Calcium addition to steel to increase notch-toughness - at very low temp suitable for steel pipelines in artic regions

摘要

Addition of Ca to molten steel contg. (by % wt.) 0.02-0.55 C, 0.5 Si, 0.2-2.5 Mn, the usual alloying elements, balance Fe, comprises holding the molten steel at 1480-1800 degrees C (which contains 0.01%, pref. 0.007% S, and 100 ppm total O2), and adding 0.1-2 kg/tonne of Ca so that ratio of Ca:S is 0.05-0.8:1. The pref. compsn. of the steel is 0.02-0.55% C, 0.5% Si, 0.2-2.5% Mn, 0.05% Cu, 0-1.5% Cr, 0-0.5% Mo, 0-10% Ni, 0-0.05% Nb, 0-0.1% V, 0-0.05% Ti, balance Fe. The steel is pref. killed to obtain 0.005-0.085% soluble Al before adding the Ca and also blowing an inert gas through the melt before adding Ca. The Ca is pref. added as Ca-Si or Ca-Ba-Al. Used for steel for pipelines in artic regions. Improved notch-toughness at low temp. is obtd.