JPS5938336A - Production of ultra thin steel sheet for can having high yield strength and drawability - Google Patents

Abstract

PURPOSE:To obtain a titled ultra thin steel sheet by hot rolling a continuous casting billet contg. specific amts. of C, Si, Mn, P, S, Al, N, coiling the same in a specific temp. range to form a hot rolled steel strip, cold rolling the steel strip at a specific draft after pickling to produce cold rolled steel plate then treating the steel strip in a continuous annealing furnace under specific conditions. CONSTITUTION:A continuous casting billet is composed, by weight, of <0.1 C, <0.06 Si, <0.5 Mn, <0.03 P, <0.03 S, <0.15 Al, <0.008 N, and the balance Fe. The billet is hot rolled at the finish rolling temp. of the Ar3 point or above and is coiled at 640-700 deg.C coiling temp. to a hot rolled steel strip. The steel strip is cold rolled at 80-95% draft after pickling. The resulted cold rolled steel strip is held for >=20sec at >=680 deg.C in a continuous annealing furnace, is cooled at 10-500 deg.C/sec cooling rate down to <=500 deg.C, is held at 500-350 deg.C for >=20sec and is cooled down to a room temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an ultra-thin steel plate as a raw material for can making by drawing. The ultra-thin can material has excellent drawing workability and the quality of the produced cans.In particular, the can material has smaller selvage, which is caused by the in-plane anisotropy of the steel sheet, compared to conventional cans. This invention relates to a method for manufacturing steel plates.

Edible cans have traditionally had bodies, large parts (lids), and base parts (bottoms).
The main body is a three-piece one-piece can, and some are so-called λ-piece cans, in which the body t'JlN and base are integrally molded using breath painting, and the top is joined to the body.

In recent years, the can-making method has been attracting attention because the Kopis-gai method has the advantages of excellent can functionality and high can-making efficiency. In addition, conventional materials have a degree of tempering (
In JIS C+3Jo3, four furanyl T hardness H
(It is specified that this is expressed by the value of R30T) is T1 to T3. Plate thicknesses of approximately 0.2 to Q-41wm are used. However, recently, in order to reduce costs and reduce the amount of material used, thinner plates have begun to be used.

2-piece cans are painted and printed on a flat plate before drawing, but this method is done using a roll coater, so the yield strength of the steel plate used in the conventional method is low, so it warps in the direction of travel after painting. In the baking process immediately after, the warped painted plates are
; Z It There was a problem that scratches were generated. This tendency is further exacerbated as the plate thickness becomes thinner. Therefore, even though it is a steel sheet for drawing, a steel sheet with a higher yield strength is suitable as a steel sheet for cans.

The drawability of ultra-thin steel sheets used as material for cans that are generally made by drawing is that they generally have a large r value, similar to cold-rolled steel sheets for drawing used for automobile bodies. is considered desirable. In addition, in order to reduce the amount of trimming of the flange part after can manufacturing and improve material yield, we have developed a material with a small r-value in-plane anisotropy (Δr), which has less ears on the flange part of the container 7. Thin steel plates are required.

Note that the r value is an index indicating the deep drawing workability of a cold-rolled Oki 1 sheet, and is expressed as the ratio of strain in the width direction to strain in the thickness direction in a tensile test. This r value differs depending on the sampling direction of the tensile test. . .

The one taken in the direction of is the highest, followed by □. There are many cases of anisotropy in which the direction is high< and the 4I3' direction is the lowest. The degree of culm of this anisotropy differs depending on the manufacturing method of the steel sheet.

Therefore, regarding the r value, from the r value in each direction,
The average value 7 is calculated using the following formula and used to evaluate the drawability of the blank.

rl, +r□+korD Here rL: r value ro in the direction parallel to the rolling direction:
r value rD in the direction perpendicular to the rolling direction: rolling direction and 9
r value in the 5° direction On the other hand, anisotropy appears in the circumferential thickness distribution and height of the can flange portion after drawing, and this phenomenon occurs due to the in-plane anisotropy of the r value. That is,
In contrast to the compression in the circumferential direction during deep drawing, the plate thickness tends to increase in the direction where the r value is small, and the material is difficult to stretch in the radial direction. On the other hand, in the direction of large r value, the plate thickness increases and <<,
The material tends to stretch in the radial direction. Therefore, the can becomes higher in the direction of the larger r value (the peak of the ear), and becomes lower (the trough of the ear) in the direction of the smaller r value.

The height of the ears varies considerably depending on the processing conditions, but this r
The larger the M6LFi plate has a larger Δr, which shows the anisotropy of the value, the larger the edge becomes, and the yield decreases.

Note that Δr is defined by the following formula.

The r value has a close relationship with the crystal texture of the net plate, and therefore the Δr value also has a close relationship with the crystal texture.

This Δγ value varies greatly depending on (1) the reduction ratio of cold rolling, (2) the hot rolling temperature before cold rolling, and (3) the precipitation behavior and dispersion state of precipitates such as AJN during the recrystallization process. It has been known.

From this, it is possible to minimize the occurrence of selvage at the container flange by using a very M steel plate with a small Δr in accordance with the design of the mold. However, in general, F with small Δr
T5 thin steel sheets have the disadvantage of having a poor r value, which inhibits deep drawing itself.Furthermore, in order to increase the yield strength, it is necessary to reduce the grain size.
As a result, the r-accuracy also deteriorates.

Conventionally, low carbon At killed 111 was used to manufacture a drawing arrangement plate with a small r value, and the hot finish rolling temperature (FT) was A r
3 transformation point or higher, the coiling temperature (CT) is as low as Sio'C, and annealing has been performed by a box annealing method. However, with this manufacturing method, (The yield strength is high, but the yield strength is low.) Low yield strength and high r value are desirable quality rarity when used for automobile bodies, etc., but they are used for can steel sheets. As mentioned above, □ is unfavorable because of the warping that occurs during the painting process.

The reason why the yield strength is low is that the box annealing makes it non-aging. On the other hand, as an annealing method for increasing the yield strength, there is a continuous annealing (CAL) method. In the conventional method, CA
After recrystallization, L is carried out through a thermal cycle in which the steel is simply cooled to room temperature, and although the yield strength of the steel annealed using this method is high, the yield strength is low, and it was concluded that it could not be used for drawing. However, it can be seen that even in the CAL method, when rapid cooling and overaging treatment are added after recrystallization in the thermal cycle, the yield strength increases and the lower value also increases. However, the dispersion of the bottom price is large.

The present invention improves the drawbacks of the above-mentioned conventional method due to; and has a high yield strength while having a! iJi! The object of the present invention is to provide a method for pickling thin yui-ban.

In other words, the gist of the present invention is as follows.

0: 0.70% or less + Si: 0.04% or less IM21I: 0, A: 0% or less r P': 0.03
% or less, 3: 0.03% or less, kl: 0.
Hot 111J:
, hot-rolled at a finishing temperature of A r 3 transformation point or higher, )! The temperature was set at 4110"C to 700"C, the coiling was carried out to form a hot-rolled strip, and after pickling, the rolling reduction was 0 to 700"C.
The cold-rolled steel sheet obtained by cold rolling at R% is held at a temperature of Agθ°C or higher for 20 seconds or more in a continuous annealing furnace, and then so
IO”C/sec = !;00 to temperature below o℃
``Cooled at a cooling rate of C/eea, and further soo'c~3
An ultra-thin steel sheet for cans with good yield strength and excellent warp workability, especially with small in-plane anisotropy, which is maintained at a temperature of Sθ゛C for more than a second and then cooled to room temperature. Production method.

Hereinafter, Honzuo Akira will be explained in detail.

In order to produce an ultra-thin copper plate for drawing with a high yield strength of high <-C, L, and a low value of Δr, the present inventors considered that (1) ki plate component affects the yield strength. , (2) hot rolling conditions (finishing temperature FT' + coiling temperature OT), (3) annealing conditions (box annealing, normal continuous annealing method without over-aging treatment, continuous with rapid cooling and over-aging treatment) As a result of intensive research on the annealing method, the following facts were discovered and the present invention as summarized above was conceived.

Figure 7 shows the use of ordinary low carbon Aj killed fM continuous cast material.
For hot rolling, FT is g5θ℃, OT is Sco'c~10
It is a chart showing the relationship between the 7 values and yield strength for the annealing conditions when three types of annealing were performed after cold rolling of a hot rolled steel strip obtained by performing the rolling at 0"C. In the figure, Areas with hatches indicate areas with few wrinkles or ears and no problems with paintability.

According to FIG. 1, it can be seen that a continuously annealed steel plate made from the continuously cast mass can obtain a large lower value and a high yield strength by selecting certain hot rolling conditions and overaging treatment conditions.

Figure 2 shows the effects of C content and OT on Δr and 7 in a steel plate that has been hot-rolled, cold-rolled, and continuously annealed under the conditions shown in the figure from a continuously cast convex material with a low-carbon An-killed handle. The hatched areas in the figure are the same as in Figure 7.

According to the figure, Δr becomes smaller on average as the lower value becomes higher, but there is a condition in which the lower value is especially large and Δr becomes small. t, go oO,,'.

Under this condition, the phenomenon in which the lower value is large and Δr is small is as follows.
This is thought to be due to the fact that when the CT becomes high, the crystal grain size increases due to self-annealing that occurs in the coil burr state, and the carbides aggregate and coarsen.

From the above results, the yield strength is high, warping does not occur even when coating with a roll coater, stable drawing properties are obtained in the can manufacturing method using the Shikamaka drawing damage method, and the edges are smooth. Regarding the manufacturing conditions of ultra-thin steel sheets, which are becoming smaller, we have conducted repeated research on the premise of using low-carbon A/killed copper continuous cast material, and have found that hot rolling conditions are important, especially by setting FT to the Ar3 transformation point or higher. After winding at a high temperature of A'lO''C or higher, pickling, cooling, and recrystallization by continuous annealing →
It was newly discovered that the desired ultra-thin 61 plate for can manufacturing can be manufactured by performing rapid cooling/overaging treatment.

However, as mentioned above, the present invention first involves continuous casting of the material.
Limit the composition range of the pieces. This composition range is necessary to impart the desired properties to the resulting ultra-thin steel sheet. The reason for limiting the composition range for each component will be explained.

Q is an important component that suppresses the growth of recrystallized grains.If the amount of C is increased, the grain size becomes smaller and a product with a high degree of thermal refinement can be obtained. If the value exceeds 0, the value becomes harder and the lower value decreases, so C becomes 0.
The content must be 10% or less.

Sl deteriorates the corrosion resistance of tinplate, makes the material extremely hard, impedes cold rolling, and deviates from the desired degree of tempering, so the content of Sl must be 0.806% or less. Therefore, it is not necessary to intentionally add 8102 at the time of manufacturing, and it is necessary to limit the amount of 8102 in the refractory to the extent that it is lent by AI in the molten steel and remains.

Mn needs to be added to promote removal of S and to prevent edge cracking in the hot rolled coil. However, if the amount of S is small, excessive addition is economically undesirable, so it is necessary to limit the amount to prevent the occurrence of edge cracking, and Mn needs to be contained in an amount of O, SO% OT.

Since P hardens the material and further deteriorates the corrosion resistance of tinplate etc., it is necessary to suppress P to 0.03% or less.

If S is contained excessively in relation to -,)4n, edge cracks and MnS-based inclusions will be present in the hot rolled coil, causing cracking defects during can manufacturing, which is undesirable, so S is 0.03%.
It is necessary to keep it below.

AJ is a component that plays the role of a deoxidizing agent in the steel manufacturing process, and as the content in the steel increases, the cleanliness of the steel increases, but it is not preferable to add it in excess, and it also reduces recrystallized grains. Since growth is suppressed, AJ is 0. /! It is necessary to make the content less than i%. In addition, the less A4 is, the better.
It is sufficient to complete deoxidation by adding an amount commensurate with the amount of dissolved oxygen in L#1, and there is no need to substantially leave gold 1iAI. However, if the amount of residual gold M )l (1) is too small, the cleanliness of the steel as it is will be poor, so it is necessary to promote the flotation and separation of inclusions in the l@copper steel. One of the methods is to forcibly stir the molten steel through vacuum degassing treatment, etc., but this process has become standardized in recent years, and it allows for low A7 steel with high cleanliness.
! It is easy to manufacture li4.

Therefore, it is necessary to suppress N to θ, oog% or less.

Steel having the above-mentioned composition range can be easily produced by a process of various types of converters, vacuum degassing treatment, and continuous casting.

Next, in the present invention, as described above, the hot rolling finishing temperature (FT) and the winding temperature (OT) are limited as the hot rolling conditions. This limited hot rolling condition is the most important in the present invention. The reason for this limitation will be explained below.

Hot rolling finishing temperature: Ar3 transformation point or higher When FT is set to a temperature (9) lower than Ar3 transformation point,
Since the value becomes small, it is necessary to set it above the Ar3 transformation point.

Winding temperature (OT): blIo'c ~ too°c
OT needs to be in the range of AQO''C: ~700''C in order to enlarge the crystal grains and improve drawing workability. That is, the lower limit of OT for enlarging crystal grains by self-annealing is 490° C., and the grain size becomes even larger when the temperature is higher. Excessively high temperatures are not preferred because as the GT increases, the scale on the surface of the steel sheet becomes thicker, and the pickling properties in the next step deteriorate. Therefore, the upper limit is set at 7θ0°C in order not to deteriorate the pickling property extremely.

Cold rolling reduction ratio: io-95% In the subsequent cold rolling, the rolling reduction ratio is adjusted. ~95%.

This is because a normal 6-stand Kundem mill for ultra-thin steel sheets has a rolling capacity of go~95%, so this was also followed in the present invention.

Continuous annealing conditions Recrystallization annealing: A temperature of θ°C or more, held for more than a second, then continuous annealing was used. By holding the temperature at a temperature of .degree. C. or higher for 20 seconds or more, recrystallization is performed and crystal grains are grown to increase the grain size. This improves drawing workability. If the annealing temperature is lower than AtO''C, but the holding time is shorter than 2 seconds, the grain size cannot be increased, which results in hardening and deterioration of drawability.

Cooling speed! IO"C/see ~!;00'C,/
Sea quenching stop temperature: 500℃ or less As cooling conditions after recrystallization annealing, it is necessary to cool to a temperature of 10''C or less and a cooling rate of 10''C/sea or more and SOO''C/F3ec or less to a temperature of 00''C or less.The reason is as follows.

That is, at a cooling rate slower than 10"C/s θ0, cementite precipitates halfway during cooling, and the degree of supersaturation of 0 becomes low, so subsequent overaging does not proceed sufficiently. On the other hand, SOθ"C/n Rapid cooling exceeding e o is not preferable because the surface shape of the tin plate will deteriorate significantly. Furthermore, if quenching is stopped at a temperature higher than soO'c, the solid solubility of C decreases to near the equilibrium solubility of 0 in ferrite at that temperature, and overaging does not proceed in this case either. Therefore, after recrystallization annealing, 10℃/sea =
! It is important to rapidly cool to a temperature below SOO''C at a cooling rate of 00°C/gee to increase the degree of supersaturation of C.

Over-aging treatment: soo”c~3so℃2.The conditions for continuous aging treatment for 20 seconds or more are soo” for the following reasons.
It should be held at a temperature of c~3so''C for more than 20 seconds. That is, at temperatures lower than 310'C, the diffusion rate of 0 is small and overaging does not proceed, while at temperatures higher than SOO℃ Since the solid solubility limit is large, the amount of solid solubility cannot be kept low, causing age hardening.Furthermore, if the holding time does not reach one second, overaging will not be fully completed.

Through the continuous annealing described above, the steel plate becomes softer due to the precipitation of C and N, and the lower value becomes larger, while Δr becomes smaller. Although it is further softened, the yield strength is higher because the residual amount of solid solution C is larger and the grain size is smaller than that of conventional box-annealed steel sheets.

Example Steel slabs having the composition shown in Table 1 below were melted in a converter. Especially 0. , 0% by weight was subjected to vacuum degassing treatment after melting, and was made into a steel billet with excellent cleanliness using a continuous casting machine.

These steel pieces were hot rolled under the hot rolling conditions shown in Table 1.
After making it into a hot-rolled steel strip, it was pickled and descaled.

Then, it was cold rolled (reduction ratio of about t7.%) to □ and J4 in a 6-stand tandem mill, and then annealed under various annealing conditions shown in Table 2.

/ /' / / /'' Table - Table 1?In Table 1, "CAL-A" is continuous annealing in which an overaging treatment is performed by rapid cooling after recrystallization, and "0AL-B"
"Box annealing" is a continuous annealing process with a simple cycle of cooling to room temperature after recrystallization, and "box annealing" is a batch annealing furnace in which the entire process from temperature rise to recrystallization and subsequent cooling to room temperature is performed over approximately 100 hours. It's a method.

Note that the temper rolling was performed at a reduction ratio of 1%.

The thus obtained tin plate was subjected to tin plating using a halogen electrolytic tin plating line, and then samples were taken.

A tensile test was conducted on each sample to measure the yield strength, a separate tensile test was conducted to determine the lower value and the Δr value, and the hardness was further measured. In addition, we actually applied the coating using a single roll coater and investigated the occurrence of scratches on the painted surface due to coater warping.

Subsequently, the sample was drawn and made into a one-piece can, and the can was evaluated. There are three types of defects that occur in cans:

Broken: Cans that break at some point on the can body during squeezing and do not become a can.

Wrinkling: A can that could be formed into a can, but wrinkles appeared on the can body wall.

The degree of ears in the 7-rung part after the ear-forming nibless processing is shown.

The above comprehensive judgments are shown in Table 1. In Table 1, the underlined items are those that do not meet the conditions of the present invention.

As is clear from the comparison between the examples and comparative examples shown in Table 1, the ultra-thin steel sheets produced by the method of the present invention have a high yield strength, a large lower value, and a small Δr value. It has excellent processability, and the cans obtained by drawing after painting with this coating have good surface quality, with no scratches or blemishes caused by roll coater warping. It was excellent, and the bulge was small.Furthermore, no breakage occurred during the drawing process.

[Brief explanation of drawings]

Figure 7 is a chart showing the influence of the type of annealing method on the yield strengths Y, P, and lower values of ultra-thin steel plates, and Figure 1 shows the effects of r41 and volume on the 7 value and Δγ value of ultra-thin steel plates. It is a chart showing the influence of taken temperature OT. Patent applicant Kawasaki Steel Co., Ltd. Representative patent attorney Mura 1) Politics jI) Figure 2

Claims (1)

[Claims] 1, 0 + 0.70% or less, Si: 0.0/
, % or less + Mn: O, SO% or less, P: 0.
0.03% or less, S: 0.03% or less, A/:
A continuously cast steel billet containing N: 0.00 g% or less and the remainder being substantially Fe is hot rolled at a hot rolling finish temperature of Ar3 transformation point or higher, and then rolled up. The temperature is t, qo''C ~ 7oo''c, and the steel sheet is rolled into a hot-rolled temperate zone, then pickled, and then cold-rolled at a rolling reduction of gθ~95%, and the obtained cold-rolled steel sheet is passed through a continuous annealing furnace. AgO”
C, IJJ, keep at the above humidity for more than 20 seconds, and then continue □s
70℃/sec to temperature above oo℃ = soo℃/
Cooled at a cooling rate of n e c, and further cooled to SOO″C~3
An ultra-thin steel sheet for cans with high yield strength and excellent drawing workability, especially with small in-plane anisotropy, which is maintained at a temperature of O'C for more than 1 second and then cooled to room temperature. Production method.