avrami equation, which yields the proportion of recrystallized structure as a function of various deformation- related variables. Modern technique uses the stress relaxation phenomenon. By analysing the stress vs. time plot, one can obtain information on the specimen‘s flow stress during the hold after deformation. A Gleeble simulator was used for an experiment with four temperatures (800 °C to 1 100 °C) and five strain rates (from 10-2 to 50 s-1) and the resulting strain magnitude of 0,2 or 0,4. Points denoting the start and end of recovery were identified on the curve. Constants of the Avrami equation were determined using these points. The advantages of stress relaxation tests include their simplicity, the opportunity to obtain a full-range curve for the volume fraction of recrystallized structure in a single test run and the effectiveness of mapping the softening phenomena.

PL

Zdrowienie może być opisane za pomocą równania Avramiego, co oddaje zależności stopnia zrekrystalizowania struktury w zależności od różnych zmiennych opisujących odkształcenie. Nowoczesna technika wykorzystuje zjawisko relaksacji naprężeń. Analizując zmiany naprężenia w funkcji czasu, można uzyskać informację na temat naprężenia płynięcia materiału próbki podczas wytrzymania po odkształceniu. Symulator Gleeble użyto do przeprowadzenia eksperymentu dla czterech wartości temperatury wybranych z zakresu od 800 °C do 1 100 °C, pięciu wartości prędkości odkształcenia od 10-2 do 50 s-1 oraz końcowego zakresu wartości odkształcenia 0,2 lub 0,4. Punkty oznaczające początek i koniec zdrowienia zostały zidentyfikowane na krzywej. Stałe równania Avramiego oznaczano za pomocą tych punktów. Zalety badania relaksacji naprężeń obejmują ich prostotę, możliwość uzyskania krzywej dla pełnego zakresu ułamka objętościowego frakcji zrekrystalizowanej w pojedynczej próbie oraz skuteczności odwzorowywania zjawisk podczas mięknięcia materiału.

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Metoda umacniania cielnego prętów do betonu sprężonego

Kuziak R., Molenda R., Pietryka J., Zygmunt T., Dylka H.

Prace Instytutu Metalurgii Żelaza

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2003

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T. 55, z. 2

49-54

PL

W Hucie Królewska Sp. z o.o. opracowano nową technologię wytwarzania wysokowytrzymałych prętów z żebrowaniem gwintowym do betonu sprężonego. Metodę opracowano w wyniku badań przeprowadzonych metodą symulacji fizycznej procesów przemysłowych z wykorzysttaniem symulatora Gleeble oraz za pomocą dylatometru DIL 805. Zastosowanie tych metod pozwoliło opracować skład chemiczny oraz warunki chłodzenia, zapewniających uzyskanie pożądanych własności mechanicznych prętów. Istota nowej metody polega na przyspieszonym chłodzeniu prętów za stali perlitycznej zawierającej chrom za pomocą wentylatorów o regulowanej wydajności.

EN

In Huta Królewska Ltd. a new method was developed for manufacture of high strength threaded bars for concrete pre-stressing. The method was developed as a result of a series of experiments involving physical simulation of industrial processes with the use of a Gleeble simulator and a DIL 805 dilatometer. These methods made it possible to select chemical composition of steel and cooling conditions necessary for nanufacture of bars with specified mechanical properties. The principle of the new method is based on controlled cooling of chromium-alloyed pearlitic steel bars by means of variable capacity fans.