JPS58197224A - Manufacture of base plate for tin plate and tin-free steel plate by continuous annealing - Google Patents

Abstract

PURPOSE:To manufacture a soft base plate for tin plate and a tin-free steel plate by hot rolling a continuously cast Al killed steel slab contg. Mn and a very small amount of C under specified conditions and subjecting it to coiling, pickling, cold rolling, continuous annealing and temper rolling. CONSTITUTION:A continuously cast steel slab consisting of, by weight, <=0.004% C, <=0.04% Si, 0.05-0.3% Mn, <=0.02% S (Mn/S>=8), <=0.02% P, 0.02-0.15% Al, <=0.004% N and the balance essentially Fe or further contg. Nb in 0.3-1 atomic ratio of Nb/C is hot rolled at 700-880 deg.C finishing temp. and coiled at 500- 600 deg.C. It is pickled, cold rolled, continuously annealed at 690-820 deg.C, and temper-rolled. Thus, a base plate for tin plate and a tin-free steel plate provided with T1-T3 refining degree by the continuous annealing is manufactured.

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing a base plate for tinplate and tin-free steel plate, and in particular, the present invention relates to a method for manufacturing a base plate for tinplate and tin-free steel plate, and in particular, the present invention relates to a method for producing a base plate for tinplate and tin-free steel plate.
The present invention relates to a method for producing a base plate for tinplate and tin-free steel plate having T3.

The tempering degree of tinplate is specified by JI8G3303, which ranges from soft Rockwell hardness (HR-30T) to TI (49±3) and T2 (53±3).

T3(57±3), T4(61±3),'r5(・6
5±3) and T6 (69±3). Among these, the so-called soft plates of T1 to T3 are manufactured by the box annealing method.
Hard plates of 4 to T6 are manufactured by continuous annealing.

By the way, since the conventional continuous annealing furnace does not have a quenching zone and an overaging treatment zone, only 14 or more hard plates could be manufactured using the conventional continuous annealing furnace.

However, recently, continuous annealing furnaces with a quenching zone and an overaging zone have been put into operation, and patents have been published for the technology for manufacturing soft plates of T3 or less. Even if we use rainbow-killed steel or soft-killed steel with a low M content, we can only obtain a hardness of T2-grade steel. Therefore, T1-equivalent materials still have no choice but to use the box annealing method. However, as described below, there were various problems with the box annealing method, so there was a demand for the development of a method for manufacturing T1 to T3 materials by a continuous annealing method.

That is, it is known that the box annealing method has the following drawbacks (1) to (3).

(1) Since annealing is performed in a tight coil state, increasing the annealing temperature may cause sticking defects (StickingBr).
eak ) occurs and the yield decreases.

(2) Because soaking requires several hours or more, C, Mu, etc. are enriched and concentrated in the grain boundaries on the surface of the steel sheet during annealing, and as a result, surface defects caused by graphite occur. In some cases, the corrosion resistance of tinplate may deteriorate.

(3) The temperature of the coil is high in the outer and inner windings, and low in the middle winding, so the variation in the internal hardness of the coil becomes large and it is difficult to obtain a homogeneous original plate, resulting in flatness. It was also worse.

As can be seen from the above, it has been difficult to manufacture so-called soft tin blanks of good quality T1-T3 grade using the conventional box annealing method.

Soft tin is mainly used for the bodies of three-piece cans, but it is also used for can bodies made by press working. When used for can bodies, in addition to being soft, it must also have excellent press workability, and in particular, it is required that the in-plane anisotropy of the r value be small. Generally, when press working is applied to tinplate, the tin layer on the surface plays the role of lubrication during the press process, so the r value does not need to be very large, but if the in-plane anisotropy is large, the earrings will not be large enough. , yield is reduced and it is not economical.

The present invention is based on the fact that not only the conventional continuous annealing method but also the box annealing method has not been able to produce tinplate and tin-free steel plates with a quality that satisfies the element content. Continuous annealing method achieves high quality T1 heat quality.
The object of the present invention is to provide a method for manufacturing a soft tin plate and a tin-free steel plate material having excellent press workability of T3, and the above object is achieved by providing the method described in the claims. be able to.

That is, the present invention provides C0,004 and below, Si0
．． 04% or less, Mn 0.05-0.3%, 80.0
Less than 2%.

However, Mn/8 ratio is 8 or more, Po is 0.02% or less, 1L10.
02 to 0.15%, N O, 004% or less, when hot rolling is applied to a continuously cast steel billet containing Nb at an Nb/C atomic ratio of 0.3 to 1 if necessary, and the remainder substantially consisting of Fe. The finishing temperature was set at 700 to 880 t:', and the material was rolled up at a coiling temperature of 500 to 640 C, and then sequentially subjected to pickling and cold rolling, followed by continuous annealing at 690 to 8201:l'. The present invention also relates to a method for producing original plates for soft tinplate and nine-free steel sheets having a temper degree of T1 to T3 by continuous annealing, which is further characterized by performing temper rolling.

Next, the present invention will be explained in detail.

The present inventors have successfully made use of vacuum degassing treatment during steel manufacturing to use rainbow-killed steel slabs with an extremely small amount of C, thereby producing an original plate with a tempering degree of T1 even by continuous annealing. In addition, by using an acid-killed steel slab in which Nb, a carbide-forming element, is optionally added to the Niji-killed steel slab, the r value is large and △r is small, making it possible to draw. The present invention was completed based on the idea that it is possible to manufacture an original plate with a heat treatment degree of T1 using a continuous annealing method using a material more suitable for making cans.

The present inventors systematically investigated the relationship between solid solute C9N and crystal grain size on the hardness of tinplate, and found that the smaller the solid solute C and N and the larger the crystal grain size, the softer it becomes. Based on this knowledge, it was thought that in order to reduce the amount of solid solute C after annealing, the amount of C in the starting material, molten steel for continuous casting billet production, should be reduced.

On the other hand, when box annealing is performed on a cold-rolled steel plate made from a continuous casting slab of Niji-killed steel using the normal process, the cooling rate after annealing is slow for C, so that the C melted in the C melting temperature range is also Since sufficient precipitation is possible, the remaining amount of solid solution C becomes minute. In addition, since the annealing temperature and time in the rainbow N precipitation temperature range (4000 or higher) are sufficient, almost all of the N is precipitated as UN, and the long annealing time makes it difficult to measure sufficient grain growth. Therefore, it is known that the original plate after box annealing becomes soft and non-aging, so that the hardness of the tin plate becomes sufficiently soft.

The present inventors previously invented a method for manufacturing a soft tin blank plate by continuous annealing and filed a patent application for the same in Japanese Patent Application No. 125996/1982. According to the above method, the amount of fat is small;
In addition, an acid-killed steel material containing a certain amount of C is used, and during hot rolling, the finishing temperature is set to the α-10-γ coexistence region or the γ region, and the coiling temperature is set to a medium temperature within a range where carbides do not agglomerate. A soft original plate could be obtained by annealing the plate at a temperature higher than the recrystallization temperature in a continuous annealing furnace having a quenching zone and an overaging zone. However, the hardness of tinplate was T2 to T3, and it was not possible to obtain a tinplate with a hardness of T1. The reason for this is that in order to precipitate the solid solute C dissolved during annealing, in order to densely distribute cementite as precipitation sites, continuous annealing is performed with a certain amount of C included and the coiling temperature below medium temperature. Even if over-aging treatment was performed in a furnace, cementite was not sufficiently precipitated. In order to promote the precipitation of cementite, it is possible to lengthen the overaging treatment time, but this requires increasing the length of the overaging treatment equipment, which is difficult to implement on an industrial scale. Have difficulty. In addition, the plated steel plate in which solid solution C and N remain does not simply undergo work hardening in the next process of temper rolling, but also undergoes water quenching from about 400C due to flow treatment (molten tin treatment) after plating. As a result, strain age hardening is added, so the increase in hardness increases in proportion to the amount of solid solution elements. Therefore, the present inventors have come to the conclusion that in order to produce a soft tin plate, it is important to adjust the residual amount of solid solution elements to the same level as that of box annealed material.

Based on the above considerations, the inventors of the present invention have conducted intensive research and found that by using the same material and changing the continuous annealing conditions, the tempering degree of tinplate can be increased from T1 to T3, and further annealing can increase the tempering degree of tinplate to T1 to T3. By manufacturing a tin plate with a T1 value and changing the reduction ratio of temper rolling on this plate, a T1 plate is produced.
The present invention was completed based on the new finding that T3 original plates can be made separately.

In general, it is important to increase the r value when making tinplate cans by press working, but as described above, it is also important to reduce Δr. The present inventors investigated a method for further reducing Δr of the tin plate, and found that it is effective to increase the hot-rolling temperature as shown in Fig. 1, and also add Nb to the steel if necessary. Nb
It has been found that it is also effective to contain a /C atomic ratio of 0.3 to 1.0. When the hot rolling coiling temperature is increased, Δr
Although it is not clear why the value becomes smaller, C in steel coarsely precipitates at the ferrite grain boundaries as cementite (Fe3C), and the amount of solid solute C in the ferrite decreases, which improves the r value and reduces Δr. considered to be a thing.

Further, the effect of containing Nb is similar to that described above, and since Nb is a carbide-form element, it is thought that the effect is due to the precipitation of NbC.

Next, the behavior of the constituent elements of the continuous cast steel billet, which is the starting material, and the reason for limiting the composition will be explained.

C is an important element that greatly controls the recrystallization temperature and suppresses the growth of the recrystallized grain size. According to the box annealing method, increasing the amount of C causes the grain size to become smaller and become harder, but in the continuous annealing method In this case, there is no simple tendency for the steel to become harder as the amount of C increases. Figure 2 shows the effect of C content on tinplate hardness at hot rolling finishing temperature (hereinafter referred to as FT) and hot rolling winding temperature (hereinafter referred to as CT at this temperature).
It is shown in relation to the recrystallization temperature of continuous annealing (hereinafter referred to as CAL), and as can be seen from the figure, it shows a very complicated tendency. To explain this from a metallurgical perspective, as the amount of C decreases to a very small amount of about 0.004% or less, it becomes softer, while as the amount of C increases, a peak of the highest hardness is seen at about 0.0 x 4. On the contrary, as the C content increases, the hardness decreases, reaching a trough within the C content range of 0.03 to 0.06%, and as the C content increases, the hardness increases again.When the C content is approximately 10- The reason why it becomes soft when it is less than 0.004% is thought to be that the absolute value of the amount of C dissolved at the melting temperature during annealing is small, so that strain age hardening due to C becomes small.
．． The reason why a peak appears at 01% is that when dissolving C is precipitated, the amount of C is small, so there is less Fe5C as a precipitate nucleus, so the precipitate travel distance becomes longer, and as a result, the amount of precipitate during the cooling process decreases and increases. This is because it remains. Therefore, a material containing a certain amount of C exceeding 0.01% is effective for softening. However, when the amount of C increases further, although Fe5C is present in sufficient quantity, the crystal grain size becomes smaller and becomes hard.

Therefore, in order to produce a soft tin plate with a refining degree of T3 or less using a continuous annealing furnace, it is necessary to reduce the C to 0.004% or less.

Si is an element that not only deteriorates the corrosion resistance of tinplate but also makes the material extremely hard, so it should be avoided to contain Si in excess. Therefore, it is important to apply pressure so that the amount of 8i02 in the refractory is reduced as much as possible during the steelmaking stage. Care must be taken, such as using zircon refractories. That is, if Si exceeds 0.04%, it will become hard and it will not be possible to produce a tin plate with a heat treatment degree of T1 to T3, so it is necessary to keep the Si content at 0.04% or less.

Mn needs to be added to prevent the occurrence of edge cracks in hot-rolled coils, but the above edge cracks are directly controlled by S, and the addition of Mn suppresses the occurrence of edge cracks caused by S. . Therefore, if Si is small, M
Although it is not necessary to add n, it is necessary to add Mn because S is inevitably contained in steel. Mn
If the Mn is less than 0.05%, it will not be possible to prevent the occurrence of ear cracks, while if the Mn is more than 0.3%, it will become hard, so the Mn should be within the range of 0.05 to 0.3%. There is a need.

In relation to the amount of Mn, if excessive S is contained, it will cause edge cracks in the hot-rolled coil, and it will also become S-based inclusions that will cause press defects, so S needs to be kept at 0.02% or less.
In particular, if the Mn/S ratio is less than 8, the above-mentioned edge cracking or pressing defects will occur, so Mn/S must be 8 or more.

P is an element that hardens the material and deteriorates the corrosion resistance of tin plate, so excessive content is undesirable, and P is 0.
．． It is necessary to keep it below 0.02%.

M is an element that performs the function of a deoxidizing agent in the steel manufacturing process, and as its content increases, the purity of the steel increases, but excessive addition is economically unfavorable, and it also reduces recrystallized grains. In order to suppress the growth of the diameter, υ needs to be 0.15% or less.

On the other hand, as for the lower limit amount of rainbow, it is essentially enough to complete deoxidation by adding an amount of rainbow corresponding to the amount of solid solution oxygen in molten steel, so there is no need for it to remain in the steel as metallic rainbow. Although this will not happen, the cleanliness of the tinplate will deteriorate if you do this. Furthermore, to obtain soft tinplate, solid solution N is added.
It is necessary to fix it with a rainbow and reduce its remaining amount.

If the rainbow is less than 0.02%, the amount of solid solution N in the steel will increase, so ht needs to be 0.02% or more.

Therefore, rainbow is limited to the range of OO2 to 0.15%.

13-N is contained as a result of N mixed in the air during the manufacturing process of steel, but if N is dissolved in steel, a soft steel plate cannot be obtained and N is an unnecessary element. It is necessary to suppress the incorporation of N from the air during the steelmaking process to the extent possible to reduce the N content to 0.004% or less.

Nb is a carbide-forming element and has the function of reducing the remaining amount of solid solution C. On the other hand, if a large amount is added, the manufacturing cost will increase, so it is desirable to keep Nb to the minimum necessary. By adding Nb, it is possible to improve the r value and reduce Δr as described above. Furthermore, even if the recrystallization temperature during continuous annealing is lower than that of a material without Nb added, the same level of hardness can be obtained. Therefore, when producing thin plates depending on the purpose of tinplate, if the continuous annealing temperature is raised, the workability of pulling and passing the plate will deteriorate, so Nb
A method is adopted in which the annealing temperature is lowered by adding . Nb
If the Nb/C atomic ratio is smaller than 0.3, the effect of Nb addition cannot be obtained, while if it is larger than 1, it is uneconomical, so the Nb/C atomic ratio needs to be within the range of 0.3 to 1. be.

= 14- To manufacture the steel that is the starting material of the present invention, the amount of C is 0.0.
Care must be taken to keep the amount of C to 0.4% or less, and for this purpose, there is a method of causing a decarburization reaction using a vacuum degassing treatment method to lower the C content.

On the other hand, the normal degassing method takes a long time and also
,004% or less, and the temperature of the molten steel decreases significantly during the degassing process, which not only makes casting work difficult in the next continuous casting process.
As the temperature of the molten steel decreases, the floating separation of inclusions becomes poor and the cleanliness of the steel deteriorates, making it impossible to obtain tinplate of satisfactory quality. Therefore, in order to obtain the starting material used in the present invention, it is important to improve the degassing efficiency by subjecting molten steel to vacuum degassing treatment. For this purpose, in the case of a bottom-blowing converter, it is effective to reduce the blow-off C to 0.03% or less and to increase the circulation speed of degassed molten steel. After removal, increase the amount of recirculation by 7 hours. is important. According to experiments conducted by the present inventors, in normal vacuum degassing treatment for decarburizing molten steel with CO, 03%, even if the ladle molten steel was circulated 5 times, the o, oos% CK decreased only to 4. By increasing the amount of reflux gas and increasing the reflux speed as described above, not only can CO2 be reduced to 4% or less with the same rotational reflux, but also the same rotational reflux treatment can be achieved in a short time. Temperature drop can also be suppressed to a minimum.

The continuously cast steel billet used in the present invention can be obtained by subjecting molten steel in a converter to vacuum degassing treatment at a high recirculation rate as described above, and then continuously casting the steel.

When hot-rolling the steel slab obtained in this way, it is necessary to wind it at a FT of 700 to 880 tl:' and a CT of 500 to 640 C.

By the way, FT and CT have the following metallurgical effects. In other words, whether a normal Ci steel billet is rolled in the γ (austenite) region or in the α (ferrite) + γ region has a large effect on the grain size and texture, which affects drawability. . However, according to the present invention, since the C content was very low at 0.004% or less, there was not much difference in the recrystallized grain size by FT, but there was a difference in r value, and FT high temperature It was also found that as the r value increases, Δr decreases. On the other hand, when CT is heated to medium temperature, the grain size becomes larger, the r value becomes larger, and △r tends to become smaller.
Since the effect was sufficiently observed within the temperature range of 580 to 640C, it was found that there was no need to raise the temperature higher than that. Note that, as a matter of course, when the temperature is increased, the pickling efficiency also deteriorates.

As a result of the above, FT is used for items that only need to be bent and flanged, like the body of a 3-piece can.

CT can be carried out at a low temperature, but for cans made by press working or plates that are thin and difficult to annealing at high temperatures, CT is set to medium temperature, i.e. 580 to 540 C, in order to coarsen the crystal grain size. things are suitable. This effect is due to the development of the (111) texture by increasing the grain size, the increase in the size of carbides, the cleaning of the grains, the effect of inhibiting the amount of C dissolved during annealing, and the effect of increasing the CT temperature to medium. This is considered to have the additional effect of increasing the precipitation rate of A7N and reducing the amount of solid solution N. In order to obtain a high thermal quality T1, it is suitable to use CT at a medium temperature, that is, 580 to 640C.

The hot-rolled copper strip produced in this way is descaled by ordinary pickling, then cold rolled and then continuously annealed, but the recrystallization temperature becomes high because the amount of C is small. FIG. 3 is a diagram showing the relationship between CT and HMV, and shows the relationship between the amount of C and the recrystallization temperature, and it can be seen that the recrystallization temperature becomes higher as the amount of C decreases. The reason why this phenomenon occurs is that as the amount of C decreases, the dislocation density decreases and the internal strain energy decreases. Therefore, in order to obtain the softest material with a tempering degree TI, it is necessary to sufficiently recrystallize by annealing at a high temperature of 750 C or higher using a material made of medium-temperature CT. However, annealing at 700C
The inventors of the present invention have found that if the steel is applied with a heat treatment, an unrecrystallized structure remains in some parts and becomes slightly hard, resulting in a refining degree equivalent to T3. Therefore, by combining the hot rolling temperature and the continuous annealing temperature, it has become possible to obtain a heat quality of 18-TI, which was previously considered impossible, through continuous annealing, and a heat quality of T3 can also be obtained without performing overaging treatment. reached.

Furthermore, as mentioned above, it was also found that T1 to T3 can be separately produced as shown in FIG. 4 by using a soft material that can obtain the material of T1 after continuous annealing and utilizing work hardening by temper rolling. It has been found that since this soft material is almost non-aging, it can be made hard simply by increasing the rolling rate in temper rolling.

On the other hand, in the tinplate plating process, reflow treatment is applied, but the increase in hardness due to this treatment is approximately 1 point (r-tR
-3o'I') or less, and it was found that products that are not subjected to reflow treatment, such as tin-free steel plates, can be sufficiently manufactured using the above-mentioned ideas and policies.

Next, the present invention will be explained by comparing examples with comparative examples.

Steel 270 having the composition shown in the Examples table was melted in a bottom blowing converter, and the steel was tapped to a CO of 0.03%. Then R, -
After performing H vacuum degassing treatment to decarburize to below C08005%, Niji was added and then Nb was added, and Nb was not added. Each of these was cast using a continuous casting machine to promote flotation and separation of inclusions to obtain steel slabs with excellent cleanliness and dust.

These steel pieces were rolled at the hot rolling temperatures shown in the table.2.
After forming a hot-rolled coil with a thickness of 6 mm, it was descaled by pickling. Next, 0.3rn in a 6-stand tandem cold rolling mill
After rolling to an ultra-thin plate thickness of m (cold rolling rate 87.7%),
Continuous annealing was performed. Heat cycles are 650C, 700C,
750t; and 800C for 60 seconds each. Subsequently, the rolling rate was 1% in a temper rolling mill and Example 16
-21 were subjected to the same conditions up to annealing, and only the rolling reduction was set to 3 levels of 1.3.5% to determine the high degree of thermal refinement due to work hardening.

After temper rolling, #25 tin plating and reflow treatment (molten tin treatment) were successively performed in a halogen-type electrolytic tin plating process to produce tinplate. Sample materials were collected from tinplate and hardness ([IR-3oT) r, Δr (Δr=
-The length of each piece was measured, and a fluting resistance test was conducted by bending the sample. In the fluting test, the bending process is performed to correspond to the shaping of the body of a can, and the bending process is performed on cases where the body is bent to the extent that it cannot be sold as a product (marked with an X) and cases where it is not (marked with an O). ).

As is clear from the table, the annealing temperature of 650 G resulted in hardness due to the low temperature and poor fluting properties. Moreover, the hardness of a material not according to the present invention with a C content of 0.005% was high, and it was not possible to obtain a soft tinplate. −
The ones invented by the strength wood are made of soft tin that can be bent easily.
The following characteristics can be seen.

(a) Those with annealing temperature of 750C or higher have a refining degree of T1, but those with an annealing temperature of 700tZ: have a refining degree of 'r2. '['The hardness is equivalent to 3. The reason for this is thought to be that it became hard because it was not sufficiently recrystallized. Therefore, by changing the annealing temperature to two levels for the material manufactured under the same conditions before annealing, T1. Since it can be made separately into T, 2° and T3, there is a big advantage that it can be made by integrating the materials.

60) After annealing, temper rolling is performed at a rolling rate of 1% to achieve temper degree T.
By using a material that can obtain T1 and increasing the rolling rate, the tempering degree TI, T3. It can be made separately from T5. Therefore, even when such a method is used, materials can be integrated, which is a great advantage.

(c) Furthermore, if Nb is not added, although the material quality deteriorates slightly, it is possible to obtain a tin plate that fully satisfies the object of the present invention.

2) For cans made by press working, it is suitable to have an r value of a certain value or more and a small △r, but for this purpose, it is suitable to make cans with high FT and CT. It can also be seen that the Nb-added material is superior.

22- According to the present invention, it is possible to produce base sheets for brushed and tin-free steel sheets having a heat treatment degree of T1 to T3, and to obtain heat treatment degrees of T1 to T3 from a starting material having a heat treatment degree of T1.
You can freely create different original plates.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the coiling temperature C of a hot-rolled sheet and Δr,
Figure 2 shows the influence of C amount on tinplate hardness by FT and C
A diagram showing the relationship between T and recrystallization temperature of CAL, Figure 3 is a diagram showing the relationship between hardness HMV and CT and recrystallization temperature,
FIG. 4 is a diagram showing the relationship between temper rolling ratio (%) and tinplate hardness. Patent applicant Kawasaki Steel Co., Ltd. Representative patent attorney Mura 1) Politics 24-

Claims (1)

[Claims] /, CO, 004% or less, 8i 0.04% or less, Mn O, '05 to 0.3qb, so, o2% or less, provided that on Mn/Sn/S. Po, 0.02% or less, At0.02-0.15%,
Contains N, 0.004% or less, Nb as necessary at a Nb/C atomic ratio of 0.3 to 1, and the remainder is substantially Fe when hot rolled at a finishing temperature of 700. ~880
C, rolled at a winding temperature of 500-640C, then pickled. Production of original plates for tinplate and tin-free steel sheets having a temper degree of T1 to T3 by continuous annealing, characterized in that cold rolling is performed sequentially, followed by continuous annealing at 690 to 820 C, and further temper rolling is performed. Method. When hot rolling the continuously cast steel billet, the finishing temperature is set to 7.
00 to 880C, coiled at a winding temperature of 580 to 640 tl:', then pickled and cold rolled sequentially, then continuously annealed at 740 to 820C, and then rolled at a rolling rate of 1
The manufacturing method according to claim 1, characterized in that skin pass rolling is performed within the range of .about.5.