JPH0152450B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a tin-plated or stain-free steel sheet, and more particularly, the present invention relates to a method for manufacturing a tin-plated or stain-free steel sheet having a tempering degree of T ₁ to T ₃ by continuous annealing. The tempering degree of tinplate is specified by JISG3303, from soft Rockwell hardness (H _R -30T) to T ₁ (49±3), T ₂ (53±3), and T _3.
(57±3), T ₄ (61±3), T ₅ (65±3) and T ₆ (69
±3). Among these, the so-called soft plates T ₁ to _{T 3} are manufactured by the box annealing method, and the hard plates T ₄ to _{T 6} are manufactured by the continuous annealing method. By the way, since conventional continuous annealing furnaces do not have a quenching zone or an overaging treatment zone, only hard plates of T ₄ or higher have been manufactured using conventional continuous annealing furnaces.
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 to manufacture soft plates with _T3 or less. Even with the currently used Al-killed steel or soft-killed steel with a low Al content, only a hardness equivalent to T ₂ can be obtained. Therefore, T1 _- equivalent materials still had to be produced using the box annealing method. However, as described below, the box annealing method has had various problems, so there has been a demand for the development of a method for producing _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 (sticking defects).
Break) occurs and the yield decreases. (2) Because soaking requires several hours or more, C, Mn, etc. are enriched and concentrated in the grain boundaries on the surface of the steel sheet during annealing, resulting in surface defects caused by graphite. In addition, the corrosion resistance of tinplate sometimes deteriorated. (3) The temperature of the coil is high at the outer and inner windings, and low at the middle winding, so the internal hardness of the coil varies widely and it is difficult to obtain a homogeneous original plate. It was also worse. As can be seen from the foregoing, it has been difficult to manufacture so-called soft tin blanks of good quality T ₁ to T ₃ class by conventional box annealing methods. Soft yellowtail 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 serves as a lubricant 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 become large. It is not economical because the yield decreases. The present invention provides a heat treatment degree T ₁ that can be sufficiently satisfied not only by the conventional continuous annealing method but also by the box annealing method.
In view of the fact that it has not been possible to produce tin-plated or stain-free steel sheets with a temperature of ~T ₃ , we developed a soft tin-plated steel plate with a high quality tempering degree of T ₁ ~ _{T 3} and excellent press workability using a continuous annealing method. Alternatively, the object is to provide a method for manufacturing a stain-free steel plate, and by providing the method described in the claims, the above object can be achieved. That is, in the present invention, C0.004% or less and Si0.04%
Below, Mn0.05-0.3%, S0.02% or less, however, Mn/
S ratio 8 or more, P 0.02% or less, Al 0.02 to 0.15%,
The finishing temperature when hot rolling a continuously cast steel billet containing 0.004% or less of N and the remainder essentially consisting of Fe.
After rolling at a temperature of 700 to 880℃, then winding at a winding temperature of 500 to 640℃, then pickling and cold rolling in sequence.
Continuous annealing is performed at 690 to 820℃, and further the rolling rate is 1 to 820℃.
Production of soft tin plate and stain-free steel sheet having a temper degree of T ₁ to _{T 3} by continuous annealing, which is characterized by performing temper rolling within a range of 5% and then tin plating or stain-free treatment. The method is a specified invention. Next, the present invention will be explained in detail. The present inventors have made effective use of vacuum degassing during steel manufacturing to use Al-killed steel slabs with an extremely small amount of C, thereby making it possible to produce original plates with a tempering degree of T ₁ even by continuous annealing. that it can be manufactured;
In addition, by using the Al-killed steel slab in which Nb, which is a carbide-forming element, is optionally added to the Al-killed steel slab, the r value is large and △
Due to the small r value, the material is more suitable for making cans by drawing, and the material is tempered by continuous annealing.
The present invention was completed based on the idea that a _T1 original plate could be manufactured. The present inventors have investigated the effect of solid solution C on the hardness of tinplate,
As a result of systematically investigating the relationship between N and grain size, we found that the less solid solute C and N are present and the larger the grain size becomes, the softer the material becomes.Based on this knowledge, we reduced the amount of solid solute C after annealing. Therefore, it was thought that it would be better to reduce the amount of C in the starting material, molten steel for producing continuously cast billets. On the other hand, when box annealing is performed on a cold-rolled steel plate made from an Al-killed steel continuous casting slab using the normal process, the cooling rate after annealing is slow, so that the C melted in the C melting temperature range is also reduced. Since the solid solution C can be sufficiently precipitated, the remaining amount of solid solution C becomes minute. Also, N is AlN precipitation temperature (400℃ or higher)
Since the annealing temperature and time in the box annealing area are sufficient, almost all of the particles precipitate as AlN, and the annealing time is long, so sufficient grain growth can be measured. It is known that the hardness of tinplate becomes sufficiently soft to allow aging. The present inventors previously invented a method for manufacturing soft tinplate blanks by continuous annealing, and filed a patent application for patent application No. 56-125999.
A patent application was filed under No. According to the method, N
Using Al-killed steel material with a small amount of C and a certain amount of C, the finishing temperature during hot rolling was set in the α + γ coexistence region or γ region, and the coiling temperature was set to a medium temperature within the range in which carbides do not agglomerate. By using a hot-rolled sheet and annealing it at a temperature higher than the recrystallization temperature in a continuous annealing furnace having a quenching zone and an overaging zone, a soft original sheet could be obtained. but,
The hardness of tinplate was T ₂ to T ₃ , and it was not possible to obtain one of T ₁ . The reason for this is that in order to precipitate the solid solute C dissolved during annealing, in order to densely distribute cementite as a precipitation site, the C content is higher than a certain level, and the coiling temperature is set to a medium temperature or lower during continuous annealing. This was because cementite was not sufficiently precipitated even if over-aging treatment was performed in a furnace. 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. It is. In addition, the plated steel sheet with residual solid solution C and N not only undergoes work hardening in the next process of temper rolling, but also undergoes reflow treatment (molten tin treatment) after plating, which makes the plated steel sheet approximately
Since strain age hardening is added after water quenching at 400°C, the increase in hardness increases in proportion to the amount of dissolved 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 extensive research and found that by using the same material and changing the continuous annealing conditions, the tempering degree of tinplate can be increased from T ₁ to _{T 3} .
Furthermore, by producing a tin plate with a temper degree of T ₁ through annealing, and by changing the rolling reduction ratio of the temper rolling on this plate, it is possible to separately produce plates of T ₁ to _{T 3} . The present invention was completed based on the new findings. In general, it is important to increase the r value when making tinplate by press working, but in addition, △r
As mentioned above, it is important to make the value small. The present inventors investigated a method of further reducing △r of the tin plate, and found that it is effective to increase the hot rolling winding temperature as shown in Figure 1, and furthermore, if necessary, Nb It has been found that it is also effective to contain Nb/C in an atomic ratio of 0.3 to 1.0. It is not clear why △r becomes smaller when the hot rolling coiling temperature is increased, but C in steel coarsely precipitates as cementite (Fe ₃ C) at ferrite grain boundaries, and the amount of solid solute C in ferrite decreases. Therefore, it is thought that the r value improves and Δr also decreases. Further, the effect of containing Nb is the same as above, and since Nb is a carbide-forming 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).
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 an extremely small amount of approximately 0.004% or less, it becomes softer, while as the amount of C increases, it becomes approximately 0.01%.
A peak with the highest hardness can be seen in C
On the contrary, as the amount of carbon increases, the hardness decreases, reaching a valley within the range of 0.03 to 0.06%, and as the amount of carbon increases, the hardness increases again. The reason why the steel becomes soft when the amount of C is about 0.004% or less is thought to be that the absolute value of the amount dissolved at the melting temperature of C during annealing is small, so that strain age hardening due to C becomes small. Also, the reason why a peak appears at a C content of 0.01% is that when dissolving C is precipitated, the amount of C is small, so there are few Fe ₃ C as precipitation nuclei, so the migration distance of the precipitation becomes longer, and this causes precipitation to occur during the cooling process. This is because the amount decreases and more remains. Therefore, those containing a certain amount of C exceeding 0.01% are effective for softening. However, when the amount of C increases further, although Fe ₃ C 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 T ₃ or less using a continuous annealing furnace, it is necessary to reduce the C content 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 excessive Si content should be avoided. Therefore, it is important to reduce the amount of SiO 2 as much as possible during the steelmaking stage, and in order to suppress the reduction of SiO ₂ in the refractory by Al in the molten steel, the SiO2 refractory used conventionally is used. Care must be taken, such as using zircon refractories instead. That is,
If Si is more than 0.04%, it will become hard and the tempering degree will be T ₁ to _{T 3.}
Since it is not possible to manufacture a blank base plate, Si is
Must be 0.04% or less. Mn needs to be added to prevent edge cracking in hot-rolled coils, but the edge cracking mentioned above is directly controlled by S, and the addition of Mn can suppress the occurrence of edge cracking caused by S. It's suppressed. Therefore, if the amount of S is small, there is no need to intentionally add Mn, but since S is inevitably contained in steel, it is necessary to add Mn. Mn 0.05%
If it is less than 0.3%, it will not be possible to prevent ear cracking, while if it is more than 0.3%, it will become hard.
Mn needs to be within the range of 0.05-0.3%. In relation to the Mn content, excessive S content will cause edge cracks in the hot-rolled coil, and S-based inclusions will result in press defects, so S must be kept at 0.02% or less, especially when Mn/S If the ratio is less than 8, the above-mentioned edge cracks or press defects will occur, so Mn/S must be 8 or more. Since P is an element that hardens the material and deteriorates the corrosion resistance of the tin plate, it is not preferable to contain it in excess, and the P content must be kept at 0.02% or less. Al is an element that functions as a deoxidizer in the steel manufacturing process, and as its content increases, the purity of the steel increases, but adding too much is economically undesirable, and Since it suppresses the growth of recrystallized grain size, Al needs to be 0.15% or less. On the other hand, the lower limit of Al is essentially added in an amount commensurate with the amount of solid solution oxygen in molten steel.
Since it is sufficient to complete deoxidation, there is no need for Al to remain in the steel as metallic Al, but if this is done, the cleanliness of the tin plate will deteriorate. Furthermore, in order to obtain soft tinplate, solid solution N is added.
It is necessary to fix it with Al and reduce its residual amount. If Al is less than 0.02%, the amount of solid solution N in the steel will increase, so Al needs to be 0.02% or more. Therefore, Al is limited to a range of 0.02 to 0.15%. N is contained as a result of N in the air being mixed in during the steel manufacturing process, but if N is dissolved in steel, a soft steel plate cannot be obtained and N is an unnecessary element, so Therefore, it is necessary to suppress the incorporation of N from the air as much as possible to reduce the N content to 0.004% or less. Nb is a carbide-forming element and has the function of reducing the residual 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, the value can be improved and Δr can be reduced as described above. In addition, even if the recrystallization temperature during continuous annealing is lower than that without adding Nb,
A product with the same level of hardness can be obtained. When manufacturing thin plates for use as tinplate, increasing the continuous annealing temperature will impair threading workability, so a method of lowering the annealing temperature by adding Nb is adopted. If the Nb/C atomic ratio is less than 0.3, the above
The effect of Nb addition cannot be obtained, and on the other hand, if it is larger than 1, it is uneconomical, so the Nb/C atomic ratio is 0.3 to 1.
Must be within the range. In order to manufacture steel, which is the starting material of the present invention, it is necessary to keep the C content to a very small amount of 0.004% or less, and for this purpose, a decarburization reaction must be caused by a vacuum degassing treatment method. There are ways to lower C. On the other hand, the conventional degassing method takes a long time,
Furthermore, it is difficult to reduce C to 0.004% 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, but also reduces the temperature of the molten steel. This causes inclusions to float and separate, resulting in poor steel cleanliness, 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 the 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. It is important to increase the amount of recirculated gas. According to the experiments of the present inventors,
In normal vacuum degassing treatment to decarburize molten steel with a carbon content of 0.03%, even if the ladle molten steel is circulated 5 times, the carbon content remains 0.005%.
However, by increasing the amount of recirculated gas and increasing the recirculation speed as described above, it is not only possible to reduce the C to 0.004% or less with the same rotational recirculation, but also to reduce the C in a short period of time. The same rotational reflux treatment can be achieved within an hour, and furthermore, the temperature drop can 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 billet obtained in this manner, it is necessary to roll the FT at 700 to 880°C and the CT at 500 to 640°C. By the way, FT and CT have the following metallurgical effects. In other words, a steel billet with a normal C content is γ
Depending on whether rolling is performed in the (austenite) region or in the α (ferrite) + γ region, the grain size and texture, which affects drawing workability, are greatly influenced. However, according to the present invention, since the C content was very low at 0.004% or less, no large difference was observed in the recrystallized grain size by FT.
It was also found that there were differences in the r value, and in the case of high temperature FT, as the r value increased, the Δr decreased.
On the other hand, when CT is heated to a medium temperature, the crystal grain size becomes larger, the r value becomes larger, and △r tends to become smaller. Therefore, it was found that there was no need to raise the temperature any higher than that. Note that it is a matter of course that the pickling efficiency deteriorates when the temperature is increased. As a result of the above, FT,
CT can be carried out at a low temperature, but for cans made by press working or plates that are thin and difficult to anneal at high temperatures, the CT should be set to a medium temperature, i.e. 580 to 640°C, in order to coarsen the grain size. things are suitable. This effect is due to the development of the (111) texture by increasing the crystal grain size, as well as the effect of increasing the size of carbides, cleaning the inside of the grains, and inhibiting the amount of C dissolved during annealing, and increasing the CT temperature to medium. This is thought to have the added effect of increasing the AlN precipitation rate and reducing the amount of solid solution N. Also, the degree of tempering
To obtain T ₁ , CT should be heated to medium temperature i.e. 580-640℃
The one that is set is suitable. After descaling the hot-rolled steel strip produced in this way by ordinary pickling and then cold rolling it,
Although continuous annealing is performed, 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 as the amount of C decreases, the recrystallization temperature increases. The cause of this phenomenon is C.
The smaller the amount, the smaller the dislocation density,
This is because internal strain energy becomes smaller. Therefore, in order to obtain the softest tempering degree T ₁ ,
It is necessary to perform high-temperature annealing at 750°C or higher using a medium-temperature CT material to sufficiently recrystallize it.
However, when annealing is performed at 700℃, unrecrystallized structures remain in some areas and become slightly hard, resulting in a lower degree of tempering.
The present inventors found that it becomes equivalent to _T3 . Therefore, by combining the hot rolling temperature and the continuous annealing temperature, it has become possible to obtain a degree of thermal refinement T ₁ due to continuous annealing, which was previously considered impossible, and a degree of thermal refinement T ₃ can also be achieved by performing overaging treatment. I was able to get it without any problems. Furthermore, as mentioned above, by using a soft material that yields a material equivalent to T ₁ after continuous annealing and by utilizing work hardening through skin pass rolling, T ₁ to _{T 3} can be produced separately as shown in Figure 4. I found out. 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 that treatment is less than about 1 point (H _R -30T), and even for materials that are not subjected to reflow treatment, such as stain-free steel sheets, It was found that the ideas and policies described above were sufficient. Next, the present invention will be explained by comparing examples with comparative examples. Example Steel having the composition shown in the table was melted in a 270t bottom blowing converter, and the steel was tapped with a carbon content of 0.03%. Subsequently, after performing R-H vacuum degassing treatment to decarburize carbon to below 0.005%, Al 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. These slabs were rolled at the hot rolling temperatures shown in the table.
After forming a hot-rolled coil with a thickness of 2.6 mm, it was descaled by pickling. Next, it was rolled to an extremely thin plate thickness of 0.3 mm (cold rolling ratio 87.7%) using a 6-stand tandem cold rolling mill, and then subjected to continuous annealing. The heat cycle is 650
℃, 700℃, 750℃, and 800℃ for 60 seconds each. Next, in a temper rolling mill, the rolling rate was 1%, and for Examples 16 to 21, the rolling rate was changed to three levels of 1, 3, and 5%, and the rolling rate was set to 3 levels, 1, 3, and 5%, and the work hardening was performed under the same conditions for Examples 16 to 21. The quality was determined. After temper rolling, #25 tin plating and reflow treatment (molten tin treatment) were sequentially performed in a halogen type electric tinning process to produce tinplate. A sample material was taken from tinplate and its hardness (H _R -30T), r, △
r (△r=rL+rC- _2rD /2) was measured, and a fluting resistance test was performed by bending the sample. The evaluation of the fluting test involves bending the body to correspond to the shaping of the body of a can, and evaluating cases where the body is bent to the extent that it cannot be seen as a product (indicated by an x mark) and cases where it is not (indicated by an ○ mark). ). As is clear from the table, those with an annealing temperature of 650°C became hard due to the low temperature and had poor fluteability. In addition, a material having a C content of 0.005% and not according to the present invention had high hardness and could not obtain a soft tinplate. On the other hand, all of the products according to the present invention are made of soft tinplate, and have the following characteristics. (a) Those annealed at a temperature of 450°C or higher have a heat refining degree of T ₁ , while those annealed at 700°C have a hardness corresponding to a heat refining degree of T ₂ or T 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, T ₁ ,
Since it can be made separately into T ₂ and T ₃ , it has the great advantage of being able to integrate the materials. (b) By using a material that can be temper-rolled at a rolling rate of 1% after annealing to obtain a temper degree T ₁ , by increasing the rolling rate, temper degrees T ₁ , T ₂ , and T ₃ can be obtained. Can be divided. 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. (d) For cans made by press working, those with an r value of a certain value or more and a small △r are suitable, but for this purpose, cans made with high FT and CT are suitable. It can be seen that Nb-added material is suitable and that Nb-added material is superior. Furthermore, instead of the above-mentioned tin plating, a stain-free treatment was applied in a conventional manner to produce a stain-free steel plate, and various properties similar to those of the tin plate were measured. )～(d)
Almost the same characteristics were obtained.

【table】

[Table] According to the present invention, it is possible to produce a tin-plated or stain-free steel sheet having a heat treatment degree of T ₁ to _{T 3} , and to produce a tin-plated or stain-free steel sheet having a heat treatment degree of T ₁ to T 1 from a starting material having a heat treatment degree of T ₁ to T ₃ steel plates can be made freely.

[Brief explanation of drawings]

Figure 1 shows the relationship between the hot-rolled sheet coiling temperature °C and △r, and Figure 2 shows the influence of the amount of C on the tinplate hardness and the relationship between FT, CT, and recrystallization temperature of CAL. Figure 3 is a diagram showing the relationship between hardness HMV and CT and recrystallization temperature, and Figure 4 is a diagram showing the relationship between temper rolling ratio (%) and tinplate hardness.

Claims (1)

[Claims] 1 C 0.004% or less, Si 0.04% or less, Mn 0.05 to 0.3
%, S0.02% or less, however, Mn/S ratio 8 or more, P0.02
% or less, Al 0.02 to 0.15%, N 0.004% or less, and the balance substantially Fe. Coiling at a rolling temperature, followed by pickling and cold rolling, followed by continuous annealing at 690-820°C, followed by temper rolling at a rolling reduction of 1-5%, followed by tin plating. Alternatively, a method for manufacturing a tin-plated or stain-free steel sheet having a tempering degree of T ₁ to _{T 3} by continuous annealing, characterized by subjecting it to a stain-free treatment. 2 C0.004% or less, Si0.04% or less, Mn0.05~0.3
%, S0.02% or less, however, Mn/S ratio 8 or more, P0.02
% or less, Al0.02~0.15%, N0.004% or less, Nb
Contains 0.3 to 1 in Nb/C atomic ratio, with the remainder being substantially Fe
When hot rolling a continuously cast steel billet made of
Continuous annealing is performed at 690 to 820℃, and further the rolling rate is 1 to 820℃.
Manufacture of tin-plated or tin-free steel sheet having a temper degree of T ₁ to _{T 3} by continuous annealing, characterized by performing temper rolling within a range of 5% and then subjecting it to tin-plating or stain-free treatment. Method.