JPH0368716A - Production of grain-oriented silicon steel strip reduced in iron loss - Google Patents

Abstract

PURPOSE:To produce a grain-oriented silicon steel strip reduced in iron loss by relaxing the apparent partial pressure of oxygen in an atmosphere to a specific value or below in the process for removing inhibitors from a grain-oriented silicon steel strip stock in which Si content and crystalline grain texture are specified, respectively. CONSTITUTION:A grain-oriented silicon steel strip stock containing 2-8wt.% Si and having a (100) [001] crystalline grain texture is cold-rolled so as to be formed into an intermediate extra thin foil of <=150mu sheet thickness having (100) [112] texture. Subsequently, the above foil is subjected to heat treatment including a stage of rising temp. from the ordinary temp. up to 1000-1400 deg.C at >=1.5 deg.C/sec temp.-rise rate, heating at the above temp. for >=1.5hr under a reduced pressure of the prescribed degree of vacuum, and removing tertiary recrystallized grain growth inhibitors and a crystalline grain growing stage consisting of heat treatment under higher pressure for >=3hr in a nonoxidizing atmosphere. At this time, He gas purging is performed in the inhibitor-removing stage, by which the apparent partial pressure of oxygen can be relaxed to <=2X10<-6>Torr, and the degree of vacuum in the heat treatment atmosphere can be reduced to <= about 8X10<-2>Torr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a grain-oriented silicon steel strip, and particularly to a method for producing an ultra-thin grain-oriented silicon steel strip with high magnetic flux density and low iron loss. This invention relates to a preferred manufacturing method.

[Conventional technology]

Contains Sf: 2 to 8% by weight, (001) [001
] By cold rolling a unidirectional silicon steel strip material having a grain texture, a (II
I) Create an intermediate ultrathin strip with a (112) texture and inject it with an inert gas or hydrogen gas.

Approximately 1.5℃ from room temperature in a mixed atmosphere of inert gas and hydrogen gas or a vacuum atmosphere.
A method of obtaining an ultra-thin grain-oriented silicon steel strip with high magnetic flux density and low iron loss by raising the temperature to approximately 1000 to 1400°C at a heating rate of 1/sec or more and holding it at that temperature for 3 hours or more (special method) 171827), the intermediate ultra-thin strip is heated under reduced pressure with a predetermined degree of vacuum to remove the tertiary recrystallized grain growth inhibiting substance contained in the intermediate ultra-thin strip, and then the pressure is reduced. A method for obtaining a grain-oriented silicon steel strip with low core loss by performing heat treatment in a highly non-oxidizing atmosphere to further grow the tertiary recrystallized grains in the intermediate ultra-thin strip (Japanese Patent Application No. 63-28671)
No. 1) has been proposed.

[Problem to be solved by the invention]

The above proposal had the following problems.

That is, the initial heat treatment in a reduced pressure atmosphere is 1X 10
-' ~ 5 X 10-6 TorrO High vacuum degree is required, which requires the use of a rotary pump and oil diffusion pump in combination, which increases operating costs, and heat treatment is performed under high temperature and high vacuum, so heat-treated materials cannot be used. The problem was that it volatilized, causing material loss.

The purpose of the present invention is to solve the above-mentioned problems by further relaxing the degree of vacuum required for initial heat treatment in a reduced pressure atmosphere, and efficiently producing ultra-thin grain-oriented silicon steel strips with low iron loss at low cost. The purpose is to provide a manufacturing method.

[Means to solve the problem]

Relaxation of the degree of vacuum in the initial reduced pressure atmosphere heat treatment for the above purpose can be achieved by reducing the oxygen partial pressure in the atmosphere as much as possible. At least the apparent oxygen partial pressure is 2
By reducing the pressure to 10 −6 Torr or less, the vacuum degree of the heat treatment atmosphere can be reduced to 8×10 Torr. In other words, the degree of vacuum is reduced to the conventional I x 10-'
~5 X 10 Torr range to 8 X 10 Torr
Even when the temperature is reduced to 6 Torr, the target ultra-thin grain-oriented silicon steel strip with low iron loss can be obtained by heat treatment at that degree of vacuum and subsequent heat treatment in a normal pressure hydrogen atmosphere.

One way to actually reduce the oxygen partial pressure in the heat treatment atmosphere is to reduce the pressure while supplying a small amount of He gas to the atmosphere.

The present invention was discovered as a result of heat treatment in an initial reduced pressure atmosphere using this method using He gas.
As purge gas, in addition to He gas, H2 gas, Ar
It has been confirmed that using gas, Nt gas, or a mixed gas thereof is also effective in alleviating the degree of vacuum.

[Effect]

The heat treatment in the conventional technology is heat treatment in a reduced pressure air atmosphere, whereas the oxygen partial pressure in the heat treatment atmosphere at 8 X 10-6 Torr while performing the He gas barge according to the present invention is apparently 2 X 10-6 Torr or less. It is.

In order to reduce core loss, as stated in the prior art proposal, sufficient growth of tertiary recrystallized grains with (110)[001) orientation is required, and for this growth to occur, the surface of the material Energy contributes greatly. When a trace amount of oxygen exists in the heat treatment atmosphere, it is thought that the surface of the material is oxidized, the surface energy decreases, and the growth of tertiary recrystallized grains is inhibited. The need for a high vacuum atmosphere in the prior art is to volatilize and remove oxides generated on the surface. In contrast, the present invention reduces the oxygen partial pressure of the atmosphere more than the prior art, suppresses oxidation of the material during heat treatment, and alleviates the need for high vacuum for volatilization and removal of oxides.

Note that the oxygen partial pressure is an apparent value calculated from the oxygen concentration in the air or He gas and the degree of vacuum of the atmosphere, as a value before the oxygen in the atmosphere is reduced by reaction with the treated ribbon.

The effects of the present invention described above include a heat treatment process in a reduced pressure atmosphere for 2 hours at a heat treatment temperature of 1230 °C, including a temperature increase process at a temperature increase rate of 6 °C/sec, followed by heat treatment in a normal pressure hydrogen atmosphere. The ultrathin copper strip obtained by a 5-h heat treatment process at a temperature of 1230°C was subjected to 2X treatment in a so-called conventional reduced-pressure air atmosphere without He gas purge.
It was estimated from the surface observation of the treated material at 10-6 Torr and the analysis of oxygen atoms by an X-ray microanalyzer while performing He gas purge according to the present invention.

As a result, the surface of the material that had not been purged with He gas had a white color in parts, whereas the surface of the material that had been purged with He gas had no such areas and had a metallic luster.

As a result of analyzing the above white part with an X-ray microanalyzer, the presence of oxygen atoms (0) was observed as shown in Figure 3 (bl). As shown in Figure 3ial, the presence of oxygen atoms was not observed.In other words, the white part was caused by oxidation of the material, which supported the effect of the present invention described above.

) [In addition to e gas, N2 gas and Ar gas.

The same effect as above was obtained by reducing the amount of oxygen mixed in N2 gas and mixed gases thereof, but H
This is due to the same effect as in the e-gas barge.

[Embodiments of the invention]

Next, specific examples of the present invention will be explained in detail. FIG. 4 is a diagram showing the manufacturing process of a low core loss grain-oriented silicon steel strip according to the present invention, and each main process is shown as a block. Arrows indicate the flow of the process.

101 in the figure contains 2 to 8% by weight of Si (110
) [001) A unidirectional silicon steel strip material having a grain texture, 102 is a step of removing an insulating film and an oxide film formed on the surface of the silicon steel strip material 101, and 104 is a silicon steel strip after the film has been removed. Cold rolling process of steel strip 103, 106,1
08 is a heat treatment process of the silicon steel strip 105 after cold rolling, and the former 106 includes 1.
A heat treatment step in a reduced pressure non-oxidizing atmosphere for 5 hours or more, the latter 108 being a heat treatment step in a normal pressure non-oxidizing atmosphere.

The silicon steel strip 107 that has been heat-treated in a reduced-pressure non-oxidizing atmosphere is preferably subjected to the normal-pressure non-oxidizing atmosphere treatment in step 108 while the heat treatment temperature in step 106 remains unchanged; You may do so. However, 1.5
It is necessary to perform the heat treatment through a temperature increase rate of .degree. C./second or higher. The heat treatment time in steps 106 and 108 is required to be 3 hours or more.

Step 110 is a step of applying and baking an insulating film to the surface of the silicon steel strip 109 after heat treatment, and is a step of forming the insulating film and applying tension to the silicon steel strip to further reduce iron loss.

The present invention consists of the above-mentioned main steps, and it is possible to obtain a low core loss grain-oriented silicon steel strip 111 in which the core loss of the material 101 is significantly reduced. Next, each of the above steps will be explained in more detail.

The silicon content of the silicon steel strip used in the present invention is preferably regulated within the range of 2 to 8% by weight. 2 silicon
Since silicon steel strips containing more than % by weight do not undergo γ transformation, they can be annealed at high temperatures to enlarge the crystal grains or cause secondary and tertiary recrystallization to form a desirable texture. If it is less than 2% by weight, the above-mentioned features will not be exhibited. On the other hand, if the silicon content exceeds 8% by weight, the saturation magnetic flux density becomes less than about 1.7 T, which is not only unsuitable as a magnetic material, but also makes it mechanically extremely fragile, which is not preferable. Particularly, one having a silicon content of 2.5 to 4.0% by weight is suitable because it has excellent mechanical properties such as rolling and has a saturation magnetic flux density of 1.95 T or more.

For example, Mn, AA, S, Se in the silicon steel strip.

The total amount of Sn, Sb, MnS, MnSe/Sb, AfN, etc. is about 0.5% by weight, and unavoidable mixed elements such as Ni, Cu, Mo, W, Go, and Cr may be contained in small amounts. Furthermore, the content of unavoidable impurities such as O, N, and C must be limited depending on the quality of the final target ribbon.

Note that a commercially available grain-oriented silicon steel strip can be used as the material used in the present invention. As commercially available grain-oriented silicon steel strips, for example, those shown in Table 1 below can be used.

Table 1 Iron loss Wl'l/S in the table. is a magnetic flux density of 1.7T,
It is the iron loss when the frequency is 50 Hz, and B1 is the magnetizing force 8
This is the magnetic flux density at 00 A/m.

For example, in Table 1, a material having an iron loss (W, 1., .) of 1.10 or less and a magnetic flux density (Bll) of 1.75 T or more can be used.

Commercially available grain-oriented silicon steel strips have a thickness of 0 as shown in Table 1.
．． 30mm (300, cam) and 0.35mm (35
0pm>. These silicon steel strips are used as raw materials and cold rolled to a thickness of 150 μm or less. It is sufficient if the reduction rate is 50% or more, and the original purpose of cold rolling is to produce a grain-oriented silicon steel strip with a (110) [001) orientation that has a large deviation angle with respect to the rolling direction. The objective is to obtain an ultrathin intermediate band having (111) [112) orientation with crystal distortion.

In addition, in the present invention, for plate thickness exceeding 150 μm (110
) It was confirmed that recrystallized grain growth in the [001) orientation is difficult to occur. The reason for this is that for plate thicknesses exceeding 150 μm,
This is thought to be because the plate is too thick for the (110) plane, which has the lowest surface energy, to grow due to the surface energy acting as a driving force.

FIG. 5 is a characteristic diagram showing the relationship between heat treatment temperature and crystal grain size, and the heat treatment time was 1 hour. As is clear from this figure, the grain size of the secondary recrystallized grains increases rapidly when the heat treatment temperature exceeds 1000°C. The texture of these secondary recrystallized grains is not only the crystal structure of the (110) [001) orientation, but also the (120) [001) orientation, (1i 1) ct 10) orientation, and (111) orientation.
) [100) orientation, etc., and these secondary recrystallized grains become the nucleus of the subsequent tertiary recrystallized grains, which is an important point in heat treatment.

On the other hand, since the melting point of grain-oriented silicon steel strip is approximately 1500°C, in order to prevent the grain-oriented silicon steel strip from fusing during heat treatment, the heat treatment temperature must be set to 14
It is necessary to keep the temperature below 00°C. For this reason, the heat treatment temperature is io.

It should be regulated within the range of ~1400°C.

After cold rolling, in an initial stage including a temperature increasing process at a temperature increase rate of about 1.5°C/sec or more, preferably 6°C/sec or more, a heat treatment temperature of 1000 to 1400°C, preferably 1150 to 1
Heat treatment is performed at 250° C. and a reduced pressure non-oxidizing atmosphere, preferably a vacuum atmosphere for 1.5 hours or more. Subsequently, switch to a normal pressure non-oxidizing atmosphere, preferably a normal pressure hydrogen atmosphere or a normal pressure inert (argon, etc.) atmosphere, and heat treatment temperature 1.
000~1400℃, preferably 1150~1250℃
and the holding time is 1.5 hours or more, preferably 1.5 to 6°5.
Perform heat treatment for an hour.

Figure 1 shows He with a purity of 99.995% or more according to the present invention.
It is a characteristic diagram showing the relationship between the degree of vacuum (apparent oxygen partial pressure), iron loss, and magnetic flux density when initial stage heat treatment is performed while supplying a small amount of gas.The heating rate is 6°C/sec, and the heat treatment temperature is The temperature is 1230°C.

As is clear from this figure, the degree of vacuum is 8X10-”T
If it is more than orr, it is possible to obtain a oriented ultra-thin silicon strip with low iron loss and high magnetic flux density.

The amount of oxygen mixed in the He gas used was 20 ppm,
The apparent oxygen partial pressure in an atmosphere with a degree of vacuum of 8 x 10 -6 Torr is 1.6 x 10 -6 Torr.

That is, at least the oxygen partial pressure is 2 X 10-6To
By making it less than rr, an ultra-thin grain-oriented silicon steel strip with low core loss can be obtained. Note that the amount of oxygen mixed in He is shown here as the sum of the amount of O, CO□+H2O and 1/2 amount of CO. That is, it is believed that the oxygen in COzC○, H, and O also oxidizes the material at high temperatures.

As described above, the degree of vacuum of the heat treatment atmosphere according to the present invention is 8.
X 10-6 Torr is preferred. 8X10-2T
If the degree of vacuum is lower than orr, the oxygen partial pressure in the atmosphere cannot be sufficiently reduced, leading to oxidation of the material, and it becomes impossible to remove components that inhibit the growth of tertiary crystal grains on the surface that were already present. .

Next, a specific example of the processing method according to the present invention will be explained.

The material is grain-oriented silicon steel strip (30ZH1 manufactured by Nippon Steel Corporation).
05) was used. The properties of this grain-oriented silicon steel strip are shown in Table 2 below.

Table 2 The insulating film and oxide film formed on the surface of the copper strip were removed by immersing it in a solution, then washing it with water, pickling it with an aqueous nitric acid solution, and washing it with water.

Next, it was rolled to 100 μm using a four-roll rolling mill. The material is 10mm wide and 15mm long excluding each end.
A heat-treated sample with a size of 0 mm was used. The heat treatment was performed in a transparent quartz glass tube with a diameter of 30 mm, and heating was performed using an infrared furnace. The transparent quartz glass tube was equipped with a cylinder, a pressure regulator, a conduit for supplying He gas through a flow needle, and an outlet conduit connected to a vacuum pump. Note that the He gas may be supplied by refining the He gas discharged from the outlet conduit through an impurity adsorption removal tower, and then circulating and resupplying the He gas.

Specific examples and comparative examples of the method of the present invention will be shown below. The heat-treated samples prepared as described above were heat-treated using a heating furnace under the conditions shown in Table 3 while supplying He gas containing 20 ppm or less of oxygen at a flow rate of INl/h. The cases in Table 3 differ only in the reduced pressure conditions, and the other heat treatment conditions are the same. The magnetic properties of the ultra-thin grain-oriented silicon steel strip obtained as a result are shown in FIG. 1 above. Incidentally, the iron loss value is the value when a tension of 2 kg/mm'', which is the same tension as that of a special coated copper strip, is applied.

Table 3 As shown in Figure 1, the degree of vacuum in the heat treatment atmosphere is 8.
A low iron loss silicon steel plate has been stably obtained under conditions higher than X 10-6 Torr.

On the other hand, FIG. 2 shows the results when the heat treatment according to the present invention was performed only by decompression operation without supplying He gas. The conditions for the heat treatment are the same as in Table 3 except that He gas is not supplied and the degree of vacuum is different.

As is clear from a comparison of FIGS. 1 and 2, the degree of vacuum is relaxed by at least two orders of magnitude according to the present invention.

〔Effect of the invention〕

As shown in the examples, according to the present invention, the vacuum degree of the heat treatment atmosphere can be relaxed by at least two orders of magnitude, and 8
Since heat treatment can be performed under a reduced pressure of I O-6 Torr, it is now possible to use only a rotary vacuum pump instead of the combination of a rotary vacuum pump and an oil diffusion vacuum pump, reducing equipment costs and operation. This has the effect of reducing costs. In addition, due to the relaxation of the degree of vacuum,
This suppresses the continuous loss and decrease in mold volume of heat-treated materials that occurred under high temperature and high vacuum conditions, and has the effect of reducing material costs.

[Brief explanation of drawings]

Figure 1 is a characteristic diagram showing the relationship between the vacuum degree (apparent oxygen partial pressure) of the heat treatment atmosphere and the magnetic flux density and iron loss of the obtained material, showing the effects of the present invention, and Figure 2 is a characteristic diagram showing the relationship between the vacuum degree and magnetic flux density in the conventional technology. , is a characteristic diagram showing the relationship between iron loss. Figure 3 is X
Figure 4 is a diagram showing the analysis results of the material surface by a wire microanalyzer, Figure 4 is a diagram showing the manufacturing process of grain-oriented silicon steel strip according to the present invention, and Figure 5 is a characteristic diagram showing the relationship between heat treatment temperature and grain size. . 101... Unidirectional silicon steel strip material, 104... Cold rolling process, 106, 108... Heat treatment process, 111.
...Low iron loss grain-oriented silicon steel strip. Fig. 4 Torr (a)

Claims (4)

[Claims] (1) Contains Si: 2 to 8% by weight, (110) [00
1] By cold rolling a unidirectional silicon steel strip material having a grain texture, a (111
) [112] An intermediate ultrathin strip having a texture is created, and in the heat treatment process, the temperature is raised from room temperature to 1000 to 1400 °C at a heating rate of 1.5 °C/sec or more, and at that temperature 1.5 An inhibitor removal step in which tertiary recrystallized grain growth inhibitors contained in the intermediate ultrathin strip are removed by heating under reduced pressure with a predetermined degree of vacuum for more than an hour, and then an inhibitor removal step. In the heat treatment method for improving the magnetic properties of the grain-oriented silicon steel strip, the method includes a grain growth step in which the intermediate ultra-thin strip is heat-treated for a total time of 3 hours or more under high pressure conditions and in a non-oxidizing atmosphere, The apparent oxygen partial pressure in the atmosphere in the inhibitor removal process was set to 2×10^-^6 Torr.
1. A method for producing a grain-oriented silicon steel strip with a low iron loss, characterized in that the iron loss is less than or equal to r. (2) In claim (1), the oxygen partial pressure is set to 2×
A method for producing a grain-oriented silicon steel strip with low iron loss, characterized in that the means for reducing the temperature to 10^-^6 Torr or less is purging the heat treatment atmosphere with a non-oxidizing gas. (3) In claim (2), the non-acidic gas is
A method for producing a low core loss grain-oriented silicon steel strip, characterized in that the mixed gas is one or more of He gas, H_2 gas, Ar gas, and N_2 gas, with an amount of oxygen mixed in at least 20 ppm or less. (4) In claim (2) or claim (3),
A method for producing a grain-oriented silicon steel strip with low iron loss, characterized in that a non-oxidizing gas is led out of a heat treatment atmosphere, oxygen compounds are removed, purified, circulated and supplied for reuse.