High yield ratio and high-strength thin steel sheet superior in weldability and ductility, high-yield ratio high-strength hot-dip galvanized thin steel sheet, high-yield ratio high-strength hot-dip galvannealed thin steel sheet, and methods of production of same

1. A hot rolled steel sheet for spot welding comprising by mass %,

C: over 0.030 to less than 0.10%,

Si: 0.54 to 0.65%,

Mn: 1.7 to 2.49%,

P: 0.001 to 0.02%,

S: 0.0001 to 0.006%,

Al: 0.060% or less,

N: 0.0001 to 0.0070%,

Ti: 0.01 to 0.055%,

Nb: 0.012 to 0.055%,

Mo: 0.07 to 0.55%,

B: 0.0005 to 0.0040%, and simultaneously satisfying

1.1≦14×Ti(%)+20×Nb(%)+3×Mo(%)+300×B(%)≦3.7,

having a balance comprised of iron and unavoidable impurities,

having a microstructure composed of lower bainite or bainitic ferrite as a main phase which constitutes over 85% of the area of the microstructure,

having a yield ratio of 0.68 to less than 0.92, a TS×(El) 1/2 of 3320 or more, an YR×TS×(El) 1/2 of 2320 or more, and a maximum tensile strength (TS) of 780 MPa or more,

having a minimum value of CTS (cross-tensile strength) of 0.8 or more among 10 values of CTS obtained by welding 10 test pieces by a welding current of (CE+1.5) kA, where CE is welding current immediately before expulsion and surface flash, and wherein the minimum value of CTS among 10 values obtained by welding 10 test pieces by a welding current of CE is defined as “1”, and

having an X-ray intensity ratio of a {110} plane parallel to the sheet surface at ⅛ the thickness of the steel sheet of 1.0 or more.

2. The hot-rolled steel sheet of claim 1 , further comprising, by mass %, one or two of

Cr: 0.01 to 1.5%,

Ni: 0.01 to 2.0%,

Cu: 0.001 to 2.0%,

Co: 0.01 to 1%, and

W: 0.01 to 0.3%.

3. The hot-rolled steel sheet of claim 1 , wherein said steel sheet is hot-dip galvanized.

4. The hot-rolled steel sheet of claim 1 , wherein said steel sheet is hot-dip galvanized and alloyed.

5. The hot-rolled steel sheet of claim 1 , wherein said yield ratio is 0.72 to less than 0.90.