High-strength hot dip-coated steel strip with plasticity brought about by microstructural transformation and method for production thereof

A method for producing a hot-dip coated high-strength steel strip with plasticity brought about by microstructural transformation, comprising the following steps:

• producing a hot-rolled steel strip from a slab heated to above 1200° C. consisting of the following elements in wt. %:
• C:
• from 0.15 to 0.205,
• Mn:
• from 1.9 to 2.6,
• Al:
• from 0.2 to 0.7,
• Si:
• from 0.5 to 0.9,
• Cr:
• from 0.2 to 0.5,
• Nb:
• from 0.01 to 0.06,
• Mo:
• <0.15,
• B:
• ≤0.001,
• P:
• ≤0.02,
• S:
• ≤0.005,
• and optionally one or more of the following elements in wt. %:
• Ti:
• 0.005 to 0.060,
• V:
• 0.001 to 0.060,
• N:
• 0.0001 to 0.016,
• Ni:
• 0.01 to 0.5 and
• Cu:
• 0.01 to 0.3,
• with the remainder being iron including typical steel-associated elements, wherein for a value μ=4.5×([Si]+0.9×[Al]+[Cr])+200×[Nb], in which [Si], [Al], [Cr] and [Nb] are the proportions of the corresponding elements in wt. %, 8≤μ≤16;
• acid-cleaning and optionally cold-rolling the hot-rolled steel strip to form a cold-rolled steel strip;
• subsequently continuously annealing during a continuous hot-dip coating process of the cold- or hot-rolled steel strip at a maximum temperature between 80° and 870° C. for the total duration of 50 s to 650 s;
• subsequently cooling the cold- or hot-rolled steel strip to an intermediate temperature in a temperature range of 620 to 760° C. at an average cooling rate CR1 of up to 10 K/s;
• subsequently further cooling the cold- or hot-rolled steel strip from the intermediate temperature to a cooling stop temperature in a temperature range between 280° C. and 450° C. inclusive, at an average cooling rate CR2>CR1 and at most 150 K/s and then maintaining the temperature in the temperature range between 280° C. and 450° C. inclusive, for 25 to 500 s;
• subsequently hot-dip coating the cold- or hot-rolled steel strip at a temperature between 38° and 500° C.;
• and
• subsequently finally cooling the hot-dip coated cold- or hot-rolled steel strip at an average cooling rate of 1 K/s to 50 K/s to ambient temperature.