1 School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China 2 Engineering Research Institute, University of Science and Technology Beijing, Beijing 100083, China 3 Baosteel Research Institute, Baoshan Iron and Steel Co. Ltd., Shanghai 200431, China
Cite this article:
Zhi FANG,Jingyuan LI,Yulai CHEN,Laizhu JIANG,Wei DU. RESEARCH ON RIDGING OF 17%Cr ULTRA PURE FERRITIC STAINLESS STEEL AFTER ENLONGATED ALONG VARIOUS DIRECTIONS. Acta Metall Sin, 2016, 52(1): 33-40.
Improved mechanical and chemistry properties of ferritic stainless steel (FSS), such as stamping formability and corrosion resistance, have been attained by decreasing the contents of C and N. Therefore, the ultra pure ferritic stainless steel with low content of C and N is a good candidate to replace the conventional Cr-Ni austenitic stainless steel for specific applications to save the higher price of Ni. As compared to conventional austenitic stainless steel, however, the ferritic stainless steel is susceptible to develop narrow ridges on the sheet surface during forming operations. The ridges, which can extend over the whole sheet length and have a depth of 20~50 μm, destroy the smooth appearance and surface shine of the product and thereby reduce the quality of the formed work pieces. This is one of the most serious problems of ferritic stainless steel sheets. Hence, the improvement for resistance of ridging is desired for further wide applications of ferritic stainless steel. In this work, laser scanning confocal microscopy, XRD and EBSD were used to observe the corelation between surface ridging and the evolution of grain orientation of 17%Cr ultra pure ferritic stainless steel after elongated along three different directions. Furthermore, the mechanism of tensile ridging of ferritic stainless steel was discussed. The results show that the ridging direction always parallels to the original rolling direction when the 17%Cr ultra pure ferritic stainless steel is enlongated along 0° (rolling direction, RD), 45° and 90° (transverse direction, TD) with the rolling directions, respectively. However, the height of ridging gradually decreases with the increase of the angle betweeen the rolling direction. Meanwhile, tensile texture of <110>//TA (tensile axis) gradually forms after enlongated along three different directions. The most important phenomenon is that the crystal plane almost does not rotate when enlongated along TD, while {112} and {221} orientations form when enlongated along RD. Thus it can be deduced that there is no relationship between ridging and <110>//TA orientation in 17%Cr ultra pure ferritic stainless steel. Moreover, the rotation of crystal direction in rolling plane has little effect on the ridging. However, the formation of ridging can be attributed to the rotation of crystal plane in rolling plane with cluster distribution.
Fig.1 Schematic of surface ridging (a), surface morphologies at low (b) and high (c) magnification of 17%Cr ultra pure ferritic stainless steel after elongated along 0° (RD), 45° and 90° (TD) (RD—rolling direction, TD—transverse direction)
Fig.2 Surface profiles of 17%Cr ultra pure ferritic stainless steel after elongated 25% along RD (a), 45° (b) and TD (c)
Direction
Ridging / mm
Ra / mm
Rt / mm
Peak
Valley
RD
23.01
-15.53
6.82
38.54
45°
7.58
-5.27
2.44
12.85
TD
4.28
-4.77
1.20
9.05
Table 1 Ridging parameters of 17%Cr ultra pure ferritic stainless steel after elongated 25% along 3 directions
Fig.3 Orientation distribution function (ODF) figures of 17%Cr ultra pure ferritic stainless steel at annealing state (a) and elongated 25% along RD (b) and TD (c) (F, j1—Eular angle)
Fig.4 Distribution of grains with <110>//RD (a) and <110>//TD (b) at annealing state, <110>//RD (c) and <110>//TD (d) after elongation 25% along RD and TD
Fig.5 ND-IPF (a, c, e) and RD-IPF (b, d, f) of grain orientation in 17%Cr ultra pure ferritic stainless steel at annealing state (a, b), elongated 25% along RD (c, d) and TD (e, f)
Fig.6 Schematic of relationship between ridging and rotation of crystal orientation and crystal plane
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