Steel test specimen and method for manufacturing the same

Abstract

The present invention provides a steel test specimen that can secure an evaluation area with sufficient volume, or where the rolling (forging) direction differs from the axial direction of the long test specimen, even when the size of the raw steel material is insufficient. [Solution] A steel test piece 1 is provided with parallel bar-shaped evaluation section 11, flanked by handle sections 12 and 13 on both sides thereof, each larger in diameter than the evaluation section 11, and between the evaluation section 11 and each handle section 12 and 13, a boundary section 14 is interposed, in which the outer diameter gradually increases from the side of the evaluation section 11 to avoid stress concentration, wherein three separate members 21, 22, and 23 are joined in series to form the evaluation section 11, the handle sections 12 and 13, and the joint portions 24 of members 21, 22, and 23 are located other than the evaluation section 11.

Description

Technical Field

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[0001] The present invention relates to a steel specimen, and particularly to a steel specimen that can be suitably used for ultrasonic fatigue testing.

Background Art

[0002] An example of this type of steel specimen is shown in Patent Document 1. As shown in FIG. 6, the steel specimen 1' includes a parallel bar-shaped evaluation part 11 (the shaded part in FIG. 6) to be tested, and at both ends thereof, boundary parts 14 whose outer diameters gradually increase from the side of the evaluation part 11 so as to avoid stress concentration, and large-diameter handle parts 12 and 13 are formed in series via the boundary parts 14. When the steel specimen 1' is used for ultrasonic fatigue testing, one of the handle parts becomes a gripping part 12 provided with an internal thread part 121 for fixing the steel specimen 1' to a testing device, and the other becomes a weight part 13 constituting a resonator.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, since the above-mentioned conventional steel specimen 1' is generally manufactured by integrally cutting out the evaluation part 11, the gripping part 12, and the weight part 13 from a melted raw steel material, depending on the size of the raw steel material, the size of the long steel specimen 1' provided with the gripping part 12 and the weight part 13 that can be cut out therefrom is limited, and the volume of the evaluation part 11 cannot be sufficiently ensured, or there are problems such as the steel specimen 1' having an evaluation part 11 in a direction orthogonal to the rolling (forging) direction cannot be cut out.

[0005] Therefore, the present invention aims to solve these problems by providing a steel test piece and a method for manufacturing the same that can secure an evaluation portion with sufficient volume, or in which the rolling (forging) direction is different from the axial direction of the long test piece, even when the size of the raw steel material is insufficient. [Means for solving the problem]

[0006] To achieve the above objective, the steel test piece (1) of the first invention is a steel test piece (1) in which a parallel bar-shaped evaluation section (11) is flanked by handle sections (12, 13) on both sides thereof, the handle sections having a larger diameter than the evaluation section (11), and a boundary section (14) is interposed between the evaluation section (11) and each of the handle sections (12, 13) so as to avoid stress concentration, wherein three separate members (21, 22, 23) are joined in series with respect to form the evaluation section (11), the handle sections (12, 13), and the boundary section (14), and each of the joining portions (24) of the members (21, 22, 23) is located other than the evaluation section (11).

[0007] According to this first invention, since the evaluation section and the handle section can be formed from separate components, it is possible to cut out an evaluation section of sufficient volume even when the size of the raw steel material is insufficient. Furthermore, it is possible to secure an evaluation section in which the rolling (forging) direction is different from the axial direction of the long test piece.

[0008] In the steel test specimen of this second invention, the member (21) located in the center and the members (22, 23) located on both sides of the member (21) are made of different materials.

[0009] According to this second invention, since it is not necessary to cut the member that forms the handle from the raw steel material, it becomes easier to secure a sufficient volume of evaluation section even when the size of the raw steel material is insufficient.

[0010] The method for manufacturing a steel test specimen of the third invention involves joining three separate members (21, 22, 23) in series with each other, and processing the joined members (21, 22, 23) to form handle portions (12, 13) on both sides of a parallel bar-shaped evaluation portion (11) that are larger in diameter than the evaluation portion (11). Furthermore, a boundary portion (14) is formed between the evaluation portion (11) and each of the handle portions (12, 13) such that the outer diameter gradually increases from the side of the evaluation portion (11) to avoid stress concentration, and the joint portions (24) of the members (21, 22, 23) are positioned other than the evaluation portion (11).

[0011] According to this third invention, the same effects as those of the first invention can be obtained.

[0012] The symbols in parentheses above are for reference only to indicate the correspondence with the specific means described in the embodiments described later. [Effects of the Invention]

[0013] As described above, according to the steel test specimen and its manufacturing method of the present invention, it is possible to secure an evaluation section with sufficient volume, or where the rolling (forging) direction is different from the axial direction of the long test specimen, even when the size of the raw steel material is insufficient. [Brief explanation of the drawing]

[0014] [Figure 1] These are side views of each component used to manufacture steel test specimens. [Figure 2] This is a side view showing the components joined together. [Figure 3] This is a diagram showing the roughly machined parts of the joined components. [Figure 4] This is an overall side view showing an example of a steel test specimen of the present invention. [Figure 5] This flowchart shows an example of the manufacturing process for steel test specimens according to the present invention. [Figure 6] This is an overall side view of a conventional steel test specimen. [Modes for carrying out the invention]

[0015] Note that the embodiments described below are merely examples, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

[0016] When manufacturing a steel material test piece of the present invention, as shown in FIG. 1, a parallel bar-shaped (regardless of round bar or square bar) member 21 cut out from the melted original steel material to be tested, and parallel bar-shaped (regardless of round bar or square bar) members 22 and 23 with a larger diameter than this are prepared. Note that the members 22 and 23 do not necessarily have to be parallel bar-shaped, nor do they have to be the same shape as each other. Also, the members 22 and 23 do not necessarily have to be cut out from the above-mentioned original steel material. That is, the members 22 and 23 may be of the same material as the member 21 or of different materials.

[0017] As shown in FIG. 2, the prepared members 21 to 23 are joined with one end face of the members 22 and 23 at both ends with the member 21 in the center. In this embodiment, the axial centers C are made to coincide with each other (step 101 in FIG. 5). The joining is preferably friction stir joining, but welding or the like may also be used.

[0018] After that, the whole is annealed (step 102 in FIG. 5), and then rough machining is performed (step 103 in FIG. 5). The rough machining is to cut the outer periphery of the joined members as shown by the broken line in FIG. 3. As a result, as shown in FIG. 4, a parallel bar-shaped evaluation part 11 (the shaded part in FIG. 4) and, at both ends of this, boundary parts 14 where the outer diameter gradually increases from the side of the evaluation part 11 so as to avoid stress concentration are formed. The non-cut parts of the respective members 22 and 23 become the holding parts 12 and 13. In this embodiment, in order to perform ultrasonic fatigue testing, a female screw part 121 for fixing to the test device is formed at the center of the end face of the holding part 12 to serve as a gripping part, while the holding part 13 becomes a weight part constituting a resonator.

[0019] Following rough machining, the entire workpiece is subjected to annealing treatment (step 104 in FIG. 5), and then finish machining (step 105 in FIG. 5) is performed to polish and remove the decarburized layer formed on the surface. Through such machining, the steel material test piece 1 as the final product is manufactured. In the steel material test piece 1 of the present embodiment, each joint portion 24 of the members 21, 22 and the members 21, 23 is located at each boundary portion 14 as shown in FIG. 4. Alternatively, the machining may be performed such that each joint portion 24 is located at the gripping portions 12, 13.

[0020] Here, in Table [1], the case where an ultrasonic fatigue test was conducted on the steel material test piece 1 with the joint portion 24 located at the boundary portion 14 other than the evaluation portion 11 is taken as an example, and the case where an ultrasonic fatigue test was conducted on the steel material test piece with the joint portion located at the evaluation portion is taken as a comparative example, and the test results are shown. According to Table [1], in both Example 1 and Comparative Example 1 where the axial direction of the evaluation portion is parallel to the rolling (forging) direction, and in both Example 2 and Comparative Example 2 where the axial direction of the evaluation portion is perpendicular to the rolling (forging) direction, the fatigue test could be successfully conducted on the steel material test piece with the joint portion located at the boundary portion. In contrast, in the steel material test piece with the joint portion located at the evaluation portion, fracture occurred at the joint portion located at the evaluation portion, and the fatigue test could not be successfully conducted.

[0021]

Table 1

[0022] Note that the steel material test piece 1 of the present invention is not only used for ultrasonic fatigue tests, but can also be used for other tests such as tensile tests and rotating bending tests. In this case, the shapes and structures of the gripping portions 22, 23 are not limited to those of the above embodiment.

Explanation of Reference Numerals

[0023] 1... steel material test piece, 11... evaluation portion, 12, 13... gripping portions, 14... boundary portion, 21, 22, 23... members, 24... joint portion.

Claims

1. A steel test specimen having a parallel bar-shaped evaluation section flanked by handle sections with a larger diameter than the evaluation section on both sides, and a boundary section interposed between the evaluation section and each of the handle sections, wherein the boundary section gradually increases in outer diameter from the side of the evaluation section to avoid stress concentration, wherein three separate members are joined in series to form the evaluation section, the handle sections, and the boundary sections, and each of the joining parts of the members is located outside the evaluation section.

2. The steel test piece according to claim 1, wherein the member located in the center and connected in series, and the members located on both sides of the member, are made of different materials.

3. A method for manufacturing a steel test piece, comprising joining three separate members in series with each other, and processing the joined members to form handle portions with a larger diameter than the evaluation portion on both sides of a parallel rod-shaped evaluation portion, and forming boundary portions between the evaluation portion and each of the handle portions, where the outer diameter gradually increases from the side of the evaluation portion to avoid stress concentration, and positioning each of the joining parts of the members other than the evaluation portion.

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