C: 0.15% to 0.35%;

Si: 0.8% to 2.5%;

Mn: 0.8% to 2.5%;

Al: 0.03% to 2.0%;

N: 0.002% to 0.010%;

P: 0.01% or less;

S: 0.01% or less;

O: 0.01% or less;

B: 0.0001% to 0.005%;

Nb: 0.0% to 0.05%;

Ti: 0.0% to 0.2%;

V: 0.0% to 0.05%;

Mo: 0.0% to 1.0%;

Cr: 0.0% to 1.0%;

Ni: 0.01% to 1.0%;

Cu: 0.05% to 1.0%;

at least one of Ca, Mg and REM (rare earth metals): 0.0005% to 0.01%; and the balance being Fe and impurities,

wherein the steel has a martensite phase or/and a bainite phase in which ε-carbide having a size of 2 nm or more to 150 nm or less is dispersedly precipitated at a density of 1×10⁶ or more per 1 mm², and wherein the ε-carbide has a hexagonal crystal structure containing hydrogen trapping carbon vacancy sites inside a crystal grain thereof, the hydrogen trapping carbon vacancy sites being stable from 0° C. to about 300° C., and wherein the steel is substantially free of cementite.