JPH0598354A - Production of hot-dip galvanized steel sheet for deep drawing - Google Patents

Abstract

PURPOSE:To produce a hot-dip galvanized steel sheet for deep drawing reduced in manufacturing costs by reducing the number of stages. CONSTITUTION:A steel having a composition containing <=0.01% C, <=0.5% Si, <=2.0% Mn, 0.01-0.15% Al, <=0.15% P, h0.05% S, <=0.01% N, and 0.01-0.2% Ti and/or 0.001-0.2% Nb is hot-worked. At this time, rolling is done under the conditions of 60-98% total draft in the range between the Ar3 transformation point and 500 deg.C and <=7500 finishing temp., an, within 5sec after the completion of the above rolling, the steel is cooled down to <=550 deg.C, coiled at <=550 deg.C, pickled, and then subjected to annealing at 700-950 deg.C for 1sec-10min and to hot-dip galvanizing treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a method for producing a hot-dip galvanized steel sheet for deep drawing which can be advantageously applied to steel sheets for automobiles. In recent years, in thin steel sheets used for automobile steel sheets and the like, various surface-treated steel sheets are often used for the purpose of improving corrosion resistance, and the demand thereof is increasing. Among these surface-treated steel sheets, the hot-dip galvanized steel sheet is advantageously used as one of the excellent surface-treated steel sheets in view of its manufacturing cost, especially surface treatment cost and characteristics.

By the way, as the properties required for a hot-dip galvanized steel sheet, not only excellent corrosion resistance but also excellent deep drawability is important. That is, since the outer plates and inner plates of automobiles are subjected to a high degree of press forming, a hot dip galvanized steel sheet having a high Rankford value (r value) and a large elongation is required. On the other hand, it is always desired to reduce the manufacturing cost from the viewpoint of economy.

[0003]

2. Description of the Related Art As a method of producing such a hot-dip galvanized steel sheet having excellent deep drawability, for example, JP-A-57-29555 is known.
Japanese Unexamined Patent Publication (Kokai) discloses a non-aging hot-dip galvanized steel sheet having excellent formability and a method for producing the same.
Si: 0.009 wt%, Nb: 0.043 wt%, N: 0.0045 wt
% Hot rolled steel, then pickled and cold rolled, and then subjected to recrystallization annealing and plating in a continuous hot-dip galvanizing line to obtain characteristic values of r = 2.0 and El = 49%. The means for obtaining the above is also disclosed in JP-A-59-74231.
As a method for producing a super deep-drawing hot-dip galvanized steel sheet, C:
0.003 wt%, Ti: 0.012 wt%, Nb: 0.007 wt%,
Steel containing S: 0.010 wt% and N: 0.005 wt% is hot-rolled, then pickled, cold-rolled, and then subjected to recrystallization annealing and plating in a continuous hot-dip galvanizing line.
Means for obtaining characteristic values of r = 2.1 and El = 51% are disclosed.

All of these are excellent as hot-dip galvanized steel sheets having excellent deep drawability and a method for producing the same, but since the steps leading to the final product are long, as a result, a product is obtained. There is a problem that the required energy, personnel and time are large and the economy is poor.

[0005]

SUMMARY OF THE INVENTION The present invention eliminates the conventional cold rolling step or pickling-cold rolling step by optimizing the steel composition and manufacturing conditions, and has a deep drawability comparable to that of the conventional method. An object of the present invention is to propose a method for producing a novel hot-dip galvanized steel sheet for deep drawing, which is excellent in economic efficiency and is capable of obtaining a hot-dip galvanized steel sheet that does not have a steel sheet. Another object of the present invention is to propose a method for manufacturing a hot-dip galvanized steel sheet for deep drawing, which is excellent in secondary processing brittleness resistance, which is a problem in secondary processing after deep drawing.

[0006]

Means for Solving the Problems As a result of intensive studies conducted by the inventors, the hot-dip galvanized steel sheet for deep drawing omits the cold rolling step by limiting the steel composition and manufacturing conditions as follows. This is due to the fact that it can be manufactured.

That is, the gist of the present invention is that C: 0.01 wt% or less, Si: 0.5 wt% or less, Mn: 2.0 wt% or less, Al: 0.01 wt% or more, 0.15 wt% or less, P: 0.15 wt% or less. , S: 0.05 wt% or less, N: 0.01 wt% or less, and Ti: 0.01 wt% or more, 0.2 wt% or less and Nb: 0.001 wt% or more, 0.2 wt% or less 1
Containing species or two, with the balance of the steel to become composition of iron and unavoidable impurities hot working, this time, A _r3 transformation below, 50
Roll at a total rolling reduction of 60% or more and 98% or less in the temperature range of 0 ℃ or more, and a finishing temperature of 750 ℃ or less, and cool it to a temperature of 550 ℃ or less within 5 seconds after the completion of rolling. And then coil it up at a temperature below 550 ° C,
After the subsequent pickling treatment, annealing treatment in the temperature range of 700 ° C or higher and 950 ° C or lower for 1 second or more and 10 minutes or less,
And a hot dip galvanizing treatment, which is a method for producing a hot-dip galvanized steel sheet for deep drawing (first invention),

[0008] B: 0.0001 wt% or more and 0.0030 wt% or less are contained by substituting a part of iron of the balance component of the first invention (second invention),

[0009] The rolling in the first invention or the 2 A _r3 transformation point to 500 ° C. in the invention, be a method for manufacturing a deep drawing for galvanized steel sheet which is characterized in that while performing lubrication (third invention) ,

A method for producing a hot-dip galvanized steel sheet for deep drawing, characterized in that the pickling, annealing and hot dip galvanizing treatments in the first, second or third invention are carried out continuously. Invention).

Here, in the hot working, the above-mentioned limitation is indispensable for the working process after the finish rolling, but the hot rolling and the processes related thereto prior to this are conventionally known. Needless to say, the starting material may be, for example, a rough rolled material of a continuous casting slab, or a continuous casting strip with a sheet caster. Further, when pickling, annealing and hot dip galvanizing are continuously performed, a continuous hot dip galvanizing line may be used.

[0012]

First, the results of a study on the influence of the temperature transition of the finish rolled steel strip, which is the basis of the present invention, especially on the relation between the residence time in the temperature range of 750 to 550 ° C and the scale thickness will be described.

C: 0.002 wt%, Si: 0.02 wt%, Mn
: 0.13 wt%, Al: 0.045 wt%, P: 0.012 wt%,
S: 0.008wt%, N: 0.002wt%, Ti: 0.038wt%
And Nb: 0.014 wt% hot-rolled steel strip is heated to 750 ℃ and soaked, then rolled at a rolling reduction of 65% in one pass. After this rolling, the cooling rate is changed to 750 to 550 ℃. The residence time in the temperature range was changed in the range of 1 to 20 seconds, and the scale thickness of the obtained steel sheet was measured. These results are summarized in FIG.

FIG. 1 shows the scale thickness of the steel sheet 750.
It shows the effect of residence time in the temperature range of ~ 550 ℃,
As can be seen from this figure, the scale thickness is 750 to 550 ° C.
It is shown that depending on the residence time in the temperature range, the scale thickness becomes thin as 3 μm or less when the residence time is within 5 seconds. If the scale thickness is 3 μm or less, it is possible to remove the scale by pickling for a short time.
Further, since the surface properties of the steel sheet are less deteriorated by pickling, the plating adhesion is improved. Further, it was confirmed that the same scale formation behavior as the above research results is exhibited within the component composition range of the present invention.

Next, the reasons for limiting the component composition and manufacturing conditions of the present invention will be described.

Component Composition of Steel In the present invention, the component composition of steel is important for improving deep drawability, and C: 0.01 wt% or less, Si: 0.5
wt% or less, Mn: 2.0 wt% or less, Al: 0.01 to 0.15 wt
%, P: 0.15 wt% or less, S: 0.05 wt% or less, and N: 0.
01 wt% or less and Ti: 0.01 to 0.2 wt% and Nb:
One or two of 0.001 to 0.2 wt% must be contained. Furthermore, in order to improve the secondary processing brittleness resistance,
B: It is necessary to contain 0.0001 to 0.0030 wt%. The reasons for limiting each component composition will be described below.

C: 0.01 wt% or less It is preferable that the C content be as small as possible because the smaller the content, the better the deep drawability. Therefore, its content is 0.0
1 wt% or less.

Si: 0.5 wt% or less Si has the effect of strengthening steel, and is contained in a required amount according to the desired strength, but if it is contained in excess of 0.5 wt%, deep drawability and surface properties are adversely affected. Affect. Therefore,
Its content shall be 0.5 wt% or less.

Mn: 2.0 wt% or less Mn has an action of strengthening steel, and is contained in a required amount according to desired strength, but if it exceeds 2.0 wt%, deep drawability is adversely affected. Therefore, its content is
2.0 wt% or less.

Al: 0.01 to 0.15 wt% Al is contained in a necessary amount in order to improve the yield of carbonitride forming components by deoxidizing, but if the content is less than 0.01 wt%, it is not effective and 0.15 wt% If it is contained in excess of%, further deoxidizing effect cannot be obtained. Therefore, its content should be 0.01 wt% or more and 0.15 wt% or less.

P: 0.15 wt% or less P has an action of strengthening steel and is contained in a necessary amount according to the desired strength, but if it is contained in excess of 0.15 wt%, deep drawability is adversely affected. Therefore, its content is
0.15 wt% or less.

S: 0.05 wt% or less S is preferably small because the smaller the content, the better the deep drawability. However, up to a content of 0.05 wt%, it does not have a bad influence. Therefore, its content is 0.0
5 wt% or less.

N: 0.01 wt% or less N is as small as S, because the deeper drawability is improved as it is smaller, but it is preferable that N is small, but up to 0.01 wt% N is not badly affected. Therefore, its content should be 0.01 wt% or less.

Ti: 0.01 to 0.2 wt% Ti is a carbonitride forming component and is a solid solution C and N in steel.
Is effectively reduced, and the deep drawability is improved. If the content is less than 0.01 wt%, there is no effect, and if the content exceeds 0.2 wt%, no further effect is obtained, and the steel sheet surface properties deteriorate. Therefore, its content is 0.01
It should be more than wt% and less than 0.2 wt%.

Nb: 0.001 to 0.2 wt% Nb is a carbide-forming component and has the effect of reducing the solid solution C in the steel and improving the deep drawability. Content 0.001
If it is less than wt%, its effect is not obtained, and if it exceeds 0.2 wt%, no further effect is obtained. Therefore, its content should be 0.001 wt% or more and 0.2 wt% or less. Also Nb
Also has the effect of refining the structure before finish rolling.

B: 0.0001 to 0.0030 wt% B is contained in order to improve the secondary work embrittlement resistance. If the content is less than 0.0001 wt%, there is no effect, and 0.0030 wt%
If the content is exceeded, the deep drawability deteriorates. Therefore, its content should be 0.0001 wt% or more and 0.0030 wt% or less.

Manufacturing Conditions Steel Making As for the steel making method, for example, a converter or the like may be used according to a usual method, and the conditions are not particularly limited.

Rough rolling In rough rolling, for example, after reheating or continuous casting of the continuously cast slab, A _r3
Immediately without lowering the temperature below the transformation point, or after heat-insulating treatment, rough rolling may be performed into a sheet bar, and rough rolling conditions include a rough rolling end temperature for the purpose of refining the structure before finish rolling. The temperature is preferably 950 ° C or lower.

Finish rolling The finish rolling process is the most important in this invention,
After rough rolling, a total rolling reduction 60 to 98% in the temperature range A _r3 transformation point to 500 ° C., and subjected to a rolling finish temperature is 750 ° C. or less, 550 ° C. within 5 seconds after the completion of rolling It is necessary to cool to the following temperature, to make the residence time in the temperature range of 750 to 550 ° C be 5 seconds or less, and to wind the coil at a temperature of 550 ° C or less.

Further, in order to further improve the deep drawability, it is important to carry out rolling within a temperature range not higher than the _{Ar 3} transformation point and not lower than 500 ° C. while lubricating. The reason for limiting the above is described below.

Rolling temperature: A _r3 transformation point to 500 ° C. The rolling temperature is a low average r in the temperature range above the _{Ar 3} transformation point because the texture is randomized by the γ → α transformation no matter how much rolling is performed. I can only get the value. On the other hand, even if the rolling temperature is lowered to a temperature lower than 500 ° C., further improvement of the average r value cannot be expected, and only the rolling load increases. Therefore, the rolling temperature is set to the _{Ar 3} transformation point or lower and 500 ° C. or higher.

Finishing temperature: 750 ° C or less When the finishing temperature exceeds 750 ° C, the amount of processing strain introduced during rolling is small, so that the {111} orientation advantageous for deep drawability is not preferentially formed, and the average No improvement in r-value can be expected.
Therefore, the finishing temperature should be 750 ℃ or less.

[0033] · A _r3 total reduction ratio in the temperature range of the transformation point to 500 ° C.: it is less than 60 to 98% A _r3 the total reduction ratio in the temperature range of the transformation point ~500 ℃ 60% {111} orientation is preferential Is not formed, and improvement of the average r value cannot be expected. Further, if it exceeds 98%, an unfavorable texture is formed for the r value. Therefore, A _r3 transformation point ~ 50
The total rolling reduction in the temperature range of 0 ° C shall be 60% or more and 98% or less.

[0034] · A _r3 when the rolling lubricating rolling A _r3 temperature range of the transformation point to 500 ° C. in a temperature range of the transformation point to 500 ° C. to unlubricated rolling, due to the frictional force between the roll and the steel sheet Due to the shear deformation, {110} orientation, which is unfavorable for deep drawability, is preferentially formed in the surface layer of the steel sheet, which hinders the improvement of the average r value. Therefore, in order to ensure better deep drawability is important that the lubricating rolling rolling in the temperature range of A _r3 transformation point to 500 ° C..

Cooling after rolling: 550 ° C. or less within 5 seconds Regarding cooling after rolling, as is apparent from the above-mentioned research results, the residence time in the temperature range of 750 to 550 ° C. after rolling is 5 seconds. When it exceeds the limit, the scale thickness increases rapidly and exceeds 3 μm. If the scale thickness becomes thick, not only the pickling time for removing the scale increases but also the surface property of the steel sheet deteriorates due to the pickling. Therefore, the residence time in the temperature range of 750 to 550 ° C. is within 5 seconds, that is, cooling after rolling is performed within 5 seconds after rolling to a temperature of 550 ° C. or less. Here, in order to perform the above cooling, rapid cooling after finish rolling is effective, and for that purpose, a cooling device may be installed on the exit side of the finish rolling mill.

The roll diameter, roll structure, lubricant type, rolling mill structure, etc. are not particularly limited and may be arbitrary.

Pickling / annealing: 700 to 950 ° C./hot dip galvanizing In the present invention, since the scale thickness of the steel sheet is as thin as 3 μm or less, in addition to the usual pickling line, a pretreatment process for a continuous hot dip galvanizing line. The acid treatment may be performed only in the pickling tank installed as.

If the annealing temperature is less than 700 ° C., a high average r value cannot be obtained, while if it exceeds 950 ° C., the texture becomes random due to α → γ transformation, resulting in material deterioration. Therefore, the annealing temperature should be 700 ° C or higher and 950 ° C or lower.

The hot dip galvanizing may be carried out according to a conventional method, and it can be advantageously applied to both conventionally known alloyed plating and non-alloyed plating.

In this invention, since pickling-annealing-hot dip galvanizing can be continuously performed by a continuous hot dip galvanizing line, the surface of the steel sheet before plating is in an activated state,
Therefore, there is an advantage that the plating adhesion is good. That is, the hot-rolled sheet that has undergone the usual process is pickled, and then left for several hours, and then the plating adhesion is excellent as compared with the case where hot-dip galvanizing is performed.

Temper rolling The hot-dip galvanized steel sheet produced according to the present invention can be temper-rolled at a rolling reduction of 5% or less.

[0042]

EXAMPLE A steel slab having the composition of components shown in Table 1 which was melted in a converter was heated to 1050 ° C.-soaked and rough-rolled, and a steel plate having a thickness of 1.0 mm was produced under the finish-rolling conditions shown in Table 2. The scale thickness was measured.

[0043]

[Table 1]

[0044]

[Table 2]

Of the above steel plates, the samples with sample numbers 11, 17, 18 and 19 had a large scale thickness, so after being subjected to a pickling treatment through a normal pickling process, 48 hours later, the other samples were continuously processed as they were. Through a hot dip galvanizing line, light pickling in the above line pretreatment process, temperature: 850
C., time: 40 seconds annealing, hot dip galvanizing (including alloying) treatment.

The pickling in the normal pickling step has a concentration of 15
% Hcl, bath temperature: 70 ° C., pickling time: 60 seconds. In addition, the concentration of light pickling in the continuous hot dip galvanizing line is 10%.
Hcl, bath temperature: 70 ° C, pickling time: 10 seconds. Furthermore, hot-dip galvanizing is performed with a bath temperature of 475 ° C, an infiltration plate temperature of 475 ° C,
The alloying temperature was 460 ° C. and the basis weight was 40 g / m ² . About hot-dip galvanized steel sheet thus obtained El
The average r value, secondary processing brittleness resistance, plating adhesion, etc. were investigated. The results of these investigations are summarized in Table 2 above.

Here, El was measured using a JIS No. 5 tensile test piece, and the average r value was 3 after applying a 15% prestrain.
Measured by the point method, the average value in the L direction (rolling direction), the D direction (45 ° direction to the rolling direction) and the C direction (90 ° direction to the rolling direction) is the average r value = (r _L + 2r _D + r _C ) / 4. In addition, the secondary processing brittleness is the limit drawing ratio.
The cylindrical sample processed in 3.8 was cooled to -50 ° C and then subjected to a crushing test to evaluate whether brittle cracks had occurred.For plating adhesion, a sample was peeled off by attaching an adhesive tape to the sample and a peeling test was conducted. The evaluation was based on the presence or absence of plating delamination.

As can be seen from Table 2, the conforming example of the present invention omits the cold rolling process, but El is 47
%, The average r value is 1.7 or more, which is a good value, and the samples containing B (sample symbols 3, 6 to 10, 12, 15 and 16) are excellent in secondary work embrittlement resistance and further have acid resistance. Despite the omission of the washing step, the plating adhesion is also good.

A comparative example (sample code
As for the plating adhesion of Nos. 11, 17 to 19), since the steel sheet was pickled for a long time and left in the atmosphere for a long time after the pickling, the surface properties of the steel sheet deteriorated and the plating adhesion was poor.

[0050]

According to the present invention, by deepening the deep drawing without optimizing the conventional cooling step or pickling-cold rolling step by optimizing the manufacturing conditions mainly including the composition of steel and rolling conditions. It is possible to manufacture a hot-dip galvanized steel sheet for deep drawing that has sufficient deep drawability as a steel sheet for use and is also excellent in secondary work brittleness resistance, and the manufacturing cost can be reduced by omitting steps. Therefore, the present invention can be advantageously applied as a method of manufacturing a hot-dip galvanized steel sheet for deep drawing which is excellent in economic efficiency.

[Brief description of drawings]

[Fig. 1] Effect on scale thickness of rolled steel plate 750-55
It is a graph which shows the influence of the residence time in the temperature range of 0 degreeC.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Sakata 1 Kawasaki-cho, Chiba-shi, Chiba Inside Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. Research headquarters

Claims (4)

[Claims] 1. C: 0.01 wt% or less, Si: 0.5 wt% or less, Mn: 2.0 wt% or less, Al: 0.01 wt% or more, 0.15 wt% or less, P: 0.15 wt% or less, S: 0.05 wt% The following and N include 0.01 wt% or less, and Ti: 0.01 wt% or more and 0.2 wt% or less and Nb: 0.001 wt% or more and 0.2 wt% or less 1
Steel containing two or more species, the balance of which is iron and inevitable impurities, is hot worked, with a total reduction of 60% or more in the temperature range of _Ar3 transformation or less and 500 ° C or more, 98% or less, and finishing temperature is 750 ℃
Apply the following rolling process, cool to a temperature below 550 ° C within 5 seconds after the end of rolling,
Then, coil it at a temperature of 550 ° C or lower, and then perform pickling treatment, then anneal treatment for 1 second or more and 10 minutes or less in the temperature range of 700 ° C or more and 950 ° C or less,
And a hot dip galvanizing treatment, the method for producing a hot-dip galvanized steel sheet for deep drawing. 2. C: 0.01 wt% or less, Si: 0.5 wt% or less, Mn: 2.0 wt% or less, B: 0.0001 wt% or more, 0.0030 wt% or less, Al: 0.01 wt% or more, 0.15 wt% or less, P: 0.15 wt% or less, S: 0.05 wt% or less and N: 0.01 wt% or less, and Ti: 0.01 wt% or more, 0.2 wt% or less and Nb: 0.001 wt% or more, 0.2 wt% or less 1 selected from
Containing species or two, with the balance of the steel to become composition of iron and unavoidable impurities hot working, this time, A _r3 transformation below, 50
Roll at a rolling reduction of 60% or more and 98% or less and a finishing temperature of 750 ° C or less in the temperature range of 0 ° C or more, and cool it to a temperature of 550 ° C or less within 5 seconds after the completion of rolling. Then, wind it around a coil at a temperature of 550 ° C or lower, and then subject it to pickling, then 700 ° C or higher and 950 ° C or higher.
A method for producing a hot-dip galvanized steel sheet for deep drawing, which comprises performing an annealing treatment for 1 second or more and 10 minutes or less in the following temperature range and a hot dip galvanizing treatment. 3. A method for producing a hot-dip galvanized steel sheet for deep drawing, which comprises rolling in a temperature range not higher than the _{Ar 3} transformation point and not lower than 500 ° C. in accordance with claim 1 or 2 with lubrication. .. 4. A method for producing a hot-dip galvanized steel sheet for deep drawing, which comprises successively performing the treatments of pickling, annealing and hot dip galvanizing according to claim 1, claim 2 or claim 3.