JPH05156366A - Manufacture of surface treated original plate by continuous annealing - Google Patents

Abstract

PURPOSE:To provide the method for manufacturing a surface treated original plate by continuous annealing capable of high temp. annealing and capable of manufacturing T-3 to T-4 by compact super rapid heating short time annealing and that is low in equipment cost. CONSTITUTION:This cover is (1) the method in which a slab constituted of 0.020 to 0.070% C, 0.05 to 0.60% Mn, 0.001 to 0.025% P, 0.001 to 0.025% S, 0.012 to 0.090% solAl, <=0.0035% N, <=0.0070% T.O and the balance iron with inevitable impurities is subjected to heating and hot rolling under ordinary hot rolling conditions and is coiled into a hot rolled steel strip, which is subjected to cold rolling of >=85 draft and is thereafter subjected to continuous annealing of heating it in the temp. range of at least >=500 deg.C to 650 to 850 deg.C at 300 to 2000 deg.C/s heating rate, holding it <=3sec, cooling it to <=550 deg.C at 40 to 550 deg.C/s cooling rate, staying it at 550 to 400 deg.C for 2 to 15sec and executing cooling to a room temp. and is (2) the method in which C.T is regulated to 660 to 750 deg.C, and the regulation value of C and N is widen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of continuously annealing a surface-treating original plate having a hardness level of 3 to 4 in terms of temper degree, which is subjected to a surface treatment such as tin plating or chromic acid treatment. It is about.

[0002]

2. Description of the Related Art The hardness level of a surface-treated original plate to which a surface treatment such as tin plating or chromic acid treatment is applied is 3 in terms of temper degree.
The surface-treating original plates (hereinafter, referred to as T-3 and T-4) of Nos. 4 to 4 are conventionally heated at a heating rate of 10 to 40 ° C./s and uniformly soaked at 600 to 700 ° C. for 20 to 30 seconds to 10 to 20.
Although it was manufactured by a continuous annealing furnace in which it takes about 2 minutes to cool to 500 ° C. at 50 ° C./s and to room temperature at 20 to 40 ° C./s, in this case (1) the annealing time is long. The length of the coil staying in the annealing furnace is more than 1000 m and the equipment length becomes long, which increases the construction cost of the continuous annealing equipment. (2) Such a furnace has a hearth roll to shorten the installation space of the equipment. A vertical pass furnace is used in which the steel strips are placed vertically and the steel strip passes vertically between them.
Therefore, high-temperature annealing that exceeds 700 ° C., which is effective for producing a softer plated original plate, causes a large decrease in the strength of the steel plate, causing wrinkling, which makes it impossible to pass the plate. Therefore, high temperature annealing cannot be performed and it becomes difficult to manufacture a soft steel sheet. (3) In the case of such a furnace,
Since a high-temperature furnace is used for heating and soaking, if the plate thickness changes or if the heating soaking temperature changes, the temperature tracking will be delayed and it will take some time to reach the specified temperature, so it will pass through the adjustment coil. It becomes necessary to adjust the temperature. Therefore, in order to avoid productivity loss, energy loss, etc., it is necessary to schedule the order of sheet passing so that changes in sheet thickness and set temperature are as small as possible, which causes problems such as delivery management of products and inventory increase. Above (1), (2),
There are problems such as (3).

On the other hand, the short-time continuous annealing method has also been devised and studied, and Japanese Patent Publication No. 36-10052, Japanese Patent Publication No. 36-21115, and Japanese Patent Publication No. 40-30.
No. 20, Japanese Patent Publication No. 46-19781, and
"Recrystallization '90 Ed
ited by Chandra The Miner
als, Metals & Materials So
Citation, 1990 ”(hereinafter referred to as Document 1).
There is. However, Japanese Patent Publication No. 36-21155 discloses 20
It must be wound as a coil at 0 to 300 ° C., and there are problems of oxidation, winding equipment, cooling method of the wound coil, and uneven cooling of the inner and outer circumferences of the coil during cooling. Further, Japanese Patent Publication No. 40-3020 has a temper degree of 6
According to the above manufacturing method, Japanese Patent Publication No. 46-19781 discloses H
R ₃₀ T is a method of producing a surface-treated original plate of extremely hard material having a value of 72 or more, and T-3 to T-4 cannot be produced by these methods. Japanese Examined Patent Publication No. Sho 36-10052 discloses that the annealing time for rapid heating and quenching with almost no soaking is about 15
Although it is a short time annealing method of sec, the major problem of this method is that the hardness of the obtained material is HR ₃₀ T of 65 and the temper degree is 5 (hereinafter T-) as shown in Table 1 of the publication. It is the only thing that can be done.

The contents introduced in the literature 1 are 1)
Decarburized annealing of hot rolled rimmed steel, C content 0.005
% Steel is cold-rolled to 70%, 0.2se
As a result of heating at c (about 3500 ° C./s), soaking for 0.1 sec, and quenching with a water spray, 0.5 sec, 0.3
2) that the recrystallization temperature was remarkably lowered as compared with the case of sec heating (about 2000 ° C / s to 3000 ° C / s).
0.5sec, 0.3sec heating (about 2000 ° C / s ~
In the case of 3000 ° C / s), it is introduced that the temperature can be about 830 ° C, 800 ° C or higher. That is, the method of Reference 1 is a decarburization annealing of a hot rolled sheet and a heating rate of 0.2 sec (about 3500 ° C./s) at which it is extremely difficult to control the heating temperature, that is, an extremely minute heating such as 0.01 sec. It can be seen that this method is not suitable for practical use because it requires a heating rate condition that makes it extremely difficult to put it into practical use, in which the temperature fluctuates as much as 35 ° C. due to time variations. As described above, the conventional method of ultra-rapid heating and short-time annealing, which is compact and capable of high-temperature annealing and has a high degree of freedom in threading scheduling, cannot produce soft materials or even at the laboratory level. Method 1) There is still only the method that cannot be put to practical use economically and industrially.

[0005]

The problem to be solved by the present invention is a super rapid heating and short time annealing equipment which is capable of high temperature annealing, has a high degree of freedom in the scheduling of sheet passing, is compact, and has a small equipment cost. It is to provide a method for producing a surface-treated original plate by continuous annealing capable of producing T-3 to T-4.

[0006]

In order to solve the above-mentioned problems, the present inventors comprehensively studied the content of components, hot rolling conditions, cold rolling conditions, and continuous annealing conditions, and the manufacturing method of the present invention. I found it. The gist of the present invention is as follows. (1) C: 0.020 to 0.070% Mn: 0.05 to 0.60% P: 0.001 to 0.025% S: 0.001 to 0.025% Sol Al: 0.012 0.090% N: ≤0.0035% TO: ≤0.0070% A steel slab consisting of the balance unavoidable impurities and iron is heated and hot-rolled under normal hot-rolling conditions, and the winding heat is applied. A steel strip is used, cold rolling is performed at 85% or more, and then continuous annealing is performed at a temperature range of at least 500 ° C. to 300 to 2000.
It is heated to 650 to 850 ° C. at 3 ° C./s and retained for 3 seconds or less, cooled to 550 ° C. or less at a cooling rate of 40 to 500 ° C./s, and allowed to stay at 550 to 400 ° C. for 2 to 15 seconds, A method for producing a surface-treated original plate by continuous annealing, which comprises cooling to room temperature.

(2) C: 0.020 to 0.080% Mn: 0.05 to 0.60% P: 0.001 to 0.025% S: 0.001 to 0.025% Sol Al: 0 0.020 to 0.100% N: ≤ 0.0070% TO: ≤ 0.0070% A steel slab composed of the balance unavoidable impurities and iron is heated and hot-rolled to a temperature of 660 ° C to 750 ° C. Rolling hot rolled steel strip at a winding temperature in the range (hereinafter referred to as CT)
% Cold-rolling is performed, and thereafter, a temperature range of at least 500 ° C. or higher is heated to 650-850 ° C. at 300-2000 ° C./s by continuous annealing, and retained for 3 seconds or less.
Cooling to 550 ° C or lower at a cooling rate of ~ 500 ° C / s,
A method for producing a surface-treated original plate by continuous annealing, characterized in that it is allowed to stay at 550 to 400 ° C. for 2 to 15 seconds and cooled to room temperature.

The present invention will be described in detail below. In order to solve the above problems, the present inventors comprehensively examined the component content, hot rolling conditions, cold rolling conditions, and continuous annealing conditions for the production method thereof, and at least 500 in the heating of continuous annealing. 300 to 2000 in the temperature range above ℃
In order to increase the crystal grain size after recrystallization annealing by heating to 650 to 850 ° C. at C / s, C: 0.020 to 0.070%, N: ≦ 0.0035 as (1) of the invention.
%, And a method that enables winding at low temperature, C: 0.020 to 0.0800%, so as (2) of the invention.
Al: 0.020 to 0.100%, N: ≤ 0.007
A steel slab consisting of 0%, the balance unavoidable impurities, and iron was heated to form a C.C. A method of significantly relaxing the restrictions on the C and N contents of the hot-rolled steel strip taken up by T, cooling after soaking at a cooling rate of 40 to 500 ° C / s to 550 ° C or less, and 550 to 400 2 between ℃
A method of reducing the C content of solid solution by allowing it to stay for 15 seconds,
By using 3 points of, and
Content is C: 0.020 to 0.07 as (1) of the invention.
0%, C: 0.020 to 0.080 as (2) of the invention
% And a C content that can be easily obtained by an ordinary steelmaking method, T-3 to T-4 with extremely compact continuous annealing equipment.
It was the first time that it was possible to manufacture.

FIG. 1 shows that the temperature range of at least 500.degree.
Heating to 650-850 ° C at 0-200 ° C / s "
It is a figure showing the effect of. The C content was 0.05%, the cold-rolled sheet having a plate thickness of 0.25 mm rolled at a cold rolling rate of 90% produced by the method of the present invention was heated at a heating rate (αH) in the heat cycle shown in FIG. And soaking temperature (T) are changed, time (t)
For 0.1 sec, cooling after soaking was cooled to 500 ° C. at a cooling rate of 300 ° C./s, allowed to stay for 5 seconds between 520 and 450 ° C., and the structure of the steel sheet cooled to room temperature was investigated,
FIG. 6 is a diagram showing the result of finding the temperature at which recrystallization is completed.

It can be seen from FIG. 1 that the recrystallization completion temperature is remarkably lowered by setting the heating rate to 300 ° C./s or more. From this, in order to produce T-3 to T-4 with a compact continuous annealing equipment with almost no soaking time,
300 ° C in the heating of continuous annealing which is the point of the present invention
It can be seen that it is extremely important to perform ultra-rapid heating of not less than / s. Note that in Reference 1, about 1700 ° C./s (t ₁ =
When the heating rate is about 0.5 sec, the recrystallization completion temperature is 8
Although it remarkably rises to 00 to 830 ° C., the result shown in FIG. 1 is a very different result. The reason for this is to be examined in detail in the future, but the cold rolling ratio is 70%, which is significantly higher than 90%, and the components, especially T.I. It is considered that the difference may be due to the influence of different conditions such as the fact that the material obtained by decarburizing and annealing a hot rolled sheet of rimmed steel having a high O content of 0.0375% was used as the test steel.

The mechanism by which a material softer than the conventional 20 ° C./s can be obtained by heating at 300 ° C./s or more as described above has not been sufficiently clarified. In the case of ultra-rapid heating, since the moving speed of the grain boundaries of the subgrains at the start of recrystallization and the moving speed of the grain boundaries during grain growth are extremely fast, the segregation elements move to the grain boundaries. The number of segregated elements that do not follow and hinder the movement of grain boundaries decreases. As a result, by performing ultra-rapid heating, recrystallization occurs at a lower temperature and grain growth becomes easier, and a softer material can be obtained. It is considered that the cold rolling rate, composition, etc. may affect the generation and size of this subgrain.

B. In the case of ultra-rapid heating, the time between recrystallization and grain growth is so short that AlN fine precipitation hardly occurs before and during recrystallization during grain growth. As a result, by performing ultra-rapid heating, recrystallization was performed at a lower temperature, grain growth was facilitated, and a softer material was obtained. It is presumed that this is due to the effects of the above. The effects of A and B are 30 at least in the temperature range of 500 ° C. or higher during heating in continuous annealing.
It was obtained by heating to 650 to 850 ° C at 0 ° C / s or more.

The point of the present invention is the components and hot rolling conditions for exhibiting the ultra-rapid heating effect of the point. As (1) of the invention, C: 0.020 to 0.070.
%, N: ≤ 0.0035%, which is a method that enables winding at low temperature, the main condition being that the adverse effect of C becomes too large when the C content exceeds 0.070%.
Further, if the N content exceeds 0.0035%, fine AlN will begin to precipitate even with ultra-rapid heating, and it is necessary to regulate the C and N contents. As (2) of the invention, C:
0.020-0.080%, sol Al: 0.020
˜0.100%, N: ≦ 0.0070%, the balance unavoidable impurities and a steel slab composed of iron are heated to 660 ° C. to 75 ° C.
C. in the range of 0 ° C. With the method of winding hot rolled steel strip at T,
C. in the range of 660 ° C to 750 ° C. The point is to significantly relax the regulation of C and N contents by winding C at T to coagulate and precipitate as coarse cementite to purify the matrix and coarsely precipitate N as AlN to mitigate the adverse effect. Is the way.

The point of the present invention is that after the heating during recrystallization annealing and the crystal grains are grown sufficiently large during soaking by the method of the point of the present invention or the like, the subsequent cooling after soaking is 40 to 40 ° C. It is to cool to 550 ° C. or lower at a cooling rate of 500 ° C./s, and to make it stay between 550 to 400 ° C. for 2 to 15 seconds. By controlling the cooling conditions in this manner, a large amount of solid solution C that had been re-dissolved during soaking was about 4
It becomes possible to make it 0 to 50 ppm or less. As a result, it is possible to manufacture the surface-treated original plate of T-3 to T-4 with the total effect of.

The manufacturing conditions will be described in detail below. C
Is an element that greatly affects the hardness of T-3 to T-4 as described above, and is an important element that affects the crystal grain size after recrystallization annealing during super rapid heating annealing. In the method (1) of the invention, when the C content exceeds 0.070%, T-3 to T-.
Since the hardness of 4 cannot be obtained, the upper limit of the C content is 0.0
70%, and in the method (2) of the invention, the C content is 0.
If it exceeds 080%, the hardness of T-3 to T-4 cannot be obtained, so the upper limit of the C content was made 0.080%. Incidentally, C
If the amount is less than 0.020%, it is necessary to blow down C in the converter. As a result, the T. The O content increases, the inclusions in the steel increase, and the workability of the product deteriorates. Further, as a method for avoiding this, there is a decarburization treatment method by degassing in a steelmaking plant, but there is a problem that the treatment cost becomes too high, so the lower limit C content was set to 0.020%.

If the Mn content exceeds 0.60%, T-
Since the hardness of 3 to T-4 cannot be obtained, 0.60% was made the upper limit. In addition, since less than 0.05% cannot be obtained by an ordinary manufacturing method, the lower limit value is set to 0.05%. P content is
If it exceeds 0.025%, the hardness of T-3 to T-4 cannot be obtained, so 0.025% was made the upper limit. In addition, 0.0
Since less than 01% cannot be obtained by an ordinary manufacturing method, the lower limit value was made 0.001%. If the S content exceeds 0.025%, the hardness of T-3 to T-4 cannot be obtained, so 0.0
25% was made the upper limit. In addition, since less than 0.001% cannot be obtained by an ordinary manufacturing method, the lower limit is set to 0.001%.

According to the method (1) of the invention, when the content of sol Al exceeds 0.090%, sol Al is large in sol Al even if ultra-rapid heating annealing is carried out, so that a large amount of fine AlN is precipitated. Therefore, 0.090% was set as the upper limit. If the content is less than 0.012%, the T. Since the O content becomes too high to be 0.0070% or less, the lower limit is set to 0.012%. or,
In the method (2) of the present invention, N is converted to A by high-temperature winding.
Since it is an element necessary for fixing as 1N, so
l When Al content is less than 0.020%, sol Al
Is insufficient and N cannot be sufficiently precipitated as coarse AlN, and fine AlN comes to be precipitated.
During recrystallization annealing, crystal grains are refined to harden the material and T-3
Since the hardness of T-4 cannot be obtained, the lower limit of sol A
The amount of 1 was 0.020%. On the other hand, if it exceeds 0.100%, the material is hardened by solid solution hardening and the hardness of T-3 to T-4 cannot be obtained, so 0.100% was made the upper limit.

In the method (1) of the invention, the N content is N
If the content exceeds 0.0035%, fine AlN will be precipitated due to a large amount of N even after performing ultra-rapid heating annealing, so 0.0035% was made the upper limit. Further, in the method (2) of the present invention, since N is fixed as AlN by high-temperature winding, a soft material can be obtained even if the N content is large, but if the N content exceeds 0.0070%. Since the precipitation amount of AlN becomes too large and the material becomes hard and the hardness of T-3 to T-4 cannot be obtained, 0.0070% was made the upper limit value. It should be noted that the lower the N content, the softer the steel sheet can be obtained, so there is no need to regulate the lower limit value.

T. If the O content exceeds 0.0070%, air bubbles are generated near the surface layer of the slab, and scratches on the plating base plate increase, so that a good product cannot be obtained.
70% was made the upper limit. The lower limit is not regulated because it does not need to be regulated. The hot rolling conditions do not have to be particularly restricted as the method (1) of the invention, and ordinary hot rolling conditions may be used. The method (2) of the invention is an important step for rendering C and N harmless during winding of hot rolling.
At a winding temperature of T less than 660 ° C, the material is hardened and T-
Since a hardness of 3 to T-4 cannot be obtained, 660 ° C was set as the lower limit value. On the other hand, if the winding temperature exceeds 750 ° C, the scale becomes abnormally thick and the pickling property deteriorates significantly, so 750 ° C was set as the upper limit. The heating conditions for hot rolling do not need to be particularly restricted and may be those that are normally performed.
In order to obtain a softer steel plate, a heating temperature of 1150 ° C. or lower (referred to as SRT) is preferable.

If the cold rolling ratio during cold rolling is less than 85%, the recrystallization temperature during recrystallization annealing becomes high and the material becomes hard, making it difficult to obtain T-3 to T-4, and the plated product becomes a plate. Since the thickness is thin, if the cold rolling ratio is less than 85%, the thickness of the hot-rolled sheet becomes too thin, which makes hot rolling difficult.
It was set to 5%. It should be noted that the upper limit value is not regulated because it does not need to be regulated. The heating rate of recrystallization annealing at the time of continuous annealing is the most important point of the present invention, and its effect and its mechanism are as previously inferred. Heating rate is 3
If it is less than 00 ° C./s, the effect of ultra-rapid heating cannot be obtained, the material is hardened, and the hardness of T-3 to T-4 cannot be obtained.
° C / s was set as the lower limit. If the heating rate is higher than 2000 ° C./s, the heating rate is too fast, and the control of the ultimate temperature of heating becomes unstable, and it becomes difficult to obtain stable quality. Therefore, the upper limit is 2000 ° C./s.

When the annealing temperature during the recrystallization annealing is less than 650 ° C., sufficient recrystallization does not occur even in the super rapid heating annealing, and T-3.
The hardness of ˜T-4 cannot be obtained, so 650 ° C. is set as the lower limit value. If the annealing temperature exceeds 850 ° C., the steel sheet is softened and easily spreads when passing through the soaking zone, and the stripability deteriorates. Therefore, 850 ° C. was set as the upper limit value. As for the soaking time during recrystallization annealing, in the ultra-rapid heating annealing, sufficient recrystallization and grain growth occur and hardness of T-3 to T-4 can be obtained even if there is no soaking time, so the lower limit of the soaking time is No need to regulate. The upper limit of the soaking time is set to 3 sec, which is the object of the present invention "due to the continuous annealing capable of producing T-3 to T-4 with an extremely compact continuous annealing equipment capable of greatly reducing the equipment cost. Therefore, the upper limit is set to 3 sec, because it deviates from the idea of "a method for producing a surface-treated original plate".

Cooling after recrystallization annealing is one of the important points of the present invention, and in order to obtain T-3 to T-4, at the time of cooling after soaking, as shown in FIG. It turns out that it is necessary to stay for 2 seconds or more. If the staying time exceeds 15 seconds, the equipment length becomes too long, which is outside the provision of compact equipment, which is the gist of the method of the present invention.

FIG. 3 shows a heat rolled sheet shown in FIG. 2 which is manufactured by the method of the present invention and has a C content of 0.05% and a cold rolling rate of 90% and a thickness of 0.25 mm. Cycle: αH: 1000 ° C / s, T ₁ : 710 ° C, t ₁ : 0.1s
ec, cooling after soaking is cooled to T ₂ at a cooling rate of 300 ° C./s, the temperature range of T _{2 to} T ₃ is kept at 10 ° C./s for toa seconds, and cooled to room temperature at 300 ° C./s. 1.2% temper rolling is applied to the annealed steel sheet to make a surface-treated original sheet,
Measured HR ₃₀ T of the steel sheet is a diagram showing the results. From FIG. 3, in cooling after soaking, 500 to 4
The effect of staying at 00 ° C. for an extremely short time of 2 to 15 seconds is extremely remarkable, and the HR ₃₀ T is greatly reduced even after a slight stay of 2 to 3 seconds. It is also understood that when the temperature of T ₃ is 300 ° C., which is outside the range of the invention of the present application, softening hardly occurs. As described above, the HR ₃₀ T sharply decreases because a large amount of solid solution C re-dissolved during soaking during recrystallization annealing is 550 to 550.
This is because during the retention of 400 ° C. for 2 seconds or more, the temperature is remarkably lowered.

The cooling condition up to 550 ° C. is 500 ° C.
If it exceeds / s, the controllability of rapid cooling will deteriorate, and if it is less than 40 ° C / s, the cooling time will increase and the equipment length will increase, which is a compact feature of the method of the present invention. Since it will be out of provision of equipment, it was regulated to 40 to 500 ° C / s. Furthermore, 550-4
The cooling conditions after the retention of 2 to 15 seconds between 00 ° C do not need to be particularly limited, and the cooling may be performed promptly. The temper rolling may be performed at 0.5 to 2.0% which is usually performed, if necessary.

[0025]

EXAMPLES The effects of the present invention will be described below with reference to examples. The composition shown in Table 1 and a hot rolled steel strip of 2.5 mm were manufactured under the hot rolling conditions and cold rolled at a cold rolling ratio of 90% to 0.25 m.
The cold-rolled steel sheet of m was continuously annealed in the heat cycle shown in FIG. 2 under the conditions of temperature, time and αc ₂ of 300 ° C./s shown in Table 2, and temper-rolled to 1.2% to obtain a surface-treated original sheet. Got The hardness (HR ₃₀ T) of the obtained surface-treated original plate was measured,
The results are shown in Table 2. Steel A has manufacturing conditions within the range of the method (1) of the present invention, and steels B and C have manufacturing conditions within the range of the method of (2) of the present invention. D and E are manufacturing conditions outside the range of the method of the present invention.

[0026]

[Table 1]

[0027]

[Table 2]

Samples 1, 2, 3, 4, 5, and 6 are examples of the method of the present invention, and all of them have a hardness range of T-3 to T-4 (H
A plated original plate of R ₃₀ T = 58 ± 3 to 61 ± 3) is obtained. As shown in Table 1, sample 1 is an example in which components such as C and N contents, hot rolling conditions, and annealing conditions were within the range of the method (1) of the present invention. It is understood that according to the method (1) of the present invention, an original plating plate having an HR ₃₀ T of 59.0 and a hardness range of T-3 to T-4 can be obtained. Samples 2.3, 4, 5,
As shown in Tables 1 and 2, 6 and 6 are examples in which the amounts of C and N and the annealing conditions were changed within the range of the method (2) of the present invention. It is understood that the plating original plate having the hardness range of T-3 to T-4 can be obtained within the range of the method (2) of the present invention. Sample 7 is C.I. (1) of the present invention having a low T
In the comparative example in which the amounts of C and N are high in the above method, T-3 to T-
It can be seen that a plating original plate having a hardness range of 4 cannot be obtained.

Specimen 8 is a comparative example in which the residence time (toa) between 550 and 400 ° C. after annealing in the method (2) of the present invention was as low as 1 second, and it was T-3 to T-4. It can be seen that the original plating plate in the hardness range cannot be obtained. Sample 9 has a high C and N content of the method (2) of the present invention and deviates, and the heating rate is 20 ° C./s, which is the same level as that of the conventional method and is 550 after further annealing.
In Comparative Example, there was almost no residence time (toa) between 400 ° C. and 400 ° C., and a plating original plate having a hardness range of T-3 to T-4 could not be obtained. Sample 10 has a soaking time of 30 se during annealing.
This is a conventional example of continuous annealing conditions that are currently industrially performed for a long time.

[0030]

Although the present invention has been described in detail above, according to the present invention, it is possible to perform high temperature annealing, have a high degree of freedom in the scheduling of sheet passing, be compact, and reduce the equipment cost for ultra-rapid heating in a short time. With continuous annealing equipment, T-3 to T-
The surface-treated original plate of No. 4 can be manufactured, and its industrial value is great.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a heating rate and hardness in continuous annealing,

FIG. 2 is a diagram showing a heat cycle of continuous annealing used in investigation experiments and examples,

FIG. 3 is a diagram showing a relationship between cooling conditions after soaking and HR ₃₀ T.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiro Doi 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Shin Nippon Steel Co., Ltd. Hirohata Works

Claims (2)

[Claims] 1. C: 0.020 to 0.070% Mn: 0.05 to 0.60% P: 0.001 to 0.025% S: 0.001 to 0.025% Sol Al: 0.0. 012 to 0.090% N: ≤ 0.0035% TO: ≤ 0.0070% A steel slab composed of the balance unavoidable impurities and iron is heated under normal hot rolling conditions, hot rolled, and wound. Hot-rolled steel strip, cold-rolled at 85% or more, and then continuously annealed at a temperature range of at least 500 ° C to 300-2000.
It is heated to 650 to 850 ° C. at 3 ° C./s and retained for 3 seconds or less, cooled to 550 ° C. or less at a cooling rate of 40 to 500 ° C./s, and allowed to stay at 550 to 400 ° C. for 2 to 15 seconds, Method for producing surface-treated original plate by continuous annealing characterized by cooling to room temperature 2. C: 0.020 to 0.080% Mn: 0.05 to 0.60% P: 0.001 to 0.025% S: 0.001 to 0.025% Sol Al: 0.0. 020 to 0.100% N: ≤ 0.0070% TO: ≤ 0.0070% A steel slab composed of the balance unavoidable impurities and iron is heated and hot-rolled in the range of 660 ° C to 750 ° C. It is made into a hot rolled steel strip at a coiling temperature of 85%, cold rolled at 85% or more, and then heated at a temperature range of at least 500 ° C to 650 to 850 ° C at 300 to 2000 ° C / s by continuous annealing. Hold for 3 seconds or less, cool to 550 ° C or less at a cooling rate of 40 to 500 ° C / s, let it stay between 550 to 400 ° C for 2 to 15 seconds, and cool to room temperature. Method for manufacturing surface-treated original plate by annealing