JP4598709B2 - Non-oriented electrical steel sheet with excellent magnetic properties after strain relief annealing and its manufacturing method - Google Patents

Description

  The present invention relates to a non-oriented electrical steel sheet used as an iron core material for electrical equipment and a manufacturing method thereof, and particularly to a non-oriented electrical steel sheet having excellent magnetic properties after strain relief annealing.

  In recent years, due to the increase in energy saving of electric appliances worldwide, non-oriented electrical steel sheets used as iron core materials for rotating machines have been required to have higher performance characteristics.

  As is well known, increasing the Si and Al contents to increase the specific resistance and increasing the crystal grain size are the main methods for reducing the iron loss. In recent years, non-oriented electrical steel sheets having a high Si and Al content and a large crystal grain size have been used up to small general-purpose motors and compressor motors. However, increasing the crystal grain size increases the sagging and burrs, and has the problem of significantly deteriorating the punching processability of the motor core.

  Regarding the technique to improve the punching workability, the impurities in the steel, S and Ti, are reduced or made harmless, and the grain size before strain relief annealing to be processed is reduced, and grain growth is achieved by strain relief annealing. The following methods have been proposed for achieving both low iron loss and low iron loss.

Patent Document 1 adds REM, Patent Document 2 mixes and adds Ca alloy and desulfurization flux, Patent Document 3 adds Ca alloy, Patent Document 4 combines Mg or Mg, Ca, and REM. It is a method of adding. All of these methods add desulfurized flux, REM, Ca alloy, and Mg alloy to molten steel that has been adjusted for components such as Si and Al to reduce S in the molten steel, while remaining in the steel. And produces coarse sulfides. However, these additive elements have strong oxidizing power, and in some cases, Ti in the molten steel is remarkably increased by reducing TiO ₂ in the slag. In this case, even if the reduction and the coarsening of the sulfide can be achieved at an angle and manufacturing cost, a new problem arises that the crystal grain growth after the stress relief annealing is rather deteriorated.

  Therefore, as shown in Patent Document 5, the present applicant has proposed a method for improving the grain growth after strain relief annealing by coarsening the precipitate by combining MnS and Ti precipitate, In some cases, precipitation of Ti is not sufficient, and the effect is not sufficiently exhibited. Further, Patent Document 6 discloses a method for improving grain growth after strain relief annealing even if mixing of Ti: 15 to 50 ppm is allowed, but for that purpose, 700 to 900 ° C. before the final cold rolling. Therefore, annealing for 30 minutes to 10 hours and slow cooling to 500 ° C. at 50 ° C./min or less are necessary, and the productivity is remarkably deteriorated.

  On the other hand, as shown in Patent Document 7, the present applicant has proposed a method for improving grain growth after strain relief annealing by utilizing precipitation and re-solidification of Ti precipitates that significantly worsen grain growth. . Although this method provides low iron loss due to coarse grains grown abnormally, new problems arise that the grain growth itself is unstable and the magnetic flux density decreases.

JP-A-8-325678 Japanese Patent Laid-Open No. 10-183227 Japanese Patent Laid-Open No. 10-183309 Japanese Patent Laid-Open No. 2002-302746 JP 2005-179710 A JP-A-11-158589 JP 2005-179746

  In view of the above-mentioned problems, the present invention stably obtains a non-oriented electrical steel sheet excellent in crystal grain growth and magnetic properties after strain relief annealing without inhibiting productivity while allowing a certain amount of Ti content. A method is provided.

The present invention has been made to solve the above-described problems, and has the following gist.
(1) By mass%, Si: 3.5% or less, Mn: 0.15% or less, Al: 0. 1% to 3.0%, C: 0.0050% or less, Ti: 0.0020% to 0.010%, S: 0.0010% to 0.0050%, the balance Fe and inevitable In the non-oriented electrical steel sheet made of impurities, the solid solution Ti in the steel sheet before strain relief annealing is less than 0.0020% by mass , the average crystal grain size before strain relief annealing is 40 μm or less, and both Ti and S A non-oriented electrical steel sheet having a precipitate of Ti sulfide or Ti carbosulfide containing at least 60 μm in average grain size after strain relief annealing.
(2) The non-oriented electrical steel sheet according to (1) , further containing Sn: 0.0050% to 0.20% by mass.
(3) When producing the non-oriented electrical steel sheet according to (1) or (2) , in the production process comprising steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, and finish annealing, components in steelmaking A method for producing a non-oriented electrical steel sheet, wherein the molten steel after adjustment is not subjected to desulfurization treatment with any one or more of desulfurization flux, Ca alloy, Mg alloy, or REM.
(4) The method for producing a non-oriented electrical steel sheet according to (3) , wherein the slab heating temperature before hot rolling is 1000 ° C. or higher and 1150 ° C. or lower.
(5) The method for producing a non-oriented electrical steel sheet according to (3) or (4) , wherein hot-rolled sheet annealing is performed at 900 ° C. or higher and 1150 ° C. or lower prior to pickling.

  The present invention improves crystal grain growth and magnetic properties after strain relief annealing without reducing Ti or annealing for a long time, and can solve the problems of increased cost and reduced productivity.

  The inventors of the present invention have conducted intensive research on a method for improving crystal grain growth after strain relief annealing without extremely reducing Ti and without annealing for a long time during the manufacturing process. As a result, it was found that a considerable amount of Ti was dissolved before strain relief annealing, and that it was finely precipitated as Ti carbide during strain relief annealing, which markedly hindered crystal grain growth. As a result of further research on the method of reducing this solid solution Ti, it was found that the generation of Ti sulfide or Ti carbon sulfide reduces the amount of solid solution Ti and improves the grain growth after strain relief annealing. As a result, the present invention has been completed.

  The reason for limiting the numerical values of the steel composition in the non-oriented electrical steel sheet according to the present invention will be described below.

  Si is an effective element for increasing the electric resistance, but if added excessively, the cold rolling property is remarkably deteriorated, so the upper limit was made 3.5%.

  Mn is an element that generates sulfide (MnS), and is generally added to about 0.2% or more in a non-oriented electrical steel sheet. However, in the present invention for forming Ti sulfide or Ti carbon sulfide, it is necessary to suppress the formation of MnS, and the upper limit of Mn is defined as 0.15%. More desirably, it is 0.10% or less.

  Al is an element necessary for deoxidation and fixing nitrogen in steel, and for that purpose, it is necessary to add 0.1% or more. In addition, it is an element effective for increasing electrical resistance like Si, but if the added amount exceeds 3.0%, it causes hardness increase like Si and deteriorates castability. The upper limit was 3.0%.

  Since C is well known to cause magnetic aging, it is defined as 0.0050% or less. However, since it is an element necessary for the production of Ti carbon sulfide, it is preferably 0.0010% or more.

  Ti is an essential element of the present invention, and is specified to be 0.0020% or more from the viewpoint of producing sulfide or carbon sulfide. However, if the Ti content becomes too high, the crystal grain growth becomes worse regardless of the control, so the upper limit was made 0.010%.

  S is an essential element of the present invention. If it is less than 0.0010%, Ti sulfide or Ti carbon sulfide is insufficiently produced, so it was specified to be 0.0010% or more. In order to produce a precipitate more stably, it is preferably 0.0020% or more, and more preferably 0.0030% or more. However, if the S content becomes too large, the crystal grain growth deteriorates regardless of the control, so the upper limit was made 0.0050%.

  The amount of solid solution Ti was specified to be less than 0.0020% because 0.0020% or more significantly suppresses crystal grain growth. More preferably, it is less than 0.0015%, More preferably, it is less than 0.0010%. The solute Ti amount specified here is obtained by obtaining the Ti concentration of the extraction residue collected by electrolytic treatment after removing the surface coating with mechanical polishing or hot alkali on the steel plate sample before strain relief annealing, and from the total amount of Ti in the steel plate It is obtained by subtracting.

  Sn has the effect of improving the magnetic flux density by reducing the {111} -type orientation which is undesirable for magnetism. Moreover, it has the effect of suppressing iron loss deterioration by suppressing the nitrogen contained in the annealing atmosphere from entering the steel sheet during finish annealing or strain relief annealing. You may add actively for these purposes. In that case, 0.0050% at which the effect was obtained was defined as the lower limit, and 0.20% at which the effect was saturated was defined as the upper limit.

  Ti sulfide or Ti carbon sulfide is an important precipitate in the present invention. In the idea of the present invention, it has been found that the precipitation temperature of Ti carbide is around 800 ° C., while the precipitation temperature of Ti sulfide or Ti carbon sulfide is around 1000 ° C. As mentioned above, it was found that the grain growth during strain relief annealing was improved by making the solid solution Ti amount before strain relief annealing 0.0020% or less, but when considering the manufacturing process, the precipitation temperature of both The difference is big. That is, if the Ti carbide precipitation treatment is performed, it is necessary to perform the treatment at about 800 ° C. However, in order to obtain a sufficient precipitation amount at such a low temperature, a long annealing time of 10 minutes or more is required. In order not to increase the number of conventional manufacturing processes, for example, it is necessary to double the hot-rolled sheet annealing, but the crystal grain size of the hot-rolled sheet, which is the purpose of hot-rolled sheet annealing at an annealing temperature of 800 ° C, is increased. In order to do so, annealing for 30 minutes or more is required. Therefore, as an actual manufacturing process, for example, restrictions such as performing hot-rolled sheet annealing by box annealing may occur. On the other hand, in the case of Ti sulfide or Ti carbosulfide, since it is a relatively high temperature of about 1000 ° C., the precipitation treatment is sufficient in a short time. For example, continuous annealing for about 60 seconds at 1000 ° C. is sufficient for hot-rolled sheet annealing, and it is not necessary to add an extra process or to anneal for a long time. In order to obtain such an effect, it is necessary that Ti sulfide or Ti carbosulfide be present inside the steel plate before strain relief annealing. An example of a method for confirming the presence is to extract an extract replica from a sample before strain relief annealing, observe the precipitate with a transmission electron microscope (TEM), and confirm both Ti and S peaks by EDS analysis. it can.

  The average grain size before strain relief annealing was specified to be 40 μm or less in order to improve the punching workability. When the crystal grain size exceeds 40 μm, the sagging and burrs of the punched end face become large, and the steel sheets cannot be laminated successfully. In order to obtain such a crystal grain size, the finish annealing temperature and the annealing time can be adjusted as appropriate. The crystal grain size after strain relief annealing was set to 60 μm or more because sufficient iron loss improvement could not be obtained if it was less than 60 μm.

  Next, the reasons for limiting the production conditions of the non-oriented electrical steel sheet in the present invention will be shown.

  Adding desulfurized flux, Ca alloy, Mg alloy and REM to the molten steel whose component adjustment has been completed is an effective means to reduce S or coarse precipitates in the steel. By these treatments, Ti sulfide or Ti carbon sulfide Since there is no point in depleting the S that produces, it is necessary not to perform these desulfurization treatments.

  In the slab heating before hot rolling, it is preferable to produce and coarsen Ti sulfide or Ti carbosulfide. The upper limit was set to 1150 ° C. or lower because it would dissolve at a temperature exceeding 1150 ° C. The lower limit was set to 1000 ° C. or higher in consideration of hot ductility.

  Similarly to hot rolling, hot-rolled sheet annealing was set to 900 ° C or higher and 1150 ° C or lower from the viewpoint of precipitate control. When the temperature is lower than 900 ° C., it takes time for precipitation and coarsening, and when the temperature exceeds 1150 ° C., solid solution of the precipitate advances, and the crystal grain growth worsens.

  Since the crystal grain size before cold rolling is an important factor that particularly affects the magnetic flux density, it can be appropriately adjusted in this temperature range in order to obtain the required grain size before cold rolling. The annealing time can be appropriately adjusted according to the crystal grain growth.

  In a laboratory vacuum melting furnace, it contains, in mass%, C: 0.0015%, Si: 1.5%, Al: 0.6%, S: 0.0029%, Ti: 0.0032%, Sn: 0.02%, the remaining Fe and inevitable A steel slab made of steel impurities with Mn changed from 0.05 to 0.5% by mass in 8 levels was prepared. These steel slabs were heated at 1100 ° C for 60 minutes, then immediately hot rolled to a sheet thickness of 2.5mm, and subjected to hot rolled sheet annealing at 1000 ° C for 60 seconds, with a single cold rolling. The plate thickness was 0.50 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 800 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. The crystal grain size before strain relief annealing was 30 μm or less for all samples. As shown in Table 1, in Mn: 0.15% or less of samples A1 to A4 that satisfy the conditions of the present invention, a good iron loss of 3.0 W / kg or less was obtained when the crystal grain size after strain relief annealing was 60 μm or more. .

  In a laboratory vacuum melting furnace, steel containing mass: C: 0.0032%, Si: 2.1%, Mn: 0.10%, Al: 0.3%, Ti: 0.0037%, the balance being Fe and inevitable impurities And the steel piece which changed S to 0.0005 to 0.0080% was produced. These steel slabs were heated at 1050 ° C for 60 minutes, and then immediately hot-rolled to a thickness of 2.0 mm, and subjected to hot-rolled sheet annealing at 950 ° C for 60 seconds, with a single cold rolling. The plate thickness was 0.50 mm. The cold-rolled sheet thus obtained was subjected to finish annealing at 770 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. The crystal grain size before strain relief annealing was 40 μm or less for all samples. As shown in Table 2, S: 0.0010% or more and 0.0050% or less of sample B3 to B6 satisfying the conditions of the present invention, the grain size after strain relief annealing is 60 μm or more and good iron loss of 3.0 W / kg or less. Obtained.

  In a laboratory vacuum melting furnace, steel containing mass: C: 0.0032%, Si: 2.1%, Mn: 0.10%, Al: 0.3%, Ti: 0.0037%, the balance being Fe and inevitable impurities In this case, the S was changed from 0.0005 to 0.0080%, and the molten steel after the component adjustment was subjected to desulfurization treatment with one or more of desulfurization flux, Ca alloy, Mg alloy and REM, and desulfurization treatment was not performed. A steel piece was prepared. These steel slabs were heated at 900-1250 ° C for 60 minutes, and then immediately hot-rolled to a sheet thickness of 2.0 mm, and then subjected to hot-rolled sheet annealing at 800-1250 ° C for 60 seconds. The plate thickness was 0.50 mm by cold rolling. The cold-rolled sheet thus obtained was subjected to finish annealing at 770 ° C. for 30 seconds and then subjected to strain relief annealing at 750 ° C. for 2 hours. As shown in Table 3, in the sample satisfying the conditions of the present invention, a good iron loss was obtained in which the crystal grain size after strain relief annealing was 60 μm or more and 3.0 W / kg or less.

Claims (5)

In mass%, Si: 3.5% or less, Mn: 0.15% or less, Al: 0. 1% or more and 3.0% or less, C: 0.0050% or less, Ti: 0.0020% or more and 0.010% or less, S: 0.0010% or more and 0.0050% or less, balance Fe and inevitable In the non-oriented electrical steel sheet made of impurities, the solid solution Ti in the steel sheet before strain relief annealing is less than 0.0020% by mass , the average crystal grain size before strain relief annealing is 40 μm or less, and both Ti and S A non-oriented electrical steel sheet having a precipitate of Ti sulfide or Ti carbosulfide containing at least 60 μm in average grain size after strain relief annealing.   Furthermore, Sn: 0.0050% or more and 0.20% or less are contained in the mass%, The non-oriented electrical steel sheet according to claim 1 characterized by things. In manufacturing the non-oriented electrical steel sheet according to claim 1 or 2 , in the manufacturing process consisting of steelmaking, hot rolling, hot-rolled sheet annealing, pickling, cold rolling, and finish annealing, the molten steel after component adjustment in steelmaking A method for producing a non-oriented electrical steel sheet, wherein the desulfurization treatment is not performed with any one or more of desulfurization flux, Ca alloy, Mg alloy, and REM. The method for producing a non-oriented electrical steel sheet according to claim 3 , wherein the slab heating temperature before hot rolling is set to 1000 ° C or higher and 1150 ° C or lower. The method for producing a non-oriented electrical steel sheet according to claim 3 or 4 , wherein the hot-rolled sheet annealing is performed at 900 ° C or higher and 1150 ° C or lower prior to pickling.