JP3875792B2 - Manufacturing method of cold-rolled steel sheet for deep drawing with excellent material uniformity - Google Patents

Description

【００３５】
【表２】

【００３６】
【表３】

【００３７】
【表４】

【００３８】
【発明の効果】
本発明の製造方法を用いれば、材質均一性に優れ、かつ、高ｒ値を有する冷延鋼板を、新たに潤滑装置を設置することなく、有利に得ることができる。
【図面の簡単な説明】
【図１】鋼板の材質均一性、および、ｒ値に及ぼす潤滑剤中の油量、および、潤滑剤の液温の影響を示すグラフである。
【図２】鋼板の材質均一性、および、ｒ値に及ぼす潤滑剤中の油量、および、潤滑剤の噴射圧力の影響を示すグラフである。
【図３】鋼板の材質均一性、および、ｒ値に及ぼす潤滑剤の液温、および、潤滑剤の噴射圧力の影響を示すグラフである。
【図４】潤滑剤の供給装置と圧延装置を示す模式図である。
【符号の説明】
１ 圧延ロール
２ 被圧延材
３ 噴射ノズル
４ 流量計
５ 定量ポンプ
６ オリフィス
７ 潤滑油タンク
８ キャリア水タンク[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a cold-rolled steel sheet for deep drawing having excellent material uniformity, which can be particularly useful in the field of manufacturing industrial products such as electric products and automobiles.
[0002]
[Prior art]
Deep drawn steel sheets are widely used in industrial products such as electrical products and automobiles. It is known that steel plates used in such applications are required to have a high Rankford value (average r value, hereinafter simply referred to as “r value”). A steel sheet having a high r value is generally produced by a method in which a steel slab is heated, rolled in a temperature range equal to or higher than the Ar ₃ transformation point, and further subjected to cold rolling and recrystallization annealing.
[0003]
However, in recent years, in order to obtain a steel sheet having a higher r value, hot rolling is performed while lubrication is performed in a temperature range below the Ar ₃ transformation point, and the obtained steel sheet is further cold-rolled and annealed. Manufacturing methods have been proposed.
[0004]
For example, in Japanese Patent Application Laid-Open No. 61-119621, steel having a predetermined chemical component is lubricated so that the friction coefficient is 0.2 or less in a temperature range of 550 ° C. or more and Ar ₃ transformation point or less. However, a method of obtaining a cold-rolled steel sheet having excellent deep drawability by rolling at a total rolling reduction of 50% or more, winding in a temperature range of 400 ° C. or higher, and further pickling, cold-rolling, and annealing is disclosed. Has been. Japanese Patent Application Laid-Open No. 8-92656 discloses a hot finish with a total rolling reduction of 50 to 95% while lubricating a steel having a predetermined chemical component in a temperature range of Ar ₃ transformation point to 500 ° C. After performing rolling and then performing hot rolling sheet recrystallization treatment, cold rolling with a rolling reduction of 50 to 90% is performed, and then cold drawing sheet recrystallization annealing is performed at 700 to 950 ° C. A method of obtaining a cold-rolled steel sheet that is superior to the above has been proposed.
[0005]
[Problems to be solved by the invention]
However, the prior art described above does not describe any lubrication method which is the most important technical element. That is, Japanese Patent Laid-Open No. 61-119621 simply describes that hot rolling is performed while lubrication is performed so that the friction coefficient is 0.2 or less, which is indispensable for actual steel sheet production. No specific lubrication method is shown. Japanese Patent Laid-Open No. 8-92656 discloses an example in which a friction coefficient is set to 0.15 using a mineral oil-based lubricating oil. No mention is made.
[0006]
On the other hand, in the field of manufacturing industrial products such as automobiles, advanced integrated molding techniques such as tailored blanks are beginning to be adopted mainly for the purpose of reducing the number of parts and simplifying the manufacturing process. Steel sheets in such applications are required to have not only high r values but also higher material (strength and ductility) uniformity. This is because the non-uniformity affects the product shape after molding, which in turn reduces the yield of the material.
[0007]
In general, when hot rolling is performed while lubrication is performed, the difficulty in controlling the sheet passing increases, so that the unevenness of the plate thickness increases. And when the steel plate obtained in this way is cold-rolled, it results in a steel plate with poor material uniformity, and there is a concern that it affects the product shape after deep drawing. Therefore, although lubrication rolling must be performed so as not to impair the uniformity of the thickness at the hot-rolled sheet stage, no example has been found in which a manufacturing method has been studied from such a viewpoint.
[0008]
Therefore, the present invention has a higher r value than a cold-rolled steel sheet obtained by a conventional manufacturing method, and at the same time, the uniformity of the material that can withstand use in advanced integrated forming techniques such as tailored blanks. It aims at providing the manufacturing method of the cold-rolled steel plate provided.
[0009]
[Means for Solving the Problems]
The present invention has been made to achieve the above object, and is expressed in mass%.
C: 0.01% or less, Si: 2.0% or less,
Mn: 3.0% or less, P: 0.2% or less,
S: 0.05% or less, Al: 0.005% or more, 0.1% or less,
N: 0.01% or less, and
Ti: 0.001% or more, 0.2% or less, and
When hot rolling a steel slab comprising Nb: 0.001% or more and 0.2% or less, the balance being Fe and inevitable impurities, at least one pass of finish rolling, the lubricating oil viscosity 40 ° C. has a viscosity of less than 450 mm ² / s, the temperature of its 30 ° C. or more, and adjusted to below 80 ° C., in a water-injection system, the injection pressure of its 0.05MPa or more, 2 was adjusted to less than .0MPa, by adjusting the amount of oil in it to the 0.2~10ml / ^{m 2,} while subjected to lubrication supplied to the roll, rolled in a temperature range of Ar less than ₃ transformation point, and the Performed so that the total rolling ratio of the rolling under the temperature range and the lubrication condition is 50% or more, then recrystallized in the winding process or annealing process, pickled in a conventional manner, and then rolled. Cold pressure with a rate of 50-95% Was carried out, further characterized by applying recrystallization annealing at a temperature range of six hundred fifty to nine hundred and twenty ° C., it is an gist a method for manufacturing a cold-rolled steel sheet for deep drawing having excellent material homogeneity.
In addition to the above chemical components, 0.0001% or more and 0.005% or less of B is added for the purpose of improving secondary work brittleness, and 0.01% or more and 1.5% or less of Cu is further added. The manufacturing method of the steel plate contained as needed for the purpose of increasing the strength and the manufacturing method in which the recrystallization annealing after the cold rolling is performed in the hot dip galvanizing step are also summarized.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
According to the investigation by the present inventors, a general hot rolling mill is often equipped with a water injection type lubricant supply device. In the present invention, the lubricating medium to be used is a liquid and the supply thereof is the water injection method. The manufacturing method proposed in the present invention can be executed without using any special equipment modification. This is because.
[0011]
Further, desirable chemical components of the steel sheet, hot rolling conditions, lubricant conditions, cold rolling conditions, and the like were limited based on the following experimental results. Among the experiments, the hot rolling was performed using a lubricant supply device and a rolling device schematically shown in FIG. In the figure, 1 is a rolling roll, 2 is a material to be rolled, 3 is an injection nozzle, 4 is a flow meter, 5 is a metering pump, 6 is an orifice, 7 is a lubricating oil tank, and 8 is a carrier water tank.
[0012]
Prior to this experiment, the viscosity of the lubricating oil was first examined. The temperature of the lubricating oil and carrier water was set to 40 ° C., and an experiment was conducted to examine the stability of the concentration by continuously injecting the lubricant onto the roll using lubricating oil having various viscosities. 10 times every 5 minutes after the start of the injection of lubricant, 100 ml each was collected in the immediate vicinity of the nozzle, and the concentration was analyzed. In all 10 times, if the fluctuation range was less than 5 / 100th of the set concentration, it was stable as a pass Sex was evaluated. As a result, if the lubricating oil had a viscosity of less than 450 mm ² / s, the concentration stability was acceptable regardless of the type of lubricating oil. The reason why the viscosity of the lubricating oil used in the present invention is less than 450 mm ² / s is that the lubricating rolling can be stably performed as described above. In addition, the value of the viscosity was set to a value of 40 ° C., which is generally used for expressing the viscosity of fats and oils.
[0013]
Next, C: 0.0025%, Si: 0.01%, Mn: 0.10%, P: 0.012%, S: 0.0095%, Al: 0.035%, N: 0.0017 % And Ti: 0.062% of the balance, and the balance consisting of Fe and inevitable impurities is rolled after heating at 750 ° C., followed by recrystallization at 750 ° C. for 3 hours. The experiment was conducted. The rolling was scheduled to roll 60% in one pass, and the lubrication conditions were changed by changing the oil concentration, total supply amount, temperature, and injection pressure in the lubricant to be injected. Thereafter, further cold rolling at a rolling rate of 75%, recrystallization annealing at 800 ° C. for 60 seconds, and the strength, ductility, and r value of the obtained steel sheet were investigated. In the survey, 10 points were obtained at a rate of 1 point for every 45000 mm ^{2 of} steel plates (survey parameter n = 10). For the strength and ductility, the difference between the maximum and minimum values, ΔTS and ΔEl, is obtained, and if the values obtained by dividing each by the average value are both less than 0.075, the material uniformity is “good”, at least one Was 0.075 or more, it was determined to be “bad”.
[0014]
The results are shown in FIGS. From these figures, the amount of oil supplied per unit area of the material to be rolled is 0.2 ml / m ² or more and 10 ml / m ² or less, the liquid temperature of the lubricant is 30 ° C. or more and less than 80 ° C., and the injection pressure is When the pressure is 0.05 MPa or more and less than 2.0 MPa, it became clear that a steel sheet having a good material uniformity and a high r value can be obtained. However, the average value of 10 points was adopted as the r value.
[0015]
Based on these experimental results, further studies were conducted to limit the present invention.
First, the chemical composition of the steel sheet will be described.
C is an element closely related to the deep drawability, and if it exceeds 0.01%, the deep drawability is deteriorated, so the upper limit is made 0.01%.
[0016]
Si, Mn, and P each have an action of increasing the strength of steel, and a necessary amount may be added depending on the strength of the steel to be manufactured. Si> 2.0%, Mn> Deep drawability deteriorates when 3.0% and P> 0.2%, so upper limit is limited to Si: 2.0% or less, Mn: 3.0% or less, P: 0.2% or less did. The smaller the S, the better the deep drawability, but if it is 0.05% or less, there is no particular problem, so 0.05% is made the upper limit.
[0017]
Al is added for the purpose of deoxidation and denitrification of steel. However, if the content is less than 0.005%, the effect cannot be obtained. Since deterioration is brought about, it is made 0.005% or more and 0.1% or less.
N deteriorates the ductility with the formation of nitrides and the increase in the amount of solid solution, so it must be 0.01% or less.
[0018]
Ti has a function of reducing solid solution C and solid solution N, and is an extremely effective element for increasing the r value. However, if it is less than 0.001%, there is no effect. On the other hand, if it exceeds 0.2%, no further effect is obtained and the cost of the steel is increased. Therefore, the content is made 0.001% to 0.2%.
[0019]
Nb works to reduce the solid solution C and to refine the crystal grain size before finish rolling, so it is effective in increasing the r value. However, if Nb is less than 0.001%, there is no effect. Even if the content exceeds 2%, no further effect can be expected, so the content is made 0.001% or more and 0.2% or less.
[0020]
B has an effect of improving secondary work brittleness, and can be added as necessary. However, if it is less than 0.0001%, the effect cannot be obtained. Conversely, if it exceeds 0.005%, the deep drawability is adversely affected, so the content is made 0.0001% or more and 0.005% or less.
[0021]
Since Cu has the effect | action which raises steel strength, it can be added as needed. The effect can be obtained by addition of 0.01% or more, but if it exceeds 1.5%, the deep drawability is deteriorated, so the content is made 0.01% or more and 1.5% or less.
[0022]
Next, rolling conditions and lubricating conditions will be described.
In order to increase the r value of the cold rolled steel sheet, it is effective to increase the r value of the hot rolled steel sheet as a cold rolled material. In order to increase the r value of the hot-rolled steel sheet, it is effective to perform a texture control using rolling and a recrystallization treatment process and accumulate a high {111} plane parallel to the plate surface. For this purpose, it is necessary to perform hot rolling in a temperature range below the Ar ₃ transformation point. This is because the texture formed by rolling in the temperature range above the Ar ₃ transformation point is randomized during the subsequent phase transformation from the γ phase to the α phase, and thus is not effective in forming a desirable texture. Because. This is the reason why the hot rolling temperature range in the present invention is less than the Ar ₃ transformation point. On the other hand, the lower limit of the hot rolling temperature range does not exist for the purpose of obtaining a high r-value steel plate, but the lower the temperature, the deformation resistance of the steel increases and the load on the rolling mill increases, so the lower limit is 500 ° C. Is desirable.
[0023]
Without lubrication during hot rolling, due to shear deformation caused by friction between the rolling roll and the material to be rolled, the surface of the material to be rolled, particularly in the surface layer portion, is not preferable for deep drawability, and is parallel to the plate surface { 110} planes are formed, and lubrication is indispensable. In addition, as shown in the experimental results described above, what kind of lubrication is performed is very important.
[0024]
When supplying lubricant by the water injection method, the concentration of lubricating oil in the lubricant, the amount of lubricant supplied, the temperature of the lubricant, and the injection pressure are the main control indices. As a result, it became clear that the lubrication conditions that affect the r value of the steel sheet are aggregated into three indicators of oil amount, lubricant temperature, and lubricant injection pressure determined by the product of concentration and supply amount. .
[0025]
When the amount of oil per unit area of the material to be rolled is less than 0.2 ml / m ² , or the liquid temperature is less than 30 ° C., or the injection pressure is less than 0.05 MPa, the comb is 2.0 MPa or more Since the effect of suppressing the formation of the {110} plane is not sufficient, a high r-value steel plate cannot be obtained. Therefore, the oil amount was limited to 0.2 ml / m ² or more, the liquid temperature to 30 ° C. or more, and the injection pressure to 0.05 MPa or more and less than 2.0 MPa.
[0026]
On the other hand, if the lubrication effect is too high, there is no problem for the purpose of obtaining a high r-value steel plate, but the control of the plate to be rolled becomes more difficult, and the shape of the steel plate after rolling is adversely affected. To come. Specifically, when the oil amount is supplied exceeding 10 ml / m ² or the liquid temperature is 80 ° C. or higher, the uniformity of the plate thickness becomes poor. Therefore, the oil amount was limited to 10 ml / m ² or less and the liquid temperature was limited to less than 80 ° C.
[0027]
The mechanism by which the liquid temperature and jet pressure of the lubricant affect the r value is not clear, but these factors have a strong influence on the film formation process on the roll surface of the oil contained in the lubricant. It is presumed to be caused by this.
[0028]
The component of the lubricating oil is not particularly limited. The use of a lubricating oil to which various compounds or polymers are added in addition to mineral oil or synthetic ester does not impair the gist of the present invention.
[0029]
The reason why the total rolling ratio of hot rolling in the temperature range below the Ar ₃ transformation point is set to 50% or more is that if it is less than this, a {111} plane parallel to the plate surface is formed after cold rolling and annealing. This is because such a texture does not accumulate enough to obtain a high r value.
[0030]
The steel sheet immediately after hot rolling exhibits a processed structure, and is not preferable for subsequent cold rolling as it is, and is also recrystallized to form a recrystallized texture for obtaining a cold rolled material having a high r value. It is necessary to perform processing. The recrystallization treatment may be performed by a self-annealing method by winding a steel sheet around a coil, or may be performed using a box-type annealing furnace or a continuous annealing furnace.
[0031]
Cold rolling is an essential process for obtaining a high r value. If the rolling rate is less than 50%, a high r value cannot be obtained. If it exceeds 95%, not only the effect of obtaining a high r value is saturated, but also the cold rolling load increases. Therefore, the rolling rate of cold rolling is limited to 50% or more and 95% or less.
[0032]
The steel sheet that has undergone the cold rolling process needs recrystallization annealing in order to impart the ductility of the steel sheet and, further, to form a recrystallized texture and impart deep drawability. This annealing may be performed in either a box-type annealing furnace or a continuous annealing furnace, or may be performed in a hot dip galvanizing process. In order to form an appropriate recrystallization texture, it must be performed in a temperature range of 650 ° C. or more and 920 ° C. or less.
[0033]
【Example】
Steel slabs having chemical components shown in Table 1 were heated and roughly rolled, and then hot finish rolling was performed while supplying a lubricant to the roll by a water injection method. Furthermore, after the recrystallization treatment, pickling, cold rolling, and recrystallization annealing were performed, and the strength, ductility, and r value of the obtained steel sheet were investigated. Based on the method described above, the material uniformity was evaluated from the measurement results of strength and ductility. Tables 2 to 4 show the hot rolling conditions, the lubricating conditions, the cold rolling conditions, the recrystallization annealing conditions, the determination results of the material uniformity of the steel sheet, and the r value. In these tables, comparative examples that are outside the scope of the present invention are also described.
Thus, it can be seen that the cold-rolled steel sheet manufactured within the scope of the present invention has excellent material uniformity and deep drawability.
[0034]
[Table 1]

[0035]
[Table 2]

[0036]
[Table 3]

[0037]
[Table 4]

[0038]
【The invention's effect】
By using the production method of the present invention, a cold-rolled steel sheet having excellent material uniformity and a high r value can be advantageously obtained without newly installing a lubricating device.
[Brief description of the drawings]
FIG. 1 is a graph showing the effects of the material uniformity of a steel sheet, the amount of oil in the lubricant, and the liquid temperature of the lubricant on the r value.
FIG. 2 is a graph showing the effects of material uniformity of a steel sheet, the amount of oil in the lubricant and the injection pressure of the lubricant on the r value.
FIG. 3 is a graph showing the influence of the liquid temperature of the lubricant and the injection pressure of the lubricant on the material uniformity of the steel sheet and the r value.
FIG. 4 is a schematic view showing a lubricant supply device and a rolling device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Roll 2 Roll material 3 Injection nozzle 4 Flowmeter 5 Metering pump 6 Orifice 7 Lubricating oil tank 8 Carrier water tank

Claims (4)

% By mass
C: 0.01% or less,
Si: 2.0% or less,
Mn: 3.0% or less,
P: 0.2% or less,
S: 0.05% or less,
Al: 0.005% or more, 0.1% or less,
N: 0.01% or less
Containing, and
Ti: 0.001% or more, 0.2% or less, and
Nb: 0.001% or more, 0.2% or less
When hot-rolling a steel slab comprising one or two of the following, the balance being Fe and inevitable impurities,
At least one pass of finish rolling, viscosity at 40 ° C is 450mm ² A lubricating oil having a viscosity of less than / s and having a temperature adjusted to 30 ° C. or higher and lower than 80 ° C. is obtained by a water injection method with an injection pressure of 0.05 MPa or more and less than 2.0 MPa. 2 to 10 ml / m ² While supplying lubrication to the roll at a ratio of Ar, ₃ Rolling is performed in a temperature range below the transformation point, and the total rolling ratio of rolling under the temperature range and the lubrication condition is 50% or more,
Then, after performing recrystallization treatment in the winding process or annealing process, pickling by a conventional method, performing cold rolling with a rolling rate of 50 to 95%, and further in a temperature range of 650 to 920 ° C A method for producing a cold-drawn steel sheet for deep drawing excellent in material uniformity, characterized by performing recrystallization annealing. The steel is further mass%,
B: It contains 0.0001% or more and 0.005% or less, The manufacturing method of the cold-rolled steel sheet for deep drawing excellent in the material uniformity of Claim 1 characterized by the above-mentioned. The steel is further mass%,
Cu: 0.01% or more and 1.5% or less, The manufacturing method of the cold-rolled steel sheet for deep drawing excellent in the material uniformity of Claim 1 or 2 characterized by the above-mentioned. The cold drawn steel sheet for deep drawing excellent in material uniformity according to any one of claims 1 to 3 , wherein the recrystallization annealing after the cold rolling is performed in a hot dip galvanizing process. Manufacturing method.

Images