High yield ratio and high-strength hot-dip galvanized steel sheet excellent in workability and production method thereof

A hot-dip galvanized steel sheet containing

• C:
• 0.05 to 0.3% (in terms of mass %, hereunder same as above with respect to chemical composition),
• Si:
• 0.005 to 3.0%,
• Mn:
• 1.5 to 3.5%,
• Al:
• 0.005 to 0.15%,
• P:
• 0.1% or less, and
• S:
• 0.05% or less,
• with the remainder comprising of iron and unavoidable impurities, wherein:
• in percentage in a metallographic structure,
• the area ratio of ferrite is 5 to 85%,
• the area ratio of martensite is 15 to 90%,
• the area ratio of retained austenite is 20% or less, and
• the sum of the area ratios of said ferrite, said martensite, and said retained austenite is 70% or more;
• in the ferrite structure, when the length per unit area of the grain boundaries of crystal grains the crystal orientation differences of which are 10 degrees or more is defined as La and the length per unit area of the grain boundaries of crystal grains the crystal orientation differences of which are less than 10 degrees is defined as Lb, the expression 0.2≦(Lb/La)≦1.5 is satisfied;
• when the circle equivalent diameter of each of ferrite grains surrounded by the grain boundaries of crystal grains the crystal orientation differences of which are 10 degrees or more is defined as D,
• the average value of D is 25 μm or less, and
• the area ratio of crystal grains satisfying the expression D≦30 μm in the ferrite grains surrounded by the grain boundaries of crystal grains the crystal orientation differences of which are 10 degrees or more is 50% or more;
• and
• the tensile strength of said hot-dip galvanized steel sheet is 980 MPa or more.