PRODUCTION OF HIGH STRENGTH LOW YIELD RATIO HIGH DUCTILITY COMPOSITE STRUCTURE STEEL PLATE OF SUPERIOR WORKABILITY AND HIGH ARTIFICIAL AGE HARDENING CHARACTERISTIC AFTER WORKING

摘要

PURPOSE:To obtain a titled composite structure steel plate by cooling a steel plate made of C, Si, Mn of specific compositions as its essential components at specific patterns in the case of subjecting said steel plate to continuous annealing and heating then cooling the same. CONSTITUTION:After the steel made of 0.01-0.12% C, =1.2% Si and 0.7-17% Mn as its essential components and consisting of Fe and unavoidable impurities for the balance is hot-rolling-finished and coiled, it is hot-rolled or is further cold-rolled, thence it is subjected to continuous annealing and heating of 730-900 deg.C, followed by cooling. At this time, the mean cooling rate R1 down to an intermediate temp. T of 420 deg.C=T=700 deg.C is kept at 1 deg.C/sec. =R1=30 deg.C/sec. and the mean cooling rate R2 from T deg.C down to =200 deg.C is kept at 100 deg.C/sec.=R2=300 deg.C/sec. In this way, the high strength low yield ratio high ductility composite structure steel plate of =40kg/mm.2 tensile strength, superior workability and high artificial age hardening characteristic of which the major structure constituting elements are ferrite phase and quenched transformation phase is obtained.