KR102362666B1 - Method for annealing non-oriented electrical steel sheet - Google Patents

Abstract

One embodiment of the present invention provides a method for final annealing of a non-oriented electrical steel sheet, comprising: a preheating zone and a heating zone for increasing the temperature of the steel sheet; a crack zone that maintains temperature using electrical resistance heat; and a cooling zone for reducing the steel sheet temperature, wherein the cooling zone is divided into an slow cooling zone and a rapid cooling zone, and the slow cooling zone is divided into 1 to 6 sections in order from the steel plate inlet direction to the exit direction, and the slow cooling zone 2 sections And by injecting a high-temperature atmosphere gas of 380 ℃ or more in section 3 to control the cooling rate of the steel sheet from section 1 to section 4 of the slow cooling zone low.

Description

Final annealing method of non-oriented electrical steel sheet {METHOD FOR ANNEALING NON-ORIENTED ELECTRICAL STEEL SHEET}

In the manufacture of non-oriented electrical steel sheet, it relates to a final annealing method. Specifically, it relates to cooling rate control in the final annealing step to improve the quality of the non-oriented electrical steel sheet.

The quality of non-oriented electrical steel sheet is a motor iron core material used in automobiles, and it is required to have a large magnetic flux density characteristic when rotating at low speed, and to have low high-frequency iron loss when rotating at high speed.

As the eco-friendly car market grows, the demand for top-quality materials is continuously increasing, and the production of high-end non-oriented electrical steel (Hyper NO) products is expected to increase in the future.

However, the production capacity of the existing annealing coating line (ACL) for the high-end non-oriented electrical steel sheet is facing a situation that is insufficient compared to the required amount.

Therefore, there is a need for a technology capable of improving the quality of non-oriented electrical steel sheets and increasing the production of the annealing coating line (ACL) of the highest grade non-oriented electrical steel sheet.

By controlling the cooling rate of the final annealing step of the non-oriented electrical steel sheet, it provides a final annealing method of the non-oriented electrical steel sheet that can improve magnetic quality and reduce iron loss.

The final annealing method of a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preheating zone and a heating zone for raising the temperature of the steel sheet; a crack zone that maintains the temperature using electrical resistance heat; and a cooling zone for reducing the steel sheet temperature.

The cooling zone may be divided into a slow cooling zone and a rapid cooling zone.

The slow cooling zone may be divided into 1 to 6 sections sequentially from the entrance direction to the exit direction of the steel plate.

It may be to lower the cooling rate of the steel sheet from the 1st to the 4th section of the slow cooling zone by injecting a high-temperature atmosphere gas of 380 ° C. or more to the second section and the third section of the slow cooling zone.

The high-temperature atmosphere gas input to the second and third sections of the slow cooling zone may include hydrogen gas and nitrogen gas.

The high-temperature atmospheric gas input to the second and third sections of the slow cooling zone may have a temperature of 380 to 450°C.

The atmospheric gas may be introduced into sections 2 and 3 by increasing the temperature by heat exchange in section 4 of the slow cooling zone.

When the atmospheric gas is input to the second and third sections of the slow cooling zone, the amount of atmospheric gas is decreased to satisfy the following [Equation 1], and the ratio of hydrogen gas in the atmospheric gas is increased.

[Formula 1]

V1 _H2 /(V0 _N2 + V1 _H2 + V1 _N2 ) = V2 _H2 /(V0 _N2 + V2 _H2 + V2 _N2 )

(V1 _H2 : H ₂ gas volume in the atmosphere gas before reduction,

V1 _N2 : volume of N ₂ gas in the atmosphere gas before reduction,

V2 _H2 : H ₂ gas volume in the reduced atmosphere gas,

V2 _N2 : the volume of N ₂ gas in the reduced atmosphere gas,

V0 _N2 : Volume of N ₂ gas fed to the quenching zone)

The ratio of atmospheric gas input to the second section and the third section of the slow cooling zone may be the same, or the ratio of atmospheric gas input to the third section than the second section may be greater.

The temperature difference between the input and output side of the slow cooling zone may be 260 to 280°C.

The average cooling rate of the slow cooling zone may be 12.38 to 13.33 ℃ / sec.

By controlling the cooling rate of the final annealing step of the non-oriented electrical steel sheet, the iron loss of the non-oriented electrical steel sheet is reduced, and the magnetic quality is improved.

Specifically, by lowering the initial cooling rate of the slow cooling zone of the final annealing step, temperature deviation and stress can be reduced, and magnetic quality can be improved.

1 shows a temperature pattern (Heat Pattern) according to time of an annealing coating process of a non-oriented electrical steel sheet.
2 is a temperature pattern (Heat Pattern) showing a general temperature drop from the electric immersion section (ESS) section 4 to the rapid cooling section (RJCS) section 6;
3 is a view showing the cooling zone (slow cooling zone and rapid cooling zone) of the annealing coating equipment.
4 is a diagram in which a radiation heat transfer equation is applied for analysis of high-temperature strip cooling.
5 is a comparative diagram of the change in strip temperature according to the result of heat flow analysis of the steel sheet in the cooling zone.
6 is a graph comparing cooling rates for each cooling temperature zone of the slow cooling zone (SJCS) in order to analyze the cooling rate for each section of the slow cooling zone.
7 is a strip thermal stress distribution diagram in the slow cooling zone (SJCS).
7A is a view showing the stress distribution of the strip steel sheet at 21 seconds of the Case 1 strip.
7B is an enlarged view showing the portion where the maximum stress occurs at 21 seconds of the Case 1 strip.
7c is a view showing the stress distribution of the strip steel sheet at 21 seconds of the Case 2 strip.
7d is an enlarged view showing the portion where the maximum stress occurs at 21 seconds of the Case 2 strip. Figure 7e is a view showing the temperature corresponding to the strip color in the slow cooling zone (SJCS).
Figure 8 is an analysis of the iron loss (W10/400) value according to the strip temperature difference (ΔT) between the slow cooling zone (SJCS) entering and exiting of the actual operation data.
9 is a schematic diagram of annealing coating line (ACL) slow cooling zone (SJCS) cooling control process technology.
FIG. 10 is a diagram analyzing heat flow for predicting the change in atmospheric temperature in the slow cooling zone (SJCS) according to the input of atmospheric gas of Inventive Example 1 and Comparative Example 1. FIG.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

In the present invention, the correlation between actual operation data and iron loss is derived based on the core loss prediction technology according to the temperature pattern through the neural network analysis of Korean Patent No. 2018-0062466, and the cooling of the strip through heat flow and structural analysis The correlation between speed, thermal stress and iron loss was analyzed.

The present invention provides a method for improving the quality of a non-oriented electrical steel sheet by controlling the cooling rate of the final annealing process, which is the main influence on the quality of the non-oriented electrical steel sheet. Specifically, in the final annealing process of non-oriented electrical steel sheet, the correlation between cooling rate, thermal stress, and magnetism was derived, and the initial cooling rate of the slow cooling zone, which had the most influence on the magnetism according to the cooling rate among the cooling zone, was determined. By controlling it low, it is possible to improve the quality of the non-oriented electrical steel sheet.

The final annealing method of a non-oriented electrical steel sheet according to an embodiment of the present invention includes a preheating zone and a heating zone for raising the temperature of the steel sheet; a crack zone that maintains temperature using electrical resistance heat; and a cooling zone for reducing the steel sheet temperature.

The cooling zone is divided into a slow cooling zone and a rapid cooling zone.

The slow cooling zone is divided into 1 to 6 sections sequentially from the steel plate entry direction to the exit direction.

1 shows a temperature pattern (Heat Pattern) according to time of an annealing coating process of a non-oriented electrical steel sheet.

As shown in FIG. 1 , the annealing coating process (ACL) may be largely divided into a heating zone, a crack zone, and a cooling zone.

Pre-heating section (PHS, Pre-Heating Section) for preheating zone, Non-Oxidizing Furnace (NOF), Radiant Tube Heating Section (RHS) for heating zone, and electric immersion section (ESS, Electric Soaking Section), cooling zone includes slow cooling section (SJCS, Slow Jet Cooling Section, hereinafter referred to as slow cooling zone) and rapid cooling section (RJCS, Rapid Jet Cooling Section, hereinafter referred to as rapid cooling zone).

The temperature raised by the preheating zone and the heating zone is maintained at a constant temperature using electric resistance heat in the crack zone, and the temperature is reduced in the slow cooling zone and the rapid cooling zone in the cooling zone through a double heat exchange method and a turbo fan.

2 is a temperature pattern (Heat Pattern) showing a general temperature drop from the electric immersion section (ESS) section 4 to the rapid cooling section (RJCS) section 6. The crack zone is divided into 5 sections, and the cooling zone is divided into 6 sections for slow cooling (SJCS) and 6 sections for rapid cooling (RJCS).

3 shows the cooling zone (slow cooling zone and rapid cooling zone) of the annealing coating facility, and the slow cooling zone (SJCS) is composed of 4 sections for indirect cooling and 2 sections for direct cooling. The rapid cooling zone (RJCS) consists of 6 sections for direct cooling.

Indirect cooling is a method of indirectly lowering the temperature in the annealing furnace by placing a cooling tube at the upper and lower parts of the annealing furnace and air from the upper and lower parts flows in through the cooling tube.

Direct cooling is a method in which air is directly introduced into the annealing furnace through suction, lowering the temperature in the annealing furnace, and cooling the steel sheet faster than indirect cooling.

The non-oriented electrical steel sheet final annealing method according to an embodiment of the present invention may be to reduce the iron loss of the non-oriented electrical steel sheet by controlling the cooling rate of the slow cooling zone low.

In particular, it may be to control the initial cooling rate of the slow cooling zone low.

Table 1 shows the iron loss of the strip samples.

Iron loss (W/kg) Case 1 12.25 Case 2 13.39

It can be seen that the strip of Case 1 has lower iron loss and superior quality than the strip of Case 2.

FIG. 4 shows that a radiation heat transfer equation is applied for the analysis of high-temperature strip cooling. Through this, when the steel sheet is cooled in the cooling zone, it is possible to check the temperature change of the steel sheet.

As a result of analysis of the strip temperature distribution for Case 1 (12.25 W/kg) and Case 2 (13.39 W/kg), it was confirmed that the cooling rate of Case 1 was slower than that of Case 2 over the entire cooling zone. It was confirmed that the cooling rate difference in the cold zone (SJCS) section was large. This shows that the cooling rate affects the iron loss in the slow cooling zone.

5 is a comparative diagram of the change in strip temperature according to the result of heat flow analysis of the steel sheet in the cooling zone.

As a result of comparing the cooling rates of the steel plates in Case 1 (12.25 W/kg) and Case 2 (13.39 W/kg), the cooling rates were similar in the rapid cooling zone (RJCS), whereas in the slow cooling zone (SJCS), Case 1 ( 12.25 W/kg) has a lower cooling rate than Case 2 (13.39 W/kg). That is, it shows that the low cooling rate of the slow cooling zone affects the reduction of iron loss.

The non-oriented electrical steel sheet final annealing method according to an embodiment of the present invention may be to lower the cooling rate of the first to fourth sections among the slow cooling zones.

Specifically, by introducing a high-temperature atmosphere gas to the second section and the third section of the slow cooling zone, it may be to lower the cooling rate of the steel sheet in the initial stage of the slow cooling zone. In this case, it is possible to reduce the iron loss of the non-oriented electrical steel sheet, and to manufacture a non-oriented electrical steel sheet of excellent quality.

Specifically, the high-temperature atmospheric gas injected into the slow cooling zone 2 and 3 sections may have a temperature of 380° C. or higher. When the temperature range is satisfied, the average cooling rate of the slow cooling zone can be controlled to 14.28° C./sec or less, and it can contribute to the reduction of iron loss of the non-oriented electrical steel sheet to be manufactured.

More specifically, the high-temperature atmospheric gas input to the second and third sections of the slow cooling zone may be 380 to 450 °C, or 386 to 442 °C.

6 is a graph comparing cooling rates for each cooling temperature zone of the slow cooling zone (SJCS) in order to analyze the cooling rate for each section of the slow cooling zone.

The cooling rates of Case 1 and Case 2 were analyzed at each point where the cooling temperature was 900 °C, 800 °C, and 700 °C during the slow cooling zone (SJCS).

It is confirmed that the cooling rate of Case 1 is low in all sections of the slow cooling zone (SJCS), and the difference in cooling rates between Case 1 and Case 2 is large, especially in the sections 1~4 of the slow cooling zone (SJCS).

This shows that the initial slow cooling in the slow cooling zone (SJCS) 1 to 4 is an important factor affecting the iron loss.

The temperature difference between the input and output side of the slow cooling zone may be controlled to 300° C. or less. Specifically, it may be controlled to 240 to 300 ℃, 260 to 280 ℃ or 270 ℃.

In this case, the iron loss of the non-oriented electrical steel sheet to be manufactured can be reduced, and in particular, when the temperature is controlled to 260 to 280°C, the lowest iron loss can be realized.

Figure 8 is an analysis of the iron loss (W10/400) value according to the strip temperature difference (ΔT) between the slow cooling zone (SJCS) entering and exiting of the actual operation data. When the temperature difference (ΔT) between the entrance and exit of the slow cooling zone (SJCS) < 260°C, it was confirmed that the iron loss decreased when ΔT increased, and when ΔT > 280°C, the iron loss increased when ΔT increased.

It can be seen that the lowest iron loss can be realized in the section of 260 ≤ ΔT ≤ 280 ° C.

The average cooling rate of the slow cooling zone may be controlled to 14.5 °C / sec or less. Specifically, the upper limit may be controlled to 14.28°C/sec or less or 13.33°C/sec or less. In addition, the lower limit of the average cooling rate may be controlled to 12° C./sec or more, or 12.38° C./sec or more.

The average cooling rate of the slow cooling zone means the average cooling rate of the steel sheet in the entire slow cooling zone from section 1 to section 6 of the slow cooling zone.

The temperature difference between the entrance and exit of the slow cooling zone may be an average cooling rate of 12.38°C/sec when ΔT is assumed to be 260°C, and an average cooling rate of 13.33°C/sec when ΔT is assumed to be 280°C.

That is, when the average cooling rate range of the slow cooling zone is satisfied, the temperature difference of the steel sheet in the slow cooling zone can be controlled to 260 to 280 ° C., and consequently, the iron loss of the non-oriented electrical steel sheet can be reduced or minimized.

Table 2 shows the cooling rates of Case 1 and Case 2 strips of FIG. 6 .

Case average cooling
Rate (℃/s) maximum cooling
Rate (℃/s) Slow cooling (SJCS)
Strip temperature difference between input and output sides (℃) iron loss
(W/kg) One 13.84 17.59 291 12.25 2 14.71 20.10 309 13.39

Compared to Case 2, Case 1 strip with excellent quality had a smaller temperature difference ΔT at the entrance/exit side of the slow cooling zone (SJCS), and the cooling rate was lower in all sections of the slow cooling zone.

7 is a strip thermal stress distribution diagram in the slow cooling zone (SJCS).

7A shows the stress distribution of the strip steel sheet at 21 seconds of the Case 1 strip, and FIG. 7B is an enlarged view of the portion where the maximum stress occurs at the time of 21 seconds of the Case 1 strip.

7c is a view showing the stress distribution of the strip steel sheet at 21 seconds of the Case 2 strip.

7d is an enlarged view showing the portion where the maximum stress occurs at 21 seconds of the Case 2 strip.

7E is a diagram illustrating a temperature corresponding to a strip color.

Overall, the stress distribution between the roll area and the roll area appears in a similar pattern.

In case 1, a relatively high maximum stress of 12.9 to 13.5 MPa occurs in the region placed on the roll, and is relatively high compared to other regions due to the influence of temperature deviation and contact with the roll at the front end of the steel plate. stress is highly distributed.

In case 2, the maximum stress is 16.1 MPa, and the stress distribution is relatively high compared to case 1. High stress due to temperature deviation is distributed at the front end of the steel plate, and the maximum stress is occurring in the roll region.

That is, it can be seen that Case 1, which has excellent quality, has a reduced temperature deviation from the front edge of the steel plate, has a relatively low stress distribution, and consequently has a smaller iron loss than Case 2. In particular, such a low temperature deviation can be effectively achieved by controlling the cooling rate of the initial slow cooling zone, which has a large difference in cooling rates between Case 1 and Case 2, to be low.

It can be confirmed that the steel plate of the slow cooling zone (SJCS) section corresponds to the elastic region of the entire section, so that there is no plastic deformation.

Table 3 is an analysis of the thermal stress deviation and end stress values of the edge and center parts of Cases 1 and 2.

location Case 1 (12.25W/kg) Case 2 (13.39W/kg) Stress deviation (MPa) End stress (MPa) Stress deviation (MPa) End stress (MPa) Edge 0.61 6.68 0.68 8.09 Center 0.49 4.23 0.54 4.87 Edge - Center 0.12 2.45 0.14 3.22

Referring to Table 3, it can be seen that as the absolute value of the stress deviation and thermal stress between the edge-center is small, the iron loss (W10/400) is reduced and the quality is improved.

Figure 8 is an analysis of the iron loss (W10/400) value according to the strip temperature difference (ΔT) between the slow cooling zone (SJCS) entering and exiting of the actual operation data.

It was confirmed that the iron loss decreases when ΔT increases when the strip temperature difference ΔT < 260℃ between the entrance and exit of the slow cooling zone (SJCS), and when ΔT increases when ΔT > 280℃, the iron loss increases.

This indicates that the lowest iron loss can be realized in the section of 260 ≤ ΔT ≤ 280°C in the strip temperature difference between the input and output sides of the slow cooling zone.

Assuming ΔT = 270℃, it is necessary to realize the average cooling rate of 12.85℃/s, which shows that cooling control in the slow cooling zone is important.

9 is a schematic diagram of annealing coating line (ACL) slow cooling zone (SJCS) cooling control process technology.

In the case of general high-quality non-oriented electrical steel sheets, in order to lower the cooling rate in the slow cooling zone, the direct cooling fan (FAN) output rate and the indirect cooling damper opening rate are minimized. However, the atmospheric gas (HN gas) having an average temperature of 17 ℃ in the 2nd and 5th sections of the slow cooling zone (SJCS) causes a temperature deviation in the steel sheet cooled to about 992 to 666 ℃, and adversely affects the quality by increasing the residual stress There is a problem affecting

Therefore, when the temperature of the atmospheric gas injected into the slow cooling zone is higher than 17° C., it is possible to reduce the decrease in the atmospheric temperature in the annealing furnace, accelerate the cooling of the steel sheet, and the occurrence of a temperature deviation of the steel sheet according to the introduction of the atmospheric gas.

In addition, by injecting high-temperature atmospheric gas into sections 2 and 3, rather than putting it into sections 2 and 5 as in the prior art, it contributes to lowering the initial cooling rate of the slow cooling zone, that is, the cooling rate of sections 1 to 4 of the slow cooling zone. can

The atmospheric gas may have a temperature increased by heat exchange in the 4th section of the slow cooling zone, and may be introduced into the 2nd and 3rd sections of the slow cooling zone. Accordingly, the effect of the present invention can be achieved without a separate facility for increasing the atmospheric gas temperature.

Specifically, the atmospheric gas is introduced into a cooling tube, which is a double pipe structure of 4 sections, and the high-temperature atmospheric gas that is heat exchanged is divided into 2 sections and 3 sections of the slow cooling zone to control the initial cooling rate of the slow cooling zone. have.

The atmospheric gas having an elevated temperature obtained by heat exchange in the slow cooling zone 4 section may be 380 to 450 °C. Specifically, it may be 386 to 450 °C.

The temperature of the atmospheric gas having an increased temperature obtained by heat exchange in the fourth section of the slow cooling zone may vary depending on the amount of atmospheric gas input for heat exchange in the fourth section.

The amount of atmospheric gas heat-exchanged in section 4 of the slow cooling zone may be equal to the sum of the amount of atmospheric gas injected into sections 2 and 3 of the slow cooling zone.

The sum of the amount of high-temperature atmospheric gas input to the second and third sections of the slow cooling zone may be 100 to 500 Nm ³ . Specifically, the lower limit may be 100 Nm ³ or more, 150 Nm ³ or more, 200 Nm ³ or more, or 300 Nm ³ or more, and the lower limit is 500 Nm ³ or less, 450 Nm ³ or less, 400 Nm ³ or less, 350 Nm ³ or less, or It may be 300 Nm ³ or less. However, the amount of the atmosphere gas may be adjusted, and the present invention is not limited thereto.

When the atmospheric gas is input to the second and third sections of the slow cooling zone, the amount of atmospheric gas is decreased to satisfy the following [Equation 1], and the ratio of hydrogen gas in the atmospheric gas is increased.

[Formula 1]

V1 _H2 /(V0 _N2 + V1 _H2 + V1 _N2 ) = V2 _H2 /(V0 _N2 + V2 _H2 + V2 _N2 )

(V1 _H2 : H ₂ gas volume in atmospheric gas before reduction, V1 _N2 : N ₂ gas volume in atmospheric gas before reduction, V2 _H2 : H ₂ gas volume in reduced atmospheric gas, V2 _N2 : N ₂ in atmospheric gas reduced Gas volume, V0 _N2 : N ₂ gas volume fed into the quench zone)

In this case, by reducing the amount of the atmosphere gas input, it is possible to reduce the cost and contribute to lowering the initial cooling rate of the slow cooling zone.

The ratio of atmospheric gas input to the second section and the third section of the slow cooling zone may be the same, or the ratio of atmospheric gas input to the third section than the second section may be greater. In this case, it is possible to improve the initial slow cooling effect of the slow cooling zone. In the case of the second section, even if the atmospheric gas whose temperature is increased by heat exchange is input, the temperature of the steel sheet is higher than the input atmospheric gas temperature. . In addition, since the atmospheric temperature of the slow cooling zone 3 section is similar to the heat exchanged high temperature atmospheric gas temperature, the high temperature atmospheric gas input to the third section suppresses the decrease in the atmospheric temperature of the slow cooling zone 3 section, contributing to lowering the cooling rate have.

10 is a heat flow analysis result for predicting the atmospheric temperature change in the slow cooling zone (SJCS) according to the atmospheric gas input of Inventive Example 1 and Comparative Example 1. In the case of the comparative example in which the 17 ℃ atmospheric gas is input to the 2nd and 5th sections of the slow cooling zone, it can be confirmed that the atmospheric temperature is rapidly decreased at the point where the atmospheric gas of the 2nd section of the slow cooling zone is input, causing a large temperature deviation.

On the other hand, in the case of Inventive Example 1, in which atmospheric gas of high temperature of 386° C. is injected into sections 2 and 3, it can be seen that there is almost no temperature change according to the input of atmospheric gas in section 2, and in the third section, As a result, it can be seen that the atmospheric temperature of section 4 is increased. Through this, in the case of Inventive Example 1, the effect of slow cooling was confirmed by increasing the atmospheric temperature of the slow cooling zone in the annealing furnace.

Table 4 shows specific experimental conditions for confirming the change in the cooling rate of the slow cooling zone according to the atmospheric gas input method when the high-temperature atmospheric gas heat-exchanged in the 4th section of the slow cooling zone is input to the 2nd and 3rd sections.

In the case of Inventive Example 3, it can be seen that the atmospheric gas temperature is higher than Inventive Examples 1 and 2. Through this, in Inventive Example 3, it was confirmed that the atmospheric gas input flow rate was reduced to 200 Nm ³ , and thus a higher temperature atmospheric gas could be obtained by heat exchange in the fourth section.

atmosphere gas
Temperature atmosphere gas
input flow atmosphere gas
distribution rate Comparative Example 1
(existing) 17℃ 400Nm ³ Section 2 : Section 5 = 50% : 50% Invention Example 1 386℃ 400Nm ³ Segment 2 : Segment 3 = 50% : 50% Invention Example 2 386℃ 400Nm ³ Section 2 : Section 3 = 30% : 70% Invention example 3 442℃ 200Nm ³ Segment 2 : Segment 3 = 50% : 50%

Table 5 shows the results of coil production and measurement under the corresponding conditions after the device installation of the actual annealing coating line (ACL). It was confirmed that the quality was improved by lowering the iron loss when the high-temperature atmosphere gas was introduced (Inventive Examples 1 and 3) compared to the case where the existing room temperature (17°C) atmosphere gas was introduced. In addition, in the case of Inventive Example 3, by reducing the flow rate, it was confirmed that the iron loss was reduced by 0.2 W/kg compared to Inventive Example 1 to bring about an ultra-slow cooling effect. As such, it was confirmed that there is an effect of improving the quality of the non-oriented electrical steel sheet by reducing the temperature deviation due to the reduction of the cooling rate in the slow cooling zone.

number of N iron loss
(10/400)
(W/kg) slow cooling
entry/exit side
temperature difference
ΔT(℃) slow cooling
inlet temperature
(℃) slow cooling
exit temperature
(℃) Invention Example 1
(400m ³ , 2nd section 50%, 3rd section 50%) 2 12.54 274 975 701 Invention example 3
(200m ³ , 2nd section 50%, 3rd section 50%) 4 12.34 262 965 703 Comparative Example 1
(existing) 3 12.65 284 985 701

According to an embodiment of the present invention, the predicted temperature of the outflow of the atmospheric gas heat-exchanged through the 4-section cooling tube is approximately 386 °C based on the input flow rate of the general atmospheric gas of 400Nm ³ .

Table 6 shows the predicted exit side steel plate temperature and stress values when Inventive Examples 1, 2, and 3 are applied.

atmosphere gas
input flow 2nd segment
(flow, temperature) 3 sections
(flow, temperature) 5 segments
(flow, temperature) Inlet temperature of slow cooling zone of steel plate (℃) Criteria for exiting the slow cooling zone
Thermal fluid analysis results von Mises stress (MPa) Center
(℃) Edge (℃) Edge-Center temperature difference
(℃) Center
(℃) Edge
(℃) Edge-Center
temperature difference
(℃) Case 2
(conventional) - 160 Nm ³ /h,
17℃ - 240 Nm ³ /h,17℃ 975 670.57 654.30 16.27 5.78 10.53 4.72 Invention Example 1
(400m ³ , 2nd section 50%, 3rd section 50%) 400 m ³ /h 200 Nm ³ /h,
386℃ 200 Nm ³ /h,
386℃ - 975 671.88 655.49 16.39 5.44 9.89 4.45 Invention Example 2
(400m ³ , 2nd section 30%, 3rd section 70%) 400 m ³ /h 120 Nm ³ /h,
386℃ 280 Nm ³ /h,
386℃ - 975 671.78 656.06 15.72 5.23 9.69 4.46 Invention example 3
(200m ³ , 2nd section 50%, 3rd section 50%) 200 m ³ /h 100 Nm ³ /h,
442℃ 100 Nm ³ /h,
442℃ - 975 673.25 657.24 16.01 6.10 9.17 3.07

In the case of Inventive Examples 1, 2, and 3, it was confirmed that the exit side steel sheet temperature and stress value were lower than before when compared with the comparative example (case 2) according to the conventional method.

In particular, in the case of Inventive Example 3, it can be seen that the exit temperature is the highest. This reduces the input flow rate of the atmospheric gas by half, thereby further increasing the temperature of the atmospheric gas heat-exchanged in the fourth section to 442°C. As a result, by injecting a small amount of a higher temperature atmospheric gas into the annealing furnace, it is possible to achieve an ultra-slow cooling effect and a cost reduction by reducing the input flow rate.

The high temperature atmosphere gas input reduces the temperature deviation and residual stress of the steel sheet during cooling due to the increase in the atmospheric temperature in the furnace, and the final stress value at the exit side is lower than before. have.

Table 7 is a table showing the ratio of H ₂ in the total atmospheric gas and the ratio of H ₂ to the total input gas in the annealing furnace when the atmospheric gas input flow rate (in the case of 50% hydrogen consumption) is reduced by half and input.

Soden furnace input gas Input gas amount (Nm ³ /h) N ₂ dose (Nm ³ /h) H ₂ Dosage (Nm ³ /h) H ₂ compared to the total input gas in the furnace
ratio
(%)
N ₂ Purging 928 928 ① 290 290 ② 178 178 Sum 1396 1396 existing atmosphere gas
(H ₂ 51%+N ₂ 49%) ③Section 2 250 122.5 127.5 25%
=⑥/(①+②+③+④) ④ Section 5 200 98 102 Sum 450 213 225(⑥) Invention example 3 atmosphere gas
(H ₂ 80%+N ₂ 20%) ⑤
2+3 sections 200 40 160 24%
=⑦/(①+②+⑤) Sum 200 40 160(⑦)

In the non-oriented electrical steel sheet, the ratio of H ₂ gas in the atmospheric gas supplied to the slow cooling zone (SJCS) is 20 to 60%, which varies depending on the type of steel. In the case of the highest grade electrical steel sheet (Hyper NO), the ratio of H ₂ gas in the total atmospheric gas input flow rate of 450 Nm ³ /h is about 50 to 55% by volume. At this time, the ratio of H ₂ to the total input gas in the annealing furnace is 25% by volume. At this time, when the atmospheric gas input flow rate is 200 Nm ³ /h, if the H ₂ gas ratio of the atmospheric gas is increased to 80 vol%, the H ₂ ratio to the total input gas in the annealing furnace is 24 vol% similar to the previous one. As described above, by reducing the atmospheric gas input flow rate of 250 Nm ³ /h, the effect of ultra-slow cooling according to the increase in atmospheric temperature and economic benefits according to cost reduction are secured. In addition, since the ratio of H ₂ to the total input gas in the annealing furnace may be maintained the same, the process may not be affected by the decrease in the amount of atmosphere gas input.

It was confirmed through correlation with cooling rate, thermal stress, and iron loss that the initial slow cooling of the high-grade material non-oriented electrical steel sheet, specifically, the slow cooling of the slow cooling zone 1 to 4 was an important factor. In addition, by introducing high-temperature atmospheric gas into sections 2 and 3, it was confirmed that the initial slow cooling of the slow cooling zone was achieved, and the quality of the highest grade electrical steel sheet could be improved.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

Claims (8)

In the final annealing method of non-oriented electrical steel sheet,
a preheating zone and a heating zone for raising the temperature of the steel sheet; a crack zone that maintains the temperature using electrical resistance heat; and a cooling zone for reducing the steel plate temperature;
The cooling zone is divided into a slow cooling zone and a rapid cooling zone,
The slow cooling zone is divided into sections 1 to 6 in order from the entrance direction to the exit direction of the steel plate,
It is to control the cooling rate of the steel sheet from the 1st section to the 4th section of the slow cooling zone to a low level by injecting atmospheric gas of a high temperature of 380 ° C or more to the 2nd and 3rd sections of the slow cooling zone,
When atmospheric gas is input to the second and third sections of the slow cooling zone,
To reduce the amount of atmospheric gas to satisfy the following [Equation 1], and to increase the ratio of hydrogen gas in the atmospheric gas to input,
Final annealing method for non-oriented electrical steel sheet:
[Formula 1]
V1 _H2 /(V0 _N2 + V1 _H2 + V1 _N2 ) = V2 _H2 /(V0 _N2 + V2 _H2 + V2 _N2 )
(V1 _H2 : H ₂ gas volume in the atmosphere gas before reduction,
V1 _N2 : volume of N ₂ gas in the atmosphere gas before reduction,
V2 _H2 : H ₂ gas volume in the reduced atmosphere gas,
V2 _N2 : the volume of N ₂ gas in the reduced atmosphere gas,
V0 _N2 : Volume of N ₂ gas fed to the quenching zone)
According to claim 1,
The high-temperature atmosphere gas input to the second and third sections of the slow cooling zone includes hydrogen gas and nitrogen gas,
Final annealing method of non-oriented electrical steel sheet.
According to claim 1,
The high-temperature atmospheric gas input to the second and third sections of the slow cooling zone has a temperature of 380 to 450 °C,
Final annealing method of non-oriented electrical steel sheet.
The method of claim 1,
The atmospheric gas is to increase the temperature by heat exchange in section 4 of the slow cooling zone and input to section 2 and section 3,
Final annealing method of non-oriented electrical steel sheet.
delete The method of claim 1,
The ratio of atmospheric gas input to the second section and the third section of the slow cooling zone is the same, or the ratio of atmospheric gas input to the third section is greater than that of the second section,
Final annealing method of non-oriented electrical steel sheet.
According to claim 1,
That the temperature difference of the steel plate in the cold zone in the slow cooling zone is 260 to 280 ℃,
Final annealing method of non-oriented electrical steel sheet.
8. The method of claim 7,
The average cooling rate of the slow cooling zone will be 12.38 to 13.33 ℃ / sec,
Final annealing method of non-oriented electrical steel sheet.

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