MANUFACTURE OF HIGH STRENGTH AND HIGH TOUGHNESS HOT ROLLED STEEL PLATE HAVING SUPERIOR RESISTANCE TO HYDROGEN INDUCED CRACKING AND STRESS CORROSION CRACKING

摘要

PURPOSE:To obtain a high strength and high toughness hot rolled steel plate having superior resistance to hydrogen induced cracking and stress corrosion cracking by subjecting a steel billet contg. specified amounts of C, Si, Mn and Al to rough rolling, regulated finish rolling, cooling at a regulated cooling rate and slight rolling-down. CONSTITUTION:The steel consisting of, by weight, 0.03-0.3% C, 0.01-1.0% Si, 0.5-2.0% Mn, 0.005-0.5% Al and the balance Fe with inevitable impurities is rough-rolled and finish-rolled at 900-800 deg.C at =30% total draft in a temp. range below an austenite recrystallization temp. The resulting steel plate is cooled to 750-650 deg.C at 15-80 deg.C/sec average cooling rate, and it is slightly rolled down at 3-20% reduction of area. By such method, a large number of fine cementite grains are deposited in the ferrite grains while the precipitation of cementite on the ferrite grain boundaries is suppressed. The steel may further contain the proper amount of Nb, Ti, V, Cr, Cu, Mo, Ni, Ca, etc., is necessary.