Jfe Steel Corporation

Tadachika Chiba

Shinjiro Kaneko

Yoshihiko Ono

Noriaki Kohsaka

Yuma Honda

Yasushi Kitani

Junya Tobata

Akinori Nakamura

A thin steel sheet has a specific chemical composition. The thin steel sheet has a microstructure in which ferrite is present in an area fraction of 5% or more and 60% or less, as-quenched martensite is present in an area fraction of 10% or less (including 0%), retained austenite is present in an area fraction of 5% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite are present in a total area fraction of more than 15% and less than 85%; BCC iron that has a misorientation of 1° or less and surrounds retained austenite having an aspect ratio of 2.5 or higher is present in an area fraction of 5% or more and 70% or less; and a top 10% of retained austenite in terms of an equivalent circular diameter has an average aspect ratio of 2.5 or higher.

Thin steel sheet and method for manufacturing same

A thin steel sheet has a specific chemical composition. The thin steel sheet has a microstructure in which ferrite is present in an area fraction of 4% or less (including 0%), as-quenched martensite is present in an area fraction of 10% or less (including 0%), retained austenite is present in an amount of 7% or more and 20% or less, and upper bainite, lower bainite, and tempered martensite are present in a total area fraction of more than 71% and less than 93%; and BCC iron that has a misorientation of 1° or less and surrounds retained austenite having an equivalent circular diameter of 1 μm or less is present in an area fraction of 4% or more and 50% or less, and BCC iron that has a misorientation of more than 1° is present in an area fraction of 25% or more and 85% or less.

Growing community of inventors

Tokyo, Japan

Tadachika Chiba