EP1473371B1 - Process for manufacturing non grain-oriented magnetic steel sheet and sheet obtained by this process - Google Patents

Abstract

The manufacture of magnetic strip with non-orientated grains comprises: (a) the production of a steel under vacuum with a given composition; (b) production of a slab; (c) hot rolling the slab at a reheat temperature lower than 1300[deg]C and a finishing temperature lower than 950[deg]C; (d) coiling the hot rolled strip at a temperature greater than 550C; (e) submitting the coiled strip to static annealing at a temperature between 700 and 1050[deg]C for longer than 1 hour; (f) submitting the annealed strip to a shot blasting operation; (g) submitting the treated strip to a pickling operation; (h) cold rolling the pickled strip, with a reduction rate of between 25 and 90%, in a single cold rolling operation to a thickness of less than or equal to 1.5 mm; (i) submitting the cold rolled strip to a final annealing operation effected in defilement.

Description

The present invention relates to a method of manufacturing non-oriented grain magnetic steel sheet.

The so-called non-oriented grain magnetic sheets, ie having isotropic magnetic properties are particularly intended for the construction of electromagnetic devices in which the magnetic flux generated by the electric windings is not constant, as for example in machines rotating. Some transformers used in the field of household appliances use this type of sheet for economic reasons.

These electromagnetic devices consist of cut and assembled sheets. The plates have an efficiency which is evaluated according to two parameters which are the induction, on the one hand, and the specific losses, on the other hand.

The induction is limited by the saturation magnetization of the sheets and this magnetization is all the higher as the steel is rich in iron. The addition of alloying elements in the steel results in an increase in the electrical resistivity, the function of which is to reduce the eddy current losses.

The evacuation of the steel vacuum improves on the one hand, cleanliness and purity of the steel and on the other hand, to reduce losses by hysteresis.

Also, it is necessary to find a compromise, from the point of view of composition, between the magnetization and the losses.

Patent EP 0 469 980 discloses a method used in the field of the manufacture of non-oriented grain magnetic sheets, the process comprising successively, after vacuum forming of a steel, a hot rolling operation followed by a winding, rapid annealing said parade hot-rolled sheet, an optional shot blasting operation, a stripping operation, a cold rolling operation in one or more steps followed by annealing, the final annealing being carried out under an atmosphere controlled, decarburizing if necessary.

The sheets obtained by this method, for a final thickness of about 0.50 millimeters, have specific losses of less than 6.5 W / Kg under an induction of 1.5 Tesla and a frequency of 50 Hertz as well as a higher magnetization at 1.74 Tesla under an electric field of 5000 A / m.

For a sheet thickness of about 0.65 millimeters, the total mass losses are less than 7.5 W / Kg under an induction of 1.5 Tesla and a frequency of 50 Hertz. The magnetization is greater than 1.75 Tesla under a field of 5000 A / m.

The object of the invention is to improve the magnetic characteristics of non-oriented grain sheets made with a steel containing only very little silicon, that is to say to reduce the magnetic losses and to increase the magnetization under a field. electrical determined.

• élaborer sous vide un acier de composition suivantes :
  • carbone < 0,01%
  • silicium < 0,5%,
  • manganèse, de 0,05 à 0,5%
  • aluminium < 0,03%,
  • phosphore < 0,20%,
  • soufre < 0,015%;
  • azote < 0,01%,
  • oxygène < 0,01%,
  le reste étant du fer et des impuretés invévitables,
• mettre l'acier sous forme de brame,
• laminer à chaud la brame avec une température de réchauffage inférieure à 1300°C, une température de fin de laminage à chaud inférieure à 950°C,
• bobiner la bande laminée à chaud à une température supérieure à 550°C,
• soumettre la bande en bobine à un recuit statique à une température comprise entre 700 et 1050°C pendant un temps supérieur à 1 heure,
• soumettre la bande recuite à une opération facultative de grenaillage,
• soumettre la bande recuite et éventuellement grenaillée, à une opération de décapage, puis
• laminer à froid la bande décapée, avec un taux de réduction compris entre 25 et 90%, en une seule opération de laminage à froid à une épaisseur inférieure ou égale à 1,5 mm, puis
• soumettre la bande laminée à froid à un recuit final effectué au défilé.
• après le recuit final, on soumet la tôle préalablement découpée à un recuit d'élimination des contraintes

Les autres caractéristiques de l'invention sont :

• le recuit final au défilé est réalisé à une température comprise entre 700 et 1050 °C pendant un temps inférieur à 10 mn.
• Le recuit d'élimination des contraintes peut être effectué à une température supérieure à 650 °C pendant un temps supérieur à 3 mn.

It relates to a method of manufacturing a non-oriented grain magnetic sheet comprising the steps of:

• develop vacuum a steel of the following composition:
  • carbon <0.01%
  • silicon <0.5%,
  • manganese, from 0.05 to 0.5%
  • aluminum <0.03%,
  • phosphorus <0.20%,
  • sulfur <0.015%;
  • nitrogen <0.01%,
  • oxygen <0.01%,
  the rest being iron and unavoidable impurities,
• put steel in slab form,
• hot rolling the slab with a reheating temperature below 1300 ° C, a hot rolling end temperature below 950 ° C,
• wind the hot-rolled strip at a temperature above 550 ° C,
• subjecting the strip in a coil to static annealing at a temperature of between 700 and 1050 ° C for a time greater than 1 hour,
• subject the annealed strip to an optional shot blasting operation,
• subject the annealed and possibly shot-peened strip to a stripping operation, then
• cold roll the stripped strip, with a reduction rate between 25 and 90%, in a single cold rolling operation to a thickness less than or equal to 1.5 mm, then
• subject the cold-rolled strip to a final annealing performed at the parade.
• after the final annealing, the pre-cut sheet is subjected to stress-relieving annealing

The other features of the invention are:

• the final annealing is carried out at a temperature between 700 and 1050 ° C for a time less than 10 minutes.
• Stress removal annealing may be performed at a temperature greater than 650 ° C for a time greater than 3 minutes.

The following description giving a series of exemplary embodiments will make clear the invention.

The single figure shows a magnetization curve as a function of the cold rolling rates, the cold rolling being carried out in a single operation.

• carbone < 0,01%
• silicium < 0,5%,
• manganèse, de 0,05 à 0,5%
• aluminium < 0,03%,
• phosphore < 0,20%,
• soufre < 0,015%;
• azote < 0,01%,
• oxygène < 0,01%,

le reste étant du fer et des impuretés invévitables.According to the invention, the method for manufacturing a steel of a non-oriented grain magnetic sheet comprises the vacuum elaboration of a steel of the following composition:

• carbon <0.01%
• silicon <0.5%,
• manganese, from 0.05 to 0.5%
• aluminum <0.03%,
• phosphorus <0.20%,
• sulfur <0.015%;
• nitrogen <0.01%,
• oxygen <0.01%,

the rest being iron and unavoidable impurities.

The presence of silicon and manganese in solid solution in iron considerably increases the electrical resistivity and, consequently, decreases the energy losses that accompany the variation of the magnetic induction flux. However, the saturation magnetic polarization decreases with the silicon, aluminum, manganese content. This results in a lower magnetic permeability of the steel at the usual point of operation of the machines. It is therefore necessary to find the best compromise between the content of alloying elements and the magnetic performances targeted. As a result, the steel according to the invention has a silicon mass content of less than 0.5%, and a manganese content of less than 0.5% to obtain a high permeability.

Thermal conductivity is an important parameter in the construction of electrical machines. Indeed, the Joule energy losses in the materials are discharged to the outside via the magnetic circuit consisting of stacked cut sheets. The addition of silicon, manganese and aluminum in the iron results in a decrease in the thermal conductivity.

From this point of view, the steel must be unalloyed or very little alloyed, the low silicon, manganese and aluminum content of the steel according to the invention makes it possible to limit the heating of the engines which is detrimental to the good holding insulation insulating conductors. The better evacuation of the calories can also allow an increase of the mass power, by the increase of the levels of induction, without increase of the temperature.

In other words, the composition of the invention, by virtue of the thermal conductivity which it confers on the steel, provides cooling by thermal conduction of the electrical devices.

After elaboration, the steel is slab-cast, then the slab is hot-rolled with a reheat temperature below 1300 ° C, and a hot-roll end temperature below 950 ° C.

The hot-rolled sheet is wound at a temperature greater than 550 ° C., and then subjected to static annealing at a temperature of between 700 and 1050 ° C. for a time greater than 1 hour.

After the static annealing step, the web may undergo an optional shot blasting operation prior to being stripped.

Finally, the stripped strip is cold-rolled, with a reduction rate of between 25 and 90%, in a single cold rolling operation to a thickness of less than or equal to 1.5 mm, and then it undergoes a final annealing carried out at parade. The final annealing is carried out preferably at a temperature between 700 and 1050 ° C, for a time less than 10 min.

It is shown that mass magnetic losses can be reduced below 4.5 W / Kg for a sheet metal thickness of 0.35 mm, below 5.30 W / Kg for a sheet thickness of 0.50 mm, below 7 W / Kg for a sheet thickness of 0.65 mm, below 12.5 W / Kg for a sheet thickness of 1 mm and to obtain a magnetization equal to or greater than 1.77 Tesla by performing a static annealing of the hot-rolled sheet strip, associated with a cold rolling in a single operation followed by a continuous annealing at the parade.

Examples 1 to 6 illustrate this feature.

Example 1

A No. 4 steel slab whose chemical weight composition is given in Table 1 is heated to 1173 ° C. and then subjected to a first hot rolling with a reduction rate of 86% and a second hot rolling with a 93% reduction. The hot rolling end temperature is 843 ° C, the hot rolled strip is wound at the temperature of 738 ° C. The coil sheet was subjected to static annealing at 800 ° C for 10 hours under an atmosphere of hydrogen or hydrogen and nitrogen. The sheet is then cold rolled with a reduction rate of 80% to obtain a sheet of thickness of 0.50 mm. The final annealing is carried out at a temperature of 880 ° C. for 2 minutes under a nitrogen and hydrogen atmosphere. <b> TABLE 1 (Steel # 4) </ b> VS mn Yes S al P 0.002% 0.343% 0.322% 0.006% 0.001% 0.159%

The magnetic characteristics obtained are presented in Table 2. <b> TABLE 2. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.50 mm thickness according to the invention 4.9 1.80

Example 2

A No. 4 steel slab, the weight composition of which is given in Table 1, is treated in the same way as the steel of Example 1, that is to say with the same rates of heat reduction and Cold.

The reheating temperature of the slab is 1185 ° C, the hot rolling end temperature is 857 ° C. The hot rolled strip is wound at a temperature of 636 ° C. A portion of the coil is subjected to static annealing at 800 ° C for 10 hours under an atmosphere of hydrogen or hydrogen and nitrogen. The sheet is then cold rolled to obtain a sheet of 0.50 mm thick. The final annealing is carried out at a temperature of 880 ° C. for 2 minutes under a nitrogen and hydrogen atmosphere.

The magnetic characteristics obtained are presented in Table 3. <b> TABLE 3. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.50 mm thickness according to the invention 4.7 1.79

Example 3

A No. 4 steel slab, the weight composition of which is given in Table 1, is treated in the same way as the steel of Example 1, that is to say with the same rates of heat reduction and Cold.

The reheating temperature of the slab is 1221 ° C, the hot rolling end temperature is 910 ° C. The hot-rolled strip is wound at 785 ° C. The coil sheet was subjected to static annealing at 800 ° C for 10 hours under an atmosphere of hydrogen or hydrogen and nitrogen. The sheet is then cold rolled to obtain a sheet of 0.50 mm thick. The final annealing is carried out at a temperature of 880 ° C. for 2 minutes under a nitrogen and hydrogen atmosphere.

The magnetic characteristics obtained are presented in Table 4. <b> TABLE 4. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.50 mm thickness according to the invention 4.62 1.82

Under the same processing conditions, steel No. 2, whose composition is given in Table 5, which comprises in its composition a manganese content of 0.87% leads to magnetic properties identical to those in Table 4. The manganese content must however be limited to less than 0.5% to improve the thermal conductivity.

At lower static annealing temperature, it is necessary to increase the duration of this one. <b> TABLE 5 (Steel # 2) </ b> VS mn Yes S al P 0.003% 0.870% 0.342% 0.008% 0.001% 0.188%

Example 4

A section of the hot-rolled sheet metal coil obtained under the conditions described in Example 2 is subjected to static annealing at a temperature of 710 ° C. for 40 hours under an atmosphere of hydrogen or nitrogen and hydrogen. .

The magnetic characteristics obtained are presented in Table 6. <b> TABLE 6. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.50 mm thickness according to the invention 4.88 1.79

Example 5

A No. 4 steel slab whose weight composition is given in Table 1 is treated in the same way as in Example 1, that is to say with the same reduction rates under hot and cold conditions.

The No. 4 steel slab is heated to 1188 ° C, the hot rolling end temperature is 816 ° C. The hot-rolled sheet strip is wound at a temperature of 702 ° C. A coil sheet section is subjected to static annealing at 1000 ° C for 10 hours under an atmosphere of hydrogen or hydrogen and nitrogen. The sheet is then cold rolled to obtain a sheet of 0.50 mm thick. The final annealing is carried out at a temperature of 880 ° C. for 2 minutes under a nitrogen and hydrogen atmosphere.
The magnetic characteristics obtained are presented in Table 7. <b> TABLE 7. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.50 mm thickness according to the invention 4.59 1.80

Example 6

A section of the hot-rolled sheet metal coil obtained under the conditions described in Example 2 is subjected to static annealing at the temperature of 740 ° C. for 40 hours under an atmosphere of hydrogen or of hydrogen and of nitrogen. After annealing the section is divided into four parts which are respectively cold rolled with a reduction rate of 60%, 74%, 80% and 86% to obtain a sheet of 1 mm 0.65 mm, 0.50 mm, and 0.35 mm thick.

The sheet 0.5 mm thick and the sheet 0.35 mm thick are annealed at a temperature of 880 ° C for 2 minutes. The sheet 0.65 mm thick is annealed at a temperature of 880 ° C for 2 minutes 30 seconds.

The sheet 1 mm thick is annealed at a temperature of 880 ° C for 3 minutes 40 s.

The final annealing is carried out in an atmosphere of hydrogen and nitrogen. The magnetic characteristics obtained are presented in Table 8. <b> TABLE 8. </ b> According to the invention: W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.35 mm thick 3.76 1.78 Sheet of 0.50 mm thick 4.70 1.79 Sheet of 0.65 mm thick 6.36 1.80 Sheet of 1 mm thick 11.80 1.80

The single figure shows that the cold rolling rate must be less than 90% to obtain a magnetization equal to or greater than 1.77 Tesla when static annealing is performed after hot rolling.

In the case where the sheet is made with static annealing after hot rolling, it has been found that annealing carried out on magnetic cores made by cutting and stacking the sheet according to the invention generates a reduction in losses without degradation. magnetization, the annealing being intended to eliminate the internal stresses due to cutting. It is thus possible to produce sheets having a final thickness of 0.35 mm, which after post-cutting annealing have magnetic losses of less than 4.0 W / Kg with a magnetization equal to or greater than 1.77 Tesla. It is thus possible to produce sheets having a final thickness of 0.50 mm, which after post-cutting annealing have mass losses of less than 4.70 W / kg with a magnetization equal to or greater than 1.77 Tesla. Under certain conditions, it is possible to make sheets with losses less than 4W / Kg with a magnetization greater than 1.80 Tesla. These performances are essentially due to the fact that in the process according to the invention the sheet is subjected to a static annealing before cold rolling.

The invention comprises the following steps: a static annealing before cold rolling, a cold rolling in a single operation, a final annealing as shown in Examples 1, 2, 3, 4, 5 and 6. After cutting the elements of circuit and stack, an annealing of elimination of internal stresses is performed on said circuits.

The elimination annealing of the internal stresses generated by cutting enables the losses to be reduced significantly without any degradation of the magnetization of the sheet according to the invention.

Preferably, the sheet undergoes stripping annealing at a temperature above 650 ° C, for a time greater than 3 minutes.

Example 7 illustrates this point.

Example 7

The Epstein test pieces having a thickness of 0.35 mm, 0.50 mm, 0.65 mm and 1 mm, used to measure the magnetic characteristics of the sheets presented in Examples 1, 3, 4 and 5, were subjected to an annealing of 750 ° C for 2 hours under an atmosphere of nitrogen and hydrogen.

Sheet of 0.50 mm thick with annealing according to the invention: Example 1 4.13 1.80 Example 3 3.80 1.82 Example 4 4.15 1.79 Example 5 3.62 1.80

Example 8 .

The Epstein test pieces used in Example 6 to measure the magnetic characteristics are subjected to annealing at 750 ° C. for two hours under a nitrogen and hydrogen atmosphere.
The magnetic characteristics obtained are presented in Table 9. <b> Table 9. </ b> W 1.5 / 50
(W / kg) B5000
( You're here ) Sheet of 0.35 mm thick. 3.37 1.78 Sheet of 0.5 mm thick. 3.94 1.79 Sheet of 0.65 mm thick. 5.36 1.80 Sheet 1 mm thick according to the invention. 10.62 1.80 In the case where the sheet according to the invention is produced with static annealing after hot rolling, it is thus possible to obtain sheets having a final thickness of 0.35 mm, 0.50 mm, 0.65 mm and 1 mm and which, after post-cutting annealing respectively have mass losses of less than 4 W / Kg, 4.70 W / kg, 6 W / Kg and 11.5 W / Kg, and a magnetization equal to or greater than 1.77 Tesla.

According to the invention, it is shown that it is possible to achieve with a steel having a chemical composition determined to the realization of sheet metal magnetic having remarkable properties, performing a long-term static annealing of the hot-rolled sheet strip followed by a single cold rolling.

When the sheet according to the invention is hot rolled and subjected to a long-lasting static annealing followed by a single cold rolling, it has a thickness of 0.50 mm and 0.65 mm, a significant reduction in losses. mass and an improvement of the magnetization ability.

At the thickness of 1 mm, static annealing before cold rolling makes it possible to increase the ability to magnetize with, in return, a degradation of the losses.

The sheet obtained by the process can be subjected, after cutting and assembly of the magnetic circuits, to stress-relieving annealing.

This annealing of elimination of stresses due to cutting causes a significant reduction in losses without degradation of the magnetization ability, with static annealing of the hot-rolled strip and then cold-rolled in a single operation.

Claims (3)

1. Process for manufacturing a non-grain-oriented magnetic steel sheet, comprising the steps consisting in:

   - a steel of the following composition is vacuum-smelted:

   carbon < 0.01%

   silicon < 0.5%

   manganese, from 0.05 to 0.5%

   aluminium < 0.03%

   phosphorus < 0.20%

   sulphur < 0.015%

   nitrogen < 0.01%

   oxygen < 0.01%,

   the balance being iron and inevitable impurities;

   - the steel is formed into a slab;

   - the slab is hot-rolled with a reheat temperature below 1300°C, and a temperature at the end of hot rolling below 950°C;

   - the hot-rolled strip is coiled at a temperature above 550°C;

   - the coiled strip undergoes a static anneal at a temperature between 700 and 1050°C for a period of time longer than 1 hour;

   - the annealed strip undergoes an optional peening operation;

   - the annealed and optionally peened strip undergoes a pickling operation; then

   - the pickled strip is cold-rolled, with a reduction ratio of between 25 and 90%, in a single cold-rolling operation down to a thickness of 1.5 mm or less;

   - the cold-rolled strip undergoes a final anneal carried out on the run; and then

   - the strip is cut in order to form sheets, and said sheets undergo a stress-relieving anneal.
2. Process according to Claim 1, characterized in that the final anneal on the run is carried out at a temperature between 700 and 1050°C for a period of time shorter than 10 min.
3. Process according to Claim 1 or 2, characterized in that the stress-relieving anneal is carried out at a temperature above 650°C for a period of time longer than 3 min.

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