engleski

Oxide scales and hot rolled steel strip

Iron oxides formed at temperature above 570°C have three different phases: FeO (wüstite), Fe_3O_4 (magnetite) and Fe_2O_4 (hematite). Wüstite has stabile phase at temperature over 570°C. This range of temperature the mechanism of oxidation of iron has been well established [B. K. Kim, J. A. Szpunar, Scr. Mater 1 (2001) 2605 – 2610]. However, when the temperature changes during slab preheating and hot rolling operation strip mechanism is not well understood. In this investigation structure and phase composition of oxide scale formed a hot rolled strip, St. 37.8 are systemically investigated by x – ray diffraction aim of evaluating the process of descaling. The samples for the investigation were pieces of the hot rolled strip collected from along side and width on their beginning, middle and the end. On the each place, pieces 20 x 325 mm strips cut out. Every strip was further cut into 20 x 32.5 mm plates. Oxides scales was scraped off, ground and homogenized for ten minutes in a WC attachment of Spex Mixer Mill. Part of prepared samples was homogenized with CaF_2 as internal standard in ratio 2 : 1. Prepared sample were measured using a Philips diffractometric system (the photographic technique and CoK_α radiation). The obtained Debye – Scherrer patterns was microphotometered on microphotometer, type Officina Electrotenica di Tenno. The intensity of reflection 220 Fe_3O_4, 211 α Fe_2O_3, 200 FeO and 111 CaF_2 was measured. The obtained values were treated mathematically and presented greatest differences between the border and middle of hot rolled strip. So, concentration of FeO was changed from 30 to 60 %, Fe3O4 from 35 to 45 %, Fe_2O_3 from 5 to 10 % at border ; Fe_3O_4 from 85 to 100 %, FeO from 0 to 5 % and Fe_2O_3 from 0 to 5 % at the middle of hot rolled strip. Obtained results indicated that behavior of oxide scale have considerable effects on temperature distribution during hot rolling [J. Iron Steel Res. Inst. 9(2002) 21 – 23] and the process of descaling.

oxide scales; hot rolled steel strip; x - ray diffraction; standard deviation

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