Effects of centerline macrosegregation on necking of P-added extra low carbon steel sheet |
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Authors: | Seung Chul Baik Joo Dong Lee Ohjoon Kwon |
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Affiliation: | (1) Technical Research Lab., Pohang Iron & Steel Co., Ltd., 1 Goydong-dong, Natn-ku, 790-785 Pohang, Korea |
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Abstract: | Effects of centerline macrosegregation on necking was examined by the stretching experiment for cold rolled P-added extra
low carbon steel sheets. The centerline macrosegregated zone containing high concentration of Mn and P was elongated in the
rolling process. The elongated macrosegregated zone induced instability in the strain state when the sheet was stretched,
thus resulted in the waved sheet surface. The formability of cold rolled steel sheet was deteriorated due to the wave formed
by the macrosegregation. The waved surface was thought to be caused by the higher hardness in the macrosegregated zone compared
to the segregation free zone. The experiments on the stretching of sheet including macrosegregation showed that the macrosegregation
was the important source of instability in that of the cold rolled steel sheets. A 3D FEM analysis was carried out for the
quantitative evaluation of waved surface. It was confirmed that the main source of the waved surface was the macrosegregation.
Stretching in the transverse direction under the plane strain condition made the cold rolled steel sheet more inhomogeneous
than stretching in any other strain condition. The thickness difference in the stretched sheet was linearly increased when
the ratio of hardness in the macrosegregated zone to that of the segregation free zone was increased. The macrosegregation
formed in the internal crack close to the surface was more harmful to the formability in the cold rolled steel sheet than
the centerline macrosegregation. |
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Keywords: | centerline macrosegregation P-added cold rolled steel formability |
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