Method and Installation for Producing Light Gauge Steel with a High Manganese Content

Abstract

The production of steels with high contents of manganese (Mn), aluminum (Al), and silicon (Si) with TWIP properties (Twinning-Induced Plasticity) by continuous casting is considered difficult or impossible in the present state of the art for various reasons. These reasons include low strength of the strand shell during solidification due to intense microsegregation of Mn, high strength at relatively low temperatures, reactions of the aluminum in the steel with the flux powder, macrosegregation, depletion of the alloying elements near the surface, and oxidation of the grain boundaries during the reheating of slabs in the pusher furnace. Therefore, in accordance with the invention, successively arranged process steps are used to cast light gauge steel with a given chemical composition of 15-27% Mn, 1-6% Al, 1-6% Si, ≦0.8% C, with the remainder consisting of Fe and accompanying impurity elements on a thin-slab casting machine ( 1 ) (d≦120 mm) with the use of suitable flux powders, to cut slabs ( 3 ) from the endless strand ( 2 ) immediately after solidification, to bring about temperature equalization in a continuous-type intermediate furnace ( 4 ), and then to hot roll the slab ( 3 ) immediately without intermediate cooling.

1 . Method for producing hot-rolled strip ( 6 ) from a highly cold-workable, high-strength, austenitic light gauge steel with increased contents of manganese (Mn), aluminum (Al), and silicon (Si) with TWIP properties (Twinning-Induced Plasticity), wherein the light gauge steel is first cast into an endless strand ( 2 ) in a continuous casting installation ( 1 ), cut into slabs ( 3 ), and then rolled to the final thickness, wherein successive process steps are used, in which a light gauge steel with the given chemical composition of 15-27% Mn, 1-6% Al, 1-6% Si, ≦0.8% C, with the remainder consisting of Fe and impurities
 is cast on a thin-slab casting machine ( 1 ) (d≦120 mm) with the use of flux powders and cut into slabs ( 3 ), such that suitable mineral substances are added to the flux powders to reduce the reaction rate of the SiO 2  reduction by the Al in the steel and/or to reduce the amount of Al 2 O 3  that is formed by lowering the viscosity in the mold,   immediately after the solidification of the endless strand ( 2 ) and cutting of a slab ( 3 ), temperature equalization is brought about in a continuous-type intermediate furnace ( 4 ), and then   the slab ( 3 ) is immediately hot rolled without intermediate cooling.   
     
     
         2 . Method in accordance with  claim 1 , wherein the flux powder has an increased Al 2 O 3  content of >10%. 
     
     
         3 . Method in accordance with  claim 1 , wherein the flux powder has an increased SiO 2  content with a basicity (CaO/SiO 2  ratio) of 0.5-0.7. 
     
     
         4 . Method in accordance with  claim 1 , wherein the flux powder contains MnO 2  and/or TiO 2 . 
     
     
         5 . Method in accordance with  claim 1 , wherein, to lower the viscosity of the flux powder in the mold, the flux powder contains B 2 O 3  (borate), Na 2 O, and/or LiO 2 . 
     
     
         6 . Method in accordance with  claim 1 , wherein the intermediate furnace ( 4 ) is a roller hearth furnace. 
     
     
         7 . Installation for producing hot-rolled strip from a highly cold-workable, high-strength, austenitic light gauge steel with increased contents of manganese (Mn), aluminum (Al), and silicon (Si) with TWIP properties (Twinning-Induced Plasticity) for carrying out the method in accordance with  claim 1 , which consists of a CSP installation (Compact Strip Production) with the successively arranged installation units thin-slab casting machine ( 1 ), intermediate furnace ( 4 ), and hot rolling mill ( 5 ), wherein the distances between the individual installation units are changed in such a way that immediately after the solidification of the endless strand ( 2 ), temperature equalization of a cut slab ( 3 ) is brought about in a continuous-type intermediate furnace ( 4 ), and then the slab ( 3 ) is immediately hot rolled without intermediate cooling.