JPS607032B2 - How to prevent enamel thin steel sheets from popping - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method for preventing the occurrence of skipping when enameling a thin steel plate, and in particular controls the cooling rate after enameling irrespective of the enameling agent or the composition of the steel plate. This provides a method for suppressing the occurrence of skipping.

As is well known, clumping is one of the most serious defects that occur in enamel products.

The cause of the skipping is that the hydrogen stored in the steel sheet during enamel firing accumulates in a gaseous state at the interface between the steel sheet and the enamel coating as the hydrogen storage capacity of the steel sheet decreases during cooling after firing. The idea is to gradually build up high pressure and blow away the enamel coating. The time it takes for this kind of blistering to occur, that is, the time it takes to reach such high pressure that the enamel film is blown off, varies depending on the steel type, enameling conditions, etc.
It is unknown when it will occur for up to several months, and there is no inspection method for the tendency of chipping to occur, so the occurrence of chipping has become an extremely serious problem in the production of enamel products. Conventionally, in order to deal with the above-mentioned problems, we selected and used steel plates that were less prone to skipping.
Alternatively, methods have been adopted such as pre-treating the steel plate such as pickling or Ni bonding, or using pongee which is less likely to cause skipping. A steel plate that is difficult to cause skipping is a steel plate that has a large amount of hydrogen that can be stored in the steel after enameling, and has a large amount of inclusions in the steel.

Steel sheets containing carbides, nitrides, or sulfides are produced by adding rare earth elements such as Ti, Nb, Zr, B, or Ce, and these inclusions contain a large amount of hydrogen. It was designed to be a place for storage. However, in recent years, the manufacturing of steel sheets has become more widespread in order to save energy, and capped steel is no longer being manufactured.In addition, in the case of steel sheets with special elements added, not only are costs unavoidable, but the surface roughness is also reduced. Unfortunately, there were drawbacks such as bubbles and streak-like defects occurring after enameling. On the other hand, it is known that pretreatment of steel sheets, especially Ni bonding, is effective in suppressing skipping because it reduces the amount of hydrogen occluded in the steel sheets during firing.

However, in AI-killed steel that does not contain inclusions or special elements, even if Ni infiltration is performed, it is not possible to completely suppress the occurrence of chipping, and the enameling process is complicated, so It has the disadvantage of increasing costs. Furthermore, pongee powder that is less likely to cause skipping is pongee powder that generates a large number of bubbles that can absorb hydrogen at the interface between the steel plate surface and the enamel coating, and is also a pongee powder that can be fired at a relatively low temperature.

In other words, in the former case, hydrogen in the gaseous state is absorbed by many bubbles at the interface, which suppresses the skipping, while in the latter, low-temperature firing reduces the amount of hydrogen occluded during firing, resulting in a suppressing effect on the skipping. can get. However, the former type of enamel with a lot of bubbles has a brittle enamel coating layer and is prone to chipping, that is, enamel peeling off at the corners of the product, and other enamel defects.On the other hand, the latter type of pongee, which is fired at a low temperature, has poor corrosion resistance. There are drawbacks. Therefore, it is not possible to use this type of citron in all enamel products that are used for this purpose. In addition, it has been empirically known that the occurrence of skipping can be suppressed by reducing the cooling rate after firing the enamel.

This method is said to be particularly effective when enameling one side of a hot-rolled steel sheet that has poor splinter resistance. That is, the hydrogen occluded in the steel sheet during firing is released from the un-enameled surface during cooling, thereby suppressing the occurrence of splatter. However, in order to slow down the cooling rate, it is necessary to increase the length of a tunnel-type continuous furnace, and when firing in a batch furnace, it is necessary to install multiple heat retention furnaces, which increases equipment costs and increases productivity. There is also the problem of decreased sex. This invention was made in view of the above circumstances, and it solves the drawbacks of the prior art as described above, and is manufactured by continuous casting, which was considered to be unsuitable as a steel plate for enameling due to poor chipping resistance. The purpose is to enable the enameling of ordinary killed steel without chipping defects. In other words, the present inventors have conducted various studies on the influence of the cooling rate after enamel firing on the occurrence of skipping in enamel products, and have found that skipping occurs when the cooling rate is about 2°C/second or more and less than 10 qo/second. It has been found that clumping is suppressed not only at extremely slow cooling rates of about 2°C/second or less, but also at far cooling rates of 1,000/sand or more, particularly 1,500/s or more. That's what happened. Therefore, the method of preventing the occurrence of sagging according to the present invention is to apply enameling to a thin steel plate as a flat plate or after forming it into a shape according to the intended use, and then firing it at a temperature of 90,000 degrees Celsius or less, which is suitable for the pongee. When cooling, the average cooling rate from the firing temperature to 300o0 is set to 100
0/sec or more, preferably 1500/sec or more, looqo
It is characterized by cooling at a cooling rate of /second or less.

As mentioned above, it is not clear why the occurrence of flaking is suppressed by increasing the cooling rate after enamel firing to 10°C/second or more, especially 15°C/second or more, but as the cooling rate increases, It is assumed that the main cause is that the enamel after firing is cooled to a lower temperature in a softened state.

In other words, hydrogen diffusion in steel at temperatures above 300 qo is sufficiently rapid, and at cooling rates below 10,000 qo/sand, the amount of hydrogen in steel is close to the average solubility, so it takes until the enamel completely solidifies. The lower the temperature at which the enamel solidifies, the more hydrogen accumulates at the interface with the enamel coating, and the less hydrogen remains in the steel. It is thought that the hydrogen that causes jumps is the hydrogen that accumulates at the interface between the steel plate and the enamel coating after the enamel solidifies, so the lower the temperature at which the enamel solidifies, the greater the amount of hydrogen in the steel that causes the jumps. It is thought that this will reduce the occurrence of skipping. The method for preventing the occurrence of skipping according to the present invention will be explained in more detail below.

First, the firing temperature after the enameling of the enamel enamel will be explained. The optimum enamel firing temperature is usually determined depending on the type (component) of the pure enamel selected according to the intended use of the enamel product.

In other words, in the case of general fixtures, household electrical appliances, building material panels, etc., Si
A pongee with a low proportion of 02 and a high proportion of alkali metal oxide, which can be fired at a low temperature, is used. On the other hand, for products such as chemical containers and heat exchangers that require excellent chemical and heat resistance, pongee with a high proportion of Si2 is used, so the firing temperature must be raised to some extent. However, the firing temperature is 9
If the temperature exceeds 00q0, the base steel plate will be fired entirely in austenite, and the amount of hydrogen absorbed will increase significantly, causing cracks to easily occur. Furthermore, if the temperature exceeds 90,000°C, the product will deform due to its own weight during firing, making it impossible to obtain a good product shape. Therefore, in the method of this invention, the upper limit of the firing temperature was set to 900C. Next, conditions regarding the cooling rate after enameling firing will be explained.

In the case of this invention, the cooling rate after enamel firing is defined as the average cooling rate from the firing temperature to 300 oo.

After firing, the enamel agent solidifies at about 300 qo, but cooling below 300°C in the solidified state has no effect on suppressing splintering at all.In fact, if the cooling rate after solidification is too fast, the enamel film and steel plate will be damaged. Due to the difference in the thermal expansion coefficients, non-uniform distortion remains, which tends to cause shape defects. In addition, in order to increase the cooling rate to the level specified in this invention, it is usually necessary to perform blast cooling as described later, but blast cooling to 30,000 or less, which does not require high-speed cooling, is not cost-effective. It will be disadvantageous. For these reasons, as mentioned above, 30
It was defined by the average cooling rate to 0q0. In the method of this invention, it is most important to set the cooling rate from the firing temperature to the temperature of 30,000 ℃ at which the enamel powder solidifies to be at least 10 qo/sec. The occurrence of can be effectively suppressed. In the case of ordinary enameling of a secondary enameling, it is common to let it cool naturally after firing, and the cooling rate in this case varies depending on the size of the enameled product and the thickness of the steel plate, but it is usually 1~ The temperature is about 5°C/second. At such a cooling rate, skipping is extremely likely to occur. On the other hand, the cooling rate was changed to 10qo/
It is a novel finding obtained as a result of detailed experiments by the present inventors that the occurrence of skipping can be effectively suppressed by setting the time to 2 seconds or more, as shown in the Examples described later. In order to obtain a cooling rate of 10 qo/sec or more in this way, it is sufficient to perform so-called blast cooling, in which cold air is blown onto the product after firing. However, when firing at a high temperature of about 850 qC or higher, the amount of absorbed hydrogen increases, so some lumps may occur with a cooling rate of 10°C/sec or higher. If the time is longer than seconds, the occurrence of skipping can be almost completely prevented. Therefore, usually 1
A cooling rate of 0 qo/second or more is sufficient, but if the firing temperature is particularly high (although it is less than 900 qo/sec), 1
It is desirable that the cooling rate be 5 qo/sec or more. On the other hand, in order to obtain a cooling rate higher than about 100°C/sec, the amount of air blown for cooling must be significantly increased, which increases energy costs, saturates the effect of suppressing the skipping, and If the cooling rate is 150 oo/sec or more, the enamel coating is likely to crack or break, so in this invention, the upper limit of the cooling rate after firing is set to 10,000/sec.

Examples of this invention will be described below.

Example 1 For two types of steels A and B having the chemical components shown in Table 1, a hot rolled steel plate with a thickness of 2.3 mm was cut at an elevation angle of 12 mm, shot blasted, and then sold under commercially available steel. Hiki Tsumugi' was sewn on one side and fired at three temperatures: 820 qo, 850 qo, and 880 qo.

After firing, the specimen is placed in a bag in a heat retention furnace or compressed air is blown onto the specimen, so that the average cooling rate from the firing temperature to 300 q0 is in the range of 2.5 oo/sec to 40 oo/sec. changed within. FIG. 1 shows the results of examining the presence or absence of skipping in one sample for each firing condition for Steel A and Steel B. From the results shown in Figure 1, A
For both steel and steel B, it is observed that as the firing temperature increases, skipping tends to occur more easily, but even when fired at 880 qo, the occurrence of skipping was completely prevented when the cooling rate was 1500/sec.

When steel B was fired at 880 q○ and cooled at 1000 q/s, some of the specimens were smeared, but in other cases, they were completely slumped at a cooling rate of 10 q 0/s or more. occurrence is prevented. Unless high acid resistance is required, ordinary enamel is generally fired at a firing temperature of 850q0 or less, so by setting the cooling rate to 1000/sec or more, there are fewer inclusions and no lumps. It is clear that the occurrence of chipping can be effectively suppressed even with AI-killed steel, which is easy to kill.Example 2 Plate thickness 1 of two types of steel C and D having the chemical composition shown in Table 2
．． A cold-rolled steel plate was cut into 12 squares, completely degreased in an alkaline solution, pickled in a 10% sulfuric acid aqueous solution of 8000 for 2 minutes, and commercially available Shimohiki pongee was applied on both sides. Then, 82
Firing was performed at three temperatures: 0oo, 850oo, and 88,000.

As in Example 1, the cooling rate from the firing temperature to 300 qo was varied between 2.500/sec and 40 qo/sec. Table 2 shows the results of examining one female sample for each firing condition for Steel C and Steel D to see if the occurrence of splatter occurred. Table 2: Chemical composition of the steel of Example 2 (wt*2nd
As shown in the table, in the case of C steel, skipping does not occur when the cooling rate is 15°C/sec or more at a firing temperature of 850°C or higher, and at a cooling rate of 10°C/sec or more at a firing temperature of 82,000°C. No jumps occurred.

On the other hand, in the case of D steel, the cooling rate is 40o at the firing temperature of 880℃.
o/sec or more, 15°C/sec or more at a firing temperature of 850q0,
At a firing temperature of 82,000 and a cooling rate of 1,000/sec or more, no sputtering occurred. Enamel products made from cold-rolled steel sheets are mainly used for household appliances, building panels, etc., and there are few products that require high acid resistance, so it is best to use low-temperature firing pongee with a firing temperature of 850℃ or less. It is normal and
Therefore, by cooling at a cooling rate of 15° C./second or more after firing, the occurrence of skipping can be sufficiently prevented. In particular, if you use yuzu, which can be fired at temperatures below 820℃,
Even at a cooling rate of 00/sec or more, the occurrence of skipping can be sufficiently prevented. As shown in the examples above, in both cases of enameling one side of a hot-rolled steel sheet (Example 1) and enameling both sides of a cold-rolled sheet (Example 2), the cooling rate must be at least 10q0/sec. The effect of suppressing jumps is recognized.

That is, of course, when using pongee medicine that is fired at a high temperature, it is desirable to have a cooling rate of 1500/sec or more, but when using pure medicine that is usually fired at 800 to 850 oo, the cooling rate is 1000/sec. However, the effect of suppressing the swelling can be sufficiently obtained. In particular, steel B and steel D in the examples are N-killed steels that were conventionally considered to be unsuitable for use in enameling due to the occurrence of chipping. This eliminates the need to use special steel plates, making it possible to significantly reduce the cost of enamel products.

Note that the method of the present invention may be used in combination with other methods for suppressing jumps, such as performing Ni bonding during pretreatment, and in that case, an even better effect of suppressing jumps can be obtained.

As is clear from the above explanation, according to the method of this invention,
Simply by controlling the cooling rate after firing, it is possible to effectively prevent the occurrence of porridge, regardless of the type of steel or the type of enamel. It is possible to obtain enamel products with few defects at low cost without causing defects, and in particular, it has been considered unsuitable for application to enamel products in the past.

Various industrially beneficial effects can be obtained, such as continuous castable AI killed steel being applicable to enameled products.

[Brief explanation of the drawing]

Figure 1 is a correlation diagram showing the influence of the enamel firing temperature and cooling rate after firing on the occurrence of jumps in Example 1, and Figure 2 is a correlation diagram showing the influence of the enamel firing temperature and cooling rate after firing in Example 2 on the occurrence of jumps. It is a correlation diagram showing the influence on occurrence. Figure 1 Figure 2

Claims (1)

[Claims] 1. Applying an enamel glaze to the surface of a thin steel plate, firing the glaze at a temperature of 900°C or less, and then cooling it,
A method for preventing the occurrence of splintering of enameled thin steel sheets, characterized by setting the average cooling rate from the firing temperature to 300°C to 10°C/second or more and 100°C/second or less. 2. The method for preventing the occurrence of skipping according to claim 1, wherein the average cooling rate is 15° C./second or more and 100° C./second or less.