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3 2021

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Study on the influence of sheet straightening process on residual stress distribution, mechanical properties and structure of deep-drawing steel sheets

100%

Radwański K. , Adamiec A. , Kuziak R. , Zaława D. , Sozańska-Jędrasik L.

2021

tom Vol. 73, no. 4

3--10

The article describes the impact of the stretch levelling process of DC03 and DC04 steel sheets on their quality in terms of further application for products formed in technologies used in the automotive industry. The straightening process was carried out in a demonstration line developed as part of a project carried out by DAR STAL Dariusz Zaława together with the Łukasiewicz Research Network - Institute for Ferrous Metallurgy. The study examined the influence of stretch levelling on waviness and the state of internal stresses of the sheets. It was found that the use of stretch levelling with a controlled elongation value results in obtaining a favourable and stable state of stress in the sheets. No significant influence of the straightening process on the structure and mechanical properties of the sheets was found.

W ramach artykułu opisano wpływ procesu prostowania naciągowego blach ze stali DC03 i DC04 na ich jakość pod kątem dalszego przeznaczenia na wyroby kształtowane w technologiach stosowanych w przemyśle motoryzacyjnym. Proces prostowania prowadzono w linii demonstracyjnej opracowanej w ramach projektu realizowanego przez firmę DAR STAL Dariusz Zaława wspólnie z Sieć Badawcza Łukasiewicz - Instytutem Metalurgii Żelaza. W ramach pracy badano wpływ prostowania naciągowego na falistość i stan naprężeń własnych blach. Stwierdzono, że zastosowanie prostowania naciągowego, z kontrolowaną wartością wydłużenia, powoduje uzyskanie korzystnego i stabilnego stanu naprężenia w blachach. Nie stwierdzono znaczącego wpływu procesu prostowania na strukturę oraz właściwości mechaniczne blach.

Decomposition mechanisms of continuously cooled bainitic rail in the critical heat-affected zone of a flash-butt welded joints

100%

Królicka A. , Żak A. , Kuziak R. , Radwański K. , Ambroziak A.

2021

tom Vol. 39, No. 4

615--625

The joining process of bainitic rails is significant in terms of their industrialization in high-speed and heavy-loaded railways. This paper demonstrates the microstructure changes in the critical zone of the welded joint, which is responsible for the greatest deterioration in mechanical properties. Extensive progress in the decomposition of the retained austenite and bainitic ferrite occurs in the low-temperature heat-affected zone (LTHAZ) of the flash-butt welded joint of low-carbon bainitic rail. The decomposition products of the retained austenite were mainly a mixture of cementite and ferrite. The cementite was mainly precipitated at the boundary of the bainitic ferrite laths, which indicates lower thermal stability of the filmy austenite. Moreover, it was found that a part of the refined blocky retained austenite was decomposed into the ferrite and nanometric cementite, while another remained in the structure. The decomposition mechanisms are rather heterogeneous with varying degrees of decomposition. A relatively high proportion of dislocations and stress fields prove the occurrence of residual stresses formed during the welding process.

Mechanical and thermal stability of retained austenite in plastically deformed bainite-based TRIP-aided medium-Mn steels

86%

Kozłowska A. , Grajcar A. , Janik A. , Radwański K. , Krupp U. , Matus K. , Morawiec M.

tom Vol. 21, no. 3

807--820

Advanced medium-Mn sheet steels show an opportunity for the development of cost-effective and light-weight automotive parts with improved safety and optimized environmental performance. These steels utilize the strain-induced martensitic transformation of metastable retained austenite to improve the strength–ductility balance. The improvement of mechanical performance is related to the tailored thermal and mechanical stabilities of retained austenite. The mechanical stability of retained austenite was estimated in static tensile tests over a wide temperature range from 20 °C to 200 °C. The thermal stability of retained austenite during heating at elevated temperatures was assessed by means of dilatometry. The phase composition and microstructure evolution were investigated by means of scanning electron microscopy, electron backscatter diffraction, X-ray diffraction and transmission electron microscopy techniques. It was shown that the retained austenite stability shows a pronounced temperature dependence and is also stimulated by the manganese addition in a 3–5% range.