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Li H.,Shougang Institute of Technology | Zhu G.,Shougang Jingtang United Iron and Steel Co. | Gao P.,Shougang Institute of Technology | Niu T.,Shougang Institute of Technology | And 2 more authors.
Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015 | Year: 2015

It is well known that non-metallic inclusions and band structure are the main factors affecting the performance of anti- H2S corrosion pipeline steel. In the present study, the new strategy for inclusion and central segregation control were put forward to improve the corrosion resistance of H2S for pipeline steel in Shougang Corporation. The results were summarized as follows, (1) In the ladle furnace refining process, reasonable refining slag composition and strong stirring were adopted to accelerate inclusions transformation from solid to liquid or partial liquid phases near the surface, which were more easily removed during RH treatment; (2) For acquiring CaS-CaO type inclusions with size smaller than 5μm in slab, Ca/S ratio was controlled 1-2 by proper calcium feeding amount in liquid metal; (3) In HFW welding process, micro cracks are apt to emerge initially surrounding the CaO-CaS type inclusions because of different thermal expansion coefficient with steel substrate at high temperature, and then in subsequent squeezing process, the micro cracks are likely to extend and eventually lead to the unqualified for anti-HIC test. Therefore, in the new developed process, the inclusion type for pipeline steel, welded by HFW welding process, was controlled to CaS-CaO-Al2O3 type (the mass percent of Al2O3 must be less than 10%), because the thermal expansion coefficient between these type inclusions and steel are almost the same. (4) Quantitative evaluation grade for band structure is less than or equal to 1 can meet the requirements of anti-H2S test, when the central line segregation grade was controlled below C 1.0 in slab. Finally, with the optimization of refining and casting process parameters, the crack ratio for anti-H2S corrosion B to X65 grade pipeline steel in H2S corrosion circumstance, is less than 3%. Source

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