Effect of Austempering Temperature on the Microstructure and Retained Austenite of Cast Bainitic Steel Used for Frogs in Railway Crossovers

• Autorzy: Parzych S. , Dziurka R. , Goły M. , Kulinowski B.

Identyfikatory

DOI

10.24425/amm.2020.133714

• Języki publikacji: EN

Abstrakty

EN

This work deals with the effect of austempering temperature and time on the microstructure and content of retained austenite of a selected cast steel assigned as a material used for frogs in railway crossovers. Bainitic cast steel was austempered at 400°C, 450°C and 500°C for two selected times (0.5 h, 4.0 h) to study the evolution of the microstructure and retained austenite content. The microstructure was characterized by optical microscopy, X-ray diffraction analyses (XRD), and hardness tests. Phase transformations during and after austempering were determined by dilatometric methods.The increase in isothermal temperature causes an increase in time to start of bainitic transformation from 0.25 to 1.5 s. However, another increase in temperature to 500°C shifts the incubation time to as much as 11 s. The time after which the transformations have ended at individual temperatures is similar and equal to about 300 s (6 min.). The dilatation effects are directly related to the amount of bainite formation. Based on these we can conclude that the temperature effect in the case of cast steel is inversely proportional to the amount of bainite formed. The largest effect can be distinguished in the case of the sample austempered at 400°C and the smallest at 500°C. Summarizing the dilatometric results, we can conclude that an increase in austempering temperature causes an increase in austenite stability. In other words, the chemical composition lowers (shifts to lower temperatures) the range of bainite transformation. It is possible that at higher austempering temperatures we will receive only stable austenite without any transformation. This is indicated by the hatched area in Figure 4b. This means that the heat treatment of cast steel into bainite is limited on both sides by martensitic transformation and the range of stable austenite. The paper attempts to estimate the content of retained austenite with X-ray diffraction.

Słowa kluczowe

EN

railway crossover; austempering of bainitic cast steel; heat treatment

• Wydawca: Institute of Metallurgy and Materials Science of Polish Academy of Sciences ; Committee of Materials Engineering and Metallurgy of Polish Academy of Sciences
• Czasopismo: Archives of Metallurgy and Materials
• Rocznik: 2020
• Tom: Vol. 65, iss. 4
• Strony: 1463--1468
• Opis fizyczny: Bibliogr. 25 poz., fot., rys., tab.

Twórcy

autor

Parzych S.

• Cracow University of Technology, Faculty of Materials Engineering and Physics, 24 Warszawska Str., 31-155 Kraków, Poland

autor

Dziurka R.

• AGH University of Science and Technology, Faculty of Metals Engineering and Industrial Computer Science, Al. Mickiewicza 30, 30-059 Kraków, Poland

autor

Goły M.

• AGH University of Science and Technology, Faculty of Metals Engineering and Industrial Computer Science, Al. Mickiewicza 30, 30-059 Kraków, Poland

autor

Kulinowski B.

• Nafto Sp. z o.o. 30 Igołomska Str., 31-983 Kraków, Poland

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