EP1473371A2 - 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 sheet metal manufacturing process of non-oriented grain magnetic steel.

Magnetic sheets called non-oriented grain, that is to say having isotropic magnetic properties are particularly intended for the construction of electromagnetic devices in which the magnetic flux generated by the electrical windings is not not constant, as for example in rotating machines. Certain transformers used in the household appliance sector use this type of sheet for economic reasons.

These electromagnetic devices are made of sheets cut and assembled. The sheets have an efficiency that is evaluated in function of 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 leads to an increase in electrical resistivity, which has the function of reducing losses by eddy currents.

The vacuum production of steel improves on the one hand, the cleanliness and purity of said steel and secondly to reduce losses by hysteresis.

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

EP 0 469 980 discloses a process used in the field of manufacture of non-oriented grain magnetic sheets, the process comprising successively, after preparation under vacuum of a steel, hot rolling operation followed by coiling, annealing fast said to the parade of hot rolled sheet, an optional operation shot blasting, pickling operation, rolling operation cold in one or more stages followed by annealing, the final annealing being performed in a controlled atmosphere, decarburizing if necessary.

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

For a sheet thickness of around 0.65 millimeters, the losses total mass is 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 invention aims to improve the characteristics magnetic of non-oriented grain sheets made with steel containing very little silicon, i.e. reducing losses magnetic and increase the magnetization under an electric field 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.

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.
• après le recuit final, on soumet la tôle préalablement découpée à un recuit d'élimination des contraintes qui peut être effectué à une température supérieure à 650 °C pendant un temps supérieur à 3 mn.

Its subject is a process for manufacturing a magnetic sheet with non-oriented grains comprising the steps consisting in:

• elaborate under vacuum a steel of the following composition: carbon <0.01% silicon <0.5%, manganese, 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 the steel in the form of a slab,
• 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 on a reel to static annealing at a temperature between 700 and 1050 ° C. for a time greater than 1 hour,
• subject the annealed strip to an optional peening operation,
• subject the annealed and possibly shot-blasted strip to a pickling operation, then
• cold laminate the pickled strip, with a reduction rate of 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 carried out at the process.

The other characteristics of the invention are:

• final annealing on parade is carried out at a temperature between 700 and 1050 ° C. for a time of less than 10 min.
• after the final annealing, the previously cut sheet is subjected to a stress elimination annealing which can be carried out at a temperature above 650 ° C. for a time greater than 3 min.

The following description giving a series of example embodiments will make the invention well understood.

The single figure shows a magnetization curve as a function cold rolling rates, cold rolling being performed in one single operation.

According to the invention, the process for manufacturing a steel from a magnetic sheet with non-oriented grains comprises the production under vacuum of a steel of the following composition: carbon <0.01% silicon <0.5%, manganese, 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 the iron considerably increases the electrical resistivity and, by therefore, decreases the energy losses that accompany the variation of the magnetic induction flux. However, the magnetic polarization at saturation decreases depending on the content of silicon, aluminum, manganese. This results in a lower magnetic permeability of the steel at the usual operating point of the machines. So it is necessary to find the best compromise between the content of alloying elements and the magnetic performances targeted. As a result, the steel according the invention has a mass content of silicon 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 energy losses by Joule effect in the materials are evacuated outside by through the magnetic circuit made up of cut sheets stacked. The addition of silicon, manganese and aluminum in the iron results in a decrease in thermal conductivity.

From this point of view, the steel must be non or very little alloyed, the weak silicon, manganese and aluminum content of steel according to the invention makes it possible to limit the overheating of the motors which is detrimental to the good performance of the insulators coating the conductors. The better removal of calories can also allow an increase mass power, via increased induction levels, without temperature increase.

In other words, the composition of the invention, by the thermal conductivity that it gives to steel, ensures thermal conduction cooling of electrical devices.

After production, the steel is poured in the form of a slab, then the slab is hot rolled with reheating temperature below 1300 ° C, and an end temperature of hot rolling below 950 ° C.

Hot rolled sheet is coiled at a higher temperature at 550 ° C, then is subjected to static annealing at a temperature between 700 and 1050 ° C for a time greater than 1 hour.

After the static annealing step, the strip can undergo an operation optional shot peening, before being subjected to an operation of stripping.

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

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

Examples 1 to 6 illustrate this characteristic.

Example 1 .

A steel slab N ° 4 whose chemical composition by weight is given in table 1 is reheated to 1173 ° C then undergoes a first hot rolling with a reduction rate of 86% and a second hot rolling with a rate of 93% reduction. The end of hot rolling temperature is 843 ° C, the hot rolled sheet strip is wound at the temperature of 738 ° C. The sheet in the form of a coil is subjected to static annealing at the temperature of 800 ° C. for 10 hours under an atmosphere of hydrogen or of hydrogen and nitrogen. The sheet is then cold rolled with a reduction rate of 80% to obtain a sheet thickness of 0.50 mm. The final annealing is carried out at a temperature of 880 ° C. for 2 minutes under an atmosphere of nitrogen and hydrogen. (Steel n ° 4) 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. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.50 mm thick sheet according to the invention. 4.9 1.80

Example 2 .

A steel slab n ° 4 whose weight composition is given in table 1 is treated in the same way as steel Example 1, that is to say with the same hot reduction rates and at cold.

The heating temperature of the slab is 1185 ° C, the end of hot rolling temperature is 857 ° C. The sheet metal strip hot rolled is wound at a temperature of 636 ° C. A stretch of the coil is subjected to static annealing at a temperature of 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. Final annealing is carried out at the temperature of 880 ° C for 2 minutes under a nitrogen and hydrogen atmosphere.

The magnetic characteristics obtained are presented in Table 3. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.50 mm thick sheet according to the invention. 4.7 1.79

Example 3 .

A steel slab n ° 4 whose weight composition is given in table 1 is treated in the same way as steel Example 1, that is to say with the same hot reduction rates and at cold.

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

The magnetic characteristics obtained are presented in Table 4. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.50 mm thick sheet according to the invention. 4.62 1.82

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

At a lower static annealing temperature, it is necessary to increase the duration thereof. (Steel # 2) 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 coil obtained in the conditions described in Example 2 is subjected to static annealing at a temperature of 710 ° C for 40 hours under an atmosphere hydrogen or nitrogen and hydrogen.

The magnetic characteristics obtained are presented in Table 6. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.50 mm thick sheet according to the invention. 4.88 1.79

Example 5 .

A steel slab n ° 4 whose weight composition is given in Table 1 is treated in the same way as in Example 1, that is, with the same hot and cold reduction rates.

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

Example 6 .

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

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

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

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

The single figure shows that the cold rolling rate should 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 produced with static annealing after hot rolling, it was found that an annealing carried out on cores magnetic produced by cutting and stacking the sheet according to the invention generates a reduction in losses without degradation of magnetization, annealing being intended to eliminate internal stresses due to cutting. It is thus possible to produce sheets having a thickness final of 0.35 mm, which after post-cutting annealing have losses magnetic less than 4.0 W / Kg with equal magnetization 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 equal magnetization 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 static annealing before cold rolling.

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

The annealing of elimination of the internal stresses generated by cutting can significantly reduce losses without no degradation of the magnetization of the sheet according to the invention.

Preferably, the sheet undergoes stress elimination annealing at a temperature above 650 ° C, for a time above 3 min.

Example 7 illustrates this point.

Example 7 .

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

Sheet 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 tubes used in Example 6 to measure the magnetic characteristics are annealed at 750 ° C for two hours under an atmosphere of nitrogen and hydrogen.
The magnetic characteristics obtained are presented in Table 9. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.35 mm thick sheet. 3.37 1.78 Sheet 0.5 mm thick. 3.94 1.79 0.65 mm thick sheet. 5.36 1.80 1 mm thick sheet 10.62 1.80 according to the invention. 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 as well as a magnetization equal to or greater than 1.77 Tesla.

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

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

At a thickness of 1 mm, static annealing before cold rolling makes it possible to increase the aptitude for magnetization with, in return a deterioration of losses.

The sheet obtained by the process can be subjected, after cutting and assembly of magnetic circuits, annealing elimination of constraints.

This annealing eliminates the stresses due to cutting, causes a significant reduction in losses without degradation of magnetizability, with static annealing of the rolled strip at hot then cold rolled in a single operation.

Claims (4)

Method for manufacturing a magnetic sheet with non-oriented grains comprising the steps consisting in: elaborate under vacuum a steel of the following composition: carbon <0.01% silicon <0.5%, manganese, 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 the steel in the form of a slab, 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 on a reel to static annealing at a temperature between 700 and 1050 ° C. for a time greater than 1 hour, subject the annealed strip to an optional peening operation, subject the annealed and possibly shot-blasted strip to a pickling operation, then cold laminate the pickled strip, with a reduction rate of 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 carried out on the parade. Method according to claims 1, characterized in that the final annealing on the run is carried out at a temperature between 700 and 1050 ° C for a time less than 10 min. Method according to claim 2, characterized in that , after the final annealing, the previously cut sheet is subjected to a stress relieving annealing. Method according to claim 3, characterized in that the stress relieving annealing is carried out at a temperature above 650 ° C for a time greater than 3 min.

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