Method for producing a steel strip with a multiphase structure, and related steel strip

A steel strip having a multiphase microstructure consisting of the following elements in wt. %:

• C:
• 0.085 to 0.149
• Al:
• 0.005 to 0.1
• Si:
• 0.2 to 0.75
• Mn:
• 1.6 to 2.9
• P:
• ≤0.02
• S:
• ≤0.005
• and optionally one or more of the following elements in wt. %:
• Cr:
• 0.05 to 0.5;
• Mo:
• 0.05 to 0.5;
• Ti:
• 0.005 to 0.060;
• Nb:
• 0.005 to 0.060;
• V:
• 0.001 to 0.060;
• B:
• 0.0001 to 0.0060;
• N:
• 0.0001 to 0.016;
• Ni:
• 0.01 to 0.5;
• and
• Cu:
• 0.01 to 0.3
• with the remainder being iron and incidental steel-associated impurities;
• wherein the steel strip has a product of Rp0.2 elasticity limit and elongation at fracture A80 of greater than 5600 MPa %, a tensile strength Rm of at least 920 MPa and an elasticity limit Rp0.2 of at least 720 MPa and the steel strip has the following microstructure components in which the percentages given refer to area proportions:
• ferrite:
• less than 60%,
• bainite+martensite:
• 30% to 98%,
• residual austenite:
• less than 10%;
• and wherein grains which are limited by large angle grain boundaries can be identified in the microstructure of the steel strip in a finally annealed and finally cooled condition and the microstructure has a KG5 characteristic value of less than 0.4, wherein the KG5 characteristic value designates the area proportion of grains with
• an equivalent diameter d, where d=√(4A/π)>5 μm and
• a shape factor F, where F=P/√{square root over (4πA)}<3
• and where P is a circumference and A is an area of a respective grain and a determination thereof is effected by means of electron backscatter diffraction.