Abstract
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.
Kurzfassung
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.
References
1 C. L.Choi, D. C.Hill: A study of microstructural progression in as deposited weld metal, Welding Journal57 (1978), pp. 232s-236sSearch in Google Scholar
2 JWS: Classification of Microstructures in Low C – Low Alloy Steel Weld Metal and Terminology, IIW DOC, IX (1983), pp. 78–83Search in Google Scholar
3 IIW Guide to the Light Microscope Examination of Ferritic Steel Weld Metal IIW DOC, XI (1988), pp. 1533–88Search in Google Scholar
4 D. J.Abson: The role of inclusions in controlling weld metal microstructures in C-Mn steel, The Welding Institute, Abington, UK, Research Report69 (1978)Search in Google Scholar
5 D. J.Abson, R. E.Dolby, P. H. M.Hart: The role of non-metallic inclusions in ferrite nucleation in carbon steel weld metals, Proceedings of International Conference of Trends in Steel and Consumables for Welding, London, The Welding Institute, Abington, UK (1978), p. 75Search in Google Scholar
6 M.Strangwood, H. K. D. H.Bhadeshia: The Mechanism of Acicular Ferrite Formation in Steel Weld Deposits, Advances in Welding Technology and Science, ASM, Metals Park, Ohio, USA (1987), pp. 209–213Search in Google Scholar
7 J. R.Yang, H. K. D. H.Bhadeshia: Thermodynamics of the Acicular Ferrite Transformation in Alloy-Steel Weld Deposits, Advances in Welding Technology and Science, ASM, Metal Parks, Ohio, USA (1987)Search in Google Scholar
8 H. K. D. H.Bhadeshia: Bainite in Steels, The Institute of Metals, London, UK (2001)Search in Google Scholar
9 S.Liu, D. L.Olson: The role of inclusions in controlling HSLA steel weld microstructure, Welding Journal65 (1986), No. 5, pp. 113sSearch in Google Scholar
10 R. C.Cochrane, P. R.Kirkwood: The effect of oxygen on weld metal microstructure, Trends in Steels and Consumables for Welding, The Welding Institute, Abington, UK (1978), pp. 103–121Search in Google Scholar
11 P. L.Harrison, R. A.Farrar: Influence of oxygen-rich inclusions on the austenite to ferrite phase transformation in high strength low alloy (HSLA) steel weld metals, Journal of Materials Science16 (1981), p. 221810.1007/BF00542384Search in Google Scholar
12 S. S.Babu, S. A.Davis: Inclusion formation and microstructure evolution in low alloy steel weld, ISIJ International42 (2002), No. 12, pp. 1344–135310.2355/isijinternational.42.1344Search in Google Scholar
13 Y.Ito, M.Nakanishi: Sumitomo Search15 (1976), pp. 42–62Search in Google Scholar
14 H. I.Aaronson: The Pro-eutectoid Ferrite and the Pro-eutectoid Cementite Reactions, Decomposition of Austenite by Diffusional Process, International Science Publishers, New York, USA (1962), p. 387Search in Google Scholar
15 R. F.Mehlf, W. C.Hagel: Decomposition of austenite by diffusional processes, Progress in Metal Physics6 (1962), Pergamum Interscience Publishers, p. 74iSearch in Google Scholar
16 H. I.Aaronson, H. A.Domian: Transactions of the Metallurgical Society of AIME, AIME236 (1966), p. 781iSearch in Google Scholar
17 E.Keehan: Microstructure and properties of novel high strength steel weld metals, Welding in the World49 (2005), pp. 9–3110.1007/BF03266487Search in Google Scholar
18 P. F.Chaveriat, G. S.Kim, S.Shah, J. E.Indacochea: Low carbon steel weld metal microstructures: The role of oxygen and manganese, Journal of Materials Engineering9 (1987), No. 3, pp. 253–26710.1007/BF02834145Search in Google Scholar
19 G. M.Evans: Effect of manganese on the microstructure and properties of all weld metal deposits, Welding Journal59 (1980), pp. 67s-75sSearch in Google Scholar
20 F.Barbaro, P.Krauklis, K. E.Easterling: Materials Science and Technology5 (1989), p. 105710.1179/mst.1989.5.11.1057Search in Google Scholar
21 W.Vanovsek, C.Bernhard, M.Fiedler, G.Posch: Influence of aluminum content on the characterization of microstructure and inclusions in high-strength steel welds, Welding in the World57 (2013), No. 1, pp. 73–8310.1007/s40194-012-0008-0Search in Google Scholar
22 L. Y.Lan, C. L.Qiu, D. W.Zhao, X. H.Gao, L. X.Du: Effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength low carbon bainitic steel, Science and Technology of Welding and Joining17 (2012), No. 7, pp. 564–57010.1179/1362171812Y.0000000048Search in Google Scholar
23 S. D.Bhole, J. B.Nemade, L.Collins, C.Liu: Effect of nickel and molybdenum additions on weld metal toughness in a submerged arc welded HSLA line-pipe steel, Journal of Materials Processing Technology173 (2006), No. 1, pp. 92–10010.1016/j.jmatprotec.2005.10.028Search in Google Scholar
© 2016, Carl Hanser Verlag, München
