JP3383532B2 - Method for producing non-oriented electrical steel strip with excellent corrosion resistance and magnetic properties - 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 producing a non-oriented electrical steel strip having excellent corrosion resistance and magnetic properties, and particularly to the deterioration of corrosion resistance which has been conventionally concerned when desulfurization is performed using metallic Ca or Ca alloy. It is an attempt to effectively prevent it.

[0002]

The most important characteristic of non-oriented electrical steel strip is
The iron loss is low, and this iron loss depends on the recrystallized grain size obtained by finish annealing after cold rolling, and the lowest iron loss is obtained when the recrystallized grain size is 150 to 250 μm. It has been known.

In order to recrystallize to such a grain size, it is necessary to reduce fine precipitates such as nitrides and sulfides as much as possible. Among these precipitates, for nitrides, AlN can be precipitated with a relatively large grain size by containing 0.15 wt% or more of Al in the steel, so that grain growth of recrystallization is hindered during finish annealing. There are few things. On the other hand, regarding sulfide, it is possible to improve the iron loss value by adding a rare earth element so that the sulfide is thermodynamically stable and does not undergo solid solution / reprecipitation, or is fixed as a relatively large precipitate. What can be done is reported in JP-A-51-62115.

In Japanese Patent Publication No. 58-17249, Ca is R
Similar to em, we focus on making thermodynamically stable sulfides, and improve the properties by including an appropriate amount of Ca in electrical steel sheets. That is, by reducing the amount of S that is unavoidably mixed in the non-oriented electrical steel sheet to a predetermined amount or less and by including Ca in an amount satisfying a predetermined range with respect to this S amount, the iron loss characteristics are extremely effective. Has been reported to be improved.

[0005]

DISCLOSURE OF THE INVENTION In electromagnetic steel strip,
From the viewpoint of preventing the deterioration of the characteristics during use, it is an absolute condition that there is no rust during use. However,
When desulfurization is carried out using Ca, rust often occurs and the corrosion resistance deteriorates.

The present invention advantageously solves the above problems and provides an advantageous method for producing a non-oriented electrical steel strip which does not deteriorate in corrosion resistance even when desulfurized with Ca or the like. The purpose is to propose.

[0007]

Means for Solving the Problems The clarification process of the present invention will be described below. FIG. 1 shows a comparison of the results of investigations on the corrosion resistance of electromagnetic steel strips containing Ca and those not containing Ca. Incidentally, the corrosion resistance test is a salt spray test (JIS Z 23
71). As shown in FIG. 1, the amount of residual Ca is much higher than that of no Ca. The reason for this is that Ca compounds such as Ca or CaS have a strong hygroscopic property, and therefore, due to the moisture absorption of the compound existing in the surface layer, rusting occurs from that point first, and they migrate to the surroundings. It is considered that this is because the rusting rate becomes extremely high as compared with the steel sheet that does not contain it.

As described above, in order to improve iron loss or improve the desulfurization method, Ca or Ca added or remaining in the steel.
Ca compounds such as S and CaO deteriorate the corrosion resistance of the non-oriented electrical steel strip. This is because Ca or Ca compounds such as CaS and CaO are very rich in affinity and reactivity with H ₂ O. An example of this reaction is shown below. Ca + 2H ₂ O → CaH (OH) + H ₂ O → Ca (OH) ₂ + H ₂ CaS + 2H ₂ O → Ca (OH) ₂ + H ₂ S CaO + nH ₂ O → CaO ・ n (H ₂ O) These reactions are performed at room temperature. It is known to easily go to the right. The CaH (OH), Ca (OH) ₂ or CaO produced by the above formula has a very high hygroscopicity and induces the adsorption of H ₂ O on the plate surface to increase the degree of rusting.

Therefore, the present inventors have paid attention to the affinity and reactivity of Ca with H ₂ O, and conversely considered to utilize this phenomenon. That is, after finishing annealing and before applying the insulating coating, the plate surface is previously immersed in an aqueous solution containing H ₂ O or sprayed with the aqueous solution to cause an adsorption reaction, and Ca
Alternatively, when compounds such as CaS and CaO were washed out of the plate, unexpected results were achieved in achieving the intended purpose. The present invention is based on the above findings.

That is, the present invention is C: 0.01 wt% or less, Si: 3.5 wt% or less, Mn: 1.5 wt% or less, Al: 2.5 wt% or less, S: 0.05 wt% or less, P: 0.1 wt% or less. Desulfurization of molten steel with a composition containing Ca using a metallic Ca or Ca alloy to form a slab, followed by hot rolling, cold rolling, and finish annealing, and then 2 seconds in water or an acid or alkaline aqueous solution. The above is a method for producing a non-oriented electrical steel strip having excellent corrosion resistance and magnetic properties, which is characterized by immersing and cleaning the surface of the steel sheet.

In the present invention, as described above, instead of immersing the steel strip in the treatment liquid, the steel sheet surface may be cleaned by spraying water or an acid or alkali aqueous solution onto the steel sheet surface. .

Further, in the present invention, it is more advantageous in terms of surface cleaning to perform brushing at a peripheral speed ratio of 3.0 or more with a brush roll in a wet state after the above-mentioned cleaning treatment. is there.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the reason why the material components are limited to the above range in the present invention will be described. C: 0.01 wt% or less C expands the γ range and lowers the α-γ transformation point. During the annealing, the γ phase is formed in the α grain boundary in a film shape and suppresses the growth of the α grain, so that it is basically necessary to reduce C. In addition, even if a large amount of α-phase stabilizing elements such as Si and Al are contained, and the γ-phase is not formed in the entire temperature range, the iron loss characteristics are deteriorated by aging. Therefore, the C content needs to be 0.01 wt% or less. There is. The lower limit is not particularly limited, but it is preferably 0.0005 wt% or more in terms of cost and the like.

Si: 3.5 wt% or less Si is a useful element that increases the specific resistance of steel and reduces iron loss, and changes the content according to the target magnetic properties.
However, at the same time, the hardness is also increased and the cold rolling property is deteriorated, so the upper limit was made 3.5 wt%. The lower limit is not specified, but from the viewpoint of increasing the specific resistance, it is 0.05
It is desirable to contain more than wt%.

Al: 2.5 wt% or less Al, like Si, is an element that increases the specific resistance of steel and decreases iron loss, and changes its content according to the target magnetic characteristics. However, when the content is high, the lubricity with the mold is lowered during continuous casting, making casting difficult, so the upper limit was set to 2.5 wt%.

Mn: 1.5 wt% Mn also has an effect of increasing the specific resistance of steel and reducing iron loss, though not so much as Si or Al, and also of improving hot rolling property. However, if a large amount is contained, the cold rolling property deteriorates, so the upper limit was set to 1.5 wt%.

S: 0.05 wt% or less S is an element that should be reduced as much as possible because it forms precipitates and inclusions and hinders grain growth. In the present invention, CaSi is used for desulfurization, and the precipitation form of S is controlled to render S harmless. However, when the residual amount in steel is large, the number of particles of inclusions increases, and S Ca for fixing
If the content of MnS is relatively insufficient, the proportion of MnS in the inclusions increases, which also adversely affects the grain growth. Therefore, S is set to 0.05 wt% or less.

P: 0.1 wt% or less P also has the effect of increasing the specific resistance of steel and reducing iron loss, though not so much as that of Si and Al, and also has a texture after cold rolling recrystallization due to grain boundary segregation. Has the effect of improving the magnetic flux density. However, if added excessively, the amount of segregation at the grain boundaries increases, rather hindering grain growth and deteriorating iron loss, so the content was made 0.1 wt% or less.

Although the essential components have been described above, various other well-known elements can be added. For example, B, Ni, Cu, Sn, Sb, Bi and Ge are added as magnetic property improving components. can do.

Next, the manufacturing method will be described. As described above, in the present invention, metal Ca and
Desulfurization is performed using a Ca alloy such as CaSi and CaAl (hereinafter simply referred to as Ca alloy). The amount of such Ca alloy added is preferably such that the amount remaining in the steel is about 5 to 100 ppm. If the residual amount is less than 5 ppm, sufficient desulfurization (S ≦ 0.001 wt%) cannot be achieved, while 100 ppm
If it exceeds, even if the cleaning treatment described later, the Ca compound remaining on the surface of the steel sheet cannot be completely removed.

The slab production conditions after the melting, the hot rolling conditions, the cold rolling conditions and the finish annealing conditions are not particularly limited, and may be carried out according to a conventional method.

In the present invention, after the above-mentioned finish annealing, the compounds such as Ca or CaS, CaO existing on the surface of the plate are utilized in water or an aqueous solution by utilizing the properties such as affinity and reactivity with H ₂ O. It is important to wash and remove Ca by a method of immersing in or spraying the aqueous solution onto the plate surface, and by performing such a washing treatment, the non-oriented electrical steel strip containing Ca It improves the corrosion resistance.

FIG. 2 shows the case where water is used as the cleaning liquid.
Cleaning time and non-oriented electrical steel strip (Ca content: 15-50 ppm)
The result of having evaluated the relation with the corrosion resistance by the salt spray corrosion resistance accelerated test is shown. As shown in the figure, by setting the cleaning time (contact time with H ₂ O) to 2 seconds or more,
Corrosion resistance is drastically improved. Therefore, in the present invention, the cleaning time by immersion in the treatment liquid is limited to 2 seconds or more. However, if the cleaning time exceeds 100 seconds, the reaction with oxygen contained in the aqueous solution will already generate rust before the insulating coating, and the corrosion resistance after coating will deteriorate. It is preferable that

Next, FIG. 3 shows a non-oriented electrical steel strip (Ca content: 15) when the surface of the steel strip was washed with various cleaning liquids.
The results of the investigations on the difference in corrosion resistance (~ 50 ppm) are shown for comparison. As shown in the figure, the corrosion resistance of the non-oriented electrical steel strip is remarkably improved by washing with water, an acid, or an alkaline aqueous solution as opposed to unwashed or washed with an organic solvent (acetone). What is important here is that the cleaning solution contains H ₂ O,
The values of (acidity, alkalinity) are not the essence of the present invention.

Next, FIG. 4 shows the relationship between the peripheral speed ratio (brush peripheral speed / plate speed) and corrosion resistance when the steel strip is washed with water and then brushed with a brush roll in a wet state. The results of the survey are shown below. As shown in the figure, by performing brushing with a brush roll after the cleaning treatment, the corrosion resistance is further improved, and especially by setting the peripheral speed ratio to 3.0 or more, the rust area ratio can be reduced to 3% or less. did it.

As described above, the reason why the corrosion resistance is further improved by using the brushing using the brush rolls together is that the brushing enables more detailed cleaning removal of Ca and Ca compounds remaining on the plate surface. It is thought to be because. The material of the brush is not particularly limited, but it should not be one that causes excessive distortion or flaws on the plate surface. The peripheral speed ratio is important for the roll diameter, and the roll diameter itself is not limited. Further, in FIG. 4, the case where water is used as the cleaning liquid has been mainly described, but it has been confirmed that the same effect can be obtained even when an acid or alkaline aqueous solution is used as the cleaning liquid.

[0027]

EXAMPLES Table 1 shows an example of the present invention. This is an evaluation of the corrosion resistance of typical steel grades due to the difference in the cleaning method before coating a non-oriented electrical steel strip containing Ca. The manufacturing conditions for the evaluated plate are 15 to 50 p.
About three kinds of non-oriented electrical steel strips containing pm Ca
Predetermined time before coating (0, 1, 2, 10, 10
(A) water (industrial water), (B) 3% hydrochloric acid aqueous solution, (C) 10% caustic soda solution, (D) organic solvent, and in some cases after immersion, a brush roll in a wet state Brushing was performed at a peripheral speed ratio of 5.0, and then draining, drying and coating were performed.

Corrosion resistance was evaluated by coating the obtained plate (before stress relief annealing) and by performing stress relief annealing at 750 ° C. for 2 hours in a nitrogen atmosphere. Z 2371, 5 hours) According to the test, after strain relief annealing, the constant temperature and humidity test (50 ° C, 14 days wet rate:
80%) promoted rusting of the plate surface, and the corrosion resistance was evaluated by the area ratio of the rusted portion. The evaluation criteria are ◎ in the table.
The rusted area ratio is 2% or less, ○ is 3-10%, □ is 11-
The results are distinguished by 20%, Δ mark 21 to 50%, and X mark 51% or more.

As is clear from Table 1, there is no difference in corrosion resistance depending on the steel type, 2 seconds or more, (A) water, (B) hydrochloric acid,
(C) The one soaked in caustic soda has improved corrosion resistance and good results are obtained as compared with those not washed, washed with an organic solvent or washed for less than 2 seconds. In particular, in the case of using brushing in combination, further improvement in corrosion resistance has been achieved. In addition, although a part of the cases have been described in the above embodiments, the present invention is not limited to this, and it has been confirmed that the same effect can be obtained by spraying an aqueous solution instead of dipping. . Further, it is important that the liquid used also contains H ₂ O, and the effects on Ca are the same even if there is a difference in pH or other components are included.

[0030]

[Table 1]

[0031]

As described above, according to the present invention, with respect to the Ca desulfurized non-oriented electrical steel strip, before the insulating coating, Ca or Ca on the steel surface is treated with water or an acid or alkaline aqueous solution.
By cleaning and removing compounds such as S and CaO, it is possible to obtain an electromagnetic steel strip excellent not only in magnetic properties but also in corrosion resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a difference in corrosion resistance depending on the presence or absence of Ca.

FIG. 2 is a graph showing the relationship between cleaning time and corrosion resistance.

FIG. 3 is a diagram showing a difference in corrosion resistance due to a difference in plate surface cleaning liquid.

FIG. 4 is a graph showing the influence of the brush roll peripheral speed ratio on corrosion resistance.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22C 38/06 C22C 38/06 C23G 1/00 C23G 1/00 H01F 1/16 H01F 1/16 A (58) Fields investigated (58) Int.Cl. ⁷ , DB name) C21D 8/12 C21D 9/46 501 C21C 7/00-7/10 C22C 38/00-38/60 C23G 1/00-1/36 H01F 1/16

Claims (3)

(57) [Claims] 1. A composition containing C: 0.01 wt% or less, Si: 3.5 wt% or less, Mn: 1.5 wt% or less, Al: 2.5 wt% or less, S: 0.05 wt% or less, P: 0.1 wt% or less. The molten steel to be desulfurized with metallic Ca or Ca alloy is made into a slab, then hot-rolled, cold-rolled and finish-annealed, and then immersed in water or an acid or alkali aqueous solution for 2 seconds or more. A method for producing a non-oriented electrical steel strip having excellent corrosion resistance and magnetic properties, which comprises cleaning the surface of a steel sheet. 2. A non-oriented steel sheet having excellent corrosion resistance and magnetic properties, characterized in that, instead of immersing the steel strip in the treatment liquid, water or an acid or alkali aqueous solution is sprayed onto the steel plate surface for cleaning. For manufacturing high-performance electromagnetic steel strip. 3. The excellent corrosion resistance and magnetic properties according to claim 1 or 2, characterized by brushing at a peripheral speed ratio of 3.0 or more with a brush roll in a wet state after cleaning the steel strip. Method for manufacturing non-oriented electrical steel strip.