Austenitic stainless steel bolts and their strengthening process

Abstract

The present invention relates to the technical field of fasteners, and discloses an austenitic stainless steel bolt and a strengthening process thereof. The strengthening process of the austenitic stainless steel bolt comprises: melting the raw materials under vacuum and casting them into round bar blanks; subjecting the round bar blanks to solid solution treatment at 1000-1100°C; rolling the blanks after solid solution treatment at 300-850°C; subjecting the rolled blanks to short-term solid solution treatment at 1000-1100°C on the surface of the blanks under a protective atmosphere; cutting the blanks after surface solid solution treatment into the required length, chamfering and gear hobbing, and obtaining austenitic stainless steel bolts. The present invention adopts a process combining sufficient solid solution treatment, medium-temperature deformation rolling processing, and short-term solid solution treatment on the surface of the blanks, which can better strengthen the austenitic stainless steel bolts, and is also suitable for strengthening large-diameter austenitic stainless steel bolts.

Description

Technical Field

[0001] The present invention relates to the technical field of fasteners, and in particular to an austenitic stainless steel bolt and a strengthening process thereof. Background Art

[0002] Austenitic stainless steel bolts are often used in complex working conditions such as high temperature, high pressure, and corrosive environments. Through strengthening treatment, it can ensure that the bolts maintain good mechanical properties and durability under these harsh conditions.

[0003] Because austenitic stainless steel is more likely to precipitate carbides between grains in the temperature range of 425-850°C, hot working in this temperature range is avoided in engineering. Therefore, the commonly used strengthening treatment methods for austenitic stainless steel bolts include solution treatment and a combination of solution treatment and cold finishing.

[0004] After solution treatment, the strength of the solid bolt is still low, and the tightening performance of the high-pressure bolt cannot be guaranteed. Cold finishing is a process of reducing the diameter by extrusion at room temperature, which can significantly improve its strength and hardness. However, as the amount of extrusion deformation of the bolt increases during cold finishing, the difficulty of reducing the diameter also increases. Under normal circumstances, the diameter reduction does not exceed 0.5mm. Therefore, although the strength and hardness of the bolt can be greatly improved, the effect of strain hardening is limited to a range of approximately 0.5mm on the bolt surface, and it cannot have a strain hardening effect on the bolt core. Moreover, the larger the diameter of the bolt, the worse the effect of cold finishing, and the effect is almost negligible.

[0005] The engineering application of large-diameter austenitic stainless steel bolts is greatly restricted, resulting in the fact that conventional austenitic stainless steel cannot be used in the use environment of many high-temperature and high-pressure austenitic stainless steel equipment, and more expensive nickel-based stainless steel bolts are used instead. Summary of the Invention

[0006] The main purpose of the present invention is to provide an austenitic stainless steel bolt and a preparation process thereof, aiming to solve the problem in the prior art that the core of the austenitic stainless steel bolt cannot be effectively strengthened, and the problem that large-diameter austenitic stainless steel bolts cannot be effectively strengthened.

[0007] To achieve the above object, the present invention proposes a strengthening process for austenitic stainless steel bolts, comprising the following steps:

[0008] S10, melting and casting austenitic stainless steel raw material with the grade of 06Cr18Ni11Nb into round bar billets under vacuum;

[0009] S20, subjecting the round bar blank in step S10 to a full solution treatment at 1000-1100° C., and water-cooling to room temperature;

[0010] S30, rolling the billet after the solution treatment in step S20 at 300-850° C., with a final cross-sectional diameter reduction of ≥5%, and water-cooling or air-cooling to room temperature;

[0011] S40, in a protective atmosphere, subjecting the billet after rolling in step S30 to surface solution treatment at 1000-1100° C. for no more than 5 minutes, and then water-cooling to room temperature;

[0012] S50, cutting the blank after the surface solution treatment in step S40 into a required length, and performing chamfering and gear hobbing to obtain the austenitic stainless steel bolt.

[0013] Optionally, in step S30, the billet is rolled at 400-550°C.

[0014] Preferably, in step S30, the billet is rolled at 500-510°C.

[0015] Optionally, in step S30, the billet is rolled twice, and after the first rolling is completed, it is returned to the furnace for heat preservation and then rolled for the second time.

[0016] Optionally, in step S30, the temperature of the reheating and insulation is the same as the temperature during the second rolling, and the insulation time is 5 to 20 minutes.

[0017] Optionally, in step S30, after the first rolling, the cross-sectional diameter reduction is 5-7.5%, and after the second rolling, the final cross-sectional diameter reduction is 7-10%.

[0018] Preferably, in step S30, after the first rolling, the cross-sectional diameter reduction is 7.0%, and after the second rolling, the final cross-sectional diameter reduction is 10.0%.

[0019] Optionally, in step S40, the surface solution treatment includes: heating the heat treatment furnace to 1100°C, feeding the billet into the heat treatment furnace, closing the furnace door, introducing argon gas into the furnace, heating the billet surface to 1000-1100°C, keeping the temperature for 2-5 minutes, taking the billet out of the furnace and water-cooling it to room temperature.

[0020] Optionally, in step S40, when the blank surface is solution treated, the blank surface is heated to 1040-1060° C. and kept warm for 3-4 minutes.

[0021] Optionally, in step S10, the diameter of the round bar blank is 24-48 mm.

[0022] Optionally, in step S20, the duration of the solution treatment is 2 to 5 hours.

[0023] The present invention also provides an austenitic stainless steel bolt, which is manufactured by using any of the aforementioned strengthening processes for the austenitic stainless steel bolt.

[0024] In the technical solution of the present invention, a round bar blank is produced using austenitic stainless steel raw material with the grade of 06Cr18Ni11Nb. The raw material composition contains the stabilizing element niobium. Due to the presence of this stabilizing element, when hot working is performed in an appropriate temperature range below the solid solution temperature, carbides are dispersed and precipitated within the grains and are not distributed at the grain boundaries, thereby ensuring the effect of diameter reduction deformation processing within the appropriate temperature range.

[0025] Thoroughly solution treating the round bar at 1000-1100°C can achieve a more uniform microstructure and chemical composition of austenitic stainless steel. By heating to the high-temperature single-phase region and holding the temperature, carbides and alloying elements are fully dissolved in the austenite, resulting in a uniform single-phase structure after cooling. This helps improve the overall performance of the material.

[0026] The billet after sufficient solution treatment is subjected to medium-temperature deformation rolling at 300~850℃, which can effectively improve the strength and hardness of the billet, and can also play a good strengthening role on the core of the billet, and is suitable for strengthening large-diameter bolts.

[0027] After the billet undergoes medium-temperature deformation and rolling, its surface hardening will re-harden at the tooth top after hobbing. The accumulation of multiple hardening processes can easily lead to microcracks at the tooth top. Therefore, the present invention subjects the billet after medium-temperature deformation and rolling to a short-term solution treatment of no more than 5 minutes to soften the processing stress within the billet's surface thickness of approximately 2 mm. Furthermore, due to the low thermal conductivity of austenitic stainless steel, the short-term heat treatment does not spread the solution heat treatment temperature to the billet's core. This ensures that the processing stress on the billet's surface is eliminated while maintaining the core strength, thereby better meeting the reliability requirements of thread processing quality.

[0028] The present invention adopts austenitic stainless steel with the grade of 06Cr18Ni11Nb as raw material to manufacture bolts, and combines them with sufficient solid solution treatment, medium-temperature deformation rolling processing, and short-time surface solid solution treatment, which can effectively strengthen the austenitic stainless steel bolts and the bolt core. The produced bolts have excellent hardness and strength and are also suitable for strengthening large-diameter austenitic stainless steel bolts. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0030] Figure 1 This is a graph showing the Vickers hardness test results of Performance Test 1 of the present invention;

[0031] Figure 2 This is a metallographic image of the bolt prepared in Example 1 in Performance Test 2 of the present invention at the top of the tooth;

[0032] Figure 3 This is a metallographic image of the bolt prepared in Comparative Example 2 in Performance Test 2 of the present invention at the top of the tooth;

[0033] Figure 4 Schematic diagram of the structure of the six test positions in the performance test 1 of the present invention.

[0034] Description of Figure Numbers:

[0035] 1. Cylindrical structure; 11. First group of test positions; 12. Second group of test positions; 13. Third group of test positions; 14. Fourth group of test positions; 15. Fifth group of test positions; 16. Sixth group of test positions.

[0036] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), such directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0039] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the meaning of "and / or" appearing throughout the text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme in which A and B are satisfied at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0040] The present invention proposes a strengthening process for austenitic stainless steel bolts, comprising the following steps:

[0041] S10, melting and casting austenitic stainless steel raw material with the grade of 06Cr18Ni11Nb into round bar billets under vacuum;

[0042] S20, subjecting the round bar blank in step S10 to a full solution treatment at 1000-1100° C., and water-cooling to room temperature;

[0043] S30, rolling the billet after the solution treatment in step S20 at 300-850° C., with a final cross-sectional diameter reduction of ≥5%, and water-cooling or air-cooling to room temperature;

[0044] S40, in a protective atmosphere, subjecting the billet after rolling in step S30 to surface solution treatment at 1000-1100° C. for no more than 5 minutes, and then water-cooling to room temperature;

[0045] S50, cutting the blank after the surface solution treatment in step S40 into a required length, and performing chamfering and gear hobbing to obtain the austenitic stainless steel bolt.

[0046] In the technical solution of the present invention, round bar blanks with a diameter of 24 to 48 mm are produced using austenitic stainless steel raw material with the grade 06Cr18Ni11Nb. The raw material composition contains the stabilizing element niobium. Due to the presence of this stabilizing element, when hot working is performed in an appropriate temperature range below the solid solution temperature, carbides are dispersed and precipitated within the grains and are not distributed at the grain boundaries, ensuring the effect of diameter reduction deformation processing within the appropriate temperature range.

[0047] Solution treatment of round bar billets at 1000-1100°C for 2-5 hours can make the microstructure and chemical composition of austenitic stainless steel more uniform. By heating to the high-temperature single-phase region and holding the temperature, carbides and alloying elements are fully dissolved in the austenite, resulting in a uniform single-phase structure after cooling. This helps improve the overall performance of the material.

[0048] The strength and hardness of the blank can be effectively improved by performing medium-temperature deformation rolling at 300~850℃ on the blank after sufficient solution treatment, and the core of the blank can also be strengthened well, and it is suitable for strengthening large-diameter bolts.

[0049] After the billet undergoes medium-temperature deformation and rolling, its surface hardening will re-harden at the tooth top after hobbing. The accumulation of multiple hardening processes can easily lead to microcracks at the tooth top. Therefore, the present invention subjects the billet after medium-temperature deformation and rolling to a short-term solution treatment of no more than 5 minutes to soften the processing stress within the billet's surface thickness of approximately 2 mm. Furthermore, due to the low thermal conductivity of austenitic stainless steel, the short-term heat treatment does not spread the solution heat treatment temperature to the billet's core. This ensures that the processing stress on the billet's surface is eliminated while maintaining the core strength, thereby better meeting the reliability requirements of thread processing quality.

[0050] It should be noted that in step S30, the "cross-sectional diameter reduction" refers to the diameter of the cross section of the original billet being D0. After the n-th deformation and rolling process, the diameter of the cross section of the billet is Dn, where n is a positive integer. For example, n can be 1, 2, etc., and the calculation formula for the cross-sectional diameter reduction after the n-th deformation and rolling process is:

[0051] Cross-section reduction .

[0052] Specifically, in step S30, the billet is rolled twice. After the first rolling, it is returned to the furnace for holding and then rolled a second time. The holding temperature is the same as the second rolling temperature, and the holding time is 5 to 20 minutes. After the first rolling, the cross-sectional diameter reduction is 5 to 7.5%, and after the second rolling, the final cross-sectional diameter reduction is 7 to 10%. This two-step, specific medium-temperature deformation rolling process effectively strengthens austenitic stainless steel bolts.

[0053] Specifically, in step S40, the solution treatment of the billet surface includes: heating the heat treatment furnace to 1100°C, feeding the billet into the heat treatment furnace, closing the furnace door, introducing argon gas into the furnace, and heating the billet surface to 1000-1100°C, keeping the temperature for 2-5 minutes, taking the billet out of the furnace and water-cooling it to room temperature.

[0054] The present invention also provides an austenitic stainless steel bolt produced using any of the aforementioned strengthening processes for austenitic stainless steel bolts. The specific preparation process for this strengthening process for the austenitic stainless steel bolt is described in the aforementioned embodiments. Since this austenitic stainless steel bolt utilizes all the technical solutions of all of the aforementioned embodiments, it exhibits at least all the beneficial effects of the technical solutions of the aforementioned embodiments, and therefore will not be further detailed here.

[0055] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention. Example 1

[0056] A strengthening process for an austenitic stainless steel bolt comprises the following steps:

[0057] S10. Melt and cast a 06Cr18Ni11Nb austenitic stainless steel raw material under vacuum into a round bar blank with a diameter of 48 mm. The chemical composition of the raw material is shown in Table 1 below.

[0058] S20, solution treating the round bar blank in step S10 at 1050-1060°C for 3 hours, and water cooling to room temperature (25°C);

[0059] S30, performing a first rolling on the billet after the solution treatment in step S20 at 500-510°C, wherein the cross-sectional diameter reduction of the billet after the first rolling is 7.0%, and then water cooling to room temperature (25°C);

[0060] S40, heating the heat treatment furnace to 1100°C, feeding the billet after rolling treatment in step S30 into the heat treatment furnace, closing the furnace door, and introducing argon gas into the furnace. When the surface temperature of the billet is raised to 1045-1055°C, the temperature is kept at this temperature for 4 minutes, and the billet is removed from the furnace and water-cooled to room temperature (25°C);

[0061] S50, cutting the blank after the surface solution treatment in step S40 into a required length, performing chamfering and gear hobbing processing to obtain an austenitic stainless steel bolt.

[0062] Table 1 Chemical composition of raw materials (unit: wt%)

[0063] C Si Mn P S Cr Ni Nb Fe and impurities content 0.05 0.85 1.50 0.040 0.025 18.00 11.00 0.80 margin

[0064] Examples 2 to 5

[0065] Examples 2 to 5 are based on Example 1, with the difference being that in step S30 , the first rolling is performed under different temperature conditions, and the rest is the same as Example 1.

[0066] Example 2: In step S30, the first rolling is performed at 300-310°C.

[0067] Example 3: In step S30, the first rolling is performed at 420-430°C.

[0068] Example 4: In step S30, the first rolling is performed at 660-670°C.

[0069] Example 5: In step S30, the first rolling is performed at 840-850°C. Example 6

[0070] This embodiment is based on Example 1, and the difference is that: in step S30, the cross-sectional diameter reduction of the billet after the first rolling is 7.0%, the billet after the first rolling is sent to a heat treatment furnace at 510°C, and the billet surface is heated to 500~510°C and kept warm for 10 minutes. The billet is then rolled for the second time at 500~510°C. After the second rolling, the final cross-sectional diameter reduction of the billet (the cumulative diameter reduction of the first and second times) is 10%, and then it is water-cooled to room temperature (25°C).

[0071] Example 7~8

[0072] Examples 7 to 8 are based on Example 6, with the difference being that in step S30 , after the first rolling, the cross-sectional diameter reduction of the billet is different, and the rest is the same as Example 6.

[0073] Example 7: In step S30, after the first rolling, the cross-sectional diameter reduction of the billet is 5.0%.

[0074] Example 8: In step S30, after the first rolling, the cross-sectional diameter reduction of the billet is 7.5%.

[0075] Comparative Example 1

[0076] This comparative example is based on Example 1, with the difference that step S30 is not included, that is, the blank after solution treatment in step S20 is directly processed according to step S40, and the rest is the same as Example 1.

[0077] Comparative Example 2

[0078] This comparative example is based on Example 1, with the difference that step S40 is not included, that is, the blank after the first rolling process is directly processed according to step S50, and the rest is the same as Example 1.

[0079] Performance Test 1

[0080] The bolts produced in Example 1, Example 6, and Comparative Example 1 were subjected to Vickers hardness testing in accordance with GB / T 4340.1-2009, "Vickers Hardness Test for Metallic Materials - Part 1: Test Method." During the test, the corresponding ends of the bolts were cut radially to obtain cylindrical structures 1 with a thickness of 1 cm. These cylindrical structures served as specimens. The first set of test locations 11 consisted of three points 50 μm from the root of the thread; the second set of test locations 12 consisted of three points 1 mm from the root of the thread; the third set of test locations 13 consisted of three points 2 mm from the root of the thread; the fourth set of test locations 14 consisted of three points 3 mm from the root of the thread; the fifth set of test locations 15 consisted of three points 4 mm from the root of the thread; and the sixth set of test locations 16 consisted of three points in the center (i.e., the core) of the thread. Six sets of data were tested in total, and each test result represents the average of the test data from the corresponding three points. There are three test groups: Example 1, Example 6 and Comparative Example 1. Each test group has 6 test positions, and each test position corresponds to 3 points. The test results are as follows: Figure 1 shown.

[0081] in, Figure 1 The yellow broken line corresponds to Example 1, the blue broken line corresponds to Example 1, and the gray broken line corresponds to Example 6, where "1" in the table corresponds to the first group of test positions, and so on, "6" corresponds to the sixth group of test positions. The table only reflects the average data of Vickers hardness, and the unit is not recorded. It can be understood that the unit is HV. For example, the column corresponding to "1" corresponds to the yellow broken line "330.60", which means that the Vickers hardness is 330.60HV.

[0082] Depend on Figure 1 The experimental structure shows that the present invention can effectively improve the hardness of large diameter austenitic stainless steel bolts by fully solution treatment, combined with medium temperature rolling deformation processing and surface short-time solution treatment. The hardness of the bottom of the tooth can reach more than 410HV, and the hardness of the core can reach more than 260HV, which has a good strengthening effect on the core. Figure 1 It can also be seen that, compared with Example 1, Example 6 can further enhance the strengthening effect by undergoing two hot rolling treatments.

[0083] Performance Test 2

[0084] The metallographic image of the bolt obtained in Example 1 at the top of the tooth is as follows: Figure 2 As shown, the metallographic image of the bolt prepared in Comparative Example 2 at the top of the tooth is as follows: Figure 3 As shown. Figure 2 and Figure 3It can be seen that the tooth tops of Comparative Example 2 cracked due to the lack of surface short-time solid solution treatment, while the tooth tops of Example 1 did not crack due to the short-time solid solution treatment. This indicates that after the bar material is subjected to medium-temperature rolling and strengthening processing, the shear stress of the mold gear is superimposed on the original strengthening stress during gear hobbing, resulting in huge internal stress. The extrusion streamlines of the internal metal grains instantly gush out like molten slurry, and under the action of shear stress, tiny cracks are very likely to appear on the tooth tops. These microcracks that appear on the tooth tops are also very easy to expand and tear when the bolts are pre-tightened, and are squeezed into the threads to form foreign matter and bite the nut to death. After the bar material is subjected to medium-temperature rolling and strengthening processing, a short-time solid solution heat treatment is performed on the shallow surface of the bar material, so that the processing stress of the shallow surface of the bar material is eliminated. During gear hobbing, the shear stress of the mold gear is not superimposed on the original strengthening stress, the metal streamlines are consistent, conventional cracks will not appear on the tooth tops, and the bolt performance is greatly improved.

[0085] Performance Test 3

[0086] The bolts produced in Examples 1-8 and Comparative Example 1 were subjected to yield strength testing in accordance with GB / T 228.2-2015, "Metallic Materials Tensile Testing - Part 2: High-Temperature Test Methods." During the test, the corresponding bolt ends were cut radially to obtain cylindrical structures with a thickness of 5 mm. These cylindrical structures served as specimens. The test temperature was 600°C. The test results are shown in Table 2 below.

[0087] Table 2 Bolt yield strength

[0088] Yield strength (MPa) Example 1 424 Example 2 357 Example 3 388 Example 4 421 Example 5 413 Example 6 429 Example 7 425 Example 8 427 Comparative Example 1 189

[0089] It can be seen from the high temperature test results in Table 2 that the present invention adopts medium temperature rolling and short surface solution treatment to effectively improve the yield strength of the bolts, and the bolts obtained can be well used in high temperature environments.

[0090] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A strengthening process for austenitic stainless steel bolts, characterized in that: The following steps are involved: S10, melting and casting austenitic stainless steel raw material with the grade of 06Cr18Ni11Nb into round bar billets under vacuum; S20, subjecting the round bar blank in step S10 to a full solution treatment at 1000-1100° C., and water-cooling to room temperature; S30, rolling the billet after the solution treatment in step S20 at 400-550°C, with a final cross-sectional diameter reduction of ≥5%, and water cooling or air cooling to room temperature; S40, in a protective atmosphere, subjecting the billet after rolling in step S30 to surface solution treatment at 1000-1100° C. for no more than 5 minutes, and then water-cooling to room temperature; S50, cutting the blank after the surface solution treatment in step S40 into a required length, and performing chamfering and gear hobbing to obtain the austenitic stainless steel bolt.

2. The strengthening process for austenitic stainless steel bolts according to claim 1, characterized in that: In step S30, the billet is rolled twice. After the first rolling is completed, the billet is returned to the furnace for heat preservation and then rolled for the second time.

3. The strengthening process for austenitic stainless steel bolts according to claim 2, characterized in that: In step S30, the temperature of the furnace is the same as the temperature during the second rolling, and the holding time is 5 to 20 minutes.

4. The strengthening process for austenitic stainless steel bolts according to claim 2, characterized in that: In the step S30, after the first rolling, the cross-sectional diameter reduction is 5 to 7.5%, and after the second rolling, the final cross-sectional diameter reduction is 7 to 10%.

5. The strengthening process for austenitic stainless steel bolts according to claim 1, characterized in that: In step S40, the surface solution treatment includes: heating the heat treatment furnace to 1100°C, feeding the billet into the heat treatment furnace, closing the furnace door, introducing argon gas into the furnace, heating the billet surface to 1000-1100°C, keeping the temperature for 2-5 minutes, taking the billet out of the furnace and water cooling it to room temperature.

6. The strengthening process for austenitic stainless steel bolts according to claim 5, characterized in that: In the step S40, when the surface of the blank is subjected to solid solution treatment, the surface of the blank is heated to 1040-1060° C. and kept at this temperature for 3-4 minutes.

7. The strengthening process for austenitic stainless steel bolts according to claim 1, characterized in that: In step S10, the diameter of the round bar blank is 24 to 48 mm.

8. The strengthening process for austenitic stainless steel bolts according to claim 1, characterized in that: In step S20, the duration of the solution treatment is 2 to 5 hours.

9. An austenitic stainless steel bolt, characterized in that: The bolt is manufactured by using the strengthening process of the austenitic stainless steel bolt as claimed in any one of claims 1 to 8.

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