Mechanism of Formation of Streak-shaped Defects on Ultra-low Carbon IF Steel for Automobile Outer Panels after Press Forming and Influence of Slab Reheating Temperature before Hot Rolling and Sb-addition on Defects

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  • 自動車外板用極低炭素IF鋼における加工後筋状欠陥の発生機構および熱延前再加熱温度とSb添加の影響
  • ジドウシャ ガイバンヨウ ゴクテイ タンソ IFコウ ニ オケル カコウ ゴキンジョウ ケッカン ノ ハッセイ キコウ オヨビ ネツエン ゼン サイカネツ オンド ト Sb テンカ ノ エイキョウ

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Abstract

Streak-shaped defects were infrequently observed on ultra-low carbon IF cold-rolled steel sheets for automotive outer panels after press-forming. The defects occurred due to heterogeneous remaining of elongated grains on the steel surface layer. Elongated grains are hard to recrystallize due to the pinning effect of small precipitates on grain boundaries. These precipitates consist mainly of Ti(NC), TiS and AlN. In order to eliminate the streak defect, lower excess Ti, lower temperature slab reheating and Sb-addition to the steel are efficient. These countermeasures result in a drastic reduction of the defect ratio. This improvement is considered to be obtained due to the reduction of small precipitates of Ti(CN), TiS and AlN in the steel surface layer.

Journal

  • Tetsu-to-Hagane

    Tetsu-to-Hagane 102 (4), 202-208, 2016

    The Iron and Steel Institute of Japan

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