JPH08170123A - Production of cold rolled steel sheet excellent in deep drawability and galvanized steel sheet - Google Patents

Abstract

PURPOSE: To control recrystallization texture so as to obtain a cold rolled steel sheet excellent in deep drawability by executing specified hot rolling and continuous annealing to the steel of specified composition consisting of C, Si, Mn, P, S, Al, N, and Fe. CONSTITUTION: A steel, which has a composition consisting of, by weight, 0.001-0.01% C, 0.01-1% Si, 0.05-1.5% Mn, <=0.1% P, <=0.015% S, 0.005-0.1% Al, <=0.005% N, as necessary one or more kinds among Ti, Nb, V, further 0.0005-0.005% B and the balance Fe with inevitable impurity elements, is continuously cast to slab. The slab after reheated or right after casting is completed with finish hot rolling at Ar transformation temp. or higher and then is coiled at 600-800 deg.C. The hot rolled sheet is cold rolled as usual after pickling. Subsequently, the cold rolled sheet for continuus annealing is heated from normal temp. to 400-700 deg.C at <=100 deg.C/sec heating rate, and thereafter successively rapidly heated to 750-910 deg.C at 100-3000 deg.C/sec heating rate, the sheet is cooled to room temp. immediately or after prescribed holding time at the heated temp. and then is subjected to temper rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cold-rolled steel sheet and a hot-dip galvanized steel sheet having an excellent deep drawability, and more specifically, to a rapid and rapid heating process during continuous annealing or recrystallization annealing. The present invention relates to a method for producing a cold-rolled steel sheet and a hot-dip galvanized steel sheet having excellent deep drawability by heat treatment for a short time.

[0002]

2. Description of the Related Art The conventional heating method in continuous annealing or recrystallization annealing is direct heating with a gas burner or radiant heating with a radiant tube. Therefore, it is heated at a constant heating rate of about 10 ° C./s until it enters the soaking zone. Therefore, it was impossible to control the texture by the heat cycle during heating. on the other hand,
A method for applying electric heating to a heating zone or a part of the soaking zone has already been disclosed, for example, Japanese Patent Laid-Open No. 2-1.
There are Japanese Patent No. 66234 and Japanese Patent Publication No. 5-57333. The former is for heating the high temperature region of the heating zone by induction heating, and the latter is for rapidly heating to a temperature higher than the soaking temperature in a part of the soaking section. In particular, the former is not characterized by the material of the obtained steel sheet, and does not actively control the recrystallization texture by the heat cycle which is the object of the present invention. The latter has a different purpose from the present invention because it is partially heated in the soaking zone. In addition, there is no regulation on the heating rate in any of them, and it is considered that the heating rate is lower than the heating rate prescribed in the present invention inferred from the heating method and the examples. Furthermore, all of them are intended for application in normal continuous annealing, and do not disclose application in hot dip galvanizing line.

[0003]

In the conventional heating zone of continuous annealing or recrystallization annealing, the temperature of the plate to be threaded is raised at a constant heating rate, so that the texture is positively controlled in this part. It was impossible. The application of electric heating to the heating zone makes it possible to positively control the texture formation in the temperature rising process, and no commercialized one has been found so far. The present invention controls the recrystallization texture by applying such electric heating to a part of the heating zone of continuous annealing or recrystallization annealing, of the cold-rolled steel sheet and hot dip galvanized steel sheet having excellent deep drawability. The purpose is to provide a manufacturing method.

[0004]

Means for Solving the Problems As a result of intensive studies in view of the above situation, the present inventors unwinded a cold-rolled steel strip and annealed it by continuous annealing, or in a hot dip galvanizing line. It was found that the recrystallization texture can be controlled by controlling the thermal history in the heating zone during plating and increasing the heating rate during heating. As a result, the present invention has been completed by inventing a heat history in a heating zone capable of forming a texture that is advantageous for deep drawability, and its gist is (1) C: 0.001 to 0 0.01 wt% Si: 0.01 to 1 wt% Mn: 0.05 to 1.5 wt% P: 0.1 wt% or less S: 0.015 wt% or less Al: 0.005 to 0.1 wt% N: 0.005 wt % Or less Steel made of balance Fe and unavoidable impurity elements is continuously cast into a slab and then reheated or immediately after casting, Ar ₃
Finish hot rolling at a temperature above the transformation point to 600-80
It is wound in a temperature range of 0 ° C., pickled, cold-rolled by a usual method, and then continuously annealed from room temperature to T ₁ : 400 to 700 ° C.
Until the temperature range 100 ° C. / s were heated by the following heating rate, followed by 100 to 3,000 ° C. / s heating rate T _2:
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises heating to a temperature range of 750 to 910 ° C, immediately or after holding for a predetermined time, cooling to room temperature, and further temper rolling.

(2) In addition to the steel components described in (1), at least one of Ti, Nb, and V is added to 0.005 in total.
0.1 wt% is contained, The manufacturing method of the cold-rolled steel sheet excellent in deep drawability as described in (1). (3) In addition to the steel composition described in (1) or (2), 0.0005 to 0.005 wt% of B is further contained, which is excellent in deep drawability described in (1) or (2). Manufacturing method of cold rolled steel sheet. (4) The method for producing a cold-rolled steel sheet having excellent deep drawability according to any one of (1) to (3), which is characterized by holding at T ₁ temperature for 30 seconds or less.

(5) C: 0.001 to 0.01 wt% Si: 0.01 to 1 wt% Mn: 0.05 to 1.5 wt% P: 0.1 wt% or less S: 0.015 wt% or less Al: 0.005 to 0.1 wt% N: 0.005 wt% or less Steel made of the balance Fe and unavoidable impurity elements is continuously cast into a slab and then reheated or immediately after casting Ar ₃
Finish hot rolling at a temperature above the transformation point to 600-80
After winding in a temperature range of 0 ° C., pickling, cold rolling in a usual method, and then recrystallization annealing from room temperature to T ₁ : 400 to 700.
Heating up to a temperature range of 100 ° C. is performed at a heating rate of 100 ° C./s or less, and then T ₂ :
Immediately or after holding for a predetermined time, hot-dip galvanizing is performed after cooling to a temperature range of 750 to 910 ° C., cooling is performed to room temperature, and then temper rolling is performed, followed by melting with excellent deep drawability. Manufacturing method of galvanized steel sheet.

(6) In addition to the steel components described in (5), at least one of Ti, Nb, and V is added to 0.005 in total.
The method for producing a hot-dip galvanized steel sheet having excellent deep drawability according to (5), characterized in that the content is 0.1 wt% to 0.1 wt%. (7) In addition to the steel components described in (5) or (6), B is further included in an amount of 0.0005 to 0.005 wt%, and the deep drawability described in (5) or (6) is excellent. Manufacturing method of hot-dip galvanized steel sheet. (8) The method for producing a hot-dip galvanized steel sheet having excellent deep drawability according to any one of (5) to (7), which is characterized by holding at T ₁ temperature for 30 seconds or less. (9) A hot-dip galvanized steel sheet having excellent deep drawability according to any one of (5) to (8), which is characterized by further performing alloying treatment and then cooling to room temperature after hot-dip galvanizing. There is a manufacturing method.

[0008]

The present invention will be described in detail below with reference to the drawings. 1 to 4 show experimental results leading to establishment of the present invention. In this experiment, C: 0.0017 wt%, Si: 0.
02 wt%, Mn: 0.1 wt%, P: 0.007 wt
%, S: 0.008 wt%, Al: 0.035 wt%,
N: 0.0015 wt%, the balance Fe and the steel consisting of unavoidable impurity elements were used. This steel was finish hot-rolled at 910 ° C. to obtain a 4 mm hot-rolled sheet, followed by cooling and winding at 700 ° C. After pickling, 80% cold rolling was performed. After that, continuous annealing was simulated on the half of the cold rolled material by a heat cycle as shown in FIG. The thermal history of the remaining cold-rolled material was simulated in the hot dip galvanizing line by a heat cycle as shown in FIG. In both cases, the annealing temperature (T ₂ ) was 850
As the temperature, T ₁ was changed in the range of 300 to 800 ° C.
Until T ₁ is heated at _{10 ℃ / s, T 1 ~T} 2 3
Heated at 00 ° C / s. 2 and 4 show the r-value results after the respective heat treatments. That is, it was found that the r value decreases when the temperature range in which rapid heating is started in continuous annealing or recrystallization annealing exceeds 700 ° C. It is presumed that this is because the grain growth did not proceed in a short time because the driving force for grain growth was small even if the rapid heating was carried out when the recovery and recrystallization proceeded to some extent.

First, the reasons for limiting the chemical components in the present invention will be described. C must be 0.01 wt% or less in order to improve the deep drawability. But,
If it is less than 0.001 wt%, the cost will increase in the steelmaking stage, so this is the lower limit. Si is added in order to increase the strength of steel, but excessive addition not only deteriorates the weldability but also reduces the adhesion of plating, so the upper limit was 1 wt%. On the other hand, 0.01 wt
If it is less than%, the cost will increase significantly, so this is the lower limit. Mn is also effective in increasing the strength of steel, but excessive addition not only lowers the ductility (El) due to the hardening of the steel, but is also concerned about the deterioration of the deep drawability (r value). The upper limit was set to 1.5 wt%. However, if the addition amount is less than 0.05 wt%, hot cracking due to S occurs during hot rolling, so this is the lower limit.

[0010] P is an effective element for increasing the strength of steel without deteriorating the deep drawability. However, if added excessively, it deteriorates the secondary workability,
The upper limit is 0.1 wt%. If S is added in excess, it causes hot cracking, so S is made 0.015 wt% or less. Al
Is required to deoxidize the steel, but 0.005 wt% or more is required. However, excessive addition will increase the cost and leave inclusions in the steel, so the upper limit is made 0.1 wt%. Like C, N is 0.
005 wt% or less.

[0011] Ti, Nb, V and Mo are added as needed, but are added especially for the purpose of fixing C or N. At that time, the total addition amount is 0.005 wt%
If less than, the effect is not exhibited. Also, 0.01 wt
If it is added in excess of%, a large number of carbides or nitrides are formed and the workability is deteriorated. B is also added if necessary, but its purpose is to fix N or to secure the secondary workability. If the added amount is less than 0.0005 wt%, the effect cannot be obtained. However, if over 0.005 wt% is added, the steel is hardened and the workability is deteriorated, so this is made the upper limit. Although not particularly specified in the present invention,
A rare earth element such as Ca, Zr or Ce may be added.

Next, the manufacturing method according to the present invention will be described. The steel having the above-mentioned chemical composition is obtained as a slab by ordinary continuous casting, but it may be produced by a thin slab continuous casting method. Then perform hot rolling without reheating or reheating but, since the Ar ₃ when cast heat finishing at a lower temperature than the transformation point of the hot rolled sheet grain coarse, temperature finishing in hot rolling Ar ₃ It is above the transformation point. After that, it is wound by an ordinary method, but it is necessary to set the temperature to 650 ° C. or higher because it is necessary to sufficiently precipitate the solid solution C as a carbide in the hot rolling plate stage. However, if the temperature exceeds 800 ° C., the pickling property deteriorates, so this is made the upper limit. Here, the cooling rate up to the winding is not particularly specified in the present invention, and the reduction rate in cold rolling is within the range that is usually carried out.

Next, heating conditions in continuous annealing or heating conditions in recrystallization annealing in a hot dip galvanizing line, which are the most important factors in the present invention, will be described.
The heating from room temperature to T ₁ is performed by direct heating with a gas burner or radiant heating with a radiant tube, and heating is performed comparatively gently to promote recovery before recrystallization to some extent. Therefore, the heating rate is limited to 100 ° C./s or less. The lower limit is not particularly limited, but a heating rate of 5 ° C / s or more is inevitably obtained.

The temperature range (T
₁ ) is 400 ° C. or higher and 700 ° C. or lower. If the temperature is less than 400 ° C., the heating range (temperature difference) in the subsequent rapid heating process becomes wide and the input energy becomes large, which is not preferable. On the other hand, if the temperature exceeds 700 ° C., the driving force for grain growth becomes small as described above, so that recrystallization is not completed even when the final annealing temperature is reached. Therefore, this is the upper limit. In addition,
The isothermal holding at T ₁ is carried out if necessary, but in that case, it is 30 seconds or less. If the holding time is made longer than this, the path length increases and the equipment cost rises, which is not preferable.

The purpose of heating after T ₁ is to control the texture obtained after annealing. For that purpose, rapid heating to the final annealing temperature is required from the stage where recovery or recrystallization has progressed to some extent. A heating rate of 100 ° C./s or more is required to control the texture. However, if it exceeds 3000 ° C./s, not only the control becomes difficult, but also the electric power required for heating becomes remarkably large, and further, the path length for carrying out the heating becomes long, resulting in a significant increase in equipment cost. Therefore, it is not preferable.

When the final annealing temperature (T ₂ ) is less than 750 ° C., grain growth is insufficient, so that sufficient ductility cannot be obtained and workability is poor. On the other hand, if the temperature exceeds 910 ° C., annealing occurs in the austenite region, and the texture is randomized so that the r value is lowered and the deep drawability is poor. The isothermal holding condition at T ₂ and the cooling after annealing are not particularly specified,
An ordinary method may be used, but isothermal holding may not be performed in order to make the equipment more compact.

Here, the heating and cooling method is not particularly specified, and is not particularly limited as long as the above specified upper limit is satisfied. For example, as a heating method, it is effective to carry out by electric heating, and as a cooling method in the continuous annealing line of the cold rolled steel sheet, it is carried out by steam cooling,
As a cooling method in the hot dip galvanizing line, cooling with gas such as H ₂ or roll cooling is effective. The hot dip galvanizing and the subsequent alloying treatment may be performed in a usual manner. The alloying treatment subsequent to the hot dip galvanizing is performed as necessary.

[0018]

【Example】

Example 1 C: 0.0015 wt%, Si: 0.01 wt%, M
n: 0.1 wt%, P: 0.005 wt%, S: 0.0
05 wt%, Al: 0.035 wt%, Ti: 0.03
Steel consisting of 8 wt%, N: 0.0015 wt%, the balance Fe and unavoidable impurity elements was tapped from the converter and continuously cast into a slab. After hot rolling at 1100 ° C., finishing temperature was 930 ° C. and plate thickness was 4 mm, and hot rolling was completed.
Winding was carried out at 0 ° C. After pickling, a reduction rate of 80% resulted in 0.
8mm and 10 ℃ / in continuous annealing up to 600 ℃
heating at a heating rate of s, holding at this temperature for 30 seconds or less as required, and then performing final annealing at various heating rates and annealing conditions as shown in Table 1 by electric heating, and further 1% Temper rolling was performed. Subsequent material evaluation J
Processed into No. 5 test piece described in IS Z 2201, JIS
A tensile test was conducted according to the test method described in Z 2241. The results are summarized in the same table. No. according to the scope of the invention. In Nos. 1, 2, 3, 4 and 5, No. 1 performed by thermal history in the conventional continuous annealing process. The r value is higher than that of No. 6. The heating rate from T ₁ and the annealing temperature were outside the range of the present invention. At 7, 8 and 9, the r value is still low.

[0019]

[Table 1]

Example 2 Steels having various compositions shown in Table 2 were taken out from a converter and continuously cast into slabs. After heating these slabs at 1150 ° C,
r ₃ points {= 916-509C (wt%) + 27Si (w
t%)-64 Mn (wt%) (° C)} or higher, the finish hot rolling was finished, and the roll was wound at 670 ° C to obtain a 3 mm hot rolled sheet. After pickling, a cold-rolled sheet of 0.7 mm with a reduction rate of 77% was heated at a heating rate of 10 ° C / s up to 600 ° C in continuous annealing, and subsequently heated at a heating rate of 100 ° C / s by electric heating After heating, final annealing was performed at 850 ° C., and temper rolling was further performed at 1%, and then the material was evaluated by the same method as in Example 1. Table 3 summarizes the results. The A, B, C, D, E, F and G steels according to the method of the present invention show high r values. However, the amount of C is high and H is off
In the steel, the I steel with a high Si content and the J content with a high P content, the r value did not reach the target value in the present invention. On the other hand, K steel suffered from hot cracking because the S content was too high.

[0021]

[Table 2]

[0022]

[Table 3]

Example 3 C: 0.0016 wt%, Si: 0.02 wt%, M
n: 0.1 wt%, P: 0.008 wt%, S: 0.0
05 wt%, Al: 0.040 wt%, Ti: 0.04
Steel consisting of 1 wt%, N: 0.0015 wt%, the balance Fe and unavoidable impurity elements was taken out from the converter and continuously cast into a slab. After hot rolling at 1100 ° C., the finishing temperature was 935 ° C. and the plate thickness was 4 mm, and hot rolling was completed.
Winding was carried out at 0 ° C. After pickling, a reduction rate of 80% resulted in 0.
8 mm, in the heating zone of the hot dip galvanizing line,
Heating up to 600 ° C at a heating rate of 10 ° C / s, holding at this temperature for 30 seconds or less if necessary, and then conducting final heating at various heating rates and annealing conditions as shown in Table 4 by electric heating. Conducted, followed by hot dip galvanizing, and No. In Nos. 12, 14, 16 and 18, alloying treatment was performed and further 1% temper rolling was performed. Then, the material was evaluated in the same manner as in Example 1. The results are summarized in the same table. No. according to the scope of the invention. 11, 12, 13,
In Nos. 14 and 15, No. performed by thermal history in the conventional continuous annealing process. The r value is higher than that of 16. The heating rate from T ₁ and the recrystallization annealing temperature were outside the range of the present invention. At 17, 18, and 19, the r value is still low.

[0024]

[Table 4]

Example 4 Steels having various compositions shown in Table 5 were taken out from a converter and continuously cast into slabs. After heating these slabs at 1160 ° C, A
r ₃ points {= 916-509C (wt%) + 27Si (w
t%)-64 Mn (wt%) (° C)} or higher, the finish hot rolling was finished, and the roll was wound at 660 ° C to obtain a 3 mm hot rolled sheet. After pickling, a cold rolled sheet of 0.7 mm with a reduction rate of 77% was heated at a heating rate of 10 ° C./s up to 600 ° C. in a heating zone of a hot dip galvanizing line, and subsequently 100 ° C. / After heating at a heating rate of s, final annealing at 850 ° C., hot dip galvanizing, alloying except M steel, and 1% temper rolling, and then Example 1 The material was evaluated in the same manner as in. The results are summarized in Table 6. L, M, according to the method of the invention
N, O, P, Q and R steels show high r values. However, the r value does not reach the target value in the present invention in the S steel with a high C content, the T steel with a high Si content, and the U steel with a high P content. On the other hand, V steel caused hot cracking because the S content was too high.

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

INDUSTRIAL APPLICABILITY The present invention controls a heating rate in a heating process in continuous annealing of a cold-rolled steel sheet or in a heating process in recrystallization annealing of a hot-dip galvanizing line to obtain a cold drawn steel having excellent deep drawability. The method for producing a rolled steel sheet and a galvanized steel sheet is clarified. According to the present invention, it is possible to control the texture that affects the deep drawability, which was impossible in the conventional continuous annealing or hot dip galvanizing process, and the cold-rolled steel sheet and hot-dip galvanized steel sheet having excellent deep drawability can be controlled. Can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a heat cycle in an experiment of continuous annealing that has led to the present invention.

FIG. 2 is a diagram showing a range of a temperature range in the present invention at which rapid heating in continuous annealing is started and an r value of a cold rolled steel sheet.

FIG. 3 is a diagram showing a heat cycle in an experiment of hot dip galvanizing according to the present invention.

FIG. 4 is a diagram showing a range of a temperature range in the present invention for starting rapid heating in recrystallization annealing and an r value of a galvannealed steel sheet.

Claims (9)

[Claims] 1. C: 0.001 to 0.01 wt% Si: 0.01 to 1 wt% Mn: 0.05 to 1.5 wt% P: 0.1 wt% or less S: 0.015 wt% or less Al: 0 0.005 to 0.1 wt% N: 0.005 wt% or less Steel made of the balance Fe and unavoidable impurity elements is continuously cast into a slab and then reheated or immediately after casting, Ar ₃
Finish hot rolling at a temperature above the transformation point to 600-80
It is wound in a temperature range of 0 ° C., pickled, cold-rolled by a usual method, and then continuously annealed from room temperature to T ₁ : 400 to 700 ° C.
Until the temperature range 100 ° C. / s were heated by the following heating rate, followed by 100 to 3,000 ° C. / s heating rate T _2:
A method for producing a cold-rolled steel sheet having excellent deep drawability, which comprises heating to a temperature range of 750 to 910 ° C, immediately or after holding for a predetermined time, cooling to room temperature, and further temper rolling. 2. The steel composition according to claim 1, further comprising:
A total of one or more of Ti, Nb, and V is 0.005-
The method for producing a cold-rolled steel sheet having excellent deep drawability according to claim 1, wherein the cold-rolled steel sheet contains 0.1 wt%. 3. Cold rolling with excellent deep drawability according to claim 1 or 2, further comprising 0.0005 to 0.005 wt% of B in addition to the steel components described in claim 1 or 2. Steel plate manufacturing method. 4. The method for producing a cold-rolled steel sheet having excellent deep drawability according to claim 1, wherein the T ₁ temperature is maintained for 30 seconds or less. 5. C: 0.001 to 0.01 wt% Si: 0.01 to 1 wt% Mn: 0.05 to 1.5 wt% P: 0.1 wt% or less S: 0.015 wt% or less Al: 0 0.005 to 0.1 wt% N: 0.005 wt% or less Steel made of the balance Fe and unavoidable impurity elements is continuously cast into a slab and then reheated or immediately after casting, Ar ₃
Finish hot rolling at a temperature above the transformation point to 600-80
After winding in a temperature range of 0 ° C., pickling, cold rolling in a usual method, and then recrystallization annealing from room temperature to T ₁ : 400 to 700.
Heating up to a temperature range of 100 ° C. is performed at a heating rate of 100 ° C./s or less, and then T ₂ :
Immediately or after holding for a predetermined time, hot-dip galvanizing is performed after cooling to a temperature range of 750 to 910 ° C., cooling is performed to room temperature, and then temper rolling is performed, followed by melting with excellent deep drawability. Manufacturing method of galvanized steel sheet. 6. The steel composition according to claim 5, further comprising:
A total of one or more of Ti, Nb, and V is 0.005-
The method for producing a hot-dip galvanized steel sheet having excellent deep drawability according to claim 5, characterized in that 0.1 wt% is contained. 7. A molten zinc having excellent deep drawability according to claim 5 or 6, further containing 0.0005 to 0.005 wt% of B in addition to the steel components according to claim 5 or 6. Manufacturing method of plated steel sheet. 8. The method for producing a hot-dip galvanized steel sheet having excellent deep drawability according to claim 5, wherein the T ₁ temperature is maintained for 30 seconds or less. 9. The hot-dip galvanized product is further alloyed and then cooled to room temperature.
9. A method for producing a hot-dip galvanized steel sheet having excellent deep drawability according to any one of items 1 to 8.