JP2011246737A - Composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress hydrogen embrittlement in a member composed of steel.SOLUTION: A composite material includes a steel material 101 and a metal plating film 102 formed on the surface of the steel material 101. The metal plating film 102 is composed of a metal which, compared to iron, shows a lower bonding energy to hydrogen and a smaller exchange current density of a chemical reaction through which hydrogen ions at the surface are converted into hydrogen molecules. The steel material 101 is e.g. well-known carbon steel.

Description

  The present invention relates to a composite material using steel, which is used for a reinforced concrete reinforcing bar or the like.

  In structures such as buildings, delayed fracture becomes a problem. Delayed fracture is a phenomenon in which steel materials used under certain conditions that are subjected to static addition suddenly break brittlely with no apparent plastic deformation after a certain period of time. is there. Although the mechanism of this delayed fracture has not been fully elucidated, it is considered to be due to hydrogen embrittlement due to the hydrogen existing in the environment entering the metal and losing its ductility (see Non-Patent Document 1). .

  Regarding this hydrogen embrittlement, the development of steel that is resistant to hydrogen embrittlement (see Non-Patent Document 2 and Non-Patent Document 3) and the development of surface treatment technology for measuring the amount of hydrogen that causes hydrogen embrittlement (Non-patent) Many researches and developments have been made, such as Reference 4). In addition, the bonding force (MH) between hydrogen and metal has also been investigated (see Non-Patent Document 5).

  There are a plurality of types of processes for intrusion of hydrogen into metal, which causes hydrogen embrittlement. For example, as shown in FIG. 3, it is reported that gaseous hydrogen molecules 301 enter the metal through a process of adsorbing hydrogen 303 onto the surface of the metal 302 (see Non-Patent Document 6). Further, in Non-Patent Document 6, as shown in FIG. 3, hydrogen ions 304 in a solution or hydrogen ions 304 generated by reducing moisture on the surface of the metal 302 are used as a base, and hydrogen 303 is formed on the surface of the metal 302. It has also been reported that the adsorbed hydrogen 303 penetrates into the metal 302. Since hydrogen hardly exists in the air, hydrogen embrittlement is thought to start from the process of adsorbing hydrogen generated on the steel surface due to reduction of adhering water.

Nagumo Michihiko, “Effect of Hydrogen on Mechanical Behavior of Steel”, Iron and Steel, Vol. 0, No. 10, pp. 766-775, 2004. Yuichi Namimura, et al., “High-strength bolt steel with excellent delayed fracture resistance”, Kobe Steel Technical Report, Vol. 50, no. 1, pp. 41-44, April 2000. Yasuhiko Takahashi, et al., “High-strength steel with excellent hydrogen embrittlement resistance”, Material and Material Research Outlook, Part 3 Future Research Trends in Material and Material Research, Chapter 5, Environment and Energy Materials, pp. 351-355, 2006. Takenori Nakayama, et al., “Development of cadmium substitute hydrogen escape prevention plating”, Materials and Processes, Vol. 13, No. 6, p. 1376, 2000. Toshiyuki Ohtsuki, Kenji Kano, Susumu Kuwabata, “Basic Electrochemistry”, published by Kagaku Doujin, pp. 153, 153, 2,007. Michihiko Nagumo, “Basics of Hydrogen Embrittlement: Behavior of Hydrogen and Embrittlement Mechanism”, published by Uchida Otsukuru, pp. 107-109, 117-119, 2008. Shozo Asahara, et al., “Metal Surface Technology Lecture 6 Electroplating Technology”, edited by Metal Surface Technology Association, Asakura Shoten Co., Ltd., pp. 150-171, 1972.

  In order to suppress the hydrogen embrittlement mentioned above, various hydrogen embrittlement countermeasure technologies such as examination of materials that are strongly constrained in the metal structure even if hydrogen invades and do not affect the metal structure, and examination of the alloy composition of steel Is being sought. In any case, however, when steel is used, depending on the environment, hydrogen is generated on the surface of the steel, which can be adsorbed on the steel and cause hydrogen embrittlement. Thus, in the examination of the composition of steel itself, there is a problem that hydrogen embrittlement is caused because generation of hydrogen on the steel surface and adsorption of hydrogen to the steel cannot be suppressed.

  The present invention has been made to solve the above-described problems, and an object thereof is to suppress hydrogen embrittlement in a member made of steel.

  The composite material according to the present invention is composed of a steel material and a metal plating film formed on the surface of the steel material. The metal plating film has a smaller binding energy to hydrogen than iron, and hydrogen ions on the surface are hydrogen molecules. The exchange current density of the chemical reaction is such that it is made of a metal smaller than iron.

  In the composite material, the composite material is used by being disposed in concrete. For example, the steel material is a reinforced concrete rebar.

  As described above, according to the present invention, the metal plating film formed on the surface of the steel material has a smaller binding energy with hydrogen than iron, and the exchange current density of a chemical reaction in which hydrogen ions on the surface become hydrogen molecules. Since it comprised from the metal smaller than iron, the outstanding effect that the hydrogen embrittlement in the member comprised from steel can be suppressed is acquired.

FIG. 1 is a cross-sectional view showing a partial configuration of a composite material according to an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between “exchange current density of chemical reaction of 2H ⁺ + 2e ⁻ → H ₂ ” and “binding energy with hydrogen”. FIG. 3 is an explanatory diagram for explaining a process of penetration of hydrogen into a metal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a partial configuration of a composite material according to an embodiment of the present invention. The composite material includes a steel material 101 and a metal plating film 102 formed on the surface of the steel material 101. Here, the metal plating film 102 is made of a metal that has a smaller binding energy with hydrogen than iron and has a smaller exchange current density of chemical reaction in which hydrogen ions on the surface become hydrogen molecules than iron. Note that the steel material 101 is, for example, well-known carbon steel.

  According to the composite material in the present embodiment having the above-described configuration, the surface of the composite material is covered with the metal plating film 102. Therefore, the generation of hydrogen gas and the adsorption of hydrogen on the surface are the surfaces of the steel material 101. Since it becomes possible to suppress more, hydrogen embrittlement in the steel material 101 can be suppressed.

  This will be described in more detail below. It is considered that hydrogen embrittlement in the steel material 101 starts from a process in which hydrogen is generated on the metal surface and the generated hydrogen is adsorbed to the metal.

Therefore, firstly, the generation of hydrogen gas is difficult to occur on the surface of “a metal with a small exchange current density of chemical reaction of 2H ⁺ + 2e ⁻ → H ₂ that generates hydrogen gas (H ₂ )”. It is considered that hydrogen intrusion can be suppressed. Second, on the surface of “metal having low binding energy with hydrogen”, it is considered that hydrogen (for example, hydrogen ions) is hardly adsorbed on the surface, so that hydrogen intrusion from the liquid phase can be suppressed.

The relationship between the above-mentioned “exchange current density of chemical reaction of 2H ⁺ + 2e ⁻ → H ₂ ” and “binding energy with hydrogen” is as shown in FIG. In FIG. 2, the horizontal axis represents “binding energy with hydrogen”, and the vertical axis represents “exchange current density of chemical reaction of 2H ⁺ + 2e ⁻ → H ₂ ”. As is clear from FIG. 2, a metal having a smaller “2H ⁺ + 2e ⁻ → H ₂ chemical reaction exchange current density” and a smaller “hydrogen binding energy” than iron (Fe) is, for example, indium (In ) And tin (Sn) and the like in the lower left quadrant of the four quadrants defined by two orthogonal straight lines through Fe. By forming the metal plating film 102 of these metals on the surface of the steel material 101, hydrogen embrittlement in the steel material 101 composed of steel can be suppressed. As is clear from FIG. 2, In is optimal as the metal that satisfies the two upper surfaces described above. Moreover, even if Sn, since the above two conditions are satisfied, the same effect can be expected.

For example, in the case of forming the Sn metal plating film 102, a plating bath prepared by preparing a plating solution having 80 to 320 g / l of potassium oxalate and 15 to 45 g / l of potassium hydroxide, and setting this to a temperature of 65 to 90 °. The steel material 101 used as a cathode is immersed in the inside. In this state, a current of 3 to 10 A / dm ² is passed. By this electrolytic plating, Sn is deposited on the surface of the steel material 101 which is a cathode, and a metal plating film 102 made of Sn can be formed on the surface of the steel material 101 (see Non-Patent Document 7).

Further, a plating solution having zinc sulfate 360 g / l, ammonium chloride 30 g / l, and glucose 120 g / l is prepared, and the steel material 101 serving as the cathode is immersed in a plating bath at 30 ° C. In this state, a current having a current density of ^{2 to} 4 A / dm ² is passed. By this electrolytic plating, a metal plating film 102 made of Zn can be formed on the surface of the steel material 101.

  If the metal satisfies the two conditions described above, the hydrogen generation reaction is unlikely to occur and hydrogen is not easily adsorbed on the surface, so that hydrogen embrittlement is less likely to occur. However, such metals are not as strong as steel and are very difficult to use as an alternative to iron. Here, by using a composite material in which the metal plating film 102 satisfying the above-described two conditions is formed on the surface of the high strength steel material 101, hydrogen can be prevented from entering the steel material 101, and further strength can be obtained. There is a feature of the present invention.

  As described above, according to the present invention, the surface of a steel material is plated with a metal that has a smaller binding energy with hydrogen than iron, and the exchange current density of a chemical reaction in which hydrogen ions on the surface become hydrogen molecules is smaller than iron. Therefore, hydrogen generated on the surface and hydrogen adsorbed on the surface can be reduced, and the amount (rate) of hydrogen entering the steel material can be suppressed. As a result, according to the present invention, it can be expected that the time until the steel material reaches the delayed fracture can be greatly extended, and the composite material according to the present invention is suitable as a member of a building element (fixed structure) of a building. is there.

  It should be noted that the present invention is not limited to the embodiment described above, and that many modifications can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, the metal plating film is not limited to Sn and Zn, but may be composed of bismuth (Bi). Further, the metal plating film may be made of an Sn—Bi alloy. Moreover, the composite material mentioned above is useful when arrange | positioning and using in concrete, such as the reinforcement of a reinforced concrete. It is difficult to replace the reinforcing bars disposed inside the concrete, and in some cases, the life of the building made of reinforced concrete is the time when the reinforcing bars are broken. On the other hand, according to the present invention, since brittle fracture can be suppressed and breakage of a reinforcing bar can be prevented, for example, the life of a building made of reinforced concrete can be extended.

  101 ... steel material, 102 ... metal plating film.

Claims (3)

It consists of a steel material and a metal plating film formed on the surface of this steel material,
The metal plating film is composed of a metal having a smaller binding energy with hydrogen than iron and a smaller exchange current density of a chemical reaction in which hydrogen ions on the surface become hydrogen molecules than iron. The composite material according to claim 1, wherein
The composite material is used by being disposed in concrete. The composite material according to claim 2, wherein
The steel material is a reinforced concrete rebar.

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