JPS6114215B2 - - Google Patents

Description

[Detailed description of the invention]

In the present invention, a continuous cast billet of low carbon Al killed steel is made into a steel plate through the steps of hot rolling, pickling and cold rolling, respectively, and then continuous annealing is performed on this steel plate to achieve a tempering degree of T. The present invention relates to a method for producing base plates for tinplate and stain-free steel sheets of T-5 and T-4. Nowadays, stain-free steel sheets (TFS) are used in various applications, from those that require strength to withstand internal pressure, such as carbonated beverage cans, to those that require softness and workability, such as squeeze cans. Various degrees of heat treatment (Rockwell T hardness HR30T)
There is something like that. In order to obtain these degrees of heat refinement, conventionally rimmed steel or capped steel has been used and produced by batch annealing and continuous annealing. The types are shown in Table 1.

[Table] However, in recent years, the continuous casting of blanks for tinplate and stain-free steel sheets has progressed, and the use of low-carbon Al-killed steel has naturally begun. The method of finishing low-carbon Al-killed steel sheets by batch annealing has been developed for a long time in the field of cold-rolled steel sheets for drawing for automobiles, etc., so it is a process to obtain the target hardness and other mechanical properties. The conditions are almost established. Therefore, in the field of tinplate as well, by applying the finishing method of batch annealing of low-carbon Al-killed steel sheets, it has become easy to obtain a specified degree of heat treatment. However, the current situation is that no stable technology has been established for T-4 and T-5, which are finished by continuous annealing and do not require over-effect treatment. On the other hand, in the can manufacturing process, as can manufacturing technology has improved, the plate thickness has been reduced to approximately 5 to 20 μm by using T-5 heat treatment instead of T-4 tin.
By making it thinner, we began to reduce material costs. Conventionally, tinplate and TFS sheets with a heat treatment level of T-5 have a high C content of 0.01 to 0.15%, or have a C content of 0.05 to 0.08% and N total 80 to
A 120PPM version has been developed and actually used. However, in this method, as the continuous casting ratio in cold rolling increased, a peculiar phenomenon appeared in cold rolling. In other words, if Al-killed continuous cast material is cold-rolled continuously, slip trouble will occur even when the cumulative rolling tonnage is small and it can still be rolled. This caused the strip to break between the stands. Although the cause of this has not yet been fully elucidated, the following phenomenon was observed. When the roll surface was observed in detail when the strip broke due to slip trouble, it was found that the grid lines that had been seen after roll grinding had disappeared and the strip had become so-called "shiny". Furthermore, when the roll surface was examined using an electron microscope, Al ₂ O ₃ particles were found to be embedded. Furthermore, when comparing the cold rolling deformation resistance of continuous cast steel with capped steel by observing slip trouble and changes in plate thickness and tension between stands just before this phenomenon occurs, it was found that continuous cast steel has greater resistance to cold rolling deformation than capped steel. was found, and the following considerations were obtained. When a continuously cast material with high deformation resistance is continuously rolled, the surface of the work roll is abraded due to the polishing action of the ultra-hard Al ₂ O ₃ particles separated from the strip, and the coefficient of friction (μ) increases. becomes smaller and slips occur between the roll and the strip. When slipping occurs, the roll speed increases, the tension between the stands increases, and the plate thickness becomes locally thinner. When the degree of slip increases, a chattering phenomenon occurs and the strip breaks. This phenomenon tends to occur in the front stand roll, so
The broken strip wraps around the roll and must be replaced, resulting in extensive damage. As countermeasures against this problem, it has been found that in cold rolling, it is effective to replace the rolls in advance or adjust the concentration of rolling oil, but this increases the manufacturing cost and is economically disadvantageous. Therefore, it was concluded that the most effective measure was to reduce the deformation resistance of the rolled material. The inventors of the present invention have separately developed a method for producing base plates for tinplate and stain-free steel sheets with a heat treatment degree of T-4 from continuous casting billets of Al kiddle steel. This method involves hot rolling an Al-killed continuous cast steel billet containing 0.04 to 0.08% C, coiling it at 500 to 580 °C, and subjecting it to continuous annealing through pickling and cold rolling processes. However, since the C content was relatively high, the hot rolled sheet became relatively hard, causing some problems in cold rolling properties. Therefore, the purpose of the present invention is to
After sequentially hot rolling, pickling, and cold rolling, a continuously cast Al-killed steel billet is used as a raw material.
Provided is a method for producing original plates for tinplate and stain-free steel sheets with a tempering degree of T-5 and T-4 by continuous annealing without causing problems in cold rolling as described above. It is about providing. By the way, a steel billet made by continuous casting of low-carbon Al-killed steel is hot-rolled and cold-rolled into a steel plate, which is then continuously annealed to produce a base plate for tinplate and stain-free steel plates. The method has already been
This method is proposed by Japanese Patent No. 55-48574. The invention described in this publication is aimed at a wide range of heat quality from T-1 to T-6, and how to adjust the material components, especially the amount of C, for each heat quality. It has not been made clear whether the product will be adjusted or what manufacturing conditions will be used to manufacture it. In particular, the manufacturing conditions required for T-4 and T-5 are not specifically explained. The present inventors have investigated in detail the manufacturing conditions that affect the hardness of tinplate based on various experiments. As a result, the hardness of tinplate is dominated by solute C, crystal grain size, and solute N in that order. It became clear that the influence of C was the largest, and from this point, it was found that there is an optimal range for the amount of C in the material for each degree of heat treatment, and there is also an optimal range for the coiling temperature (CT) of the hot-rolled sheet. Something new was discovered. The present invention is based on this knowledge, and includes:
The summary is as follows. 1 C: 0.01 to 0.04% (excluding 0.04%)
Continuously cast billets made of low carbon Al-killed steel are hot rolled and coiled at 500°C to 560°C, then pickled and cold rolled, followed by continuous annealing at a temperature above the recrystallization temperature but below the Ac ₁ transformation point. Method 2 for producing base plates for tinplate and stain-free steel sheets having a temper degree of T-5, which is characterized by carrying out heat rolling and then subjecting to temper rolling.
Continuously cast billets made of low carbon Al-killed steel are hot rolled and coiled at 560°C to 580°C (excluding 560°C), then pickled and cold rolled, then Ac 1. A method for producing a base sheet for tinplate and stain-free steel sheet having a heat treatment degree of T-4, which comprises performing continuous annealing at a temperature below ₁ transformation point and then skin pass rolling. The present inventions (1) and (2) will be explained in more detail below. First, the main manufacturing factors that affect the hardness of tinplate blanks during continuous annealing (CAL) are (1) chemical composition, (2) hot rolling coiling temperature (CT), and (3) continuous annealing conditions. . (1) Regarding chemical components, C, Mn, Si, P,
It is well known that when the content of Al, N, etc. increases, the hardness of the original plate increases when batch annealing is performed. However, in the case of continuous annealing of rapid heating and rapid cooling in the present invention, age hardening due to solid solution C and solid solution N is considered in addition to these conditions. One way to increase hardness is to add Si, Cr, etc. during steel manufacturing, but adding these elements not only improves manufacturing costs, but also increases the corrosion resistance of food cans by increasing the amount of these elements. cause significant deterioration. (2) Regarding hot rolling coiling temperature, high temperature coiling (approximately
(580℃ or higher), self-annealing occurs due to the heat held by the hot-rolled coil, and the crystal grains become larger.
This also affects the crystal grain size after cold rolling and recrystallization, resulting in a larger crystal grain size in the final product.
However, at the same time, carbides are aggregated and coarsened. When continuous annealing is performed on such a high-temperature coiled material,
Crystal grain size increases. However, a thick scale layer forms on the surface of the hot-rolled sheet after high-temperature coiling, and the pickling process before cold rolling creates a scale composition that has poor descaling properties, making pickling difficult. Problems arise. (3) Regarding continuous annealing conditions, above the recrystallization temperature
As annealing is performed at a lower temperature in the region below the _A1 transformation temperature, the crystal grains become smaller and the hardness becomes higher. Therefore, in order to obtain a T-5 tin plate, annealing at a low temperature just above the recrystallization temperature is effective in increasing hardness, but this is extremely dangerous in terms of factory production. On the other hand, as annealing is performed at a higher temperature, the crystal grains become larger. As a result, the hardness becomes low. However, high-temperature annealing naturally increases the fuel energy consumption, which is economically disadvantageous. Furthermore, if annealing is performed at a temperature higher than the Ac ₁ transformation point, carbides will precipitate at the grain boundaries, deteriorating the corrosion resistance of tinplate and tinplate, so it is necessary to keep the Ac ₁ transformation point lower or lower. On the other hand, as a phenomenon peculiar to continuously cast materials during cold rolling,
Since slip troubles occur more frequently, it is necessary to take measures against them. In addition, when producing Al-killed steel, during the steel-making process, N is mainly converted into AlN from the air and melts at a maximum of 60 PPM, and some or all of the AlN dissociates during heating of the steel billet in the hot-rolling process. It exists in steel as solid solution N. In view of the above matters, it is clear that the
T-
5 and T-4 tinplates and stain-free steel sheets, using ordinary Al-killed steel without adding special elements, the original sheet can be used to obtain hot-rolled sheets with excellent cold rollability. If manufacturing conditions are required, T-5 and T-4 tin or stain-free steel plates can be manufactured in a technically and economically valuable manner. The present inventors investigated various manufacturing conditions that could satisfy the above objectives, and as a result found the following fact, and were able to determine the above manufacturing conditions from this knowledge. First, we investigated the effects of the carbon content (%) of the tin plate and the hot rolling winding temperature (CT) of the tin plate on the grain size (GSN) and hardness of the tin plate, and the results are shown in Figure 1. That's right. In other words, the particle size increases as the C content decreases, and the CT
It got bigger as it got higher. However, when the C content is lower than 0.04%, the hardness of any CT
The level also shows a tendency to increase. And when comparing the relationship with CT at the same C amount level,
CT: At 650°C, the particle size is the largest, so although the original sheet may be softened, its hardness increases, while at 520°C, the amount of C decreases. As the grain size increases, the particle size increases, which would be expected to indicate a decrease in hardness, but this shows an increase in hardness. Figure 2 shows the tinplates shown in Table 1, C:
0.016% and C: 0.057%, the ferrite structure of tinplate, micrographs of cementite, and hardness of tinplate are shown according to the hot rolling and winding temperature. According to Figure 2, the amount of C is high (0.057
%), CT: At 520℃ and 570℃, cementite is finely and densely dispersed, and the ferrite crystal grain size is smaller, but the tin hardness is lower and reaches the T-5 level. On the other hand, those with a lower C content (0.016℃) and the same CT have larger ferrite grain sizes and less cementite, but those with a CT of 520℃ have a lower T.
It is found that it satisfies tinplate hardness of -5 level. As mentioned above, the tin plate made of Al-killed continuous casting material and continuously annealed is
As the C content decreases, the crystal grains become larger, but
It has been newly discovered that the hardness of tinplate increases, and that when the hot-rolling temperature is increased, crystal grains also become larger, but the hardness of tinplate also increases. . The above facts are very different from the tinting phenomenon caused by batch annealing. These causes are due to the fact that when the amount of C in the original sheet is small, there is less cementite as precipitation nuclei, and when the hot rolling winding temperature is increased, cementite aggregates and becomes coarser, increasing the distance that C precipitation travels. As a result, the amount of solid solute C increases because the precipitation of C cannot proceed sufficiently, and as a result, strain aging occurs, and the hardness of the tin increases beyond offsetting the softening due to coarsening of crystal grains. This is thought to have increased. It is considered that the hot rolling coiling temperature in the intermediate range is a region where cementite is not aggregated and coarsened, and the crystal grains become large, resulting in low hardness. Next, we investigated the effect of the amount of C in the hot-rolled sheet on the cold rollability of the hot-rolled sheet made of continuously cast Al-killed steel slabs.
CT: The cases of 520℃, 570℃, and 650℃ were investigated. The results are shown in FIG. According to this, as the amount of C decreases and the CT increases, HHT (Horse
It was found that rolling power (hour per ton) (rolling power consumption) was lower. In addition, as for the pickling property of the hot-rolled coil, as the CT becomes higher, the pickling efficiency becomes worse. As explained above, solid solution C has a large influence on the hardness of tin plate, and therefore, there is an optimal range for the amount of C in order to obtain the target hardness. Furthermore, the present inventors have newly found that the coiling temperature of hot rolling is related to the precipitation of solid solution C through changes in the morphology of cementite, and that there is also an optimum range for the coiling temperature. By the way, in the invention of Japanese Patent Publication No. 55-48574 mentioned above, when the hot finishing temperature is the temperature at which the Ar ₃ transformation point occurs,
The hot rolling finishing temperature was set to Ar ₃ because the generation of massive carbides reduces the number of nuclei in which C precipitates during cooling, which leads to a large amount of solid solution of C and N, which increases age hardening.
It is limited to points below. In contrast, as explained above, the present inventors found that the lower the hot rolling coiling temperature, the more finely the carbides are dispersed, and on the other hand, as the coiling temperature becomes higher, the carbides aggregate and become coarser. In other words, it has been newly discovered that the difference in the form of carbides caused by changes in the winding temperature affects the hardness of tin. Therefore, in the present invention 1, a steel piece with a predetermined hardness of T-5 class can be manufactured by easy cold rolling using an Al-killed steel piece by continuous casting and continuous annealing without overaging treatment. is necessary for
And sufficient manufacturing conditions are such that the C content of the steel billet is 0.01 to 0.04.
%, the hot rolling winding temperature is 500°C to 560°C. According to the first invention, the hot-rolled sheet can be made soft under the above conditions, so that the deformation resistance is reduced during cold rolling, and on the other hand, after continuous annealing, a hard sheet can be obtained. Although it may seem contradictory at first glance, this effect is actually produced. Therefore, by using continuously cast Al-killed steel pieces as raw materials and continuously annealing them, we can produce comparatively soft T-4 tin plate and stain-free steel plate.
As a necessary and sufficient condition that the steel billet can be manufactured by easy cold rolling, the C content of the steel billet is 0.01% to 0.04% as in accordance with the present invention 2.
% (excluding 0.04%), and the winding temperature of the hot rolled sheet is 560°C to 580°C. In order to produce a soft product by batch annealing using low carbon Al killed steel, the amount of C should be lowered.
The hot rolling coiling temperature may be set to a high temperature, but in order to produce a soft product by continuous annealing, when the amount of C is low, it is necessary to lower the coiling temperature than in the case of batch annealing. As a result, the present inventors have obtained new knowledge that it is possible to manufacture T-4 tin plate blanks by a method with excellent cold rolling properties. The present invention 2 is characterized in that it was invented based on such new knowledge. In addition, regarding the steel sheet components in Present Inventions 1 and 2, there is no need to specially control the components other than element C.
There is no need to excessively remove P or S, and there is no need to add a particularly large amount of Mn ore. Mn is 0.60% or less, P
is 0.025% or less, S is 0.030% or less, Sol.Al is 0.020
~0.150% normal low carbon Al killed steel composition is sufficient. Next, in the present inventions 1 and 2, the basis for determining the upper and lower limits of the C amount range and the hot rolling coiling temperature range as described above will be described. C: 0.01 to 0.04% (excluding 0.04%) If the C content of the steel slab is less than 0.01%, it is difficult to decarburize in steelmaking. On the other hand, if it exceeds 0.04%, the amount of cementite in the hot rolled sheet increases, the number of recrystallization nuclei increases, the crystal grains become finer, the hot rolled sheet becomes harder, slip trouble is more likely to occur, and cold rolling properties deteriorate. do. Furthermore, since the amount of solid solute C is small even after cold rolling and annealing, age hardening is weakened and the original sheet becomes soft and cannot reach the T-5 level. On the other hand, in the case of C: 0.01 to 0.04%, the crystal grains of the hot rolled sheet become relatively large and soft, resulting in low rolling deformation resistance and good cold rollability. When the hot-rolled sheet is rolled up at 500℃ to 560℃, the original sheet after annealing has a large amount of solid solute C, so age hardening due to the precipitation of C occurs sufficiently, and the original sheet satisfies the T-5 standard. can. Further, when the hot rolled sheet is wound up at a temperature of 560°C to 580°C, the age hardening of the annealed original sheet is weakened and the original sheet can satisfy the T-4 standard. Therefore, in both inventions 1 and 2, the amount of C is 0.01 to 0.04.
%. However, 0.04% will be excluded in order to avoid duplication with inventions filed on the same day as this application by the present inventors. Hot rolling coiling temperature: 500℃ to 560℃ (Invention 1) 560℃ to 580℃ (However, 560℃ is not included) (Invention 2) Until now, the lower limit of the coiling temperature is 500℃.
At temperatures lower than 500℃, except for special experimental materials,
This is because there is little experience of winding, so there is a fear that it may cause trouble to the winding equipment.Also, because the hot plate coil is not sufficiently self-annealed, the crystals in the hot rolled sheet may be fine. This is also because it is expected that the hot-rolled sheet will become hard over time, making cold rolling difficult. On the other hand, when the temperature exceeds 560℃, the hot rolled sheet contains solid solution C.
Precipitation increases and crystal grains also become larger. This affects the cold-rolled sheet after annealing, weakening age hardening, and since the crystal grains are also large, the hardness of the original sheet becomes low and cannot reach the T-5 level. Therefore, in the present invention 1, the winding temperature is set to 500°C to 560°C. On the other hand, in the second aspect of the invention, the winding temperature is set to exceed 560° C. in order to aim for a refining degree of T-4.
However, at temperatures above about 580℃, more solid solution C in the hot-rolled sheet precipitates and the crystal grains become larger, which also affects the cold-rolled sheet after annealing, weakening age hardening and making the crystal grains larger. Therefore, the hardening of the original sheet further decreases, and the degree of heat treatment becomes lower than the T-4 level. In addition, as the hot-rolling winding temperature increases, the oxide film of the hot-rolled sheet becomes mainly composed of magnetite (Fe ₃ O ₄ ) and becomes denser, which deteriorates the descaling properties and reduces the pickling time. takes a long time. Furthermore, the cementite becomes coarse and it becomes difficult to apply Sn plating on the cementite on the surface of the original plate, resulting in a decrease in the corrosion resistance of the tin plate. Figure 4 shows the hot rolling coiling temperature (CT) and the iron elution amount (μ
CT ^:
It has been revealed that the amount of iron eluted increases rapidly when the temperature exceeds 580℃. The above-mentioned ISV test is a test method that measures the amount of Fe eluted from tinplate specimens under test conditions that mimic the reaction of canned food in order to determine the corrosion resistance of the surface of the original plate and the plating layer before plating. Corrosion resistance is evaluated based on the value. As described above, in the present invention 2, the winding temperature is set to 560°C.
The temperature is set at ~580℃. Examples of the present invention (1) and (2) will be described below. Example 1 (Invention 1) In steelmaking, the amount of C was 0.01%, 0.03%, 0.07%,
The target was 0.13%, and the other components were within the range of normal Al-killed steel, and the steel was refined and tapped at one charge. In addition, those aiming at C: 0.01% and 0.03% were decarburized by vacuum degassing treatment. A slab was manufactured from this molten steel by continuous casting. Table 2 shows the analytical values of the components of the molten steel in the tongue steel at this time. The content of each component other than C is that of a normal Al-killed steel piece.

[Table] Next, the hot finishing temperature is applied in the γ region, and the plate thickness is
Hot rolling was carried out to a thickness of 2.6 mm. The coiling temperature of the hot-rolled sheet was set at 520°C, 550°C, and 600°C or higher, and the hot-rolled sheet was water-cooled and immediately wound to form a coil, thereby performing self-annealing. These hot-rolled coils were then subjected to normal pickling and cold rolling to form cold-rolled sheets with a thickness of 0.32 mm, and the maximum temperature was Annealing was performed with the targets of 600℃ and 650℃. After annealing, the rolling reduction is 1.5 using a 2-stand temper mill.
Temper rolling was carried out with a target of ±0.2%. After removing defective parts in the coil preparation line, halogen type electric tinning was performed. After plating, the tin-plated plate was electrically heated to 230 to 250°C to remelt the tin, and immediately cooled with water. After collecting representative samples of each of these tinned items, Rockwell T
Hardness was measured. The results are shown in Table 2. Note that the descaling properties (pickling properties) of the hot rolled sheets were evaluated on three levels, and the results are also shown in Table 2. In addition, in order to examine the cold rollability of the hot-rolled sheet during the cold rolling process, HHT (rolling power consumption) was measured, slip trouble phenomena were observed, and each charge example was evaluated for these. The results are also shown in Table 2. The hardness of tin plate with heat treatment level T-5 is 65±3 (target), but in Table 2, the only types that can satisfy this condition are A1, A2,
A4, B1, B2, B4 and C3, D1, D2,
It is D3, and the others are out of standard. However, regarding pickling properties, A4 and B with higher CT
4 is of course bad and lacks economy. Furthermore, when cold rolling properties are evaluated by HHT, those with a low C content are small and are excellent from the viewpoint of energy saving.
In addition, when the C content is high and the material is used for hot-rolled sheets, slip trouble occurs. Of the A and B charges with low C content, the ones that can be produced most qualitatively and economically are:
CT: A1, A2 and B of 520℃, 550℃ (target)
1, B2. Example 2 (Invention 2) In steelmaking, C content was targeted at 0.01%, 0.03%, and 0.07%, and other components were refined with one charge each within the composition range of ordinary Al-killed steel. Steel was tapped. In addition, those aiming at C: 0.01% and 0.03% were decarburized by vacuum degassing treatment.
A flap was manufactured from this molten steel by continuous casting. Table 3 shows the analytical values of the components of the molten steel in the tundish at this time. For each component other than C,
This is the content of normal Al-killed steel pieces.

[Table] Next, hot rolling, pickling cold rolling, and continuous annealing were performed in sequence under the same conditions as in Example 1, and after annealing, skin pass rolling was performed using a two-stand temper mill with a target rolling reduction of 0.8 ± 0.2%. After removing the defective parts, tin plating was performed in the same manner as in Example 1. After collecting representative samples of each of these tinned items, Rockwell T
Hardness was measured. The results are shown in Table 3. In addition, in the same manner as in Example 1, in order to examine cold rollability, HHT was measured, slip trouble phenomena were observed, and each charge example was evaluated with respect to these. The results are also shown in Table 3. The hardness of tin plate with heat treatment level T-4 is 61±3 (target)
However, A1 and A cannot satisfy this condition.
In the four cases No. 3, B1, and B3, all others satisfied the standards. However, when cold rolling property is evaluated by HHT, the charge of C ₁ to _{C 3} with high C content is HHT.
is large, which is disadvantageous from the standpoint of energy conservation. Of the A and B charges with low C content, A2 and B2 with a CT target of 570°C can be produced most economically and stably. In the above explanation, tinplate and its original plate have been explained, but it is clear that the present inventions (1) and (2) can also be applied to the original plate for stain-free steel sheets.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of the C content of the tin plate and the hot rolling winding temperature (CT) on the grain size (GSN) and hardness (HR30T) of the tin plate. FIG. 2 is a photomicrograph showing the ferrite structure and cementite of tinplates containing 0.016% C and 0.057% C, depending on the hot-rolling and winding temperature.
Note that the crystal grain size and hardness are also shown. Figure 3 shows
It is a graph showing the influence of C content of a hot rolled sheet and hot rolling winding temperature (CT) on rolling power consumption (HHT) during cold rolling. FIG. 4 is a graph showing the relationship between the winding temperature (CT) and the iron elution amount (μg/3in ² ) of #25 tin plate according to the ISV test.

Claims (1)

[Claims] 1C: 0.01 to 0.04% (excluding 0.04%)
Continuously cast billets made of low carbon Al-killed steel are hot rolled and coiled at 500°C to 560°C, then pickled and cold rolled, followed by continuous annealing at a temperature above the recrystallization temperature but below the Ac ₁ transformation point. 1. A method for producing a base sheet for tinplate and stain-free steel sheet having a temper degree of T-5, the method comprising the steps of: 2 C: 0.01 to 0.04% (excluding 0.04%)
Continuously cast billets made of low carbon Al-killed steel are hot rolled and coiled at 560% to 580°C (excluding 560°C), then pickled and cold rolled to Ac A method for manufacturing a base plate for tinplate and stain-free steel sheet having a heat treatment degree of T-4, characterized by performing continuous annealing at less than _one conversion state and then subjecting the material to skin pass rolling.