Fastener and method for manufacturing the same

Abstract

This application provides a fastener and a manufacturing method thereof. The fastener is made of material B23 in ASME SA-540 standard. The length of the screw of the fastener is 270 - 290 mm, the diameter of the screw of the fastener is 55 - 60 mm. The normal temperature tensile strength range of the fastener is 1150 - 1170 MPa, the normal temperature yield strength of the fastener is greater than 1095 MPa, the high temperature tensile strength of the fastener at 350 °C is greater than 1035 MPa, the high temperature yield strength of the fastener at 350 °C is greater than 855 MPa, and the low temperature impact energy of the fastener at -18 °C is greater than 60 J. The fastener provided by this application, as a large-size fastener applied to harsh environments, has good mechanical properties at both high and low temperatures. When the mechanical properties at normal temperature meet the standard value requirements, the mechanical properties at high and low temperatures have a large redundancy compared with the standard value, and have high safety and reliability.

Description

Technical Field

[0001] This application relates to the technical field of making metals tough through decarburization, tempering or other treatments, and particularly relates to fasteners and their manufacturing methods. Background Art

[0002] The B23 material in the ASME SA-540 standard is a high-strength alloy steel material, which is usually applied to harsh environments with extreme temperatures and pressures in nuclear power, petrochemical industry, aerospace or other fields, and is used to manufacture key components such as screws or other fasteners.

[0003] To meet the application of fasteners in harsh environments, there are upper and lower limits for their normal temperature tensile strength, and lower limits for normal temperature yield strength, high temperature tensile strength, high temperature yield strength, and low temperature impact energy. It is difficult for fasteners made by processing B23 material bars with traditional heat treatment processes to meet the above requirements simultaneously. Summary of the Invention

[0004] To at least partially solve the above problems, according to the first aspect of this application, an embodiment of this application provides a fastener. The fastener is made of B23 material in the ASME SA-540 standard. The screw length of the fastener is 270 - 290 mm, the screw diameter of the fastener is 55 - 60 mm, the normal temperature tensile strength range of the fastener is 1150 - 1170 MPa, the normal temperature yield strength of the fastener is greater than 1095 MPa, the high temperature tensile strength of the fastener at 350 °C is greater than 1035 MPa, the high temperature yield strength of the fastener at 350 °C is greater than 855 MPa, and the low temperature impact energy of the fastener at -18 °C is greater than 60 J. The fastener is made through the following method, and the method includes: obtaining a bar in the forged state, the bar is made of B23 material in the ASME SA-540 standard, and the forging ratio of the bar is greater than or equal to 9.5; performing quenching treatment on the bar; performing tempering treatment on the quenched bar. When performing tempering treatment, the bar is put into the furnace at 80 - 120 °C, the heating rate is 155 - 200 °C / h, the holding temperature is 534 - 536 °C, holding for 2 - 4 h, and air cooling; using the tempered bar to make the fastener.

[0005] In some embodiments, when performing tempering treatment, the holding temperature is 535 ± 0.5 °C.

[0006] In some embodiments, when performing tempering treatment, the heating rate is 160 ± 1 °C / h.

[0007] In some embodiments, when performing tempering treatment, the holding time is 3.5 ± 0.05 h.

[0008] In some embodiments, obtaining a bar in a forged state includes: loading a B23 ingot into a furnace and holding it at 1150 - 1300°C; blooming the heat-insulated B23 ingot to break up the coarse grains and massive substances in the ingot; upsetting and drawing the bloomed B23 ingot to increase the single-pass deformation amount to 30 - 70%, repeatedly upsetting-drawing and forging with reversed directions to accumulate the forging ratio; using a U-shaped anvil in the final forging stage and gradually forging from the center to the ends, with the final forging temperature being 850 - 1000°C.

[0009] According to the second aspect of the present application, embodiments of the present application provide a method for manufacturing a fastener, including: obtaining a bar in a forged state, the bar being of B23 material in the ASME SA-540 standard, and the forging ratio of the bar being greater than or equal to 9.5. Among them, in the B23 material, the C content is 0.37 - 0.44 wt%, the Si content is 0.15 - 0.35 wt%, the Mn content is 0.6 - 0.95 wt%, the P content is 0 - 0.025 wt%, the S content is 0 - 0.025 wt%, the Cr content is 0.65 - 0.95 wt%, the Ni content is 1.55 - 2 wt%, and the Mo content is 0.2 - 0.3 wt%; quenching the bar; performing tempering treatment on the quenched bar. During the tempering treatment, the bar is put into the furnace at 80 - 120°C, the heating rate is 155 - 200°C / h, the holding temperature is 534 - 536°C, held for 2 - 4 h, and air-cooled. The tempered bar is used to manufacture the fastener.

[0010] In some embodiments, during the tempering treatment, the holding temperature is 535 ± 0.5°C.

[0011] In some embodiments, during the tempering treatment, the heating rate is 160 ± 1°C / h.

[0012] In some embodiments, during the tempering treatment, the holding time is 3.5 ± 0.05 h.

[0013] In some embodiments, obtaining a bar in a forged state includes: loading a B23 ingot into a furnace and holding it at 1150 - 1300°C; blooming the heat-insulated B23 ingot to break up the coarse grains and massive substances in the ingot; upsetting and drawing the bloomed B23 ingot to increase the single-pass deformation amount to 30 - 70%, repeatedly upsetting-drawing and forging with reversed directions to accumulate the forging ratio; using a U-shaped anvil in the final forging stage and gradually forging from the center to the ends, with the final forging temperature being 850 - 1000°C; the forging ratio of the bar ranges from 9.5 to 12.

[0014] The fasteners provided by the embodiments of the present application, as large-sized fasteners applied to harsh environments, have good mechanical properties under both high-temperature and low-temperature conditions. When the mechanical properties at normal temperature meet the standard value requirements, the high-temperature and low-temperature mechanical properties have a large redundancy compared to the standard value, and have high safety and reliability. The manufacturing method of the fasteners provided by the embodiments of the present application can obtain fasteners with excellent performance that meet the requirements of normal-temperature tensile strength, normal-temperature yield strength, high-temperature tensile strength, high-temperature yield strength, and low-temperature impact energy by controlling the forging ratio and the holding temperature during the tempering process, combined with the control of the heating rate and the holding time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the metallographic picture of the screw obtained by the heat treatment method of Example 1;

[0016] Figure 2 is the metallographic picture of the screw obtained by the heat treatment method of Example 2;

[0017] Figure 3 is the metallographic picture of the screw obtained by the heat treatment method of Example 3;

[0018] Figure 4 is the metallographic picture of the screw obtained by the heat treatment method of Comparative Example 1;

[0019] Figure 5 is the metallographic picture of the screw obtained by the heat treatment method of Comparative Example 2;

[0020] Figure 6 is the metallographic picture of the screw obtained by the heat treatment method of Comparative Example 3;

[0021] Figure 7 is the metallographic picture of the screw obtained by the heat treatment method of Comparative Example 4. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The technical solutions of the preferred embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope protected by the present application.

[0023] The B23 material in the ASME SA-540 standard (sometimes referred to as SA-540 B23 hereinafter) is a high-strength medium-carbon alloy steel. SA-540 B23 can be applied to nuclear power, petrochemical, aerospace or other harsh environments with extreme temperatures and pressures, and is used to manufacture fasteners for critical components. The fasteners can include bolts, studs, screws or other fasteners, etc. When the fasteners are applied to harsh environments, such as the B23 material screws used for the support of the nuclear power plant pressurizer, there are upper and lower limits for its room-temperature tensile strength, and lower limits for the room-temperature yield strength, high-temperature tensile strength, high-temperature yield strength, and low-temperature impact energy. Specifically, the standard values required for the room-temperature tensile strength, room-temperature yield strength, high-temperature tensile strength, high-temperature yield strength, and low-temperature impact energy can be referred to Table 1.

[0024] Table 1

[0025] Tensile strength at room temperature (MPa) Yield strength at room temperature (MPa) Tensile strength at 350°C (MPa) Yield strength at 350°C (MPa) Low temperature impact energy at -18°C (J) / lateral expansion (mm) Standard value 1070-1170 ≥965 ≥945 ≥842 47 / 0.63

[0026] Among the parameters of room-temperature tensile strength, room-temperature yield strength, high-temperature tensile strength, high-temperature yield strength and low-temperature impact energy, there is an upper limit requirement for the room-temperature tensile strength, and the high-temperature yield strength cannot be too low. However, increasing the room-temperature tensile strength will cause the low-temperature impact energy to decrease. Therefore, balancing the above parameters to meet the standard value requirements has become an urgent technical problem to be solved.

[0027] To at least partially solve the above problems, the inventors finally obtained the present invention through continuous experimental exploration.

[0028] According to the first aspect of the present application, embodiments of the present application provide a fastener. The fastener is made of material B23 in ASME SA-540 standard. The length of the screw of the fastener is 270 - 290 mm, preferably 280 ± 6 mm. The diameter of the screw of the fastener is 55 - 60 mm, preferably 56.6 - 57.2 mm. The normal temperature tensile strength range of the fastener is 1150 - 1170 MPa. The normal temperature yield strength of the fastener is greater than 1095 MPa. The high temperature tensile strength of the fastener at 350 °C is greater than 1035 MPa. The high temperature yield strength of the fastener at 350 °C is greater than 855 MPa. The low temperature impact energy of the fastener at -18 °C is greater than 60 J. The fastener is made by the following method, and the method includes: obtaining a bar in forged state, the bar is made of material B23 in ASME SA-540 standard, and the forging ratio of the bar is greater than or equal to 9.5. Among them, in material B23, the C content is 0.37 - 0.44 wt%, the Si content is 0.15 - 0.35 wt%, the Mn content is 0.6 - 0.95 wt%, the P content is 0 - 0.025 wt%, the S content is 0 - 0.025 wt%, the Cr content is 0.65 - 0.95 wt%, the Ni content is 1.55 - 2 wt%, and the Mo content is 0.2 - 0.3 wt%; quenching the bar; tempering the bar after quenching treatment. When tempering, the bar is put into the furnace at 80 - 120 °C, the heating rate is 155 - 200 °C / h, the holding temperature is 534 - 536 °C, holding for 2 - 4 h, and then air cooling; using the bar after tempering treatment to make the fastener. In this embodiment, the bar in forged state (sometimes simply referred to as forged bar hereinafter) refers to a metal bar that is formed by forging process and has not undergone subsequent heat treatment (such as annealing, normalizing, quenching and tempering, etc.). Its performance and tissue state are directly determined by the forging process and retain the characteristics of forging processing.

[0029] Preferably, when tempering, the holding temperature is 535 ± 0.5 °C, such as 534.5 °C, 535 °C, 535.5 °C or values between the above values, etc. More preferably, the holding temperature is 535 °C.

[0030] Preferably, when tempering, the heating rate is 160 ± 1 °C / h, such as 159 °C / h, 160 °C / h, 161 °C / h or values between the above values, etc. More preferably, the heating rate is 160 °C / h.

[0031] Preferably, when tempering, the holding time is 3.5 ± 0.05 h, such as 3.45 h, 3.5 h, 3.55 h or values between the above values, etc. More preferably, the holding time is 3.5 h.

[0032] Preferably, in some embodiments, obtaining a forged bar includes: loading a B23 ingot into a furnace and holding it at 1150 - 1300°C; blooming the heat-preserved B23 ingot to break coarse grains and massive substances in the ingot; upsetting and drawing the bloomed B23 ingot to increase the single deformation amount to 30 - 70%, repeatedly upsetting-drawing and forging in different directions to accumulate the forging ratio; using a U-shaped anvil in the final forging stage and forging gradually from the center to the ends, with the final forging temperature being 850 - 1000°C.

[0033] According to the second aspect of the present application, embodiments of the present application further provide a method for manufacturing fasteners, including: obtaining a forged bar, where the bar is made of B23 material in the ASME SA-540 standard and the forging ratio of the bar is greater than or equal to 9.5. Among them, in the B23 material, the C content is 0.37 - 0.44 wt%, the Si content is 0.15 - 0.35 wt%, the Mn content is 0.6 - 0.95 wt%, the P content is 0 - 0.025 wt%, the S content is 0 - 0.025 wt%, the Cr content is 0.65 - 0.95 wt%, the Ni content is 1.55 - 2 wt%, and the Mo content is 0.2 - 0.3 wt%; quenching the bar; tempering the quenched bar. When tempering, heating the bar into the furnace at 80 - 120°C, with a heating rate of 155 - 200°C / h, holding the temperature at 534 - 536°C for 2 - 4 h, and air-cooling; using the tempered bar to manufacture fasteners.

[0034] Preferably, when tempering, the holding temperature is 535 ± 0.5°C, such as 534.5°C, 535°C, 535.5°C or values between the above values, and more preferably, the holding temperature is 535°C.

[0035] Preferably, when tempering, the heating rate is 160 ± 1°C / h, such as 159°C / h, 160°C / h, 161°C / h or values between the above values, and more preferably, the heating rate is 160°C / h.

[0036] Preferably, when tempering, the holding time is 3.5 ± 0.05 h, such as 3.45 h, 3.5 h, 3.55 h or values between the above values, and more preferably, the holding time is 3.5 h.

[0037] Preferably, obtaining a bar in a forged state includes: loading a B23 ingot into a furnace and holding it at 1150 - 1300 °C; performing cogging on the heat-preserved B23 ingot to break coarse grains and massive substances in the ingot; performing upsetting and drawing on the cogged B23 ingot to increase the single deformation amount to 30 - 70%, repeatedly upsetting - drawing and changing the forging direction to accumulate the forging ratio; using a U-shaped anvil in the final forging stage and forging gradually from the center to the end, with the final forging temperature of 850 - 1000 °C; the forging ratio of the bar can be in the range of 9.5 - 12, such as values like 9.5, 10, 11, 12, etc., to prevent insufficient tensile strength and yield strength caused by too high forging ratio.

[0038] Preferably, during quenching treatment, it can be put into the furnace at 90 - 110 °C and heated in the furnace at a heating rate of 45 - 55 °C / h to a temperature of 860 ± 5 °C, held for 2 ± 0.05 h, and then water-cooled.

[0039] The fastener provided by the embodiment of the present application, as a large-sized fastener applied to a harsh environment, has good mechanical properties in both high-temperature and low-temperature cases. When the mechanical properties at normal temperature meet the standard value requirements, the high-temperature and low-temperature mechanical properties have a large redundancy compared with the standard value, and it has high safety and reliability.

[0040] The manufacturing method of the fastener provided by the embodiment of the present application can obtain a bar with the normal-temperature tensile strength, normal-temperature yield strength, high-temperature tensile strength, high-temperature yield strength, and low-temperature impact energy all meeting the requirements by controlling the forging ratio and the heat-preservation temperature during tempering treatment, combined with controlling the heating rate and heat-preservation time, and then obtain a fastener meeting the quality requirements. Specifically, in the embodiment of the present application, the bar is heat-treated by combining a lower heat-preservation temperature during tempering treatment and a higher forging ratio, so that the fastener made of the bar has higher high-temperature yield strength and higher low-temperature impact energy while the normal-temperature tensile strength does not exceed the upper limit value. Thus, on the premise of meeting the standard value requirements, the fastener has better high-low temperature mechanical properties, and the mechanical properties of the fastener are better in both high-temperature and low-temperature cases. In the preferred embodiment, by optimizing the heating rate and heat-preservation time, a fastener with better low-temperature mechanical properties is obtained under the condition of good high-temperature performance.

[0041] Example 1

[0042] Select SA-540 B23 alloy forged bars with a forging ratio of 9.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C, and then heat the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool in water. Temper the quenched bars. The tempering process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 200°C / h to 535°C, hold for 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0043] Example 2

[0044] Select SA-540 B23 alloy forged bars with a forging ratio of 9.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C, and then heat the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool in water. Temper the quenched bars. The tempering process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 160°C / h to 535°C, hold for 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0045] Example 3

[0046] Select SA-540 B23 alloy forged bars with a forging ratio of 9.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C, and then heat the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool in water. Temper the quenched bars. The tempering process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 160°C / h to 535°C, hold for 3.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0047] Comparative Example 1

[0048] Select SA-540 B23 alloy forged bars with a forging ratio of 6.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C, and then heat the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool in water. Temper the quenched bars. The tempering process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 200°C / h to 550°C, hold for 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0049] Comparative Example 2

[0050] Select SA-540 B23 alloy forged bars with a forging ratio of 6.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C and heat them up in the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool them in water. Subject the quenched bars to tempering. The process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 200°C / h to 540°C and hold, with a holding time of 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0051] Comparative Example 3

[0052] Select SA-540 B23 alloy forged bars with a forging ratio of 6.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C and heat them up in the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool them in water. Subject the quenched bars to tempering. The process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 200°C / h to 535°C and hold, with a holding time of 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0053] Comparative Example 4

[0054] Select SA-540 B23 alloy forged bars with a forging ratio of 6.5 for the bars. Quench the bars. The quenching process is as follows: Put the bars into the furnace at 100°C and heat them up in the furnace at a heating rate of 50°C / h to 860°C, hold for 2 h, and then cool them in water. Subject the quenched bars to tempering. The process is as follows: Put the bars into the furnace at 100°C, heat at a heating rate of 200°C / h to 520°C and hold, with a holding time of 2.5 h, and then air-cool to room temperature. Use the tempered bars to make screws. The length of the screw rod part is 280 mm and the diameter is 57 mm.

[0055] Conduct room temperature tensile tests, 350°C high-temperature tensile tests, and -18°C impact toughness tests on the screws obtained in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 respectively according to the ASTM A370 test standard, record the relevant data and summarize and organize them as shown in Table 2.

[0056] Table 2

[0057] Tensile strength at room temperature (MPa) Yield strength at room temperature (MPa) Tensile strength at 350°C (MPa) Yield strength at 350°C (MPa) Low temperature impact energy at -18°C (J) / lateral expansion (mm) Standard value 1070-1170 ≥965 ≥945 ≥842 47 / 0.63 Example 1 1169 1112 1099 879 61 / 0.69 Example 2 1164 1108 1087 870 63 / 0.70 Example 3 1155 1100 1042 863 68 / 0.72 Comparative example 1 1128 1029 1025 805 72 / 0.78 Comparative example 2 1152 1062 1045 835 65 / 0.70 Comparative example 3 1194 1131 1110 882 54 / 0.62 Comparative example 4 1205 1153 1110 899 52 / 0.57

[0058] As can be seen from Table 2, the screws obtained in Example 1, Example 2, and Example 3 all meet the requirements of the standard values. Among them, Example 1 has good tensile strength and yield strength, but the low-temperature impact energy is relatively low; in Example 2, the tensile strength and yield strength slightly decrease, while the low-temperature impact energy increases; in Example 3, the tensile strength and yield strength further decrease, and the increase in low-temperature impact energy is more obvious.

[0059] The screws obtained in Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 do not meet the requirements of the standard values. Among them, the high-temperature yield strength of Comparative Example 1 is too low; the high-temperature yield strength of Comparative Example 2 is too low; the normal-temperature tensile strength of Comparative Example 3 is too high; the normal-temperature tensile strength of Comparative Example 4 is too high.

[0060] By comparing Example 1 with Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 respectively, it can be concluded that by increasing the forging ratio to 9.5 and reducing the tempering temperature to 535°C, the normal-temperature tensile strength of the screw can be made not to exceed the upper limit specified by the standard value, while the high-temperature yield strength is good, and a relatively high low-temperature impact energy can be maintained.

[0061] By comparing Example 1 and Example 2, it can be concluded that when the heating rate is reduced from 200°C / h to 160°C / h, the low-temperature impact energy can be further improved while other parameters meet the standard values.

[0062] By comparing Example 2 and Example 3, it can be concluded that after the holding time is extended from 2.5 h to 3.5 h, the low-temperature impact energy can be further improved while other parameters meet the standard values, and the screw has good low-temperature toughness.

[0063] The screws obtained in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were subjected to a metallographic test with reference to the ASTM B112-2013 standard. The test samples were taken from the ends of the broken room-temperature tensile specimens, etched with the ET06 grain size etchant, observed longitudinally on the observation surface, and magnified 100X to obtain the Figure 1 - Figure 7 metallographic pictures as shown. Among them, Figure 1 , Figure 2 , Figure 3 all reached a grain size of 8.5 grades, and Figure 4 , Figure 5 , Figure 6 , Figure 7 reached a grain size of 7.5 grades. It can be seen that through the methods provided in Example 1, Example 2, and Example 3, the obtained material has a higher grain size, a smaller grain size, and higher toughness.

[0064] Based on the above embodiments of the present application, without explicit negation or conflict, the technical features of one embodiment can be beneficially combined with one or more other embodiments.

[0065] Although some specific embodiments of the present application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and not for limiting the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified or equivalent substitutions can be made to some technical features without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A fastener, characterized in that, The fastener is made of material B23 in ASME SA-540 standard. The length of the screw of the fastener is 270 - 290 mm, the diameter of the screw of the fastener is 55 - 60 mm, the normal temperature tensile strength range of the fastener is 1150 - 1170 MPa, the normal temperature yield strength of the fastener is greater than 1095 MPa, the high temperature tensile strength of the fastener at 350 °C is greater than 1035 MPa, the high temperature yield strength of the fastener at 350 °C is greater than 855 MPa, and the low temperature impact energy of the fastener at -18 °C is greater than 60 J; The said fastener is made by the following method, and the method includes: Obtain a bar in forged state. The bar is made of material B23 in ASME SA-540 standard, and the forging ratio of the bar is greater than or equal to 9.

5. Among them, in material B23, the C content is 0.37 - 0.44 wt%, the Si content is 0.15 - 0.35 wt%, the Mn content is 0.6 - 0.95 wt%, the P content is 0 - 0.025 wt%, the S content is 0 - 0.025 wt%, the Cr content is 0.65 - 0.95 wt%, the Ni content is 1.55 - 2 wt%, and the Mo content is 0.2 - 0.3 wt%; Quench the bar; Perform tempering treatment on the quenched bar. When performing tempering treatment, put it into the furnace at 80 - 120 °C, the heating rate is 155 - 200 °C / h, the holding temperature is 534 - 536 °C, hold for 2 - 4 h, and air cool; Use the bar after tempering treatment to make fasteners.

2. The fastener according to claim 1, characterized in that, When performing tempering treatment, the holding temperature is 535 ± 0.5 °C.

3. The fastener according to claim 1, wherein, When performing tempering treatment, the heating rate is 160 ± 1 °C / h.

4. The fastener according to claim 1, wherein When performing tempering treatment, the holding time is 3.5 ± 0.05 h.

5. The fastener according to claim 1, characterized in that, Obtaining a bar in forged state includes: Load the B23 ingot into the furnace and hold at 1150 - 1300 °C; Perform cogging on the B23 ingot after holding to break the coarse grains and massive substances in the ingot; Perform upsetting and drawing on the B23 ingot after cogging, increase the single deformation amount to 30 - 70%, repeatedly upset and draw and change the forging direction to accumulate the forging ratio; in the final forging stage, use a U-shaped anvil and forge gradually from the center to the end, and the final forging temperature is 850 - 1000 °C.

6. A manufacturing method of a fastener, characterized in that, Includes: Obtain a bar in forged state. The bar is made of material B23 in ASME SA-540 standard, and the forging ratio of the bar is greater than or equal to 9.

5. Among them, in material B23, the C content is 0.37 - 0.44 wt%, the Si content is 0.15 - 0.35 wt%, the Mn content is 0.6 - 0.95 wt%, the P content is 0 - 0.025 wt%, the S content is 0 - 0.025 wt%, the Cr content is 0.65 - 0.95 wt%, the Ni content is 1.55 - 2 wt%, and the Mo content is 0.2 - 0.3 wt%; Quench the bar; Perform tempering treatment on the quenched bar. When performing tempering treatment, put it into the furnace at 80 - 120 °C, the heating rate is 155 - 200 °C / h, the holding temperature is 534 - 536 °C, hold for 2 - 4 h, and air cool, Use the bar after tempering treatment to make fasteners.

7. The method according to claim 6, wherein When performing tempering treatment, the holding temperature is 535 ± 0.5 °C.

8. The method according to claim 6, wherein During tempering treatment, the heating rate is 160 ± 1 °C / h.

9. The method according to claim 6, wherein During tempering treatment, the holding time is 3.5 ± 0.05 h.

10. The method according to claim 6, wherein Obtain bars in the forged state, including: Load the B23 ingot into the furnace and hold at 1150 - 1300 °C; Perform cogging on the B23 ingot after holding to break the coarse grains and massive substances in the ingot; Perform upsetting and drawing on the B23 ingot after cogging, increase the single deformation amount to 30 - 70%, repeatedly upset and draw and change the forging direction to accumulate the forging ratio; at the final forging stage, use a U-shaped anvil and forge gradually from the center to the end, with the final forging temperature of 850 - 1000 °C; The forging ratio of the bars ranges from 9.5 to 12.

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