KR101451824B1 - A Method for Manufacturing Oriented Silicon Steel Product with High Magnetic-flux Density - Google Patents

Abstract

A method of making a directional silicon steel product having a high magnetic flux density comprises the steps of: 1) smelting and casting, the directional silicon steel comprises 0.035-0.065 wt% C, 2.9-4.0 wt% Si, 0.05-0.20 0.005 to 0.090 wt.% Of Sn, and 0.200 to 0.800 wt.% Of Nb, with the remainder consisting of 0.001 wt.% Mn, 0.005 wt.% To 0.01 wt.% S, 0.015 wt.% To 0.035 wt.% Al, 0.004 wt.% To 0.009 wt.% N, Fe; After smelting, the molten steel is secondarily refined and subsequently cast into steel slabs; 2) hot rolling; 3) Soo Jun; 4) cold rolling; 5) decarburization annealing; 6) MgO coating; 7) high temperature annealing; The sheets are first heated to 700 - 900 캜 and then held at 1200 캜 for 20 hours; 8) Insulation layer coating. According to the present invention, the steel sheets can be completely nitrided during the high temperature annealing, which can ensure that the secondary recrystallization occurs perfectly, and thereby, the directional silicon steel sheets with high magnetic flux density can be obtained. The present invention solves the problem of nitriding encountered in the production of high magnetically induced directional silicon steel by the technique of heating steel slabs to low temperatures.

Description

Technical Field [0001] The present invention relates to a method for manufacturing a directional silicon steel product having a high magnetic flux density,

The present invention relates to a method for producing a directional silicon steel sheet and a method for producing a directional silicon steel sheet having a high magnetic flux density.

A conventional method for producing a directional silicon steel having a high magnetic flux density is as follows. After being smelted in a converter or an electric furnace, the molten steel is refined and alloyed secondarily, and then continuously cast into steel slabs. The basic chemical composition thereof is 2.5 to 4.5% of Si, 0.06 to 0.10% of C, 0.03 to 0.1% of Mn, 0.012 to 0.050 of S, 0.02 to 0.05% of Al and 0.003 to 0.012 of N. Some composition systems further contain one or more of the elements Cu, Mo, Sb, B, Bi, and the like. The remainder is Fe and inevitable impure inclusion. The steel slab is heated to a temperature of 1350 DEG C or higher in a special furnace and maintained at this temperature for more than 45 minutes to completely solubilize the beneficial content MnS or AlN and then rolled to a steel plate at a finishing temperature up to 950 DEG C or higher; The plate is then cooled rapidly to less than 500 ° C by spraying water and coiled into a coiled shape. Subsequently, during normalization, the fine, dispersed second phase particles, i.e. the depressant, are separated from the silicon steel body. After being tempered, the hot rolled steel sheets are pickled and cold rolled into sheets of thick rolled steel sheet products after removing the oxidized scale. The cold rolled sheet is decarburized annealed and coated with an anneal insulator (the main composition being MgO). The carbon in the sheet is decarburized to such an extent that it does not affect the magnetic properties of the finished steel sheet product (generally the carbon should be less than 30 ppm); During high temperature annealing, the steel sheet undergoes secondary recrystallization, formation of the bottom layer of magnesium silicate, and purification (which causes elements S, N, etc., which are detrimental to magnetism to be removed from the steel sheet) Is made of a low and high magnetic induction silicon steel sheet; Finally, after being coated with an insulating layer and tension-annealed, a sheet of silicon steel is made into an available directional silicon steel sheet product.

Disadvantages of this process are that the heating temperature must reach 1400 占 폚 in order to allow the inhibitor to be completely solubilized in solid form. This temperature is the highest level of conventional heating furnaces. Also, due to the high heating temperature, the burning loss is large and the heating furnace is frequently required to be repaired, resulting in a low utilization rate. Also, energy consumption is high. In addition, hot rolled coil-shaped plates have mainly larger edge cracks, which can cause difficulties in subsequent cold rolling procedures and result in lower yields of finished products, unsatisfactory magnetic B ₈ and higher manufacturing costs.

From the viewpoint of the above problems, domestic and foreign researchers have conducted many studies for the purpose of decreasing the heating temperature of the directional silicon steel. Research can be divided into two types. One is to heat the steel slab to a temperature in the range of 1250 to 1320 ° C and to use AlN and Cu as inhibitors. And the other is to obtain a restraining ability by heating the steel slab to a temperature in the range of 1100 to 1250 ° C and using an inhibitor formed by nitridation after decarburization.

Nowadays, there is a rapid advance in the technology for heating steel slabs at low temperatures. For example, in US patent US 5,049,205 and Japanese patent publication JPA 1993-112827, a steel slab is heated to a temperature not higher than 1200 캜 and rolled into sheets. In the finishing cold rolling procedure, the plate is rolled into sheets with a large rolling compaction ratio of 80% and the rolled steel sheet is decontaminated to obtain highly directional secondary recrystallized granules and subsequently nitrided by the use of ammonia . However, in this technique, since the suppression effect is obtained by the inhibitor generated by the nitriding of the rolled steel sheet after the rolled steel sheet is decarburized, in actual control, the steel sheet will have a strongly oxidized surface and uniformly nitrided It is very difficult to avoid difficulties. Thus, this will result in inhibitors of the form obtained in the steel sheet which are difficult to distribute evenly, which will affect the inhibitory effect and flatness of the secondary recrystallized granules and will result in uneven magnetization of the final finished silicon steel sheet product.

Chinese patent CN 200510110899 discloses a new method in which steel slabs are heated to a temperature not higher than 1200 ° C and the cold rolled steel sheets rolled to the thickness of the finished product are nitrified prior to decarburization annealing. However, in this method, it is necessary to strictly control the dew point during nitriding and a new problem will arise in which decarburization becomes more difficult.

Recently, Korean patent KR 2002074312 discloses that steel slabs are heated to a temperature not higher than 1200 ° C, and the rolled sheets are simultaneously decarburized and nitrided. Although the difficulties of post-rolling decarburization and post-rolling nitriding can be resolved, however, uneven nitriding is still inevitable and will therefore result in uneven magnetization of the finished silicon steel sheet product and higher manufacturing costs.

It is also proposed to add the element Nb. For example, in JP 6025747 and JP 6073454, 0.02-0.20% Nb is added to the composition of smelted steel. This results in the formation of niobium carbide and niobium nitride, thereby eliminating impurities in the recrystallized structure, improving the granular distribution and overall texture of the decarburized annealed steel sheet, and suppressing the growth of normal grains during high temperature annealing The aim is to improve the magnetic properties of silicon steel sheets using niobium carbide and niobium nitride. However, the problem with these patents is that the steel slabs must be heated to very high temperatures in order to finely analyze niobium nitride prior to hot rolling, which obviously results in greater burning losses, higher energy consumption, lower ratios of finished products, Leading to high manufacturing costs.

According to Japanese Patent JP 51106622 and US Patent 4,171,994, nitrides of Al, Fe, Mg and Zn are added to the separator MgO. This aims to decompose them during high temperature annealing to nitrate the steel sheets by releasing nitrogen oxides. However, nitrogen oxides and oxygen from decomposed nitrides can cause explosion hazards in actual production.

According to Japanese Patent JP 5,203,952 and US 4,010,050, sulfanilic acid is added to the separating agent MgO. It aims at decomposing sulfanilic acid at high temperature to release nitride for nitriding. However, because of the organic matter, sulfanilic acid will decompose at low temperatures (about 205 ° C), and nitrogen released at such low temperatures makes it difficult to nitrate the steel sheet.

According to Japanese Patent Nos. JP 61096080 and JP 62004811, nitridation of steel sheets during high temperature annealing is realized by adding nitrides of Mn and Si. However, the problem with this method is that these nitrides have high thermal stability. Thus, they will not break down effectively and quickly. In order to meet the nitridation requirements, it is essential to extend the duration of the high temperature annealing or to increase the amount of these nitrides.

Regarding the rate of temperature rise during high temperature annealing, Japanese Patent JP 54040227 and JP 2002119751 claim that directional silicon steels with a high magnetic flux density can be obtained by reducing the temperature rise rate during high temperature annealing. However, simply reducing the temperature rise rate can greatly reduce the production rate.

It is an object of the present invention to provide a method for producing a directional silicon steel product having a high magnetic flux density and a method in which steel slabs are heated at a low temperature has difficulty in nitriding to produce a directional silicon steel sheet having a high magnetic flux density . The present invention effectively guarantees the safe and stable operation of the smelting furnaces and the long service life by the technique of heating at a low temperature. In the production process, the directional silicon steel sheets can be completely nitrided during the high temperature annealing, which can ensure that the secondary recrystallization takes place perfectly, so that directional silicon steel sheets with high magnetic flux density and excellent magnetic properties can be obtained .

The present invention adopts the following technical solutions.

During smelting, a predetermined amount of Nb is added to the composition of the directional silicon steel to make the directional silicon steel sheet susceptible to nitriding, since it is important to determine whether the magnetic properties of the directionally silicon steel sheet product in which the nitrogen content in the steel is finished meet the requirements to be. Some of the nitrides are added to the MgO separator and the MgO separator to which the nitrides are added is applied to the surfaces of the steel sheets before the sheets are hot annealed. During the high-temperature annealing, the nitrides decompose and release nitrogen, which can fully nitride the steel sheets. The rate of temperature rise during the high temperature annealing is controlled according to the Nb content, the N content before the secondary heating and the starting temperature of the secondary heating to ensure that the secondary recrystallisation is complete, thereby providing a high magnetic flux density and excellent magnetic properties Directional oriented silicon steel sheets can be obtained.

Specifically, a method for producing a directional silicon steel product having a high magnetic flux density is provided according to the present invention. The method includes the following steps:

1) Refining and casting

The directional silicon steel contains 0.035 to 0.065 wt% of C, 2.9 to 4.0 wt% of Si, 0.05 to 0.20 wt% of Mn, 0.005 to 0.01 wt% of S, 0.015 to 0.035 wt% of Al, 0.004 to 0.009 wt% of N, 0.005 to 0.090% by weight of Sn, and 0.200 to 0.800% by weight of Nb, with the remainder being Fe and unavoidable inclusions. After being smelted, the molten steel is secondarily refined and then cast into steel slabs.

2) Hot rolling

The steel slabs are heated to 1090 to 1200 DEG C in a heating furnace, then hot-rolled to steel plates at a starting temperature of 1180 DEG C and finished in a hot rolling step at a finishing temperature of 860 DEG C, cooled by a laminar flow of water, and then coiled into coil-shaped plates.

3) Minjung

The coil-shaped plate is annealed at a normalizing temperature of 1050 to 1180 캜 for 1 to 20 seconds, then is annealed at a normalizing temperature of 850 to 950 캜 for 30 to 200 seconds, and then cooled at a cooling rate of 10 to 60 캜 / sec.

4) Cold rolling

After being tempered, the steel sheet is cold rolled into steel sheets and has a thickness of the directional silicon steel sheet product finished with a rolling compression ratio of at least 75%.

5) Decarburization annealing

The steel sheet is heated to a temperature of 800-860 ° C at a temperature ramp rate of 15-35 ° C / sec and maintained at this temperature for 90-160sec to be decarburized, where only decarburization is performed, which causes nitridation during high temperature annealing It is because it is.

6) MgO coating

After decarburization, the steel sheets are covered with a coating consisting of 0.1 to 10 wt.% Of NH ₄ Cl and 0.5 to 30 wt.% Of P ₃ N ₅ and the balance MgO, the main component.

7) High temperature annealing

Isolated and then coated with a first (isolator), steel sheet after the first heated to a temperature of 700 ~ 900 ℃, 9 ~ 17 ℃ / hr heating rate V and the second heating drive in 1200 ℃ to _{the secondary temperature rise} purification annealing Lt; RTI ID = 0.0 > 1200 C < / RTI >

8) Insulation layer coating

After high temperature annealing, the surfaces of the steel sheet are coated with an insulating layer and then stretched and leveling annealed, resulting in a directionally oriented silicon steel sheet with high magnetic flux density and excellent magnetic properties.

According to the present invention, a predetermined amount of Nb is added to the silicon steel. There are two reasons for doing this. The first reason is that the directional silicon steels with Nb in their compositions are much easier to nitrid, because the d sublayer of the lower outer spheres of the atoms of Nb is unsaturated with electrons so that Nb is converted to nitride rather than Fe and Mn And the nitride of Nb is very stable. The second reason is that the N atoms penetrating into the steel sheets during the high temperature annealing can bond with Al to generate the main inhibitor AlN, which is essential for obtaining a directional silicon steel sheet with a high magnetic flux density, and also with Nb ₂ N and NbN Lt; / RTI > These nitrides of Nb can be auxiliary inhibitors and can enhance the inhibitory effect on the growth of normal crystalline granules. Generally, this solution is very advantageous for increasing the magnetism of the directional silicon steel sheet.

In accordance with the present invention, predetermined amounts of NH ₄ Cl and P ₃ N ₅ are added to the liquid MgO coating. The intention is to use the decomposition of the two nitrides during the high temperature annealing to effect the nitridation of the steel sheets, thereby replacing the nitriding caused by the decomposition of ammonia during decarburization annealing, and the best benefit of this solution is that the steel sheets To ensure even nitriding. The reason for selecting NH ₄ Cl and P ₃ N ₅ as the nitriding material to be decomposed at high temperature is that NH ₄ Cl will be decomposed at 330 to 340 ° C. and P ₃ N ₅ will decompose at about 760 ° C. The decomposition of two different nitrides at different temperatures ensures an even release of the active atoms of nitrogen for a relatively long period of time in the procedure of high temperature annealing which keeps nitriding of the steel sheets and the N content therein within the standard limits of 200-250 ppm It is advantageous.

According to the present invention, the rate of temperature rise for the secondary heating during the high temperature annealing is controlled to ensure that the finished directional silicon steel sheet product obtains excellent magnetism by setting the appropriate secondary temperature rise rate. This is because the course of the secondary temperature rise for the high temperature annealing includes the entire temperature range of the secondary recrystallization. Thus, a suitable rate of temperature rise can ensure that the Gauss grains growing during secondary recrystallization have much better directionality (deviation angle < 3 [deg.]) And magnetism.

According to the present invention, a relatively low temperature rise rate during high temperature annealing can refine the secondary recrystallization and ensure that the finished steel sheet product has better magnetism. This is because progressive coarsening and decomposition of AlN as well as secondary recrystallization can occur simultaneously during the secondary heating for high temperature annealing, so that the suppression effect is simultaneously lost. If the temperature rises too fast in this temperature range, it will cause the inhibitor to decompose and lose its effect before the secondary recrystallization is finished. As is known, incomplete secondary recrystallization will result in poor magnetism of the finished directional silicon steel sheet product.

Are included in the scope of the present invention.

The invention will now be described in detail with the following embodiments.

First Embodiment

The material steel of the directional silicon steel sheet with the chemical composition shown in Table 1 is smelted and cast into slabs. Slabs with different chemical compositions were heated in a furnace to a temperature of 1155 占 폚 and maintained at this temperature for 1.5 hours and then hot rolled to 2.3 mm thick plates at a starting temperature of 1062 占 폚 and a finishing temperature of 937 占 폚. The hot-rolled sheets are quenched for 15 seconds at 1120 DEG C and for 150 seconds at 870 DEG C ((1120 DEG C x 15 sec) + (870 DEG C x 150 sec)) and then cooled at a rate of -15 DEG C / sec. After pickling, the hot-rolled sheets were cold-rolled into coil-shaped steel sheets having a thickness of 0.30 mm of the finished steel sheet product, followed by cold-rolled coil-shaped sheets at a temperature rising rate of 820 Lt; RTI ID = 0.0 &gt; C &lt; / RTI &gt; and decarbonized; Applying and covering a thick layer of separating agent containing MgO and 4.5% of NH ₄ Cl and 15% of P ₃ N ₅ as main components; Heated to 800 [deg.] C to obtain a nitrogen content b before high temperature annealing and secondary heating; It is heated to 1200 ° C and maintained at this temperature for 20 hours to be refined and annealed. Prior to unwinding with steel sheets of a certain length, an insulating coating layer is applied to the sheets, followed by stretching and smooth annealing. Both the nitrogen content b and the magnetism of the finished steel sheet product before the secondary heating are shown in Table 1.

Effects of Chemical Compositions on Nitrogen Content and Magnetic Properties before Secondary Heating Yes C% Si% Mn% S% Al% N% Sn% Nb% N content (ppm) before the second heating B ₈
T P17 / 50 W / kg One 0.035 3.2 0.20 0.010 0.015 0.009 0.090 0.20 202 1.92 0.97 2 0.041 2.9 0.10 0.005 0.025 0.006 0.070 0.36 211 1.92 0.99 3 0.052 4.0 0.05 0.008 0.035 0.004 0.005 0.64 234 1.93 0.97 4 0.065 3.5 0.15 0.012 0.022 0.007 0.035 0.80 244 1.92 0.98 Comparative Example 1 0.046 3.0 0.08 0.006 0.028 0.008 0.072 0.18 173 1.87 1.11 Comparative Example 2 0.053 3.5 0.15 0.011 0.019 0.006 0.014 0.84 292 1.86 1.12

As can be seen from Table 1, the selection of the various chemical compositions according to the embodiment is consistent with the standard requirements (of smelting and casting) in the production process of the present invention. However, in the comparative examples, the selection of the component Nb is not within the standard limits of 0.200 to 0.800, so that the amount of N measured before the second heating is not within the standard limits of 200 to 250 ppm and the final finished directional silicon steel sheet the products have a greater iron loss (P _17/50) and the bad magnetism (B _8).

Second Embodiment

The directional silicon steel slab is composed of 0.05 wt% of C, 3.25 wt% of Si, 0.15 wt% of Mn, 0.009 wt% of S, 0.032 wt% of Al, 0.005 wt% of N, 0.02 wt% of Sn and 0.5 wt% of Nb, Fe and unavoidable impurities. The slabs are heated to a temperature of 1155 캜 in a furnace and maintained at this temperature for 1.5 hours, followed by hot rolling to 2.3 mm thick plates at a starting temperature of 1080 캜 and a finishing temperature of 910 캜. The hot-rolled sheets were conditioned at 1110 DEG C for 10 seconds and 910 DEG C (1110 DEG C x 15 sec) + (910 DEG C x 120 sec) for 120 seconds and then cooled at a rate of -35 DEG C / sec. After pickling, the hot-rolled sheets were cold-rolled into coil-shaped sheets having a thickness of 0.30 mm of the finished steel sheet product, and subsequently cold rolled coil-shaped sheets were heated at a temperature rising rate of 25 캜 / Lt; RTI ID = 0.0 &gt; 130 C &lt; / RTI &gt; Applying and covering a thick layer of a separating agent containing MgO and a minor amount of NH ₄ Cl and P ₃ N ₅ as main components; Heated to 800 [deg.] C to obtain a nitrogen content b before high temperature annealing and secondary heating; It is heated to 1200 ° C and maintained at this temperature for 20 hours to be refined and annealed. Prior to unwinding with steel sheets of a certain length, an insulating coating layer is applied to the sheets, followed by stretching and smooth annealing. Both the nitrogen content b and the magnetism before the secondary heating of the finished steel sheet product are shown in Table 2.

Effects of NH ₄ Cl and P ₃ N ₅ contents on nitrogen content and magnetism before secondary heating Yes NH ₄ Cl P ₃ N ₅ % N content (ppm) before the second heating B ₈
T P17 / 50 W / kg One 0.1 3.9 198 1.92 0.99 2 1.2 11.3 210 1.91 1.00 3 3.6 20.8 231 1.92 0.98 3 6.4 0.5 206 1.92 0.97 4 8.3 6.6 221 1.92 1.00 5 10 12.8 222 1.93 0.96 6 2.4 19.5 234 1.92 0.98 7 5.5 26.4 252 1.91 0.99 8 1.9 30 243 1.93 0.96 Comparative Example 1 6.4 0.4 178 1.87 1.10 Comparative Example 2 2.4 30.2 268 1.88 1.06 10.5 30.5 283 1.83 1.16

As can be seen from Table 2, the choice of NH ₄ Cl and P ₃ N ₅ according to the embodiment is consistent with the standard range of 0.1 to 10% and 0.5 to 30% (of the MgO coating) in the production process of the present invention. On the contrary, in the selection of NH ₄ Cl and P ₃ N _{5 in} the comparative examples, the content of N measured before the secondary heating, which is not within the standard limits, is not within the standard limits of 200-250 ppm, directional silicon steel sheet products should have a greater iron loss (P _17/50) and the bad magnetism (B _8).

Third Embodiment

The directional silicon steel slab comprises 0.05 wt% of C, 3.25 wt% of Si, 0.15 wt% of Mn, 0.009 wt% of S, 0.032 wt% of Al, 0.005 wt% of N, 0.02 wt% of Sn and 0.2 to 0.8 wt% of Nb And the remainder Fe and inevitable inclusions. The slabs were heated to a temperature of 1155 캜 in a furnace and maintained at this temperature for 2.5 hours and then hot rolled into 2.3 mm thick plates at a starting temperature of 1050 캜 and a finish temperature of 865 캜. The hot-rolled sheets are quenched at 900 DEG C (1120 DEG C x 15 sec) + (900 DEG C x 120 sec) at 1120 DEG C for 120 seconds and for 15 seconds, and then cooled at a rate of -25 DEG C / sec. After pickling, the hot-rolled sheets were cold-rolled into coil-shaped sheets having a thickness of 0.30 mm of the finished steel sheet product, and subsequently cold rolled coil-shaped sheets were heated at a temperature ramp rate of 25 DEG C / Lt; RTI ID = 0.0 &gt; 115 C &lt; / RTI &gt; to be decarbonized; Applying and covering a thick layer of separating agent containing MgO and 7.5% of NH ₄ Cl and 12.5% of P ₃ N ₅ as main components; Heating to 700 to 900 DEG C as the starting temperature (c) of the secondary heating in the high temperature annealing and obtaining the nitrogen content (b) before the secondary heating; Heated to a temperature of 1200 DEG C at a predetermined temperature rise speed (V), and held at this temperature for 20 hours so as to be subjected to tablet annealing. Prior to unwinding with steel sheets of a certain length, an insulating coating layer is applied to the sheets, followed by stretching and smooth annealing. All of the data of the third embodiment are shown in Table 3.

Effects of different methods of sizing and nitriding on the magnetic properties of finished silicon steel sheet products Yes
nb
(%) N content (ppm) before the second heating Starting temperature of secondary heating (℃) Theoretically calculated secondary heating rate (° C / hr) Actual secondary heating rate (° C / hr) Difference (° C / hr) magnetism a b c V _{upper limit} V _Actual V _{upper limit} -V _actual B ₈
T P _17/50
w / kg One 0.20 186 700 17.9 16 1.9 1.90 1.00 2 0.20 184 800 14.3 14 0.3 1.90 0.98 3 0.20 189 900 10.5 9 1.5 1.91 1.01 4 0.40 204 720 18.2 17 1.2 1.92 0.96 5 0.40 207 810 14.8 14 0.8 1.91 0.99 6 0.40 211 880 12.2 12 0.2 1.93 0.93 7 0.60 231 750 18.0 17 One 1.93 0.95 8 0.60 229 850 14.3 14 0.3 1.92 0.99 9 0.80 248 780 17.9 15 2.9 1.91 1.00 10 0.80 252 860 14.8 12 2.8 1.92 0.96 Comparative Example 0.20 186 700 17.9 19 -1.1 1.85 1.07 One 0.20 184 800 14.3 15 -0.7 1.86 1.09 2 0.20 189 900 10.5 12 -1.5 1.85 1.08 3 0.40 204 720 18.2 20 -1.8 1.85 1.12 4 0.40 207 810 14.8 16 -1.2 1.86 1.09 5 0.40 211 880 12.2 14 -1.8 1.84 1.15 6 0.60 231 750 18.0 19 -One 1.85 1.12 7 0.60 229 850 14.3 15 -0.7 1.87 1.14 8 0.80 248 780 17.9 19 -1.1 1.86 1.10 9 0.80 252 860 14.8 17 -2.2 1.84 1.12 10 0.20 184 800 14.3 15 -0.7 1.86 1.09

As can be seen from Table 3, when the Nb content (a), the N content (b) before the secondary heating and the starting temperature (c) of the secondary heating are all the same, 17 ° C / hr and the differences between the theoretically calculated values and the actual values are positive, the magnetizations of the finished silicon steel sheet products of both the embodiments and the comparative examples are better. When the conditions are reversed, the cases of the comparative objects are disadvantageous, and therefore the electromagnetic characteristics of the comparative objects are bad.

The production of a directional silicon steel sheet by heating steel slabs at low temperatures has advantages such as long life of the furnace, lower energy consumption and lower manufacturing cost. However, in subsequent procedures there are difficulties in uneven decarburization and uneven nitriding and in efficient process control and control over long-term production. These cases have an effect on the inhibitory effect in some of the steel sheets or in the entire sheet resulting in incomplete secondary recrystallisation and incoherent magnetism of the finished product.

In conclusion, the present invention provides a new method for producing a directional silicon steel sheet having a high magnetic flux density based on a procedure for heating steel slabs at low temperatures. According to the method of the present invention, all of the above problems are solved effectively. This method can be easily nitrided during high temperature annealing by adding steel sheets to the molten steel in a predetermined amount of Nb; The steel sheets may be uniformly nitrided during the high temperature annealing by adding some nitrides in the separating MgO and causing them to decompose during the high temperature annealing; During the high temperature annealing, the temperature rising rate can be controlled according to the Nb content, the N content and the starting temperature of the secondary heating, thus ensuring the completion of a good secondary recrystallization course. All these solutions ensure the achievement of a directional silicon steel sheet with high magnetic flux density and excellent magnetic properties.

Claims (1)

A method of making a directional silicon steel product having a high magnetic flux density, comprising the steps of:
1) smelting and casting,
The directional silicon steel contains 0.035 to 0.065 wt% of C, 2.9 to 4.0 wt% of Si, 0.05 to 0.20 wt% of Mn, 0.005 to 0.01 wt% of S, 0.015 to 0.035 wt% of Al, 0.004 to 0.009 wt% of N, 0.005 to 0.090% by weight of Sn, and 0.200 to 0.800% by weight of Nb, the balance being Fe and unavoidable inclusions; After smelting through a rotary furnace or an electric furnace, the molten steel is refined and cast into steel slabs;
2) Hot rolling,
The steel slabs are heated to 1090 to 1200 DEG C in a heating furnace, then hot-rolled to steel plates at a starting temperature of 1180 DEG C and finished in a hot rolling step at a finishing temperature of 860 DEG C, And then coiled into the coil-shaped plates;
However,
The coil-shaped plates are annealed at an annealing temperature of 1050 to 1180 DEG C for 1 to 20 seconds and then annealed at an annealing temperature of 850 to 950 DEG C for 30 to 200 seconds and then cooled immediately at a cooling rate of 10 to 60 DEG C / do;
4) Cold rolling,
After being tempered, the steel sheets are cold rolled into steel sheets and have a thickness of the sheet finished with a rolling compression ratio of at least 75%;
5) decarburization annealing,
The steel sheets are heated to a temperature of 800-860 ° C at a temperature ramp rate of 15-35 ° C / sec and held at this temperature for 90-160sec to be decarburized;
6) MgO coating,
The steel sheets are covered with a coating consisting of 0.1 to 10 wt% of NH ₄ Cl and 0.5 to 30 wt% of P ₃ N ₅ and the balance MgO as the main component;
7) High temperature annealing,
The steel sheets are first heated to a temperature of 700 to 900 占 폚, then heated to 1200 占 폚 at a temperature raising rate of 9 to 17 占 폚 / hr and maintained at 1200 占 폚 for 20 hours to be refined annealed;
8) Insulation layer coating,
The surfaces of the steel sheets subjected to the high temperature annealing are coated with an insulating layer and a directional silicon steel sheet product having high magnetic flux density and excellent magnetic properties after hot drawing, tempering and annealing is obtained
&Lt; / RTI &gt;