Process for producing grain-oriented electrical steel strip

Patent metadata

Field	Value
Publication number	US-11239012-B2
Application number	US-201514638338-A
Country	US
Kind code	B2
Filing date	Mar 4, 2015
Priority date	Oct 15, 2014
Publication date	Feb 1, 2022
Grant date	Feb 1, 2022

Abstract

A process for producing grain-oriented electrical steel strip by means of thin slab continuous casting and which includes continuously casting the smelt by thin slab continuous casting, subjecting the thin slabs to homogenization annealing at a maximum temperature of 1250° C. and heating to a temperature between 1350° C. and 1380° C., and continuously hot rolling the thin slabs to form a hot-rolled strip, with cooling and reeling the hot-rolled strip to form a coil and cold rolling the hot-rolled strip to a nominal thickness, with subjecting the cold-rolled strip to recrystallization, decarburization and nitridation annealing, which includes a decarburization annealing phase and a subsequent nitridation annealing phase, with an intermediate reduction annealing phase being interposed between the decarburization annealing phase and the nitridation annealing phase, whereby a cold-rolled strip is obtained, which primary recrystallized grains have a circle equivalent mean size (diameter) between 22 μm and 25 μm.

First claim

What is claimed is:

1. A process for producing grain-oriented electrical steel strip by means of thin slab continuous casting, comprising the following process steps:
a) smelting a steel with a smelt which contains, in addition to iron (Fe) and unavoidable impurities:
Si: 2.50-4.00 wt %,
C: 0.030-0.100 wt %,
Mn: 0.160-0.300 wt %,
Cu: 0.100-0.300 wt %,
Al: 0.020-0.040 wt %
Sn: 0.050-0.150 wt %
S: <100 ppm,
N: <100 ppm,
and one or more elements selected from the group consisting of Cr, V, Ni, Mo and Nb, wherein a ratio of manganese (Mn) to sulfur (S) is greater than 6, and a ratio of aluminum (Al) to nitrogen (N) is greater than 4;
b) continuously thin slab casting the smelt, without exposure of a strand to inert gas, to form the strand having a thickness of 50-120 mm, and dividing the strand into thin slabs,
c) carrying out a homogenization annealing comprising the step of heating the thin slabs to a temperature above 1050° C.,
d) feeding the thin slabs through an induction heating device in which the thin slabs are immediately prior to a first hot-rolling pass are heated within several seconds up to a temperature above a homogenization temperature of process step c), wherein a temperature of the thin slab, immediately after exiting the induction heating device in process step is within a range of 1350°-1380° C.,
e) continuously hot rolling the thin slabs in a linear, multiple-stand hot-rolling train to form a hot strip having a thickness of 1.8 mm-3.0 mm,
f) cooling and reeling a hot-rolled strip at a reeling temperature of less than 650° C. to form a coil,
g) annealing the hot-rolled strip, after reeling and prior to a subsequent cold rolling step, at a temperature of between 920° C. and 1150° C.,
h) cold rolling the hot-rolled strip on a reversible stand, in a single process step in more than three passes, to a cold-rolled strip having a final thickness of 0.15 mm-0.40 mm, wherein during at least one or more of the final three passes, the hot-rolled strip reaches a temperature of at least 180° C. to a maximum of 260° C., resulting from processing heat produced during rolling, for a period of at least five minutes;
i) subjecting the resulting cold-rolled strip to recrystallization, decarburization and nitridation annealing, wherein the recrystallization, decarburization and nitridation annealing of the cold-rolled strip comprises following one another
a decarburization annealing phase which is carried out at a strip temperature ranging from 820° C.-890° C. for a maximum period of 150 seconds, with a moist nitrogen (N 2 ) and hydrogen (H 2 )—containing annealing atmosphere which has a water vapor/hydrogen partial pressure ratio pH 2 O/pH 2 of 0.30 to 0.60,
an intermediate reduction annealing phase which is carried out between the decarburization and nitridation annealing phases and is carried out at a temperature ranging from 820° C.-890° C. for a maximum period of 40 seconds, with a dry annealing atmosphere which contains nitrogen (N 2 ) and hydrogen (H 2 ) which has a water vapor/hydrogen partial pressure ratio pH 2 O/pH 2 of less than 0.10 and which comprises a resulting grain microstructure having an average primary recrystallized grain size having a circle equivalent mean size (diameter) between 22 μm and 25 μm, and
a subsequent nitridation annealing phase which is carried out at a temperature ranging from 850° C.-920° C. for a maximum period of 50 seconds, with a nitrogen (N 2 ) and hydrogen (H 2 )—containing annealing atmosphere which has a water vapor/hydrogen partial pressure ratio pH 2 O/pH 2 of 0.03 to 0.07, and wherein at least 2 vol. % to a maximum of 12 vol. % ammonia (NH 3 ), referred to a total gas flow rate, is added separately to the annealing atmosphere, with the ammonia being blown onto both upper and lower strip surfaces of the cold-rolled strip,
j) applying an annealing separator (non-stick layer) containing primarily MgO to a strip surface of the cold-rolled strip which has been recrystallization, decarburization and nitridation annealed,
k) subjecting the cold-rolled strip which has been coated with the annealing separator to secondary recrystallization annealing in a bell-type furnace at a temperature of >1150° C., forming a finished steel strip having a Goss texture,
l) coating a finished steel strip with an electrically insulating layer and thereafter, performing a stress-relief annealing of a coated steel strip.

2. The process according to claim 1 , characterized in that, during the annealing in process step i), which comprises a decarburization annealing phase, an intermediate reduction annealing phase and a nitridation annealing phase, the cold-rolled strip is annealed such that after annealing, the cold-rolled strip has a total nitrogen content of at least 200 ppm.

3. The process according to claim 1 , characterized in that, at the start of recrystallization annealing in process step i), the cold-rolled strip is heated at a heating rate of more than 100 K/s.

4. The process according to claim 1 , characterized in that during casting in process step b), a temperature of the smelt during casting is less than 40 K.

5. The process according to claim 1 , characterized in that the hot rolling in process step e) is carried out at an initial rolling temperature during a first working pass of greater than 1150° C., a final rolling temperature ranging between 850° C.-980° C., and a final rolling speed of less than 12 m/s.

6. The process according to claim 1 , characterized in that, during annealing of the hot-rolled strip in process step g), an annealed hot-rolled strip is quenched after annealing at a cooling rate of more than 25 K/s.

7. The process according to claim 1 , characterized in that the cold rolling in process step h) is carried out in two stages, wherein the hot-rolled strip is pickled in a pickling step prior to a first cold-rolling stage, and upon completion of the first cold-rolling stage, the rolled steel is annealed according to process step g) prior a second cold-rolling stage.

8. The process according to claim 1 , characterized in that the secondary recrystallization annealing in process step k) is carried out such that, during a heating phase of the high-temperature annealing in a bell-type furnace, quantity of nitrogen (N 2 ) in a gaseous annealing atmosphere is greater than quantity of hydrogen (H 2 ).

9. The process according to claim 1 , characterized in that, following process step 1), a process step that effects a magnetic domain refinement of the coated finished steel strip is carried out.

10. The process according to claim 7 , characterized in that in the second cold-rolling stage, the thickness of the rolled strip is reduced by at least 85%.

Assignees

• Sms Group Gmbh

Inventors

• Boettcher Andreas
• Klinkenberg Christian
• Schuster Ingo

Classifications

• C21D1/42 Primary

  Induction heating · CPC title

• H01F1/16

  in the form of sheets (H01F1/147 takes precedence) · CPC title

• C22C38/02

  containing silicon · CPC title

• C21D8/12 Primary

  during manufacturing of articles with special electromagnetic properties · CPC title

• C21D8/1272

  Final recrystallisation annealing · CPC title