JPS5938338A - Production of ultra thin steel sheet 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 then treating the steel strip in a continuous annealing furnace under specific conditions for a cold rolled steel sheet. CONSTITUTION:A continuous casting billet is composed, by weight %, of <0.07 C, <0.06 Si, <0.25 Mn, <0.03 P, <0.02 S, <0.15 Al, <0.008 N, and the balance Fe. The billet is hot rolled at 1,000-1,150 deg.C heating temp., is hot rolled at the Ar3 transformation point or above and >=700 deg.C finish hot rolling temp. and is coiled at 640-700 deg.C coiling temp. to a hot rolled steel strip. The steel strip is cold rolled at 80-90% draft after pickling. The resulted cold rolled steel strip is held for >=20sec at >=680 deg.C in a continuous annealing furnace, is cooled down to <=500 deg.C at 10-500 deg.C/sec cooling rate, is held for >=20sec at 500-350 deg.C 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 cans formed by drawing, and in particular, when making cans, the r value of the raw material is large and the Δr value is small. For cans, it has excellent drawing workability in this respect, as well as the quality of the formed can, and in particular cans with smaller selvage caused by in-plane anisotropy in the material steel plate compared to conventional cans. This invention relates to a method for manufacturing ultra-thin steel sheets.

For edible cans, the body, main part (lid), and base part (bottom) have long been used.
The main type of can is the so-called 3-piece can, which consists of 3-piece cans, and some are the so-called cobies cans, in which the body and base are integrally molded by press molding, and most of the parts are joined.

Two-piece cans have been gaining attention in recent years as a can manufacturing method because they have the advantages of excellent can functionality and high can manufacturing efficiency.

In addition, conventionally, such materials have a heat treatment degree (JIS a33
In 03, it is specified that Rockwell hardness (HK30T) is expressed as T/~Tj
, plate thickness 0.2~0. 'l B grade was used. However, recently, in order to reduce costs, thinner plates have been used to reduce the amount of material used.

- Piece cans are painted and printed on a flat plate before drawing, but this process is done using a roll coater, so steel plates made using the conventional method warp in the direction of travel after painting due to their low yield strength. In the baking process that immediately follows, there is a problem in that the warped painted plates come into contact with each other, causing scratches. This tendency is further exacerbated as the plate thickness becomes thinner. Therefore, steel sheets with higher yield strength are suitable for drawing steel sheets for cans.

The drawability of ultra-thin steel sheets, which are generally used as can materials for making cans by drawing, generally has a large r value, similar to that of cold-rolled steel sheets for drawing used for automobile bodies, etc. considered desirable. In addition, in order to reduce trimming of the flange part after can manufacturing and improve material yield, the flange part of the container 7 is made of ultra-thin material with a small in-plane anisotropy (Δr) of the so-called r value, which has less ear formation. Steel plate is required.

Here, the r value is an index indicating the deep drawability of a cold rolled steel 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 varies depending on the direction in which the tensile test piece is taken. For low carbon A/killed steel cold-rolled end plates, the r value is highest when taken in the qOo direction with respect to the rolling direction, followed by the θ0 direction, and qs Many of them are anisotropic, with the lowest point in the O direction. The degree of this anisotropy varies 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 steel plate.

Here rL: r value rc in the direction parallel to the rolling direction:
r value rD in the direction perpendicular to the rolling direction: rolling direction and i
On the other hand, the can flange portion after drawing has anisotropy in the thickness distribution and height in the circumferential direction, and this phenomenon occurs due to the in-plane anisotropy of the r value. That is, with respect to 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 where the r value is large, 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 lower (the trough of the ear) in the direction of the smaller Sr value.

The height of the ears varies considerably depending on the processing conditions, but this r
Ultra-thin steel sheets exhibiting anisotropy in value and have a large Δr have a large radius, resulting in a decrease in yield.

Note that Δr is defined by the following equation.

r + r − Δr = −−−−−−−−−−−−− The Cor value has a close relationship with the crystal texture of the steel sheet, and therefore the Δr value also has a close relationship with the crystal texture. There is.

This Δr value varies greatly depending on (1) the rolling reduction ratio of cold rolling, (g) the hot rolling temperature before cold rolling, (,?) the precipitation behavior and dispersion state of precipitates such as AIN in the recrystallization process, etc. It is known.

From this, by using an ultra-thin steel plate with a small Δr in conjunction with the design of the mold, it is possible to minimize the occurrence of flange at the container flange. but.

In general, ultra-thin steel sheets with a small Δr have a bad r value, which inhibits deep drawing.Furthermore, in order to increase the yield strength, it is necessary to reduce the grain size. As a result, the r value also becomes smaller.

Conventionally, the production of steel sheets for drawing with a high value of 7 has been carried out using low-carbon At-killed steel, with a hot rolling temperature (FT) of at least the Ar3 transformation point, a coiling temperature (OT) of about 5lIo℃, and annealing. has been performed using the box annealing method. However, this manufacturing method had the drawback that although the 7 value was high, the yield strength was low. Even if the yield strength is low, a material with a high strength is a desirable quality characteristic when used for automobile bodies, etc.
This is not preferable for steel plates for cans because of the warping of the steel plate that occurs during the coating process as described above.

Continuous annealing (
CAL). In the conventional method, after recrystallization, CAL is
This is done using a thermal □ cycle in which the steel is simply cooled to room temperature, but although the yield strength of the annealed steel is high, the Y value is low, making it difficult to use it for drawing.

However, even in the CAL method, it has been found that when quenching after recrystallization and overaging treatment (0°A treatment) are added to the thermal cycle, the yield strength increases and the f value increases. The variation in force and f-value was large, and the level thereof was also low.

On the other hand, the thickness of an ultra-thin steel plate is determined by cold rolling, but when trying to obtain an ultra-thin 6 steel plate, the reduction rate of cold rolling inevitably becomes high. For this reason, cold rolling properties deteriorate.

The present invention improves the above-mentioned drawbacks of the conventional method, and provides high yield strength. A method for manufacturing an ultra-thin steel sheet for cans that has a large value and a small Δr, that is, a small in-plane anisotropy, and has excellent drawing workability by facilitating cold rolling. The purpose is to provide the following.

That is, the gist of the present invention is as follows.

c: o, o't @ or less, Si: 0.04% or less,
Mn: o, 1sqb or more'F, P: 0.03
'lr or less, s:o, okochi or less, Al: 0. /
! r% or more)', N: Continuously cast steel billet containing 0.00t% or less, the remainder being substantially Fe, and the billet heating temperature at 1000°C ~//! It was hot-rolled to 0°C, with a finishing hot rolling temperature of below Ar3 transformation point or above 700°C, then coiled at a coiling temperature of Uθ°C to θ0°C to form a hot-rolled steel strip, and then pickled. After that, the cold rolled steel sheet was cold rolled with a reduction ratio of go to 95%, and the obtained cold rolled steel sheet was held at a temperature of t, go °C or higher for 3 seconds or more in a continuous annealing furnace, and then so
loC/mec-! to temperatures below oC! r00℃/
It is characterized by high yield strength, excellent drawing workability, especially in-plane anisotropy, and is characterized by cooling at a cooling rate of seawater, holding the temperature at 5003-330℃ for 3 seconds or more, and then cooling to room temperature. A method for manufacturing ultra-thin steel sheets for small cans.

The F1 invention will now be described in detail.

The present inventors have created an ultra-thin steel sheet for drawing that has a high yield strength, a large F value, and a small Δr.
In order to produce a steel sheet material with excellent cold rolling properties, there are several factors that are considered to affect the material properties of the cold rolled material and the product steel sheet: steel sheet composition, billet heating temperature, β)
Hot rolling conditions (hot rolling finishing temperature FT, coiling temperature 0T) 1
4) As a result of intensive research on annealing conditions (box annealing, normal continuous annealing without over-aging, continuous annealing with rapid cooling and over-aging), we found the following: The present invention was conceived.

As mentioned above, in order to manufacture ultra-thin steel sheets, it is necessary to increase the reduction ratio in cold rolling, which deteriorates the cold rolling properties of the material. The reason for poor cold rolling properties is that the rolled material is hard. As a result of studying the manufacturing conditions to make the rolled material soft and have excellent cold rolling properties, we found that by performing all rolling at a hot rolling finish temperature FT at a low temperature below the Ar3 transformation point and increasing the grain size. I found out something.

Figure 7 shows FT (hot rolling finishing temperature) and HHT (H
orse power Hour per Ton)
(Rolling power consumption)
It has been clarified that T decreases by about 70% when rolling is carried out at a temperature of F higher than the Ar3 transformation point than when rolling is carried out at a temperature of FT exceeding the Ar3 transformation point.

However, when FT is hot rolled at a temperature below the Ar3 transformation point and subjected to continuous annealing, there is a problem that the f value becomes small. Figure 2 shows ordinary low carbon At
Using continuous cast killed steel material, hot rolling is done at FT of 770°C.
It shows the relationship between the f value and the yield strength for each annealing condition when a hot-rolled steel strip obtained by performing OT at 0°C to 00°C is subjected to different annealing after cold rolling. In the figure,
The hatched areas indicate areas necessary to improve drawability and prevent warping of the steel plate during painting. As mentioned above, when the FT is low, the rollability of the cold-rolled material is improved, but as shown in Figure 2, in the continuous annealing (OAL) method that performs O, A, treatment, the f value decreases under certain conditions. It turns out that there is a fatal problem of low levels.

Therefore, we used a material obtained by hot rolling with a low FT and then cold rolling. A. We investigated a method to increase the F value using the CAL method. First, FT: 77
00C, OT: The relationship between the Mn content and the f value of the steel sheet was investigated under the CAL method conditions of 0° C. and Teo, A@ treatment. The results are shown in FIG. As a result, it was found that reducing the Mn Ji of the unsliced material can improve the f value even for FT low temperature materials.)4n:o, x(1
For 7% low Mn material, FT: 7? θ'C,C!
T: AKO'C, under the CAL method conditions of OA treatment,
The relationship between slab heating temperature (SRT) and f value was investigated.

Figure 9 shows this relationship, where SRT is 173
It was found that the Y value can be greatly improved when the temperature is lower than 0°C. The reason why these factors improved the f value is not fully understood, but it is thought that they were useful during heating in the heating furnace. In FIGS. 3 and V, hatched areas indicate areas necessary to improve drawing workability.

Furthermore, the influence of ci and winding temperature (C!T) on Δr9 is calculated by comparing Mn: 0. /S%, SRT: /1
000C, FT A sample manufactured by the CAL method with O, A, and treatment at near 70°C was investigated. The results are shown in Figure S. In the figure, the hatched area indicates the area necessary to improve drawing workability and reduce the size of the selvedge. According to the same figure, as the f value increases, Δr decreases, but there is a condition in which the Y value is especially large and Δr decreases, and this also applies to the test conducted at FT: 770°C. : Approximately o, obq6 or less, OT:
bgo°C. The reason why the T value is large and the Δr value is small under these conditions is that as the OT increases, the crystal grain size increases due to self-annealing, and carbides aggregate and coarsen, which greatly affects the recrystallized texture. This is thought to be the result of

Based on the above results, the yield strength of the steel plate is high, no curling of the steel plate occurs even when coating with a single roll coater, and stable drawability is achieved in the can manufacturing method using the drawing process. Low carbon A
/As a result of further research using cast materials for killed steel parts, we found that the hot rolling conditions are especially important, and the steel billet was rolled at 100θ prior to hot rolling.
'C~//! ;Heat to 0℃ and set FT to 7 at Ar3 point or below.
Hot rolled to 006C or higher, CT to 1IO0C~70
It was newly discovered that the desired ultra-thin steel sheet for cans can be manufactured by winding at θ0C and performing recrystallization-rapid cooling temporary aging treatment in a continuous annealing furnace as the sweet annealing conditions. It is.

As summarized above, the present invention limits the range of components of continuously cast steel slabs for trench armor plate material. This composition range is necessary to give the resulting ultra-thin steel sheet the desired attention.

The reason for limiting the component range 1 for each component will be explained below.

C is an important component that suppresses the growth of recrystallized grains, and C
If the amount is increased, the crystal grain size becomes smaller and a product with a high degree of heat treatment can be obtained. The amount needs to be 0.07 inches or more.

Sl degrades the corrosion resistance of tinplate, makes the material extremely hard, impairs cold rolling properties, and deviates from the desired degree of tempering, so its amount must be kept at 0.06% or less. be. Therefore, it is not necessary to intentionally add Sl during steel manufacturing, and it is sufficient to limit the amount of 8102 in the refractory to the extent that it is reduced by A/ in the molten steel and remains.

A certain amount of Mn is necessary to promote removal of S and prevent edge cracking in the hot rolled coil. However, as shown in FIG. 3, if the amount of Mn increases, the f-value deteriorates, so the amount needs to be less than 2 s%.

Since P hardens the material and further deteriorates the corrosion resistance of tinplate etc., it is necessary to suppress P to 3% or less.

In relation to Mn, if S is contained excessively, MnS-based inclusions will precipitate in the hot-rolled material and edge cracks will occur in the hot-rolled coil, which are undesirable causes of cracking defects during can manufacturing. must be kept below 0.02 inch.

Al 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 may also cause recrystallized grain growth. Since the amount of Al is suppressed, the amount of Al is 0. I! ; Must be less than %. Note that it is preferable that Al is added in an amount commensurate with the dissolved oxygen in the molten steel so that deoxidation can be completed, and there is no need to leave it as metal Al. However, if the remaining metal htCD1t is too small, the cleanliness of the steel as it is will be poor, so it is necessary to promote flotation and separation of inclusions in the molten steel. One method is to forcibly stir the molten steel through vacuum degassing treatment, etc., but this process has become standardized in recent years, and it is possible to manufacture low-kl steel with high purity. is easy.

If no measures are taken to prevent N contamination, o, oog% of N will be mixed in from the air. Excessive N will harden the material, so it is necessary to limit the N content to 0.00 g% or less.

Steel slabs having the above-mentioned composition range can be easily produced through the steps of various converter furnaces, vacuum degassing treatment, and continuous casting.

Next, the reason for limiting the trap manufacturing conditions will be explained.

Billet heating temperature: lθoo°C ~ t/sO'G When the billet heating temperature prior to hot rolling exceeds 1130°C, the f value of the product steel plate decreases as explained in Fig. 1;
If the temperature is lower than 000°C, the rollability in hot rolling will be extremely poor, so the billet heating temperature should be 1000°C~//! It is necessary to keep it within the range of fO°C.

Hot rolling finishing temperature = 700°C ~ Ar3 transformation point Hot rolling finish chart transformation point If the temperature is higher than the hot rolling finishing inflection point, the Y value will be improved, but as explained in FIG. Since the temperature deteriorates, A r is set to be below the 3 transformation point. In addition, when the Ar3 transformation point is lower than that, the amount of scale generated during heating and hot rolling of the steel billet decreases, so the yield improves. Also, lowering the heating furnace temperature will greatly help save energy. On the other hand, if it is lower than 70θ°C, it becomes hard and cannot be hot rolled. Therefore, the hot-rolling finishing temperature is 700'C-Ar3 transformation temperature and the winding temperature (
C! T): A410° C. to 70° C. The crystal grain size increases due to self-annealing with a coil wound at a high CT. ■The limit temperature is t, qooc, and if the temperature is raised higher than that, the grain size becomes larger. However, as the CT increases, the scale on the surface of the flange plate becomes thicker, which deteriorates the pickling properties in the next process, which is not preferable. Therefore, it is preferable to set the upper limit of CT to 7009C, which is the upper limit of high temperature that does not significantly deteriorate the pickling property. Due to the above, CT Id 4110
'C-')000G.

Cold rolling reduction ratio = gO ~ 9S In a normal 6-stand tandem mill for ultra-thin steel sheets,
Since its rolling capacity is go~9K%, in the present invention, the pressure ratio is also set to go~qs%.

Continuous annealing conditions Recrystallization annealing: Hold at AgO°C or above for m seconds or more By holding at a temperature above tgo°C for 2C seconds or more, recrystallization is performed and crystal grains are grown to increase the grain size.

This improves drawing workability. Annealing temperature is AgO'
0. Although the holding time is lower, the holding time is also shorter than 〃seconds, and the particle size cannot be increased, thus causing hardness and deterioration of drawing workability. Therefore, the recrystallization annealing temperature is bgo
The temperature should be ℃ or above and the holding time should be 〃seconds or more.

Cooling rate: 100C/sec -! ;000c/
sec quenching stop temperature: 5θ0'C or less Regarding the conditions of quenching following recrystallization annealing, 10"C
/ 1ce(!) It is necessary to cool to a temperature of jθθ°C or less at a cooling rate of not less than 5oo°C/IIec. The reason is as follows.

That is, at a cooling rate slower than 10° C./nθC, cementite precipitates halfway during cooling and the degree of supersaturation of C becomes small, so that subsequent overaging does not proceed sufficiently.

on the other hand! When rapid cooling exceeds 00 °C/s, ec, t
This is not preferable because the surface shape of the bushing board deteriorates significantly.

If the temperature at which rapid cooling is stopped exceeds 300° C., the solid solubility of C decreases to near the equilibrium solubility of C in ferrite at that temperature, and overaging does not proceed sufficiently in this case as well.

Overaging treatment = 500°C to 80°C, conditions for overaging treatment that continues for 2θ seconds or more are soo°C to 80°C for the following reasons.
It is necessary to hold the temperature at ℃ for more than m seconds.

That is, at a temperature lower than Jso °C, the diffusion rate of C is low, so overaging does not proceed. On the other hand, at a high temperature exceeding soo°C, the solid solubility limit of C is large, so the solid solubility C'fi cannot be kept low, and therefore age hardening occurs. Moreover, if the holding time does not reach m seconds, overaging will not be completed.

Through the continuous annealing process that includes the above rapid cooling and overaging treatments, the steel sheet becomes softer due to the precipitation of C and N. The value becomes larger, while Δr becomes smaller. Although it becomes softer, the residual solid solution C is larger and the grain size is smaller than that of conventional box-annealed steel sheets.
Yield strength is higher.

Example Steel slabs having the composition shown in Table 1 below were melted in a converter. In particular, those with C of O0θ/chi are subjected to vacuum degassing treatment after melting to obtain molten steel with excellent cleanliness, and then made into steel slabs using a continuous casting machine. These steel pieces were hot-rolled under the hot-rolling conditions shown in Table 7 to form a 23 mm hot-rolled copper strip, which was then pickled to descale. Then, it was cold rolled to a thickness of 0.3 in a 6-stand tandem mill (rolling ratio: about g7). Subsequently, the cold-rolled steel sheets were annealed under the various annealing conditions shown in Table 1.

Table 2 In Tables 1 and 2, "CAL-A" refers to continuous annealing in which after recrystallization, rapid cooling is performed, followed by over-aging treatment,
"AL-B" is a continuous annealing process with a simple cycle of cooling to room temperature after recrystallization, and "box annealing" involves recrystallization from the outside in a batch-type annealing furnace, followed by cooling to room temperature.
This is a method that takes time.

After the annealing, each steel plate was subjected to temper rolling at a rolling reduction ratio of 6I), and then tin-plated on a halogen-type uniform tin plating line. Samples were taken from these tinplates.

A tensile test was conducted on each sample to measure the yield strength, a separate tensile test was conducted to determine the Y value and the Δr value, and the hardness was also measured. In addition, samples were actually smoked using a roll coater, and the occurrence of scratches on the painted surface due to coater warping was investigated.

Subsequently, the sample was drawn and made into a one-piece can, and the can was evaluated. The defects that occurred in the cans were classified into the following three items.

Fracture: The can body was broken at some point during the drawing process and the can did not become a can. Wrinkling: The can was formed into a can, but "wrinkles" appeared on the can body wall. Edges formed after nibless processing. Table 1 shows the overall evaluation of the distance between the ears of the flange of the can. '4/ In the table, the underlined items do not meet the conditions of the present invention.

, 44 are shown in the table, and the comparative example shows that the extra-R steel plate manufactured by the method of the present invention has a high yield strength and a large F value.
It has excellent drawing processability in terms of its small value, and the cans obtained by tin plating and painting and drawing process will have no scratches or wrinkles on the surface caused by the roll coater. The surface quality was excellent, with no occurrence of "stains," and the ears were small. No breakage occurred during can manufacturing by drawing.

Furthermore, the cold rollability of the ultra-thin steel sheet material according to the present invention was good.

[Brief explanation of the drawing]

Figure 1 shows the rolling power consumption (HHT) and hot rolling finishing temperature (FT
Figure 2 shows the relationship between the F value and the yield strength (
Figure 3 shows the relationship between Mn1l and P value for an ultra-thin steel sheet when the hot rolling finishing temperature is below the A r 3 transformation point (770°C). The chart shown in FIG. 9 is a chart showing the effect of the heating temperature of the cumulative billet on the f-value of an ultra-thin steel sheet when the hot rolling finishing temperature is set to A r 3 transformation point or higher. Figure S is
It is a chart showing the hot rolling winding temperature (CT) of a similar ultra-thin steel sheet and the influence of Ct on the =6h material. Patent applicant Kawasaki Steel Co., Ltd. Representative patent attorney Mura 1) Politics 1.0 1.5 2.0
＃曾：I＞p element Ai 小 1t dollar million town tan: 0.15
°/,)SRT: 11006C

Claims (1)

[Claims] 1, C: 0.071% or less, Si: o, ob
% or less F, Mn: o, , 2s or less, P: 0.
03% or more 1:, S: o, o or less, Al: 0. /
! ; N: 0.0θg or less; A 4-strand cast steel piece containing F, with the remainder being substantially Fe, was heated by copper plate Il! temperature to 7000℃~/15θ℃, hot rolling finishing temperature to Ar3
Hot-rolled at 70θ°C or higher below the transformation point, coiled at a coiling temperature of 0°C to 700°C to form a hot-rolled steel strip, then pickled, and then reduced to gθ~ The obtained cold-rolled steel sheet was cold-rolled at 95° C. and held at a temperature of 480° C. or higher for 9 seconds or more in a continuous annealing furnace, then 500° C.
lO℃/@ec -soooC/s to temperatures below ℃
ec (1) Cool at the cooling rate and further cool down to 5oo0C~3
It is characterized in that it is maintained at a temperature of 30° C. for 9 seconds or more and then cooled to room temperature. A method for manufacturing ultra-thin steel sheets for cans that have high yield strength and excellent drawing workability, and particularly have small in-plane anisotropy.