Effect of Rare Earth Metals on Sulphide inclusion in Pipeline Steel

The effects of rare earth metal injection treatment on sulphide inclusions of pipeline steel have been studied in the industrial trials. The melt was stirred by nitrogen from the bottom of the ladle. As a result of addition of RE at the rate of 0.05 kg/t improved desulphurization and reduction of sulphur content from 0.03% to 0.012% took place. When RE addition was done from 0.1 to 0.2 kg/t the sulphides and oxysulphides of type lb were formed.Additi-on of 0.1 kg/t of RE resulted in refinement of inclusion size of 1,45.10'2% area below 4μm and only 0.04.102%area over 10 μm. The lowest reduction of sulphide quantity in steel (0.63.10%area) and the elongation ratio of sulphi-des below 7 was obtained after addition of RE of 0.03kg/t. The small-smooth globular inclusions of type lb were
undeformed during rolling pipe.