JPH0660422B2 - How to make enamel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for producing enamel, in particular, using ordinary ordinary steel plates used for automobiles, electric appliances, etc. It is to enable the production of a double-sided or single-sided enamel that is free from nail skipping, bubble defects, and poor adhesion to the same extent or more. Hereinafter, although described as enamel, these refer to steel plate enamel, and cast enamel is excluded.

[Conventional technology]

As is well known, the defects of enamel include nail skipping, bubbles, and poor adhesion, and defects are likely to occur when the combination of a steel plate for enamel and glaze or pretreatment is inappropriate.

Nail skipping is caused by the reaction of water in the atmosphere of a enamel glaze or a baking furnace with hydrogen during firing, and hydrogen enters into the steel, and at the time of cooling it gathers at the interface between the steel plate and the enamel coating, and the pressure of the hydrogen gas causes enameling. It is considered that the film was splashed and generated.

Therefore, as a method of improving the nail-repelling resistance, a method of increasing inclusions and precipitates in steel and occluding hydrogen in the vicinity thereof has been conventionally known, and for example, Ti-C, Ti-S and
Examples of the Ti-REM-S system for producing inclusions and precipitates include JP-A-48-222, JP-A-52-131919 and JP-B-54-3447. Japanese Patent Laid-Open No. 58-1013 discloses a method of forming inclusions and precipitates.

On the other hand, bubble-type defects include copper heads and pinholes, and it is considered that these mainly decompose in steel [C], carbide, etc. during firing and become CO _X gas, which causes bubble-type defects. As a preventive measure or a measure for improving workability, decarburization is performed during molten steel or during annealing.
1553 or JP-A-51-6813.

However, since it seems that inclusions on the surface of the steel sheet are related to the cause of the bubble-based defects, in addition to the [C] source, it is not easy to completely prevent nail popping and bubble defects at the same time.

In addition, poor adhesion is particularly likely to occur with enamelling on both sides once. Generally, in order to improve the adhesion, it is good to increase the surface roughness of the steel sheet or to strengthen the chemical bonding force between the steel sheet and the glaze. In the former, 0.025% or more of Cu is added to steel,
Increase the pickling weight loss, or in the latter case, soak in Ni solution after pickling
(Hereinafter, referred to as Ni dip), there is a method of applying glaze. However, since adhesion failure is likely to occur with enamel applied once on both sides, the surface roughness and Mn amount of the steel sheet are regulated in Japanese Patent Laid-Open No. 51-1311 and (P + S) in the steel composition in Japanese Patent Laid-Open No. 57-63661. ) / Cu is set to 2.0 or less.

On the other hand, as a coated metal product for enamel, a mixture of water-soluble or water-dispersed polymer, an oxidizer and a deliquescent substance is applied to a steel plate surface by glaze and dried. Japanese Patent Publication Sho 49
-41084, and Japanese Patent Publication No. 54-2300 which is almost similar to this.
There is No. 6 bulletin. It is said that these can be excellently processed while being glazed with enamel glaze, and that they can be fired afterwards to give good appearance, adhesion and corrosion resistance as enamel products.

Next, Japanese Patent Publication No. 36-19385 describes that the same oxidation treatment as in the present invention is performed. "The thickness of the oxide film is 0.003 to 0.04 mm (30,000 to 400,000).
It is said that the enamel property is good when it is within the range of Å), but in the present invention, the optimum thickness of the iron oxide film is 50 to 1100Å, which is completely different from the optimum thickness of the above patent.

Further, although the above-mentioned patent does not perform pickling and Ni dipping, the present invention has not been carried out in the past.
It is also a completely new method in that the enamel is applied before the enamel is applied. The coexistence of the iron oxide film and the deposition of Ni improves the adhesiveness of the enamel film, but if either is missing, the adhesiveness is extremely reduced.

Lastly, the present invention is a continuous cast steel that is difficult to be applied once on both sides, and is an ordinary steel plate that is not applicable to the application of enamels in the prior art, and is not found in the prior art. It is a thing. The above patent was applied to mold-cast capped steel where enameling was relatively easy in the era when there was no continuous cast steel, and the surface of the steel sheet was not roughened or Ni dip was performed, and oxidation was performed. Compared to the present invention, the iron oxide film is thick because it is carried out at a higher temperature for a long time, which is different from the present invention. Further, when the above patent is additionally tested, the enamel film has many scale defects and the adhesion is extremely poor.

[Problems to be solved by the invention]

As mentioned above, the enameled steel sheet has a special composition that is slightly different from ordinary ordinary steel sheets, and in particular, there are many inclusions, and the cleanliness index is about 5 times higher than ordinary steel sheets, and JIS G3133 is an enameled steel sheet. It is defined as a decarburized steel sheet. In the prior art, ordinary steel plates, that is, JIS hot-rolled steel plates (JIS G3131) and cold-rolled steel plates (JIS G314) that correspond to JIS standards.
Try to hang it once on both sides or one side using 1),
It was not possible to provide enamel that does not cause poor adhesion.

[Means for solving problems]

The present invention provides an entirely new enamel, which has not been found in the past, in which a normal steel plate is used as a enamel steel plate, and an iron oxide layer is formed on the surface of a hot-rolled ordinary steel plate or a cold-rolled ordinary steel plate having no enamel properties. If present, the iron oxide layer is removed, and the surface of the hot-rolled steel sheet or cold-rolled steel sheet is roughened to a surface roughness R _max of 15 to 60 μm, and then the surface has a thickness of 50 to 50 μm. 1100Å iron oxide layer is formed, then Ni
The gist is a method characterized by contacting with a liquid and performing enamel.

In general, it is common knowledge that enamel steel sheet is completely degreased, pickled after nipping, neutralized, and then glazed in the case of enamel with both sides once. Complete degreasing and pickling to completely remove oil and iron oxide layers. Since it is indispensable to remove the iron oxide layer from the steel plate and the glaze as in the present invention, it is not considered by conventional common sense. Further, it has not been possible to deposit Ni on the iron oxide layer. In addition, there is no conventional common knowledge that it is possible to wrap enamel on both sides of hot-rolled and cold-rolled ordinary steel sheets that are not suitable for enamels.

The present invention will be described in detail below.

The ordinary steel plates targeted by the present invention are JIS G 3131 hot rolled mild steel plates and steel strips (SPHC, SPHD, SPHE, etc.), JIS G 3141 cold rolled steel plates and steel strips (SPCC, SPCD, SPCE, etc.). And JIS
Steel plates and strips of ordinary steel including tin plate (SPB, etc.) of G 3303. Of these ordinary steel sheets and strips, JI
Ordinary steel sheets for enamel applications that do not meet the S standard, that is, ordinary steel sheets and strips that are close to enamel steel sheets and intermediate between enamel steel sheets and ordinary steel sheets and that are conventionally used for enamel applications A steel plate. Of course, JIS G 3133 decarburized steel plate for enamel and steel strip (SP
P etc.) is not included. It should be noted that when these enamel steel plates and steel strips are enameled by the method of the present invention, enamel with fewer claws and bubbles, which are not found in conventional enamel steel plates, can be obtained. Since the purpose of the steel sheet is to be a steel sheet for enamel which has a quality equal to or higher than that of the conventional steel sheet, the steel sheet for enamel and the steel strip are not covered by the present invention. Therefore, the ordinary steel plate referred to in the present invention is an ordinary steel plate excluding ordinary steel plates for enameled applications that are not in the above JIS standard, and in a broad sense, claw jumps,
This refers to a steel sheet that has not been provided with measures to prevent bubble defects and poor adhesion. The composition range of the above ordinary steel sheet is indicated in JIS standard, C: 0.15% or less, Mn: 0.60% or less, P: 0.0
50% or less, S: 0.050% or less, further, Cu is 0.08% or less, Al is 0.08% or less, and Ti is 0.10% or less. In general, if Cu exceeds 0.08%, surface defects due to Cu are likely to occur, and the cost increases, so the content was made 0.08% or less.
Also, the reason for keeping Al at 0.08% or less is that Al content is unavoidable when Al is deoxidized, and as a result of investigating the effect on the purpose, there is no particular adverse effect up to 0.08%, but if 0.08% is exceeded, there is an economic problem. Occurs.

The reason why the content of Ti is 0.10% or less is that it is added to improve the workability in addition to the non-aging property by combining with Ti and N, C to form N and C, in addition to Ti deoxidation, as in the case of Al. However, the effect of the invention of the present invention on enamel is not particularly bad up to 0.10%, but if it exceeds 0.10%, the cost becomes high.

Generally, when baking after glazing in a normal manufacturing process that uses a steel plate for enamel once on both sides, oxidation first occurs on the surface of the steel plate, then the enamel glaze melts, iron oxide dissolves in the enamel, and firing ends. At times, the iron oxide layer disappears and the enamel layer and the steel sheet adhere. At that time, it is considered that excess or deficiency of iron oxide has a great influence on adhesion. However, the proper thickness of iron oxide is unknown, and it is extremely difficult to control it because the enamel glaze clearance, heating temperature, heating rate, atmosphere, etc. are different. Therefore, it is difficult to make a steel plate for enamel having stable adhesion. Further, it is extremely difficult to increase the roughness of hot-rolled and cold-rolled steel sheets of ordinary steel sheets that are not used for enamels, and to make them with good adhesion even if Cu addition or Ni dipping is performed.

Therefore, the present invention, after removing the surface oxide film from the hot-rolled ordinary steel sheet, the surface of the cold-rolled steel sheet as it is, pickled, dull roll rolling, polishing (grinder, paper, shot blasting, electric discharge machining, etc. ) And grinding to roughen the surface. The surface oxide film removal and surface roughening of the hot-rolled steel sheet may be performed within one pickling step.

Regarding the surface roughness of steel sheets, the conventional steel sheets for enameling
R _max is 7 to 20 μm. In the present invention, the range of the surface roughness of the steel sheet is 15 to 60 μm in R _max , and the surface roughness range which is slightly rougher than the conventional one makes the enamel quality good. Here, the surface roughness R _max is represented by an average value of R _{max in} the L and C directions of the front and back surfaces of the steel sheet.

When the surface roughness R _max is less than 15 μm, an iron oxide coating is coated on the glaze and the enamel glaze is glazed and fired, and the glaze shrinkage occurs due to the surface tension of the molten glaze, and the glaze adheres on the steel plate. Occasionally, parts and parts where no glaze is attached may occur. In order to have the effect of anchoring the glaze to the steel plate, a roughness of R _max of 15 μm or more is desirable.

It takes a long time to pick up R _max of more than 60 μm by pickling, and a large amount of smut (dirt) adheres to the surface of the steel sheet, which easily causes bubble defects on the enamel, and the roughness on dull rolls. If it is more than 60 μm, it is difficult to adjust the roughness of the roll surface and wear of the roll surface is severe during use, and therefore it is necessary to change the roll frequently, which is disadvantageous in terms of cost. On the other hand, the number of peaks per inch, PPI corresponding to the above range of R _max is about 90 to 388 peaks / inch, and the center line average roughness Ra is about 0.7 to 62 μm.

Furthermore, shot blasting is suitable for roughening the surface of the steel sheet, but in order to make R _max over 60 μm, it is necessary to make the shot injection pressure extremely high, resulting in high cost in terms of equipment and power consumption. It is very disadvantageous.

The present invention has a great feature in that a uniform iron oxide layer having a proper thickness is formed on the surface of the ordinary steel sheet at least in advance.

The present inventors determined the thickness of the iron oxide layer by measuring the thickness of the iron oxide layer with a weight measurement before and after the oxidation and an ellipsometer. In addition, the iron oxide phase at low temperature (below 570 ℃) is generally Fe ₃ O ₄ .
It is said that it consists of Fe ₂ O ₃ phase, but the Fe ₃ O ₄ phase was considered to be the main component, and the weight increase was divided by the specific gravity of Fe ₃ O ₄ to obtain the above thickness.

As a result, it was found that the optimum thickness of the iron oxide phase was 50-1100Å.

The reason for limiting the thickness of the iron oxide layer to 50-1100Å is 50Å
If it is less than the above range, the iron oxide layer is too thin and the adhesion becomes poor. It is considered that this is because the reaction product of SiO ₂ and iron oxide, that is, iron silicate, is slightly formed at the interface between the steel plate and the enameled layer during firing. On the other hand, even if the iron oxide layer is more than 1100Å, the adhesion is lowered.
This is presumably because the iron oxide film was not completely dissolved in the enamel during firing, and undissolved iron oxide remained at the interface between the enamel layer and the steel sheet.

When a steel sheet with an iron oxide layer thickness of 50 to 1100Å is Ni-dipped and then enameled and baked, the iron oxide film is appropriately dissolved in the enamel, and iron silicate is generated at the interface between the enamel layer and the steel sheet, which is the enamel layer. It is believed that the adhesiveness is improved by acting as an adhesive between the steel sheet and the steel sheet.

The surface roughness of the steel sheet remains on the iron oxide surface with almost the same value. That is, since the residual strain of the deep recesses of the steel sheet surface becomes locally large and deep recess is promoted oxidation, tend to recesses are slightly flattened, the roughness R _max of the whole steel sheet oxide Almost unchanged before and after. Further, after the iron oxide is formed, the roughness of the interface of the steel sheet base iron with the iron oxide can be measured by a roughness meter, an optical microscope or an electron microscope.

In order to form these iron oxide layers on the surface of the ordinary steel sheet as described above, generally, an electric furnace, a hot-air stove, an infrared furnace, a gas furnace,
Oxidize in an oxidizing atmosphere with a high-frequency furnace, direct energization, laser beam, etc. The oxidation temperature is about 50 to 600 ° C. and the treatment is performed for several seconds to several tens of minutes. The oxidation of the treatment is performed in a shorter time as the temperature becomes higher. When oxidizing in a weakly oxidizing atmosphere, naturally, it can be performed at a high temperature for a long time. Besides this, there is also a method of oxidizing in the cooling process immediately after annealing.

The function and effect of the oxide film is to improve the adhesion of the enameled layer to the steel plate as described above, but the other effect is to improve the prevention of bubbles and nail bleeding. That is, when the surface of the steel sheet is oxidized, carbides, nitrides, sulfides, etc. are oxidized and gasified, and components (C, N, S, etc.) that cause bubbles are reduced in the oxide film on the surface of the steel sheet, and thus bubbles are generated. Hateful. Further, the cause of nail skipping is generated by hydrogen generated by the reaction between iron and water in the glaze, so if the surface of the steel sheet is masked with an iron oxide film, this reaction does not occur. This is a very effective method because there are few inclusions (generally less than 0.05%). Usually, hot-rolled and cold-rolled steel sheets that are not used for enamel are prone to claw skipping. . Next, when the enamel of the present invention is subjected to enamel applied once on both sides, Ni dip is applied to the upper layer of the iron oxide layer, or rust preventive oil is applied to the upper layer after Ni dip. Then, various enamel properties are improved by applying enamel glaze on the upper layer, drying and baking.

Contact with the Ni solution is usually made with a dip. Ni dip is an indispensable treatment when the enamel is applied on both sides once. A few percent NiSO ₄ aqueous solution (pH is about 2.5 to 3.0) is heated to about 70 ° C and immersed for a few minutes to perform Ni coating treatment. Then, to neutralize, dry, or to further improve the adhesion,
Apply rust preventive oil to the upper layer. When Ni-dipped on the iron oxide layer, the adhesion amount is 0.1-5.0 g / m ² , which is about 1 / 500-1 / 10 compared with Ni-dipped on the ordinary steel plate surface.
It's enough. In addition, you may apply instead of a dip. The effect of Ni dip is effective in preventing defects in enamel products, but especially suppresses oxidation during firing and diffuses into the silicate iron silicate at the interface between the enamel layer and the steel sheet to improve the adhesion of the enamel film to the steel sheet. .

The action and effect of the above-mentioned oil coating is that the enameled glaze softens at about 500 to 600 ° C at the time of heating, and the oil decomposes and burns at a low temperature until it melts, vaporizing and removing water and oxygen in the glaze. It is believed that this can reduce or prevent the generation of the nail pops and bubbles.

The proper amount of oil applied is 3.0 g / m ² or less per side.
If the amount of oil applied is more than 3.0 g / m ² per side, a large amount of oil will be burned and decomposition gas will be generated during baking, and the enamel glaze will float above the steel plate, peel off, or partially float and glaze Is likely to occur and the cost is high.

As the above rust preventive oil, JIS NP-0 to 11 and
It is organized into 15 kinds of NP18-20, and among these, usually,
What is called rust preventive oil, lubricating oil, machine oil, etc. are included, and a vaporizable rust inhibitor is also considered to be effective. Oiling is generally performed by spraying, a roll coater, dipping, a flow coater, brush coating or the like. For long products, spray to make the coating amount uniform with a roll after coating. When a small amount is applied uniformly, electrostatic coating is used.

Next, a series of steps from the rolled steel sheet to the enamel completion stage will be described more specifically.

1) First, in the case of a hot-rolled ordinary steel plate, the scale is completely removed and the surface is subjected to shot, sulfuric acid or hydrochloric acid pickling, or skin pass-pickling or shot-pickling the surface of the hot rolled steel sheet. Adjust the roughness to the desired value. In the case of a cold rolled steel sheet, the surface roughness is adjusted by skin pass, shot or pickling, or skin pass-pickling or shot-pickling. After the above treatment (drying when degreasing, washing with water, and drying after shot / skin pass) or washing with water after pickling and forming iron oxide, which is the feature of the present invention, during drying,
Ni dip-washing-neutralization-drying-glazing-drying-firing-
Perform air cooling.

When applying rust preventive oil, apply it before glaze. In the present invention, when the oxidized steel sheet is used as it is as a flat plate such as a white plate or a panel, it is passed through a enamel process without forming the steel plate.

2) Next, after cold-rolled steel sheet and hot-rolled steel sheet are press-formed, after the surface roughening treatment of 1) above, in the step of pickling, oxidation treatment is performed during drying, and in other cases, oxygen is used. Oxidation is carried out in an atmospheric furnace, then Ni dipping is carried out, and then enameling is carried out in the same step as in 1) above.

3) Further, in the step 2), after the rough surface is adjusted, it is subjected to an oxidation treatment, followed by press molding, followed by degreasing, washing with water, and Ni dip-enameling as described in 1) above.

Also, after adjusting the rough surface, press molding, followed by degreasing, washing with water,
When passing through the drying step, an oxide film may be formed during the drying.

4) Next, in the case of hot-rolled steel sheet, pickling shot or skin pass-pickling is performed, and in the case of cold-rolled steel sheet, skin pass is performed to roughly adjust the surface roughness and then molded, and after degreasing press oil and the like, washing with water, After final adjustment of the surface roughness by sulfuric acid pickling, washing with water → drying (also serving as oxidation) -after Ni dipping, enameling is performed in the same step as 1) above. In this case, after molding, roughening, oxidation and N
Since the i-dip is performed, it is suitable when a kettle is manufactured by, for example, a spinning process in which most of the iron oxide film is removed by the process.

5) Finally, in the case of a cold rolled steel sheet, the surface roughness is adjusted by pickling after cold rolling, and the oxidation treatment of the present invention is performed in the cooling process immediately after performing open coil annealing or continuous annealing, followed by forming,
After degreasing and Ni dipping, enamel is applied in the same step as 1) above. In this case, the oxidation may also be performed at the time of neutralization after pickling-washing with water-drying, and tight coil annealing may be performed.

The thickness of the iron oxide layer of the present invention is 50 to 1100Å, which is extremely thin,
It adheres well to steel plates and is bent and pressed to form molded products for each application, but it is difficult to peel off. Furthermore,
Since the surface is roughened before the oxidation, even if the iron oxide is peeled off, only the convex portions of roughness are left and the concave portions remain.
Since Ni attaches mainly to the convex portion of roughness in the i-dip, it is convenient to attach Ni intermittently for the enamel adhesion.

If the oxide film at the time of welding is thin, the weld may be left as it is, but if it is thick, the surface layer of iron oxide should be removed with sandpaper or the like.

Further, specific conditions of the enameled glaze process will be described.

Enamel glaze is made by adding a floating agent, colorant, and water to the glassy material (frit) that has been melted and then crushed by quenching.
These are finely pulverized to 200 mesh or less (slip), and these components differ depending on the enamel glaze component or its use, and various additives may be added.

Glazing includes spraying, dipping, electrostatic spraying, electrophoresis, etc., and is performed on one side or both sides of the steel plate. After glaze, room temperature ~ 100
Dry at ℃ for several tens of minutes and bake in a furnace at about 800 to 920 ℃, or dry, bake and cool in a connecting furnace to finish enamel products.

The enamel product manufactured by the method of the present invention has corrosion resistance,
It has excellent heat resistance, abrasion resistance, chemical resistance, and rich colors, and is used for stoves, stoves, bowls, pots, rice cookers, sinks, construction panels, white boards, etc.

(Example 1) 2.0 mm thick hot-rolled ordinary steel sheet (S
PHC) washed with hydrochloric acid and cold rolled plain steel (SPCC and SPCE)
0.5 ~ 1.2% after temper rolling or shot 100 x 150 mm
Roughness of the front and back of the steel sheet is R _max by shearing to ² , degreasing and washing with sulfuric acid.
After adjusting to about 7-61μm, the furnace temperature is 350 ℃, 500 ℃ and 7 ℃.
Oxidize in an electric heating furnace at 00 ℃ for 1 second to 20 minutes, dip Ni, and apply glaze containing frit shown in Table 2 as a main component on both sides of the glaze to a thickness of about 130 μm and dry at 100 ℃ for 30 minutes. And then baked.

In addition, the bright finish (R
_max ≒ 5 [mu] m), which is not subjected to oxidation treatment (usually double-sided 1 KaiKake treatment) and iron oxide thickness indicates outside the scope the present invention.

Figure 1 shows the temperature rise curves of the steel sheet surface at furnace temperatures of 300 ° C, 500 ° C and 700 ° C. For reference, the furnace temperature under the oxidizing conditions in Table 3
At a temperature of 350 ° C for 30 seconds, the steel plate surface temperature is about 90 in Fig. 1.
It was taken out of the furnace immediately after reaching ℃ (marked with X in the figure) and air-cooled in the atmosphere. Table 3 shows an example in which the product of the present invention is applied to both sides once, and it is clarified that the enamel characteristics of the ordinary steel sheet are improved by the roughening and the oxidation treatment.

(Example 2) A 2.0 mm-thick hot-rolled ordinary steel sheet having the components (% by weight) shown in Table 1 was washed with hydrochloric acid, and a 0.8 mm-thick cold-rolled ordinary steel sheet was used.
5 to 1.2% temper rolling or shot, shearing to 150 × 100 mm ² sample, degreasing with alkaline solution, pickling in 10% sulfuric acid solution for several minutes to adjust roughness, then neutralization, Furnace temperature is 350
Oxidation was carried out for 1 second to 5 minutes in an electric heating furnace of ℃, 500 ℃ and 700 ℃, and after rusting Ni, rust preventive oil with a flash point of 55 to 210 ℃ was uniformly applied by changing the amount of applied oil.

After that, glaze (slip) whose main component is the frit shown in Table 2
Is sprayed on both sides of a steel plate, dried at room temperature to 50 ° C. for 30 minutes, then fired and air-cooled, and various enamel properties are measured. The results are shown in Table 4.

The comparative products shown in Table 4 are those having iron oxide thicknesses outside the range of the present invention and those having a large amount of applied oil after oxidation and Ni dipping.

As you can see from Table 4, before glazing with enameled glaze
The product which had an iron oxide layer of 50 to 1100Å and was enameled on a Ni-dipped, oil-coated steel plate had no copper head or nail skipping and had good adhesion.

On the contrary, if the oxide film thickness is less than 50 μm or more than 1100 μm, the adhesiveness of the enamel film is poor. If the amount of oil applied exceeds 3.0 g / m ² per side, glaze will be generated.

(Example 3) A 2.0 mm-thick hot-rolled ordinary steel sheet having the components (% by weight) shown in Table 1 was washed with hydrochloric acid and a 0.8 mm-thick cold-rolled ordinary steel sheet was added to 0.5.
~ 1.2% temper rolling or shot, sheared into a 90 x 90 mm ² sample, transformed into an Erichsen value of 8 mm with an Erichsen tester, degreased with an alkaline solution, pickled in a 10% sulfuric acid solution for several minutes After adjusting the roughness, neutralize, furnace temperature 350 ℃, 500 ℃,
And oxidize for 1 to 30 seconds in an electric furnace at 700 ℃, N
After dipping, enamel was applied in the same manner as in Example 1. Further, molding by an Erichsen tester was performed even after the oxidation treatment. For the comparative product, the conventional enamel process with double-sided application (temper rolling etc.-molding degreasing-water washing-sulfuric acid washing-water washing-Ni plating-water washing-neutralization-drying-glazing-drying-
The one manufactured by firing is shown. The results are shown in Table 5. Inventive product 1) in Table 5 shows a product formed after temper rolling and the like, and inventive product 2) shows a product formed after oxidation treatment, and both have good enamel properties. On the other hand, the comparative product prepared by the conventional method has a poor enameling property.

[Effects of the invention] The enamel coated steel sheet according to the present invention can be applied to enamel even in the ordinary steel sheets to which enamel could not be applied in the prior art, and further, the enamel characteristics are good, so its economic effect, The work effect is extremely large.

[Brief description of drawings]

Figure 1 shows the oxidation time (holding time in the furnace) and oxidation temperature (steel plate surface temperature) for a sample with dimensions of 0.8 mm × 100 mm × 150 mm.
It is a graph which shows the relationship of and furnace temperature.

Claims (5)

[Claims] 1. A hot-rolled ordinary steel sheet or a cold-rolled ordinary steel sheet having no enameling property, if an iron oxide layer is present on the surface, the iron oxide layer is removed, and the hot-rolled steel sheet or cold-rolled steel sheet is removed. The surface roughness R _max to a surface roughness R _max of 15 to 60 μm, after which an iron oxide layer with a thickness of 50 to 1100 Å is formed on the surface, and then contacted with Ni solution and then enameling is performed. A method for producing enameled which is characterized. 2. The method for producing enamel according to claim 1, wherein after the ordinary steel sheet is formed, the roughening is performed and the iron oxide layer is further formed. 3. The method for producing enamel according to claim 1, wherein the ordinary steel sheet is roughened, the iron oxide layer is formed, and then the iron oxide layer is formed. 4. An iron oxide layer is formed by cold rolling an ordinary steel sheet having no enamel properties, then pickling to roughen it, and then forming the iron oxide layer during the subsequent drying or cooling process immediately after annealing. The method for producing enamel according to claim 1, characterized in that the enamel is molded and then brought into contact with the Ni solution and then enameled. 5. A hot-rolled ordinary steel sheet or a cold-rolled ordinary steel sheet having no enameling property, when an iron oxide layer is present on the surface, the iron oxide layer is removed, and the hot-rolled steel sheet or cold-rolled steel sheet is removed. Surface is roughened to a surface roughness R _max of 15 to 60 μm, and then an iron oxide layer having a thickness of 50 to 1100 Å is formed on the surface, followed by contact with Ni solution and oiling. A method for producing enamel, which is characterized by hanging.