JP5079375B2 - Surface treatment method for hydrogen embrittlement resistance evaluation test piece - Google Patents

Description

  The present invention relates to a method for evaluating the hydrogen embrittlement resistance of a metal material, particularly a steel material, and particularly to a method for measuring the amount of critical diffusible hydrogen.

  The higher the strength of the metal material, the higher the possibility of causing hydrogen embrittlement. In particular, in the development of high-strength steel, proposals have been made regarding steel materials having excellent delayed fracture characteristics, which is a kind of hydrogen embrittlement (for example, Patent Documents 1 to 3).

  Various evaluation methods for hydrogen embrittlement resistance have been proposed. Patent Document 1 discloses a method for measuring the critical diffusible hydrogen content, Patent Document 2 discloses a method for determining delayed fracture strength, and Patent Document 3 A method for obtaining the rupture time by a constant load test is used. In the evaluation of hydrogen embrittlement resistance, hydrogen is retained in an atmosphere of hydrogen at high temperature and high pressure in order to forcibly contain hydrogen in the test piece. Thereafter, plating is performed to suppress the release of hydrogen from the test piece during the test.

  In Patent Document 1, cadmium plating is used to prevent the release of hydrogen. However, since cadmium is harmful, there is a disadvantage that requires careful handling from the viewpoint of safety and environment. On the other hand, methods for suppressing hydrogen diffusion by galvanization have been proposed (for example, Non-Patent Document 1 and Patent Document 4). Non-Patent Document 1 proposes a method using zinc plating with a zinc sulfate bath, and Patent Document 4 proposes a method using zinc plating with an ammonium chloride bath.

Japanese Patent Laid-Open No. 11-270531 Japanese Patent Laid-Open No. 10-036940 Japanese Patent Application Laid-Open No. 09-078172 JP 2005-69815 A Takenori Nakayama, 3 others, “Development of cadmium substitute hydrogen escape prevention plating”, Materials and Processes, Japan Iron and Steel Institute, 2000, Vol. 13, No. 6, p. 1376

  As a result of studying these galvanizing methods by the present inventors, it has been found that the conventional method has insufficient hydrogen release preventing ability depending on the steel type and the shape of the test piece. The present invention relates to a method for evaluating the resistance to hydrogen embrittlement, such as measurement of critical diffusible hydrogen, which is the maximum amount of hydrogen that does not cause hydrogen embrittlement, and evaluation of delayed fracture characteristics under constant load loading. It is an object of the present invention to provide a method for efficiently applying galvanizing to the surface of a test piece, which is not affected by the shape and has an extremely small amount of hydrogen release during the test.

According to the surface treatment method of the hydrogen embrittlement resistance evaluation test piece of the present invention, a test piece made of a metal material, particularly a steel material, is charged with hydrogen by cathodic charging, and then zinc is applied under appropriate conditions in order to suppress hydrogen diffusion. Plating is performed. Moreover, if this test piece is used, the maximum amount of diffusible hydrogen leading to fracture can be determined by applying a constant load tensile stress of several tens of percent of the tensile strength. The gist of the present invention is as follows.
(1) To a test piece made of a metal material containing hydrogen,
ZnCl ₂ : more than 80 g / l and 300 g / l or less,
Brightener: 10-50 ml / l,
Sum of one or both of NH ₄ Cl and KCl: 100 to 300 g / l
A surface treatment method for a hydrogen embrittlement characteristic evaluation test piece, characterized by performing a hydrogen embrittlement characteristic evaluation test after electroplating in a plating bath containing.
(2) The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to (1) above, wherein the test piece has a threaded portion.
(3) The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to the above (1) or (2), wherein the test piece has one or both of a notch and a hole.
(4) The surface treatment method for hydrogen embrittlement resistance evaluation test piece according to any one of (1) to (3) above, wherein the cathode current density is 0.5 to 50 A / dm ^2. .
(5) The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of (1) to (4) above, wherein the temperature of the plating bath is 10 to 60 ° C.
(6) The surface treatment method for hydrogen embrittlement resistance evaluation test piece according to any one of (1) to (5) above, wherein the pH of the plating bath is 4.5 to 6.5 .
(7) The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of (1) to (6) above, wherein the plating time is 1 to 30 minutes.
(8) The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of (1) to (7) above, wherein the test piece is made of a steel material.

  According to the present invention, the measurement of the critical diffusible hydrogen amount using a galvanized test piece which is safer and less burdensome on the environment than the method using cadmium plating and has a higher ability to prevent hydrogen release during the test than before. In addition, it is possible to provide a method for evaluating hydrogen embrittlement resistance capable of performing delayed fracture tests such as constant load tests with high accuracy and high efficiency, and the industrial contribution is extremely remarkable.

  The surface treatment method for a hydrogen embrittlement resistance evaluation test piece of the present invention is to perform galvanization on the surface of a test piece that has occluded hydrogen by hydrogen charging or the like. Thereby, the release of hydrogen from the test piece can be prevented before and during the test, and the hydrogen embrittlement resistance can be accurately obtained.

  A method for measuring the amount of critical diffusible hydrogen will be described as an example of a test method for evaluating the hydrogen embrittlement resistance after hydrogen charging and plating before the test. Hydrogen is occluded in the test piece by cathodic charging, galvanized, and then subjected to a constant load test, recovered immediately after breaking or after a certain time (for example, after 100 hours), and the amount of hydrogen in steel by gas chromatography etc. Ask for. The amount of occluded hydrogen is changed by changing the current density during cathode charging, and the maximum amount of hydrogen that does not break is defined as the critical diffusible hydrogen amount, and the hydrogen embrittlement resistance is evaluated.

  The reason for limiting the plating bath composition in the surface treatment method of the present invention will be described.

ZnCl ₂ is added to supply zinc, which is the main component of galvanizing, but if the amount added is 80 g / l or less, the amount of plating deposited becomes non-uniform, especially in parts where the amount of adhesion is small. , Since the throwing power and covering power are reduced, the hydrogen release preventing ability is low. On the other hand, when the addition amount of ZnCl ₂ exceeds 300 g / l, the uniform electrodeposition deteriorates, so that uniform plating cannot be applied, and the ability to prevent hydrogen release decreases, so that over 80 g / l and over 300 g / l. The range was limited to 1 or less.

The brightener is added to improve the throwing power, and a general-purpose brightening agent may be used. However, if the added amount is less than 10 ml / l, the throwing power is inferior and uniform plating is required. Cannot be imparted, and the ability to prevent hydrogen release is reduced. On the other hand, if the brightener is added in excess of 50 ml / l, the plating becomes brittle and the ability to prevent hydrogen release decreases, so it was limited to the range of 10-50 ml / l.

Further, one or both of KCl and NH ₄ Cl are added to improve the conductivity of the plating solution. If the amount of one or both of KCl and NH ₄ Cl added is less than 100 g / l, the throwing power and covering power will be reduced, so that sufficient hydrogen release preventing ability cannot be obtained. In addition, since the ability to prevent hydrogen release decreases due to a decrease in covering power, the amount is limited to a range of 100 to 300 g / l.

  The shape of the test piece is not particularly limited, and any of a round bar, a test piece having a threaded portion, and a notch may be used. Since the plating bath of the present invention described above has good throwing power, the amount of plating deposited on a specific part is reduced even in the case of a test piece having a non-uniform shape, for example, a test piece having a threaded portion, a notch or a hole. Therefore, it is possible to reliably suppress hydrogen emission regardless of the shape of the test piece. In particular, if a test piece having a threaded portion or a hole is used, various types of constant load test can be performed. Further, the delayed fracture test with a test piece having a notch can perform tests with different stress concentration rates, and a test simulating an actual part can be performed.

When the cathode current density is less than 0.5 A / dm ² , the uniform electrodeposition deteriorates, so that the plating becomes non-uniform and the ability to prevent hydrogen release may decrease. Further, if plating is performed at a cathode current density exceeding 50 A / dm ² , pinholes may be generated during plating, and sufficient hydrogen release preventing ability may not be obtained. Therefore, to impart a dense and uniform plating is preferably in the range of cathode current density of 0.5~50A / dm ^2.

  When plating is performed at a bath temperature of less than 10 ° C. or more than 60 ° C., the throwing power decreases. Therefore, the plating becomes non-uniform, and the ability to prevent hydrogen release may be reduced. Therefore, the bath temperature of the plating bath is preferably in the range of 10 to 60 ° C.

  If the pH of the plating bath is less than 4.5, the throwing power and covering power may be reduced, and the hydrogen release preventing ability may be insufficient. Further, even if the pH of the plating bath exceeds 6.5, the throwing power and covering power may be reduced, and white precipitation may occur. Therefore, the range of 4.5 to 6.5 is preferable.

  If the plating time is less than 1 minute, depending on the composition of the plating bath, a sufficient galvanized coating for preventing hydrogen release may not be obtained. On the other hand, when the plating time exceeds 30 minutes, the ability to prevent hydrogen release is saturated and the work efficiency deteriorates. Furthermore, in the test piece having a threaded portion, if the plating thickness exceeds an appropriate value, there is a problem that the test piece cannot be attached to the screwing jig. Therefore, the plating time is desirably 30 minutes or less.

A 1000 MPa class steel material was processed into the test piece shown in FIG. 1 or FIG. 2, and hydrogen was charged into the steel by field cathode charging. The cathode electric field charge was performed for 18 hours at a current density of 0.5 mA / cm ² by immersing the test piece in a 3% NaCl + 3 g / l NH ₄ SCN aqueous solution. Thereafter, galvanization was performed under the conditions shown in Table 1. As the plating brightener, a general-purpose zinc chloride bath brightener was used. After plating, the plate was removed after standing at room temperature for 100 hr, and immediately, the amount of hydrogen remaining in the steel was measured by temperature-programmed hydrogen analysis using gas chromatography. Further, as a preliminary test, the plating was immediately removed without leaving after plating, and the temperature rising hydrogen analysis was performed. As a result, the amount of remaining hydrogen was 2.6 ppm.

  In studying the present invention, after cathodic hydrogen charging, plating is performed using a zinc sulfate bath as described in Non-Patent Document 1 or an ammonium chloride bath under the conditions described in Patent Document 4, and 100 hr at room temperature. The amount of hydrogen after being allowed to stand was measured, all of which were less than 2.6 ppm, and the hydrogen release preventing ability was insufficient. The cause is considered to be insufficient galvanization around the screw part, the notch part and the hole from the macro appearance observation. That is, it has been clarified that these plating baths have insufficient rolling characteristics. Based on this, the results of a search for bath compositions and plating conditions that are excellent in throwing characteristics and excellent in hydrogen release prevention performance are shown below.

  No. in Table 1 1 to 17 are examples of the present invention, and the remaining hydrogen amount is not reduced at 2.6 ppm, that is, the hydrogen release preventing ability is sufficiently excellent.

No. 18 to 24 are examples of the present invention, but are examples in which at least one of the plating bath temperature, pH, cathode current density, and plating time is out of the preferred range. No. No. 18 has a bath temperature of less than 10 ° C. Since the bath temperature of No. 19 exceeds 60 ° C., the amount of remaining hydrogen is slightly reduced. No. No. 20 has a plating bath pH of less than 4.5. In No. 21, since the pH of the plating bath exceeds 6.5, the amount of remaining hydrogen is slightly reduced. No. No. 22 is an example in which the cathode current density of plating is less than 0.5 A / dm ² . No. No. 23 has a cathode current density of plating exceeding 50 A / dm ² . In No. 24, the plating time is shorter than 1 minute, and the amount of remaining hydrogen is slightly reduced.

On the other hand, no. 25-33 are comparative examples, ZnCl _2, brighteners, NH ₄ Cl, at least one concentration of the KCl which is outside the scope of the present invention. No. No. 25 has a ZnCl ₂ concentration of less than 80 g / l, and the amount of remaining hydrogen is reduced. No. In No. 26, since the ZnCl ₂ concentration is less than 80 g / l and the cathode current density of plating is less than 0.5 A / dm ² , the amount of remaining hydrogen is reduced. No. In No. 27, the ZnCl ₂ concentration exceeded 300 g / l, the cathode current density of plating exceeded 50 A / dm ² , and the plating time was less than 1 minute, so the amount of remaining hydrogen was small.

No. No. 28 has an NH ₄ Cl concentration of less than 100 g / l. In No. 29, the NH ₄ Cl concentration exceeded 300 g / l, so the amount of remaining hydrogen was small. No. No. 30 has a KCl concentration of less than 100 g / l. Since the NH ₄ Cl concentration of No. 31 exceeded 300 g / l, the amount of remaining hydrogen was small. No. No. 32 has a brightener amount of less than 10 ml / l. Since the amount of brightener No. 33 exceeded 50 ml / l, the amount of remaining hydrogen was small.

No. in Table 1 Using the plating solution No. 6, a 1000 MPa class test material was subjected to a delayed fracture test. The specimen shape shown in FIGS. 1 and 2 is used. After the cathode is charged, plating is performed, a constant load of 90% of the tensile strength is applied, and the maximum hydrogen amount that does not break (limit diffusible hydrogen amount H _C ) Asked. As a result, the critical diffusible hydrogen amount H _C of the material under this condition is 1.2 ppm, and the difference in hydrogen amount between the broken point A and the unbroken point B shown in FIG. 3 is the amount of hydrogen in the steel. Therefore, it is considered that hydrogen was not released during the test, and that the amount of limit diffusible hydrogen was precisely required.

It is a schematic diagram of the delayed fracture test piece which has a thread part and a notch part. It is a schematic diagram of a delayed fracture test piece having a hole and a notch. It is a schematic diagram of a delayed fracture test piece. It is a schematic diagram of the delayed fracture test piece which has a thread part. It is a schematic diagram of the delayed fracture test piece which has a hole. It is a limit diffusible hydrogen content measurement result when 90% of tensile strength is loaded on the 1000MPa class steel material of the test piece shape shown in FIG.

Claims (8)

To a test piece made of a metal material containing hydrogen,
ZnCl ₂ : 90 g / l or more and 300 g / l or less,
Brightener: 10-50 ml / l,
One or both of NH ₄ Cl and KCl in total 100 to 300 g / l
Cathode current density is 0.4 to 55 A / dm ² , plating bath temperature is 5 to 70 ° C., plating bath pH is 4.0 to 6.6, and plating time is 0.9 minutes or more. so,
A surface treatment method for a hydrogen embrittlement resistance evaluation test piece, characterized by performing electroplating.   The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to claim 1, wherein the test piece has a threaded portion.   The surface treatment method for hydrogen embrittlement resistance evaluation test piece according to claim 1 or 2, wherein the test piece has one or both of a notch and a hole. The surface treatment method of the hydrogen embrittlement resistance evaluation test element according to any one of claims 1 to 3, wherein the cathode current density is 0.5~50A / dm ^2.   The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of claims 1 to 4, wherein the temperature of the plating bath is 10 to 60 ° C.   The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of claims 1 to 5, wherein the plating bath has a pH of 4.5 to 6.5.   The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of claims 1 to 6, wherein the plating time is 1 to 30 minutes.   The surface treatment method for a hydrogen embrittlement resistance evaluation test piece according to any one of claims 1 to 7, wherein the test piece is made of a steel material.

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