JP4648797B2 - Method for producing grain-oriented electrical steel sheet with excellent coating adhesion - Google Patents

Description

  The present invention relates to a grain-oriented electrical steel sheet, which is a soft magnetic material that is most commonly used industrially as an iron core material for transformers, rotating machines, reactors, and the like, and particularly relates to a manufacturing method thereof.

  The grain-oriented electrical steel sheet is expressed by the Miller index used in physics as <100>, and the most easily magnetized orientation based on the crystal lattice is relatively aligned for each crystal grain. Therefore, it is a material desirable as an industrial product having excellent magnetization characteristics in a specific direction as if it were a single-crystal steel plate even though it is a polycrystalline steel plate. A grain-oriented electrical steel sheet utilizes a phenomenon generally called secondary recrystallization to align the easy axis of crystal in a specific direction. N. Patent Document 1 by Goss, Patent Document 2 by Taguchi and Sakakura, Patent Document 3 by Imai and Saito, and the like. According to these techniques, secondary recrystallization is performed by combining cold rolling and annealing by precipitating MnS and other various compounds as a second dispersed phase commonly referred to as an inhibitor in steel containing a large amount of Si. Secondary recrystallization is developed.

  A common feature of these production methods is that after cold rolling, decarburization annealing is performed prior to finish high temperature annealing. Carbon is actually an element that is completely unnecessary for the progress of secondary recrystallization itself, but in the method of Patent Document 2 of Taguchi and Sakakura, a component for appropriately distributing and precipitating MnS and AlN, that is, secondary recrystallization. It must be removed from the steel before the final high-temperature annealing step for secondary recrystallization. Further, in this method, the steel ingot or slab must be heated at an ultrahigh temperature of 1350 ° C. or higher prior to hot rolling.

  In order to avoid this burden, Tatsu et al. Invented a new technique disclosed in Patent Document 4, and this method reduces the necessity of previously containing carbon in the steel and omits decarburization annealing. However, in this method, it is necessary to dope nitrogen into the steel from the outside of the steel sheet from cold rolling to finish high temperature annealing, and the introduction of the resulting annealing process is inevitable. In conclusion, in the prior art, in view of the metallurgical principle of secondary recrystallization, the annealing process as an independent process sandwiched between decarburization annealing or cold rolling and finishing high-temperature annealing that is originally unnecessary is omitted. Is difficult. Regarding this problem, the invention by Kawakami et al., For example, Patent Document 5 can be further studied. They applied an old method and succeeded in obtaining a secondary recrystallized steel sheet without containing carbon in the steel at the melting stage. In practice, however, annealing after cold rolling prior to finish high temperature annealing cannot be completely omitted. Because, in order to form a film, which is a product requirement for grain-oriented electrical steel sheets, a slight oxidation layer must be formed on the steel sheet surface to react with a part of the annealing separator necessary for finishing high temperature annealing. It was technically easier to introduce annealing in a humid atmosphere. Furthermore, the steel ingot or slab heating temperature prior to hot rolling must be an extremely high temperature of 1350 ° C. or more, and it is still a technology that imposes a heavy burden.

  On the other hand, it is also possible to manufacture grain-oriented electrical steel sheets by adding appropriate amounts of Ti and C to steel and precipitating TiC precipitates as inhibitors, and subjecting the cold-rolled sheet directly to finish high temperature annealing. At this time, the slab heating temperature is 1250 ° C., which is equivalent to that of ordinary steel, and can be established as a manufacturing technique with less burden.

However, the TiC inhibitor has a point to be improved. The precipitate used as an inhibitor has the effect of remarkably hindering the movement of the 180 ° magnetic domain in the magnetization process as a final electrical steel sheet, and therefore, in order to exert the iron loss characteristic, which is the most important magnetic characteristic, It must be completely removed after recrystallization is complete. That is, so-called purification must be performed. For example, MnS and AlN used before TiC are high-temperature annealing that sometimes reaches 1200 ° C. after secondary recrystallization, and by introducing dry hydrogen into the atmosphere, H ₂ S and NH ₃ It was possible to remove completely using a gasification reaction. However, in the case of TiC, the CH4 production reaction, which is a hydrogenation reaction, is unstable at such a high temperature and is insufficient to complete purification. The TiC inhibitor deposited in the steel forms a TiC film on the steel plate surface by annealing at high temperature and long time in dry hydrogen, and the inclusions in the steel plate may be substantially eliminated. Requires enormous consumption of heat energy.

U. S. Pat. 1965559 Japanese Patent Publication No. 38-4710 Japanese Patent Publication No. 38-8214 JP 59-56522 A JP-A-55-73818

  The present invention provides a final method for producing magnetic properties in a method for producing a grain-oriented electrical steel sheet using TiC as an inhibitor, which can reduce a large process burden when compared with general steel in the production of a grain-oriented electrical steel sheet. The aim is to efficiently purify the high-temperature finishing process, which is a process, and to reduce energy consumption during production.

  Therefore, in the present invention, when a carbon element such as Ti, Zr, and Hf is attached to the surface of the steel sheet by sputtering and carbon is sucked up during the finish high temperature annealing, the same coating as TiC formed by annealing in dry hydrogen. I thought that it would be possible to remove the inclusions in the steel and tried it.

  However, in this case, conversely, the parent carbon element diffused and penetrated into the steel, and TiC could not be removed, resulting in failure. Then, next, the present inventors can reprecipitate TiC in the steel on the surface of the steel sheet by finish high temperature annealing (for a long time) to form a stable film. We worked on elucidating the mechanism of whether C could not be sucked up to form a stable film. That is, many experiments such as changing the coating amount of the parent carbon element or alloying were conducted to investigate whether the decarburization reaction proceeds. Among them, there are some cases where the parent carbon element does not enter the steel, a carbide film is formed on the surface layer of the steel sheet, and the TiC precipitate which is an inhibitor is sufficiently removed in the base iron under the film. Things were found. Therefore, when the common points of these conditions were examined, it was found that these were all cases in which an alloy of parent carbon element and Fe was coated.

  Therefore, the reason why the carbide film formed by alloying with Fe is stabilized and can be purified is considered. Here, all of the parent carbon element groups used in the experiment are metal elements and can be alloyed with Fe. Therefore, it can be considered that diffusion in Fe is easy. On the other hand, the physical parameter causing diffusion is the gradient of chemical potential according to Fick's second law. This is an activity gradient macroscopically, and in the case of an alloy, it is often proportional to the concentration gradient. Therefore, when a metal element such as Ti, Hf or the like is coated on the steel plate as it is, the concentration difference is 100% and 0%. However, if the Fe alloy is coated and coated, the concentration difference between the coating composition and the base iron composition is I thought that the driving force of diffusion would decrease.

  For example, in an alloy sputtering of Fe and Ti, the coating on the surface of the steel sheet after coating with a composition of 1: 3 and having a thickness of 2 μm and purifying annealing while completing secondary recrystallization by annealing up to 1200 ° C. in dry hydrogen. -The surface property of the ground iron was analyzed by glow discharge spectroscopic analysis: GDS. The result is shown in FIG. Moreover, (b) what annealed after coating pure Ti as a comparative material, and (c) what did not coat and formed the stable film in high temperature finishing annealing in dry hydrogen (long time) are shown collectively. In the figure, the coating part, the interface part, and the ground iron part are clearly shown, but in the figure (a), the width of the interface region is equivalent to (c), and it is understood that sufficient smoothness is obtained. Further, it can be understood that the interface region is wide under the condition (b), that is, the interface between the ground iron and the coating is not smooth, and the iron loss property is not preferable. In addition, the magnetic material at this time is a material having a thickness of 0.23 mm. (A) B8 = 1.91T, W17 / 50 = 0.83 w / kg, (b) B8 = 1.92T, W17 / 50 = 1.15 w / kg, (c) B8 = 1.90 T, W17 / 50 = 0.87 w / kg, (b) was extremely bad in iron loss, whereas (a) was (c) And the same level.

The present invention has clarified the principle as described above, but the present inventors have further searched and studied this applied technology based on the above principle. That is, in this technique to which a compound reaction of a parent carbon element was applied, a test was performed on the assumption that the starting material for the reaction may be a compound instead of an element. As an example, TiO ₂ was applied. TiO ₂ could be supplied in a fine powder of about 1 μm, and the application to the steel plate surface was carried out with a water slurry, and it was possible to sufficiently adhere to the steel plate by drying immediately. In this way, an amount of 10 g / m ² was applied to a cold-rolled steel sheet, made into a tight coil and subjected to finish annealing, and a residual C content of 25 ppm could be achieved by annealing at 1150 ° C. × 40 hr. When MgO was applied to the steel plate used at this time instead of TiO ₂ , the amount of residual C was 95 ppm under the same conditions. Moreover, since the reaction activity of Ti in the compound is low, the coating film-base metal interface was smooth although it was a natural result.

Possible reactions here are:
TiO ₂ +3 C → TiC + 2CO ↑
The Carbothermal reaction represented by Here, C is solute C in steel. This reaction is a reaction involving gas, and proceeds more and more as CO on the right side is replaced with atmospheric gas and removed from the reaction.

  In this method, the effect was also exhibited by oxides of Ti, Nb, Hf, Ta, V, and Zr, which are IVa and Va group elements. Even when nitrides and sulfides were used, the effect sometimes appeared, but this was limited to when the atmosphere was only dry hydrogen. That is, this is a case where the combined N and S are considered to be released into the atmosphere by NH3 and H2S which are gases, respectively. This is because in other Ar and vacuum atmospheres, N and S instead penetrate into the steel, and TiN, TiS, etc. are formed as inclusions, resulting in deterioration of iron loss characteristics.

The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%, Si: 2% to 4.5%, Ti: 0.1% to 0.4%, C: 0.035% to 0.1%, the balance Fe and inevitable impurities After steel is cast, hot-rolled, cold-rolled to obtain a product sheet thickness, one or more oxides, nitrides or sulfides of Nb, Hf, Ta, Zr are formed on the steel plate surface . A method for producing a grain-oriented electrical steel sheet, characterized in that oxides, nitrides or sulfides containing 50% or more in total are applied or adhered, and then subjected to finish high temperature annealing.

  According to the present invention, in the method for producing a grain-oriented electrical steel sheet using TiC as an inhibitor, the inhibitor is efficiently removed after the completion of secondary recrystallization, while suppressing the energy consumption in the purification of finishing high-temperature annealing, and providing good magnetic properties. Can be secured.

  Next, an embodiment of the present invention will be described.

  First, the components of steel will be described.

  When the Si content exceeds 4.5%, embrittlement becomes severe, and it becomes difficult to obtain a predetermined shape by processing such as slitting and shearing, so the Si content is set to 4.5% or less. If it falls below 2%, eddy current loss of energy loss generated by use at a commercial frequency increases and the magnetic properties deteriorate, so it was made 2% or more.

  When Ti was less than 0.1%, extreme iron loss characteristic deterioration due to secondary recrystallization failure occurred, so it was made 0.1% or more. If it exceeds 0.4%, a large amount of oxide inclusions are formed in the molten steel during casting after refining, causing nozzle clogging and extremely deteriorating productivity.

  When C is less than 0.035% at the time of melting, secondary recrystallization does not occur due to high-temperature annealing after cold rolling, so 0.035% or more. If it exceeds 0.1%, it is difficult to make the amount of carbon in the steel 0.0005% or less by purification annealing after the completion of secondary recrystallization, so it was made 0.1% or less.

  Regarding elements applied to the steel sheet surface prior to purification annealing, first of all elements other than gas or liquid at room temperature, such as O, N, and Hg, from Li of atomic number 3 to U of atomic number 92, Application to the steel sheet surface was performed. For metal elements, a sputtering method was used, and for nonmetal elements, a powder was dissolved in ethyl alcohol to form a slurry and then dried. As a result, the purification behavior could be classified completely corresponding to the group number of the periodic table. That is, Ia, IIa and IIIa groups did not react with various impurities in the steel or O and H2O which are slightly present in the atmosphere, and the effect of sucking up C in the steel was not recognized. Groups VIa, VIIa, VIIIa and groups I-VIIb have alloyed or formed compounds with Fe rather than C. As a result, only the 6 elements of IVa and Va group Ti, Nb, Hf, Ta, V, and Zr reacted with C in the steel and exhibited the purification ability.

  Next, it is the situation of magnetic characteristics when these elements are applied and purified, but when applied using pure materials that are not combined, sputter coating, powder slurry coating, plating coating, etc. Irrespective of the coating form, the unevenness of the interface between the coating and the ground iron was severe, and even if a sufficient B8 value was obtained, the iron loss characteristics were poor. Therefore, when alloyed with Fe, Co, Ni, Mn, and Cr, and coated, when these alloying elements were 20% or more, a sufficiently smooth interface was obtained, and good iron loss characteristics were obtained. , Hf, Ta, V, Zr were made into an alloy of 80% or less.

  Furthermore, when the oxide of Ti, Nb, Hf, Ta, V, Zr is made into fine powder of 10 μm or less, dissolved in slurry with water, dried, and subjected to purification, the interface between the formed carbide coating and the iron As a result, the purification was completed with a smoothness, and a sufficiently good iron loss value was obtained. In addition, N and S were also applied, but when annealing was performed in He, Ar, and a vacuum atmosphere, N and S diffused into the steel and deteriorated the iron loss. On the other hand, when annealed in H2, there was no entry of N or S into the steel, and good iron loss characteristics were obtained.

  Here, the temperature of the finish high temperature annealing is performed in the range of 1000 ° C. to 1250 ° C., and if it is less than 1000 ° C., purification is insufficient, and if it exceeds 1250 ° C., the energy is expensive.

After continuously casting a steel of Si: 3.3 wt%, Ti: 0.21 wt%, C: 0.08 wt% to form a slab having a width of 1 m, the slab is heated at 1270 ° C. to a thickness of 2.0 mm. And cold-rolled to a thickness of 0.22 mm. Thereafter, the powder having the components shown in Table 1 and adjusted to have an average particle size of 1 to 5 μm was mixed at a rate of 35 g with respect to 100 g of water, and stirred for 30 minutes with a homogenizer to obtain a uniform slurry. It was coated with a roll coater made of a rubber roll and wound up on a tight coil having an inner diameter of 500 mm. This coiled sample was loaded into a box annealing furnace, heated to 1200 ° C. at a heating rate of 50 ° C./hr by gas heating, and then maintained for 15 hours. Such experiments were performed in three atmospheres in Ar: (i) H2, (ii) Ar, (iii) 1/20 atm. The results of iron loss at this time are shown in Table 2 .

In the case of annealing in hydrogen, good iron loss values are obtained except for the condition of l which does not include the compounds of Zr, Ta, Nb and Hf .

(A) is a figure which shows the GDS analysis result of the coating-base metal interface property of the steel plate surface at the time of refined annealing after coating Ti: 75% and Fe: 25% alloy, (b) is purified annealing after coating pure Ti The figure which shows the GDS analysis result of the coating film-steel interface property of the steel plate surface in the case of carrying out, (c) is the coating film of the steel plate surface-iron in the case where a stable coating film is formed by annealing at high temperature and long time during drying without coating. It is a figure which shows the GDS analysis result of an interface property.

Claims (1)

Steel comprising, by mass%, Si: 2% to 4.5%, Ti: 0.1% to 0.4%, C: 0.035% to 0.1%, the balance being Fe and inevitable impurities Is cast, hot-rolled, cold-rolled to obtain a product plate thickness, and a total of 50 oxides, nitrides or sulfides of one or more of Nb, Hf, Ta, and Zr on the steel plate surface. A method for producing a grain-oriented electrical steel sheet, comprising applying or adhering an oxide, nitride or sulfide containing at least 50% , followed by finish high temperature annealing.

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