Clad steel plate and method of producing the same

A clad steel plate comprising:

• a base steel;
• and
• a cladding metal made of a corrosion resistant alloy bonded to one surface of the base steel;
• wherein the base steel has a chemical composition containing, in mass %,
• C:
• 0.020% or more and 0.100% or less,
• Si:
• 0.05% or more and 0.50% or less,
• Mn:
• 0.75% or more and 1.60% or less,
• P:
• 0.010% or less,
• S:
• 0.0010% or less,
• Al:
• 0.010% or more and 0.070% or less,
• Nb:
• 0.005% or more and 0.080% or less,
• Ti:
• 0.005% or more and 0.030% or less,
• N:
• 0.0010% or more and 0.0060% or less,
• Ca:
• 0.0005% or more and 0.0040% or less,
• O:
• 0.0030% or less, and
• at least one selected from the group consisting of
• Cu:
• 0.01% or more and 0.50% or less,
• Cr:
• 0.01% or more and 0.50% or less,
• Mo:
• 0.01% or more and 0.50% or less,
• V:
• 0.010% or more and 0.100% or less, and
• Ni:
• 0.01% or more and 0.50% or less,
• so as to satisfy relations given by the following formulas (1) and (2), with the balance being Fe and inevitable impurities:
• 1.00≤ACR≤6.00 (1),
• where ACR is defined by:
• ACR=([Ca]−(0.18+130[Ca])×[O])/(1.25[S]),
• where [Ca], [O], and [S] respectively represent the contents in mass % of Ca, O, and S in the base steel, and
• PHIC<1.000 (2),
• where PHIC is defined by:
• PHIC=4.46[C]+2.37[Mn]/6+(1.18[Cr]+1.95[Mo]+1.74[V])/5+(1.74[Cu]+1.7[Ni])/15+22.36[P],
• where [C], [Mn], [Cr], [Mo], [V], [Cu], [Ni], and [P] respectively represent the contents in mass % of C, Mn, Cr, Mo, V, Cu, Ni, and P in the base steel,
• wherein the base steel has a steel microstructure in which
• bainite is present in an area fraction of 94% or more at a ½ thickness position in a thickness direction of the base steel, and with an average crystal grain size of 25 μm or less,
• wherein shear strength at a bonded interface between the base steel and the cladding metal is 300 MPa or more, and
• wherein a crack area ratio obtained by HIC test in accordance with NACE Standard TM0284-2003 is 5.0% or less.