The present invention presents a high tensile strength cold rolled steel sheet having excellent
formability,
impact resistance and strain age hardening characteristics, and the production thereof. As a specific means, a slab having a composition which contains, by
mass %, 0.15% or less of C, 0.02% or less of Al, and 0.0050 to 0.0250% of N at N / Al of 0.3 or higher, and has N in a
solid solution state at 0.0010% or more, is first
hot rolled at the finish rolling delivery-side temperature of 800° C. or above, and is subsequently coiled at the coiling temperature of 750° C. or below to prepare a
hot rolled plate. Then, after cold rolling, the
hot rolled plate is continuously cooled at a temperature from the recrystallization temperature to 900° C. at a
holding time of 10 to 120 seconds, and is cooled by primary cooling in which the hot rolled plate is cooled to 500° C. or below at a
cooling rate of 10 to 300° C. / s, and furthermore if necessary, by secondary cooling in which a
residence time is 300 seconds or less in a temperature range of the primary cooling stopping temperature or higher and 350° C. or higher. Provided is a steel sheet containing a ferritic phase having an average
crystal grain size of 10 mum or less at an
area ratio of 50% or more, and if necessary, a martensitic phase at an
area ratio of 3% or more as a second phase.