Nippon Steel Corporation

Hiroshi Katoh

Kazuo Koyama

Yasumitsu Onoe

Osamu Akisue

Kunihiko Komiya

Hiromi Toyota

Nobuyuki Takahashi

Koe Nakajima

Hiroshi Takechi

Atsushi Itami

Yoshikazu Matsumura

Kishio Mochinaga

Nobuhiko Matsuzu

Shozo Sekino

Kazuhide Usami

Toshiro Nishihara

Touru Ishimaru

Koichi Kawamura

Disclosed are processes for producing cold rolled steel sheets and strips having excellent press formability and ageing property by a continuous annealing method, in which specific heating cycles are adopted in combination with steel compositions with lowered phosphorus contents.

Process for producing cold rolled steel sheets having excellent press

An r value of a hot-rolled steel sheet is enhanced by: a specific composition consisting of not more than 0.015 wt % of C, from 1.0 to 2.5 wt % of Mn, from 0.005 to 0.10 wt % of Al, from 0.01 to 0.06 wt % of Nb, from 0.01 to 0.1 wt % of Ti; and, controlled rolling, characterized by in the rough rolling, imparting, in a temperature range of from 980.degree. to 1100.degree. C., a heavy reduction of not less than 20% per pass to the steel sheet; completing a finishing rolling at from Ar.sub.3 to 930.degree. C. and maintaining a total reduction at a temperature of not more than Ar.sub.3 +150.degree. C. to not less than 90%; and, coiling at a temperature of from 600.degree. to 800.degree. C.

Process for producing hot-rolled steel sheet having high r value

A high strength cold rolled strip having excellent deep drawability and resistance to deterioration by natural aging and to planar cracking and useful for motor vehicles, is produced by hot rolling a steel slab comprising

Process for producing cold rolled steel strip having excellent

A method for producing a low carbon deep drawing quality steel or high strength steel in the form of a strip or sheet. At least one of carbide or nitride forming elements is added to the low carbon steel to provide therein 0.015 to 0.10% Sol Al, 0.01 to 0.10% Nb, 0.01 to 0.10% Ti and 0.01 to 0.15% V. The steel is cast or bloomed to form a slab which is held above the Ar.sub.3 point for keeping the carbide and nitride forming elements in a dissolved state. Then, without allowing the temperature to fall below the Ar.sub.3 point, hot rolling and hot finishing rolling are directly carried out at a temperature above the Ar.sub.3 point. Thereafter, if necessary and desirable, the thus-rolled slab or sheet is subjected to cold rolling and annealing.

Method for producing steel strip or steel sheet containing carbide and

A method for treating a continuously cast steel slab suitable for production of a hot rolled or cold rolled steel sheet, the steel slab being obtained by continuously casting a molten steel containing 0.01 to 2.5% by weight of Al, which method comprises holding the slab at a temperature within the range of from the Ar.sub.3 point to 650.degree. C for at least 20 minutes to precipitate nitrides, and hot rolling the slab.

Method for treating continuously cast steel slabs

A process for producing a steel having excellent strength and toughness, which comprises continuously casting a molten steel containing 0.01 - 0.10% Al and 0.002 - 0.009% N with an average cooling rate of not lower than 3.degree. C/min. down to 500.degree. C to obtain a steel slab heating the steel slab to a temperature ranging from 900.degree. to 1150.degree. C and rolling the steel slab.

Process for producing a steel having excellent strength and toughness

A method for preparing a steel blank which is less susceptible to ear occurrence during its press-working into a pressed article, which comprising cutting a cold rolled steel sheet in a planar shape obtained by overlapping a circle having a diameter R and a square having a side length of about 13/14 R with their center points being at the same point and cutting the unoverlapped portions to form a blank with a periphery having alternating arcuate and straight edges. A blank is thus provided having less material due to the straight edges in those areas where large ears would otherwise occur during working.

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Chiba, Japan

Hiroshi Katoh