Steel sheet for gas soft nitriding

A steel sheet for gas soft nitriding comprising, as a chemical composition, by mass %:

• C:
• 0.02% to 0.10%;
• Si:
• 0.001% to 0.100%;
• Mn:
• 0.70% to 1.65%;
• P:
• 0.060% or less;
• S:
• 0.005% or less;
• sol. Al:
• 0.020% to 0.450%;
• Ti:
• 0.020% to 0.120%;
• Cr:
• 0.100% to 0.450%;
• N:
• 0.0003% to 0.0070%;
• Cu:
• 0% to 0.40%;
• Ni:
• 0% to 0.30%;
• Nb:
• 0% to 0.080%;
• V:
• 0% to 0.080%;
• Mo:
• 0% to 0.100%;
• B:
• 0% to 0.0020%;
• Ca:
• 0% to 0.0100%;
• REM:
• 0% to 0.0100%;
• Sn:
• 0% to 0.0300%;
• Sb:
• 0% to 0.0100%;
• As:
• 0% to 0.0100%;
• Mg:
• 0% to 0.0300%;
• and
• a remainder including Fe and impurities,
• wherein Formulas (1) and (2) are satisfied,
• a metallographic structure of the steel sheet for gas soft nitriding contains, by area %,
• ferrite:
• 30.0% to 100.0%,
• martensite:
• 0% to 5.0%,
• bainite:
• 0% to 70.0%,
• retained austenite:
• 0% to 3.0%, and
• pearlite:
• 0% to 3.0%,
• when a sheet thickness is indicated as t, a sheet width, which is a width in a direction perpendicular to a rolling direction, is indicated as w, and effective grain sizes are measured at seven positions of w/8, w/4, 3w/8, w/2, 5w/8, 3w/4, and 7w/8 in a width direction from an end portion in the width direction at a t/4 depth position from a surface, an average effective grain size, which is an average of the effective grain sizes at the seven positions, is 8.0 to 35.0 μm, and
• an effective grain size difference, which is a difference between a maximum value and a minimum value among the effective grain sizes at the seven positions, is 10.0 μm or less,
• [sol. Al]+[Cr]≤0.482 Formula (1)
• 94<64×[Mn]+156×[Cr]+190×[sol. Al]−9×[Mn]2−86×[Cr]2−328×[sol. Al]2 Formula (2)
• where [element symbol] is an amount of an element represented by the element symbol by mass %.