KR960006025B1 - Process for production of oriented electrical steel sheet having excellent magnetic properties - Google Patents

Abstract

The iron based steel slab comprises 2 to 4wt.% silicon, 0.03 to 0.10wt.% carbon, 0.02 to 0.04wt.% soluble aluminum, 0.030 to 0.100wt.% manganeses, 0.015 to 0.040wt.% sulphur, 0.0050 to 0.0150wt.% nitrogen, and the balance of iron and inevitable impurities. The magnetic steel sheet is produced by the processes of hot rolling the steel slab having the same composition as mentioned above as a starting material, pre-annealing, cold rolling, decarburizing annealing, and high temperature annealing. The conditions of pre-annealing process are the following: (a) the heating temperature of the hot rolled sheet is 1,000 to 1,200deg.C for under 2 min., (b) cooling rate is 5 to 30deg.C/sec, (c) the temperature range for cooling is 1,150-3,333[wt.% C to 1,210-3,333[wt.% C deg.C for 30sec to 2min holding time, and (d) quenching to room temperature with the cooling rate of over 15deg.C/sec. The produced sheet by the properly controlled pre-annealing is used for the iron core material of a current transformer requiring good magnetic properties.

Description

Manufacturing method of high magnetic flux density oriented electrical steel with excellent magnetic properties

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used in iron core materials such as transformers, and more particularly, to a method for manufacturing a high magnetic flux density grain-oriented electrical steel sheet having excellent magnetic properties by appropriately controlling preanneal conditions. .

Oriented electrical steel is mainly used as the core material of transformers. In order to reduce the energy loss of transformers, the iron loss of electrical steel sheets used as materials should be low. Iron loss of a grain-oriented electrical steel sheet is affected by various factors such as the amount of silicon contained in the steel sheet, the grain size of the steel sheet, the grain orientation, the amount of impurities, the internal strain, and the thickness of the steel sheet. Lowering the iron loss in electrical steel sheet is the maximum goal of researchers and technicians involved in the production of electrical steel sheet and strives to optimize the above factors.

Researches to improve the magnetism can be divided into fields related to component system, steel plate thickness and manufacturing process, and the representative method of improving the magnetization by improving the pre-annealing process in the manufacturing process technology is US Patent 3,636,579, etc. are mentioned.

In the US patent, the pre-annealing treatment is divided into three types according to the content of Si and C, and the maximum heating temperature is adjusted to improve magnetic properties.

However, the US patent has a problem in that the magnetic enhancement is limited only by considering only precipitate control of MnS and AlN.

Accordingly, the present inventors have derived a high magnetic flux density oriented electrical steel sheet can be manufactured by improving the magnetic properties by performing pre-annealing in a new method while pursuing the optimization of the manufacturing process for improving the magnetic properties of the high magnetic flux density oriented electrical steel sheet, The present invention has been proposed on the basis of the present invention. In the manufacturing process of a high magnetic flux density oriented electrical steel sheet which performs steelmaking, hot rolling, preannealing, cold rolling, decarbonization annealing, and high temperature annealing, the holding temperature depends on the carbon content. It is an object of the present invention to provide a method for manufacturing a high magnetic flux density oriented electrical steel sheet having excellent magnetic properties by performing a preliminary annealing to control the temperature.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the present invention, Si: 2 to 4%, C: 0.03 to 0.10%, Sol-Al: 0.02 to 0.04%, Mn: 0.030 to 0.100%, S: 0.015 to 0.040%, N: 0.0050 to 0.0150 A method for producing a high magnetic flux density oriented electrical steel sheet by hot rolling, preannealing, cold rolling, decarbonization annealing, and hot annealing of steel slab containing%, balance Fe and other unavoidable impurities in this order, wherein The hot rolled steel sheet (hot rolled sheet) was kept at 1000 to 1200 ° C for 2 minutes or less, and then cooled at 5 to 30 ° C / sec at 1150-3333 [wt% C] ° C to 1210-3333 [wt% C] ° C. The present invention relates to a method of manufacturing a high magnetic flux density oriented electrical steel sheet having excellent magnetic properties, which is cooled to a temperature section of and maintained at that temperature for 30 seconds to 2 minutes, and then rapidly cooled to a room temperature at a cooling rate of 15 ° C./sec or more.

Hereinafter, the present invention will be described in more detail.

Steel grades applicable to the present invention may be any steel grade for producing a grain-oriented electrical steel sheet, and the preferred steel grades are by weight%, Si: 2-4%, C: 0.03-0.10%, Sol-Al: 0.02-0.04 %, Mn: 0.030-0.100%, S: 0.015-0.040%, N: 0.0050-0.0150%, balance Fe and other inevitable impurities.

The hot rolling of the steel slab formed as described above is performed by a conventional method, and the thickness of the hot rolled sheet is preferably limited to 0.76-2.3 mm.

In particular, the more preferable hot-rolled sheet thickness control is such that the final cold rolling rate is about 87%, and the thickness may be adjusted by pre-rolling before the pre-annealing step, which is a later step.

As described above, the hot rolled hot rolled sheet is preannealed. In the present invention, the hot rolled sheet is characterized by the preannealing process.

In the production of grain-oriented electrical steel sheet, the hot rolling process differs in various aspects such as microstructure and precipitates in the longitudinal direction of the steel sheet due to its process characteristics. Preliminary annealing is primarily intended to homogenize the difference in the longitudinal direction generated in the hot rolling process, and to improve the workability in the cold rolling process, which is the next process. In addition, the pre-annealing process is a process that plays an important role in the microprecipitation and uniform dispersion of the grain growth inhibitor (Inhibitor), securing the amount of precipitate, formation of the surface equiaxed crystal in the development of secondary recrystallization.

According to the present invention, if the heating temperature (annealing temperature) during the pre-annealing is too low, the amount of precipitated AlN is insufficient to deteriorate the magnetism, if too high, the precipitated AlN, MnS, etc. grows coarse and also deteriorates the magnetism, annealing temperature Is preferably limited to 1000-1200 ° C.

If it is maintained at the annealing temperature for 2 minutes or more, since the precipitates adversely affect the growth, the holding time at the annealing temperature is preferably limited to within 2 minutes.

After maintaining as above, it is cooled at a cooling rate of 5-30 ° C./sec to a temperature of 1150-3333 [wt% C] ∼1210-3333 [wt% C] ° C. and maintained at this temperature for 30 seconds-2 seconds. Rapid cooling to room temperature, preferably at 15 ° C / sec or more.

At this time, if the cooling rate is 5 ° C / sec or less, transformation is gradually progressed, so that the required bainite phase is not obtained, it is preferable to limit to 5 ° C / sec-30 ° C / sec.

Maintaining a large amount of magnetism by maintaining it at an appropriate temperature for a proper time during cooling is related to the phase transformation (δ → α + γ → α) during cooling in pre-annealing, and is maintained at an appropriate temperature by δ → α + γ It is considered that the equilibrium is reached at the time of transformation, and the bainite phase at the time of α + γ → α transformation is formed by the rapid quenching thereafter to increase the stored energy during cold rolling. And according to such a thought, it is necessary to hold | maintain for a suitable time in the temperature range in which (gamma) phase is formed most. The reason why the proper holding temperature changes in accordance with the C content is that the temperature at which the amount of the γ phase is maximum changes in accordance with the C content. Therefore, the holding temperature is preferably limited to 1150-3333 [wt% C] ° C to 1210-3333 [wt% C] ° C. On the other hand, if the holding time at this holding temperature is too short, the γ phase is not sufficiently secured in the δ → α + γ transformation, and if the holding time is too long, it is not economical, and precipitates are formed by the growth of precipitates such as AlN and MnS that are already precipitated It is preferable to limit the holding time to 30 seconds to 2 minutes because the ability to suppress grain growth is weakened and rather disadvantageous.

The cold-rolled, decarbonized and hot-annealed hot-rolled sheet pre-annealed as mentioned above is manufactured by the conventional method, and the condensed bundle density oriented electrical steel sheet is manufactured.

At this time, the cold rolling rate is preferably 60-95%, preferably cold rolling at a final thickness of 0.30-0.10 mm with a cold rolling rate of 80-95%.

And, the decarbonization annealing temperature is preferably limited to a temperature range of 800-870 ℃.

In addition, after the decarbonization annealing is applied to the annealing separator, and then subjected to a high temperature annealing, the high temperature annealing is preferably performed at about 1200 ℃ for about 20 hours.

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

Example 1

The hot rolled sheet containing 3.1% Si, 0.07% C, 0.025% Sol-Al, 0.052% Mn, 0.027% S, 0.081% N remainder Fe and other unavoidable impurities by weight was prepared and then heated to 1150 ° C. After preliminary annealing by changing the cooling conditions as in 1, it was cold rolled at a cold rolling rate of 87% to a thickness of 0.20 mm. Then, decarbonized annealing at 830 ℃, annealing separator was applied to the decarbonized annealing plate to annealing at 1200 ℃ high temperature. The magnetic properties of the specimens thus prepared were measured, and the results are shown in Table 1 below.

TABLE 1

As shown in Table 1, in the case of the present invention (1-5) it can be seen that the iron loss is lower than the comparative material (1-5) and the magnetic flux density is excellent.

Example 2

A hot rolled sheet containing 3.1% Si, 0.05% C, 0.027% Sol-Al, 0.052% Mn, 0.027% S, 0.083% N balance Fe and other unavoidable impurities by weight was prepared and then heated to 1135 ° C. After pre-annealing by changing the cooling conditions as shown in 2, it was cold rolled at a cold rolling rate of 87% to a thickness of 0.18 mm. Then, decarbonized annealing at 830 ℃, annealing separator was applied to the decarbonized annealing plate to annealing at 1200 ℃ high temperature. The magnetic properties of the specimens thus prepared were measured, and the results are shown in Table 2 below.

TABLE 2

As shown in Table 2, it can be seen that the case of the present invention (6-10) is lower in iron loss and excellent low-speed density than the comparative material (6-10).

Example 3

A hot rolled sheet containing 3.15% Si, 0.09% C, 0.026% Sol-Al, 0.054% Mn, 0.026% S, 0.080% N balance Fe and other unavoidable impurities by weight was prepared and then heated to 1150 ° C. After pre-annealed by changing the cooling conditions as shown in 3, it was cold rolled at a cold rolling rate of 87% to a thickness of 0.15 mm. Then, decarbonized annealing at 830 ℃, annealing separator was applied to the decarbonized annealing plate to annealing at 1200 ℃ high temperature. The magnetic properties of the specimens thus prepared were measured, and the results are shown in Table 3 below.

TABLE 3

As shown in Table 3, the case of the present invention (11-15) can be seen that the iron loss is low and the magnetic flux density is superior to the comparative material (11-15).

As described above, the present invention has an effect of providing magnetic flux density oriented electrical steel sheet having excellent magnetic properties even at a thin thickness while properly controlling the pre-annealing conditions.

Claims (1)

By weight% Si: 2-4%, C: 0.03-0.10%, Sol-Al: 0.02-0.04%, Mn: 0.030-0.100%, S: 0.015-0.040%, N: 0.0050-0.0150%, balance Fe and In the method for producing a high magnetic flux density oriented electrical steel sheet by hot rolling, pre-annealing, cold-rolling, de-carbon annealing, and hot annealing the steel slab containing other unavoidable impurities, the hot rolled steel sheet in the pre-annealing step It is heated to 1000 ~ 1200 ℃ and kept at this temperature for 2 minutes or less, and then the temperature range of 1150-3333 [wt% C] ℃ ~ 1210-3333 [wt% C] ℃ at a cooling rate of 5-30 ℃ / sec Method of producing a high magnetic flux density oriented electrical steel sheet having excellent magnetic properties, characterized in that cooled to and maintained at that temperature for 30 seconds-2 minutes, and then quenched at a cooling rate of 15 ℃ / sec or more to room temperature.