塑性と加工
Online ISSN : 1882-0166
Print ISSN : 0038-1586
ISSN-L : 0038-1586
論文
超高強度薄鋼板材の伸びフランジ変形限界に及ぼす端面加熱による材料組織変化の影響
松木 優一 飛田 隼佑中川 欣哉新宮 豊久山﨑 雄司玉井 良清
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2022 年 63 巻 736 号 p. 65-71

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Fracture at sheared edges upon stretch flanging is a severe problem for ultrahigh-strength steel (UHSS). This study was focused on the improvement of stretch flangeability by heat treatment of the sheared edge of UHSS samples. The materials studied were dual-phase steel and full martensite steel. The steel samples were pierced with 10 mmΦ holes then heat-treated by whole-area, or partial-area heating. The heated materials were tested by the hole-expansion test to determine the hole-expansion ratio (λ). The mechanical properties and microstructural transformation depending on the heat-treatment temperature were also investigated. The experimental results of whole-area heating showed that the λ of the steels improved with heat-treatment temperature up to Ac1 (the temperature at which austenite starts to transform from ferrite). The λ significantly decreased with heat treatment between Ac1 and Ac3 (the temperature at which austenite is completely transformed from ferrite). The λ increased again with heat treatment over Ac3. The λ dependence on the heat-treatment temperature was explained by the alleviation of work hardening and microstructural transformation. The experimental results of partial-area heating showed that instant and partial-area heat treatment was sufficient to improve λ.

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