Technology For Control Of Equiaxed Grain Of B443NT Stainless Steel Continuous Casting Slab

B443NT steel is a kind of super pure ferritic stainless steel developed by Baosteel.It is of very low carbon and nitrogen content and some niobium titanium content,to improve its anti-corrosion and jointing capability.The slabs of B443NT steel have strong columnar grains,lead to ribbing defect on the sheet in process of cold rolling and punching.To increase the equiaxed grain ratio of the slabs is of great meaning to improve surface quality and punching capability of this steel.In this article,the effect of main chemical elements on the solid-liquid two phase temperature range was studied in the normative component range.the precipitation temperature of TiN inclusions at different Ti?N content,as well as its effect on equiaxed grain ratio of the slabs was analyzed by thermodynamic calculations.The morphology of TiN inclusions under weak and strong cooling intensity,and the equiaxed grain ratio of the slabs under different cooling intensity were investigated.The magnetic field distributions of S-EMS equipment of continuous caster,the effect of current intension,frequency,and slab width on the stirring result as well as the equiaxed grain ratio were also investigated.The results showed that elements such as C,N,Si,Nb and Ti can enlarge solid-liquid two phase temperature range,but the influence is very weak,because the normative content range of these elements is very narrow.While Ti and N content increased to upper limit of B443NT steel,the TiN inclusions would precipitate at nearby liquidus,which promoted the formation of equiaxed grains,and equiaxed grain ratio of the slabs could reach over 50%steadily.To increase cooling speed of the slabs,in one hand it could be propitious to get great deal of tiny TiN inclusions,but in the other hand,it could increase temperature gradient of solidifying front,lead to fast gro'wing up of columnar grains,the action of TiN to equiaxed grain forming was weaken,finally equiaxed grain ratio decreased.Magnetic field of the S-EMS equipment is uniform along the width direction of the slab,electromagnetic force is in direct proportion to square of current intension,so that to increase current intension could improve equiaxed grain ratio;the electromagnetic force reached peak value while current frequency was 9 Hz.Under the same conditions,the bigger the width of the slab,the more liquid flow velocity of the electromagnetic stirring area,and the better stirring effect.