JPH01119622A - Production of grain oriented electrical steel sheet having excellent magnetic characteristic and glass film characteristic - Google Patents

Abstract

PURPOSE:To stabilize secondary recrystallization by the stabilized nitriding reaction of a material and to stably form glass films, by removing only the extreme surface layer of the oxide film formed in a decarburization annealing process by light pickling, then by specifying the atmosphere conditions in the final finish annealing process. CONSTITUTION:A slab for a grain oriented electrical steel sheet consisting by weight, 0.0010-0.10% C, 2.5-4.0% Si, 0.010-0.06% acid solAl, <=0.014% S, and the balance Fe and inevitable impurities is heated to the temp. below 1,200 deg.C and is then subjected to hot rolling and the annealing of the hot rolled sheet. This steel sheet is subjected to one pass of cold rolling or >=2 passes of cold rolling including annealing to the final sheet thickness. The material after the final cold rolling is subjected to decarburization annealing in the 800-900 deg.C region in the wet hydrogen atmosphere of 0.25-0.60 ratio PNZO/PNZ of the steam partial pressure to the hydrogen partial pressure; thereafter, only the MxOy layer except SiO2 formed on the extreme surface layer of the material is removed by the light pickling at 0.02-2g per 1m<2> of the material surface. An annealing and separation agent is then coated thereon and further, the steel sheet is subjected to the final annealing.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to the modification of an oxide film layer on the surface of a material obtained in the decarburization annealing step of the manufacturing process of unidirectional electrical steel sheets, and in particular, The present invention relates to a method for producing grain-oriented electrical steel sheets that simultaneously stabilizes secondary recrystallization of the material during final annealing and improves the properties of the glass coating.

(Prior art) A unidirectional electrical steel sheet has (110) (00
1) A plate with a thickness of 0, usually containing 4.5% by weight or less of Si, consisting of oriented crystal grains (Goss-oriented grains)
．． 10 to 0.35 round steel plate. Its surface is usually covered with forsterite for the purpose of ensuring insulation.

In other words, the unidirectional electrical steel sheet has an extremely high degree of integration (11
0) (001) St with collective texture (Goss texture)
It is a composite material consisting of a thin steel plate and a surface layer of forsterite, which is an oxide ceramic with a thickness of 0.1 to several μm.

The two distinct processes of achieving an extremely high degree of Goss structure integration and forming a thin forsterite insulating film on the surface of the material are achieved through a process called final annealing in the current manufacturing process of grain-oriented electrical steel sheets. During one box annealing process, these are performed at approximately the same time. In the former case, the increase in the degree of accumulation of the Goss structure is due to catastrophic grain growth (abnormal grain growth) of Goss-oriented grains called secondary recrystallization.
Used industrially.

On the other hand, the latter formation of a thin forsterite insulating film on the surface of the material is due to the combination of SiO□ in the oxide film previously formed on the surface of the material (steel plate) and MgO in the annealing separator applied thereon. It is made by solid phase reaction.

These two phenomena, secondary recrystallization and the formation of forsterite, which are completely different in wood quality, are caused by the decarburization annealing conditions and annealing conditions that determine the structure and thickness of the oxide film formed on the material surface during the decarburization annealing process. Easily affected by separating agents. Also, these 2
It is thought that this phenomenon is actually the result of a reaction progressing while mutually interfering between the inside of the material (III plate) and the surface layer part surface.

From this point of view, many studies have been conducted on decarburization annealing conditions and annealing separators.

On the other hand, for the purpose of improving productivity, the unit weight of strip coils handled in the final annealing process tends to increase. ) variation,
In particular, variations in temperature cannot be avoided. In order to alleviate as much as possible the non-uniformity of temperature and atmospheric conditions inside the material (strip coil) during the final finish annealing process, the oxide film layer formed on the material surface during the decarburization annealing process, Annealing separators are important and have motivated research in this area.

The effect of the oxide film layer formed on the material surface during the decarburization annealing process is
Thick (There are two parts.

One is stable formation of a glass film (forsterite film) on the material surface, and the other is stabilization of secondary recrystallization.

In the former case, the thickness of the oxidized layer on the surface of the material, its constituent components, etc. are important, and in the latter case, it is important to determine the mechanism by which secondary recrystallization is performed in terms of the material.

These are important criteria for selecting decarburization and sintering conditions.

As is well known, the presence of fine precipitates called inhibitors is essential for the secondary recrystallization of the material to proceed in the final annealing process. Normally, secondary recrystallization is stabilized by strengthening and maintaining the dispersed phase of the fine precipitates up to the high temperature range of the final annealing process. (N2
) If the main component is sulfide, maintain the sulfur partial pressure appropriately.

Nitrogen (N2) in the annealing atmosphere during the final annealing process
Regarding maintaining an appropriate partial pressure, for example, Japanese Patent Publication No. 46-937 discloses the usefulness of annealing a M-containing silicon steel sheet under a nitrogen cloud, and this method is Tokuko Sho 4 proposed nitriding silicon steel sheets containing U, Ti, Zr, V, etc. by various methods.
The process was developed into the process disclosed in Publication No. 6-40855.

Furthermore, Japanese Patent Publication No. 49-6455 points out the usefulness of selectively nitriding the surface layer of M-containing silicon steel sheets, and Japanese Patent Publication No. 54-19850 also states that appropriate nitriding is necessary. In order to cause absorption, it has been proposed that the dew point of the atmosphere during final annealing be in the range of -20°C to +30°C.

Furthermore, Japanese Patent Publication No. 54-22408 proposes that final annealing be performed in a hydrogen/nitrogen mixed atmosphere containing 20% or less hydrogen.

On the other hand, a method of mitigating the effects of atmospheric variations in the length and width directions of the material (strip coil) during the final annealing process was developed by adding metal nitrides to the annealing separator. It is disclosed in Japanese Patent No. 14568. Specifically, by adding chromium nitride, titanium nitride, and vanadium nitride to the annealing separator, the nitrogen partial pressure in the atmosphere in the strip width direction of the strip coil during the final annealing process is made uniform, and secondary recrystallization is achieved. The aim is to achieve the stability of

On the other hand, there is a method proposed in Japanese Patent Laid-Open No. 53-50008 for the purpose of ensuring the sulfur partial pressure in the atmosphere during the final annealing process. This is because sulfur compounds such as FezS are added to the annealing separator in order to stabilize the secondary recrystallization of silicon steel, which uses sb and a precipitated dispersed phase mainly composed of S and/or Se as an inhibitor. In this method, final annealing is performed in an atmosphere containing H and S.

As seen in these prior art techniques, the secondary recrystallization of silicon steel tends to be stabilized by ensuring nitrogen partial pressure and sulfur partial pressure in the final annealing process, and the additives in the annealing separator also stabilize this process. Often added for a purpose.

As mentioned above, the glass film formation, which is one of the functions of the oxide film formed on the material surface during the decarburization annealing process, is caused by the reaction between MgO in the annealing separator and SiO□ in the oxide film. Therefore, it is important that the oxide film is rich in SiOg as a constituent component and that the film thickness is above a certain level.

Regarding the stabilization of secondary recrystallization in the final annealing process, which is the second function of the oxide film formed on the material surface during the decarburization annealing process, conventional inhibitors such as MnS and
When using MnSe, /VN, etc., in order to prevent changes in the inhibitor due to reaction with the atmospheric gas during the temperature raising process during final annealing, an oxide film that is stable against the atmospheric gas, that is, a film with good sealing properties ( There has been a demand for an oxide film that can function as a barrier.

For this purpose, for example, Japanese Patent Publication No. 57-1575 states that the degree of oxidation of the atmosphere (P2°/P M□) in the first stage region of the decarburization annealing process is set to be 0.15 or more, and that It is disclosed that the oxidation degree of the atmosphere is set to 0.75 or less and smaller than that in the former region.

In recent years, attempts have been made to produce grain-oriented electrical steel sheets in which the slab is heated to a relatively low temperature without completely solutionizing the inhibitor in the slab heating process.

In such a process, it is necessary to precipitate and disperse the inhibitor in a process other than the hot-rolled sheet annealing process. One of such means for dispersing inhibitor precipitation is a means for precipitating M in steel by nitriding, for example, at a stage before secondary recrystallization in final finish annealing.

When such a measure is adopted, the function of the oxide film formed on the material surface during the decarburization annealing process changes completely. That is, the oxide film formed on the material surface during the decarburization annealing process must not be an oxide film that is stable against the atmospheric gas in the final finish annealing as described above.

These conditions must be met, and the properties of the glass film must be improved and secondary recrystallization stabilized.

(Problems to be Solved by the Invention) The present invention aims at stabilizing the nitriding reaction of the material during the final annealing process when using a unidirectional electrical steel sheet manufacturing process in which the slab heating temperature is at a low level of less than 1280°C. The purpose of this work is to provide a method for producing grain-oriented electrical steel sheets that can stabilize secondary recrystallization and stably form a glass film.

(Means for solving the problems) The gist of the present invention is that C: 0.00% by weight
10-0.10%, Si: 2.5-4.0%, acid-soluble A1: 0.010-0.06%, S≦0.014%,
Remaining portion: After heating a unidirectional electrical steel plate slab consisting of Fe and unavoidable impurities to a temperature not exceeding 1280°C, hot rolling and hot rolled plate annealing are performed, and then once or twice with intervening annealing. In the method for manufacturing unidirectional electrical steel sheets, the final cold rolling is performed to achieve the final thickness, followed by decarburization annealing in a wet hydrogen atmosphere, followed by applying an annealing separator and final finish annealing. The material after rolling is adjusted to a ratio of water vapor partial pressure to hydrogen partial pressure, PH2°/Poz, of 0.25.
After decarburizing annealing in a temperature range of 800 to 900°C in a wet hydrogen atmosphere of ~0.60, SiO□ formed on the outermost surface layer of the material
0.02 per m2 of material surface only for the MXoy layer other than
The patent and method for producing a unidirectional electrical steel sheet with excellent glass film properties include removing ~2g by light pickling, then applying an annealing separator, and further final annealing.

The present invention will be explained in detail below.

As mentioned above, the present invention removes only the outermost layer of the oxide film formed in the decarburization annealing process by light pickling, and specifies the atmospheric conditions in the final finish annealing process. The aim is to stabilize the secondary recrystallization by stabilizing the nitriding reaction of the material and to stably form a glass film.

The inventors of the present invention have determined that as starting materials, in weight %, C:
0.055%, Si: 3.30%, Mn: 0.1
5%, acid soluble AZ: 0.030%, N: 0.
0070%, remainder: A slab consisting essentially of Fe was processed through the steps of hot rolling, hot rolling plate annealing, pickling, and cold rolling to a final thickness of 0.30%, and this material was □2゜／P
Decarburization annealing was performed by changing □, and the oxidation layer on the material surface was removed by changing the light pickling conditions. The oxidation layer of the material thus obtained was analyzed by GDS analysis and measurement of potential difference curves.

As a result, the lightly pickled material has M and O on its surface.

No system oxides were observed, and the tight oxides seen in the non-pickled material were not confirmed in the outermost layer even in the results of the potential difference curve.

The change in the material surface condition due to this light pickling treatment is due to Po in decarburization annealing. The results were similar whether /Pug was high or low. Figure 1 schematically shows the surface layer of the material after light pickling.

Next, an annealing separator is applied to this material, and N is added during the heating process.
Final annealing was performed using a 2+Hz atmosphere, and the nitridation status of the material during the temperature raising process and the characteristics of the product after final annealing were investigated.

As a result, Ni in the steel during final annealing at 900°C! The amount of light pickling is 100 to 150 within the specified conditions.
An increase in ppm was observed, and it was found that both the magnetic properties and film properties could be significantly improved when the amount of light pickling was below the predetermined conditions.

Next, the reason for limiting the light pickling conditions, which is a requirement of the present invention, will be described.

P nzo / P ut in the decarburization annealing process is 0
．． It may be within the range of 25 to 0.60. P nzo
/P Hz is less than 0.25, which is disadvantageous in terms of decarburization and oxide film formation ability, and at 0.60 m, the M, O, and layers increase significantly and the light pickling conditions must be strengthened. There are problems in that the roughness of the material surface has an adverse effect on magnetism and the film, and that variations in these factors become large.

In light pickling, 5iOd
i! It is important to remove only the outermost M, O, and other layers.

The amounts of M, O, and @ naturally vary depending on P Hzo / P Ill in decarburization annealing, so
Within the above range of P Hgo / P ox , if the light pickling amount is in the range of 0.02 to 2 g/m'', it contributes to stabilizing the glass film and secondary recrystallization.

The atmospheric conditions in the final annealing process are particularly important in terms of the component conditions in the present invention.
It is important that the annealing atmosphere contains N2, except when using a nitriding agent as in the technique disclosed in Japanese Patent No. 68.

The atmospheric gas during the temperature increase process of final annealing is as follows:
N! Single, N, +l1zSN, +Ar, NZ+H2+^
It is sufficient if it is r, etc.

Describe the reasons for limiting the material components. Since the present invention uses (St, /V) N as a precipitate necessary for secondary recrystallization, the inclusion of 5tSAl is essential. Si is 2.5
If it is less than 2.5%, the specific resistance of the material will be too low and the low core loss required as a transformer core material cannot be obtained, so it is set to 2.5% or more. Moreover, if it exceeds 4.0%, cracking during cold rolling becomes significant, so the content was set at 4.0% or less. IVN requires an acid-soluble M content of 0.010% or more in order to secure jVN or (Si, jV)N necessary for stabilizing secondary recrystallization.

However, if it exceeds 0.06%, the jVN of the hot rolled sheet becomes inappropriate and secondary recrystallization becomes unstable, so the content was set to 0.06% or less.

The reason for setting the S content to 0.014% or less is that if the S content is high, secondary recrystallization defects called linear fine grains tend to occur, and to prevent this, if the nitriding treatment is sufficient, the .01
It is desirable that it is 4% or less. If S exceeds this amount, no matter how much (St, AJ) N is created in the steel through nitriding treatment to strengthen the inhibitor, there is a high probability that secondary recrystallization defects will occur, which is undesirable.

If C is less than 0.0010%, secondary recrystallization becomes unstable, and even if secondary recrystallization is performed, only a low magnetic flux density can be obtained, so it is set to 0.0010% or more. On the other hand, if the amount of C is too large, the decarburization annealing time becomes long and it is not economical, so it is set to 0.10% or less.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example) In weight%, C: 0.048%, Si: 3.30%, s
: o, o o s%, N: O, OO75%,
Molten steel consisting of Mn: 0.15%, balance Fe and unavoidable impurities was subjected to continuous casting, hot rolling, hot rolling plate annealing, pickling, and cold rolling to a final plate thickness of 0.29 mm. Decarburization annealing was performed in an atmosphere of 25% Nt + 75% H2.
zo/P Hz (A): 0.44, (B):
The temperature was set to 0.34 at 850° C. for 150 seconds.

Next, only the outermost layer of the oxide layer formed during the decarburization annealing process was pickled in a 1lzs045% solution for different times. After that, an annealing separator is applied to this material, and final annealing is performed in an atmosphere of N225%+H! during the temperature raising process. 75%,
Atmosphere when maintaining high temperature at 1200℃ x 20hrs 82100
% dry conditions, and the N content in the steel during the temperature rising process was investigated.

Table 1 shows the results and the magnetic properties and glass film properties of the product after final annealing.

Comparative materials without light pickling had a small amount of N absorption during the final finish annealing temperature raising process, and were poor in both magnetic properties and film properties, whereas the light pickling materials of the present invention had a low amount of N absorption. The magnetic properties of the product were significantly improved, the glass coating became more uniform, and the adhesion was improved.

(Effects of the Invention) Since the present invention is configured and operated as described above, secondary recrystallization in the final finish annealing process is stabilized even when the slab heating temperature is set to a low level of less than 1280°C. The final product has excellent magnetic properties and film properties, which greatly reduces the energy required to heat the slab, reducing equipment maintenance and
It has a great effect on equipment utilization rate and work efficiency.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the step surface of the main part of the material surface after the outermost layer of the material after decarburization annealing was removed by light pickling. Diagram 1: Kidokin Senji Karukyo Senshi

Claims (1)

[Claims] In weight%, C: 0.0010 to 0.10%, Si: 2.
5-4.0%, acid-soluble Al: 0.010-0.06%
, S≦0.014%, remainder: Fe and unavoidable impurities A slab for unidirectional electrical steel sheets is heated to a temperature not exceeding 1280°C, then hot rolled and hot rolled plate annealed, and then once Or, after cold rolling two or more times with intervening annealing to achieve the final thickness, decarburization annealing in a wet hydrogen atmosphere, then applying an annealing separator and final finish annealing is performed on a unidirectional electrical steel sheet. In the manufacturing method, the material after final cold rolling is heated to a ratio of water vapor partial pressure to hydrogen partial pressure P_H_Z
After decarburizing annealing at a temperature range of 800 to 900°C in a wet hydrogen atmosphere with _O/P_H_Z of 0.25 to 0.60, only the M_xO_y layer other than SiO_2 formed on the outermost surface layer of the material was removed from the surface of the material by 1 m^. 1. A method for producing a unidirectional electrical steel sheet with excellent magnetic properties and glass film properties, characterized by removing 0.02 to 2 g per 2 g by light pickling, then applying an annealing separating agent, and further final annealing.