JP2015090314A - Hydrogen embrittlement prevention method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable preventive measures of hydrogen embrittlement to be implemented under conditions applicable to an actual environment.SOLUTION: A hydrogen embrittlement prevention method comprises the steps of: in a state where each test solution is in contact with a part of each specimen, observing presence or absence of fracture at a portion of the specimens being in contact with the test solutions respectively while a tensile stress smaller than a yield load of the specimens is applied to each of the specimens; and using a steel material made of steel of the specimens in an environment of a pH higher than a pH in which fracture is observed.

Description

  The present invention relates to a hydrogen embrittlement prevention method for preventing hydrogen embrittlement of a steel material.

  For example, high-strength carbon steel is widely used as a member for prestressed concrete structures and automobiles. In such steel materials in a stressed state such as high strength steel, delayed fracture may be a problem. Delayed fracture means that steel materials used under certain conditions that are subjected to static loads suddenly become brittlely cracked or fractured after a certain amount of time, with virtually no plastic deformation. It is a phenomenon that brings about destruction.

  Although the mechanism of this delayed fracture has not been fully elucidated, one of the causes is considered to be hydrogen embrittlement due to the penetration of hydrogen into the metal and loss of ductility. This is a hydrogen embrittlement phenomenon in which, when hydrogen enters a metal member in a state where stress is applied, the toughness, which is a characteristic of the original metal, is reduced. In steel materials in which hydrogen embrittlement has occurred, the predetermined strength in design is impaired, and there is a risk of destruction of the steel materials themselves, and further destruction of structures composed of the steel materials.

  In order to prevent the above-described problems, for example, in order to prevent hydrogen embrittlement of a steel material, a high strength bolt is made to lower the hydrogen embrittlement sensitivity by reducing the material strength (see Non-Patent Document 1). In addition, the FIP test prescribed by the International Prestress Committee determined the amount of hydrogen and the cracking time due to hydrogen embrittlement. By limiting the amount of hydrogen below the concept of the limit amount of hydrogen that does not lead to cracking, Studies have also been made to prevent embrittlement (see Non-Patent Document 2).

Tetsuo Shirakami, “Hydrogen embrittlement of high-strength steel”, Proc. 170th Corrosion Protection Technology Symposium, 1-9, 2010. Toshizo Tarai, “Hydrogen embrittlement of high-strength steel”, symposium presentation on cracking of reinforcing steel in concrete, 77-89, 2008. Hiroyuki Saito, Norihiro Fujimoto, Takashi Sawada, “Hydrogen Penetration Efficiency into High Strength Steel”, Abstracts of the 79th Annual Meeting of the Electrochemical Society, 3G07, 205, 2012.

  However, there is a problem that the measures for reducing the material strength cannot be applied when higher strength is required. Moreover, in the technique using the FIP test, it is not necessarily intended to impart the hydrogen embrittlement of steel in a real environment, and a technique applicable to the real environment is desired. In the actual environment, hydrogen embrittlement is caused by the surrounding environment and stress acting on the steel material. Therefore, it is necessary to examine hydrogen embrittlement from the results of tests simulating the environment and load stress.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to be able to take measures to prevent hydrogen embrittlement in a state applicable to an actual environment.

  The hydrogen embrittlement prevention method according to the present invention includes a first step of preparing a plurality of test solutions each having a different pH, a second step of preparing a plurality of test pieces in a steel bar shape, and each test solution. With each of the test pieces in contact with a part of the test piece, a tensile stress smaller than the yield load of the test piece is applied to each of the test pieces, and the presence or absence of breakage of each test piece in contact with the test solution is observed. The steel material comprised from the said steel is equipped with the 4th process used in the environment of pH higher than the pH of the test solution which was contacting the test piece by which the fracture | rupture was observed.

  In the hydrogen embrittlement prevention method, in the third step, a test piece may be used as an electrode to apply a potential to the test solution so that hydrogen is more likely to be generated.

  As described above, according to the present invention, measures for preventing hydrogen embrittlement can be taken in a state applicable to an actual environment.

FIG. 1 is a flowchart for explaining a hydrogen embrittlement prevention method according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a configuration example in which the test piece 201 is brought into contact with the test solution 203. FIG. 3 is a characteristic showing a state until fracture occurs in an experiment in which tensile stress is applied to two test pieces A and B made of two types of steel in contact with an aqueous solution having a predetermined pH. FIG. FIG. 4 is a characteristic showing a state until fracture occurs in an experiment in which tensile stress is applied to two test pieces A and B made of two kinds of steel in contact with an aqueous solution having a predetermined pH. FIG. FIG. 5 is a characteristic showing a state until fracture occurs in an experiment in which tensile stress is applied to two test pieces A and B made of two types of steel in contact with an aqueous solution having a predetermined pH. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining a hydrogen embrittlement prevention method according to an embodiment of the present invention. First, in the first step S101, a plurality of test solutions each having a different pH are prepared. For example, five types of test solutions A, B, C, D, and E, each having a different pH in the range of pH 8 to pH 10, may be prepared. Next, in the second step, a plurality of test pieces having a target steel rod shape are prepared. As described above, when five types of test solutions A, B, C, D and E are prepared, five rod-shaped test pieces A, B, C, D and E having the same shape made of the same steel are used. Just prepare. In addition, in each test solution, the contained substance considered to exist in the actual environment where the steel material comprised from the said steel is used may be dissolved.

  Next, in step S103, a tensile stress smaller than the yield load of the test piece is applied to each of the test pieces in a state where each test solution is in contact with a part of each test piece, and each test piece is tested. Observe the presence or absence of breakage at the point of contact with the solution. A part of the test piece A is brought into contact with the test solution A, a part of the test piece B is brought into contact with the test solution B, a part of the test piece C is brought into contact with the test solution C, The test solution D may be brought into contact with the part, and the test solution E may be brought into contact with a part of the test piece E. The test pieces A, B, C, D, and E are all steel materials having the same shape made of the same steel, but the test solutions A, B, C, D, and E have different pH values. The tensile stress to be applied is common to all the test pieces A, B, C, D, and E.

  Here, as shown in FIG. 2, the periphery of a part of the test piece 201 may be covered with a container 202 and the container 202 may be filled with the test solution 203. Thereby, a state in which a part of the test piece 201 is in contact with the test solution 203 is obtained.

  Further, the tensile stress applied to the test piece may be about 80% of the yield load of the test piece. For example, the test piece may be a commercially available reinforcing bar, and a tensile stress of 80% of the yield load published by the reinforcing bar manufacturer may be applied to each test piece. Under conditions where the tensile stress applied to the test piece is greater than the yield load, the test piece breaks regardless of the presence or absence of hydrogen embrittlement. On the other hand, if the tensile stress applied to the test piece is too small, a very long time is required until the test piece breaks. For this reason, it is good to set it as the conditions mentioned above.

  As described above, when tensile stress is applied to each test piece, a test piece in which breakage occurs and a test piece in which breakage does not occur are generated depending on the pH of the test solution being brought into contact. Here, the pH of the test solution in contact with the test piece in which breakage was observed can be considered as the pH in an environment where the test piece is likely to cause hydrogen embrittlement. Therefore, in the fourth step S104, the steel material composed of the steel constituting the test piece is used in an environment having a pH higher than the pH of the test solution in contact with the test piece in which the fracture was observed.

  As described above, if a steel material made of steel of the test piece is used in an environment having a pH higher than the pH at which the fracture is observed (fracture was observed) obtained as a result of the experiment performed using the test piece, It is thought that hydrogen embrittlement can be prevented. Thus, according to the present invention, it is possible to take measures to prevent hydrogen embrittlement in a state applicable to a real environment.

  In addition, in the test piece which was made to contact the test solution of higher pH, hydrogen generation | occurrence | production on the surface of a test piece is suppressed and it is thought that it is the conditions on which hydrogen embrittlement does not occur easily. On the other hand, in a test piece that has been in contact with a lower pH test solution, hydrogen is likely to be generated on the surface of the test piece, which is considered to be a condition where hydrogen embrittlement is likely to occur.

  In the above-described measurement, a potential is applied to the test solution using the test piece as an electrode, hydrogen is more likely to be generated than when no potential is applied, and the rupture test is performed with the reaction accelerated. May be. In an actual environment, a state in which a potential is applied can occur. Examples of reactions that occur in an actual environment include hydrogen generation from water in an alkaline solution, adsorbed hydrogen and hydroxide from water and electrons. A system in which ions are generated is known (see Non-Patent Document 3). Degradation (embrittlement) can be accelerated by maintaining the potential of the test piece and generating hydrogen from the test solution so that the production system has excess electrons in this reaction system.

  Next, the effect of the present invention will be verified. First, two first test pieces and second test pieces prepared from two types of steel are prepared. The first test piece and the second test piece are made of different steels. The first test piece and the second test piece are made in the same manner as described with reference to FIG. 2, so that a solution having a predetermined pH is brought into contact with each of the first test piece and the second test piece, and a tensile stress smaller than the yield load of the test piece is applied. Add to each. In this state, the time until the first test piece and the second test piece are broken and the hydrogen concentration (hydrogen amount) in the first test piece and the second test piece are measured. It should be noted that the hydrogen concentration at the interface between the environment and the material (test piece) should not exceed the hydrogen concentration.

  Specifically, the solution is, for example, a 1M calcium hydroxide aqueous solution, and the tensile stress is 80% of the maximum tensile load (yield load) of each test piece. Although the temperature of the environment such as a solution may be appropriately designed, room temperature (about 20 to 25 ° C.) can be used as an example. In order to maintain the conditions such that the generation system has an excessive potential, for example, an overvoltage from the natural immersion potential may be applied to the test piece at −1.5 V. For the potential control, an existing three-electrode method may be used.

  In addition, the hydrogen concentration in the test piece is periodically measured until the test piece breaks. Further, the time from the start of applying the tensile stress to the break of the test piece is measured. The hydrogen concentration of the test piece may be measured by temperature programmed desorption analysis or the like. In the measurement of the hydrogen amount, the hydrogen ion concentration in the vicinity of the test piece in the test solution may be measured, and this measured value may be used as the hydrogen amount. The amount of hydrogen in the steel and the hydrogen ion concentration in the vicinity thereof are in an equilibrium state, and the hydrogen ion concentration can substantially be the amount of hydrogen in the test piece.

  FIG. 3 shows the measurement results of the acceleration test described above. FIG. 3 shows the results of performing the above-described test on two first test pieces and second test pieces produced from two types of steel. In FIG. 3, (a) shows the result of the first test piece, and (b) shows the result of the second test piece. Further, the hydrogen ion concentration in the vicinity of the test piece in the test solution is measured, and this is approximated as the amount of hydrogen in the test piece.

  As shown in FIG. 3A, the first test piece breaks at time t1, and as shown in FIG. 3B, the second test piece breaks at time t2 longer than time t1. Yes. Moreover, the 1st test piece is fractured in a state where the amount of hydrogen is larger than that of the second test piece. Therefore, it can be seen that the time required for the first test piece and the second test piece to break depends on the hydrogen concentration (pH) at the interface with the environment.

  When the hydrogen concentration (environmental pH) at the interface with the environment is a high value (low pH) as shown in FIG. 4 with respect to the first test piece and the second test piece, the first test piece and the second test piece Both of the two specimens will break. However, in this case, the time required for the fracture is longer for the second test piece than for the first test piece.

  On the other hand, when the environment obtained by applying the present invention to the hydrogen concentration at the interface with the environment (the pH of the environment) by applying the present invention to the first test piece is examined, as shown in FIG. It becomes a state (high pH) smaller than the hydrogen amount at the time of breaking. It can be seen that in such an environment, the second test piece breaks, but the first test piece does not break. As described above, in the results shown in FIG. 3, the second test piece is considered to have higher resistance to hydrogen embrittlement. However, if the environment to be used is appropriately set according to the present invention, the first test piece is used. Can prevent fracture due to hydrogen embrittlement.

  From the above results, if the hydrogen concentration at the interface between the steel material and the environment (steel material surface) has a lower value than the steel material breaks, in other words, the pH of the environment in which the steel material is disposed has a steel material breakage. If it is in a higher state than this, it can be seen that the steel material can be used in an actual environment without being broken by hydrogen embrittlement.

  The present invention is not limited to the embodiment described above, and many modifications and combinations can be implemented by those having ordinary knowledge in the art within the technical idea of the present invention. It is obvious. For example, in the above description, the test solution is partially brought into contact with the test piece. However, the present invention is not limited to this, and tensile stress is applied to the test piece while the entire test piece is immersed in the test solution. You may do it.

  201 ... test piece, 202 ... container, 203 ... test solution.

Claims (2)

A first step of preparing a plurality of test solutions each having a different pH;
A second step of preparing a plurality of test pieces in a rod-like shape of the target steel;
A tensile stress smaller than the yield load of the test piece is applied to each of the test pieces in a state where the test solution is in contact with a part of the test piece, and the test solution is applied to each of the test pieces. A third step of observing the presence or absence of breakage at the point of contact with
The steel material comprised from the said steel is equipped with the 4th process used in the environment of pH higher than the pH of the test solution contacted with the test piece in which the fracture | rupture was observed. The hydrogen embrittlement prevention method characterized by these. In the hydrogen embrittlement prevention method according to claim 1,
In the third step, a hydrogen embrittlement prevention method characterized in that a potential is applied to the test solution by using the test piece as an electrode to make hydrogen more easily generated.