Steels for sour service applications demand stringent internal cleanliness control both in terms of non-metallic inclusions and dissolved gas contents.The current article discusses some of the key process controls adhered to during steelmaking, casting and solidification that has enabled ArcelorMittal Lazaro Cardenas (AMLC) to achieve effective resistance to hydrogen flaking in the skelp and excellent hydrogen induced cracking (HIC) resistance in the final product. The results are: (i) Inclusion characterization revealed clean microstructures of the pipeline steels cast and only globular inclusions could be observed with size mostly less than 2 µm. Ca-treatment could be effectively introduced to induce fine globular Ca-aluminate inclusions and many times jointly with (Ca,Mn)S. (ii) Controls on effective dynamic soft reduction guaranteed least centerline segregation in line pipe slabs even with higher Mn-contents and thus formation of centerline band of hard microstructural constituents in the final hot rolled products could not be observed. Introduction of 100% DRI (Direct Reduced Iron) use in EAF (Electric Arc Furnace) steelmaking ensured lowest S, P contents in the steel which also contributed in minimizing centerline segregation in such critical steel grades. (iii) HIC tests under severe environmental conditions did not give rise to any microscopic cracking which could be attributed to the globular non-metallic inclusions and near absence of the harmful influence of hydrogen. It remains to be seen how the acicular ferrite microstructure in API X70 grade HR(Hot Rolled) coils will respond to HIC tests given the clean centerline conditions and cleanliness from non-metallic inclusions but the results of the API X65/52 plate and pipe samples undeniably suggest inclusion shape control and clean centrerline are key to successful performance in HIC tests.
Internal quality control of steels during steelmaking and casting for sour service applications at ArcelorMittal Lazaro Cardenas, Mexico
Interne Qualitätskontrolle der Stähle während der Stahlerzeugung und des Giesens für Anwendungen im sauren Einsatz bei ArcelorMittal Lazaro Cardenas, Mexiko
2013
10 Seiten, 5 Bilder, 2 Tabellen, 17 Quellen
Conference paper
Storage medium
English
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