JPH10251822A - Stainless steel sheet with excellent surface film adhesion and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stainless steel sheet improved in the adhesion property of various kinds of films mainly formed by ceramic thermal spraying by etching the steel sheet with an aq. ferric chloride soln. of a specific concn. and specifying the surface roughness thereof and the relative sectional area in the specific depth position of a relative load curve by its sectional curve. SOLUTION: The surface roughness Ra of this stainless steel is 1.6 to 2.4μ, the Rmax is <=20μ and the relative sectional area (Tp50 ) in the depth 50% position of the relative load curve by its sectional curve is <=70%. This surface condition is obtd. by subjecting the steel sheet to spray etching by using the aq. ferric chloride soln. kept at 33 to 37 deg.Be' (Baume degree). As the surface roughness Ra is generally higher, the adhesion property of the films improves but >=1.6μ is necessary in order for obtaining the effect of improving the adhesion property by the shape of the relative load curve. If, on the other hand, the aq. ferric chloride soln. is excessively higher, the film thickness partially exceedingly decreases and, therefore, the surface roughness is confined to <=2.4μ and the Rmax to <=20μ. If Tp50 exceeds 70%, the sufficient adhesion property is not obtainable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stainless steel sheet having excellent adhesion of a coating for surface modification such as thermal spraying of ceramics.

[0002]

2. Description of the Related Art Stainless steel sheets are generally used as they are on the surface of the material. However, some coatings are applied to the surface of the steel sheet so that better performance is exhibited. One is ceramic coating. As a method of coating ceramics for improving the corrosion resistance of iron plates, enamel has been famous for a long time, and has been applied to stainless steel plates. Further, a thermal spraying method in which ceramics are melted and sprayed at a high temperature is widely used as a means for obtaining a surface coating having excellent heat resistance and wear resistance.

[0003] When coating an enamel, the glaze in which powder is suspended in water is applied and dried, and then heated to a high temperature, the glaze becomes a fluid state, penetrates into narrow gaps on the metal surface and anchors. And sufficient coating film adhesion can be obtained. In addition, especially in the plasma spraying method aimed at heat resistance or the high temperature combustion flame spraying method using a rod as a raw material, the sprayed particles melted at a sufficiently high temperature collide with the surface at high speed, so this is also between the surface irregularities. It is said to wrap around and obtain adhesion. Therefore, it is common practice to roughen the surface before coating with a film in order to obtain sufficient adhesion. In the case of enamel, the surface is roughened by shot blasting or pickling with sulfuric acid or the like.

In recent years, in addition to the corrosion resistance, heat resistance, or wear resistance, ceramics having special properties such as high lubricity and sterilization properties have been coated on the surface, and stainless steel sheets have been used as functional materials. Is coming out. It is unavoidable that the ceramic coating formed by thermal spraying has a certain degree of minute pores.
l.40 (1992), No.12, p.99], rather than actively using these pores and impregnating with fluororesin, etc. to obtain a completely oil-less sliding member. An antibacterial stainless steel plate, which uses a sterilizing effect of oxygen generated by spraying ceramics having the function of an optical semiconductor and decomposing water or the like by the photocatalytic action, has been considered.

[0005] Such a ceramic film having a special function different from the conventional one is applied by a so-called low-temperature spraying method. Low-temperature thermal spraying is a method developed for directly spraying and coating high-melting materials such as ceramics on substrates that do not withstand high temperatures, such as paper, cloth, and plastic, to provide new functions at low cost. is there. In this case, rather than forming a dense film, it is often the case that a high performance is provided by the combined effect of the base material and the film material. For example, the sliding portion and the like have many pores and are sufficiently impregnated with resin. In addition, since it is preferable that the contact surface area with the fluid is large for the catalytic action and the like, it is preferable that the film is not necessarily dense. Therefore, the material to be sprayed is powder, and in order to minimize the thermal effect on the base material, the melting point of the powder should be about 2000 ° C. It is melt-injected using a combustion flame of about 3000 ° C.

A problem when applying the low-temperature spraying method to a stainless steel sheet is the adhesion of the ceramic film to the surface of the steel sheet. Since the thermal spraying is performed at such a low temperature that hardly gives a thermal effect to the base material, the adhesion is not sufficient, and the ceramic is easily peeled off when the steel sheet is bent. The method of roughening the surface roughness, which was effective in the enamel and the conventional spraying method, improved the adhesion, but was not sufficient, and sometimes the surface was too coarse and the sprayed ceramic sufficiently covered the surface. I can't do it. For this reason, the steel sheet may not be sufficiently modified by the intended surface coating in some cases.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stainless steel sheet having improved adhesion of various coatings mainly to ceramics sprayed on the surface, and a method of manufacturing the same.

[0008]

[Means for Solving the Problems] On the surface of a stainless steel plate,
When a ceramic film is formed by the thermal spraying method, the thermal spray particles in the molten state solidify and solidify in a very short time on the surface, so there is no time to go into the gaps on the surface irregularities like enamel glaze, and the base material by reaction No chemical bond occurs. Therefore, in order to enhance the adhesion of the film, it was considered that the form of the surface roughness should be controlled so as to be in a state most suitable for the film to be coated.

There are mechanical methods and chemical methods for changing the surface roughness. The most versatile stainless steel plate used is SUS304, and the grit size is changed by the typical shot blast method as a mechanical method.
The surface roughness is changed and the ceramic film is made of TiO
₂ , 30μm by low temperature thermal spraying method using acetylene-oxygen flame
Was formed, and the quality of the adhesion was examined. Although a slight improvement effect was recognized when the surface roughness was increased, the film was peeled off only by slightly bending the steel sheet, and sufficient adhesion was not obtained. Next, as a chemical method, a method of roughening the surface using an aqueous solution of ferric chloride capable of effectively etching stainless steel was studied.

[0010] The concentration of ferric chloride is 40 ゜ Be '(degree of Baume)
If sufficiently high, the dissolution rate is low and the resulting stainless steel surface is smooth. As the concentration decreases, the surface becomes rougher, and as the concentration decreases, the reaction slows down and the dissolution becomes pitting. Dissolution treatment was performed using the solution having a moderately coarse concentration, and a ceramic film was formed on the obtained steel sheet by the low-temperature thermal spraying method in the same manner as described above. Therefore, the surface roughness was measured using a stylus type surface roughness meter, and the relationship with the adhesion was examined. As a result, if the value was within a certain range indicated by the center line average roughness (Ra), the adhesion was measured. Showed a tendency to improve. The larger the maximum height (Rmax), the better the adhesion. However, the thicker the ceramic film, the easier it is to peel off, and since the thickness is at most 100 μm or less, if Rmax is too large, portions that cannot be coated or portions where the film thickness is small will be formed.

Although it has been found that the adhesion and the surface roughness have a close relationship in this way, there are those having particularly good adhesion and those not having the same Ra even with the same Ra value. In order to understand the reason for this difference, when the shape of the cross-sectional curve of the obtained surface roughness was further examined, the following became clear.

The cross-sectional curve of the surface roughness is recorded, for example, as shown on the right side of FIG. 1A. When a straight line parallel to the plate surface is drawn on this curve when measured on a plate without warpage, the center line is the straight line where the area of the part enclosed by the straight line and the roughness curve is equal on both sides of this straight line. The value obtained by dividing the total area surrounded by a certain length by the length is Ra.
It is. Now, considering the line parallel to this center line and the line that touches the peak and the valley bottom of the cross-sectional curve, the total length of the line below the curve is 0 for the line that touches the peak, On the line that touches the valley bottom, it is the full length. Therefore,
Taking a certain reference length L, the ratio of the total length of the line segments below the curve to L is 0% at the summit and 100% at the valley bottom.
%, And if it lies between them, it will take on various values between 0% and 100%. In this way, when the depth from the peak to the valley is set to 100 and the change in the total length ratio of this line segment to the depth position between them, that is, the straight line at the relative depth position, is shown on the left side of FIG. 1A. The curve shown is obtained. This is called a relative load curve. The vertical axis in the figure is the relative depth, and the horizontal axis is the line segment. The line segment is based on the reference length L parallel to the surface of the uneven steel sheet at the relative depth position.
Is equal to the area ratio of the total of the cross-sectional areas of the projections to S when cut by the reference plane S corresponding to Therefore, this is hereinafter referred to as a relative sectional area ratio.

From the form of the relative load curve, the form of the surface roughness can be grasped quantitatively to some extent. For example, in the case of a cross-sectional curve of the surface roughness as shown in the right of FIG. 1B, that is, when the shapes of the peaks and valleys are not similar, the peaks are trapezoidal, and the valleys are narrow and deep, the relative load as shown in FIG. A curve is obtained.

The relative load curve is processed by the recording mechanism of the stylus type surface roughness meter, and can be easily known when measuring the surface roughness. As a result of examining the shape of this relative load curve and the quality of adhesion of the film, it was found that there was a close relationship. That is, when the relative sectional area ratio is approximately 60 to 70% at the position where the relative depth is 50%, even if Ra is substantially the same,
The adhesion is greatly improved. For example, the same level of Ra as the one that showed the result with the best adhesion was examined.
Can be achieved by short-time etching using a lower-concentration aqueous solution of ferric chloride, but the improvement effect is not great. Looking at the cross-sectional curve, it is shaped like the curve on the right in FIG. 1B where there are no peaks and only valleys. Looking at the relative load curve, the relative cross-sectional area ratio at the position of 50% depth (hereinafter abbreviated as Tp ₅₀ ) ) Was over 70%.

As described above, when the surface roughness and the shape of the cross-sectional curve are set to a specific state, the adhesion of the ceramic film is greatly improved because the sprayed particles of the powder by the low temperature spraying method reach the steel sheet surface. It seems that the anchor effect becomes the most effective form when it is done. It was confirmed that the steel sheet with this improved surface condition can greatly improve the film adhesion when spraying and coating plastics, but the same improvement effect was obtained for other films. It is estimated that it can be expected.

This surface state can be obtained by etching the surface of the steel sheet using an aqueous solution of ferric chloride having an appropriate concentration. In order to improve the productivity and make the entire surface of the steel sheet have a uniform surface roughness, etching by spray spraying is preferable.
Therefore, as a result of examining conditions such as solution concentration, temperature, time, spray spraying, etc., it was found that the solution concentration was the largest factor in controlling the surface morphology. The surface roughness represented by Ra and Rmax can be controlled by adjusting the temperature and time so that the weight loss due to dissolution becomes a predetermined value. However, in order to form a relative load curve effective for improving the adhesion, the concentration of the solution is extremely important, and its management is essential.

Based on the above findings, the range of conditions for providing surface roughness for improving the adhesion of the film and the limit of the manufacturing conditions for obtaining the same were clarified. It is. That is, the gist of the present invention is:
"The surface roughness Ra is 1.6 to 2.4 μm, Rmax is 20 μm or less, and the relative cross-sectional area at the position of 50% depth of the relative load curve by the cross-sectional curve, that is, Tp ₅₀ is 70% or less. Stainless steel sheet with excellent film adhesion
And "a method for producing the same, characterized by performing spray spray etching using an aqueous ferric chloride solution of 33 to 37 ° Be '".

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The stainless steel sheet of the material is not particularly limited, such as austenitic and ferritic, but austenitic is desirable from the viewpoints of corrosion resistance, workability, and performance after thermal spraying of the material.

Generally, the larger the surface roughness Ra, the greater the anchoring effect of the film and the better the adhesion. But,
Ra must be at least 1.6 μm in order to obtain the effect of improving the adhesion by the shape of the relative load curve of the present invention described below. The thickness of the sprayed ceramic film that is the main object of the present invention is usually 100 μm or less, and if the surface roughness is too rough, the base material cannot be sufficiently covered, and the film thickness becomes partially extremely thin. Therefore, Ra is limited to 2.4 μm or less and Rmax is limited to 20 μm or less. However, only by such a limitation of Ra and Rmax, a sufficiently good film adhesion cannot be obtained, and it is necessary to control the form of the surface roughness. Tp ₅₀ of the relative load curve obtained from the cross-sectional curve is used as an index to indicate the form, and the value is 70
%. When Tp ₅₀ exceeds 70%,
This is because a sufficient improvement in adhesion cannot be obtained. This is considered to be because the anchoring effect of the coating is maximized when the surface is roughened and this configuration is obtained.

In order to keep the values of Ra and Rmax within the above ranges and to set Tp _{50 of the} relative load curve to 70% or less, it is desirable to use an aqueous solution of ferric chloride for etching the surface.
In this case, the concentration of the aqueous ferric chloride solution is 33 to 37 ° Be ′. If it is less than 33 ° Be ′, the values of Ra and Rmax can be within the range defined by the present invention, but the dissolution of stainless steel proceeds in a pitting manner, and Tp ₅₀ exceeds 70%.
On the other hand, when the solution concentration exceeds 37 ° Be ′, it is not only difficult to increase Ra to 1.6 μm or more, but also the dissolution rate is greatly reduced, and productivity is deteriorated.

The etching of the steel sheet is preferably performed by spraying a solution. Although spray immersion in a solution is not impossible, spray spraying can uniformly etch the entire surface of the steel sheet, and has excellent productivity. The solution temperature, pre-spray time, spray pressure and the like during etching are not particularly limited, but are preferably about 40 to 60 ° C., about 1 to 10 minutes, and about 1.0 to 3.0 kgf / cm ² , respectively. When the temperature is lower than 40 ° C., the dissolution rate is remarkably reduced and the processing efficiency is deteriorated.
The dissolution rate increases as the temperature increases.However, generally used equipment made of vinyl chloride is limited to about 60 ° C., and it is not preferable to use a temperature higher than this because a large investment is required to improve the heat resistance of the apparatus. . The spray spraying time for etching cannot be said unconditionally because the dissolution rate is greatly affected by temperature, solution concentration, spraying pressure, etc., but if it is less than 1 minute, it cannot reach the target surface roughness property, Approximately 10 minutes is optimal, and if it exceeds 10 minutes, the amount of dissolution increases, but the surface roughness properties are often not further improved.
The spray pressure also has a significant effect on the dissolution rate, but has little bearing on the nature of the roughness. When the dissolution rate is less than 1.0 kgf / cm ² , the dissolution rate is too slow. On the other hand, when the dissolution rate exceeds 3.0 kgf / cm ² , the pressure limit of a commonly used solution such as a pipe made of vinyl chloride is exceeded, which is dangerous.

[0022]

【Example】

[Example 1] SUS304 CSP H specification thickness 0.3mm, width 400mm
After degreasing and cleaning with an alkaline water-based degreasing cleaning solution, the steel sheet was used for etching. The etching conditions are variously changing the concentration of the aqueous ferric chloride solution in the range of 25 to 45 ° Be ′,
The solution temperature was 50 ° C., and the spray pressure was 1.5 kgf / cm ² , and spraying was performed for 1 to 5 minutes. The surface after etching was measured for roughness by a stylus method and measurement of a relative load curve. The ceramic film is 30 μm thick, the etched surface is pickled with 3% hydrochloric acid, washed with water, and dried. Then, TiO ₂ fine powder having a particle size of 5 to 10 μm is used as a raw material. It was constructed by the low temperature spraying method. Film thickness is 30μm
And A test piece having a width of 10 mm and a length of 100 mm was cut out from the steel plate after the thermal spray coating, and the sprayed surface was outwardly bent at 120 ° with an inner diameter r of 2 mm perpendicular to the longitudinal direction to observe the state of peeling.

FIG. 2 shows the relationship between the obtained surface roughness Ra after etching and Rmax or Tp ₅₀ (relative sectional area ratio at a position with a relative depth of 50%). The points in the figure
A sample having good film adhesion is indicated by a circle, a sample having a peeled portion is indicated by a triangle, and a sample having completely peeled is indicated by a cross. From this, it can be seen that, as defined in the present invention, a film satisfying the surface roughness Ra of 1.6 μm or more and at the same time of 70% or less can obtain a film having good adhesion. When Ra exceeds 2.4 μm, Rm
In many cases, ax is remarkably large exceeding 20 μm, and even though the adhesiveness is good, the coating of the substrate with the film becomes insufficient.

[Embodiment 2] As in Embodiment 1, CS of SUS304 was used.
Using a 0.3 mm thick, 400 mm wide steel plate with PH specifications, the solution temperature is 50 ° C, the spray pressure is 1.5 kgf / cm ² , and the time is 5 minutes. 20-50
The etching was performed by spray spray while changing within the range of ゜ Be '. After etching, the surface roughness was measured in the same manner, the ceramics were sprayed under the same conditions, and the adhesion of the coating was evaluated.

Table 1 shows the concentration of the aqueous ferric chloride solution, the surface roughness, Tp ₅₀ , and the results of the adhesion test. FIG. 3 is a graph showing the results of this table. From now on, the concentration of the aqueous ferric chloride solution is 33-37 ° C. as defined in the present invention.
In the range of Be ', it is clear that all of Ra, Rmax and Tp ₅₀ fall within the range of the present invention, and that the film has excellent adhesion.

[0026]

[Table 1]

[0027]

When the surface of the stainless steel sheet of the present invention is coated with a ceramic film or the like, good film adhesion can be obtained. In particular, excellent adhesion can be obtained when performing low-temperature spraying for the purpose of imparting a special function to the ceramics on the surface.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a relationship between a cross-sectional curve of surface roughness and a relative load curve based on the cross-sectional curve.

FIG. 2 shows the surface roughness Ra of a steel sheet whose surface has been etched.
FIG. 4 is a diagram showing the relationship between the surface roughness Rmax or the relative cross-sectional area ratio at a position at a relative depth of 50% and the adhesion of a ceramic film.

FIG. 3 is a diagram showing the relationship between the concentration of ferric chloride used for etching, the surface roughness Ra, Rmax, or the relative sectional area ratio at a position of 50% relative depth, and the adhesion of a ceramic film. .

Claims (2)

[Claims] 1. A surface roughness Ra of 1.6 to 2.4 μm and Rmax of 20 μm
Less than the depth of the relative load curve by its cross-sectional curve
A stainless steel sheet with excellent film adhesion, characterized in that the relative sectional area ratio at the 50% position is 70% or less. 2. The method for producing a stainless steel sheet according to claim 1, wherein the spray spray etching is performed using an aqueous ferric chloride solution having a temperature of 33 to 37 ° Be ′ (degree of Baume).