JPH07228921A - Production of starting sheet for surface treated steel sheet, excellent in workability - Google Patents

Abstract

PURPOSE:To obtain a starting sheet for surface treated steel sheet, excellent in workability, with superior productivity by successively subjecting a slab of ultralow carbon steel containing specific amounts of Mn, Nb, Ni, etc., to hot rolling, coiling, cold rolling, annealing, and temper rolling under respectively specified conditions. CONSTITUTION:A steel, having a composition consisting of, by weight, <=0.005% C, <=0.04% Si, >0.5-1.0% Mn, <=0.02% P, 0.010-0.15% Al, <=0.004% N 0.002-0.02% Nb and the balance Fe with inevitable impurities, is refined. A slab of steel with this composition is heated to 1150-1300 deg.C, hot-rolled at >=(Ar3 transformation point -30 deg.C) finish rolling temp., and coiled at 450-700 deg.C. After acid pickling, cold rolling is done at >=80% draft. Successively, the resulting steel sheet is annealed under the conditions of 700-800 deg.C soaking temp. and 10-20sec soaking time and then temper-rolled at 1.0-50% draft. It is preferable that, if necessary, Mn among steel components is regulated to 0.1-0.6% and, further, Ni is incorporated by 0.01-1.0%.

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 base plate for a surface-treated steel sheet such as tin plate or tin-free steel having good workability.

[0002]

2. Description of the Related Art The tempering degree of a tin plate is specified by JIS as follows. That is, softness is classified into temper grades T1, T2 ... T6 in order, and when expressed as Rockwell hardness (HR30T) as a hardness target value of each classification, T1
Is 49 ± 3, T2 is 52 ± 3, T3 is 57 ± 3, T4 is 61 ± 3, T5 is 65 ± 3, and T6 is 70 ± 3.

Of the tin plate having such a temper degree, T
The so-called soft tin plate from 1 to T3 is annealed by applying a box-type annealing method in the annealing step, and the hard tin plate from T4 to T6 is annealed by applying a continuous annealing method. It is generally done. When the tin plate is manufactured by the box-type annealing method, the annealing step takes too much time, resulting in poor productivity. Further, since the material in the coil has a large variation, the continuous annealing method is preferable.

As a method for producing a tin plate which is soft and has good workability by the continuous annealing method, there is disclosed in Japanese Patent Laid-Open No. 58-197.
The one described in Japanese Laid-Open Patent Publication No. 224 is known. In this technique, when a continuous cast steel slab containing C in an amount of 0.004 wt% or less and optionally Nb in an Nb / C atomic ratio of 0.3 to 1 is subjected to hot cold rolling, the finish rolling temperature is 700-880
C., wound at 500 to 640.degree. C., pickled, cold-rolled, and then temper-rolled to produce a soft tin plate having a temper T1 to T3 by a continuous annealing method. Is the way.

When a tin plate is pressed to form a can, such as a two-piece can consisting of a body and a lid, in addition to the hardness that determines the temper, it is also excellent in press workability. Necessary for the plate. In particular, from the viewpoint of reducing the cost of a can body, a tin plate having a small ear height generated during press working and a small yield in r-value in-plane anisotropy (Δr) is desired.

According to the technique described in Japanese Patent Laid-Open No. 58-197224, a tin plate material which is soft and has good workability can be manufactured. However, when it is desired to reduce Δr particularly during hot rolling, It is necessary to further increase the coiling temperature and to add a large amount of Nb of about 0.02 wt%. When the coiling temperature is increased, the carbide in the hot-rolled sheet has a structure in which it is aggregated at the grain boundaries. This structure is cold rolled, annealed,
Since the tempering rolling and the plating process are maintained, the corrosion resistance of tinplate is significantly deteriorated.

Further, when a large amount of Nb is added, Nb fixes a large amount of solid solution C in steel, so that the strength of the can can be secured only by work hardening due to the introduction of strain during working. Therefore, in order to obtain a tin plate having a desired hardness, secondary cold rolling with a relatively high reduction ratio is required after annealing. However, due to the residual strain caused by the secondary cold rolling, not only the workability of the steel sheet is deteriorated, but also the shape is deteriorated in manufacturing, and the operational burden is large. Also, N
Since the addition of a large amount of b leads to an increase in the recrystallization temperature, the conditions of the annealing step after cold rolling become severe.

When ultra-low carbon steel is used as a tin plate material, since the Ar ₃ transformation point of ultra-low carbon steel is high, the finish rolling temperature during hot rolling is A over the entire length of the coil.
It is difficult to secure the temperature above the r ₃ transformation point. Therefore, the finish rolling temperature partially falls below the Ar ₃ transformation point, which causes problems such as non-uniformity of material and roughening of the tin plate due to coarsening of crystal grains of the hot rolled sheet.

On the other hand, in the technique disclosed in Japanese Patent Laid-Open No. 4-228526, C is set to 0.005 wt% or less and Nb
The in performing the hot rolling ultra low carbon steel with less 0.004 wt%, to coarsen the precipitates by heating at a relatively low temperature steel pieces, by reducing the solute N, Ar ₃ Even if finish rolling is performed at a temperature not higher than the transformation point, a tin plate precursor that is soft and has excellent workability can be manufactured. Further, by controlling the amount of Nb added, a tin plate having a good Δr can be manufactured.

However, according to this method, a tin plate material having a small in-plane anisotropy of the steel sheet and a good workability can be produced by adding a trace amount of Nb without significantly increasing the recrystallization temperature. Deterioration of corrosion resistance due to stripping, roughing of tin plate due to finish rolling in the ferrite area,
Alternatively, problems such as heavy operational burden due to annealing at high temperature remain.

[0011]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a method for producing an original plate for a surface-treated steel sheet which is excellent in workability.

[0012]

As a result of repeated studies to solve the above problems, the inventors of the present invention obtained the following findings and completed the present invention. That is, the material by Mn is utilized that an element lowering the Ar ₃ transformation point, to reduce the Ar ₃ transformation point of the material, to secure stable finish rolling temperature during hot rolling than Ar ₃ transformation point Eliminate the problems of unevenness and rough skin. Further, the problem of insufficient strength is solved by using Mn as a solid solution strengthening element. Then, they have found that the recrystallization temperature is lowered by the addition of Mn and Nb in combination, and by utilizing this, the conditions of the continuous annealing step can be relaxed as compared with the case of the conventional ultra-low carbon steel.

Further, it has been found that the recrystallization temperature is lowered by adding Ni, and by utilizing this, the conditions of the continuous annealing step can be relaxed as compared with the case of the conventional ultra low carbon steel. Furthermore, it has been found that the corrosion resistance is improved by adding Ni, and by utilizing this, the corrosion resistance can be improved only by adjusting the steel composition without increasing the plating amount.

Specifically, the method for producing the original plate for surface-treated steel sheet having excellent workability of the present invention for achieving the above object is as follows: C: 0.005 wt% or less, Si: 0.04 wt%
Below, Mn: more than 0.5 wt% and 1.0 wt% or less,
P: 0.02 wt% or less, Al: 0.01 to 0.15 w
t%, N: 0.004 wt% or less, Nb: 0.002-
A steel slab containing 0.02 wt% or less and the balance consisting of Fe and unavoidable impurities is heated to a temperature in the range of 1150 to 1300 ° C., and the finish rolling temperature is set to (Ar ₃ transformation point-3
0 ° C) or higher, hot rolling, winding at a temperature in the range of 450 to 700 ° C, pickling, cold rolling at a reduction rate of 80% or more, soaking temperature 700 ° C to 800 ° C, soaking Time 10
It is characterized in that annealing is carried out for up to 20 seconds, and temper rolling with a rolling reduction of 1.0% or more and 50% or less is performed.

Here, Mn may be 0.1 to 0.6 wt%, and 0.01 to 1.0 wt% Ni may be further contained.

[0016]

First, the reasons for limiting the chemical composition of steel to which the method of the present invention is applied will be explained. C: 0.005 wt% or less In the present invention, the C content of the material is very important.
In order to produce a soft tin plate having a temper T1 class in the continuous annealing method, it is necessary to sufficiently reduce the C content to achieve an extremely low carbon content.

Further, even if a small amount of Nb is added, the upper limit is made 0.005 wt% in order to make Δr good and to lower the yield elongation amount (Y-El). Si: 0.04 wt% or less When a large amount of Si is added, the amount of oxidation during the surface treatment increases, which causes problems such as peeling of the plating layer due to heating for a long time, so the upper limit is made 0.04 wt%. Mn: more than 0.5 wt% and 1.0 wt% or less Mn is an element effective in preventing hot cracking due to S, and it is necessary to add Mn according to the amount of S contained, but in the present invention, It is one of the extremely important additive elements for the reasons described below.

First, by adding Mn, although the detailed mechanism is unknown, the Ar ₃ transformation point is lowered, so that the rough surface, the uneven material, etc., which are considered to be caused by the finish rolling in the ferrite region as described above. The problem of can be solved. However,
Since the thickness of the hot-rolled mother plate for the tin plate is thin, it is necessary to add more than 0.5 wt% in order to stably secure the finish rolling above the Ar ₃ transformation in the current hot-rolling equipment.

Further, since the material is solid-solution strengthened by the addition of Mn, the reduction ratio of the secondary cold rolling necessary for obtaining the desired hardness can be reduced. Therefore, the deterioration of the workability of the steel sheet due to the residual strain after rolling can be suppressed, and the operational burden in the secondary rolling step can be reduced. However, if the content is 0.5 wt% or less, almost no effect on solid solution strengthening can be obtained, so that
It is necessary to add more than 5 wt%.

Further, although the detailed mechanism is unknown by the combined addition of Mn and Nb, it has the effect of lowering the recrystallization temperature, and as a result, it is annealed at a lower temperature than the conventional ultra low carbon steel in the continuous annealing step. It is possible to However,
If the content exceeds 1.0 wt%, the steel sheet becomes hard and the workability deteriorates significantly. Therefore, in the present invention, the upper limit is 1.
It was set to 0 wt%. Ni: 0.01 to 1.0 wt% Ni is one of the extremely important elements in the present invention for the reason described below. First, by adding Ni, although the detailed mechanism is unknown, the Ar ₃ transformation point decreases, so
It is possible to solve the above-mentioned problems such as rough surface and uneven material which are considered to be caused by finish rolling in the ferrite region. However, since the hot-rolled mother plate for the tin plate is thin, it is desirable to add 0.5 wt% or more in order to stably secure the finish rolling above the Ar ₃ transformation in the current hot-rolling equipment.

Further, although the detailed mechanism is not known by adding Ni, it has an effect of lowering the recrystallization temperature, which makes it possible to anneal at a lower temperature than the conventional ultra low carbon steel in the continuous annealing step. It is possible. Furthermore, the corrosion resistance of the steel sheet is improved by adding Ni in an amount of 0.3 wt% or more. On the other hand, if Ni is added in excess of 1 wt%, the above effect is saturated and the economic demerit becomes large, so the upper limit is made 1 wt%.

When Ni is added in an amount of 0.01 to 1.0 wt%, Mn is set to 0.1 to 0.6 wt%.
The same effect is obtained by adding Mn in an amount of more than 0.5 wt% and 1.0 wt% or less. P: 0.02 wt% or less P is an element that hardens the material and deteriorates corrosion resistance, so excessive content is not preferable, and the upper limit is 0.02.
wt%. Al: 0.01 to 0.15 wt% Al is an element necessary for precipitating solid solution N as AlN, and it is necessary to contain at least 0.01 wt% or more, and in relation to N (Alwt% / Nwt%) ≧ 20
However, since the addition of a large amount leads to an increase in cost, the upper limit is made 0.15 wt%. N: 0.004 wt% or less If N exists in a solid solution state, it hardens the steel sheet and causes stretcher strain, so its upper limit is 0.0.
It was set to 04 wt%. Nb: 0.002 wt% to 0.02 wt% By adding 0.002 wt% or more of Nb, the in-plane anisotropy of the steel sheet can be improved. It is also effective for making the crystal grains finer, and it is desirable to add a small amount from the viewpoint of preventing rough skin during molding. On the other hand, the addition of Nb has the effect of refining the crystal grains after hot rolling, which increases the sites of recrystallization nuclei during recrystallization annealing, so that the recrystallization temperature can be lowered. In order to obtain this effect, it is necessary to add 0.01 wt% or more, and the effect is increased by adding it together with Mn. But 0.02
If added in excess of wt%, the above effect is saturated and the recrystallization temperature is increased, which impairs the stripability during continuous annealing, so the upper limit was made 0.02 wt%.

Next, the reasons for limiting the manufacturing conditions will be described. Slab heating temperature: 1150 to 1300 ° C. The temperature at which the slab after continuous casting is heated prior to hot rolling is 1
If the temperature is lower than 150 ° C, it is difficult to secure a sufficiently high hot rolling finish temperature in hot rolling. If the rolling temperature can be secured by modifying the equipment, it is advantageous in terms of material to reduce the reheating temperature. However, if the reheating temperature is reduced, the load at the time of hot rolling also increases. Therefore, assuming the current equipment, 1150 ° C. is the lower limit of the reheating temperature. On the other hand, when the heating temperature exceeds 1300 ° C., the properties of the steel sheet surface are significantly deteriorated finally. Therefore, the upper limit is set to 1300 ° C. Finish rolling temperature: (Ar ₃ transformation point -30 ° C) or more In order to improve workability represented by r value after cold rolling and annealing, the finish rolling temperature is (Ar ₃ transformation point -30 ° C) or more. And If it is less than this, the structure tends to become coarser in the end, which is not desirable as a steel plate for a can from the viewpoint of surface roughness. Furthermore, when the finish rolling temperature is lower than this, the ridging phenomenon is likely to occur,
Poor appearance may be pointed out at the user use stage. Therefore, in the present invention, the finish rolling temperature is set to (Ar ₃ transformation point −30 ° C.) or higher, preferably Ar ₃ transformation point or higher. Winding temperature: 450 to 700 ° C. If the winding temperature is too low, the shape of the hot-rolled sheet deteriorates and the pickling and cold rolling in the next step are hindered. On the other hand, if the temperature is too high, the pickling property deteriorates as the scale thickness increases on the surface of the steel sheet, and the microstructure of the mother plate becomes coarse, which eventually leads to a reduction in the steel sheet. Further, a structure in which carbide is aggregated is formed in the hot rolled mother plate, and this structure adversely affects the corrosion resistance of the steel plate. Therefore, the upper limit is set to 700 ° C. Cold rolling rate: 80% or more If the cold reduction rate is less than 80%, sufficient deep drawability cannot be obtained. Therefore, the lower limit was set to 80%, but as in the present invention, an extremely low carbon containing a trace amount of Nb is used. In order to secure good workability with very small Δr in steel, it is preferable to give a large strain energy before annealing to promote the development of an advantageous plane orientation during recrystallization. For this reason, the higher the cold rolling reduction, the better the workability, and it is desirable that the workability be 85% or more. Annealing temperature: 700 to 800 ° C. The annealing temperature is 700 at which recrystallization is completed.
C is specified. On the other hand, if the annealing temperature is excessively increased, not only the possibility of causing defects such as heat buckle and plate rupture during continuous annealing is increased, but also the surface treatment property is deteriorated due to an increase in surface concentration, which is not desirable. Therefore,
The upper limit was 800 ° C. Heat treatment after annealing Reduction ratio: 1% or more and 50% or less Since the material is not stable due to the elongation at yield point in the state annealed to the mother plate, the heat treatment is 1% or more except for very special applications. It needs to be rolled. Also, in order to finish the original plate with the tempering degree according to each application, a maximum of 50% secondary rolling is performed, but if the reduction ratio exceeds 50%, the operational burden will increase and the productivity will decrease. This value was set as the upper limit.

The cold rolled steel sheet produced by the above method has excellent workability.

[0025]

EXAMPLES Examples of the present invention will be described below together with comparative examples.
It First, containing the composition of components shown in Tables 1 and 2, the balance is
This steel slab is produced by melting steel that consists essentially of Fe in a converter.
Was rolled under the hot rolling conditions shown in Tables 3 and 4. this
In this case, for some, measure the heat history of the sample during hot rolling
And their steel Ar ₃ I investigated the transformation point. Then pickled
Then, a cold-rolled plate having a final finished plate thickness of 0.3 mm was obtained. Next
The recrystallization temperature of each steel, and
After annealing under the soaking conditions shown in No. 4, temper rolling was performed.
It was After that, on the halogen type electric tin plating line
25th tin plating is continuously applied to finish the tin plate
It was For the steel sheet for cans thus obtained, the hardness
(HR30T), tensile strength TS, average r value, Δr value
Tables 5 and 6 show the results of the investigation. In addition,
Tensile properties were measured using ordinary JIS No. 5 test pieces.

As is clear from Tables 5 and 6, the steel sheet produced by the method of the present invention has an Ar ₃ transformation point lowered to 860 ° C. or lower, and a finish at (Ar ₃ transformation point −30 ° C.) or higher. Stable rolling was ensured, and there were very few variations in the material in the width direction of the product and the longitudinal direction of the coil, and surface roughness was extremely small. In addition, due to the increase in the amount of Nb added and the addition of Nb and Mn in combination, the recrystallization end temperature is very low carbon steel (steel No.
Compared to 1), the recrystallization temperature is high, and it is extremely effective for extremely low carbon steel materials that require annealing at high temperatures. Further, compared with the conventional low carbon steel material (steel No. 26) produced by the box-type annealing method, the steel sheets produced by the present invention all have a high average r value and a small Δr value, and are excellent in can-making property. There is.
Since it is solid-solution strengthened by the addition of Mn, even when manufacturing a relatively hard tin plate of T3 or more, the rolling reduction of temper rolling can be reduced as compared with the case of the conventional ultra-low carbon steel material. At the same time, it is possible to reduce deterioration of workability due to rolling.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

[Table 6]

Next, another embodiment of the present invention will be described together with a comparative example. Steel containing the composition shown in Table 7 and the balance being substantially Fe was melted in a converter, and this steel slab was rolled under the same hot rolling conditions as shown in Table 7. At this time, for some of them, the thermal history of the sample during hot rolling was measured, and the Ar ₃ transformation point of each steel was investigated. Then, it pickled and it set it as the cold rolling board of the final finish board thickness 0.3 mm. Next, the recrystallization temperature of some of the materials was investigated, and after annealing under the soaking conditions shown in Table 7, temper rolling was performed. Then, No. 25 equivalent tin plating was continuously applied on a halogen type electric tin plating line to finish it in a tin plate. Table 8 shows the results of an examination of the hardness (HR30T), the tensile strength TS, the average r value, the Δr value, and the corrosion resistance of the can steel sheet thus obtained.

The tensile properties were measured by using a standard JIS No. 5 test piece, and the corrosion resistance was I.V. S. V test value (Iron
Evaluation by the Solution Test Value). I. S. The V test is a method of simulating the reaction between the contents in the can and the steel plate in order to determine the corrosion resistance of the surface of the original plate before plating and the plating layer, and determining the amount of iron eluted from the specimen at this time. In the present invention, I.D. S. V ≦
In the case of 3 μg / 3 in ^2, the corrosion resistance is marked with ◯ and I. S. V ≦ 1
In the case of μg / 3 in ^2, the corrosion resistance is marked with ⊚.

As is clear from Table 8 and FIG. 1, among the steel sheets manufactured by the method of the present invention, the Ni content is 0.3 wt.
% Or more has an Ar ₃ transformation point of about 860 ° C. or less, and even with the current hot rolling equipment, it is possible to stably secure finish rolling at (Ar ₃ transformation point −30 ° C.) or more, and the sheet width direction of the product. Also, there was very little variation in the material in the longitudinal direction of the coil and rough skin. Further, as shown in FIG. 2, the recrystallization end temperature is lowered by adding Ni, which makes it possible to relax the annealing conditions in the continuous annealing step, and the high recrystallization temperature causes the annealing at high temperature. It is extremely effective for ultra-low carbon steel, which is essential. Further, as compared with the conventional material manufactured by the box-type annealing method, as shown in FIG. 3, all the steel plates manufactured by the method of the present invention have a high average r value and a small Δr value,
Excellent in can manufacturing. Further, when the Ni content was 0.3 wt% or more, a plated plate having good corrosion resistance was obtained. However, only comparative steels with poor corrosion resistance were obtained.

Although the tin plate was used in the above embodiment, a tin-free steel plate, a composite plated steel plate, or the like may be used, or an oil-coated steel plate may be used without plating. Further, Ni plating may be applied before annealing.

[0037]

[Table 7]

[0038]

[Table 8]

[0039]

As described above, according to the method for producing a base plate for a surface-treated steel sheet having excellent workability of the present invention, by adding Mn to lower the Ar ₃ transformation point, a thin plate for a tin plate can be obtained. Even in the hot-rolled mother plate, it is possible to stably secure the finish rolling at the Ar ₃ transformation point or higher, so that the problem of quality defects such as the variation of the material and the rough surface is solved, and the yield is improved. Also, N
By controlling the addition amounts of b and Mn, the recrystallization temperature can be effectively lowered, the process conditions of continuous annealing can be relaxed, and productivity and economic efficiency can be improved. Further, the addition of Mn increases the strength of the raw material, so that the reduction ratio of the temper rolling required to obtain a steel sheet having a desired temper can be reduced, and the productivity and the economical efficiency can be improved.

Further, by lowering the Ar ₃ transformation point by adding Ni, it becomes possible to secure stable finish rolling at the Ar ₃ transformation point or higher even with a thin hot-rolled base plate for tin plate, so that there is variation in material. The problems of poor quality such as rough skin and skin are solved, and the yield is improved. Further, since the recrystallization temperature is lowered by adding Ni, the process conditions of continuous annealing can be relaxed, and the productivity and the economical efficiency can be improved. Furthermore, by using the steel sheet of the present invention, it is possible to obtain a surface-treated steel sheet having excellent corrosion resistance only by adjusting the steel composition without adopting a special surface treatment method or technique, which is a great industrial advantage.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of Ni added and the Ar ₃ transformation point of a steel sheet.

FIG. 2 is a graph showing the relationship between the amount of Ni added and the recrystallization temperature.

FIG. 3 is a graph showing the relationship between the amount of added Ni and the r value and Δr value.

Claims (2)

[Claims] 1. C: 0.005 wt% or less, Si: 0.04 wt% or less, Mn: more than 0.5 wt% and 1.0 wt% or less, P: 0.02 wt% or less, Al: 0.01 to 0 15% by weight, N: 0.004% by weight or less, Nb: 0.002 to 0.02% by weight or less, and the balance being Fe and unavoidable impurities, and a temperature within the range of 1150 to 1300 ° C. And hot rolling at a finish rolling temperature of (Ar ₃ transformation point −30 ° C.) or higher, winding at a temperature in the range of 450 to 700 ° C., pickling, and cold rolling at a reduction rate of 80% or more. An original plate for a surface-treated steel sheet, which is characterized by rolling, annealing at a soaking temperature of 700 ° C. to 800 ° C., annealing at a soaking time of 10 to 20 seconds, and temper rolling at a rolling reduction of 1.0% to 50%. Manufacturing method. 2. The Mn is set to 0.1 to 0.6 wt%,
Furthermore, 0.01-1.0 wt% of Ni was contained, The manufacturing method of the original plate for surface-treated steel plates of Claim 1 characterized by the above-mentioned.