JPH0586454B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for producing an electrical steel sheet that has excellent magnetic properties and extremely good punchability. <Background technology> Generally, electromagnetic steel sheets are used as iron core materials for various transformers, ballasts, and various electric motors, but in recent years, from the viewpoints of downsizing, high performance, and energy saving of electrical products, There is an increasing demand for high-performance electrical steel sheets with even better magnetic properties. On the other hand, electromagnetic steel sheets undergo a punching and laminating process when being formed into the cores of transformers and electric motors, so they not only have excellent magnetic properties but also have good punchability. requested. For this reason, conventionally, when punching and forming electrical steel sheets, the surface is coated with an organic component such as acrylic resin to ensure electrical insulation and provide lubricity for the punching process. However, when assembling electrical products, the ends of the laminated iron cores are sometimes welded to secure them, and in this case, organic components in the coating film are removed during welding. Since it tends to evaporate and cause welding defects such as blowholes, there is a problem that the thickness of the coating film is inevitably limited. For this reason, there has been a strong desire to develop an electrical steel sheet whose material itself has excellent punchability. By the way, as the punching work of electromagnetic steel sheets continues, the punching die wears out, the clearance between the punch and the die gradually decreases, and the "burr" of the punched product increases. Therefore, when the "burr" becomes larger than a certain value, it becomes necessary to perform mold polishing. Therefore, in electromagnetic steel sheets, it is evaluated that a steel sheet that can be punched out more in one round of die polishing has better punching properties. In other words, to improve the punchability of electrical steel sheets,
As seen in free-cutting steel, it is said to be effective to increase the "tearability" of steel sheets during punching by including large amounts of precipitates and inclusions. However, in order to improve the magnetic properties of electrical steel sheets, it is necessary to reduce impurity elements such as C as much as possible, as well as suppress precipitates and inclusions, and the higher the quality of the electrical steel sheets, the worse the punching properties. There was an extremely troublesome problem. <Means for Solving the Problems> The present inventors have conducted research in order to solve the above-mentioned problems in the production of electrical steel sheets and to provide electrical steel sheets that have both excellent magnetic properties and good punchability. As a result of repeated efforts, the following findings were obtained. That is, (a) Steel containing a much larger amount of C than is commonly known in conventional electrical steel sheets is hot-rolled and cold-rolled in accordance with the normal electrical steel sheet manufacturing process, and then annealed under specific conditions. (b) When coarse graphite precipitates as described above, coarse graphite precipitates in the steel sheet substrate, and this improves the "tearability" of the steel sheet, resulting in a marked improvement in punchability. Since the amount of solid solute C is extremely small, and the precipitated graphite does not interfere with grain growth or movement of domain walls, the base material is made of silicon containing elements such as Si and Al that are effective in reducing overcurrent loss. If a ferrite structure is used, an electromagnetic steel sheet with magnetic properties comparable to conventional ultra-low C electromagnetic steel sheets can be obtained. This invention was made based on the above knowledge, and C: 0.1 to 1.0% (hereinafter, % representing the component ratio).
), Si: 3.5% or less, Ni: 2.0% or less, Al: 1.0% or less, Cu: 1.0% or less, and the balance is Fe and unavoidable impurities. An electrical steel sheet having both excellent punchability and magnetic properties can be obtained by hot rolling and cold rolling a steel made of It has the following characteristics. Next, the reason why the composition and treatment conditions of the steel material are numerically limited as described above in the method of the present invention will be explained. A Composition of material steel a C C is a component that precipitates as coarse graphite in the steel plate by prescribed annealing and improves the punchability of the steel plate, but if its content is less than 0.1%, coarse graphite will form. Precipitation becomes difficult and a sufficient effect of improving punching property cannot be secured, and on the other hand, if the content exceeds 1.0%, hot rolling becomes difficult.
The content was set at 0.1-1.0%. b Si Si is an effective component for improving the magnetic properties of electrical steel sheets and promoting the precipitation of graphite, but its content is
If it exceeds 3.5%, the workability of steel deteriorates, so
The Si content was set at 3.5% or less. Although Si exhibits a certain effect even in a very small amount, it is preferable to ensure a content of 0.1% or more. C Ni, Al, and Cu These components are also effective elements for promoting the precipitation of graphite, and even if added in a very small amount, they exhibit a certain effect, so one or more of them can be included. Even if more than 2.0% of Ni, more than 1.0% of Al, and more than 1.0% of Cu are contained, the effect of promoting graphite precipitation is not significantly improved, and this is not economically preferable, so the Ni content is 2.0%. and the Al content is 1.0% or less, and
The Cu content was set at 1.0% or less. B Recrystallization annealing temperature The recrystallization annealing carried out in the method of this invention is not only used to ensure the necessary structure for the electrical steel sheet, but also to improve punchability and solid solution C by precipitating graphite in the steel sheet matrix. This is to prevent the tendency of deterioration of magnetic properties due to
If the annealing temperature is less than 600℃, sufficient graphite precipitation will not be achieved and it will be difficult to stably secure satisfactory magnetic properties, and if the annealing temperature is 800℃.
Since the same result occurs even when the temperature exceeds 100°C, the recrystallization annealing temperature was set at 600 to 800°C. In this way, in the case of the above component system, the recrystallization annealing temperature that also serves as graphite precipitation is 600 to 800.
℃ is the most effective, but in order to complete the precipitation of graphite, it is preferable to adjust the soaking time depending on the components. Note that normal conditions are sufficient for hot rolling and cold rolling carried out in the method of the present invention, and box annealing is preferably employed for recrystallization annealing. Next, the present invention will be explained using examples and comparing with comparative examples. <Example> First, a steel slab having the composition shown in Table 1 was obtained by a conventional method (converter melting, ingot making, and blooming rolling), and then hot rolled to obtain 2.3 A hot-rolled coil with a thickness of mm was obtained, which was then pickled and then cold-rolled into a cold-rolled coil with a thickness of 0.5 mm. Next, the cold-rolled coil was further subjected to recrystallization annealing that also served as graphite precipitation annealing, and the magnetic properties and punchability of the obtained electrical steel sheet were measured.

[Table] (Note) * indicates that the conditions are outside the conditions of the present invention.

【expressed. The results obtained are shown in Table 3 together with the processing conditions. The punchability of electrical steel sheets is generally evaluated by measuring the number of punches until the burr reaches 50 μm, but this requires a huge number of test pieces and requires a large amount of mold. It also takes a lot of time to set up and measure. However, the present inventor found that by measuring the "variation relationship between punch stroke and punching load during one punching process" as shown in Figure 1, and comparing the results, it is possible to accurately evaluate the punchability of electrical steel sheets. It was discovered by et al. That is, in FIG. 1, the shear stroke (S) indicated by the arrow corresponds to the part where the material breaks in a shear manner due to its viscosity during punching, and the part that appears as a shear fracture surface on the punching fracture surface. It is.
Therefore, the smaller this shear stroke is compared to the plate thickness, the more brittle the material is punched and the smaller the burr. Therefore, when comparing the shear strokes, in particular, the formula: Shear stroke ratio=S /t×100(%) [where S: shear stroke, t: plate thickness] By comparing the shear stroke ratio, punching performance can be accurately evaluated. Therefore, "punching property" is expressed here as "shearing stroke". From the results shown in Table 2, it is clear that by treating steel with a composition that satisfies the conditions specified in the present invention according to the conditions specified in the present invention, an electrical steel sheet with excellent magnetic properties and punchability can be obtained. That is clear. Furthermore, Figure 2 shows the relationship between the shear stroke ratio and the shear strength for a steel sheet manufactured by the method of the present invention and a steel sheet manufactured from a conventional steel (extremely low C steel) having almost the same composition except for the C content. This is a graph comparing the relationship, and as can be seen from Fig. 2, the steel plate produced by the method of the present invention has less burr during punching and less wear on the mold than the conventional one. It is obvious at a glance that this is an electrical steel sheet with markedly improved punchability. In addition, “return”
For example, the actual number of punching cycles until the diameter was 50 μm was approximately 30,000 times for Comparative Example 10, whereas it exceeded 400,000 times for Inventive Example 1. By the way, Fig. 3 is a microscopic photograph showing the cross section of the electrical steel sheet manufactured by the method shown in Test No. 1, and sufficient graphite precipitation was clearly observed, and the punching property was improved. I can understand why it was done. In addition, when the amount of C dissolved in the matrix at this time was measured, it was confirmed that the value was 50 ppm or less. <Overall Effects> As described above, according to the present invention, it is possible to stably produce an electrical steel sheet that not only has excellent magnetic properties but also has extremely good punchability. This brings about industrially useful effects.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between punch stroke and load during punching of electrical steel sheets, Figure 2 is a graph comparing shear strength and shear stroke ratio between the inventive material and conventional material, and Figure 3 1 is a microscopic structure photograph of a cross section of an electrical steel sheet of the present invention obtained in an example.

Claims (1)

[Claims] 1 Contains C: 0.1 to 1.0%, Si: 3.5% or less, and Ni: 2.0% or less, Al: 1.0% or less, Cu: 1.0% or less, in terms of weight percentage. Contains more than one species, and the remainder is Fe.
Excellent punchability and magnetic properties are obtained by hot-rolling and cold-rolling steel containing unavoidable impurities and then recrystallizing it at 600 to 800°C to precipitate graphite. A manufacturing method for electrical steel sheets.