Steel with Reduced Density and Method for Producing a Flat Steel or Long Steel Product from Such a Steel

Abstract

The invention provides a density-reduced material based on iron, whose mechanical properties make it suitable for a wide range of applications. The steel has a density of less than 7.25 kg/dm 3 and includes (in wt %) C: up to 0.20%, Si: 0.1-3.50%, Mn: 0.1-3.50%, N: up to 0.020%, S: up to 0.40%, P: up to 0.009%, Al: 6.0-25.0%, Ti: 0.55-10.0%, Cr: up to 6.0%, Mo: up to 3.0%, Ni: up to 4.0%, V: up to 1.0%, W: up to 1.0%, Cu: up to 4%, B: up to 0.08%, Nb: up to 1.5%, remainder iron and unavoidable impurities caused during production. In this case, the structure of the steel has more than 85 vol % ferrite and up to 10 vol % austenite and as the remainder contents of intermetallic phases and proportions of carbide, nitride, bainite or perlite.

1 . A steel with a density of less than 7.25 kg/dm 3  and comprising (in wt %)
 C: up to 0.20%   Si: 0.1-3.50%   Mn: 0.1-3.50%   N: up to 0.020%   S: up to 0.40%   P: up to 0.009%   Al: 6.0-25.0%   Ti: 0.55-10.0%   Cr: up to 6.0%   Mo: up to 3.0%   Ni: up to 4.0%   V: up to 1.0%   W: up to 1.0%   Cu: up to 4%   B: up to 0.08%   Nb: up to 1.5%   remainder iron and unavoidable impurities caused during production, wherein the structure of the steel has more than 85 vol % ferrite and up to 10 vol % austenite and as the remainder contents of intermetallic phases and proportions of carbide, nitride, bainite or perlite.   
     
     
         2 . The steel according to  claim 1 , wherein the C content is less than 0.02 wt %. 
     
     
         3 . The steel according to  claim 1 , wherein % Mn/% S>2.0 applies for the ratio % Mn/% S of the Mn content % Mn and the S content % S. 
     
     
         4 . The steel according to  claim 1 , wherein the sum of the contents of Ni and Mn is at most 5 wt %. 
     
     
         5 . The steel according to  claim 1 , wherein the N content is at most 0.005 wt %. 
     
     
         6 . The steel according to  claim 1 , wherein the Al content is at least 10 wt %. 
     
     
         7 . The steel according to  claim 6 , wherein the Al content is more than 12 wt % and the contents of Cr, Mo, Mn, Si, V, W, Ni, Nb, and Ti meet the following condition:
   (% Cr+2*% Mo+% Mn+% Si+% V+% W+% Ni+% Nb+% Ti)>0.05*% Al   with % Cr: Cr content of the steel,   % Mo: Mo content of the steel,   % Mn: Mn content of the steel,   % Si: Si content of the steel,   % V: V content of the steel,   % W: W content of the steel,   % Ni: Ni content of the steel,   % Nb: Nb content of the steel,   % Ti: Ti content of the steel,   % Al: Al content of the steel.   
     
     
         8 . The steel according to  claim 1 , wherein the B content is at least 0.0005 wt %. 
     
     
         9 . A method for producing a flat steel or long steel product comprising:
 a) providing a primary product consisting of a steel formed according to  claim 1 , wherein the primary product is a slab, a flat slab, a billet or a cast strip;   b) heating the primary product to a hot forming temperature of 700-1280° C.; and   c) hot forming the primary product heated to the hot forming temperature into the flat steel or long steel product.   
     
     
         10 . The method according to  claim 9 , wherein the hot forming temperature is at most 1000° C. 
     
     
         11 . The method according to  claim 9 , wherein the flat steel and long steel product obtained is cooled following the hot forming at a cooling speed of at most 3 K/min. 
     
     
         12 . The method according to  claim 9 , wherein the Ti content of the steel is at least 0.60 wt % and in that the flat steel or long steel product obtained after the hot forming is cooled either in a first heat treatment step directly from the hot forming or after solution annealing at a temperature of more than 700° C. at a cooling speed of at least 25.0K/min. 
     
     
         13 . The method according to  claim 12 , wherein the flat steel or long steel product is aged in a further heat treatment step at temperatures of 150-700° C. for a period of 15 mins to 30 hours. 
     
     
         14 . The method according to  claim 13 , wherein the flat steel or long steel product is mechanically processed between the first heat treatment step and the further heat treatment step.