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Licensed Unlicensed Requires Authentication Published by De Gruyter September 22, 2016

Acicular ferrite nucleation as a diffusion controlled process in high strength low alloyed (HSLA) steel weld metal

Die Bildung von nadelförmigem Ferrit als diffusionskontrollierter Prozess im Schweißgut aus hochfestem niedriglegierten (HSLA)-Stahl
  • Mir Mostafa Hosseinioun and Ghazal Moeini
From the journal Materials Testing


Acicular ferrite is a desirable microstructure in high strength low alloy steel weld metal. This is due to its improved toughness and the enhanced mechanical properties of the weld metal. Although the nucleation of acicular ferrite has been studied by many researchers, the exact mechanisms of its nucleation and growth are still under discussion and remained unclear. In this research work, the mechanism of acicular ferrite formation in the weld metal as cast structure has been clarified as diffusion controlled solid state phase transformation. This is based on the classic theory of nucleation and growth which can contribute to possible increase of nucleation sites and growth of intergranular ferrite in HSLA steel weld metal. Therefore, it could be considered that inclusions are not acting as a nucleation site for the intergranular acicular ferrite. Consequently, our results revealed that, in austenite transformation to pro-eutectoid and acicular ferrite, manganese as an austenite stabilizer alloying element is playing an important role in the nucleation and growth of the ferrite grains. It should be added that cooling rate accompanied with the presence of other alloying elements has influenced the type and morphology of the final ferrite microstructure and constituent products.


Nadelförmiger Ferrit ist im Schweißgut aus hochfestem niedriglegierten Stahl eine wünschenswerte Mikrostruktur, weil er die Zähigkeit und die mechanischen Eigenschaften des Schweißgutes verbessert. Obwohl die Keimbildung von nadelförmigem Ferrit von vielen Forschern untersucht worden ist, werden die genauen Mechanismen der Keimbildung und des Wachstums noch diskutiert und sind unklar. Der Bildungsmechanismus von nadelförmigem Ferrit im Schweißgut als Gussstruktur wird in dieser Forschungsarbeit als diffusionskontrollierte Festphasenumwandlung geklärt. Dies beruht auf der klassischen Theorie von Keimbildung und Wachstum, die zu einer möglichen Erhöhung von Keimstellen und zum Wachstum von intergranularem Ferrit im Schweißgut von HSLA-Stahl beitragen kann. Deshalb könnte berücksichtigt werden, dass Einschlüsse nicht als Keimstelle für intergranularen nadelförmigen Ferrit wirken. Folglich zeigten unsere Ergebnisse, dass in der Umwandlung von Austenit zu pro-eutektoidem und nadelförmigem Ferrit das Legierungselement Mangan als Austenitstabilisator in der Keimbildung und des Wachstums der Ferritkörner eine wichtige Rolle spielt. Es sollte hinzugefügt werden, dass die Abkühlrate, in Verbindung mit anderen Legierungselementen, die Art und Morphologie der finalen Mikrostruktur und die Bestandteile des Ferrits beeinflusst hat.

*Correspondence Address, Prof. Mir Mostafa Hosseinioun, Amirkabir University of Technology, Department of Marine Engineering, Polytechnic, Tehran, Iran, E-mail:

Prof. Mir Mostafa Hosseinioun, born in 1947, received his Master degree in Welding Metallurgy (CNAA England) from the Metallurgy Department, London City Polytechnic and his doctorate in Materials Technology (PhD) in Welding from Brunel University, London, UK in 1983 and 1986, respectively. He is a member of the scientific committee of Amirkabir University of Technology, Tehran polytechnic, Iran and part-time lecturer in the Department of Material Science and the Department of Marine Engineering since 1987. He has been a member on the scientific board of many research institutions in Iran, i.e. Islamic Azad University, Dept. of Material Science, Science and Research Branch Center Tehran. He has published over 50 scientific articles and been advising professor for more than 50 Ms degrees and industrial projects in the fields of physical metallurgy, welding technology. His research interests focus on HSLA steel and Austenitic stainless steel weld metal phase transformation as well as the relationship between the micro structure and mechanical properties i. e. toughness and fatigue strength.

Ghazal Moeini is currently a PhD student at Bauhaus university of Weimar, Germany. Her research interest includes materials testing, the numerical simulation of welding processes, micro structure characterization and fatigue failure in welded joints.


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Published Online: 2016-09-22
Published in Print: 2016-10-04

© 2016, Carl Hanser Verlag, München

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