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- 저자 : Carlos Garcia-Mateo (검색결과 2 건)
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Composition Design of Nanocrystalline Bainitic Steels by Diffusionless Solid Reaction
Carlos Garcia-Mateo,Francisca G. Caballero,Thomas Sourmail,Juan Cornide,Veronique Smanio,Roberto Elvira 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.3
NANOBAIN is the term used to refer to a new generation of advanced steels capable of producing by isothermaltransformation at low homologous temperatures, T/Tm~0.25 where Tm is the absolute melting temperature,a nanocrystalline microstructure, composed exclusively of two phases, thin plates of bainitic ferriteseparated by C enriched austenite. Such alloys are exclusively designed on the basis of bainitic transformationtheory and some physical metallurgy principles. In this work, by designing a new set of alloys capable ofproducing such microstructure, a further step toward the industrialization of NANOBAIN is taken. Some importantindustrial requirements, including circumventing the inclusion of expensive alloying elements and theneed for faster transformations, are also considered. For all the alloys, the experimental results validate thedesign procedure and they illustrate that the NANOBAIN concept is a step closer to industrialization, probingthat it is possible to obtain nanocristalline bainite in simpler alloy systems and in shorter times than thosereported previously.
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Hadi Torkamani,Shahram Raygan,Carlos Garcia Mateo,Jafar Rassizadehghani,Yahya Palizdar,David San-Martin 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.4
In this research Rare Earth elements (RE), La and Ce (200 ppm), were added to a low carbon cast microalloyed steel todisclose their infl uence on the microstructure and impact toughness. It is suggested that RE are able to change the interactionbetween the inclusions and matrix during the Solidification process (comprising peritectic transformation), which couldaff ect the microstructural features and consequently the impact property; compared to the base steel a clear evolution wasobserved in nature and morphology of the inclusions present in the RE-added steel i.e. (1) they changed from MnS-based to(RE,Al)(S,O) and RE(S)-based; (2) they obtained an aspect ratio closer to 1 with a lower area fraction as well as a smalleraverage size. Besides, the microstructural examination of the matrix phases showed that a bimodal type of ferrite grain sizedistribution exists in both base and RE-added steels, while the mean ferrite grain size was reduced from 12 to 7 μm andthe bimodality was redressed in the RE-added steel. It was found that pearlite nodule size decreases from 9 to 6 μm in theRE-added steel; however, microalloying with RE caused only a slight decrease in pearlite volume fraction. After detailedfractography analyses, it was found that, compared to the based steel, the signifi cant enhancement of the impact toughnessin RE-added steel (from 63 to 100 J) can be mainly attributed to the Differences observed in the nature of the inclusions, theferrite grain size distribution, and the pearlite nodule size. The presence of carbides (cementite) at ferrite grain boundariesand probable change in distribution of Nb-nanoprecipitation (promoted by RE addition) can be considered as other reasonsaff ecting the impact toughness of steels under investigation.
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