Nippon Steel Corporation

Nippon Steel Sumitomo Metal Corporation

Hideo Mizukami

Manabu Kubota

Akira Shiga

Hajime Hasegawa

Suguru Yoshida

Shinya Teramoto

Akihiro Yamanaka

Toshihiko Murakami

Tomoaki Sera

Hideyoshi Yamaguchi

Hirofumi Onishi

Shinji Nagai

There is provided a hot forging steel including, by mass %, C: more than 0.30% and less than 0.60%, Si: 0.10% to 0.90%, Mn: 0.50% to 2.00%, S: 0.010% to 0.100%, Cr: 0.01% to 1.00%, Al: more than 0.005% and 0.100% or less, N: 0.0030% to 0.0200%, Bi: more than 0.0001% and 0.0050% or less, Ti: 0% or more and less than 0.040%, V: 0% to 0.30%, Ca: 0% to 0.0040%, Pb: 0% to 0.40%, and a remainder including Fe and impurities, in which P and O in the impurities are respectively P: 0.050% or less and O: 0.0050% or less, an expression d+3&#x3c3;&#x3c;20 is satisfied, and a presence density of MnS having an equivalent circle diameter of smaller than 2.0 &#x3bc;m is 300 pieces/mmor more in a cross section parallel to a rolling direction of a steel.

Hot forging steel and hot forged product

A steel according to an aspect of the present invention has a chemical composition within a predetermined range, in which a hardenability index Ceq ranges from greater than 7.5 to smaller than 44.0, a metallographic structure includes ferrite ranging from 85 to 100 area %, an average distance between sulfides, which are observed in a cross section parallel to a rolling direction of the steel and have an equivalent circle diameter ranging from 1 &#x3bc;m or greater to smaller than 2 &#x3bc;m, is shorter than 30.0 &#x3bc;m, and a presence density of the sulfides, which are observed in the cross section parallel to the rolling direction of the steel and have an equivalent circle diameter ranging from 1 &#x3bc;m or greater to smaller than 2 &#x3bc;m, is 300 pieces/mmor more.

Steel, carburized steel component, and method for manufacturing carburized steel component

There is a hot-rolled steel according to one aspect of the invention including predetermined chemical compositions including 0.0001 to 0.0050 mass % of Bi, in which 90 area % or more of a metallographic structure is configured with a ferrite and a pearlite, and an average number density of Mn sulfides extending along a rolling direction and having an aspect ratio exceeding 10 and equal to or smaller than 30, which is measured on a cross section parallel to the rolling direction, is 50 to 200 number/mm.

Hot-rolled steel and steel component

A method for manufacturing a forged steel roll comprises: casting, by the ESR method, a steel ingot which contains, by mass %, C: 0.3% or more, Si: 0.2% or more, Cr: 2.0-13.0% and Mo: 0.2% or more, and further contains Bi at 10-100 ppm by mass; and forging the steel ingot to manufacture the roll. According to this method, since freckle defects can be sealed near the center of the steel ingot, the roll can be stably used over a long period of time.

Method for manufacturing forged steel roll

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Kashima, Japan

Hideo Mizukami