Steel sheet pile and method for manufacturing the same

1. A steel sheet pile, wherein

a chemical composition consists of, in terms of mass %:

C: 0.05 to 0.18%;

Si: 0.10 to 0.50%;

Mn: 0.50 to 1.50%;

Nb: 0.040 to 0.050%;

V: 0.20 to 0.30%;

Cu: 0 to 0.40%;

Ni: 0 to 1.00%;

Mo: 0 to 1.00%;

Cr: 0 to 1.00%;

Al: limited to less than 0.05%;

P: 0.040% or less;

S: 0.040% or less;

and

remainder including Fe and impurities,

a carbon equivalent calculated by Expression 1 and Expression 2 is 0.260 to 0.500,

a structure includes a ferrite, a pearlite, a Widmanstätten ferrite, and a precipitate,

the precipitate is one or both of Nb carbonitride and V carbonitride,

a number density of the precipitate is 0.10 to 0.30 pieces/μm 2 ,

a total area ratio of the ferrite and the pearlite is 70% or more,

an area ratio of the Widmanstätten ferrite is 1% or more,

an average grain size of the ferrite and the pearlite is 10 to 80 μm,

a yield strength is 460 to 550 MPa and a tensile strength is 550 to 740 MPa,

CE N =<C>+ f (C)×{<Mn>/6+<Si>/24+<Ni>/20+(<Cr>+<Mo>+<Nb>+<V>)/5}:  Expression 1,

f (C)=0.75+0.25×tan h {20×(<C>−0.12)}:  Expression 2, and

<C>, <Mn>, <Si>, <Ni>, <Cr>, <Mo>, <Nb>, and <V> express amounts of each element in terms of mass %, in which an amount of an element which is not included is considered to be 0%.

2. A method for manufacturing the steel sheet pile according to claim 1 , the method comprising:

heating a steel slab consisting of the chemical composition according to claim 1 to 1100 to 1350° C.;

hot-rolling the steel slab under a condition in which a cumulative reduction at a region of 900° C. or more is 90% or more and a finishing temperature is 850° C. or more to obtain the steel sheet pile; and

cooling the steel sheet pile.