Ultrahigh strength multiphase steel and method for producing a steel strip from said multiphase steel

Abstract

The invention relates to an ultrahigh strength multiphase steel having a minimum tensile strength of 980 MPa containing (in wt.%): C >= 0.075 to <= 0.115; Si >= 0.400 to <= 0.500; Mn <= 1.900 to <= 2.350; Cr >= 0.250 to <= 0.400; AI >= 0.010 to <= 0.060; N >= 0.0020 to <= 0.0120; P <= 0.020; S <= 0.0020; Ti >= 0.005 to <= 0.060; Nb >= 0.005 to <= 0.060; V >= 0.005 to <= 0.020; B >= 0.0005 to <= 0.0010; Mo >= 0.200 to <= 0.300; Ca >= 0.0010 to <= 0.0060; Cu <= 0.050; Ni <= 0.050; Sn <= 0.040; H <= 0.0010; and residual iron, including customary steel-accompanying smelting-related impurities, wherein the total content of Mn+Si+Cr is >= 1.750 to <= 2.250 wt.% with a view to a processing window which is as wide as possible during the annealing process, in particular during the continuous annealing process, of cold strips of said steel.

Description

technical field [0001] The invention relates to a high-strength multiphase steel with a dual-phase or multi-phase microstructure and small amounts of austenite, in particular for lightweight construction of vehicles, according to the preamble of claim 1, which has an improved Manufacturable properties with outstanding material properties in subsequent processing. Advantageous developments are the subject-matter of subclaims 2-24. [0002] The invention also relates to a method according to claim 25 for producing a steel strip from such a steel and a steel strip produced by this method according to claim 38 . [0003] The invention relates in particular to steels for the production of components having a tensile strength in the unquenched state of at least in the region of 980 MPa, which components have improved formability, for example with regard to hole expansion, and have improved bonding Properties such as soldering characteristics. Background technique [0004] The f...

AI Technical Summary

Problems solved by technology

[0085] In summary, the problem with the known steel grades is that in terms of the minimum rolling rate required in cold rolling for complete recrystallization after continuous annealing, in a given roughing strip thickness after hot rolling in order to produce the main hot strip thickness In the case of steel thicknesses, there is no longer manufacturing flexibility in terms of the different cold-rolled strip thicknesses to be achieved (see figure 1 , so process steps 6, 8 and 9 are required)

In particular, the process window is too small to produce different cold strip thicknesses with similar material properties on the resulting cold strip while the main hot strip thickness is constant

Additionally, setting a constant pre-strip thickness in order to produce a defined constant main hot strip thickness additionally limits manufacturing flexibility

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