Process and device for producing hot-rolled strip from silicon steel

Abstract

A method and a combined casting/rolling installation for production/processing of high-quality hot-rolled strip into grain-oriented electrical steel strip at low cost, provides for: a) melting a steel having a chemical composition in wt % of Si 2 to 7%, C 0.01 to 0.1%, Mn<0.3%, Cu 0.1 to 0.7%, Sn<0.2%, S<0.05%, Al<0.09%, Cr<0.3%, N<0.02%, P<0.1%, remainder Fe and impurities; b) casting a strand having a thickness of 25 to 150 mm on a continuous casting installation; c) rolling into a strip in up to 4 rolling passes directly after casting the strand, wherein at least in one rolling pass a true strain is >30% or the total true strain of all passes is >50%; d) heating the strip to a final temperature of 1050 to 1250° C., preferably 1100 to 1180° C.; e) finish rolling the strip in a second rolling train, then f) cooling and winding the strip.

1 . A process for producing hot-rolled strip from silicon-alloyed steels on a combined casting/rolling installation for further processing to form grain-oriented magnetic steel strip, comprising the following process steps in the sequence given:
 a) melting a steel having a chemical composition (in % by weight) of Si 2 to 7%, C 0.01 to 0.1%, Mn<0.3%, Cu 0.1 to 0.7%, Sn<0.2%, S<0.05%, Al<0.09%, Cr<0.3%, N<0.02%, P<0.1%, remainder Fe and impurities;   b) casting a strand having a thickness of 25 to 150 mm on a continuous casting installation;   c) rolling a strip in up to 4 roll passes immediately after the strand has been cast, wherein at least in one roll pass a degree of deformation is >30% or the total degree of deformation of all the passes is >50%;   d) heating the strip to a final temperature of 1050 to 1250° C. or 1100 to 1180° C.;   e) finish-rolling the strip in a second rolling mill train, and then   f) cooling and coiling the strip.   
     
     
         2 . The process according to  claim 1 , wherein the final temperature after the strip has been heated is maintained for a duration t, where t>15 s or >60 s. 
     
     
         3 . The process according to  claim 2 , wherein the final temperature of the strip is maintained in a continuous furnace. 
     
     
         4 . The process according to  claim 1 , wherein the final temperature of the strip is maintained during winding-up and subsequent unwinding in a coiling furnace. 
     
     
         5 . The process according to  claim 1 , wherein the strip is finish-rolled in 2 to 6 or 3 to 5 roll passes in the second rolling mill train. 
     
     
         6 . The process according to  claim 1 , wherein the strip has a final rolling temperature of 900 to 1050° C. after the finish-rolling. 
     
     
         7 . The process according to  claim 1 , wherein the strip is cooled to a coiling temperature of 300 to 600° C. by means of an intensive cooling step within 10 s or within 6 s after the finish-rolling. 
     
     
         8 . The process according to  claim 7 , wherein, at the start of the intensive cooling step, the strip is cooled at a cooling rate which is twice as high or three times as high as the cooling rate at the end of the cooling step. 
     
     
         9 . The process according to  claim 1 , wherein the sum of the alloying elements Cu+Mn in the steel melt is >0.35% by weight or >0.55% by weight. 
     
     
         10 . The process according to  claim 1 , wherein the sum of the alloying elements S+N in the steel melt is >100 ppm or >200 ppm. 
     
     
         11 . The process according to  claim 1 , wherein the quotient of the alloying elements Cu/Mn in the steel melt is >2.5 or >3.5. 
     
     
         12 . A combined casting/rolling installation for producing hot-rolled strip from silicon-alloyed steels for further processing to form grain-oriented magnetic steel strip, comprising a continuous casting installation, a first rolling mill train, a heating device, a second rolling mill train, a cooling section and a winding up device, wherein the first rolling mill train is arranged directly downstream of the continuous casting installation, and a coiling furnace or a continuous furnace for at least one of introducing heat and maintaining the temperature of the hot strip is located between the heating device and the second rolling mill train. 
     
     
         13 . The installation according to  claim 12 , wherein the continuous casting installation is in the form of a thin-slab continuous casting installation. 
     
     
         14 . The installation according to  claim 12 , wherein the first rolling mill train comprises up to four rolling stands. 
     
     
         15 . The installation according to  claim 12 , wherein the second rolling mill train comprises 2 to 6 or 3 to 5 rolling stands. 
     
     
         16 . A system for producing hot-rolled strip from silicon-alloyed steels and further processing to form grain-oriented magnetic steel strip, comprising:
 a) means for melting a steel having a chemical composition (in % by weight) of S±2 to 7%, C 0.01 to 0.1%, Mn<0.3%, Cu 0.1 to 0.7%, Sn<0.2%, S<0.05%, Al<0.09%, Cr<0.3%, N<0.02%, P<0.1%, remainder Fe and impurities;   b) means for casting a strand having a thickness of 25 to 150 mm;   c) means for rolling a strip in up to 4 roll passes immediately after the strand has been cast, wherein at least in one roll pass a degree of deformation is >30% or the total degree of deformation of all the passes is >50%;   d) means for heating the strip to a final temperature of 1050 to 1250° C. or 1100 to 1180° C.;   e) means for finish-rolling the strip, and   f) means for cooling and coiling the strip.   
     
     
         17 . The system according to  claim 16 , wherein the system is configured to maintain the final temperature after the strip has been heated for a duration t, where t>15 s or >60 s. 
     
     
         18 . The system according to  claim 17 , wherein the system is configured to maintain the final temperature of the strip in a continuous furnace. 
     
     
         19 . The system according to  claim 16 , wherein the system is configured to maintain the final temperature of the strip during winding-up and subsequent unwinding in a coiling furnace. 
     
     
         20 . The system according to  claim 16 , wherein the system is configured to finish-roll the strip in 2 to 6 or 3 to 5 roll passes in the second rolling mill train.