NLMK Dansteel A/S (Fredriksvaerk, Denmark):

Goli-Oglu E. A., Cand. Eng., Chief Technologist, e-mail: ego@nlmk.com

The article describes the study results of one of the indicators of steel heavy plates quality namely an uneven micro- and nanostructure in different thickness layers for plate thickness after normalizing. Heavy plates with thickness 150 mm low carbon steel, additionally alloyed with copper and chromium, which provides improved atmospheric corrosion resistance of steel, were used as a material for investigations. This type of steel is used in transport sector, especially in bridge building and overpasses. The article provides estimation and comparison of qualitative and quantitative parameters of microstructure in 150 mm thick heavy plate from C–Mn–Si–Cr–Cu steel with two micro-alloying systems: V and V+Nb+Ti. Differences in average conditional grain size for different thickness layers of plates are determined, the corresponding histograms of grain distribution, which allows comparing the degree of heterogeneity of microstructure of the researched steels by grain sizes, are built. The article defines the type, size and density of the particles of nano-carbonitrides in the 1/2 and 1/8 of depth thickness of 150 mm thick plates. Obtained level of strength and impact toughness of the investigated steels is displayed.

1. European standard EN 10025-5. Hot rolled products of structural steels — Part 5: Technical delivery conditions for Structural steels with improved atmospheric corrosion resistance. Brussels, 2004. 26 p.
2. Kimura M., Kihira H. Nanoscopic mechanism of protective rust formation on weathering steel surface. Nippon Steel technical report. 2005. No. 91. pp. 86–90.
3. Yamashita M., Miyuki H., Matsuda Y., Nagano H., Misawa T. The long term growth of the protective rust layer formed on weathering steel by atmospheric corrosion during a quarter of a century. Corrosion Science. 1994. No. 36. pp. 283–299.
4. Kamimura T., Hara S., Miyuki H., Yamashita M., Uchida H. Composition and protective ability of rust layer formed on weathering steel exposed to various environments. Corrosion Science. 2006. No. 48. pp. 2799–2812.
5. Goli-Oglu E. A. Microalloying of structural low-carbon steel with improved atmospheric corrosion resistance for bridge building. Chernye Metally. 2016. No. 11. pp. 35–40.
6. Goli-Oglu E. A. Development of production technology of structural steels DANSteel S420K2W and DANSteel S460K2W, resistant to atmospheric corrosion. Stal. 2016. No. 12. pp. 64–67.
7. Sarkits I. G., Bokachev Yu. A., Goli-Oglu E. A. Production of heavy plates in the 4200-mm heavy plate mill at NLMK DanSteel. Chernye Metally. 2014. No. 10. pp. 21–24.