MANUFACTURE OF 60KGF/CM2 CLASS LOW YIELD RATIO STEEL BY QUENCHING AND TEMPERING

摘要

PURPOSE:To obtain the 60kgf/cm2 class low yield ratio steel plate, by separately prescribing staring temp., pass time and finishing temp. in rolling at the final step of controlled rolling, immediately quenching and tempering under specified conditions, at rolling steel plate composed of a specified compsn. CONSTITUTION:Steel plate contg. by weight =0.18% C, =1.50% Mn, 0.10-0.080% Al, =0.004% N, further =0.50% one kind or more among Cu, Ni, Cr, Mo, V, Nb and Ti is rolled as follows. Namely, the plate is rolled at higher than Ar3 starting temp. and =1min pass time at the final step of con trolled rolling. As the result, without releasing stress accumulated by rolling at unrecrystallized state, fine Y particles are obtd. and fine ferrites are uniform ly dispersed. Finishing temp. of rolling is regulated to Ar3 - (Ar3-40 deg.C), then the plate is immediately quenched to =200 deg.C at =3 deg.C/sec rate, then tempered at lower than Ac1 temp. to obtain the titled plate.