Si添加鋼のFe-Zn合金化反応に及ぼすMn添加量の影響

• Published in: 鉄と鋼 Vol. 102; no. 10; pp. 583 - 590
• Main Authors: 牧水, 洋一, 鈴木, 善継, 谷本, 亘, 青山, 朋弘, 吉見, 直人
• Format: Journal Article
• Language: Japanese
• Published: 一般社団法人 日本鉄鋼協会 2016
• Subjects: galvannealing; high strength steel; Mn content; selective oxidation; Si-added steel
• ISSN: 0021-1575; 1883-2954
• DOI: 10.2355/tetsutohagane.TETSU-2016-038

The influence of the Mn content of Si-added steel sheets on the Fe-Zn galvannealing reaction was investigated. Three steel sheets, 1.5 mass%Si-1.4, 1.9 and 2.7 mass%Mn, were annealed in a 10vol%H2-90vol%N2 atmosphere. Si and Mn oxides were analyzed by reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. SiO2 and Mn2SiO4 formed as selective oxides at the steel surface after recrystallization annealing. The ratio of the oxide species changed depending on the Mn content in the steel. When the Mn content was lower, formation of SiO2 was promoted and that of Mn2SiO4 was suppressed. In the selective oxide layer which formed on the surface of the 1.5 mass%Si-1.4 mass%Mn steel sheets, Mn2SiO4 formed at the outer side, and SiO2 formed at the inner side. This can be explained by consideration of the thermodynamic oxygen potential gradient. Furthermore, areas where SiO2 mainly formed and those where Mn2SiO4 mainly formed were distributed on the surface of the 1.5 mass%Si-1.4 mass%Mn steel sheets. In this case, the Fe-Zn intermetallic compound (IMC) formed preferentially on the Mn2SiO4 between the zinc coating and the substrate steel after galvanizing, and the Fe-Zn galvannealing reaction was suppressed on the SiO2 layer. It is considered that a dense and continuous protective SiO2 layer acted as a barrier to the Fe-Zn galvannealing reaction.