KR20040056259A - Method for manufacturing non-oriented electrical steel sheet having low core loss after stress relief annealing - Google Patents

Abstract

PURPOSE: A method for manufacturing non-oriented electrical steel sheet having low core loss after performing stress relief annealing even when hot rolled strip does not pass through annealing and skin-pass processes is provided. CONSTITUTION: The method comprises the steps of reheating a steel slab comprising 0.005 wt.% or less of C, 0.0005 to 0.005 wt.% of S, 0.0005 to 0.005 wt.% of N, 0.1 to 1.5 wt.% of Si, 0.1 to 1.0 wt.% of Al, 0.1 to 1.0 wt.% of Mn, 0.016 to 0.160 wt.% of P and a balance of Fe and other impurities in the temperature range of 1,050 to 1,250 deg.C; hot rolling the reheated steel slab to a thickness of 1.8 to 3.0 mm; coiling the hot rolled coil in the temperature range of 600 to 800 deg.C; pickling the coiled hot rolled strip; cold rolling the pickled strip to a thickness of 0.2 to 0.65 mm for one time; annealing the cold rolled strip to a temperature controlled according to P content in the temperature range of 700 to 800 deg.C, that is, Ta=400-100xlog(P/160)±5 deg.C for 30 to 300 seconds, wherein Ta is proper annealing temperature of cold rolled strip, and P is P content (wt.%); processing the annealed strip by end users; and stress relief annealing the annealed strip processed by the end users in the temperature range of 700 to 850 deg.C.

Description

Method for manufacturing non-oriented electrical steel sheet having excellent iron loss characteristics after stress relief annealing {Method for manufacturing non-oriented electrical steel sheet having low core loss after stress relief annealing}

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet with low iron loss after stress relief annealing, more specifically, excellent iron loss characteristics after stress removal annealing without undergoing hot rolling and annealing (Skin-Pass) process It relates to a method for producing a non-oriented electrical steel sheet.

Since non-oriented electrical steel has excellent magnetic properties, it is widely used as an iron core material for electric machines such as various motors, small transformers, and ballasts, and semi-process that must be subjected to stress relief annealing after the demand is processed. Products and demand are broadly divided into fully-process products that do not require stress relief annealing.

The semi-process products are usually shipped in a modified state in the manufacturing process of steelmaking → continuous casting → slab reheating → hot rolling → winding → hot rolled sheet annealing → cold rolling → annealing → skin-pass rolling → insulation coating After purchasing a thin product and processing the product into the desired shape, stress relief annealing must be performed to obtain magnetic properties suitable for the product.

In addition, pulley process products are shipped in a state where deformation is solved through the manufacturing process of steelmaking → continuous casting → slab reheating → hot rolling → winding → hot rolled sheet annealing → cold rolling → final annealing → insulation coating. It has the advantage that it can be used without.

Recently, according to the trend of increasing the efficiency of electrical equipment in terms of energy saving, the demand for products having excellent iron loss characteristics (low iron loss) is gradually increasing even in steel sheets which are iron core materials. In general, the iron loss is expressed in W / kg as electrical loss (Watt) per weight (kg) of the iron core, that is, electrical energy loss caused by heat generation at a specific magnetic flux density and frequency. Therefore, the iron core material having a low iron loss is more preferable for manufacturing high-efficiency electric equipment.

Accordingly, the present inventors have prepared a non-oriented electrical steel sheet having excellent iron loss characteristics after stress relief annealing containing Si, Al, Mn, Ni, etc. in Korea Patent Application No. 2000-82818 to provide a non-oriented electrical steel sheet having a low iron loss I have suggested a method.

However, this necessitates the addition of expensive Ni, and since a large amount of Si must be added, the manufacturing cost is increased, and the punchability is deteriorated due to the increase in strength and brittleness of the steel sheet. If the punchability is not good, the demand increases the wear and breakage rate of the mold during processing, which causes a problem that the processing cost increases rapidly.

Thus, the present inventors improve the punchability by controlling and reducing the Si content at the same time as not adding Ni during steelmaking in Korea Patent Application No. 2001-82121 to provide a method for solving the above problems, and Ni addition and A method of manufacturing non-oriented electrical steel sheet having low iron loss and excellent punchability by performing slab reheating and hot rolled sheet winding at a controlled temperature for deterioration of magnetic properties due to the reduction of Si addition amount has been proposed.

However, this method has no problem when the content of P incorporated as impurities in the steel is less than 0.015%. However, recently, when the iron content is added in an amount exceeding 0.015%, iron loss is recently found. Usually, molten steel produced by the blast furnace method contains a large amount of P, so in order to lower the P content to 0.015% or less, it is necessary to add a delineation process during the converter operation, thereby reducing productivity. In addition, even when P is reduced by the dephosphorization process, when bubbling operation of molten steel is carried out to control S to 0.005% or less, the content of P is reduced due to the phenomenon that P in the slag melts back into the molten steel. Controlling less than 0.015% is a very difficult technique industrially.

The present invention is to manufacture a non-oriented electrical steel sheet with low iron loss after the stress relief annealing as described above according to a more simplified method, even if the molten steel contains a normal level of P after the punching and fastening work after the stress relief annealing The purpose is to provide a method for producing a non-oriented electrical steel sheet having excellent iron loss characteristics.

Method for producing a non-oriented electrical steel sheet having excellent iron loss characteristics according to the present invention for achieving the above object, by weight% of less than 0.005% C, S: 0.0005 ~ 0.005%, N: 0.0005 ~ 0.005%, Si: 0.1 ~ 1.5%, Al: 0.1 ~ 1.0%, Mn: 0.1 ~ 1.0%, P: 0.016 ~ 0.160%, steel slab composed of remainder Fe and other impurities is reheated in the temperature range of 1050 ~ 1250 ℃, 1.8 ~ 3.0 After hot rolling to a thickness of mm, the hot rolled coil is wound in a temperature range of 600 to 800 ° C., and then, once pickled, cold rolled to a thickness of 0.2 to 0.65 mm, and then controlled according to the P content in the temperature range of 660 to 760 ° C. Temperature, Ta = 360-100xlog (P / 160) ± 5 ° C. [where Ta: appropriate cold rolled sheet annealing temperature, P: P content (wt%)] annealing for 30 to 300 seconds, and then the demand is 700 to It comprises a stress relief annealing at a temperature of 850 ℃.

Hereinafter, the present invention will be described in detail.

The present inventors control the annealing temperature at the time of cold rolling annealing according to the P content even in a normal case that it is difficult to control the P content to an extremely small amount (0.015% P or less), even if the demand is not processed after hot rolling Grain growth during stress relief annealing is easy to confirm that the non-oriented electrical steel sheet excellent in iron loss characteristics can be produced through research and experiments to complete the present invention.

The present invention is largely classified into the composition of steel slab, hot rolling, cold rolling, annealing and stress relief annealing. It provides a non-oriented electrical steel sheet having low iron loss characteristics after stress relief annealing without eliminating hot rolled sheet annealing and light rolling by controlling the process conditions of each step, in the following the effect of each step will be described in detail.

[Steel slab composition stage]

Prior to the component composition step for steel slab production, steelmaking, molten steel and ingot or continuous casting process are usually preceded. First, in the steelmaking step, the content of C, N, S in the molten steel is controlled low, and an appropriate amount of Si, Al, Mn, etc. is added. Subsequently, the steel slab containing an appropriate amount of components is manufactured by performing a molten steel in the ingot or continuous casting process. Among the components of the slab steel of the present invention, C, N, and S are elements that interfere with grain growth, so it is necessary to control the content in the steelmaking step low, and Si, Al, and Mn are used in the steel to lower iron loss. Add. The reason for the composition range limitation is explained.

C: 0.005% or less

When C is excessively contained, slabs are formed during the manufacturing of the electrical steel sheet of the present invention, thereby inhibiting grain growth, and also causing magnetic aging during use as an iron core of an electric device. It is preferable to contain in a steel so that it may have a composition of 0.005 or less.

N: 0.005% or less

N tends to react with Al during the steel sheet manufacturing process of the present invention to form AlN precipitates, thereby suppressing grain growth, so that it has a minimum amount as much as possible. Therefore, the content of N is preferably 0.005% or less. .

S: 0.005% or less

In addition to C and N, S tends to react with Mn to form MnS, which is a fine precipitate, to suppress grain growth, so it is important to have a minimum amount as much as possible. desirable.

Si: 0.1 ~ 1.0%

If the content of Si is less than 0.1%, the specific resistance of the steel is small and the iron loss characteristics are not preferable. If the content of Si is more than 1.0%, the excellent magnetic flux density is not obtained and the punchability is deteriorated. Not good.

Al: 0.1 ~ 1.0%

If Al is less than 0.1%, the specific resistance of the steel is small and iron loss characteristics are deteriorated, and if it is more than 1.0%, the cold rolling property is deteriorated.

Mn: 0.1 ~ 1.0%

In the case of Mn, less than 0.1% is not preferable because the specific resistance of the steel is small and the iron loss characteristics are deteriorated, and if it is more than 1.0%, the roll load increases and the cold rolling property is deteriorated.

In addition to the above components, the steel contains Fe and other unavoidable impurities. P, which is contained as an impurity in steel during steelmaking, is segregated at grain boundaries and suppresses grain growth, thereby degrading iron loss. The lower the content, the better. However, in the case of containing a very small amount of less than 0.016%, the iron loss improvement effect by the control of the cold-rolled sheet annealing temperature according to the P content, which is a characteristic of the present invention, is insignificant. Therefore, in the case of the present invention, the content of P is limited to the range of 0.016 ~ 0.16%.

[Hot Rolling Step]

The steel slab is charged into a heating furnace and reheated as a pretreatment step of the hot rolling step performed after the composition step. In this case, in order to facilitate hot rolling, the reheating temperature of the steel slab should be 1050 ° C. or higher, but if it exceeds 1250 ° C. Precipitates, which are harmful to iron loss characteristics such as AlN and MnS, are re-dissolved and tend to cause excessive generation of fine precipitates after hot rolling. Such fine precipitates are undesirable because they hinder grain growth and deteriorate iron loss characteristics. Therefore, in the case of the present invention, it is preferable to heat to a temperature of 1050 ~ 1250 ℃.

The hot rolling is performed as described above, and the operating conditions are performed according to a conventional method. In this case, in order to prevent excessive generation of an oxide layer of the hot rolled sheet, the finishing rolling temperature is preferably adjusted to 800 to 950 ° C. If the thickness of the hot rolled plate is less than 1.8 mm, the shape of the hot rolled plate becomes poor, which is not preferable. If the thickness of the hot rolled plate exceeds 3.0 mm, a good texture is not obtained and the magnetic flux density deteriorates.

Subsequently, the hot rolled sheet winding may be performed at a temperature of 800 ° C. or lower so that an oxide layer is not excessively generated in the hot rolled sheet, but is preferably performed at a temperature of 600 ° C. or higher for grain growth of the hot rolled sheet. After cooling in air in a coil state, or more preferably furnace cooling.

[Cold rolling stage]

Subsequently, the hot rolled sheet is cold rolled immediately after pickling without performing hot rolled sheet annealing. In this case, when rolling at a reduction ratio of less than 64%, rolling productivity is reduced, so it is preferable to roll once at a reduction ratio of 64% or more. At this time, if the cold rolling thickness is less than 0.20mm, the strength of the (111) plane, which is an unfavorable texture after annealing, is not preferable because the magnetic flux density decreases. If the thickness exceeds 0.65mm, the eddy current loss is increased with the increase of the plate thickness. This is not good because (eddy current loss) increases and total iron loss increases.

[Annealing Step]

In the cold annealing step performed according to the above method, in the subsequent annealing step, if the annealing temperature is lower than 700 ° C., the rolling structure remains excessively in the material, so that the demand is difficult to process during processing, and if it is higher than 800 ° C., residual stress in the material Since there is a disadvantage that the demand is low after the stress relief annealing, the improvement rate of the magnetic properties of the steel sheet is low, it is preferable to anneal at a temperature of 700 ~ 800 ℃.

On the other hand, the present inventors have found that the cold rolling annealing temperature has an effect on the grain growth and texture formation during the stress relief annealing results. It was found that the higher the annealing temperature, the higher the annealing temperature, the higher the iron annealing property was obtained, while the higher the annealing temperature, the higher the annealing temperature was obtained. It was concluded that annealing at a temperature controlled by Equation 1 below is desirable.

(Relationship 1)

Ta = 400-100 × log (P / 160) ± 5 ℃

Where Ta is the appropriate cold roll annealing temperature and P is the P content (% by weight)

Explaining that the proper annealing temperature depends on the P content is as follows. P influences grain growth and formation of aggregates during stress relief annealing due to grain boundary segregation. When P is contained in a predetermined amount as in the present invention, P is segregated at grain boundaries during annealing, thereby suppressing grain growth during stress relief annealing, resulting in deterioration of iron loss characteristics. Therefore, in order to reduce the amount of grain boundary segregation of P, it is necessary to bring the annealing temperature low. However, in terms of texture, the higher the annealing temperature, the better. This is because the increase in the annealing temperature increases the initial temperature rise rate of the steel sheet and decreases the strength of the (111) plane, which is disadvantageous to the magnetic properties during stress relief annealing.

Taken together, it is important to reduce the annealing temperature by reducing the annealing temperature in the case of a large P content, while the annealing temperature is higher when the P content is small, so long as the damage by grain boundary segregation is not large. It can be concluded that improved iron loss properties are obtained.

The steel sheet annealed in the annealing step is processed immediately with organic, inorganic and organic / inorganic composite coatings or coated with other insulating coatings without going through the skin-pass rolling step. Punch into shaped products.

[Stress Removal Annealing Step]

After the stress removal annealing step in which the demand for removing the residual stress is a heat treatment process, the residual stress in the steel sheet may remain when the temperature is lower than 700 ℃, if the temperature higher than 850 ℃ may damage the insulating film 700 in the present invention It is preferable to adjust to -850 degreeC temperature. Under such a temperature, it is performed in a non-oxidizing atmosphere for 30 minutes or more.

Hereinafter, although this invention is demonstrated more concretely, this invention is not limited only to these examples.

(Example 1)

To prepare a steel slab having the components shown in Table 1, the steel slab was heated at a temperature of 1150 ℃ and hot-rolled under the finish rolling temperature conditions of 850 ℃ to make a hot rolled plate with a thickness of 2.0mm, then 700 ℃ After winding at the temperature, it was cooled in the air. The cold rolled hot rolled plate was annealed without performing hot rolled sheet annealing, and then cold rolled to 0.5 mm thickness, and finally annealed as shown in Table 2 below.

The final annealing atmosphere was 25% hydrogen and 75% nitrogen. After the annealing plate is coated with an organic / inorganic composite coating, the annealing plate is subjected to stress relief annealing with a non-oxidizing atmosphere at a temperature of 780 ° C. for 1 hour 30 minutes, and then the magnetic properties, grain size and (111) surface strength are investigated. It is shown in Table 2 below. At this time, iron loss and W15 / 50 are energy loss consumed by heat when inducing magnetic flux density of 1.5 Tesla to iron core at AC of 50Hz, magnetic flux density, B50 is induced value at excitation force of 5000A / m, The cross section of the stress-annealed specimen was polished and then etched with 3% nital and measured with an image analyzer. The surface strength is represented by the aggregate structure strength according to the Horta equation, and as the (111) surface strength decreases, the magnetization becomes easier and the magnetic properties are improved.

As shown in Table 2, it was found that the invention material (1-4) is superior in iron loss characteristics than the comparative material (1-10). In detail, the comparative materials (1, 3, 5, 7) exceeded the proper annealing temperature, and the grain loss of P was excessive, resulting in the decrease of the grain size of the annealing plate after the stress relief annealing. , The comparative materials (2,4,6,8) were annealed below the proper annealing temperature, and after the stress relief annealing, the (111) surface strength increased and the magnetic flux density decreased.

In addition, Comparative Material 8 was annealed at 700 ° C. or lower, and insufficient removal of residual stress applied during cold rolling on the annealing plate resulted in poor punchability during processing. The comparative material (9,10) contained less than 0.015% of P in steel, and the calculated annealing temperature exceeded 800 ℃. The crystal grains did not grow significantly after stress relief annealing, so excellent iron loss characteristics were not obtained. .

As described above, the present invention has the effect of providing a non-oriented electrical steel sheet having excellent iron loss characteristics after stress removal annealing in the case that P in the steel is not controlled to a very small amount (more than 0.016P%).

In addition, according to the present invention, it is possible to secure excellent magnetic properties without undergoing hot rolling annealing and light rolling, thereby reducing the manufacturing process.

Claims (1)

By weight% C: 0.005% or less, S: 0.0005 to 0.005%, N: 0.0005 to 0.005%, Si: 0.1 to 1.5%, Al: 0.1 to 1.0%, Mn: 0.1 to 1.0%, P: 0.016 to 0.160% , Re-heat the steel slab composed of the balance of Fe and other impurities in the temperature range of 1050 to 1250 ℃, hot rolled to 1.8 ~ 3.0mm thickness and wound the hot rolled coil in the temperature range of 600 ~ 800 ℃, and then pickling Once cold rolled to 0.2 ~ 0.65mm thickness, then controlled temperature according to P content in 700 ~ 800 ℃ temperature range, Ta = 400-100xlog (P / 160) ± 5 ℃ {where Ta: suitable cold rolled sheet annealing temperature , P: P content (% by weight)}, followed by annealing for 30 to 300 seconds, and then excellent stress loss after stress relief annealing, characterized in that the demand is made including the stress relief annealing at a temperature of 700 ~ 850 ℃ after processing Method for producing non-oriented electrical steel sheet.