High-tensile steel having improved hydrogen embrittlement resistance

A flat steel product for hot forming, comprising a steel substrate composed of comprising iron and in % by weight:

• C:
• 0.25-0.8%,
• Si:
• 0.01-2.0%,
• Al:
• 0.001-1.0%,
• B:
• 0.0005-0.01%,
• P:
• ≤0.03%,
• S:
• ≤0.02%,
• N:
• ≤0.03%,
• Sn:
• ≤0.03%,
• As:
• ≤0.01%,
• Sb:
• ≤0.02%, and
• unavoidable impurities, and
• at least one of the elements in the group comprising Ti, Nb and V, with the proviso that the contents are as follows:
• Ti:
• 0.008-0.10%,
• Nb:
• 0.01-0.07%, and
• V:
• 0.01-0.4%,
• where a degree of dispersion D1 of precipitates in the near-surface third of the steel substrate is subject to the following condition:
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A process for producing a flat steel product for hot forming with an anticorrosion coating, comprising the following steps:

• a) providing a slab or thin slab which is composed of steel comprising iron and in % by weight:
• C:
• 0.25-0.8%,
• Si:
• 0.01-2.0%,
• Al:
• 0.001-1.0%,
• B:
• 0.0005-0.01%,
• P:
• ≤0.03%,
• S:
• ≤0.02%,
• N:
• ≤0.03%,
• Sn:
• ≤0.03%,
• As:
• ≤0.01%,
• Sb:
• ≤0.02%, and
• Unavoidable impurities, and
• at least one of the elements in the group comprising Ti, Nb and V, with the proviso that the contents are as follows:
• Ti:
• 0.008-0.10%,
• Nb:
• 0.01-0.07%, and
• V:
• 0.01-0.4%;
• b) through-heating the slab or thin slab at a temperature (T1) of 1100-1320° C.;
• c) prerolling the through-heated slab or thin slab to give a preliminary strip having a preliminary strip temperature (T2) of 800-1200° C.;
• d) hot rolling the preliminary strip to give a hot-rolled flat steel product by means of a rolling mill, where the local temperature of the preliminary strip is adjusted before and during the hot rolling of the preliminary strip such that the temperatures of the individual sections of the preliminary strip do not vary by more than 60 K in the course of hot rolling and where the final rolling temperature (T3) is 750-910° C.;
• e) cooling the hot-rolled flat steel product to a coiling temperature (T4) of 500-670° C.;
• f) coiling the hot-rolled flat steel product;
• g) descaling the hot-rolled flat steel product;
• h) optionally cold-rolling the flat steel product, where the degree of cold rolling is at least 30%;
• i) annealing the flat steel product at an annealing temperature (T5) of 650-900° C.;
• j) cooling the flat steel product to an intermediate temperature (T6) of 650-800° C., preferably 670-800° C.;
• k) optionally coating the flat steel product having an anticorrosion coating that has been cooled to the intermediate temperature by hot dip coating in a melt bath having a melt temperature (T7) of 660-800° C., preferably 680-740° C.;
• l) cooling the flat steel product to room temperature, where the first cooling period tMT in the temperature range between 600° C. and 450° C. is more than 10 s, especially more than 14 s, and the second cooling period tLT in the temperature range between 400° C. and 300° C. is more than 8 s, especially more than 12 s;
• m) optionally skin pass rolling the flat steel product.

A shaped sheet metal part formed from a flat steel product comprising a steel substrate composed of steel comprising iron and in % by weight:

• C:
• 0.25-0.8%,
• Si:
• 0.01-2.0%,
• Al:
• 0.001-1.0%,
• B:
• 0.0005-0.01%,
• P:
• ≤0.03%,
• S:
• ≤0.02%,
• N:
• ≤0.03%,
• Sn:
• ≤0.03%,
• As:
• ≤0.01%,
• Sb:
• ≤0.02%, and
• unavoidable impurities, and
• at least one of the elements in the group comprising Ti, Nb and V, with the proviso that the contents are as follows:
• Ti:
• 0.008-0.10%,
• Nb:
• 0.01-0.07%, and
• V:
• 0.01-0.4%,
• and one or more of the elements “Cr, Mn, Co, Cu, Mo, Ni, Ca, W, Ce, La” in the following contents:
• Cr:
• 0.01-1.0%,
• Mn:
• 0.01-3.5%,
• Co:
• 0.05-1.0%,
• Cu:
• 0.01-0.2%,
• Mo:
• 0.002-1.0%,
• Ni:
• 0.01-2.0%,
• Ca:
• 0.0005-0.01%,
• W:
• 0.001-1.0%,
• Ce+La:
• 0.01-0.03%,
• where a degree of dispersion D1 of precipitates in the near-surface third of the steel substrate is subject to the following condition:
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• and optionally an anticorrosion coating.