EP0786528B1 - 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.

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%, fer et impuretés inévitables,

ledit acier, mis sous forme de brame, étant soumis successivement à :

un laminage à chaud avec une température de réchauffage de brame inférieure à 1300°C, une température de fin de laminage à chaud inférieure à 950°C, la bande laminée à chaud étant bobinée à une température supérieure à 550°C,

une opération facultative de grenaillage,

une opération de décapage,

puis laminée à froid en au moins une opération de laminage à froid à une épaisseur inférieure ou égale à 1,5 mm, la bande laminée à froid étant soumise à un recuit final.It relates to a process for manufacturing a magnetic sheet with non-oriented grains from the vacuum production of a steel having a composition of less than 0.5% of silicon in particular

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%, iron and unavoidable impurities,

said steel, put in the form of a slab, being successively subjected to:

hot rolling with a slab reheating temperature below 1300 ° C, a hot rolling end temperature below 950 ° C, the hot rolled strip being wound at a temperature above 550 ° C,

an optional shot peening operation,

a pickling operation,

then cold rolled in at least one cold rolling operation to a thickness less than or equal to 1.5 mm, the cold rolled strip being subjected to a final annealing.

dans une forme de l'invention,

• le laminage à froid en une opération est réalisé sous un taux de réduction compris entre 25 et 90%.

dans une autre forme de l'invention,

• le recuit final au défilé est réalisé à une température comprise entre 700 et 1050 °C pendant un temps inférieur à 10 mn.

The other characteristics of the invention are:

in one form of the invention,

• cold rolling in one operation is carried out at a reduction rate of between 25 and 90%.

in another form of the invention,

• final annealing on parade is carried out at a temperature between 700 and 1050 ° C. for a time of less than 10 min.

• le recuit d'élimination des contraintes est effectué à une température supérieure à 650 °C pendant un temps supérieur à 3 mn.

In addition, after the final annealing, the previously cut sheet is subjected to a stress relieving annealing.

• stress elimination annealing is 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.

• un laminage à chaud avec une température de réchauffage de brame inférieure à 1300°C, une température de fin de laminage à chaud inférieure à 950°C, la bande laminée à chaud étant bobinée à une température supérieure à 550°C, puis laminée à froid avec un taux de réduction supérieur ou égal à 25 %, en une opération de laminage à froid à une épaisseur inférieure ou égale à 1,5 mm, la bande laminée à froid étant soumise à un recuit final.

According to the present invention, it is demonstrated that the mass losses can be reduced to 1.5 Tesla and 50 Hertz, to less than 5 W / Kg for a sheet thickness of approximately 0.35 mm, unless 6 W / Kg for a sheet thickness of approximately 0.50 mm; less than 8W / Kg for a sheet thickness of approximately 0.65 mm, less than 11 W / Kg for a sheet thickness of approximately 1 mm, and obtain a magnetization equal to or greater than 1.72 T under an electric field of 5000 A / m for a sheet of 0.35 mm thick, a magnetization equal to or greater than 1.75 Tesla for sheets of 0.50 mm, 0.65 mm, and 1 mm thick by subjecting according to the process of the invention, a steel having the composition given to:

• hot rolling with a slab reheating temperature lower than 1300 ° C, a hot rolling end temperature lower than 950 ° C, the hot rolled strip being wound at a temperature higher than 550 ° C, then rolled at cold with a reduction rate greater than or equal to 25%, in a cold rolling operation to a thickness less than or equal to 1.5 mm, the cold rolled strip being subjected to a final annealing.

In this process there is no rapid annealing of the sheet hot rolled.

Examples 1 to 5 which follow illustrate the characteristics of the present invention. Example 1.

A steel slab No. 1, the chemical composition of which by weight is given in table 1, is reheated to 1200 ° C. then undergoes a first hot rolling with a reduction rate of 86% and a second hot rolling with a 93% reduction rate. The temperature at the end of hot rolling is 860 ° C., the strip of hot rolled sheet 2.5 mm thick is wound at the temperature of 710 ° C. (Steel # 1) VS mn Yes S al P 0.003% 0.308% 0.347% 0.010% 0.001% 0.160%

• une partie des tronçons subissent un recuit rapide de 2,5 minutes à 1050°C avant laminage à froid pour servir de référence.
• les autres tronçons sont selon l'invention, laminés à froid sans effectuer de recuit avant le laminage à froid.

To make comparative measurements, the sheet metal strip thus obtained is divided into sections:

• part of the sections undergo rapid annealing for 2.5 minutes at 1050 ° C. before cold rolling to serve as a reference.
• the other sections are according to the invention, cold rolled without annealing before cold rolling.

The sections undergo cold rolling in a single operation to obtain sections with a final thickness of 0.35 millimeters, 0.50 millimeter, 0.65 millimeter and 1 millimeter, which corresponds to cold reduction rate of 86%, 80%, 74% and 60%.

Final annealing is carried out at a temperature of 880 ° C. for 2 min for the 0.35 mm, 0.50 mm and 1 mm sheet sections thick. Final annealing is carried out at a temperature of 920 ° C for 2.5 minutes (min) for the sections of sheet metal of final thickness of 0.65 mm.

Table 2 presents the mass loss characteristics in Watt / Kilogram at 1.5 Tesla and 50 Hertz and the magnetization in Tesla under an electric field of 5000 A / m for a sheet thickness of approximately 0.35 mm, d '' about 0.50 mm, about 0.65 mm and about 1 mm. W 1.5 / 50
(W / kg) B5000
( You're here ) 0.35 mm sheet with annealing (reference) 3.95 1.78 0.50 mm sheet with annealing. (reference) 4.70 1.78 0.65 mm sheet with annealing. (reference) 5.90 1.78 1 mm sheet with annealing (reference) 11.16 1.79 W 1.5 / 50
(W / kg) B5000
(You're here) Sheet without annealing. (invention) 0.35 mm thick sheet 4.10 1.75 Sheet 0.50 mm thick. 5.20 1.77 0.65 mm thick sheet. 6.72 1.77 1 mm thick sheet 9.60 1.76

The magnetizability of the sheet of final thickness of 1 mm, 0.65 mm and 0.50 mm is equal to or greater than 1.75 Tesla under a field of 5000 A / m when the thickness before rolling cold varies from 2 mm to 3.3 mm (as summarized in table 2a) in the case of winding of hot-rolled sheet at a temperature above 650 ° C and in the absence of annealing before cold rolling . For the sheet of final thickness of 0.35 mm, the thickness before cold rolling must be less than 3.3 mm to obtain a magnetization equal to or greater than 1.75 Tesla. Final thickness (mm) Thickness before cold rolling (mm) B 5000 (Tesla) 1 3.3 1.77 - 2.5 1.76 - 2 1.77 0.65 3.3 1.77 - 2.5 1.77 - 2 1.78 0.50 3.3 1.75 - 2.5 1.77 - 2 1.77 0.35 3.3 1.74 - 2.5 1.75 - 2 1.76

Example 2.

A slab of steel n ° 1 is hot rolled in the same way than in example 1, but with a winding at the temperature of 610 ° C, a section of the sheet being cold rolled with a rate of 80% reduction, the other section with a 74% reduction rate, without initial annealing, i.e. without annealing before cold rolling.

After the same final annealing as in Example 1, the magnetic characteristics presented in Table 3 were obtained W 1.5 / 50 B5000 (W / kg) ( You're here ) Sheet without annealing. (invention) Sheet 0.50 mm thick. 5.95 1.74 0.65 mm thick sheet. 7.67 1.74

Example 3.

A slab of steel n ° 1 is hot rolled in the same way than in Example 1, but with a rolling end temperature at 910 ° C hot, the sheet being cold rolled with a reduction rate 80% without initial annealing.

After the same final annealing as in Example 1, the magnetic characteristics presented in Table 4 were obtained W 1.5 / 50 B5000 (W / kg) ( You're here ) Sheet without annealing. (invention) Sheet 0.50 mm thick. 5.25 1.72

The preceding comparative examples demonstrate, by the variation of the values obtained in losses and induction, and with the composition of the present invention, the need to increase the winding temperature as well as limiting the end temperature of hot rolling in the absence of strip annealing treatment hot rolled.

Example 4.

A steel slab No. 2, the weight composition of which is given in Table 5, is treated under the same conditions as the steel slab No. 1 of Example 1, the sheet being cold rolled without initial annealing. (Steel # 2) VS mn Yes S al P 0.003% 0.870% 0.342% 0.008% 0.001% 0.188%

The magnetic characteristics obtained are presented in Table 6 W 1.5 / 50 B5000 (W / kg) ( You're here ) Sheet without annealing. Sheet 0.50 mm thick. 5.32 1.71 0.65 mm thick sheet. 6.32 1.72

Example 5.

A steel slab n ° 3 whose weight composition is given in table 7 is treated under the same conditions as the slab n ° 1 of example 1, the sheet being cold rolled without initial annealing. (Steel # 3) VS mn Yes S al P 0.003% 0.106% 0.326% 0.007% 0.001% 0.173%

The magnetic characteristics obtained are presented in Table 8 W 1.5 / 50 B5000 (W / kg) ( You're here ) Sheet without annealing. (invention) Sheet 0.50 mm thick. 5.80 1.77 0.65 mm thick sheet. 7.03 1.77

We note by comparing examples 4 and 5 and the tables of values 6 and 8 that the manganese content must be less than 0.5% because a high manganese content generates a decrease in the magnetization. However, a minimum of 0.05% manganese is necessary because a decrease in the manganese content tends to generate increased losses.

From the composition point of view, the presence of silicon and manganese in solid solution in iron significantly increases the electrical resistivity and therefore decreases the energy losses which accompany the variation of the magnetic induction flux. However, magnetic polarization at saturation decreases as a function of the content silicon, aluminum, manganese. This results in less magnetic permeability of steel at the usual operating point of machines. It is therefore necessary to find the best compromise between the content of alloying elements and the magnetic performance targeted. Consequently, the steel according to the invention has a mass content less than 0.5% silicon, and a manganese content 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.

• sans effectuer de recuit rapide de la tôle laminée à chaud, grâce à un meilleur contrôle de la température de fin de laminage à chaud et de bobinage, et à condition de limiter la teneur en manganèse contenu dans la composition de l'acier.

According to the invention, it is shown that it is possible, with a steel having a determined chemical composition, to produce magnetic sheet having remarkable properties:

• without rapid annealing of the hot-rolled sheet, thanks to better control of the temperature at the end of hot rolling and of winding, and provided that the manganese content contained in the composition of the steel is limited.

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

• en l'absence de recuit initial et avec un seul laminage à froid.

This annealing of elimination of the stresses due to cutting, causes a significant reduction in losses without degradation of the aptitude for magnetization:

• in the absence of initial annealing and with a single cold rolling.

Claims (5)

1. Method for manufacturing a non-grain-oriented magnetic steel sheet starting from the vacuum smelting of a steel having a composition of:

   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 rest being iron and inevitable impurities, said steel, made in slab form, being subjected in succession to: a hot-rolling operation with a slab reheat temperature below 1300°C and a temperature, at the end of hot rolling, of below 950°C, the hot-rolled strip being coiled at a temperature above 550°C; an optional shot-peening operation; and a pickling operation, and then cold-rolled with a reduction ratio of greater than or equal to 25% in one cold-rolling operation down to a thickness of less than or equal to 1.5 mm, the cold-rolled strip being subjected to a final annealing operation.
2. Method according to claim 1, characterized in that the one cold rolling operation is carried out with a reduction ratio of between 25 and 90%.
3. Method according to claims 1 to 2, characterized in that the final annealing is carried out on the run at a temperature between 700 and 1050°C for a time of less than 10 min.
4. Method according to claims 1 to 3, characterized in that, furthermore, after the final annealing, the precut steel sheet is subjected to a stress-relief annealing operation.
5. Method according to claim 4, characterized in that the stress-relief annealing is carried out at a temperature above 650°C for a time of greater than 3 min.

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