Transformable Lightweight Structural Steel

Abstract

A transformable lightweight structural steel, which exhibits a resistance to hydrogen embrittlement, has TRIP and TWIP properties and contains the following elements (in wt.-%): C 0.05 to <=1.0; Al 0.0 to <=11.0; Si 0.0 to <=6.0; Al+Si>0.05; Mn 9.0 to =25.0; H<20 ppm, the remainder being iron including incidental steel companion elements, whereby different phases are present depending on the alloy composition. The lightweight structural steel is characterized by associating a higher C content with a lower Mn content and associating a low C content with a higher Mn content, with the C—Mn value pairs being positioned in a C—Mn coordinate system approximately on a straight connecting line that is distant from the connecting line of the C—Mn value pairs being in balance between the austenite and martensite phases.

1 .- 4 . (canceled) 
   
   
       5 . A transformable lightweight structural steel with TRIP and TWIP characteristics, comprising the elements, in weight-%,
 C 0.05 to ≦1.0   Al 0.0 to ≦11.0   Si 0.0 to ≦6.0   Al+Si>0.05   Mn 9.0 to ≦25.0   H<20 ppm, remainder iron including incidental steel elements, wherein different phases may be present in dependence on the alloy composition, wherein a higher C content is associated to a lower Mn content and a lower C content is associated to a higher Mn content, with C—Mn value pairs 0.7C/15Mn and 0.4C/18Mn lying approximately in a C—Mn coordinate system on a straight connection line which is distant to a connection line of C—Mn value pairs in balance between γ (austenite) and α′phases (martensite).   
   
   
       6 . The lightweight structural steel of  claim 5 , wherein the content of Al and Si is substantially the same. 
   
   
       7 . The lightweight structural steel of  claim 5 , wherein the C content has a tolerance range of ±0.15% and the Mn content has a tolerance range of ±2.5% in relation to the straight connection line. 
   
   
       8 . The lightweight structural steel of  claim 5 , wherein the C content has a tolerance range of ±0.1% and the Mn content has a tolerance range of ±1.5% in relation to the straight connection line.