High strength hot rolled steel sheet and manufacturing method thereof

1. A high strength hot rolled steel sheet comprising, by mass %:

C: 0.02% or more and 0.30% or less;

Si: 0.20% or more and 2.0% or less;

Mn: 0.5% or more and 3.0% or less;

P: 0.10% or less;

S: 0.010% or less;

Al: 0.10% or more and 1.0% or less;

N: 0.010% or less;

Ti: 0.06% or more and 0.20% or less;

Nb: 0% or more and 0.10% or less;

Ca: 0% or more and 0.0060% or less;

Mo: 0% or more and 0.50% or less;

Cr: 0% or more and 1.0% or less; and

a remainder of Fe and impurities,

wherein a structure of the high strength hot rolled steel sheet contains a martensite in an area ratio of 20% or more and 60% or less and a ferrite in an area ratio of 40% or more, and a total area ratio of the martensite and the ferrite is 90% or more,

an average grain size of the martensite is 5.0 μm or more and 50 μm or less,

a ratio of a hardness of the martensite to a hardness of the ferrite is 0.6 or more and 1.6 or less, and

a tensile strength of the high strength hot rolled steel sheet is 980 MPa or more.

2. The hot rolled steel sheet according to claim 1 , wherein the hot rolled steel sheet comprises one or more of, by mass %:

Nb: 0.01% or more and 0.10% or less;

Ca: 0.0005% or more and 0.0060% or less;

Mo: 0.02% or more and 0.50% or less; and

Cr: 0.02% or more and 1.0% or less.