JPH0331764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for efficiently manufacturing a grain-oriented silicon steel sheet having excellent magnetic properties in the rolling direction.

Conventionally, unidirectional silicon steel sheets are produced by heating slabs containing about 0.020% or more of C, about 3% of Si, and inhibitor-forming elements such as S and Se at about 1300℃.
The plate is heated for a long time at a high temperature above, and after hot rolling, it is cold rolled once or twice or more with intermediate annealing to achieve the final thickness, and after decarburization annealing, an annealing separator is applied. It is usually manufactured by subjecting it to high-temperature finish annealing and then applying an insulating coating.

The above-mentioned unidirectional silicon steel sheet has excellent magnetic properties in the rolling direction due to secondary recrystallization of crystal grains having the {110}<001> orientation, the so-called Goss orientation, during the high-temperature finish annealing process. However, in order to generate such Goss-oriented secondary recrystallized grains with sharpness and high concentration accuracy, it is necessary to use normal grain growth inhibitors such as MnS, MnSe, and AlN that are finely and uniformly dispersed. It is necessary that an appropriate amount of the inhibitor be present and that the primary recrystallized structure be fine and homogeneous.

Conventionally, in order to satisfy the above-mentioned requirements,
First, the slab is heated at a high temperature of approximately 1,300°C or higher for a long period of time to fully dissolve inhibitor-forming elements such as Mn, S, and Se, and the inhibitors are properly removed from hot rolling to final annealing. The second method is to contain approximately 0.020% or more of C in the material and locally generate an austenite layer during the hot rolling process, which results in a layer of several tens of millimeters in size during the slab heating stage. A combination of the above two methods has been used to split and destroy coarse grains to reduce the thickness of elongated grains in the hot-rolled structure. These measures have made it possible to manufacture unidirectional silicon steel sheets with excellent magnetic properties, but these conventional measures require the material to contain approximately 0.020% or more of C. A problem like this arose.

In other words, as the C content of the material increases, the slab heating temperature required to sufficiently dissociate and dissolve the inhibitor-forming elements increases, resulting in an increase in fuel consumption and an increase in the amount of scale generated. This causes various problems in the manufacturing process, such as a decrease in yield and an increase in the frequency of heating furnace repairs due to slag estimation, resulting in a significant increase in manufacturing costs. In addition, from a quality perspective, as the slab heating temperature increases as mentioned above, flaking due to surface oxidation and grain boundary oxidation during high-temperature heating becomes more likely to occur, resulting in poor product appearance. Otherwise, if the C content is high, α-Υ transformation occurs locally during hot rolling, changing the hot-rolling texture and increasing the Goss orientation strength, which is inconvenient for obtaining good product magnetic properties. There are problems such as making it look weak.

This invention was made in view of the above circumstances, and provides a method for efficiently manufacturing unidirectional silicon steel sheets with excellent magnetic properties and excellent appearance quality at a low cost without causing the problems described above. The purpose is to provide

The present inventors have determined that it is effective to reduce the C content of the material in order to solve the above-mentioned problems. Conventionally, as mentioned above, a large amount of C was added to the material as a means of splitting and destroying the crystal grains of the slab to refine the elongation in the hot-rolled structure. Although it was difficult to obtain suitable magnetic properties, the present inventors conducted various experiments and studies, and as a result, the injection ratio of secondary cooling water during continuous casting of slab material, slab heating temperature, and rough rolling conditions were determined. The present invention was completed based on the discovery that a unidirectional silicon steel sheet with an appropriate secondary recrystallization structure and excellent magnetic properties could be obtained by appropriately selecting the material without containing a large amount of C. That's what I came to do.

In other words, the method for producing a unidirectional silicon steel sheet of the present invention includes C0.020% or less, Si2.5~4.0%, Mn0.01~
Molten steel for unidirectional silicon steel sheet containing 0.020% and at least one of S and Se in a total of 0.005 to 0.10% is poured into a continuous casting mold, and the slab that comes out of the mold is poured at a pouring ratio of 1.6/Kg. After secondary cooling at 4.0/Kg or less, and then heating the slab to 1100 to 1320℃, rolling passes with a reduction rate of 30% or more and 90% or less, and a strain rate of 0.5sec ^-1 or more and 20sec ^{-1 or} less. After performing rough rolling including at least one pass or more, followed by finish rolling, one cold rolling or two or more cold rollings with intermediate annealing is performed to obtain the final plate thickness, and as necessary. After decarburizing and annealing,
This is characterized by applying an annealing separator and performing final annealing.

This invention will be explained in more detail below.

First, to explain the new findings from experiments conducted by the present inventors, the present inventors discovered that Si content of 2.9 to 3.2%,
When creating slabs by continuous casting using molten steel containing 0.006 to 0.008% Mn and 0.020 to 0.030% S, the C content is varied by adding various amounts of graphite to the tundish. By varying the injection ratio of secondary cooling water, slabs with thicknesses ranging from 150 mm to 300 mm were manufactured, and then slabs with a C content of 0.020% or less were heated at 1250°C to reduce the C content to 0.020%. The overlapping slab was heated to 1350°C in the same manner as before, and unidirectional silicon steel products were manufactured using conventional methods. Figure 1 shows the results of investigating the influence of the secondary cooling water injection ratio on the secondary recrystallization defect rate of each product obtained. However, the secondary recrystallization failure rate here refers to the area ratio occupied by fine grains with a grain size of 1 mm or less. From Figure 1, in the case of slabs with a C content exceeding 0.020%, the injection ratio of continuous casting secondary cooling water has almost no effect on the secondary recrystallization defect rate, while the C content exceeds 0.020%. In the slab below, 2
It is clear that the water injection ratio of the secondary cooling water has a large effect on secondary recrystallization defects, and that when the water injection ratio is 1.6/Kg or more, the secondary recrystallization defect rate is low and an excellent product can be obtained. Furthermore, if the water injection ratio exceeds 4.0/Kg,
Overcooling causes cracks to form at the corners, causing edge cracks. Therefore, the water injection ratio of continuous casting secondary cooling water needs to be 1.6/Kg or more and 4.0/Kg or less.

Furthermore, the present inventors cut out small steel pieces from slabs manufactured by the same method as above, and heated them at 1000°C to 1400°C.
The material was heated at various temperatures within the range of 1, hot rolled in a small rolling mill, and unidirectional silicon steel sheets were produced in a conventional manner. The influence of slab heating temperature on the secondary recrystallization defect rate of each product obtained was investigated in the second study.
As shown in the figure. From Figure 2, it is necessary to heat the slab at a high temperature of about 1300°C or higher for slabs with a C content exceeding 0.020% in order to reduce the secondary recrystallization defect rate, but when the C content is below 0.020%. It is clear that it is preferable to heat the slab at a temperature in the range of 1100 to 1320°C, which is lower than conventional slabs.

In addition, when hot rolling small steel slabs obtained in the same manner as above at 1250°C, the inventors varied the rolling reduction rate and strain rate in one pass, and Then, repeat rolling with the same rolling reduction and strain rate 1 to 14 times to achieve a cumulative rolling reduction of 85% as rough rolling, then finish rolling, and then perform unidirectional rolling according to the usual method. Manufactured silicon steel plate products. FIG. 3 shows the results of investigating the relationship between the secondary recrystallization defect rate and hot rolling rough rolling conditions for each product obtained. However, in Figure 3, the ○ mark indicates that the C content in the material is 0.020% or less and the secondary recrystallization defect rate is less than 10%, and the ● mark indicates that the C content in the material is less than 10%.
Secondary recrystallization defect rate is 10% when the content is 0.020% or less
In the above cases, △ indicates that the C content in the material is 0.020%.
, and the secondary recrystallization defect rate is less than 10%, ▲
The mark also indicates that the C content in the material exceeds 0.020%,
The cases where the secondary recrystallization defect rate is 10% or more are shown. From Figure 3, when the C content in the material exceeds 0.020%, a good product can be obtained regardless of the rough rolling conditions;
If it is 0.020% or less, the reduction rate in rough rolling is
It is clear that a good product with a low secondary recrystallization defect rate can be obtained only when a rolling pass with a strain rate of 30% or more and a strain rate of 20 sec ^-1 or less is applied.
Generally speaking, the purpose of rough rolling is simply to reduce the thickness, and from the standpoint of productivity, it is advantageous to increase the rolling speed and, therefore, the strain rate. Above, strain rate
Low speed rolling such as 20 sec ^-1 or less has not been adopted at all, and the inventors discovered for the first time that such low speed rolling conditions have an important meaning in unidirectional silicon steel slabs with low C content. It is. In addition, if the rolling reduction ratio of the low-speed rolling pass in the rough rolling described above exceeds 90%, roughness will occur due to the rapid rolling, which will ^{significantly} reduce the product yield. If it decreases in a pass with a low strain rate, the plate temperature decreases excessively during hot rolling, causing incomplete areas of secondary recrystallization, resulting in a decrease in magnetic properties. Therefore, in the rough rolling pass, the rolling reduction is
The strain rate must be 30% or more and 90% or less, and the strain rate must be 0.5sec ^-1 or more and 20sec ^-1 or less.

As mentioned above, in order to manufacture a grain-oriented silicon steel sheet with a good secondary recrystallization structure using a material with a C content of 0.020% or less, which is lower than conventional materials,
A method different from the conventional manufacturing method that used materials with a high C content, namely a high water injection ratio of secondary cooling water of 1.6/Kg or more and 4.0/Kg or less in continuous casting, and a slab heating temperature of 1100 ~ Slab heating at a low temperature of 1320℃ and rolling reduction of 30 during rough rolling
% or more and 90% or less and strain rate 0.5sec ^-1 or more,
The present inventors have newly found that it is necessary to apply a method that combines a low-speed rolling pass of 20 sec ^-1 or less, and by such a method, good magnetic properties and product appearance can be obtained. It became possible to manufacture unidirectional silicon steel plates at low cost.

Note that the passes in the rough rolling stage in hot rolling are usually several passes or more, and in this case, all the passes in the rough rolling stage are performed at a reduction rate of 30% or more and 90% or less, 0.5sec ^-1 as described above. As mentioned above, it is most desirable to set the strain rate to 20 sec ^-1 or less, but the point is that it is sufficient if there is at least one pass that satisfies the above conditions, and even in that case, the effect will be proportional to the number of passes within the condition range. can get.

Next, the reason for limiting the material components in the method of this invention will be explained.

C: If C exceeds 0.020%, the slab heating temperature required to form a solid solution of the inhibitor-forming elements becomes too high, which deviates from the purpose of this invention, which is to produce a grain-oriented silicon steel sheet at low cost. was limited to 0.020 or less.

Si: If Si is less than 2.5%, a sufficiently low iron loss value cannot be obtained, and if it exceeds 4.0%, it becomes brittle and fractures during cold rolling increase rapidly, so it was limited to a range of 2.5 to 4.0%.

Mn, S, Se: These suppress the normal grain growth in the secondary recrystallization stage, thereby increasing the Goss orientation.
MnS acts as an inhibitor to promote the formation of secondary recrystallized grains, and is an element necessary to form MnSe. However, if Mn is less than 0.01% and S and/or Se are less than 0.005% in total, The amount of inhibitor necessary for the development of crystalline structure is insufficient, and a good secondary recrystallized structure cannot be obtained.
Mn is 0.02%, total amount of S and/or Se is
If it exceeds 0.10%, the slab heating temperature for complete solid solution of these elements becomes high, which is contrary to the purpose of the present invention. Therefore, Mn is 0.01-0.20%,
S and/or Se in total amount 0.005-0.10%
limited to the range of

In addition to the above-mentioned components, grain boundary segregation type elements such as Sb, As,
Bi, Pb, Te, Mo, W, etc. may be added alone or in combination.

In the manufacturing method of the present invention, unidirectional silicon steel plate molten steel containing the above-mentioned components is poured into a continuous casting mold to form a continuous casting slab. In this continuous casting, the injection ratio for secondary cooling of the slab coming out of the mold, that is, the amount of secondary cooling water shower per 1 kg of slab, is set to 1.6/Kg or more as described above.
4.0/Kg or less. The slab thickness is 150mm.
~300mm. In addition, during this continuous casting, in order to increase the equiaxed crystallinity and reduce center segregation,
It is desirable to apply electromagnetic stirring to the molten steel in the casting by a known method.

Next, for slabs, 1100~
It is heated to a temperature of 1320°C and subjected to hot rolling consisting of rough rolling and finish rolling to form a hot rolled coil with a thickness of 1.5 to 3.5 mm. Here, the rough rolling stage is performed at a reduction rate of 30% or more and 90% or less and a strain rate of 0.5sec ^-1 as described above.
The above rolling schedule is carried out using a rolling schedule that includes at least one pass of 20 sec ^-1 or less.

As mentioned above, setting the injection ratio of secondary cooling water, slab heating temperature, rolling reduction ratio and strain rate of rough rolling in continuous casting is important for secondary recycling using a low C material with a C content of 0.020% or less. This is necessary to obtain a product with excellent magnetic properties and a low crystal defect rate.

For hot-rolled coils, it is desirable to perform continuous annealing for a short time at a temperature of 700°C to 1100°C, then rapidly cool the coil, and then cold-roll the coil. Excellent magnetic properties can be obtained. Cold rolling was carried out according to the conventional method.
The final plate thickness is obtained by performing intermediate annealing twice or more with short-time continuous annealing at 700 to 1100°C.

A cold-rolled sheet that has been cold-rolled to its final thickness is usually subjected to continuous annealing in wet hydrogen at 700 to 900°C with the main purpose of decarburization. Due to the effects of decarburization and surface oxide layer formation due to this annealing,
The magnetic properties and glass film formation of the product can be stabilized. However, in this invention, C in the material
Since the content is small, such decarburization annealing can be omitted in some cases, and therefore decarburization annealing can be performed as necessary. After performing decarburization annealing as necessary, a slurry-like annealing separator mainly composed of MgO is applied to both sides of the coil and dried, followed by high-temperature finish annealing at a temperature of 1000°C or higher in a hydrogen stream. , a product made of unidirectional silicon steel sheet.

Examples of this invention are described below.

Example 1 Molten steel containing 0.005% C, 3.05% Si, 0.04% Mn, and 0.015% S was continuously cast into a 200 mm thick slab, and the secondary cooling water in the continuous casting was poured at a water injection ratio of 1.8.
/Kg, and then cooled the slab to 1180℃.
After heating the slab for 30 minutes at
Rough rolling was performed by repeating 4 passes at a strain rate of 10 sec ^-1 .
It was further finished rolled into a 2.2 mm thick hot rolled coil.
Next, the final plate thickness was 0.30 mm by cold rolling twice with intermediate annealing at 950°C for 1 minute, and then
Apply MgO slurry, dry it, and place it in hydrogen.
Finish annealing was performed at 1200°C for 10 hours. The magnetic properties of the obtained product are as follows: magnetic flux density _B10 value is 1.85 Tesla, iron loss
It was confirmed that the W ₁₇ / ₅₀ value was 1.31 w/Kg, which was a good value, and was completely recrystallized.

Example 2 Molten steel containing 0.015% C, 2.95% Si, 0.04% Mn, and 0.015% Se was poured 2.1 m from the meniscus in the mold.
Continuous casting was carried out with electromagnetic stirring at the position , and secondary cooling was performed at a secondary cooling water injection ratio of 1.8/Kg. The resulting 230 mm thick slab was heated at 1250°C for 30 minutes, and then rough rolled. Rough rolling was performed under the conditions that the final pass of the 5 passes had a reduction rate of 70% and a strain rate of 6 sec ^-1 , and then finish rolling was performed to obtain a 2.7 mm thick hot rolled coil. Next, after continuous annealing at 900°C for 2 minutes, cold rolling was performed twice with intermediate annealing at 950°C for 1 minute to give a final thickness of 0.35 mm, and further annealing at 800°C for 1 minute in wet hydrogen was performed. Perform decarburization annealing,
After applying MgO slurry and drying, place it in hydrogen.
Finish annealing was performed at 1200°C for 10 hours. The magnetic properties of the obtained product showed good values, with a magnetic flux density B ₁₀ value of 1.87 Tesla and an iron loss W ₁₇ / ₅₀ value of 1.33 W/Kg, and a perfect secondary recrystallized structure was obtained. This was confirmed.

As is clear from the above explanation, according to the method for manufacturing a unidirectional silicon steel sheet of the present invention, a material with a low carbon content, which has been difficult to obtain in the past, is used, and By appropriately setting the secondary cooling water injection ratio, slab heating temperature, and hot rolling rough rolling pass conditions, it has become possible to obtain grain-oriented silicon steel sheets with excellent magnetic properties equivalent to conventional ones. . As mentioned above, in the method of this invention, the C content in the material is low and the slab heating temperature is 1,100 to 1,320°C, lower than conventional methods, so the fuel consumption is small and the amount of scale generated is small. Various effects can be obtained, such as the durability of the furnace being high, manufacturing costs being lower than conventional methods, and appearance quality being improved.

[Brief explanation of the drawing]

Figure 1 is a correlation diagram showing the relationship between the injection ratio of secondary cooling water and the defective rate of second recrystallization in continuous casting.
The figure is a correlation diagram showing the relationship between the slab heating temperature and the secondary recrystallization failure rate, and Figure 3 shows the influence of the rolling reduction rate and strain rate of one pass in the hot rolling rough rolling stage on the secondary recrystallization failure rate. It is a correlation diagram.

Claims (1)

[Claims] 1 C0.020% (weight%, same below) or less, Si2.5
~4.0%, Mn0.01~0.20%, and at least one of S and Se in a total of 0.005~0.10%. Molten steel for unidirectional silicon steel plate is poured into a continuous casting mold, and from the mold. 1.6/Kg or more of the slab that came out,
After secondary cooling with a water injection ratio of 4.0/Kg or less, and then heating the slab to 1100 to 1320℃, the rolling reduction is 30% or more and 90% or less, and the strain rate is 0.5sec ^-1 or more.
After performing rough rolling including at least one pass of 20 sec ^-1 or less, followed by finish hot rolling,
The final plate thickness is achieved by performing one cold rolling or two or more cold rollings with intermediate annealing in between, and after performing decarburization annealing as necessary, an annealing separator is applied and final annealing is performed. A method for producing a unidirectional silicon steel sheet, characterized in that: