AN IMPROVED PROCESS FOR PRODUCING WELDABLE QUALITY STEEL OF INCREASED YIELD STRENGTH AND CORROSION RESISTANCE

摘要

An improved process for producing weldable quality steel of increased yield strength and corrosion resistance, suitable for construction of bridges and buildings, characterised in that the process comprises the following steps in sequence : (a) producing primary steel of minimum sulphur content 0.04% by weight in a L.D. converter of Basic Oxygen France (BOF); (b) tapping the molten primary steel into a pre-heated ladle with addition of ferro-alloys like low- and high-carbon ferro-manganese, ferro-silicon, ferro-vanadium and silicon- manganese, and alloying metals like Nickel, Copper and Aluminium to the extent of 4 to 5% by weight and in proportion required to produce molten steel of composition (by weight %): C-0.08 to 0.15, Mn-0.80 to 1.25, S-0.03 max., P-0.03 max., Si-0.32 to 0.60, Cr-0.42 to 0.65, Ni-0.20 to 0.30, Cu-0.25 to 0.40, V-0.02 to 0.06 and Fe- the balance; (c) casting the molten steel into ingots in moulds with addition of known misch metal in required quantity to the molten steel during teeming thereof into the moulds; (d) soaking the ingots in soaking pits at 1320°C for 6 to 8 hours; (e) hot rolling the ingots into slabs of size 150/160 mm x 1490 mm followed by hot shearing, cooling in stacks and scarf in thereof; (f) reheating the slabs to 1280°C in an atmosphere containing 0.5% oxygen by volume; and (g) finish rolling the slabs at 870 ± 10°C, followed by coiling thereof at 640 + 10°C.