Corrosion resistant steel sheets improved in corrosion resistance and other characteristics

A corrosion resistant steel sheet having improved corrosion resistance and formability that is treated with a Zn--Cr alloy plating which is an alloy consisting of Zn and Cr as formed by electrodeposition and which is substantially solely composed of a phase .GAMMA.x having a cubic crystal system with a lattice constant a=3.00-3.06 .ANG., and any portion of said alloy not composed of said phase is substantially composed of at least one phase selected from the group consisting of a phase .eta.x having a hexagonal crystal system with lattice constants a=2.66-2.74 .ANG. and c=4.61-4.95 .ANG., and a phase .delta.x having a hexagonal system with lattice constants a=2.72-2.78 .ANG. and c=4.43-4.60 .ANG..

A corrosion resistant steel sheet having improved resistances to corrosion and chipping that is treated with a Zn--Cr alloy plating which is an alloy consisting of Zn and Cr as formed by electrodeposition and which is substantially composed of a phase .eta.x having a hexagonal crystal system and lattice constants a=2.66-2.74 .ANG. and c=4.61-4.95 .ANG., as well as a phase .delta.x having a hexagonal crystal system and lattice constants a=2.72-2.78 .ANG. and c=4.43-4.60 .ANG., and any portion of said alloy not composed of said phase is substantially composed of a phase .GAMMA.x having a cubic crystal system with a lattice constant of a=3.00-3.06 .ANG..

A corrosion resistant steel sheet having improved corrosion resistance both before and after forming that is treated with a Zn--Cr alloy plating which is an alloy consisting of Zn and Cr as formed by electrodeposition and which is substantially composed of a phase .eta.x having a hexagonal crystal system and lattice constants a=2.66-2.74 .ANG. and c=4.61-4.95 .ANG., as well as a phase .GAMMA.x having cubic crystal system and a lattice constant a=3.00-3.06 .ANG., and any portion of said alloy not composed of said phases is substantially composed of a phase .delta.x having a hexagonal crystal structure with lattice constants a=2.72-2.78 .ANG. and c=4.43-4.60 .ANG..

A corrosion resistant steel sheet having improved corrosion resistance and water resistant secondary adherence of coating that is treated with a Zn--Cr alloy plating which is an alloy consisting of Zn and Cr as formed by electrodeposition and which is substantially composed of a phase .delta.x having a hexagonal crystal system and lattice constants a=2.72-2.78 .ANG. and c=4.43-4.60 .ANG., as well as a phase .GAMMA.x having a cube crystal system and a lattice constant a=3.00-3.06 .ANG., and any portion of said alloy not composed of said phases is substantially composed of a phase .eta.x having a hexagonal crystal structure with lattice constants a=2.66-2.74 .ANG. and c=4.61-4.95 .ANG..

A corrosion resistant steel sheet having improved resistances to corrosion and perforation corrosion that is treated with a Zn--Cr alloy plating which is an alloy consisting of Zn and Cr as formed by electrodeposition and which is substantially solely composed of a phase .eta.x having a hexagonal crystal system with lattice constants a=2.66-2.74 .ANG. and c=4.61-4.95 .ANG., and a phase .delta.x having a hexagonal crystal system with lattice constants a=2.72-2.78 .ANG. and c=4.43-4.60 .ANG., as well as a phase .GAMMA.x having a cubic crystal system with lattice constant a=3.00-3.06 .ANG..