Rail and production method therefor
A rail provided by the present invention includes: has a predetermined chemical components, wherein a value of Mn/Cr, which is a ratio of Mn content with respect to Cr content, is within a range of 0.30 to 1.00, structures in a region from a head surface constituted of a surface of a top head portion and a surface of a corner head portion to a depth of 10 mm is 98% by area or more of bainite structures, and an average hardness of the region from the head surface to a depth of 10 mm is in a range of Hv 380 to Hv 500.
1. A rail comprising:
a rail head portion having a top head portion which is a flat region extending toward a top portion of the rail head portion in a extending direction of the rail, a side head portion which is a flat region extending toward a side portion of the rail head portion in the extending direction of the rail, and a corner head portion which is a region combining a rounded corner portion extending between the top head portion and the side head portion and an upper half of the side head portion,
wherein the rail consists of, as a chemical components, in terms of mass %:
C: 0.70% to 1.00%,
Si: 0.20% to 1.50%,
Mn: 0.30% to 1.00%,
Cr: 0.50% to 1.30%,
P: 0.0250% or less,
S: 0.0250% or less,
Mo: 0% to 0.50%,
Co: 0% to 1.00%,
Cu: 0% to 1.00%,
Ni: 0% to 1.00%,
V: 0% to 0.300%,
Nb: 0% to 0.0500%,
Mg: 0% to 0.0200%,
Ca: 0% to 0.0200%,
REM: 0% to 0.0500%,
B: 0% to 0.0050%,
Zr: 0% to 0.0200%,
N: 0% to 0.0200%, and
a remainder of Fe and impurities,
wherein a value of Mn/Cr, which is a ratio of Mn content with respect to Cr content, is within a range of 0.30 to 1.00,
wherein structures in a region from a head surface constituted of a surface of the top head portion and a surface of the corner head portion to a depth of 10 mm includes 98% by area or more of bainite structures, and
wherein an average hardness of the region from the head surface to a depth of 10 mm is in a range of Hv 380 to Hv 500.
2. The rail according to claim 1 ,
wherein the rail contains as the chemical components, in terms of mass %, one or more selected from the group consisting of:
Mo: 0.01% to 0.50%,
Co: 0.01% to 1.00%,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
V: 0.005% to 0.300%,
Nb: 0.0010% to 0.0500%,
Mg: 0.0005% to 0.0200%,
Ca: 0.0005% to 0.0200%,
REM: 0.0005% to 0.0500%,
B: 0.0001% to 0.0050%,
Zr: 0.0001% to 0.0200%, and
N: 0.0060% to 0.0200%.
3. A production method for a rail, comprising:
hot-rolling a bloom or a slab in a rail shape to obtain a material rail,
accelerated-cooling the head surface of the material rail from a temperature region of 700° C. or higher which is a temperature region that is equal to or higher than a transformation start temperature from austenite to a temperature region of 350° C. to 500° C. at a cooling rate of 3.0° C./sec to 20.0° C./sec after the hot-rolling,
holding a temperature of the head surface of the material rail in the temperature region of 350° C. to 500° C. for 100 sec to 800 sec after the accelerated-cooling, and
naturally-cooling or further accelerated-cooling the material rail to room temperature after the holding, wherein
the bloom or the slab contains, as a chemical components, in terms of mass %;
C: 0.70% to 1.00%,
Si: 0.20% to 1.50%,
Mn: 0.30% to 1.00%,
Cr: 0.50% to 1.30%,
P: 0.0250% or less,
S: 0.0250% or less,
Mo: 0% to 0.50%,
Co: 0% to 1.00%,
Cu: 0% to 1.00%,
Ni: 0% to 1.00%,
V: 0% to 0.300%,
Nb: 0% to 0.0500%,
Mg: 0% to 0.0200%,
Ca: 0% to 0.0200%,
REM: 0% to 0.0500%,
B: 0% to 0.0050%,
Zr: 0% to 0.0200%,
N: 0% to 0.0200%, and
a remainder of Fe and impurities, and
wherein a value of Mn/Cr, which is a ratio of Mn content with respect to Cr content, is within a range of 0.30 to 1.00.
4. The production method for a rail according to claim 3 , further comprising:
preliminarily-cooling the hot-rolled rail and then reheating the head surface of the material rail to an austenite transformation completion temperature+30° C. or higher between the hot-rolling and the accelerated-cooling.
5. A production method for a rail, comprising:
hot-rolling a bloom or a slab in a rail shape to obtain a material rail,
accelerated-cooling the head surface of the material rail from a temperature region of 700° C. or higher which is a temperature region that is equal to or higher than a transformation start temperature from austenite to a temperature region of 350° C. to 500° C. at a cooling rate of 3.0° C./sec to 20.0° C./sec after the hot-rolling,
holding a temperature of the head surface of the material rail in the temperature region of 350° C. to 500° C. for 100 sec to 800 sec after the accelerated-cooling, and
naturally-cooling or further accelerated-cooling the material rail to room temperature after the holding, wherein
the bloom or the slab contains, as a chemical components, in terms of mass %:
C: 0.70% to 1.00%,
Si: 0.20% to 1.50%,
Mn: 0.30% to 1.00%,
Cr: 0.50% to 1.30%,
P: 0.0250% or less,
S: 0.0250% or less,
one or more selected from the group consisting of:
Mo: 0.01% to 0.50%,
Co: 0.01% to 1.00%,
Cu: 0.05% to 1.00%,
Ni: 0.05% to 1.00%,
V: 0.005% to 0.300%,
Nb: 0.0010% to 0.0500%,
Mg: 0.0005% to 0.0200%,
Ca: 0.0005% to 0.0200%,
REM: 0.0005% to 0.0500%,
B: 0.0001% to 0.0050%,
Zr: 0.0001% to 0.0200%, and
N: 0.0060% to 0.0200%, and
a remainder of Fe and impurities, and
wherein a value of Mn/Cr, which is a ratio of Mn content with respect to Cr content, is within a range of 0.30 to 1.00.
6. The production method for a rail according to claim 5 , further comprising:
preliminarily-cooling the hot-rolled rail and then reheating the head surface of the material rail to an austenite transformation completion temperature+30° C. or higher between the hot-rolling and the accelerated-cooling.