JP4665417B2 - Method for producing grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for producing a grain-oriented electrical steel sheet, and more particularly to a method for producing a method-oriented electrical steel sheet having excellent magnetic properties including a step of performing final cold rolling with a tandem rolling mill.

The _grain- oriented electrical steel sheet is required to have excellent magnetic properties, that is, high magnetic permeability represented by B ₈ value and low iron loss value represented by W _17/50 . Therefore, various means for accumulating crystal grains in the Goss orientation, that is, (110) [001] as much as possible have been proposed.

  Many proposals have been made in a process from a hot-rolled sheet annealing process to a decarburized annealing process. For example, in Patent Document 1, a cold-rolled sheet is heat-treated at a low temperature during rolling (hereinafter referred to as an aging process). Thus, means for improving the magnetic characteristics have been proposed. This means that interstitial solid solution elements C and N are diffused at a low temperature and fixed to the dislocations generated by rolling to prevent the movement of dislocations, and further shear deformation proceeds during cold rolling to form a rolling texture. It is to improve. Patent Document 2 discloses that the cooling rate at the time of hot-rolled sheet annealing or annealing before finish cold rolling (final cold rolling) is 30 ° C./s or more, and further during the finish cold rolling, the sheet temperature is 150 to 300 ° C. for 2 minutes. A technique for performing the above-described aging between passes twice or more is disclosed.

  All of the above means are static aging treatment means in which aging treatment is performed between passes of cold rolling, but unlike these, the dislocation generated by rolling deformation is immediately increased by increasing the steel plate temperature during rolling. , Means using the dynamic aging effect to fix N have also been proposed. For example, in Patent Document 3 and Patent Document 4, in the cold rolling process by a tandem rolling mill, the temperature of the rolled plate that is bitten into the work roll pair in at least one pass is 300 to 500 ° C. (Patent Document 3), 100 to 500 ° C. (Patent Document 4) has been proposed. These means are effective means for producing grain-oriented electrical steel sheets using a highly productive tandem rolling mill.

Japanese Patent Laid-Open No. 50-16610 JP-A-8-253816 Japanese Unexamined Patent Publication No. 1-215925 Japanese Unexamined Patent Publication No. 1-218705

  However, if the proposal described in Patent Document 1 or 2 is applied to a method of manufacturing a grain-oriented electrical steel sheet using a tandem rolling mill, the distance between stands in the rolling process is short in tandem rolling, and the sheet passing speed is Therefore, the heating and holding time of 2 minutes or more cannot be obtained, and the diffusion of C and N becomes insufficient, so that the magnetic characteristics cannot be sufficiently improved.

  On the other hand, the means disclosed in Patent Document 3 or 4 needs to increase the rolling temperature in order to obtain the effect sufficiently. In other words, the optimum temperature for dynamic aging of the steel sheet depends on the strain rate, and the higher the rolling speed, the higher the optimum temperature. Therefore, using a rolling mill with a high rolling speed such as a tandem rolling mill inevitably moves. The optimum temperature for target aging is also increased, and the tandem rolling mill has a short distance between stands, so that aging between passes cannot be expected so much. Therefore, it is necessary to further increase the rolling temperature. However, if the rolling temperature is shifted to the high temperature side and exceeds 300 ° C, the rolling oil is locally baked on the surface of the steel plate during rolling, resulting in unstable friction coefficient during rolling and variations in the finished plate thickness. This causes problems such as Furthermore, the surface oxide film (subscale) generated in the subsequent decarburization / primary recrystallization annealing process becomes non-uniform in the part where the rolling oil is baked, and the appearance deteriorates due to defective formation of the coating film or generation of patterns. Further, there arises a problem that the magnetic properties are deteriorated due to poor adhesion of the film.

  An object of the present invention is to solve the above-mentioned problems, and avoid the occurrence of events that are harmful to quality such as seizure of rolling oil while performing final rolling using a highly productive tandem rolling mill. It aims at proposing the manufacturing method of the grain-oriented electrical steel sheet from which the outstanding magnetic flux density is stably obtained.

  When the present inventor performs the final cold rolling by a tandem rolling mill, first, after expressing static aging, immediately after rolling at a predetermined temperature and a predetermined reduction ratio, the deformation band in the steel plate is obtained. The present invention has been completed with the knowledge that the formation form of is changed, and that the effect of improving the texture is promoted in combination with dislocation fixation by static aging.

In the present invention, by hot rolling a slab for grain- oriented electrical steel sheets containing C: 0.005 to 0.10% and Si: 2.0 to 4.5% by mass ratio , the obtained hot rolled sheet is subjected to hot rolled sheet annealing. When producing a grain-oriented electrical steel sheet by performing cold rolling by a tandem rolling mill and finishing it to the final thickness, and performing decarburization annealing and final finishing tempering on this, (1) the hot-rolled sheet annealing The subsequent cooling rate is 10 ° C./s or more between 700 and 150 ° C., and (2) the steel plate temperature T (K) and the residence time between stands between any of the stands until the final stand of the tandem rolling mill t (s) satisfies the following formula (1), and (3) the rolling material biting temperature of any of the stands after and between the stands of the tandem rolling mill is reduced to 80 ° C. or more and 300 ° C. or less. Rolling is performed at a rate of 20% or more.
Record
t ≧ 2 × 10 ^-9 × exp (10568 / T) (1)

In addition, the present invention, by mass rolling, slabs for grain- oriented electrical steel sheets containing C: 0.005 to 0.10% and Si: 2.0 to 4.5% are subjected to intermediate annealing on the obtained hot rolled sheets. When producing a grain-oriented electrical steel sheet by performing cold rolling with a tandem rolling mill twice or more across the surface and finishing it to the final thickness, and performing decarburization annealing and final finishing tempering on this, (1) Among the annealing, the cooling rate of the final intermediate annealing is set to 10 ° C / s or more between 700 to 150 ° C, and (2) the steel plate temperature T (K) between any of the stands up to the final stand of the tandem rolling mill And the residence time t (s) between the stands satisfy the formula (1), and (3) the rolling material biting temperature of any one of the stands after the last stand of the tandem rolling mill is 80 ° C. The rolling is performed at a temperature of 300 ° C. or lower and a rolling reduction of 20% or higher. In this case, hot-rolled sheet annealing can be performed on the hot-rolled sheet.

  According to the present invention, while performing final rolling using a highly productive tandem rolling mill, avoiding the occurrence of events that are harmful to quality such as seizure of rolling oil, stable and excellent magnetic flux density Can be manufactured.

  As the slab used as the starting material, those used for producing grain-oriented electrical steel sheets can be used without particular limitation. When showing a typical composition, it contains C: 0.005 to 0.10% by mass ratio, Si: 2.0 to 4.5%, and if necessary, precipitation type inhibitor components such as Al, N, S, Se, and Mn, or Contains grain boundary segregation type inhibitor components such as Cu, Sn, Sb, Mo, Te, Bi, and P. The basic component system and the preferred component system are as follows (the unit of component content is based on the mass ratio).

(Basic component system)
C: 0.005-0.10%, Si: 2.0-4.5%
C improves the crystal structure of the hot-rolled sheet by γ-α transformation during hot rolling, and fixes and disperses the dislocations generated during the final cold rolling, resulting in a static aging effect. It is a necessary element. If the content is less than 0.005%, the above effect is poor. On the other hand, if it exceeds 0.10%, it is difficult to perform sufficient decarburization by subsequent decarburization annealing, so the content in the starting material is 0.005 to 0.10%.

  Si is a useful component that improves the iron loss characteristics by increasing the electric resistance. However, if the content is less than 2.0%, the effect is small, and good iron loss characteristics cannot be obtained. However, if it exceeds 4.5%, cold rolling becomes difficult. Therefore, the Si content is in the range of 2.0 to 4.5%.

(Inhibitor component)
In addition to the above basic components, the starting material in the present invention is a known process, that is, hot rolling, hot rolling sheet annealing and / or one or more tandem rolling mills sandwiching intermediate annealing. Any component system capable of obtaining a unidirectional electrical steel sheet by sequentially performing cold rolling, decarburization annealing (also serves as primary recrystallization annealing) and final finish annealing (also serves as secondary recrystallization annealing and purification annealing). There are no restrictions due to the type and content of the inhibitor component. It is also possible to develop secondary recrystallized grains using the inhibitor component as described below, and as shown in JP-A-2000-129856 and the like, precipitation type inhibitors (AlN, MnS, It is also possible to develop secondary recrystallized grains without using MnSe or the like. According to the type of inhibitor component, its preferred content will be described as follows.

When using AlN inhibitors
Sol.Al: 0.01 to 0.05%, N: 0.004 to 0.012%
If the content of Sol. Al is less than 0.01%, the magnetic flux density decreases, and if it exceeds 0.05%, secondary recrystallization becomes unstable. Therefore, when using an AlN inhibitor, the content is in the range of 0.01 to 0.05%.

  If the content of N is less than 0.004%, the amount of AlN inhibitor is insufficient and the magnetic flux density is lowered. N, together with C, has the effect of fixing to dislocations and increasing static aging during the final cold rolling performed at 80 ° C. or higher. However, if its content exceeds 0.012%, surface defects called blisters frequently occur. Therefore, the content is made 0.004 to 0.012% of range.

When using MnSe and / or MnS inhibitors
Mn: 0.03-0.30%, Se and / or S (total): 0.01-0.05%
If the content of Mn is less than 0.03%, the absolute amount is insufficient as an inhibitor component. On the other hand, if it exceeds 0.30%, the inhibitor particle diameter becomes coarse and the crystal grain growth inhibiting power decreases. Therefore, when using MnSe and / or MnS type | system | group inhibitor, the content shall be 0.03-0.30% of range.

  If the total content of Se and S is less than 0.01%, the absolute amount is insufficient as an inhibitor component. On the other hand, if it exceeds 0.05%, purification by finish annealing becomes difficult. Therefore, these contents are in the range of 0.01 to 0.05% in total. S and Se can be used as inhibitors as MnS or MnSe, respectively, or can be used as a composite thereof, Mn (S, Se). Note that the AlN inhibitor and the MnSe and / or MnS inhibitor can coexist and a synergistic effect can be obtained.

In the case where no precipitation type inhibitor component is contained In this case, the contents of Al, N, Se and S which are precipitation type inhibitor forming elements are limited to be extremely low. Specifically, it is limited to Al: less than 100 ppm, S: 50 ppm or less, Se: 50 ppm or less. When these amounts are exceeded, it becomes difficult to obtain a secondary recrystallized structure by the action of texture inhibition. N is preferably 50 ppm or less in order to prevent the formation of Si nitride after purification annealing. It is also desirable to reduce the nitride forming elements Ti, Nb, B, Ta, and V to 50 ppm or less, respectively. This is to prevent the iron loss from deteriorating without disturbing the action of the texture inhibition.

  Inhibitor content and restrictions are as described above. In addition to these, as grain boundary segregation type inhibitors, Cu, Sn, Sb, Mo, Te, Bi, P, etc. are in the range of 0.005 to 0.3%, respectively. It can be included. These elements can be used alone or in combination, thereby improving iron loss. Further, Ni can be contained in the range of 0.005 to 1.50% for the purpose of improving the hot rolled sheet structure and improving the magnetic properties.

(Hot rolling)
The slab, which is a starting material having the above composition, is slab-heated at an appropriate temperature according to the component system, and then hot-rolled by hot rolling including rough rolling and finish rolling. When the precipitation type inhibitor component is contained, the slab heating temperature is heated to a temperature range of 1350 to 1450 ° C. in order to completely dissolve Al, Se, S and the like. On the other hand, in the case of a component system that does not contain a precipitation-type inhibitor component, if the slab heating temperature is too high, the inhibitor-forming component that is solid-dissolved during heating precipitates nonuniformly during hot rolling, thereby causing grain boundary migration. Since it is locally suppressed and the particle size distribution becomes extremely non-uniform and the development of secondary recrystallized grains in the Goth orientation is impeded, it is recommended to use a relatively low heating temperature, for example, 1250 ° C or less. . The hot rolling conditions do not need to be particularly limited, and may be performed under the conditions adopted for the production of the normal grain-oriented electrical steel sheet.

(Hot rolled sheet annealing, intermediate annealing)
The hot-rolled sheet thus obtained is directly subjected to cold rolling after the hot-rolled sheet annealing or without performing the hot-rolled sheet annealing to obtain a cold-rolled sheet having a final thickness. In the present invention, this cold rolling is performed by a tandem rolling mill, and the cooling rate after heating is set to 700 to 150 ° C. immediately before the rolling stage (hereinafter referred to as “final rolling stage”) for finally reducing the sheet thickness to the product sheet thickness. An annealing process is performed at 10 ° C./s or more. This has significance as a pretreatment for dissolving elements such as C before the final rolling stage, and synergistically expressing the effects of static aging and subsequent warm reduction in the subsequent final rolling stage.

  The annealing immediately before the final rolling stage is performed by hot-rolled sheet annealing when a so-called one-time method in which hot-rolled sheet annealing is performed to immediately cold-roll to the final sheet thickness is adopted. On the other hand, in the case of a so-called two-time method in which the cold rolling is performed by a plurality of rollings with the intermediate annealing interposed therebetween, the intermediate annealing immediately before the cold rolling finally performed corresponds to this.

  The heating temperature for annealing immediately before the final rolling stage may be 1150 ° C. or higher in order to completely dissolve interstitial elements such as C, and the holding time may be 30 s or longer. On the other hand, the cooling rate must be 10 ° C./s or more between 700 and 150 ° C. This is because when the cooling rate is lower than this, C precipitates as carbides in the cooling process, and the effect of the aging treatment cannot be sufficiently obtained in the subsequent rolling process.

(Final rolling stage)
As described above, a steel sheet (hot rolled sheet or intermediate cold rolled sheet) in which an interstitial element such as C is in a solid solution state is subjected to final cold rolling to obtain a final thickness. This final cold rolling is carried out using a tandem rolling mill, so that the conditions described below are applied to improve the magnetic properties and stabilize the operation by synergistic expression of the effects of static aging and subsequent warm reduction. Plan. Note that cold rolling is performed by using a tandem rolling mill regardless of the so-called one-time method or two-time method.

First, between the steel plate temperature T (K) between any of the stands up to the final stand of the tandem rolling mill and the residence time t (s) between the stands.
t ≧ 2 × 10 ^-9 × exp (10568 / T) (1)
Keep the relationship.

This relational expression is calculated as follows as the minimum time required for the static aging effect to occur between the stands of the tandem rolling mill.
(1) In order for static aging to appear, it is necessary for C and N atoms to move and reach dislocations by diffusion. The average dislocation density in the steel sheet depends on the strain and temperature existing in advance, but is generally known to be about 10 ¹⁰ pieces / cm ² , and the distance between dislocations can be obtained from this.
(2) The diffusion coefficient of C was measured by Smith et al. (Trans. AIME (1962), vol.224, p105) and is given as shown in Table 1. Using this diffusion coefficient, C is the distance between dislocations. The time t (s) required to move can be obtained.
(3) This time depends on the steel plate temperature T (K) and becomes a curve shown in FIG.
(4) Therefore, in order to diffuse and fix dislocations between the stands by static aging, between the steel plate temperature T (K) between the stands and the residence time t (s) between the stands.
t ≧ 2 × 10 ^-9 × exp （10568 × 1 / T） ・ ・ ・ (1)
Must maintain the relationship.

In addition to the above static aging conditions, in the present invention, the rolling material biting temperature of the stands immediately after the stands of the tandem rolling mill is 80 ° C. or higher and the rolling reduction is 20% or more. This is a method in which after the static aging is expressed as described above, a warm reduction is immediately applied, which affects the formation of deformation bands in the steel sheet, thereby causing dislocation fixation and a combination with the static aging. Thus, the improvement effect of the texture is promoted. Therefore, the performing the rolling temperature and reduction ratio biting the stand immediately after satisfying the expression (1).

  When the rolling material biting temperature is less than 80 ° C., or the rolling reduction is less than 20%, the generation of the static aging deformation band is insufficient, and the texture improving effect is insufficient. Become. Therefore, the rolling material biting temperature must be 80 ° C. or higher and the rolling reduction must be 20% or higher.

  Here, the rolling material biting temperature refers to the temperature immediately before the steel plate bites into the roll of the stand. When the rolled material bites into the stand, the temperature of the rolled material is lowered by the roll cooling spray on the stand entry side, and for example, the temperature of the temperature drop due to the cooling spray is measured by running the rolled material separately. At that time, a table of the temperature drop of the rolled material and these operating conditions is prepared by variously changing the rolling temperature before cooling, the type of coolant, the flow rate, the rolled material conveying speed, the rolled material sheet thickness, and the like. Then, the rolling material biting temperature is obtained by referring to the table according to the conditions during actual operation.

If the rolling material biting temperature exceeds 300 ° C., problems such as seizure of the rolling oil occur, so the temperature is set to 300 ° C. or less .

  The cold-rolled sheet rolled by the tandem rolling mill under the above conditions is subjected to decarburization annealing, and then applied to the steel sheet surface with an annealing separator mainly composed of MgO and subjected to final finish annealing to obtain a product sheet. . As these means, means widely used for producing grain-oriented electrical steel sheets can be used without particular limitation. In addition, it is also possible to reduce the iron loss by forming a phosphoric acid-based insulating coating on the product plate obtained in this way or by applying a mirror finish. It is also possible to carry out the magnetic domain subdivision process.

  Hot rolling a steel slab containing C: 0.074%, Si: 3.26%, Mn: 0.068%, Al: 0.025%, Se: 0.021% and N: 0.0081% to a thickness of 2.7mm I got a plate. After heating at 1000 ° C. for 1 minute, hot-rolled sheet annealing was performed at various cooling rates shown in Table 2 (No. 1 to 24). For some hot-rolled sheets, (a) cold-rolled with intermediate annealing for 1 minute at 1000 ° C without hot-rolled sheet annealing (No. 25), or (b) hot-rolled sheet After annealing, it was cold-rolled with an intermediate annealing at 1000 ° C. for 1 minute (No. 26).

  The final cold rolling was performed by a tandem rolling mill with 4 stands. At that time, the residence time t (s) between the third stand (one before the final stand) and the fourth stand (final stand) and the rolling reduction at the fourth stand are changed as shown in Table 2. did. The temperature between the stands was changed by changing the flow rate of the rolling oil in the first stand to the third stand. The residence time between the stands was changed by changing the rolling speed. The biting temperature was changed by adjusting the flow rate of the rolling oil sprayed on the fourth stand entering side.

The obtained cold-rolled sheet was subjected to decarburization annealing at 840 ° C for 2 minutes in wet hydrogen, and after applying MgO containing 5% TiO ₂ by mass ratio as an annealing separator, at 1200 ° C A final finish annealing for 10 hours was performed to obtain a product plate. Table 2 shows the results of measuring iron loss W _17/50 (W / kg) by the Epstein method defined in JIS C2550 for the obtained product plate. It can be seen from Table 2 that sufficient magnetic properties can be obtained even in tandem rolling when manufactured under conditions according to the present invention.

C is a required time-temperature curve for moving the distance between dislocations.

Claims (3)

After hot rolling a slab for grain- oriented electrical steel sheet containing C: 0.005-0.10% and Si: 2.0-4.5% by mass ratio , the obtained hot-rolled sheet was subjected to hot-rolled sheet annealing and one time. In producing a grain-oriented electrical steel sheet by performing cold rolling with a tandem rolling mill and finishing it to the final thickness, performing decarburization annealing and final finishing tempering on this,
The cooling rate after the hot-rolled sheet annealing is 10 ° C./s or more between 700 and 150 ° C., and between the steel plate temperature T (K) and the stand between any stands up to the final stand of the tandem rolling mill The residence time t (s) satisfies the following formula (1), and
A method for producing a grain-oriented electrical steel sheet, wherein rolling is performed at a rolling material biting temperature of 80 to 300 ° C. and a reduction rate of 20% or more immediately after the stands of the tandem rolling mill.
Record
t ≧ 2 × 10 ^-9 × exp (10568 / T) (1) After hot rolling a slab for grain- oriented electrical steel sheets containing C: 0.005-0.10% and Si: 2.0-4.5% by mass ratio , the obtained hot-rolled sheet is subjected to intermediate annealing at least twice. In producing a grain-oriented electrical steel sheet by performing cold rolling with a tandem rolling mill and finishing to the final sheet thickness, performing decarburization annealing and final finishing tempering on this,
Among the intermediate annealing, the cooling rate of the final intermediate annealing is 10 ° C./s or more between 700 and 150 ° C., and the steel plate temperature T (K) between any one of the stands until the final stand of the tandem rolling mill The residence time between stands t (s) satisfies the following formula (1), and
A method for producing a grain-oriented electrical steel sheet, comprising rolling at a rolling material biting temperature of 80 ° C. to 300 ° C. and a reduction rate of 20% or more immediately after between the stands of the tandem rolling mill.
Record
t ≧ 2 × 10 ^-9 × exp (10568 / T) (1) After hot rolling a slab for grain- oriented electrical steel sheet containing C: 0.005-0.10% and Si: 2.0-4.5% by mass ratio , hot-rolled sheet annealing is performed on the obtained hot-rolled sheet. The method for producing a grain-oriented electrical steel sheet according to claim 2.

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