JPH0660421B2 - Coated steel plate for enamel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a coated steel sheet for enamel, and in particular, makes it possible to use an ordinary ordinary steel sheet used for automobiles, electric appliances and the like as a enamel steel sheet, It is an object of the present invention to provide a steel sheet which enables production of a double-sided or single-sided enameled product which is free from claw skips, bubble defects and poor adhesion as compared with conventional steel sheets for enameling.

[Conventional technology]

As is well known, defects in enamel products include nail jumps, bubbles, and poor adhesion, and defects are likely to occur when the combination of a enamel steel plate 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.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 flying resistance, inclusions in steel,
A method of increasing the number of precipitates and occluding hydrogen in the vicinity thereof is conventionally known, and for example, Ti-C, Ti-S and Ti-
Japanese Patent Application Laid-Open No. 48-48480 discloses a method of forming inclusions and precipitates in the REM-S system.
-222, JP-A-52-131919 and JP-B-54-
Japanese Patent Laid-Open No. 58-1013 discloses a method of forming inclusions and precipitates in a B—N system, such as 3447.

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 annealing, and, for example, JP-A-56-515.
53, JP-A-51-6813 and the like.

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 the nail jump and the 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 the steel, or the pickling weight loss is increased. In the latter, there is a method of applying Ni glaze after pickling and then applying a glaze. But both sides 1
Adhesion failure is more likely to occur with a wrapping enamel, so see Japanese Patent Application Laid-Open No. 51-
In Japanese Patent No. 1311, the surface roughness and Mn amount of a steel plate are regulated, and in Japanese Patent Laid-Open No. 57-63661, (P + S) / Cu in the steel is set to 2.
It is set to 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 49-4
There is Japanese Patent Publication No. 1084 and Japanese Patent Publication No. 61-12974, which is almost similar to this. 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.

[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.
It was not possible to provide a enamel-coated product that does not cause poor adhesion by using 1) as a double-sided or single-sided enamel product.

[Means for solving problems]

The present invention provides a plain steel sheet as a coated steel sheet for enamel by forming an iron oxide layer having a thickness of 50 to 1100Å on the surface of a plain steel sheet having no enamel properties in order to provide the steel sheet for enamel. is there.

In general, it is common knowledge that enamel steel plates are completely degreased, pickled, Ni-plated, neutralized, and then glazed in the case of enamel, which is applied once on both sides. 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. In addition, there is no conventional common sense that it is possible to hang enamel on ordinary hot-rolled and cold-rolled ordinary steel sheets that are not suitable for enamel once.

The present invention will be described in detail below.

Ordinary steel sheet that is the subject of the present invention is JIS G3131 hot rolled mild steel sheet and steel strip (SPHC, SPHD, SPHE, etc.), JIS G3141 cold rolled steel sheet and steel strip (SPCC, SPCD, SPCE, etc.), and JIS G3303.
Steel plates and strips of plain steel including non-tinted original plates (SPB, etc.), decarburized steel sheets and strips for enamels of JIS G3133 (SP)
P, etc.), JIS standards, and steel plates and steel strips for hot rolling enamels and mild steel sheets and steel strips of cast-molded capped steel are not included.

Incidentally, when these enamel steel plates and steel strips are subjected to a coating treatment for enamel by the method of the present invention, a nail enamel product and a enamel product having few bubble defects, which are not found in conventional enamel steel plates, can be obtained. The purpose of the invention method is to make the ordinary steel plate a steel plate for enamel which has a quality equivalent to or better than that of the conventional steel plate, and therefore the above steel plate for enamel and the steel strip are excluded from the scope of the present invention. Therefore, in the broad sense, the ordinary steel sheet referred to in the present invention refers to a steel sheet that has not been subjected to nail popping, bubble defect prevention, and adhesion failure countermeasures, that is, ordinary steel sheet having no enameled properties.

The composition range of the above-mentioned ordinary steel sheet is indicated in JIS standard, C: 0.15% or less, Mn: 0.60% or less, P: 0.050% or less, S: 0.050% or less, and Cu is 0.08% or less, Al
Is 0.08% or less and Ti is 0.10% or less. Cu is generally
If it exceeds 0.08%, surface defects due to Cu are likely to occur, and the cost will increase, so the content was made 0.08% or less. Also, Al
The reason why the content is 0.08% or less is originally due to Al deoxidation A
l Content is unavoidable, and as a result of investigating the effect on the purpose, up to 0.08% has no particular adverse effect, but if it exceeds 0.08%, an economic problem occurs.

The reason why Ti is set to 0.10% or less is that Ti is the same as Al described above.
In addition to deoxidation, it is combined with N and C to form nitrides and carbides, which are added to improve workability in addition to non-aging property, but the effect on the enamel of the present invention is particularly bad up to 0.10%. However, if it exceeds 0.10%, the cost will be high.

In general, when baking enamel in both single-sided and normal manufacturing processes using enamel steel plate, first the oxidation occurs on the steel plate surface, then the enamel glaze melts, the iron oxide dissolves in the enamel, and the 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. In addition, it is extremely difficult to increase the roughness of ordinary cold-rolled ordinary steel sheets (SPCC, etc.), and to make a material with good adhesion even if Cu addition or Ni plating is performed.

Therefore, the present invention has a great feature in that a uniform iron oxide layer having a proper thickness is formed in advance 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 (up to 570 ℃) is generally Fe ₃ O ₄ and Fe.
It is said that it consists of the ₂ O ₃ phase, but the Fe ₃ O ₄ phase was 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 layer was in the range of 50 to 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 of 50 to 1100Å is enameled and baked, the iron oxide film dissolves in the enamel moderately and iron silicate is generated at the interface between the enamel layer and the steel sheet, which is It is thought that the adhesiveness is improved by playing the role of an adhesive.

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. for a few seconds to a few tens of minutes, and the high temperature oxidation is performed in a short time. When oxidizing in a weakly oxidizing atmosphere, naturally, it can be performed at a high temperature for a long time.

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 coated steel sheet for enamel of the present invention is enameled on both sides once, the upper layer of the iron oxide layer is plated with Ni, or
Or, after plating with Ni, apply rust preventive oil on the upper layer. Then, various enamel properties are improved by applying enamel glaze on the upper layer, drying and baking.

Ni plating is generally used when enamel is applied once on both sides.
For essential treatment, several% NiSO ₄ aqueous solution (pH is about 2.5 to 3.0) is about 70 ° C, it is immersed for a few minutes for plating treatment, then neutralized and dried, or to further improve adhesion. ,
Apply rust preventive oil to the upper layer. When Ni is plated on the iron oxide layer, the amount of plating is 0.1 to 5.0 g / m ² , which is about 1/500 to 1/10, as compared with the case where Ni is plated on the surface of a normal steel plate.

The effect of Ni plating is effective in preventing defects in enamel products, but in particular it suppresses the oxidation during firing and improves the adhesion of the enamel film to the steel sheet by diffusing into the iron silicate at the interface between the enamel layer and 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. Therefore, it is considered that it is possible to reduce or prevent the generation of the nail skipping 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
There are 15 types of NP18 to 20. Among them, those usually called rust preventive oils, lubricating oils, machine oils, etc. are included, and it is considered that a vaporizing rust inhibitor is also 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.

Regarding the surface roughness of steel sheets, the conventional steel sheets for enameling
R _max is 7 to 20 μm. The steel sheet used in the present invention can form an excellent enamel coating even in the upper limit of about 60 μm in addition to this surface roughness range. A particularly preferred range of the surface roughness of the steel sheet is R _max of 15 to 60 μm. As a method of adjusting the surface roughness, generally pickling, dull roll rolling,
It is carried out by polishing (grinding, paper, shot blasting, electric discharge machining, etc.) and grinding. Where surface roughness R
_max is represented by the average value of R _{max in} the L and C directions on the front and back surfaces of the steel sheet.

On the other hand, the number of peaks per inch, PPI, which corresponds to the above range of R _max , is about 223-10.4 peak / inch, and the center line average roughness Ra is about 0.7-62 μm.

First, in the case of a hot-rolled steel sheet, the surface of the hot-rolled steel sheet is completely removed by performing shot or hydrochloric acid washing to completely remove the scale and adjust the surface roughness to a desired value. The same treatment as above is performed by washing-shot. In the case of a cold rolled steel sheet, the surface roughness is adjusted by skin pass or shot if necessary.

The formation of iron oxide, which is a feature of the present invention, performed after the above treatment may be performed at any step.

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. When the steps of degreasing-washing with water-pickling-washing with water-neutralization-drying-glazing-drying-firing-air cooling, which are enameling steps, are preferably carried out after drying before glazeing and subsequent oxidation.

In addition, when performing Ni plating, after performing acid washing and water washing, N
i When plating and then applying rust preventive oil, apply oil before glaze.

In the present invention, the oxidized steel sheet is used as a white plate, a flat plate such as a panel, or is bent, pressed, welded or the like to be formed into a molded product for each application. Even if such processing is applied, the extremely thin iron oxide layer of pressed parts, etc. is difficult to peel off. In fact, there is no problem because the concave portions are filled.

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.
Finely crushed to 200 mesh under (slip)
Then, these components differ depending on the enamel 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 800-920 ℃, or dry, bake, and cool in a connecting furnace to finish enamel products.

Enamel products manufactured from the products of the present invention have 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.

The case where the ordinary steel plate is enameled once by the present invention has been described above. On the other hand, for enamel coated twice, CoO, NiO, etc. are added to the lower glaze to improve the adhesiveness with the steel sheet. Therefore, the iron oxide coating of the present invention further improves the adhesiveness. Moreover, since the amount of P ₂ O ₅ , Al ₂ O ₃ and ZrO _{2 is} increased in the lower glaze, the fluidity of the glaze during melting is improved, gas is released, and then the upper glaze is removed from the lower glaze. Since it is fired at a low temperature, it is less likely to cause bubble defects and nail skipping.

As described above, according to the present invention, the enamel characteristics were extremely good even with the ordinary steel plate to which the enamel could not be applied by the above technique. When it is applied twice, Ni plating is of course unnecessary.

(Example 1) An ordinary hot-rolled steel sheet having a thickness of 2.0 mm and containing the components (% by weight) shown in Table 1
(SPHC) washed with hydrochloric acid and 0.8 mm thick cold rolled steel
(SPCC and SPCE) is tempered by 0.5 to 1.2%, or after shot, it is sheared to 100 × 150 mm ² and degreased and washed with sulfuric acid to adjust the roughness of the front and back surfaces of the steel sheet to about 7 to 61 μm with R _max. After that, the furnace temperature is 350
Oxidation in an electric heating furnace at ℃, 500 ℃ and 700 ℃ for 1 second to 20 minutes, Ni plating, and a glaze containing frit shown in Table 2 as a main component on the upper layer of the glaze for about 130 μm on both sides of the steel plate, ℃
It was dried for 30 minutes and then baked.

The comparative products are those that have not been subjected to oxidation treatment (normal double-sided single treatment) and iron oxide thicknesses outside the range of the present invention.

Fig. 1 shows the temperature rising curves of the steel sheet surface at furnace temperatures of 300 ° C, 500 ° C and 700 ° C. For reference, when the furnace temperature is 350 ° C and the charging time is 30 seconds under the oxidizing conditions in Table 3, the steel plate surface temperature is about 9 in Fig. 1.
Immediately after reaching 0 ° C (marked with X in the figure), the sample was taken out of the furnace 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 characteristic of the ordinary steel sheet is improved by the oxidation treatment.

(Example 2) 0.5 to 1.2 of a 2.0 mm thick ordinary hot-rolled steel sheet of which the components (% by weight) shown in Table 1 were washed with hydrochloric acid and a 0.8 mm thick ordinary cold-rolled steel sheet were used. % Temper rolling or shot, 150 × 100m
A sample of m ² was sheared, degreased with an alkaline solution, pickled in a 10% sulfuric acid solution for several minutes to adjust the roughness, and then neutralized.
Oxidation was performed for 1 second to 3 minutes in an electric heating furnace at 350 ° C, 500 ° C and 700 ° C, and rust preventive oil having a flash point of 55 to 210 ° C after Ni plating was uniformly applied by changing the amount of applied oil.

After that, glaze (slip) whose main component is the frit shown in Table 2
Was spray-glazed, dried at room temperature to 50 ° C. for 30 minutes, calcined and air-cooled, and various enamel properties were measured. The results are shown in Tables 4 and 5.

The comparative products shown in Table 4 are those whose iron oxide thickness is outside the range of the present invention and those which have been coated with 3 g / m ² or more of oil on one surface after Ni plating by the conventional method.

The comparative products in Table 5 are those with a large amount of oil applied after oxidation and Ni plating.

As can be seen from Tables 4 and 5, the product which was enameled on the steel plate having the iron oxide layer of 50 to 1100Å before glaze with enameled glaze had no copper head, no nail skipping and good adhesion. .

On the contrary, ordinary cold-rolled steel sheets, which have been manufactured by conventional methods such as degreasing, pickling, Ni plating, applying a proper amount of oil, glaze and enamel, have poor adhesion. Further, if the oxide film thickness is less than 50 μm or exceeds 1100 μm, the adhesiveness of the enamel film is poor.
If the amount of oil applied exceeds 3.0 g / m ^{2 on} one side, glaze will be generated.

Adhesion is set to 80% or more as a standard for passing in all the examples.

〔The invention's effect〕

The enamel coated steel sheet according to the present invention can be applied to enamel even in the ordinary steel sheet to which enamel could not be applied in the prior art, and moreover, the enamel characteristics have the same degree of enamel defects as those of the conventional steel sheet for enamel. Because it can be prevented, its economic effect and work effect are extremely large.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the oxidation time (holding time in the furnace), the oxidation temperature (steel plate surface temperature) and the furnace temperature for a sample having a size of 0.8 mm × 100 mm × 150 mm.

Claims (1)

[Claims] 1. A coated steel sheet for enamel, which comprises an iron oxide layer having a thickness of 50 to 1100Å on the surface of a plain steel sheet having no enamel properties.