JP5978650B2 - Method for surface treatment of steel materials - Google Patents

Description

  The present invention relates to a surface treatment method of a metal material for forming an oxide layer on the surface of the metal material, and a metal material having an oxide layer formed by the surface treatment method on the surface.

  Metal materials such as steel materials and alloy materials may be subjected to a treatment for forming an oxide layer on the surface for the purpose of changing the properties of the surface or in the manufacturing process of the product. For example, Patent Document 1 discloses a technique for forming an oxide layer mainly composed of FeO on a metal material surface for blackening treatment on the metal material surface. Further, in Patent Document 2, when a hot dip galvanizing treatment is performed on a steel material containing a large amount of an easily oxidizable element such as Si, the surface of the easily oxidizable element is suppressed by reduction treatment after oxidizing the steel surface. A technique for improving plating properties is disclosed. Patent Document 3 discloses a technique for preventing adhesion between steel sheets and improving press formability by forming an oxide layer on the surface of the steel sheet when processing the steel sheet.

  On the other hand, the surface softening treatment that softens only the surface layer of the material lowers the notch sensitivity of the surface and improves the impact resistance. The surface softening treatment is known to suppress stress corrosion cracking of the liquid ammonia storage tank. Furthermore, it is known that by forming a softened layer on the surface of high-strength steel, the occurrence of cracks on the surface during bending is suppressed, and bending workability is improved. From the above, surface softening treatment is an important technology for many products. In addition, as a softening layer forming method, a method of quenching after forming a decarburized layer on the surface is known, a method by controlling the heating, rolling, and cooling conditions of the steel slab, the surface of the high carbon steel by heat treatment There are known a method of forming a decarburized layer and a method of combining a material softer than the base material portion with the surface of the base material (see Patent Document 4, Non-Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 02-228466 JP 2010-196083 A Japanese Patent Laid-Open No. 03-285024 JP-A 61-139622

Decarburization treatment, “Manufacture of surface softened high carbon steel strip by open annealing”, Kawasaki Steel Technology, vol.13, No.2, p.210-217 (1981) Clad steel sheet, "Application of surface softened double-layer clad steel sheet to liquid ammonia tank", Kawasaki Steel Technology, vol.15, No.1, p.19-28 (1983)

  In general, the treatment for forming an oxide layer on the surface of a metal material is performed by directly or indirectly heating the metal material using a batch-type or continuous-type heating furnace. According to the surface oxidation treatment by heating, the thickness and composition of the oxide layer can be easily changed by controlling the heating temperature, the heating atmosphere, or the heating time. However, in the surface oxidation treatment by heating, it is difficult to control the fine structure of the oxide layer surface. The fine structure on the surface of the oxide layer affects the appearance of the metal material, slidability, and coating adhesion when applied. In addition, when a catalyst substrate is formed using a metal material with an oxide layer formed on the surface as a base material, the surface area changes according to the microstructure of the oxide layer surface. Affects. For this reason, provision of the surface treatment method of the metal material which can form a desired fine structure on the oxide layer surface was anticipated.

  On the other hand, among the surface softening treatment techniques, the conventional technique by controlling the heating, rolling, and cooling conditions of the steel slab requires a complicated rolling technique while controlling the temperature of the steel material, and is not a simple method. The prior art used can only be applied to steels rich in carbon. Further, in the technique of quenching after decarburization, a lot of labor is required for controlling the decarburized layer, for example, if the surface layer carbon is not reduced to 0.3 mass% or less, a burning crack occurs. In addition, the technique of combining a material softer than the base material portion with the surface of the base material requires many manufacturing steps and requires a lot of cost. For this reason, provision of the surface treatment method of the metal material which can form a surface softening layer at low cost without using a complicated rolling process and a decarburization process was anticipated.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is a surface treatment method for a metal material capable of forming a metal material having an oxide layer having a desired microstructure on the surface, and the surface treatment method. Another object is to provide a metal material having an oxide layer formed on the surface thereof.

  Another object of the present invention is to provide a surface treatment method for a metal material capable of forming a surface softening layer at low cost without using a decarburization treatment, and a softening layer formed by this surface treatment method on the surface. It is to provide a metal material.

  In order to solve the above-mentioned problems and achieve the object, the surface treatment method for a metal material according to the present invention comprises a material to be treated as a cathode electrode made of a metal material having a surface to be treated and an anode electrode in an electrolytic solution. A complete plasma state is formed between the step of dipping and the cathode electrode and the anode electrode, and the surface to be treated is oxidized, and a voltage that does not melt is applied to the surface to be treated. Forming an oxide layer.

  The surface treatment method for a metal material according to the present invention is characterized in that, in the above invention, the material to be treated is stainless steel, low alloy steel, or carbon steel.

  The metal material surface treatment method according to the present invention is characterized in that, in the above invention, the material to be treated is high strength steel having a tensile strength of 440 MPa or more.

  In order to solve the above problems and achieve the object, a metal material according to the present invention includes a metal material substrate and an oxide layer formed on a surface of the metal material substrate, and the oxide layer includes: The metal material substrate and the anode electrode are immersed in an electrolytic solution, and a complete plasma state is formed between the metal material substrate and the anode electrode, and the surface of the metal material substrate is oxidized. And it is formed by applying the voltage which is not melted.

  According to the present invention, there is provided a metal material surface treatment method capable of forming a metal material provided with an oxide layer having a desired microstructure on the surface, and a metal material provided with an oxide layer formed by the surface treatment method on the surface. can do.

  ADVANTAGE OF THE INVENTION According to this invention, the surface treatment method of the metal material which can form a surface softening layer at low cost, and the metal material which equips the surface with the softening layer formed by this surface treatment method can be provided.

FIG. 1 is a flowchart showing a flow of surface treatment of a metal material according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a configuration example of a processing apparatus used in the metal material surface treatment method according to an embodiment of the present invention. FIG. 3 is a SEM photograph showing the sample surface of Example 1 when the applied voltage is 145V. FIG. 4 is a diagram showing a secondary electron image and an EDS spectrum on the sample surface of Example 2 when the applied voltage is 135V. FIG. 5 is a diagram showing the measurement results of the secondary electron image, EDS spectrum, and friction coefficient on the surface of the test piece of Example 3. FIG. 6 is a diagram showing the measurement results of the secondary electron image, EDS spectrum, and friction coefficient on the surface of the test piece of the comparative example. FIG. 7 is a diagram showing a secondary electron image on the surface of the test piece of Example 4 and a measurement result of the friction coefficient. FIG. 8 is a diagram showing the hardness measurement results of the test piece of Example 5. FIG. 9 is an SEM photograph of the test piece of Example 5 at a position 5 mm deep from the liquid surface.

  Hereinafter, a metal material surface treatment method according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a flowchart showing a flow of surface treatment of a metal material according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a configuration example of a processing apparatus used in the metal material surface treatment method according to an embodiment of the present invention. As shown in FIG. 1, in the surface treatment of a metal material according to an embodiment of the present invention, first, a material to be treated as a cathode electrode made of a metal material having a surface to be treated and an anode electrode are placed in an electrolytic solution. Immerse (step S1). Then, a complete plasma state is formed between the cathode electrode and the anode electrode, and the surface to be processed is oxidized and a voltage that does not melt is applied, so that an oxide layer having a fine structure is applied to the material to be processed. Form on the surface (step S2). More specifically, as shown in FIG. 2, in the surface treatment of the metal material according to an embodiment of the present invention, the anode electrode 3 and the material to be treated 4 are immersed in the electrolytic solution 2 in the container 1, An oxide layer having a fine structure is formed on the surface of the material to be processed 4 by applying a voltage from the power source 6 to the anode electrode 3 and the material to be processed 4 through the conductive wire 5 such as a copper wire.

The electrolytic solution 2 is not particularly limited, but has electrical conductivity, and when the surface treatment of the material to be treated 4 is performed, the surface of the material to be treated 4 is excessively etched, or the anode electrode and the material to be treated are treated. It is a solution that hardly adheres to or precipitates on the surface of 4 or forms a precipitate. Examples of the electrolyte of the electrolytic solution 2 include potassium carbonate (K ₂ CO ₃ ), sodium carbonate (Na ₂ CO ₃ ), sodium hydrogen carbonate (NaHCO ₃ ), ammonium carbonate ((NH ₄ ) ₂ CO ₃ ), water Lithium oxide (LiOH), sodium hydroxide (NaOH), potassium hydroxide (KOH), ammonium hydroxide (NH ₄ OH), sodium chloride (NaCl), potassium chloride (KCl), ammonium chloride (NH ₄ Cl), sulfuric acid Citric acid such as sodium salt of sodium, potassium salt of sulfuric acid, ammonium salt of sulfuric acid, sodium salt of nitric acid, potassium salt of nitric acid, ammonium salt of nitric acid, sodium citrate (NaH ₂ (C ₃ H ₅ O (COO) ₃ )) Examples of sodium salt, potassium salt of citric acid, ammonium salt of citric acid, nitric acid, and hydrochloric acid Can show.

  The electrolytic solution 2 can have any pH and concentration as long as an oxide layer can be formed on the surface of the material to be treated 4. For example, when a potassium carbonate aqueous solution is used as the electrolytic solution 2, the concentration thereof is not particularly limited and can be 0.001 mol / L or more, more preferably 0.005 mol / L or more. This is because if the concentration of the electrolytic solution 2 is too low, it may be difficult to maintain a suitable discharge state when a voltage is applied between the anode electrode 3 and the material to be processed 4. The upper limit of the concentration of the electrolytic solution 2 is not particularly set, but can be set to 0.5 mol / L or less, for example. The pH of the electrolytic solution 2 can be set to an arbitrary value unless excessive corrosion or etching of the electrode is caused, for example, pH 10 to 12.

  The anode electrode 3 is formed of a material that is thermally and chemically stable during discharge. Examples of such an anode electrode 3 include Pt, Ir, and graphite.

  The material to be treated 4 is not particularly limited as long as it is a metal material, and a cold-rolled material, a hot-rolled material, a cast material, and a processed product thereof (including welding) can be used if it is a steel material. The steel type is not particularly limited, and carbon steel, low alloy steel, stainless steel, or high strength steel having a tensile strength of 440 MPa or more can be used. Plated steel sheets including electrogalvanized steel sheets can also be used. The shape of the to-be-processed material 4 is not specifically limited, A plate shape, linear shape, rod shape, pipe shape, or a processed component can be utilized. The to-be-processed material 4 needs to be immersed in the electrolyte solution 2, and needs to be deepened at least 1 mm or more from the liquid level.

  As the discharge condition, a complete plasma state is formed, and the voltage range in which the surface of the material to be processed 4 is oxidized and not melted can be used. Specifically, the discharge voltage is adjusted within a range from a voltage at which the material to be processed 4 exhibits orange point light emission in a dark place to a voltage immediately before the entire material to be processed 4 is heated red. The discharge voltage is preferably in the range of about 110 to 160 V, more preferably in the range of 135 to 160 V, when the size of the material to be processed 4 is 1 mm × 1 mm × 20 mm. This voltage range is applicable to most steel materials including alloy steels such as stainless steel. This voltage range changes depending on the type and arrangement of the material to be processed 4 and in some cases exceeds the above value. Therefore, the surface of the material to be processed 4 processed by changing the voltage condition is scanned with a scanning electron microscope (Scanning Electron Microscope). : Determined by observation with SEM).

  It is a necessary condition that the discharge voltage is a voltage that can form an oxide layer on the surface of the material to be treated 4. If the voltage is lower than the lower limit voltage, the surface of the material to be treated 4 is hardly oxidized, so that a voltage higher than the lower limit voltage needs to be applied. The lower limit voltage can be easily determined by examining the voltage at which the surface is oxidized using an SEM and an energy dispersive X-ray spectrometer (EDS) attached to the SEM. When oxygen is detected with the same X-ray intensity as the oxide of the material 4 to be processed, it is determined that the surface is oxidized. In addition, the material to be treated with respect to the X-ray intensity of oxygen normalized by the intensity of the L-line of Fe of the oxide of the material to be treated 4 (for example, it means an oxide of Fe in cold-rolled steel sheet or low alloy steel) When the X-ray intensity normalized with the Fe-L line intensity of oxygen in 4 is 1/3 or less, it is determined that the surface is not oxidized. The surface inspection is performed by changing the voltage and discharging for 30 minutes, taking out the material 4 to be treated, washing it with water, drying it, introducing it into the SEM, and observing it. On the other hand, when the applied voltage exceeds the upper limit voltage, the surface of the workpiece 4 is melted. Therefore, the voltage at which the surface of the workpiece 4 is melted can be determined as the upper limit voltage.

  The discharge processing time needs 3 seconds or more. However, the discharge treatment time can be as long as, for example, 60 minutes. However, if the discharge treatment time is too long, the material to be treated 4 may be worn out, so a treatment time of 30 minutes or longer is not preferable.

[Example 1]
In Example 1, a commercially available cold-rolled steel sheet having a thickness of 0.8 mm was cut into a width of 2 mm and a length of 25 mm, and conduction was made with a copper wire to form a cathode electrode. The anode electrode used was a 50-cm long Pt wire bent so as not to contact each other and formed into a planar shape. The connecting portion between the cold-rolled steel plate and the copper wire was heat-pressed with a heat resistant resin so that the copper wire did not touch the electrolytic solution, and the 20 mm long portion of the electrode was immersed in the electrolytic solution. The electrolytic solution used was an aqueous K ₂ CO ₃ solution having a concentration of 0.3 mol / L, and was discharged for 30 minutes while changing the applied voltage.

  3A and 3B are SEM photograph diagrams showing the surface of the surface to be treated of the cold-rolled steel sheet when the applied voltage is 145V. As shown in FIGS. 3 (a) and 3 (b), it was confirmed that a crater-like circular structure was formed everywhere on the surface when the applied voltage was 145V. Further, as a result of elemental analysis by EDS mounted on the SEM, it was confirmed that the surface of the cold rolled steel sheet was oxidized. Moreover, the surface of the cold-rolled steel sheet was not oxidized at an applied voltage of 140 V or lower, and the tip of the cold-rolled steel sheet was blown at an applied voltage of 160 V or higher. From the above, it was confirmed that the lower limit value and the upper limit value of the applied voltage were 145 V and 160 V, respectively, in this experimental condition and sample.

[Example 2]
In Example 2, a commercially available SUS430 stainless steel having a thickness of 1 mm was cut into a width of 2 mm and a length of 100 mm, and mirror polishing was performed up to 20 mm from the tip, and then conduction was made with a copper wire to obtain a cathode electrode. About 3 mm from the tip of the cathode electrode (lower side when immersed in the electrolytic solution) was sharpened with a file. The anode electrode used was a 50-cm long Pt wire bent so as not to contact each other and formed into a planar shape. A 15 mm long portion from the tip of the cathode electrode was immersed in the electrolytic solution. The electrolytic solution was a K ₂ CO ₃ aqueous solution having a concentration of 0.1 mol / L, discharged for 30 minutes while changing the applied voltage, and washed with water immediately after completion.

  As a result, it was confirmed that the surface of the stainless steel was oxidized within an applied voltage range of 130 to 160V. 4A and 4B are diagrams showing a secondary electron image and an EDS spectrum of the surface to be processed of the cathode electrode when the applied voltage is processed at 135V, respectively. As shown in FIGS. 4A and 4B, it is confirmed that an oxide layer having a fine structure different from that of Example 1 can be formed by changing the applied voltage to stainless steel as the material 4 to be processed. It was done. That is, as shown in FIG. 4A, in this embodiment, an intricate fine structure having a depression is formed on the surface. Thereby, since the sample of Example 2 has a large specific surface area, utilization as a catalyst substrate can be expected.

Example 3
In Example 3, a test piece having a width of about 3 mm and a length of 70 mm was cut out as a cathode electrode from a cold rolled steel sheet having a thickness of 0.7 mm containing 0.02% by mass of C and 0.14% by mass of Mn. One end of the test piece (the side that becomes the lower part when immersed in the electrolytic solution) was shaved with a file and then pickled and degreased with dilute hydrochloric acid for 1 second. The electrolytic solution was a K ₂ CO ₃ aqueous solution having a concentration of 0.1 mol / L, and the anode electrode was discharged using Pt at an applied voltage of 115 V for 30 minutes, and immediately after completion, washed with water. In this example, a portion 10 mm long from the tip of the electrode was immersed in the electrolytic solution. And the surface of the obtained test piece was observed by SEM, and the presence or absence of surface oxidation was evaluated by the elemental analysis by EDS. In addition, the friction coefficient at a position of 5 mm from the tip of the sample (lower side when immersed in the electrolytic solution) was evaluated using a nano tribometer manufactured by CSM. Specifically, a metal sphere having a diameter of 1.5 mm (material SUJ2) is pressed against the surface of the test piece with a load of 5 mN, and rotated on a circumference having a diameter of 0.5 mm at a speed of 5 mm / s. A total of 9 m was slid on the test piece. Then, the ratio of the tensile load to the pressing load was obtained as a friction coefficient, the change of the friction coefficient during sliding for 9 m was recorded, and the average value of the friction coefficient and the standard deviation σ were obtained. In addition, oiling is not performed.

  5 and 6 show measurement of secondary electron images, EDS spectra, and friction coefficient between the surface of the test piece of Example 3 subjected to the above-described treatment and the surface of the sample piece of the comparative example not subjected to the above-described treatment, respectively. Results are shown. As is clear from the comparison between FIG. 5 and FIG. 6, it was confirmed that an oxide layer having a crater structure was formed on the surface of the test piece of Example 3. Further, it was confirmed that the surface of the test piece of Example 3 had a low friction coefficient compared with the surface of the test piece of the comparative example, and was excellent in slidability. Further, it was confirmed that the appearance of the test piece of Example 3 was uniform gray and good.

Example 4
In Example 4, a 1.5 mm square and 50 mm long square-shaped test piece was cut out as a cathode electrode from a commercially available tool steel SKD11 containing approximately 13% by mass of Cr, and the tip was sharpened in the same manner as in Example 3. The electrolytic solution was a K ₂ CO ₃ aqueous solution having a concentration of 0.1 mol / L, and discharge was performed at an applied voltage of 125 V for 60 minutes using Pt for the anode electrode. During discharge, the length of the electrode immersed in the electrolytic solution was 12 mm. In the present embodiment, washing after the treatment is not performed. And the evaluation similar to Example 3 was performed about the processed test piece, and the comparison with an untreated test piece was performed.

  As a result of measurement by EDS, it was confirmed that an oxide layer was formed on the surface of the test piece of Example 4. 7A and 7B are diagrams showing a secondary electron image on the surface of the test piece of Example 4 and a measurement result of the friction coefficient, respectively. As shown in FIG. 7A, it was confirmed that an oxide layer having a fine structure as shown in FIG. 4A was formed on the surface of the test piece of Example 4. Moreover, as shown in FIG.7 (b), although the friction coefficient of the test piece surface of Example 4 is larger than the friction coefficient of the test piece surface of the comparative example which is not performing the above-mentioned process while the sliding distance is short. Even when the sliding distance increased, the increase in the coefficient of friction was smaller than that of the comparative example, and both reversed at a sliding distance of about 2.5 m. For this reason, the surface of the test piece of this example has a small change in the coefficient of friction when sliding over a long sliding distance. For example, in the mold during continuous press molding or the contact portion that repeatedly slides, The effect of keeping the state stable for a long time can be expected.

Example 5
In Example 5, a steel material containing 0.6% by mass of C, 2% by mass of Si, and 2% by mass of Cr was cold-rolled at a reduction rate of 80%, and the thickness was 1 mm, the width was about 2 mm, and the length was 20 mm The test piece was cut out as a cathode electrode. The electrolytic solution was an aqueous solution of K ₂ CO ₃ having a concentration of 0.3 mol / L, and discharge was performed at an applied voltage of 150 V for 30 minutes using Pt as the anode. And the cross-sectional sample was created in the position of depth 5mm from the liquid level of the obtained test piece, the structure of the cross-sectional sample was observed with SEM, and the surface layer was confirmed. Moreover, the hardness of the surface layer in the sample cross section and the inside was measured by a micro Vickers method with a load of 25 g. The hardness was measured at 5 points for each of the surface layer and the inside, and the average value was calculated.

  FIG. 8 is a diagram showing the hardness measurement results of the test piece of Example 5. FIG. 9 is an SEM photograph of the test piece of Example 5 at a depth of 5 mm from the liquid level of the test piece. As shown in FIG. 9, a surface layer having a thickness of about 30 μm and an oxide layer having a thickness of about 15 μm were formed at a position 5 mm deep from the liquid surface of the test piece. Moreover, as shown in FIG. 8, the micro Vickers hardness of a cross-sectional center part and a surface layer is 900 and 200 in the position of a depth of 5 mm from the liquid level of a test piece, respectively, and the hardness below 1/4 of an inside It was confirmed that the surface softening layer which has this was formed. From this, it can be expected that the test piece of this example is based on an ultra-high strength steel plate exceeding 2 GPa and has impact resistance, bending crack resistance, and high surface lubricity. In addition, the surface softening layer can be expected to have a merit that the bead bites into and fixes easily when the plate is fixed with a bead of a mold at the time of processing, for example. In this example, an Fe oxide layer was formed on the surface of the softened layer. Since this oxide layer had a fine structure similar to that of Example 4 described above, it can be used as it is as an effect of improving long-distance slidability. Further, since the surface layer is formed inside the oxide layer, if the oxide layer is unnecessary or has an adverse effect when painting, the oxide layer is formed using an acid to which an inhibitor is added after the discharge treatment. Remove it.

DESCRIPTION OF SYMBOLS 1 Container 2 Electrolytic solution 3 Anode electrode 4 Material to be processed (cathode electrode)
5 Conductor 6 Power supply 7 Thermometer

Claims (3)

A step of immersing a material to be treated as a cathode electrode made of a steel material having a surface to be treated and an anode electrode in an electrolytic solution;
A complete plasma state is formed between the cathode electrode and the anode electrode, and the surface to be treated is oxidized and applied with a voltage that does not melt, thereby applying vanadium, molybdenum, and Forming an oxide layer free of tungsten components;
A method for surface treatment of a steel material, comprising: The steel material surface treatment method according to claim 1, wherein the material to be treated is stainless steel, low alloy steel, or carbon steel. The surface treatment method for a steel material according to claim 2, wherein the material to be treated is high-strength steel having a tensile strength of 440 MPa or more.