Method of making magnetically soft intermediate product

Abstract

A method of making a soft magnetic intermediate product of metal with particularly good magnetization behavior, the method comprising the following method steps: production or provision of a metallic, rollable blank of a metallic product, preliminary rolling of the metallic blank with a defined degree of deformation to an intermediate thickness, the degree of deformation being matched to a critical or postcritical degree of rolling to be observed during subsequent rolling, heat treatment of the prerolled blank, preferably annealing of the prerolled blank, rolling of the blank with a critical or postcritical degree of rolling to a final thickness and subsequent annealing to set a defined grain size and finishing of the intermediate product.

Claims

1. A method of making a soft, metallic, and magnetic intermediate product, the method comprising the steps of: manufacturing or providing a metallic, rollable blank, prerolling the metallic blank with a defined degree of deformation to an intermediate thickness, the defined degree of deformation being matched to a critical or postcritical degree of rolling to be maintained during subsequent rolling, heat treating the prerolled blank, rolling the heat-treated blank with a critical or postcritical degree of rolling to a final thickness, thereafter annealing the rolled blank to set a defined grain size therein, and finishing the the annealed blank.

2. The method according to claim 1, wherein the blank is a hot strip made of a ferritic or unalloyed steel.

3. The method according to claim 1, wherein the blank is prerolled by rough rolling with a degree of deformation of 30-80%.

4. The method according to claim 1, wherein heat treating of the prerolled blank takes place at a temperature of 550° C.-700° C.

5. The method according to claim 4, wherein the annealing is carried out for up to 50 hours.

6. The method according to claim 1, wherein the critical degree of rolling is between 8 and 25%.

7. The method according to claim 1, wherein the annealing following the rolling with the critical degree of rolling takes place at a temperature of up to 710° C.

8. The method according to claim 7, wherein the annealing following the rolling with the critical degree of rolling takes place over a period of up to 80 hours.

9. The method according to claim 1, further comprising the step of: carrying out an upstream heat treatment before the prerolling of the blank.

10. The method according to claim 9, wherein the upstream heat treatment takes place at a temperature between 650° C. and 800° C.

11. The method according to claim 9, wherein the upstream heat treatment is carried out over a period of up to 60 hours.

12. The method according to claim 1, the finishing comprises the step of: finish rolling the blank.

13. The method according to claim 12, wherein the finish rolling takes place with a degree of deformation between 0.1 and 2%.

Description

(1) In the drawing, an embodiment of the method according to the invention is shown and described in more detail below.

(2) Therein:

(3) FIG. 1 shows a schematic sequence of the method;

(4) FIG. 2 is a table of the magnetic and mechanical properties of a carbon steel after completing the method with different degrees of rolling.

(5) FIG. 1 shows schematically the sequence of a method of making a metallic soft magnetic intermediate product with particularly good magnetization behavior.

(6) The method is used to produce an intermediate product in the form of a cold strip made of steel.

(7) For this purpose, a metallic, rollable blank made of steel is produced or provided as the starting product, namely a semifinished product, preferably hot strip made of an unalloyed steel whose material has isotropic properties.

(8) The hot strip is first prerolled, the prerolling being carried out to an intermediate thickness. The degree of deformation during prerolling is between 30 and 80% and is matched to a critical or postcritical degree of rolling to be set during subsequent rolling to the final thickness, so that when rolling to the final thickness only a slight deformation in the critical or postcritical deformation area of the material with a small amount of rolling is necessary. The degree of deformation during prerolling to the intermediate thickness is therefore dependent on the critical or postcritical degree of rolling during rolling to the final thickness.

(9) The prerolled blank is then heat-treated, with annealing preferably being carried out at a temperature between 550 and 700° C. for a period of up to 50 hours.

(10) After annealing, rolling takes place, with the blank being rolled to its desired final thickness with the critical or postcritical degree of rolling, and further annealing connected to rolling at a temperature of up to 710° C. over a period of up to 80 hours. By rolling with the critical or postcritical degree of rolling and the subsequent annealing, grain growth is brought about in the metallic structure, which enables easier and faster magnetization and demagnetization of the material.

(11) The deformation must be carried out with at least a critical degree of rolling, since if the material is deformed by rolling with a degree of rolling that is less than the critical degree of rolling, no or at least no significant grain growth occurs in the structure. Only when the deformation has reached the critical degree of rolling is a clear grain growth brought about in the structure, with the maximum grain size being set during deformation with the critical degree of rolling. If the degree of rolling is greater than the critical degree of rolling (postcritical degree of rolling), the grain size decreases again, the grain size becoming smaller as the postcritical degree of rolling increases. In this way, at least one critical or a postcritical degree of rolling is set, it being possible to set the grain size in a defined manner via the degree of rolling and, moreover, the magnetic properties. In the example shown, the degree of rolling [ε] is between 11 and 25%. The results obtained with regard to the magnetic and mechanical properties, which are achieved by forming the material with such degrees of rolling, are shown in the table in FIG. 2. The lower the degree of rolling selected, the larger the created grains in the structure and the better the magnetization properties, that is the easier and faster the material can be magnetized. At the same time, however, the mechanical properties of the material deteriorate with increasing grain size.

(12) The grain size and the associated magnetic and mechanical properties are therefore set specifically via the critical or postcritical degree of rolling and adapted to the respective later application of the material, so that a suitable intermediate product can be provided specifically for the respective application.

(13) The soft magnetic properties that are introduced into the material in this way enable the intermediate product to be further processed, also by forming, for example deep-drawing or bending, into end products with particularly good soft magnetic properties, without the end products having to be subjected to a subsequent special annealing. This eliminates the need for time-consuming and expensive posttreatment of the individual products.

(14) After rolling and subsequent annealing, the blank is finish rolled with a degree of deformation of for example 0.7%. This sets the exact thickness of the material as well as the flatness and the quality of the surface.

(15) In addition, there is the possibility of initially supplying the blank to annealing before roughing in order to prepare the material for the subsequent method steps and to bring the structure to an improved initial state. This annealing is preferably carried out at a temperature between 650 and 800° C.

(16) The annealing results in a change in the carbon content in the structure. Before the heat treatment, the carbon is randomly distributed in the structure and is deposited on the grain boundaries due to the annealing. As a result, the carbon does not later negatively hinder the magnetization of the material and the soft magnetic properties of the intermediate product can be improved. An intermediate product of particularly good quality can be provided.

(17) After the upstream heat treatment, the further method steps are carried out.

(18) The method makes it possible to provide an intermediate product with particularly good soft magnetic properties, which can be set in such a way that a subsequent reshaping of the material, for example into deep-drawn or stamped-bent parts with particularly good soft magnetic properties, is possible without affecting the end products must then be subjected to a special annealing or comparable heat treatment.

(19) The invention is not restricted to the embodiment, but is variable in many ways within the scope of the disclosure.

(20) All individual and combination features disclosed in the description and/or drawing are regarded as essential to the invention.