SURFACE TREATED STEEL SHEET EXCELLENT IN WORKING STRENGTH AFTER HEAT TREATMENT AND ITS PRODUCTION

PROBLEM TO BE SOLVED: To improve the weldability, coating film adhesion, corrosion resistance after coating and working strength after heat treatment in a steel sheet by controlling the X-ray diffraction intensity ratio in an Fe-Ni-Sn series alloy layer and the Ni concn. in an Ni coating layer on the outermost surface of the steel sheet to specified ranges. SOLUTION: The surface of a steel sheet is provided with an Fe-Ni-Sn alloy layer and a metallic Sn layer, and furthermore, the outermost side is coated with a chromate film to form a surface treated steel sheet. In this surface treated steel sheet, the X-ray diffraction intensity of the Fe-Ni-Sn layer is controlled so as to satisfy the formula of Id2.95 /Id2.56 =0 to 0.12. In the formula, Id2.95 denotes the X-ray diffraction intensity equivalent to d=2.95A, and Id2.56 denotes the X-ray diffraction intensity equivalent to d=2.56. For this purpose, preferably, the coating weight of Ni in the Fe-Ni-Sn alloy layer is controlled to 3 to 300 mg/m per side, and the coating weight of Sn is controlled to 100 to 500 mg/m per side. The coating weight of the metallic Sn layer is preferably controlled to 150 to 1500 mg/m per side.