PRODUCTION OF ULTRATHICK TEMPER TYPE HIGH TENSILE STEEL

摘要

PURPOSE:To produce a titled steel under low carbon equiv. and low Ni by subjecting the specific composition steel contg. C, Si, Mn, Ni, Cr, Mo, V in accordance with product thickness and further contg. B, Al, Nb to hardening and tempering after heat treatment. CONSTITUTION:The respective components of =0.20% C, =0.50% Si, =2.0% Mn, =1.0% Ni, =0.7% Cr, =0.5% Mo, =0.10% V are contained within the range of the equation I (t: plate thickness mm.) in accordance with product thicknesses. Further, the steel contained with 0.0005-0.0040 B, 0.03-0.10% acid sol Al, 0.01-0.07% Nb and consisting of the balance Fe and unavoidable impurities is subjected to the following treatment: This steel is cooled down to below the Ar1 point after hot working. Thereafter, it is subjected to one time of the pretreatment wherein it is reheated to the austenite region below, 1,000 deg.C then cooled down to below the Ar1 point. Next, it is subjected to ordinary hardening and tempering, whereby the ultra thick temper type high tensile steel of 58kgf/mm.2-70kg/mm.2 tensile strength and =100mm. plate thickness is produced.