Method for manufacturing flat steel products from a multiphase steel microalloyed with boron

Abstract

The invention relates to a method which allows high-tensile flat steel products to be manufactured with less effort in a wide range of geometric dimensions. In order to do so, a steel that forms a multiphase structure and contains 0.08 to 0.12 wt.-% of C, 1.70 to 2.00 wt.-% of Mn, up to 0.030 wt.-% of P, up to 0.004 wt.-% of S, up to 0.20 wt.-% of Si, 0.01 to 0.06 wt.-% of Al, up to 0.0060 wt.-% of N, 0.20 to 0.50 wt.-% of Cr, 0.010 to 0.050 wt.-% of Ti, 0.0010 to 0.0045 wt.-% of B, the remainder being composed of iron and inevitable impurities, is cast into a cast strip having a thickness of 1 to 4 mm, the cast strip is hot-rolled in-line into a hot-rolled strip having a thickness of 0.5 to 3.2 mm in a continuous process at a final hot-rolling temperature ranging from 800 to 1100 DEG C, the shaping degree being greater than 20 percent, and the hot-rolled strip is coiled at a coiling temperature ranging from 250 to 570 DEG C so as to obtain a hot-rolled strip which has a minimum tensile strength Rm of 800 MPA and a minimum breaking elongation A80 of 5 percent.

Description

technical field [0001] The present invention relates to a method for producing flat steel products such as strip or metal slabs from high tensile strength boron microalloyed steels. This steel belongs to the class of multiphase steels. They are generally steels whose properties depend on the type, amount and arrangement of phases in the microstructure. Therefore, at least two phases (eg, ferrite, martensite, bainite) are present in its microstructure. As a result, they have an excellent strength / formability combination compared to conventional steels. [0002] This production route poses problems in particular when it comes to casting peritectic solidifying compositions. In the case of these steel grades, there is a risk of longitudinal cracks developing during continuous casting. The occurrence of such longitudinal cracks seriously degrades the quality of hot-rolled steel strips produced from slabs or thin slabs, rendering them unusable. In order to avoid this risk, exte...

AI Technical Summary

Problems solved by technology

[0005] The process of producing flat steel products from high tensile strength multiphase steels with a tensile strength greater than 800 MPa presents the following problem: When rolling these steels, high rolling forces must be applied

However, this strength is insufficient for many applications, especially in the field of automotive construction