H-section steel and method of producing the same

1. An H-section steel comprising, by mass %:

C: 0.05% to 0.16%;

Si: 0.01% to 0.50%;

Mn: 0.80% to 2.00%;

Ni: 0.05% to 0.50%;

V: 0.01% to 0.20%;

Ti: 0.005% to 0.030%;

N: 0.0010% to 0.0100%;

O: 0.0005% to 0.0100%;

Cr: 0% to 0.50%;

Cu: 0% to 0.30%;

Mo: 0% to 0.30%;

W: 0% to 0.50%;

Al: limited to 0.005% or less;

Nb: limited to 0.010% or less;

B: limited to 0.0005% or less; and

a remainder including of Fe and impurities,

wherein a carbon equivalent C eq obtained by the following Equation 1 is 0.35% to 0.50%,

a density of Ti oxides having a grain size of 0.01 μm to 3.0 μm is 30 pieces/mm 2 or more,

a thickness of a flange is 100 mm to 150 mm,

at a ⅙ position from a surface of the flange in a length direction and at a ¼ position from the surface thereof in a thickness direction, an area fraction of bainite is 80% or more, a yield strength or 0.2% proof stress is 450 MPa or more, and a tensile strength is 550 MPa or more, and

at a ½ position from the surface of the flange in the length direction and at a ¾ position from the surface thereof in the thickness direction, a Charpy absorbed energy at 21° C. is 100 J or more, and an average austenite grain size is 50 μm to 200 μm,

C eq =C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15  Equation 1

here, C, Mn, Cr, Mo, V, Ni, and Cu represent the amount % of each element and the amount of an element not contained is 0%.

2. The H-section steel according to claim 1 , comprising, by mass %,

one of or two or more of

Cr: 0.01% to 0.50%,

Cu: 0.01% to 0.30%,

Mo: 0.001% to 0.30%, and

W: 0.01% to 0.50%.

3. The H-section steel according to claim 1 , comprising, by mass %,

Mo: 0.001% to 0.29%.

4. The H-section steel according to claim 1 , comprising, by mass %,

Mo: 0.001% to 0.20%.

5. A method of producing the H-section steel according to claim 1 , the method comprising:

a refining process of deoxidizing a molten steel to allow a concentration of oxygen in the molten steel to be 0.0005% to 0.0100%, then adding Ti, and adjusting components of the molten steel to include by mass %, C: 0.05% to 0.16%, Si: 0.01% to 0.50%, Mn: 0.80% to 2.00%, Ni: 0.05% to 0.50%, V: 0.01% to 0.20%, Ti: 0.005% to 0.030%, N: 0.0010% to 0.0100%, O: 0.0005% to 0.0100%, Cr: 0% to 0.50%, Cu: 0% to 0.30%, Mo: 0% to 0.30%, W: 0% to 0.50%; Al: limited to 0.005% or less, Nb: limited to 0.010% or less, B: limited to 0.0005% or less, and a remainder including of Fe and impurities, and to have a carbon equivalent C eq obtained by the following Equation 2 of 0.35% to 0.50%;

a casting process of casting the molten steel to obtain a steel piece;

a heating process of heating the steel piece to 1100° C. to 1350° C.;

a hot rolling process of performing hot rolling on the heated steel piece so that a surface temperature of the steel piece is 800° C. or higher, thereby obtaining an H-section steel; and

a cooling process of water-cooling the H-section steel after the hot rolling process,

wherein in the cooling process, water cooling conditions are controlled so that the cooled surface temperature bounce back to within a temperature range of 300° C. to 700° C. after heat-recuperation,

C eq =C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15  Equation 2.

6. The method of producing the H-section steel according to claim 5 ,

wherein the components of the molten steel include, by mass %,

one of or two or more of

Cr: 0.01% to 0.50%,

Cu: 0.01% to 0.30%,

Mo: 0.001% to 0.30%, and

W: 0.01% to 0.50%.

7. A method of producing the H-section steel according to claim 2 , the method comprising:

a refining process of deoxidizing a molten steel to allow a concentration of oxygen in the molten steel to be 0.0005% to 0.0100%, then adding Ti, and adjusting components of the molten steel to include by mass %, C: 0.05% to 0.16%, Si: 0.01% to 0.50%, Mn: 0.80% to 2.00%, Ni: 0.05% to 0.50%, V: 0.01% to 0.20%, Ti: 0.005% to 0.030%, N: 0.0010% to 0.0100%, O: 0.0005% to 0.0100%, Al: limited to 0.005% or less, Nb: limited to 0.010% or less, B: limited to 0.0005% or less, and one or more of Cr: 0.01% to 0.50%, Cu: 0.01% to 0.30%, Mo: 0.001% to 0.30%, W: 0.01% to 0.50% and a remainder including of Fe and impurities, and to have a carbon equivalent C eq obtained by the following Equation 2 of 0.35% to 0.50%;

a casting process of casting the molten steel to obtain a steel piece;

a heating process of heating the steel piece to 1100° C. to 1350° C.;

a hot rolling process of performing hot rolling on the heated steel piece so that a surface temperature of the steel piece is 800° C. or higher, thereby obtaining an H-section steel; and

a cooling process of water-cooling the H-section steel after the hot rolling process,

wherein in the cooling process, water cooling conditions are controlled so that the cooled surface temperature bounce back to within a temperature range of 300° C. to 700° C. after heat-recuperation,

C eq =C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15  Equation 2.