Abstract: A building low yield ratio hot-dip galvanized cold rolled steel sheet having an improved refractory property, consists essentially of, by weight, 0.1% or less of C, 0.1 to 1.5% of Mn, 0.1% of less of P, 0.06% or less of Al, 0.6 to 2.0% of Cu, and a remainder of Fe and unavoidable impurities and having a 0.6 times or more yield point strength at 600.degree. C. compared to that at normal temperatures. The method of forming the steel sheet comprises the steps of: forming a slab from a steel consisting essentially of, by weight, 0.1% or less of C, 0.1 to 1.5% of Mn, 0.1% or less of P, 0.06% or less of Al, 0.6 to 2.0% of Cu, and a remainder of Fe and unavoidable impurities, immediately or after heating the slab at a temperature of 1200.degree. C. or less, hot rolling the slab at a temperature of 750.degree. C. or more and cold rolling, effecting a continuous hot-dip galvanizing process, heating the rolled slab at a temperature of 700.degree. to 900.degree. C.

Abstract: A process for producing a cold-rolled high strength steel sheet having an excellent formability and conversion-treatability, comprising the steps of: heating to a temperature of 1150.degree. C. or lower, a steel slab comprising; 0.005 wt % or less of C, 0.5-1.5 wt % of Si, 0.1-0.5 wt % of Mn, 0.003-0.05 wt % and at least 3.4.times.N wt % of Ti, 0.003-0.05 wt % and at least 7.8.times.C wt % of Nb, 0.01-0.1 wt % of Al, 0.05-0.15 wt % of P, 0.010 wt % or less of S, 0.005 wt % or less of N, 0.0001-0.0050 wt % of B, the balance consisting of Fe and unavoidable impurities; hot-rolling the steel slab with a finishing rolling temperature of the A.sub.r3 point of the steel or higher to obtain a hot-rolled steel sheet; cooling the hot-rolled steel sheet at a cooling rate of 10.degree. C.

Abstract: A hot-rolled steel sheet suitable for enamelling on one side is disclosed. The steel consists essentially of 0.0050-0.07 wt % C, 0.05-1.5 wt % Mn, 0.03 0.15 wt % P, 0.03-0.1 wt % Al, 0.003-0.010 wt % N, provided that the N content is the sum of at least 0.002 wt % of free nitrogen not bound to Al and the content of nitrogen in other states, the nitrogen content as defined above satisfying the condition of Al/N.gtoreq.10 on the basis of weight percents and the balance being Fe and incidental impurities.

Abstract: An r value of a hot-rolled steel sheet is enhanced by: a specific composition consisting of not more than 0.015 wt % of C, from 1.0 to 2.5 wt % of Mn, from 0.005 to 0.10 wt % of Al, from 0.01 to 0.06 wt % of Nb, from 0.01 to 0.1 wt % of Ti; and, controlled rolling, characterized by in the rough rolling, imparting, in a temperature range of from 980.degree. to 1100.degree. C., a heavy reduction of not less than 20% per pass to the steel sheet; completing a finishing rolling at from Ar.sub.3 to 930.degree. C. and maintaining a total reduction at a temperature of not more than Ar.sub.3 +150.degree. C. to not less than 90%; and, coiling at a temperature of from 600.degree. to 800.degree. C.