Hot-rolled steel sheet and method for manufacturing same

A hot-rolled steel sheet comprising, as a chemical composition expressed by an average value in an entire sheet thickness direction, by mass %:

• C:
• 0.050% or more and 0.200% or less;
• Si:
• 0.05% or more and 3.00% or less;
• Mn:
• 1.00% or more and 4.00% or less;
• Al:
• 0.001% or more and 2.000% or less;
• N:
• 0.0005% or more and 0.1000% or less;
• Ni:
• 0.02% or more and 2.00% or less;
• Nb:
• 0% or more and 0.300% or less;
• Ti:
• 0% or more and 0.300% or less;
• Cu:
• 0% or more and 2.00% or less;
• Mo:
• 0% or more and 1.000% or less;
• V:
• 0% or more and 0.300% or less;
• Cr:
• 0% or more and 2.00% or less;
• Mg:
• 0% or more and 0.0100% or less;
• Ca:
• 0% or more and 0.0100% or less;
• REM:
• 0% or more and 0.1000% or less;
• B:
• 0% or more and 0.0100% or less;
• one or two or more of Zr, Co, Zn, and W:
• 0% to 1.000% in total;
• Sn:
• 0% to 0.050%;
• P:
• 0.100% or less;
• S:
• 0.0300% or less;
• O:
• 0.0100% or less;
• and
• a remainder including Fe and impurities,
• wherein Expression (1) is satisfied,
• PCM represented by Expression (2) is 0.20 or more,
• Ms represented by Expression (3) is 400° C. or higher,
• in a case where a thickness is denoted by t, a metallographic structure at a t/4 position from a surface contains one or both of tempered martensite and lower bainite at a total volume percentage of 90% or more,
• a tensile strength is 980 MPa or more,
• an average Ni concentration on the surface is 7.0% or more, and
• a standard deviation of an arithmetic average roughness Ra of the surface of the hot-rolled steel sheet is 10.0 μm or more and 50.0 μm or less,
• 0.05%≤Si+Al≤2.50% Expression (1)
• PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Mo/15+Cr/20+V/10+5×B Expression (2)
• Ms=561−474×C-33×Mn-17×Ni-17×Cr-21×Mo Expression (3)
• where a symbol of each element shown in the expressions indicates mass % of the element contained in the hot-rolled steel sheet.