Process for blowing pig-iron

Claim 1

IN A PROCESS FOR REFINING MOLTEN IMPURE PIG IRON CONTAINING LESS THAN 0.50% SILICON IN THE PRESENCE OF A SINGLE BASIC SLAG IN A VESSEL HAVING A REFRACTORY LINING WHICH COMPRISES FORMING A BASIC CALCO-FERRITIC-SILICA SLAG ON A BATH OF MOLTEN IMPURE PIG IRON, BLOWING SAID BATH WITH A STREAM OF A GAS SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND OXYGEN-ENRICHED AIR DIRECTED SUBSTANTIALLY VERTICALLY DOWNWARDLY THROUGH THE SLAG LAYER ONTO AND BELOW THE SURFACE OF A BATH OF SAID PIG IRON OF SUBSTANCE TIALLY THE CENTRAL PORTION THEREOF, TO AN EXTENT TO AVOID MATERIAL AGIATION OF THE BATH BY THE GAS STREAM, THE CONTACT OF THE GAS WITH THE BATH RESULTING IN REACTION OF THE OXYGEN WITH A PORTION OF THE IRON AND WITH TEH OXIDIZABLE IMPURITIES OF THE BATH IN A LOCALIZED REACTION ZONE SPACED A SUBSTANTIAL DISTANCE FROM THE REFRACTORY LINING, THE IMPROVEMENT FOR REDUCING THE PHOSPHOROUS CONTENT OF SAID IRON TO AN AMOUNT LESS THAN 0.05 PERCENT COMPRISING THE STEP OF RETAINING SAID SLAG ON SAID BATH DURING SUBSTANTIALLY THE ENTIRE DURATION OF BLOWING SAID GAS AND MAINTAINING A SILICA CONTENT OF FROM ABOUT 10 TO 18 PERCENT IN THE SLAG DURING SUBSTANTIALLY THE ENTIRE BLOWING TIME.