A steel having a composition, expressed in wt. %, of: 0.03.ltoreq.C.ltoreq.0.06; 0.50.ltoreq.Mn.ltoreq.1.10; 0.08.ltoreq.Si.ltoreq.0.20; 0.015.ltoreq.Al.ltoreq.0.070; N.ltoreq.0.007; Ni.ltoreq.0.040; Cu.ltoreq.0.040; P.ltoreq.0.035; S.ltoreq.0.015; Mo.ltoreq.0.008; Ti.ltoreq.0.005; and boron in an amount such that: 0.65.ltoreq.B/N.ltoreq.1.60, the rest of the composition consisting of iron and impurities resulting from preparation. Also a method for making steel plates having this composition, and the resulting plates, produced by the method.