High-strength hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having fatigue resistance corrosion resistance ductility and plating adhesion after servere deformation and a method of producing the same

A high-strength hot-dip galvanized steel sheet having high plating adhesion after severe deformation and ductility, the hot-dip galvanized steel sheet having a plated layer containing, in mass,

• Al:
• 0.001 to 0.5%, and
• Mn:
• 0.001 to 2%,
• with the balance consisting of Zn and unavoidable impurities, on the surface of a steel sheet consisting of, in mass,
• C:
• 0.0001 to 0.3%,
• Si:
• 0.01 to 2.5%,
• Mn:
• 0.01 to 3%,
• Al:
• 0.001 to 4%, and
• the balance consisting of Fe and unavoidable impurities, characterized in that:
• Si content:
• X (in mass %), Mn content:
• Y (in mass %) and Al content:
• Z (in mass %) in the steel, and Al content:
• A (in mass %) and Mn content:
• B (in mass %) in the plated layer satisfy the following equation 1;
• and the microstructure of the steel sheet has the main phase comprising ferrite at 70 to 97% in volume and the average grain size of a main phase being not more than 20 μm, and a second phase comprising austenite and/or martensite at 3 to 30% in volume and the average grain size of the second phase being not more than 10 μm:
• 3−(X+Y/10+Z/3)−12.5×(A−B)≧0 1.

A high-strength hot-dip galvannealed steel sheet having superior appearance and workability, the hot-dip galvannealed steel sheet having a plated layer containing, in mass,

• Mn:
• 0.001 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.0001 to 1%, and
• Fe:
• 5 to 20%,
• with the balance consisting of Zn and unavoidable impurities, on the surface of a steel sheet consisting of, in mass,
• C:
• 0.0001 to 0.3%,
• Si:
• 0.001 to less than 0.1%,
• Mn:
• 0.01 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.001 to 1%,
• P:
• 0.0001 to 0.3%,
• S:
• 0.0001 to 0.1%, and
• the balance consisting of Fe and unavoidable impurities, characterized in that:
• Mn content:
• X (in mass %) and Si content:
• Y (in mass %) in the steel, and Al content:
• Z (in mass %) in the plated layer satisfy the following equation 2:
• 0.6−(X/18+Y+Z)≧0 2.

A high-strength hot-dip galvanized steel sheet having superior appearance and workability, the hot-dip galvanized steel sheet having a plated layer containing, in mass,

• Mn:
• 0.001 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.0001 to 1%, and
• Fe:
• less than 5%,
• with the balance consisting of Zn and unavoidable impurities, on the surface of a steel sheet consisting of, in mass,
• C:
• 0.0001 to 0.3%,
• Si:
• 0.001 to less than 0.1%,
• Mn:
• 0.01 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.001 to 1%,
• P:
• 0.0001 to 0.3%,
• S:
• 0.0001 to 0.1%, and
• the balance consisting of Fe and unavoidable impurities, characterized in that:
• Mn content:
• X (in mass %) and Si content:
• Y (in mass %) in the steel, and Al content:
• Z (in mass %) in the plated layer satisfy the following equation 2:
• 0.6−(X/18+Y+Z)≧0 2.

A high-strength high-ductility hot-dip galvannealed steel sheet having high corrosion resistance, the hot-dip galvannealed steel sheet having a plated layer containing, in mass,

• Al:
• 0.001 to 4%, and
• Fe:
• 5 to 20%,
• with the balance consisting of Zn and unavoidable impurities, on the surface of a steel sheet consisting of, in mass,
• C:
• 0.0001 to 0.3%,
• Si:
• 0.001 to less than 0.1%,
• Mn:
• 0.001 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.001 to 1%,
• P:
• 0.001 to 0.3%,
• S:
• 0.0001 to 0.1%, and
• the balance consisting of Fe and unavoidable impurities, characterized in that:
• Al content:
• A (in mass %) and Mo content:
• B (in mass %) in the plated layer, and Mo content:
• C (in mass %) in the steel satisfy the following equation 3;
• and the microstructure of the steel consists of the main phase comprising ferrite or ferrite and bainite 50 to 97% in volume and the balance consisting of a complex structure containing either or both of martensite and retained austenite 3 to 50% in volume:
• 100≧(A/3+B/6)/(C/6)≧0.01 3.

A high-strength high-ductility hot-dip galvanized steel sheet having high corrosion resistance, the hot-dip galvanized steel sheet having a plated layer containing, in mass,

• Al:
• 0.001 to 4%, and
• Fe:
• less than 5%,
• with the balance consisting of Zn and unavoidable impurities, on the surface of a steel sheet consisting of, in mass,
• C:
• 0.0001 to 0.3%,
• Si:
• 0.001 to less than 0.1%,
• Mn:
• 0.001 to 3%,
• Al:
• 0.001 to 4%,
• Mo:
• 0.001 to 1%,
• P:
• 0.001 to 0.3%,
• S:
• 0.0001 to 0.1%, and
• the balance consisting of Fe and unavoidable impurities, characterized in that:
• Al content:
• A (in mass %) and Mo content:
• B (in mass %) in the plated layer, and Mo content:
• C (in mass %) in the steel satisfy the following equation 3;
• and the microstructure of the steel consists of the main phase comprising ferrite or ferrite and bainite 50 to 97% in volume and the balance consisting of a complex structure containing either or both of martensite and retained austenite at 3 to 50% in volume:
• 100≧(A/3+B/6)/(C/6)≧0.01 3.