| 摘要 |
The invention deals with a cold rolled and hot dip steel sheet, with a tensile strength of at least 980 MPa, with yield strength above or equal to 500 MPa, with total elongation above or equal to 8%, the composition consisting by weight percent: 0.05 < C < 0.15%, 2 < Mn≤ 3%, Al < 0.1 %, 0.3 < Si < 1.5%, 0.01 % < Nb < 0.05%, N < 0.02%, 0.1 < Cr + Mo < 1 %, 0.0001 < B < 0.0025, Ti < 0.5%, V < 0.01 %, S < 0.01 %, P < 0.05% the remainder of the composition being iron and unavoidable impurities resulting from the smelting and the microstructure contains, in surface fraction: between 50 and 95 % of martensite and between 5 and 50 % of the sum of ferrite and bainite, wherein the ferrite grain size is below 10 μιτι, and wherein the aspect ratio of the ferrite grain size is between 1 and 3. The steel according to the invention is oxidized and subsequently reduced during heating, soaking and cooling steps of the annealing. |
