Jfe Steel Corporation

Noriaki Kosaka

Yoshimasa Funakawa

Kazuhiro Seto

Hidetaka Kawabe

Takayuki Murata

Satoshi Tsutsumi

Hidekazu Ookubo

Motohiko Urabe

Tokunori Kanemura

Masato Shigemi

Hidekazu Okubo

There is provided a high strength hot rolled steel sheet having a composition comprising C: 0.040% to 0.100%, by mass %, Si: 0.50% or less, by mass %, Mn: 1.00% to 2.00%, by mass %, P: 0.03% or less, by mass %, S: 0.006% or less, by mass %, Al: 0.08% or less, by mass %, N: 0.0080% or less, by mass %, Ti: 0.14% to 0.22%, by mass %, and Fe and incidental impurities, and a method for making the same. The high strength hot rolled steel sheet includes a microstructure in which a primary phase is a ferrite phase and fine carbides containing Ti are dispersion-precipitated.

High strength hot rolled steel sheet and method for manufacturing the same

A slab has a steel composition including 0.020% to 0.065% of C, 0.1% or less of Si, 0.40% to less than 0.80% of Mn, 0.030% or less of P, 0.005% or less of S, 0.08% to 0.16% of Ti, 0.005% to 0.1% of Al, 0.005% or less of N, and the balance being Fe and incidental impurities, in which Ti*(=Ti&#x2212;(48/14)&#xd7;N) satisfies [Ti*&#x2267;0.08] and [0.300&#x2266;C/Ti*&#x2266;0.375], is subjected to hot rolling to obtain a hot-rolled steel sheet in which the steel microstructure includes, in terms of area fraction, 95% or more of a ferrite phase; the average ferrite grain size is 10 &#x3bc;m or less; the average grain size of Ti carbides precipitated in steel is 10 nm or less; and Ti in the amount of 80% or more of Ti* is precipitated as Ti carbides.

High strength hot-rolled steel sheet having excellent ductility, stretch flangeability and uniformity and method of manufacturing the same

A semi-manufactured steel material has a chemical composition including, by mass %, C: 0.055% to 0.15%, Si: not more than 0.2%, Mn: not more than 1.3%, P: not more than 0.03%, S: not more than 0.007%, Al: not more than 0.1%, N: not more than 0.01%, and Ti: 0.14% to 0.30%, the balance comprising Fe and inevitable impurities. In the composition, 1.0&#x2266;([C]/12)/([Ti*]/48) is satisfied ([C], [S], [N] and [Ti]: contents (mass %) of the respective elements, and [Ti*]=[Ti]&#x2212;3.4&#xd7;[N]&#x2212;1.5&#xd7;[S]), and the contents of niobium and boron as impurities are limited to Nb: less than 0.03% and B: less than 0.0005%.

Hot rolled steel sheet and method for manufacturing the same

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Fukuyama, Japan

Noriaki Kosaka