Hot-Rolled Flat Steel Product Produced from a Complex Phase Steel and Method for the Production Thereof

Abstract

A hot-rolled flat steel product having a tensile strength of at least 1100 MPa, good elongation properties, and good deformation properties. The flat steel product is produced from a complex phase steel, which contains, in addition to iron and inevitable impurities (in % by weight), C: 0.13-0.2%, Mn: 1.8-2.5%, Si: 0.70-1.3%, Al: 0.01 to 0.1%, P: up to 0.1%, S: up to 0.01%, Cr: 0.25-0.70%, optionally Mo, the total of the Cr and Mo contents being 0.25-0.7%, Ti: 0.08-0.2%, B: 0.0005-0.005%, and a structure which consists of at the most 10% by volume of residual austenite, 10-60% by volume of martensite, at the most 30% by volume of ferrite and at least 10% by volume of bainite. Also, a method for producing such a flat steel product.

1 . A hot-rolled flat steel product having a tensile strength of at least 1100 MPa and good elasticity and produced from a complex phase steel, comprising in addition to iron and inevitable impurities (in % by weight),
 C: 0.13-0.2%,   Mn: 1.8-2.5%,   Si: 0.70-1.3%,   Al: 0.01to 0.1%,   P: up to 0.1%,   S: up to 0.01%,   Cr: 0.25-0.70%,   optionally Mo, the total of the Cr and Mo contents being 25-0.7%,   Ti: 0.08-0.2%   B: 0.0005-0.005%,   and having a structure comprising at the most 10% by volume of residual austenite, 10-60% by volume of martensite, at the most 30% by volume of ferrite and at least 10% by volume of bainite.   
     
     
         2 . The flat steel product according to  claim 1 , wherein the C content of the complex phase steel is from 0.15 to 0.18% by weight. 
     
     
         3 . The flat steel product according to  claim 1 , wherein the C content of the complex phase steel is at the most 0.17% by weight. 
     
     
         4 . The flat steel product according to  claim 1 , wherein the Mn content of the complex phase steel is 2.05-2.2% by weight. 
     
     
         5 . The flat steel product according to  claim 1 , wherein the Si content of the complex phase steel is at least 0.75% by weight. 
     
     
         6 . The flat steel product according to  claim 1 , wherein the Si content of the complex phase steel is at the most 1.1% by weight. 
     
     
         7 . The flat steel product according to  claim 5 , wherein the Si content of the complex phase steel is at least 0.85% by weight. 
     
     
         8 . The flat steel product according to  claim 1 , wherein the Si content of the complex phase steel is at the most 0.95% by weight. 
     
     
         9 . The flat steel product according to  claim 1 , wherein the Al content of the complex phase steel is from 0.02 to 0.05% by weight. 
     
     
         10 . The flat steel product according to  claim 1 , wherein, the Cr content of the complex phase steel is from 0.30 to 0.40% by weight. 
     
     
         11 . The flat steel product according to  claim 1 , wherein the Ti content of the complex phase steel is from 0.09 to 0.15% by weight. 
     
     
         12 . The flat steel product according to  claim 9 , wherein the Ti content of the complex phase steel is from 0.11 to 0.13% by weight. 
     
     
         13 . The flat steel product according to  claim 1 , wherein the B content of the complex phase steel is 0.001-0.002% by weight. 
     
     
         14 . A method for producing a hot-rolled flat steel product, comprising the following operating steps:
 casting a complex phase steel produced according to  claim 1  to form a preliminary product,   heating the preliminary product to a temperature of 1150-1350° C.,   hot rolling the preliminary product to form a hot-rolled strip, the end temperature of the hot rolling being 800-950° C.,   cooling the hot-rolled strip obtained at a cooling speed which is at least 30° C./s, and   coiling the hot-rolled strip obtained at a coiling temperature of 400-570 ° C.   
     
     
         15 . The flat steel product according to  claim 10 , wherein the Ti content of the complex phase steel is from 0.11 to 0.13% by weight. 
     
     
         16 . The flat steel product according to  claim 6 , wherein the Si content of the complex phase steel is at least 0.85% by weight.