Hot-rolled or cold-rolled steel plate, method for manufacturing same, and use thereof in the automotive industry

Abstract

Hot-rolled or cold-rolled steel plate, method for manufacturing same and use thereof in the automotive industry A hot-rolled or cold-rolled steel plate, characterized in that its composition is in weight percentages: 0.6%≦C≦0.9%; 17%≦Mn≦22%; 0.2%≦Al≦0.9%; 0.2%≦Si≦1.1% with 0.85%≦Al+Si≦1.9%; 1.2%≦Cu≦1.9%; S≦0.030%; P≦0.080%; N≦0.1%; optionally: Nb≦0.25% and preferably comprised between 0.070 and 0.25%; V≦0.5% and preferably comprised between 0.050 and 0.5%; Ti≦0.5%, and preferably comprised between 0.040 and 0.5%; Ni≦2%; trace amounts Cr≦2%, preferably≦1%; B≦0.010%, and preferably, comprised between 0.0005% and 0.010%; the remainder being iron and impurities resulting from the production. A method for manufacturing this plate, the use of this plate in the automotive industry.

1 . A hot-rolled or cold-rolled steel plate comprising in weight percent:
 0.6%≦C≦0.9%;   17%≦Mn≦22%;   0.2%≦Al≦0.9%;   0.2%≦Si≦1.1%;   with 0.85%≦Al+Si≦1.9%;   1.2%≦Cu <1.9%;   S≦0.030%;   P≦0.080%;   N≦0.1%; and   
       the remainder being iron and impurities resulting from the production. 
     
     
         2 . The plate according to  claim 1 , comprising 0.4%≦Al≦0.8%. 
     
     
         3 . The plate according to  claim 1 , comprising 0.2%≦Si≦0.6%. 
     
     
         4 . The plate according to  claim 1 , comprising 17%≦Mn≦18%. 
     
     
         5 . The plate according to  claim 1 , wherein the steel plate comprises grains having an average size less than or equal to 5 μm. 
     
     
         6 . The plate according to  claim 1 , wherein the steel plate comprises less than or equal to 1.5% surface fraction of its precipitated carbides. 
     
     
         7 . The plate according to  claim 1 , wherein the steel plate further comprises a Zn or Zn alloy coating obtained by electro-galvanization. 
     
     
         8 . A method for manufacturing a steel plate, characterized in that:
 comprising   elaborating and casting into a slab a semi-finished steel product in a steel having the a composition according to  claim 1 ;   heating the semi-finished product to a temperature ranging from 1,100 to 1,300 ° C.;   hot-rolling the semi-finished product that results in a hot-rolled plate, wherein the temperature of said semi-finished product at the end of rolling is at least 890° C.;   fast quenching the hot-rolled semi-finished product at a rate of at least 40° C./s, while observing a delay between the end of the rolling and the beginning of the quenching such that the point defined by said delay and said temperature at the end of rolling, is located within an area defined by a diagram of ABCD′E′F′A, and wherein the metal is cooled in the open air during said delay; and   and said winding the hot-rolled plate at a temperature of less than or equal to 580° C.   
     
     
         9 . The method for manufacturing a steel plate according to  claim 8 , wherein the wound hot-rolled plate is unwound, and at least one cold-rolling/annealing cycle is applied to the unwound plate to obtain a cold-rolled plate. 
     
     
         10 . The method according to  claim 9 , wherein after said cold-rolling/annealing cycle(s), cold deformation at a reduction level of less than or equal to 30% is applied to said cold-rolled plate. 
     
     
         11 . The method according to  claim 10 , wherein the cold deformation is achieved through a method of work-hardening rolling, leveling under traction with alternating flexure or simple drawing. 
     
     
         12 . A method of manufacturing sheets for automotive use comprising applying the hot-rolled or cold-rolled plate according to  claim 1 . 
     
     
         13 . The method according to  claim 12 , wherein the plate is used under conditions that may cause corrosion under stress. 
     
     
         14 . The plate according to  claim 1 , wherein the steel plate further comprises
 Nb≦0.25%;   V≦0.5%;   Ti≦0.5%;   Ni≦2%;   trace amounts≦Cr≦2%;   B≦0.010%.   
     
     
         15 . The plate according to  claim 14 , wherein the steel plate comprises the following
 Nb in a range between 0.070 and 0.25%;   V in a range between 0.050 and 0.5%;   Ti in a range between 0.040 and 0.5%;   Cr≦1%; and   B in the range between 0.0005% and 010%.   
     
     
         16 . The method of  claim 8 , wherein the area defined by the diagram is ABCDEFA.