JP2817561B2 - Continuous production method of high silicon steel sheet excellent in bending workability and punching workability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability by Si infiltration treatment.

2. Description of the Related Art A high silicon steel sheet having a Si content of 4% by weight or more is industrially produced by a method of continuously infiltrating a low silicon steel sheet with Si as disclosed in JP-A-62-227078. It is possible. In general, a continuous Si infiltration treatment line is composed of a series of treatment zones of a heating zone, a siliconized zone, a diffusion zone, and a cooling zone, and can simultaneously perform enrichment of Si and magnetic annealing of a steel sheet.

However, the mechanical properties of a magnetically annealed high silicon steel sheet have a small elongation as shown in FIG.
In addition, since the tensile strength is as small as 10 to 15 kg / mm ² or less, it exhibits room temperature embrittlement. Also, the critical bending radius leading to fracture is large. For example, the critical bending radius of a 6.5 wt% silicon steel sheet having high magnetic properties is 15 to 30 m for a 0.1 mm thick material.
m, 0.3mm material is very large, 150-200mm. Therefore, in order to use iron cores for motors and transformers,
When processing such as slitting, shearing, punching, and bending is performed on a high-silicon steel sheet at normal temperature, there is a problem that cracks, chips, breakage, and the like occur, and it is necessary to perform these processings at a temperature of 200 to 300 ° C. there were.

For the purpose of improving the workability of silicon steel sheets (electromagnetic steel sheets), the following techniques have been conventionally proposed. JP-B-49-6731 and JP-A-61-22132
No. 8, etc., in order to improve the punchability of a low silicon steel sheet (Si: 4 wt% or less), in order to adjust the surface hardness of the steel sheet to an appropriate range (for example, HRB = 60 to 70), Techniques for optimizing the components have been proposed.
Also, JP-A-59-104430 and JP-A-60-13
No. 5,522, JP-B-61-3371, etc., have proposed a technique for optimizing the manufacturing conditions of a steel sheet for the same purpose.

[0004] In Japanese Patent Publication No. 63-16647, etc., in order to improve the brittleness of a low silicon steel sheet (Si: 1 wt% or less) after strain relief annealing, B is added to the steel in an amount of 0.0003 to 0.01 wt%.
A technique for preventing the internal oxidation of a steel sheet during annealing by adding% is proposed. Japanese Patent Application Laid-Open No. 4-165050 proposes a technique for preventing breakage during bending by adding 0.1 to 0.5 wt% of Mn for the purpose of improving the workability of a high silicon steel sheet. According to this technique, it is possible to perform 90 ° bending at a bending radius of 10 mm at 100 ° C.

[0005]

However, among the above techniques, those relating to a silicon steel sheet having a Si content of 4 wt% or less, as shown in FIG. %, The mechanical properties are extremely different from each other. Therefore, even if these techniques are applied to a high silicon steel sheet of Si: 4 wt% or more, no improvement in workability of the steel sheet can be expected at all. Further, the technique is aimed at improving the workability of a high silicon steel sheet.
It can only be wound to a radius of 10 mm at a temperature of ° C., and it is not possible to obtain the excellent workability that the present invention aims at only by optimizing such a component composition.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and provides a method of manufacturing a high silicon steel sheet in a continuous Si infiltration processing line, which has excellent workability at room temperature (such as bending workability and punching workability). It is an object of the present invention to provide a method capable of producing a high silicon steel sheet showing the following.

[0007]

Conventionally, it is well known that embrittlement of a silicon steel sheet progresses as the Si content increases.
Also, as shown in FIG. 1, magnetically annealed Si: 5w
It has also been accepted that elongation is completely absent in high silicon steel sheets of t% or more. The present inventors studied the processability of the high silicon steel sheet manufactured by the continuous Si infiltration process, and under normal manufacturing conditions (oxygen concentration: about 30 p
pm, dew point: about -10 ° C.), a 6.5 wt% silicon steel sheet is manufactured from a 3 wt% silicon steel sheet, and the mechanical properties of the obtained steel sheet are almost the same as those shown in FIG. Confirmed that there is. On the other hand, as a result of analyzing the high silicon steel sheet by the present inventors, a hard oxide layer is formed on the surface of the steel sheet, and Si or Si contained in the steel, which is a problem in Japanese Patent Publication No. 63-16647, etc. It has been clarified that grain boundary oxidation occurs instead of Al oxidation (so-called internal oxidation). It is considered that such grain boundary oxidation occurs because when a high silicon steel sheet is magnetically annealed at a high temperature, the crystals become large grains penetrating in the thickness direction.

[0008] As a result of examining the relationship between the oxidation form and brittleness of such a high silicon steel sheet, it was found that surface oxidation and grain boundary oxidation of the high silicon steel sheet had a strong correlation with brittleness. . The reason for this is that when the steel sheet is simply stretched, high strength cannot be obtained because it breaks from the interface embrittled by grain boundary oxidation, and when the steel sheet is bent, the maximum compression or It is considered that this is because a tensile stress acts to cause cracks from the brittle surface oxide layer, causing cracks and chips.

[0009] The present inventors have studied the manufacturing conditions which can suppress the oxidation of the steel sheet as described above in the Si infiltration treatment.
In a series of processes called cooling, the oxygen concentration in the atmosphere,
By controlling the dew point and the water vapor concentration under specific conditions, it has been found that a high silicon steel sheet having excellent workability can be manufactured by effectively suppressing the above-described oxidation. The present invention has been made based on such knowledge, and the characteristic configuration thereof is as follows.

(1) A silicon steel sheet containing less than 4% by weight of Si is continuously subjected to Si infiltration treatment to obtain Si: 5-1.
In producing a 0 wt% high silicon steel sheet, the atmosphere in the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the continuous Si infiltration treatment line was set to have an oxygen concentration of 45 ppm or less and a dew point of:
-30 ° C or lower and oxygen concentration [O ₂ ] (ppm)
And the water vapor concentration [H ₂ O] (ppm)

(Equation 4) A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing.

(2) C: 0.005 wt% or less, S
i: less than 4 wt%, Al: 0.008 wt% or less, M
n: 0.5 wt% or less, P: 0.01 wt% or less, S:
0.01 wt% or less, N: 0.01 wt% or less, O:
0.02 wt% or less, if necessary, B: 0.01 wt%
Hereinafter, Si: 5 to 10 wt% is obtained by continuously performing Si infiltration treatment on a silicon steel sheet including the balance of Fe and unavoidable impurities.
In manufacturing a high silicon steel sheet, the atmosphere in the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the continuous Si infiltration treatment line was set to have an oxygen concentration of 45 ppm or less and a dew point of -30 ° C.
And the oxygen concentration [O ₂ ] (ppm) and the water vapor concentration [H ₂ O] (ppm)

(Equation 5) A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing.

(3) C: 0.005 wt% or less, S
i: less than 4 wt%, Al: 0.008 wt% or less, M
n: 0.5 wt% or less, P: 0.01 wt% or less, S:
0.01 wt% or less, N: 0.01 wt% or less, O:
0.02 wt% or less, Cr, Ni, Cu, Sn and M
o at least one element selected from the group consisting of 0.03 wt% or less, and B: 0.01 wt% if necessary.
% Or less, Si: 5 to 10 wt.
% In the production of a high silicon steel sheet, the atmosphere in the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the continuous Si infiltration treatment line was set to have an oxygen concentration of 45 ppm or less and a dew point of -30.
° C or lower, and the oxygen concentration [O ₂ ] (ppm) and the water vapor concentration [H ₂ O] (ppm)

(Equation 6) A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing.

[0013]

In the present invention, the reasons for limiting the composition of the steel sheet as the material for the Si infiltration treatment are as follows. Si is 4
If the content is more than wt%, it is difficult to stably produce a thin plate due to the problem of rolling property. Therefore, the content of Si is set to less than 4 wt%.

If C exceeds 0.005 wt%, magnetic aging becomes a problem. Therefore, it is preferable that C is 0.005 wt% or less. Al is preferably not more than 0.008 wt% in order to prevent AlN precipitation accompanying nitridation by N ₂ used in the atmosphere to such an extent that magnetic characteristics are not affected. Mn combines with S to form MnS, which has the effect of improving hot workability in the slab stage, and thus can be added in an appropriate amount. However, if it exceeds 0.5 wt%, the saturation magnetic flux density is greatly reduced, so it is appropriate. Not. For this reason, Mn is preferably set to 0.5 wt% or less.

P is an element that deteriorates the soft magnetic properties,
The content is preferably as low as possible. P is preferably set to 0.01 wt% or less because the economic effect and the adverse effect can be substantially ignored if P is 0.01 wt% or less. S is an element that increases brittleness during hot rolling and also degrades soft magnetic properties. Therefore, the content of S is preferably as low as possible. Since the economic effect and the adverse effect can be substantially ignored if S is 0.01 wt% or less, it is preferable that S is 0.01 wt% or less.

N is an element that degrades the soft magnetic characteristics.
Since the magnetic properties also change with time due to aging, the content is preferably as low as possible. N is preferably set to 0.01% by weight or less since the adverse effect can be substantially ignored if the economy and N are 0.01% by weight or less. O is an element that deteriorates the soft magnetic properties, and its content is preferably as low as possible. If the economical efficiency and the O content in the steel sheet are 0.02 wt% or less, the adverse effect can be substantially ignored, so that O is 0.02 wt%.
It is preferable that the content be not more than wt%.

B is an element that improves workability and can be added in an appropriate amount. However, if added in excess of 0.01 wt%, the steel sheet becomes brittle. Therefore, B is added in an upper limit of 0.01 wt%. In addition to the above components, there are cases where Cr, Ni, Cu, Sn, Mo, and the like are contained as inevitable impurities in steel. Even if each of these is contained up to about 0.03 wt%, the effect of the present invention is impaired. Not.

Next, the conditions of the Si infiltration treatment of the present invention will be described. In examining the effect of oxidation of the high silicon steel sheet on workability, samples were prepared at a laboratory level, and tensile strength and elongation were measured by a tensile test. Further, pipes of various diameters were prepared, and the minimum radius at which cracks occurred when the pipes were wound at 180 ° was defined as a critical bending radius, and the bending workability was evaluated using this value. Evaluation of the workability is that the tensile strength at room temperature is 40 kg / mm ² or more,
Elongation of 3% or more, equivalent to a plate thickness of 0.1 mm and a critical bending radius of 2
mm or less was determined to be good in workability. Incidentally, a conventional low silicon steel plate requires a right angle bending with a bending radius of about 2 mm.

First, at a Si content of 6.5 wt% and a sheet thickness of 0.1 wt.
Prepare a sample of 1mm high silicon steel sheet,
Approximately 3 at a temperature of 1150 ° C.
The sample was held for one minute and the oxygen concentration and dew point in the furnace atmosphere were adjusted to obtain samples having different oxidation states. For each of these samples, the thickness of the surface oxide film was measured and the bending workability (critical bending radius) was evaluated. FIG. 2 shows the result. When the oxide film thickness exceeds 1000 °, the critical bending radius sharply increases, and the critical bending radius becomes 2 mm.
It is understood that the oxide film thickness of the steel sheet needs to be 1000 ° or less in order to achieve the following.

Next, the sheet thickness is 0.1 mm and the Si content is 5.0 wt%, 6.5 wt%, and 8.0 w%, respectively.
t%, 9.2 wt%, 10.0 wt%, 12.0 wt%
Were prepared, and the degree of vacuum for these samples was 1 /
Anneal at 1150 ° C. for 3 minutes in a vacuum annealing furnace of 10 ⁵ torr or less, paying sufficient attention to atmospheric oxidation during the test to obtain samples having a substantial oxide film thickness of 50 ° or less. The sex was evaluated. FIG. 3 shows the results. When the Si content exceeds 10 wt%, embrittlement due to Si becomes remarkable, and it becomes impossible to bend with a radius of 2 mm or less. This means that a high silicon steel sheet having a Si content of more than 10 wt% cannot form a wound iron core at room temperature even if its oxidation is sufficiently suppressed. The upper limit of the Si content of the high silicon steel sheet to be manufactured is 10 wt%.

The oxidation of the steel sheet, which is a problem in the continuous Si infiltration treatment, is oxidation by oxygen and water vapor in the furnace atmosphere in a series of steps of heating, siliconizing, diffusion soaking, and cooling. Then, first, the following evaluation tests were carried out using the above-mentioned test furnace, in which the dew point and the oxygen concentration in the furnace atmosphere were variously changed in order to cope with various conditions during the continuous Si infiltration treatment. In this test, N ₂ was used as the gas for the furnace atmosphere.
Using 0.1mm thickness under various dew point and oxygen concentration
A sample having an Si content of 6.5 wt% was
Annealed for 0 minutes. FIG. 4 shows the relationship between the oxygen concentration and the dew point in the furnace atmosphere and the bending workability (critical bending radius) of the steel sheet after annealing. Table 1 shows the relationship between the dew point and the water vapor concentration. According to these, when the dew point is higher than −30 ° C., since the water vapor concentration exceeds several hundred ppm, rapid oxidation occurs, and the critical bending radius becomes very large. On the other hand, when the dew point is −30 ° C. or less, the conditions under which the bending radius is 2 mm or less are summarized by water vapor concentration and oxygen concentration as shown in FIG. That is, the water vapor concentration [H ₂ O] (pp
m) and the oxygen concentration [O ₂ ] (ppm)

(Equation 7) If it can be managed to satisfy the condition of
mm, that is, from the results of FIG. 2, it can be seen that it is possible to keep the oxidation state such that the surface oxide film thickness becomes 1000 ° or less.

Further, a tensile test was performed to evaluate the punching property and the shearing property. FIG. 6 shows an example of the result. According to this, a workability improving effect is observed when the oxygen concentration is 45 ppm or less, and particularly, when the oxygen concentration is approximately 20 ppm or less, a tensile strength of 40 kg / mm ² or more and an elongation of 3% or more are secured. For the reasons described above, the present invention employs continuous Si
The atmosphere in the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the infiltration treatment line is set to have an oxygen concentration of 45 ppm or less, a dew point of -30 ° C or less, and an oxygen concentration of [O ₂ ] (pp
m) and the water vapor concentration [H ₂ O] (ppm)

(Equation 8) The requirement is to manage to satisfy the conditions of

[0023]

【Example】

Example 1 In the continuous Si infiltration processing line shown in FIG. 7, Si: 3 wt%, C: 0.003 wt%, Al:
It is a non-oriented silicon steel sheet of 0.002 wt%, the sheet width is 400 mm, the sheet thickness is 0.1 mm, 0.2 mm, respectively.
Each steel sheet of 0.3 mm is subjected to silicon infiltration treatment at 1150 ° C. × 1.5 to 10 minutes and diffusion soaking treatment at 1180 ° C. × 2 to 10 minutes in the following and each N ₂ atmosphere, A non-oriented high silicon steel sheet of Si: 6.5 wt% was manufactured. Atmosphere conditions of comparative example: oxygen concentration = 30 ppm, dew point = −10 ° C.

(Equation 9) Atmospheric conditions of the present invention: oxygen concentration = 5 ppm, dew point =
-30 ° C

(Equation 10)

With respect to the obtained high silicon steel sheet, the critical bending radius, tensile strength, and elongation were measured. In addition, in order to evaluate the presence or absence of cracks and chips at the time of punching, a rectangular sample of 20 mm × 30 mm was continuously punched from the manufactured coil, and 4 samples of 10 samples were randomly extracted.
The number of cracks and chips at the corners was measured. Table 2 shows these results.
Shown in According to the table, it is understood that a high silicon steel sheet having extremely excellent workability can be obtained by following the conditions of the present invention.

Example 2 In the continuous Si infiltration processing line shown in FIG. 7, Si: 3.2 wt%, C: 0.003
wt%, Al: 0.002 wt% directional silicon steel sheet having a sheet width: 400 mm and a sheet thickness: 0.2 mm,
5. Si infiltration treatment was performed under the same conditions as in Example 1 above,
A 5 wt% oriented high silicon steel sheet was manufactured and evaluated for workability. The results are shown in Table 3. The product manufactured under the conditions of the present invention can be wound with a radius of 5 mm at room temperature, and Mn is intentionally added to steel as in the above-mentioned Japanese Patent Application Laid-Open No. 4-165050. It can be seen that excellent workability can be obtained without adding any of these.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

According to the present invention described above, it is possible to manufacture a high silicon steel sheet having excellent workability such as bending workability and punching workability.
It can be processed at normal temperature without causing chipping, breakage and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Si content of a magnetically annealed silicon steel sheet and mechanical properties.

FIG. 2 is a graph showing the relationship between the surface oxide film thickness of a high silicon steel sheet and bending workability.

FIG. 3 is a graph showing a relationship between Si content and bending workability of a silicon steel sheet having an oxide film thickness of 50 ° or less.

FIG. 4 is a graph showing the relationship between the oxygen concentration and the dew point in the furnace atmosphere when a high silicon steel sheet is heat-treated and the bending workability of the steel sheet after the heat treatment.

FIG. 5 is a graph showing a range of a high silicon steel sheet having good bending workability in relation to oxygen concentration and water vapor concentration in a furnace atmosphere.

FIG. 6 is a graph showing the relationship between the oxygen concentration in the furnace atmosphere when a high silicon steel sheet is heat-treated and the breaking tension and elongation of the steel sheet after the heat treatment.

FIG. 7 is an explanatory view showing a continuous Si infiltration processing line.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI // C21D 8/12 C21D 8/12 A (72) Inventor Tsunehiro Yamaji 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. ( 72) Inventor Katsushi Kasai 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Yasushi 1-2-1 Marunouchi 1-chome, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (58) Field (Int.Cl. ⁶ , DB name) C23C 10 / 00,10 / 06-10/08 C23C 10/14-10/16

Claims (3)

(57) [Claims] 1. A silicon steel sheet containing less than 4% by weight of Si is continuously subjected to Si infiltration treatment to obtain 5 to 10% of Si.
% In the production of a high silicon steel sheet, the atmosphere in the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the continuous Si infiltration treatment line was set to have an oxygen concentration of 45 ppm or less and a dew point of -30.
° C or lower, and the oxygen concentration [O ₂ ] (ppm) and the water vapor concentration [H ₂ O] (ppm) are expressed as follows: A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing. 2. C: 0.005 wt% or less, Si: 4 w
Less than t%, Al: 0.008 wt% or less, Mn: 0.5
wt% or less, P: 0.01 wt% or less, S: 0.01 w
t% or less, N: 0.01 wt% or less, O: 0.02 wt%
% Or less, if necessary B: 0.01 wt% or less, balance F
e and a silicon steel sheet comprising unavoidable impurities
In producing a high silicon steel sheet of 5 to 10 wt% of Si by infiltration, the atmosphere of the heating zone, the siliconized zone, the diffusion zone, and the cooling zone in the continuous Si infiltration process line is set to have an oxygen concentration of 45 ppm or less and a dew point. : -30 ° C. or lower, oxygen concentration [O ₂ ] (ppm) and water vapor concentration [H ₂ O]
(Ppm) A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing. 3. C: 0.005 wt% or less, Si: 4 w
Less than t%, Al: 0.008 wt% or less, Mn: 0.5
wt% or less, P: 0.01 wt% or less, S: 0.01 w
t% or less, N: 0.01 wt% or less, O: 0.02 wt%
% Or less, one or more elements selected from Cr, Ni, Cu, Sn and Mo each having a content of 0.03 watts.
t% or less, if necessary, B: 0.01 wt% or less, and a silicon steel sheet comprising the balance Fe and unavoidable impurities is continuously S
In producing a high silicon steel sheet of 5 to 10 wt% of Si by performing i-penetration treatment, the atmosphere of the heating zone, the siliconized zone, the diffusion zone and the cooling zone in the continuous Si infiltration treatment line are
Oxygen concentration: 45 ppm or less, dew point: -30 ° C or less,
In addition, oxygen concentration [O ₂ ] (ppm) and water vapor concentration [H
₂ O] (ppm) A method for continuously producing a high silicon steel sheet having excellent bending workability and punching workability, characterized in that the steel sheet is controlled so as to satisfy the following conditions and suppresses surface oxidation and grain boundary oxidation of the steel sheet during processing.