A PROCESS FOR PRODUCING COPPER-BEARING, AGE-HARDENED STEEL OF INCREASED YIELD STRENGTH, BENDABILITY AND WELDABILITY

摘要

A process for producing copper-bearing age-hardened steel of increased yield strength, bendability and weldability, comprising the following steps in sequence: (a) making steel in Electric Arc Furnace/LD furnace by charging scraf containing cuttings of mild steel plates, bars and sheets, which is reasonably free from residual elements like Arsenic, Tin and Lead, lime, petroleum coke, sponge iron, iron ore and/or hot metal in required quantities in the furnace and melting the said raw materials by electric arc or oxygen lancing with addition of 0.5-3.0% by weight quantity of Fe-Mn-Nickel sinter and Fe-Mo in the BOF(LD) furnace and 3 to 4 times slag off; (b) adding Cu, Fe-Mo, Fe-Mn (high carbon), Fe-Min (low carbon), Fe-V to molten steel in ladle; (c) further adding FeMn, FeNb in VAD-I by arc degassing (below 5 torr) for 10 minutes and adjusting the composition of steel in VAD-II at 1625-1630°C; (d) injecting CaSi wire into molten steel in ladle; (e) casting the molten steel into slabs in a continuous casting machine; (f) cross-rolling the slabs into plates, as herein described; and (g) ageing the plates, as herein described; characterised in that (i) the chemical composition of the steel produced is (by weight %): C-0.045 to 0.055, Mn-0.75 to 0.90, P-0.005 to 0.010, S-0.005 to 0.010, Si-0.20 to 0.35, Ni-0.95 to 1.25, Cr-0.70 to 0.85, Mo-0.25 to 0.35, Cu-1.10 to 1.30, Nb-0.03 to 0.04, Al-0.015 to 0.020, Ti-0.005 max, V-0.02 to 0.03 and Fe-the balance; (ii) CaSi wire is injected into molten steel at a rate of 0.7 to 1.0 kg per Ton and to a depth of 2.7 to 3.0 m in ladle; (iii) slabs are cast at a speed of 0.7 to 0.8 m/min and at a superheat of 15-20°C; (iv) the slabs are conditioned by heating to 600/650°C in a walking-beam furnace, soaking for 2 hours, re-heating at a rate of 50-60°C/hour to 1280/1300°C and re-soaking for 2.5 to 3.0 hours; (v) the slabs are cross-rolled into plates of width 1700 to 1850 mm in 20 to 22 passes; (vi) plates are finish-rolled at 900-930°C, solution-treated at 920-930°C for 30 to 45 minutes, and oil-quenched; and (vii) plate are aged by soaking oil-quenched plates in a walking beam furnace having soaking temperature of 630 ± 10°C.