DE102019217491A1 - Process for the production of a cold-rolled Si-alloyed electrical steel strip with a cold-rolled strip thickness dkb <1 mm from a steel precursor - Google Patents

Abstract

The invention relates to a method for producing a cold-rolled electrical steel strip with a cold-rolled strip thickness dkb <1 mm from a steel precursor.

Description

Area:

The invention relates to a method for producing a cold-rolled electrical _{steel strip with a cold-rolled strip thickness d kb} <1 mm from a steel precursor.

State of the art:

Different process routes are known for the production of strips from Si-alloyed steel with a thickness d _{kb <1 mm.} Typically, a slab or thin slab is rolled into a hot strip in a multi-stage hot rolling process. The hot strip is then annealed continuously or discontinuously in a cold rolling mill before the first pass. In the cold rolling mill, the hot strip is also rolled into a cold strip in a multi-stage rolling process and then subjected to another annealing process. Process parameters for such methods are for example in the DE 199 18 484 A1 or WO 2016/063 118 A1 disclosed.

Electrical strips achieve optimal magnetic properties if the degree of deformation in the cold rolling mill does not exceed 85%. Furthermore, the cold formability of this group of materials is limited by their brittle behavior. For physical reasons, the finished electrical steel strip must have a particularly small strip thickness, which is typically <0.30 mm. _{The task is therefore to} provide thin hot strips (d wb <1.80 mm) as the starting material for the production of particularly thin cold strips (d _{kb <0.25 mm).}

When hot rolling these thin hot strips from a slab or thin slab in a hot rolling mill, the final rolling temperature T _EW usually falls below T _EW = 900 ° C, which consequently leads to an inhomogeneous microstructure over the cross section of the hot strip. After cooling, the surface of the strip shows strong proportions of non-fine-grained, recrystallized microstructures and the core, on the other hand, is characterized by a very coarse-grained and linear structure. Such inhomogeneous structures are difficult to cold-roll. The inhomogeneity of the hot strip is also passed on to the final structure in the fully annealed cold strip and limits the attainability of optimal magnetic parameters.

In a conventional hot rolling process, an attempt is made, by increasing the final rolling temperature, to set rolling conditions in which this inhomogeneous microstructure is less pronounced. This is usually achieved by increasing the rolling speed in the hot rolling process or by increasing the slab temperature before the first piercing in the hot rolling stand.

If the final rolling speed is too high, however, unstable conditions can arise in the hot rolling mill, which can have negative effects on the strip quality. High piercing temperatures require correspondingly more energy in the preheating furnace and / or can damage the surface of the slab or worsen the quantitative output due to increased scale formation.

In order to avoid the disadvantages in the known production processes, the thin hot strips with T _EW <900 ° C must be annealed with an inhomogeneous microstructure. This hot strip annealing is independent of the final rolling temperature selected for hot rolling.

Object of the invention:

The object to be achieved by the invention is to provide a method for producing a cold-rolled electrical _{steel strip with a cold-rolled strip thickness d kb} <1 mm from a steel pre-product via an optimized combination of final rolling temperature in the hot rolling mill and hot-strip annealing.

Invention:

The object is achieved by the method according to the invention with the features of main claim 1. The hot strip thickness d _{Wb of} a hot strip before cold rolling is d _Wb <1.80 mm and the final _{rolling temperature T EW} during hot rolling of the hot strip is set to T _EW ≤ 900 ° C. Before cold rolling, continuous hot strip annealing takes place in a furnace with a rapid heating device. The hot strip in the furnace is brought to a strip temperature of at least 700 ° C within a maximum of 5 seconds using the rapid heating device and then held at a temperature of 900 ° C - 950 ° C for at least 30 s.

Due to the significantly lower final rolling temperature in the hot rolling process compared to the prior art, a hot strip with d _Wb <1.80 mm and slight differences in the structure can be rolled at rolling speeds in the stable production range of a rolling train. Through the subsequent continuous hot strip annealing and the rapid heating device installed in the furnace, the properties of the thin hot strip necessary for the production of the cold strip can be optimally adjusted.

According to the dependent claim 2, it is preferred if the final rolling temperature of the Hot rolling is set to T _EW ≤ 750 ° C. As a result, the preheating temperature of an inserted slab can be lowered further and, in addition to further optimization of the microstructure, the hot strip surface can also be improved.

Furthermore, according to dependent claim 3, it is advantageous if the annealed hot strip is pickled. This improves the quality of the hot strip surface and the resulting cold strip surface.

1. 1. Eine Brammentemperatur vor Anstich im ersten Warmwalzgerüst von T_Br = 1150°C ergibt eine Endwalztemperatur T_EW = 750°C bei einer Warmbanddicke d_wb = 1,2 mm und einer Endwalzgeschwindigkeit V_ew = 5,8 m/s bis V_ew = 8,8 m/s.
2. 2. Eine Brammentemperatur vor Anstich im ersten Warmwalzgerüst von T_Br = 1050°C ergibt eine Endwalztemperatur T_EW = 750°C bei einer Warmbanddicke d_wb = 1,2 mm und einer Endwalzgeschwindigkeit V_ew = 6,0 m/s bis V_ew = 9,0 m/s.
3. 3. Eine Brammentemperatur vor Anstich im ersten Warmwalzgerüst von T_Br = 1050°C ergibt eine Endwalztemperatur T_EW = 790°C bei einer Warmbanddicke d_wb = 1,2 mm Endwalzgeschwindigkeitsunabhängig.

For example, in a multi-stand hot rolling mill with a permitted rolling speed of a maximum of 11 m / s, a slab with a thickness of 60 mm is rolled into a thin hot strip with the following parameters:

1. 1. A slab temperature before piercing in the first hot rolling stand of T _Br = 1150 ° C results in a final rolling temperature T _EW = 750 ° C with a hot strip thickness d _wb = 1.2 mm and a final rolling speed V _ew = 5.8 m / s to V _ew = 8.8 m / s.
2. 2. A slab temperature before piercing in the first hot rolling stand of T _Br = 1050 ° C results in a final rolling temperature T _EW = 750 ° C with a hot strip thickness d _wb = 1.2 mm and a final rolling speed V _ew = 6.0 m / s to V _ew = 9.0 m / s.
3. 3. A slab temperature before piercing in the first hot rolling stand of T _Br = 1050 ° C. results in a final rolling temperature T _EW = 790 ° C. with a hot strip thickness d _wb = 1.2 mm, regardless of the final rolling speed.

The exemplary hot strips 1 to 3 are processed into electrical strips with a thickness of d _kb = 0.20 mm in a subsequent production process in accordance with the prior art. The electrical strips produced in this way have the necessary properties in accordance with corresponding international standards.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 19918484 A1 [0002]
• WO 2016/063118 A1 [0002]

Claims (3)

Process for the production of a cold-rolled electrical _{steel strip with a cold-rolled strip thickness d kb} <1 mm from a steel precursor having the alloy components (in% by weight): - Si ≥ 1.8% - Al ≥ 0.5% - C ≤ 50 ppm - N ≤ 40 ppm - S ≤ 30 ppm - Mn 0.060% to 0.500% - sum of the alloy components Si and Al ≤ 4.6% - one or more of the elements Cu, Ni, Mo, Cr, Sn, Sb with <0.100% each, - As well as the remainder iron (Fe) and unavoidable impurities, characterized by at least one hot rolling step and at least one cold rolling step, where - the steel pre-product is hot-rolled to form a hot strip, and the hot strip thickness does not exceed 8 times the desired cold strip thickness; - A heating of the steel precursor to a maximum of T _Br = 1200 ° C before a piercing in the roll stand during hot rolling is limited; - The hot strip is subjected to continuous hot strip annealing before cold rolling; - The hot strip is heated up to a target temperature of 900 ° C - 1,000 ° C during continuous hot strip annealing; characterized in that - the hot strip thickness before cold rolling is d _Wb <1.80 mm; - The final rolling temperature of the hot rolling is set to T _EW ≤ 800 ° C; the continuous hot strip annealing takes place in a furnace, having a rapid heating device; - The hot strip in the furnace with rapid heating device is brought to a strip temperature of at least 700 ° C within a maximum of 5 seconds; - the hot strip is held at a temperature of 900 ° C - 1,000 ° C for at least 30 s during continuous hot strip annealing. Procedure according to Claim 1 , characterized in that the final rolling temperature of the hot rolling is set to T _EW ≤ 750 ° C. Method according to one of the preceding claims, characterized in that the annealed hot strip is pickled.