JP2017110242A - Electrolytic treatment liquid for stainless steel and manufacturing method of stainless steel component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve good coating even when oxide scale is generated on a surface of a stainless steel.SOLUTION: Coating is conducted on a filler pipe 10 (stainless steel component) and a breather pipe 20 (stainless steel component) after oxide scale is generated by weldment. The oxide scale is removed with an electrolytic treatment liquid containing sodium sulfate, sodium ascorbate, sodium gluconate and glycerol of 1 to 10 wt.% respectively and the coating is conducted. As the oxide scale is surely removed by the electrolytic treatment liquid, good coating can be conducted on the stainless steel.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrolytic treatment solution for stainless steel and a method for coating stainless steel parts.

  Patent Document 1 discloses a technique in which a stainless steel inlet pipe and a breather tube are connected by welding, and after the welding, a cationic electrodeposition coating is applied to the inlet pipe and the breather tube.

Japanese Patent Laid-Open No. 2002-242779

  When stainless steel is exposed to a high temperature by welding, heat treatment, or the like, an oxide scale, which is a kind of oxide film, is generated on the surface of the stainless steel by high-temperature oxidation. When the cationic electrodeposition coating is performed with the oxide scale remaining, good coating is not performed in the region where the oxide scale is generated because the coating property of the paint is low.

  The present invention has been completed on the basis of the above-described circumstances, and an object of the present invention is to realize satisfactory coating even when an oxide scale is generated on the surface of stainless steel.

The first invention is
An electrolytic treatment solution for stainless steel for removing oxide scale generated in stainless steel parts,
It is characterized in that sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin are contained in an amount of 1 to 10% by weight, respectively.

The method of painting stainless steel according to the second invention is as follows:
Electrolysis for removing the oxidized scale with an electrolytic treatment solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin, respectively, on the stainless steel part on which the oxidized scale is generated. Processing steps;
And a coating step of coating the stainless steel part from which the oxide scale has been removed by the electrolytic treatment liquid.

  According to 1st and 2nd invention, even if an oxidation scale is produced | generated by stainless steel components by welding, heat processing, etc., the oxidation scale is sodium sulfate, sodium ascorbate, sodium gluconate, and glycerol, respectively. Since it can be reliably removed by the electrolytic treatment liquid contained in an amount of 1 to 10% by weight, good coating can be applied to the stainless steel.

Front view showing the stainless steel part of Example 1 Graph showing the result of analysis of the surface of a stainless steel material by X-ray photoelectron spectroscopy (XPS), showing that the stainless steel material is not heat-treated and no oxide scale is generated. Graph showing the result of analysis of the surface of a stainless steel material by X-ray photoelectron spectroscopy (XPS), showing the state in which oxidized scale is generated on the stainless steel material by heat treatment A graph showing the result of analysis of the surface of a stainless steel material by X-ray photoelectron spectroscopy (XPS), showing the state in which electrolytic treatment was performed on the stainless steel material on which oxide scale was generated Partial enlarged cross-sectional view showing a state where oxide scale is generated on the surface of a stainless steel part Partial enlarged cross-sectional view showing a state where a coating film has been formed on the surface of the stainless steel part after the oxide scale has been removed Graph showing the amount of precipitates in the waste solution of sodium sulfate with and without sodium ascorbate and gluconate

  In the second invention, the coating may be cationic electrodeposition coating. In this case, the coating film produced | generated by cationic electrodeposition coating exhibits high anticorrosion performance. Moreover, since the paint used for cationic electrodeposition coating is a water-based paint, an organic solvent is unnecessary, and there is little adverse effect on the environment.

<Example 1>
A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows a state in which a filler pipe 10 made of stainless steel (a stainless steel part recited in claims) and a breather pipe 20 made of a stainless steel (a stainless steel part claimed in claims) are connected by welding. Indicates. The filler pipe 10 and the breather pipe 20 are subjected to cationic electrodeposition coating after welding. The thickness of the coating film 40 produced | generated by cationic electrodeposition coating is about 20 micrometers, for example. The coating film 40 produced by the cationic electrodeposition coating exhibits high anticorrosion performance. In addition, since the paint used for cationic electrodeposition coating is an aqueous paint and does not require an organic solvent, it has little adverse effect on the environment.

  When heat treatment such as welding is performed on the stainless steel parts (filler pipe 10 and breather pipe 20), the surfaces of the stainless steel parts 10 and 20 are exposed to high temperatures as shown in FIG. Oxide scale 30 is produced. The oxide scale 30 is a kind of oxide film, but differs from the passive film (oxide film) generated on the surface of the stainless steel parts 10 and 20 that has not been heat-treated, and from the surface of the stainless steel parts 10 and 20. Easy to peel off. Therefore, if the cationic electrodeposition coating is performed while the oxide scale 30 is generated on the surfaces of the stainless steel parts 10 and 20, the paint is peeled off from the surfaces of the stainless steel parts 10 and 20 together with the oxide scale 30. End up.

  As a countermeasure, in this embodiment, the following electrolytic treatment solution is used as means for removing the oxide scale 30. This electrolytic treatment solution is an aqueous solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin, respectively. The weight ratio of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin can be set and changed as appropriate.

  As an electrolytic treatment method for removing the oxide scale 30 using this electrolytic treatment liquid, for example, the stainless steel parts 10 and 20 and the cathode terminal are immersed in the electrolytic treatment liquid, and the stainless steel parts 10 and 20 are used as an anode. There is a way to energize. As another electrolytic treatment method, a cloth impregnated with an electrolytic treatment solution may be prepared, and the oxidized scale 30 may be wiped off by rubbing the surfaces of the stainless steel parts 10 and 20 with this cloth. If cationic electrodeposition coating is performed after the electrolytic treatment is performed to remove the oxide scale 30 as described above, the coating property of the coating is improved, and the coating is applied to the surfaces of the stainless steel parts 10 and 20 as shown in FIG. The coating film 40 that is reliably applied and hardly peeled off is formed.

  The inventor of the present application conducted a water resistance test for demonstrating the strength of the coating force when the cationic coating was performed after the electrolytic treatment with the electrolytic treatment solution as described above. In this water resistance test, oxidation was performed by cationic electrodeposition coating in a state where a passive film was formed on the surface of a stainless steel material (not shown) (that is, when heat treatment was not performed) and by heat treatment at 600 ° C. When the stainless steel material with scale (not shown) is subjected to cationic electrodeposition without electrolytic treatment (that is, with the oxide scale remaining), an oxide scale is generated by heat treatment at 600 ° C. Comparison was made with the case where the cation electrodeposition coating was performed after the electrolytic treatment was performed on the stainless steel material (that is, after the oxide scale was removed). The test results are shown in Table 1.

  When applied without heat treatment (that is, in a state where no oxide scale was generated), the coating film (not shown) did not peel off for 1944 hours. Moreover, even if the oxide scale was produced | generated by heat processing, even when it painted, after removing the oxide scale by electrolytic treatment, peeling of the coating film did not arise over 1944 hours. On the other hand, when the paint was applied in the state in which the oxide scale was generated by the heat treatment (that is, without performing the electrolytic treatment for removing the oxide scale), the coating film did not peel off until 980 hours. However, after 1728 hours, the coating film peeled off. From this test, if the oxide scale is removed using an electrolytic treatment solution consisting of an aqueous solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin, respectively, over a long period of time. It can be seen that a good coating film that maintains high water resistance can be produced.

  Further, the inventors of the present application have a state in which a passive film is generated on the surface of the stainless steel material (that is, a state in which heat treatment is not performed), and an oxide scale is generated on the surface of the stainless steel material by heat treatment at 600 ° C. The oxide scale is generated by heat treatment at 600 ° C. on the surface of the stainless steel material (that is, the state where the electrolytic treatment for removing the oxide scale is not performed) and the surface of the stainless steel material. In the electrolytically treated state, the surface of the stainless steel material was analyzed by X-ray photoelectron spectroscopy (XPS). The analysis results are shown in the graphs of FIGS. In these graphs, the horizontal axis represents the sputter etching depth of the film (passive film, oxide scale) and the stainless steel material (base material). The vertical axis represents the content (concentration) of each component of O, Fe, C, and Cr.

  According to XPS analysis, the thickness of the passive film (mainly Cr oxide and Cr hydroxide film) of stainless steel that has not been heat-treated is about 3 nm. The film composition of the passive film in this state is shown in the graph of FIG. Further, in the state where the oxide scale was generated on the surface of the stainless steel material by the heat treatment at 600 ° C., the thickness of the film containing the oxide scale on the surface of the stainless steel material was about 42 nm. Further, in the state where the above-described electrolytic treatment was performed on the surface of the stainless steel material on which the oxide scale was generated, the thickness of the film was about 3 nm.

  The thickness of the film after the electrolytic treatment is the same as the thickness of the passive film before the heat treatment. Moreover, when the content of each component of the film after electrolytic treatment is compared with the content of each component of the passive film before heat treatment, it is found that the contents of O, Fe, and Cr tend to be particularly close. It was. In other words, it is inferred that the film after the electrolytic treatment was almost in the same state as the passive film.

  The stainless steel parts (filler pipe 10 and breather pipe 20) of the present embodiment are subjected to cationic electrodeposition coating after the oxide scale 30 is generated by welding. In these stainless steel parts 10 and 20, the oxide scale 30 was removed by an electrolytic treatment solution composed of an aqueous solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin, respectively. Later, a cationic coating is applied. Therefore, good cationic electrodeposition coating can be applied to the stainless steel parts 10 and 20.

  Moreover, the electrolytic treatment liquid of this example is for removing the oxide scale 30 produced on the stainless steel parts 10 and 20 by welding, and sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin are These are aqueous solutions each containing 1 to 10% by weight. If the oxide scale 30 is removed by this electrolytic treatment solution, good cationic electrodeposition coating can be performed on the stainless steel parts 10 and 20.

  Further, in the stainless steel coating method of this embodiment, cationic electrodeposition coating is performed on the stainless steel parts 10 and 20 on which the oxide scale 30 is generated by welding, but prior to the cationic electrodeposition coating process. The oxidized scale 30 is removed by an electrolytic treatment solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin. According to this method, good cationic electrodeposition coating can be applied to stainless steel.

  In addition, by adding sodium gluconate to the sodium sulfate solution, it is possible to chelate mainly divalent and trivalent iron ions generated from the stainless steel material during the electrolytic treatment, and solids derived from metal ions generated on the surface of the stainless steel material And the formation of oxides can be suppressed. Then, by suppressing the generation of solids and oxides, the coating property of the paint is improved, and clogging of piping and nozzles in the electrolytic processing apparatus is suppressed. Furthermore, since the elution of metal ions into the electrolytic solution can be suppressed, adverse environmental effects are reduced.

  The inventors of the present application differed in the amount of precipitates (solid matter and oxide) in the waste liquid of a solution obtained by adding 0.1 mol / L sodium ascorbate and 0.05 mol / L sodium gluconate to sodium sulfate and a solution not added. Compared. The result is shown in FIG. As shown in this graph, the amount of the waste liquid precipitate when sodium ascorbate and sodium gluconate were not added to sodium sulfate was about 0.116 g. In contrast, the amount of waste liquid precipitate when only sodium ascorbate is added to sodium sulfate is about 0.019 g, and the amount of waste liquid precipitate when only sodium gluconate is added to sodium sulfate is about 0.011 g. In both cases, the amount of the waste liquid precipitate is greatly reduced as compared with the case where it is not added.

  Further, when both sodium ascorbate and sodium gluconate are added to sodium sulfate, the amount of waste liquid precipitate is about 0.006 g. That is, in this comparative example, the amount of waste liquid deposits was the smallest when both sodium ascorbate and sodium gluconate were added to sodium sulfate.

  Moreover, when the solution in which sodium sulfate ascorbate and sodium gluconate are added to sodium sulfate is compared with a solution in which glycerin is not added and a solution in which glycerin is not added, the state when the solution is dried by moisture evaporation is different. That is, when glycerin was added, the dryness was low, and a moist sherbet shape was obtained. This is because glycerin has a polar molecular structure having three OH groups, and thus easily forms a hydrogen bond with the water molecule and surrounds the water molecule. It is thought that the water retention of the container was increased as a result of suppressing the movement.

  Thus, the electrolytic treatment liquid obtained by adding sodium ascorbate, sodium gluconate, and glycerin to sodium sulfate has high water retention and is difficult to solidify. As a result, when the oxidized scale 30 is removed by rubbing the surface of the stainless steel parts 10 and 20 with a cloth, the amount of impregnation of the electrolytic treatment liquid that can be included in the cloth increases. Can be removed. Moreover, since the electrolytic treatment liquid to which glycerin has been added is difficult to solidify, clogging of piping and nozzles in the electrolytic treatment apparatus is suppressed. Furthermore, the electrolytic treatment solution to which glycerin has been added is also suitable for use in cold regions because freezing below the freezing point is suppressed.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiment, the stainless steel parts are the filler pipe and the breather pipe. However, the present invention can also be applied when the stainless steel part is a part other than the filler pipe and the breather pipe.
(2) In the above embodiment, the cationic electrodeposition coating is applied to the stainless steel part. However, the present invention can also be applied to the case of coating by a method other than the cationic electrodeposition coating.
(3) In the above embodiment, the cause of the generation of oxide scale is welding, but the present invention can also be applied to the case where the oxide scale is generated by heat treatment other than welding.

10 ... Filler pipe (stainless steel parts)
20 ... Breather pipe (stainless steel parts)
30 ... Oxidation scale

Claims (3)

An electrolytic treatment solution for stainless steel for removing oxide scale generated in stainless steel parts,
An electrolytic treatment solution for stainless steel, wherein sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin are contained in an amount of 1 to 10% by weight, respectively. Electrolysis for removing the oxidized scale with an electrolytic treatment solution containing 1 to 10% by weight of sodium sulfate, sodium ascorbate, sodium gluconate, and glycerin, respectively, on the stainless steel part on which the oxidized scale is generated. Processing steps;
A coating method for stainless steel, comprising: a coating step of coating the stainless steel part from which the oxide scale has been removed by the electrolytic treatment liquid.   The stainless steel coating method according to claim 2, wherein the coating is cationic electrodeposition coating.

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