Degassing method for manufacturing steel

Abstract

A method of making non-grain oriented (NGO) electrical steel is disclosed. The method includes tapping liquid steel out of a primary steelmaking furnace, deoxidizing the liquid steel before or after transferring the deoxidized liquid steel to a ladle metallurgy furnace, removing sulfur at the ladle metallurgy furnace (LMF), adding fluxes and deoxidizer to the ladle slag and/or skimming off ladle slag to prevent sulfur reversion, transferring the deoxidized liquid steel from the ladle metallurgy furnace to an RH degasser for carbon removal by blowing oxygen, and adding fluxes at the RH degasser before oxygen blowing to fortify the bottom layer of the ladle slag to prevent sulfur reversion. The removal of oxygen and sulfur prior to transferring the liquid steel to the RH degasser facilitates nitrogen removal and prevents carbon pick up during the step of adding fluxes and arcing for sulfur removal. Oxygen blowing at the RH also lowers titanium pickup. The ultra low levels of carbon, nitrogen, sulfur, and titanium in the NGO steel provide excellent magnetic properties.

What is claimed is: 
     
         1 . A method of making non-grain oriented (NGO) steel, comprising:
 tapping liquid steel out of a basic oxygen furnace;   transferring the liquid steel to a ladle metallurgy furnace;   deoxidizing the liquid steel before or after the transferring of the liquid steel to the ladle metallurgy furnace producing killed deoxidized liquid steel;   removing sulfur from the liquid steel in the ladle metallurgy furnace producing desulfurized liquid steel;   skimming off ladle slag and/or adding fluxes to the ladle slag at the ladle metallurgy furnace to prevent sulfur reversion;   transferring the desulfurized and killed deoxidized liquid steel from the ladle metallurgy furnace to an RH degasser for carbon removal, wherein the removal of oxygen and sulfur prior to transferring the liquid steel to the RH degasser facilitates nitrogen removal and prevents carbon pick up during the step of removing sulfur; and   removing carbon by oxygen blowing into the liquid steel at the RH degasser to produce decarburized liquid steel comprising 0.003 weight percent or less carbon.   
     
     
         2 . The method of making NGO steel of  claim 1 , wherein the sulfur is removed to 0.003 weight percent or less. 
     
     
         3 . The method of making NGO steel of  claim 1 , further comprising removing nitrogen while the liquid steel is in the RH degasser. 
     
     
         4 . The method of making NGO steel of  claim 1 , wherein the nitrogen is removed to 0.003 weight percent or less. 
     
     
         5 . The method of making NGO steel of  claim 1 , further comprising removing aluminum and silicon by blowing oxygen through a top lance or tuyeres of the RH degasser. 
     
     
         6 . The method of making NGO steel of  claim 5 , further comprising removing of carbon following the removal of aluminum and silicon by blowing oxygen through a top lance or tuyeres of the RH degasser. 
     
     
         7 . The method of making NGO steel of  claim 1 , further comprising removing hydrogen while the liquid steel is in the RH degasser. 
     
     
         8 . The method of making NGO steel of  claim 1 , further comprising deoxidizing the liquid steel in the RH degasser after the step of removing carbon. 
     
     
         9 . The method of making NGO steel of  claim 1 , wherein the amount of oxygen blown into the RH degasser is controlled such that the oxygen content in liquid steel is approximately 100 ppm to 200 ppm to prevent sulfur reversion from slag. 
     
     
         10 . The method of making NGO steel of  claim 1 , further comprising adding alloys to the liquid steel in the RH degasser. 
     
     
         11 . A steel sheet product produced by the method of  claim 1 .