Hot-rolled flat steel product consisting of complex-phase steel having a predominantly bainitic microstructure and method for producing such a flat steel product

Abstract

The invention relates to a hot-rolled, economically alloyed flat steel product having minimized edge-crack sensitivity characterized by a hole expansion of at least 60%, good welding suitability, a yield strength Rp0.2 of at least 660 MPa, a tensile strength Rm of at least 760 MPa, and an elongation at break A80 of at least 10%. The flat steel product is produced from complex-phase steel, which consists of (in wt%) C: 0.01-0.1%, Si: 0.1-0.45%, Mn: 1-2.5%, Al: 0.005-0.05%, Cr: 0.5-1%, Mo: 0.05-0.15%, Nb: 0.01-0.1%, Ti: 0.05-0.2%, N: 0.001-0.009%, P: < 0.02%, S: < 0.005%, Cu: < 0.1%, Mg: < 0.0005%, O: < 0.01%, optionally one or more elements from the group 'Ni, B, V, Ca, Zr, Ta, W, rare earth elements, Co' with the stipulation Ni: < 1%, B: < 0.005%, V: < 0.3%, Ca: 0.0005-0.005%, Zr, Ta, W: in total < 2%, rare earth elements: 0.0005-0.05%, Co: < 1%, and iron and unavoidable impurities as the remainder. The following equations apply to the contents %Ti, %Nb, %N, %C, %S of Ti, Nb, N, C, and S in the complex-phase steel: (1): %Ti > (48 / 14) %N + (48 / 32) %S, (2): %Nb < (93 / 12) %C + (45 / 14) %N + (45 / 32) %S. The microstructure of the flat steel product consists (in area%) of not less than 80% of bainite, less than 15% of ferrite, less than 15% of martensite, less than 5% of cementite, and less than 5 vol% of residual austenite. The invention further relates to a method for producing such a flat steel product.

Description

technical field [0001] The present invention relates to a hot-rolled flat steel product consisting of a multi-phase steel with a mostly bainite structure, which has excellent mechanical properties, excellent welding suitability and good formability, which is found in Optimized hole expansion capability has been reflected. [0002] The invention also relates to a method for producing the flat steel product according to the invention. [0003] If information is given here about the alloy content of the individual elements in the steel according to the invention, it is always based on weight (data given in % by weight), unless otherwise stated. On the contrary, unless stated otherwise, the data given here about the proportions of the structure of the steel according to the invention are based on the proportion of the corresponding structure components on the cut surface of the product made of the steel according to the invention Proportions (data given in area %). [0004] The...

AI Technical Summary

Problems solved by technology

Practical studies have shown that damage due to cracking emanating from the cut edge of the element always occurs

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