JPS5980719A - Treatment of silicon steel slab - Google Patents

Abstract

PURPOSE:To manufacture a unidirectional silicon steel plate having superior surface properties by slowly cooling a silicon steel slab contg. Si, Mn and S and/or Se taken out of a heating furnace to a specified temp. or below and conveying the slab to a hot rolling mill by means of table rolls. CONSTITUTION:A silicon steel slab contg., by weight, 2.5-4.5% Si, 0.03-0.10% Mn and 0.005-0.10% in total of S and/or Se is heated in a walking beam type heating furnace until the underside of the slab is heated to >=1,270 deg.C. The heated slab is taken out of the furnace and slowly cooled at <=3 deg.C/sec cooling rate until the under-side of the slab is cooled to <=1,250 deg.C. The slowly cooled slab is conveyed to a hot rolling mill by means of table rolls. Thus, the occurrence of linear spills is prevented, and a silicon steel plate having superior surface properties can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a slab processing method for producing unidirectional silicon steel sheets.

As is well known, unidirectional silicon steel sheets are composed of a texture in which secondary recrystallized grains with the so-called Goss orientation, that is, the (110) <001> orientation, are highly integrated, and exhibit excellent magnetic properties in the rolling direction. show. Such a secondary recrystallization texture is obtained by selectively rapid acid-lengthening the secondary recrystallization of the Goss orientation in the final high-temperature annealing step during the manufacturing process of silicon steel sheets, but at this time, It is necessary to suppress the growth of crystal grains other than the Goss orientation until the secondary recrystallization is completed, and for this purpose, a precipitated dispersed phase called an inhibitor such as MnS, MnSe, A13N, etc. is used.

In order to suppress the growth of inappropriately oriented crystal grains due to such precipitated dispersed phases, these precipitated dispersed phases are sufficiently separated from S and dissolved in solid solution during heating of the slab before hot rolling, and the subsequent process, that is, thermal Through the rolling, cold rolling, and annealing processes, the number 1
It is necessary to disperse an appropriate amount of 00X fine precipitates. In order to sufficiently dissociate and solidify the precipitated dispersed phase before hot rolling, the slab is usually heated at a high temperature of 1.300° C. or higher for a long period of time.

For high-temperature, long-term slab heating in the production of unidirectional silicon steel sheets as described above, a pusher-type heating furnace or a walking beam-type heating furnace is generally used.

In a pusher-equipped heating furnace, the slab is pushed in one direction by a pusher and is slid on the soaking hearth, so the shape of the slab extracted from the furnace is flat, but on the other hand, there are scratches on the bottom surface of the slab. There is a drawback that this occurs. Recently, walking beam heating furnaces have been increasingly used to avoid scratches. In a walking beam heating furnace, as shown in FIG. A series of operations for placing the object on the skid beam 3 placed between the beams 2 are repeated and the object is conveyed. Therefore, in the walking beam heating furnace, there are almost no scratches on the lower surface of the slab 1. However, silicon steel has significantly lower hot strength than ordinary steel, so when using a walking beam type heating furnace, when placed on the skid beams 3 placed at intervals, or the same There is a problem in that when the slab 1 is lifted up by the walking beams 2 provided at intervals, the slab 1 bends in a wave-like manner in the longitudinal direction due to its own weight as shown in FIG. After the heated slab is extracted from the furnace, it is conveyed to the rolling mill by table rollers, but if a slab that is bent in a wavy manner is extracted from the heating furnace as described above, the wavy white part on the bottom surface of the slab will be It receives impact from the table roller, which causes minute cracks in the grain boundaries. Such cracks elongate in the rolling direction during rolling, resulting in a surface defect called a linear heave at the product stage, which significantly reduces commercial value.

This invention was made in view of the above circumstances, and when a slab for unidirectional silicon steel is heated in a walking beam heating furnace and transported by a table roller after being extracted from the heating furnace, the impact from the table roller is To provide a slab processing direction for obtaining a unidirectional silicon steel sheet with excellent surface quality by reducing the frequency of microcracks that occur in the slab as much as possible, thereby preventing linear flaking of the product. The purpose is to

In other words, the present inventors have conducted extensive research and investigation into the factors that affect the occurrence of microcracks on the bottom surface of a silicon steel slab extracted from a heating furnace before it reaches a rolling mill.
The temperature on the bottom surface of the slab when impact is applied to the slab by a table roller has a major influence on the occurrence of microcracks, and the temperature on the bottom surface of the slab when impact is applied to the slab is controlled to be below a certain temperature and at the same time reaches that temperature. This invention was based on the new finding that the occurrence of microcracks on the lower surface of the slab can be significantly suppressed by slow cooling the lower surface of the slab to a certain cooling rate or less.

Specifically, the slab processing method of this invention
~4.5%, Mn 0.03~0.10%, one or both of S and Se in total amount of 0.005~0.10
% silicon steel slab is heated in a walking beam heating furnace so that the bottom surface temperature of the slab reaches 1270℃ or higher, and after extraction from the heating furnace, the bottom surface temperature of the slab is transferred to a rolling mill by a table roller. 3°
Cooling to 1250°C or less at a rate of C/sec or less,
This method is characterized in that the slab is then transported by table rollers.

The slab processing method of the present invention will be explained in more detail below.

The slab to be treated in the method of this invention contains 2.5-4.5% Si, 3-010% Mn0O3, S
and one or two types of Se in a total amount of 0.005 to 0.
．． It contains 10%. To explain the reason for limiting these components, Si is an effective element for reducing the iron loss value of products, and is essential for obtaining unidirectional silicon steel sheets with excellent properties and low iron loss values. If Si is less than 2.5%, the iron loss value will not be sufficiently reduced, while if it exceeds 45%, cold workability will decrease and brittle cracks will easily occur. range. Mn, S and/
Or Se is (110) <
MnS, MnS, which is a precipitated dispersed phase, acts as an inhibitor to suppress the growth of crystal grains with inappropriate orientation in order to selectively and rapidly grow secondary recrystallized grains with 001> orientation.
It is necessary to generate e, and Mn 0.03
%, the total amount of S and/or Se is less than 0.0051, the formation of a precipitated dispersed phase is insufficient, while MnO
If the total amount of S and/or Se exceeds 0.10%, hot and cold workability will deteriorate.

For 1m of Se, the total amount of the two types is 0.005 to 0.10
% range. In the present invention, a silicon steel slab consisting essentially of Fe and unavoidable impurities other than Si, Mn, S and/or Se within the above-mentioned range may be used; It is permissible to contain up to

In addition, in order to reinforce the effect of MnS or MnSe on suppressing the growth of crystal grains with inappropriate orientation, Sb
, Sn, Bi, Mo, W, Cu
, B, AJ3, etc. may be contained.

The method for obtaining a silicon steel slab having the above-mentioned components is not particularly limited, and a slab manufactured by a conventional method from molten steel refined by a normal steel manufacturing method by an ingot-blubber rolling method or a continuous casting method. You can use .

In the slab processing method of the present invention, slab heating is performed in a walking beam heating furnace before hot rolling a silicon steel slab having the above-mentioned components. In this slab heating, in order to sufficiently dissociate and dissolve MnS and/or MnSe, it is necessary to heat the slab at a higher temperature than when heating a normal steel slab. That is, since the degree of dissociation and solid solution of MnS and/or MnSe depends on the slab heating temperature, the slab heating temperature has a strong influence on the magnetic properties of the final product. The present inventors have discovered that Si2.8-33%, M
n0.03-0.08%, S and Se in total amount 0.
250rrrr containing 013-0.035% respectively
A continuous cast slab of A thickness is heated at various temperatures, 2.8 to 3,
After hot rolling to a thickness of 0 m + 1, the final plate thickness was made to 0.3 Ofllll by cold rolling twice with intermediate annealing in between,
Next, after decarburizing annealing at 820°C in wet hydrogen, magnesia slurry is applied as an annealing separation agent, and final high temperature annealing is performed at 1200°C for 10 hours in a hydrogen atmosphere to obtain a unidirectional silicon steel sheet product. When an experiment was conducted and the relationship between the slab heating temperature (slab F surface temperature) and the magnetic properties of the product was investigated, the results shown in FIG. 3 were obtained. From FIG. 3, it is clear that in order to stably obtain good product magnetic properties, it is necessary to heat the slab so that the bottom surface temperature of the slab reaches a high temperature of 1270'C or higher. Therefore, in the slab processing method of the present invention, the heating of the slab in the walking beam heating furnace is defined as a slab bottom surface temperature of 1270'C or higher.

If a slab is heated to the above-mentioned high temperature using a walking beam heating furnace, the slab will bend in a wavy manner in the longitudinal direction as described above, and therefore, when the slab is transported by a table roller after being extracted from the heating furnace, the curved portion of the bottom surface of the slab will be distorted. receives impact from the rollers, resulting in microcracks at grain boundaries. In order to find a way to prevent the occurrence of microcracks due to such impact, a small specimen was cut from a silicon steel slab with the same composition as that used in the experiment, and was
A test was conducted in which a weight was applied to the surface of a small specimen heated to various temperatures of 0°C and then dropped at various temperatures to apply an impact. When we investigated the relationship with the frequency, we found that, as shown in Figure 4, the frequency of microcracks strongly depends on the surface temperature of the specimen when the weight drops, that is, when the impact is applied, and especially when the specimen surface temperature is below 1250℃. It was found that the frequency of occurrence of microcracks was significantly reduced. From this, when conveying the slab extracted from the heating furnace to the table roller, it is effective to prevent the occurrence of microcracks by lowering the temperature of the bottom surface of the slab to a temperature of 1250 degrees Celsius or more before conveying it. I discovered that.

Furthermore, when performing the same weight drop test as described above, the inventors determined that the cooling rate when lowering the specimen surface temperature from the slab heating temperature to the ionization drop temperature was determined by water spray injection, forced air cooling, natural cooling, etc. Experiments were conducted by changing the temperature using methods such as air cooling and furnace cooling.
When we investigated the effect of cooling rate on the occurrence of microcracks, we found that
The results shown in FIG. 5 were obtained. However, here, the slab heating temperature was changed to three types: 1300°G, 1350°C, and 1400°C, and the surface temperature when the weight was dropped was still 1200°.
C and Toshida. From FIG. 5, it was found that slow cooling from the slab heating temperature to the weight dropping temperature at a slow cooling rate of 3°C/sec or less is effective in preventing the occurrence of microcracks. Therefore, when cooling the slab extracted from the walking beam heating furnace to a temperature of 1250°C or less on the F surface of the slab before conveying it by table rollers,
It is clear that a cooling rate of /sec or more is effective for generating microcracks.

As described above, after heating the slab, it is slowly cooled at a cooling rate of 3°C/sec or less, and by lowering the temperature of the F-face of the slab at the time when an impact is applied by the table roller, grain boundaries are The reason why microcracks can be suppressed is considered to be as follows. That is, S and/or Se in the steel dissolves in solid solution during heating of the slab, and a portion of it segregates at a high concentration at grain boundaries. For this reason, the grain boundaries become extremely brittle, and if an impact is applied in this state, microcracks will easily occur from the grain boundaries. However, if the slab is slowly cooled after it is heated and before the impact is applied, the S and/-! , or a part of Se is MnS and/or M
Since it precipitates as nSe and the grain boundary segregation concentration becomes low, the grain boundary strength is recovered and cracks are thought to be less likely to occur even when subjected to impact.

Note that during slow cooling of the slab, if MnS and/or MnSe are precipitated inside the slab and the solid solution amount of S and/or Se decreases, this will lead to deterioration of the product's magnetic properties. Since the temperature inside the slab decreases significantly slower than that at the slab surface, by the time the slab surface (lower surface) reaches an appropriate precipitation state to prevent cracking, the inside of the slab still has a sufficiently high concentration of solid solution S and/or solid solution. or Se, and therefore there is no risk of deterioration of the magnetic properties of the product, as shown in the examples described later.

After the bottom surface temperature of the slab extracted from the walking beam heating furnace as described above is slowly cooled to a temperature of 1250°C or higher at a cooling rate of 3°C/sec or less, the slab is placed on a table roller. The steel sheet is transported to a hot rolling mill, and then processed in accordance with a conventionally known method for manufacturing unidirectional silicon steel sheets. For example, after hot rolling, cold rolling is performed twice with intermediate annealing to obtain the final plate thickness, and after decarburization annealing, an annealing separator is applied and final high temperature annealing is performed. The unidirectional silicon steel plate obtained in this way does not suffer from linear flaking caused by micro-cracks when the heated slab is conveyed by table rollers, and therefore has a better surface quality compared to conventional products. It becomes much better.

Note that there is no specific lower limit temperature for conveying the slab by table rollers after heating, but there are problems with workability during subsequent hot working, and as mentioned above, there are problems with the product due to the precipitation of MnS and MnSe when it is cooled to the inside. Due to problems such as deterioration of magnetic properties, it is usually desirable to set the temperature to about 1000° C. or higher.

The embodiments of this invention are described above.

Example C0,045%, Si 3.05%, MnO,08
%, 5O1007%, SeO,0251! +, Sb
A continuously cast slab with a thickness of 250 fins containing 30% O was heated in a walking beam heating furnace, and the temperature of the r-surface of the slab at the time of extraction was 1340'C as measured by a radiation thermometer. After extracting the slab, let it cool down until the bottom temperature reaches 1150-134°C.
After reaching various temperatures within the range of 1 to 1, the slabs were conveyed by taker rollers. The slab was then hot rolled to a thickness of 3.0 M, intermediate and annealed at 00°C for 1 minute, and then subjected to primary cold rolling at a cold rolling reduction of 75 inches and secondary cold rolling at a rolling reduction of 60%. 0.
A final thickness of 30 fIlm was obtained, then 85 mm in wet hydrogen.
After decarburizing annealing for 0'CXa minutes, magnesia slurry as an annealing separator was applied and annealing was performed for 850' in hydrogen.
Final annealing was performed at CX for 30 hours and at 1200° C. for XIO hours. The linear flaking occurrence rate of the obtained product, that is, the percentage of flaking blocks when one block has a coil length of 5077 m, and the results of examining the magnetic properties were calculated from the results of the investigation of the magnetic properties after heating the slab and up to the time when table roller conveyance was started. Table 1 shows the cooling time and the slab surface temperature at the start of heating of the slab F surface at the start of table roller conveyance.

From Table 1, it can be seen that for the slabs that were allowed to cool down to 1250'''C or higher after slab extraction and then started to be transported, the occurrence of linear bald spots on the products was significantly reduced, and the magnetic properties of the products were similar to those extracted from the slabs. It has become clear that excellent values comparable to those obtained when conveyance is started when the temperature exceeds 1250°C are shown.

As is clear from the above explanation, according to the silicon steel slab processing method of the present invention, when a slab having wavy flexure extracted from a walking beam heating furnace is transported by a table roller, the convex portion on the lower surface of the slab is On the other hand, even if an impact is applied from a roller, grain boundary microcracks are prevented from occurring, and as a result, the occurrence of linear flakes on the unidirectional silicon steel sheet as a final product is effectively prevented. It is possible to obtain a unidirectional silicon steel sheet with excellent properties, and the magnetic properties of the product are not particularly deteriorated.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a walking beam heating furnace used in the method of the present invention, and FIG. 2 is a schematic cross-sectional view showing an example of a silicon steel slab extracted from the walking beam heating furnace 1. Figures 1Mi and 2g3 show the bottom surface temperature of the silicon steel slab during heating in a walking beam heating furnace and the magnetic properties (magnetic flux density) of the final unidirectional silicon steel plate. ILLB and iron loss W
Figure 04 is a phase 1 force diagram showing the relationship between the surface temperature of a small specimen of a heated silicon steel slab and the frequency of occurrence of micro-cracks during a weight drop test on a small specimen of a heated silicon steel slab. A correlation diagram showing the relationship, and Figure 5 is the phase 1 column showing the relationship between the cooling rate and the frequency of microcracks when the cooling rate after heating at a predetermined temperature and until the weight falls off in the weight drop test is changed. It is a diagram. Applicant Kawasaki Steel Co., Ltd. Agent Patent Attorney Takehito Toyota (and 1 other person) Figure 1 Figure 2 [A Figure 3 Slab cutting circle 1: Menhen &('C) @ 4 books included゛Single blade o% Nagisa is tunjongrakuge amount, &('C)

Claims (1)

[Claims] 2.5 to 4.5% Si (wt%, same below), 0.03 to 0.10% Mn, and 0.005 to 0.10% of one or both of S and Se in total amount. The silicon steel slabs containing each are heated to slab F in a walking beam heating furnace.
After heating the slab to a surface temperature of 1270°C or higher and extracting it from the heating furnace, the bottom surface temperature of the slab is reduced to 3'C/s before being transported to a hot rolling mill using table rollers.
A method for processing a silicon steel slab, which comprises slowly cooling the slab to 1250° C. or lower at a cooling rate of EC or lower, and then conveying the slab with a table roller.