Process for manufacturing high grades of specialty electrical steels

Abstract

This is a process for the production of specialty electric steel, particularly grain oriented electrical steel, and more particularly, grain oriented silicon electrical steel. The steel can be formed starting from a thin slab. The process can relate to a product formation route which enables efficient production with better yield and wider process control tolerance. The method can be employed for producing specialty electrical steel utilizes cheaper inputs, less energy, combines and overlaps production process steps, improves yields and product uniformity. This can be accomplished by making it more tolerant to a wider range of process parameters.

1 . A process for making high grades of specialty steels commonly known as electrical steels which comprises:
 a. providing a molten steel feed;   b. performing a chemical analysis of the molten steel which includes identifying which chemical components of the steel feed should be removed by conducting a chemical reaction and/or by adding a chemical component to obtain the desired chemical analysis, and then removing the requisite chemical components from the molten steel and/or adding the requisite chemicals to the molten steel;   c. casting a steel slab from the molten steel feed having a thickness of from about 1 mm to 200 mm;   d. reheating the cast slab to a temperature between 1150 degrees C. to 1400 degrees C.;   e. reducing the thickness of the cast slab to a thickness of from about 1.0 to 2.5 mm to form a hot band;   f. cooling the hot band to a temperature of about 550 degrees C.;   g. annealing and normalizing the hot band from step f. in a protective atmosphere of nitrogen;   h. pickling the annealed and normalized hot band to remove scale formed thereon with up to 5% by weight of SiO 2 ;   i. reducing the thickness of the hot band from step h. to up to about 0.65 mm;   j. decarbonizing and annealing the hot band from step i. in a protective atmosphere of N 2 ;   k. reducing the thickness of the hot band from step j. to up to about 0.63 mm;   l. coating the hot band from step k. with magnesia for preventing sticking in step m. and for forming an initial insulative coating;   m. annealing of the coated hot band to form large grains and to develop a secondary insulative coating;   n. treating the annealed and coated hot band for stress relief in a protective atmosphere which is substantially non-reactive with iron and which applies a final insulative coating thereto; and   o. straightening the hot band from step n. and forming grain oriented electric steel.   
     
     
         2 . Process according to  claim 1 , which further comprises treating the hot band from step j. in a chamber such that its surface is exposed to liquefied ammonia thereby forming high induction electric steel. 
     
     
         3 . Process according to  claim 1 , which further comprises treating the grain oriented steel from step n. such that the exposed surface is heated by a focused laser to create an incision therein and thereby forming laser scribed grain oriented electrical steel. 
     
     
         4 . Process according to  claim 2 , which further comprises treating the high induction electric steel from step n. such that the exposed surface is heated by a focused laser to create an incision therein and thereby forming laser scribed high induction electrical steel. 
     
     
         5 . Process according to  claim 1 , which further comprises
 a. reducing the thickness of the hot band from step h. to up to about 0.63 mm;   b. forming non-oriented grains within the reduced thickness hot band; and   c. applying an insulative coating to the hot band including non-oriented grains and forming non-oriented electrical steel.   
     
     
         6 . Process according to  claim 1 , wherein annealing in step m. is conducted at a temperature of at least about 1200 degrees C. 
     
     
         7 . Process according to  claim 1 , wherein annealing in step m. is conducted for at least about 130 hours. 
     
     
         8 . Process according to  claim 1 , wherein the protective atmosphere which is substantially non-reactive with iron in step n. is a nitrogen-rich atmosphere. 
     
     
         9 . Process according to  claim 1 , wherein the final protective coating in step n. is applied under tension. 
     
     
         10 . Process according to  claim 1 , wherein the second insulative coating in step m. is substantially non-conductive. 
     
     
         11 . Process according to  claim 1 , wherein in step a., the steel is melted at a temperature of about 1500 degrees C. 
     
     
         12 . Process according to  claim 1 , wherein in step b., the chemical composition of the molten steel feed is adjusted so that the amount of Aluminum is up to about 0.5% by weight, the amount of Nitrogen is up to about 0.05% by weight, the amount of Manganese is up to about 0.3% by weight, and the amount of Silicon is up to about 5%, by weight, based on the total weight of the molten steel feed. 
     
     
         13 . Process according to  claim 1 , wherein in step f. initially cooling the hot band is with ambient air. 
     
     
         14 . Process according to  claim 1 , wherein in step f. initially cooling the hot band with is ambient air and then the initially cooled hot band is rapidly cooled with water. 
     
     
         15 . Process according to  claim 1 , wherein in step h. removing from about 20 to 30 g/m 2  of the scale formed on the hot band. 
     
     
         16 . Process according to  claim 1 , wherein in step i. reducing the thickness to up to about 0.63 mm and in step k. reducing the thickness to up to about 0.60 mm. 
     
     
         17 . Process according to  claim 2 , wherein the hot band from step j. is treated with activated ammonia. 
     
     
         18 . Process according to  claim 1 , wherein in step g. annealing and normalizing in the protective atmosphere of nitrogen is conducted in a H 2 O/H 2  atmosphere. 
     
     
         19 . Process according to  claim 18 , wherein the H 2 O/H 2  ratio is from about 0.05 to 0.95. 
     
     
         20 . A process for making high grades of specialty steels commonly known as electrical steels which comprises:
 a. providing a molten steel feed;   b. performing a chemical analysis of the molten steel which includes identifying which chemical components of the steel feed should be removed by conducting a chemical reaction and/or by adding a chemical component to obtain the desired chemical analysis, and then removing the requisite chemical components from the molten steel and/or adding the requisite chemicals to the molten steel;   c. casting a steel slab from the molten steel feed having a thickness of from about 1 mm to 7 mm and forming a hot band;   d. cooling the hot band to a temperature of about 550 degrees C.;   e. annealing and normalizing the hot band from step f. in a protective atmosphere of nitrogen;   f. pickling the annealed and normalized hot band to remove scale formed thereon with up to 5% by weight of SiO 2 ;   g. reducing the thickness of the hot band from step h. to up to about 0.65 mm;   h. decarbonizing and annealing the hot band from step i. in a protective atmosphere of N 2 ;   i. reducing the thickness of the hot band from step j. to up to about 0.63 mm;   j. coating the hot band from step k. with magnesia for preventing sticking in step m. and for forming an initial insulative coating;   k. annealing of the coated hot band to form large grains and to develop a secondary insulative coating;   l. treating the annealed and coated hot band for stress relief in a protective atmosphere which is substantially non-reactive with iron which applies a final insulative coating thereto; and   m. straightening the hot band from step n. and forming grain oriented electric steel.