High-strength high-toughness steel material and heat treatment process method thereof, stud

Abstract

The application belongs to the technical field of metal heat treatment, and particularly relates to high-strength and high-toughness steel and a heat treatment process method and a stud thereof. The heat treatment process method comprises the following steps: the steel is quenched at a temperature not lower than 780 DEG C and the total time is less than or equal to 300 s, and the water cooling temperature is less than or equal to 45 DEG C; the steel is three-section continuously tempered at 520-580 DEG C, and the time is limited by the shortest time of complete austenitization and the longest time of grain size not coarser than 8, and the high-strength and high-toughness steel is obtained after cooling. Through quenching treatment, the grain coarsening is effectively inhibited while ensuring complete austenitization of the steel, and then the steel is quenched by water cooling at a temperature not higher than 45 DEG C to obtain fine and uniform martensite structure, and then the steel is fully and not overheated tempered by three-section continuous tempering to make carbides diffuse and precipitate and eliminate residual stress, so that the low-temperature toughness and fatigue resistance are significantly improved under the premise of ensuring 14.9-grade ultra-high strength, and the problems of mismatch between strength and toughness and insufficient fatigue life of the existing high-strength steel are fundamentally solved.

Description

Technical Field

[0001] This invention belongs to the field of metal heat treatment technology, specifically relating to a high-strength, high-toughness steel and its heat treatment process, as well as studs. Background Technology

[0002] Currently, in the wind power industry, blade root studs are mainly made of alloy steels such as 42CrMoA and 40CrNiMoA, with a strength grade of 10.9. Some high-power wind turbines are attempting to use high-strength studs of grade 12.9 to meet load requirements, but this leads to problems such as decreased fatigue performance and increased risk of stress corrosion. In actual service, these studs need to withstand complex periodic alternating loads for a long time—affected by the direction and magnitude of wind speed, the axial force of the stud changes sinusoidally periodically. The higher the wind speed, the faster the load change frequency. At the same time, they also need to withstand impact loads, vibration loads, and environmental corrosion, making their service conditions extremely harsh.

[0003] Existing blade root studs generally suffer from two major technical pain points: First, the mechanical properties are not synergistic enough, making it difficult to achieve both high strength and high toughness. Although some studs can meet the strength requirements, their toughness is poor, and they are prone to brittle fracture under low temperature environments or frequent load impacts. Second, their fatigue resistance is insufficient. Under long-term cyclic alternating loads, stress concentration is easily formed around the inclusions, which leads to the generation and continuous propagation of microcracks, eventually causing fatigue fracture of the stud. This is also one of the main reasons for the failure of blade root studs.

[0004] Meanwhile, as the wind power industry develops towards high-power models, higher requirements are placed on the fatigue resistance of stud materials. With the trend of larger blades, the blade root load continues to increase, and stud specifications are constantly increasing (from M30 and M36 to M42 and above). This further enhances the synergistic requirements for the strength, toughness, and fatigue performance of steel. Existing steel and stud products can no longer meet the service requirements of high-power and large-scale wind power equipment.

[0005] While existing technologies have improved the load-bearing capacity of blade root connections by optimizing stud structures (such as central necking design and the use of MJ circular arc threads), increasing the number of studs, and enlarging the blade root pitch circle, they have not fundamentally solved the core problems of insufficient mechanical properties and poor fatigue resistance of the stud materials themselves. Summary of the Invention

[0006] The purpose of this application is to provide a high-strength and high-toughness steel and its heat treatment process and studs, which to a certain extent solves the problem that existing steels are difficult to balance with low-temperature toughness and fatigue resistance when pursuing ultra-high strength, and improves mechanical properties such as strength, plasticity, toughness and hardness.

[0007] In a first aspect, this application provides a heat treatment process for high-strength and high-toughness steel, comprising the following steps: Quenching treatment: The steel to be treated is subjected to continuous quenching treatment. The heating and holding temperature of the first quenching treatment is not lower than 780℃, the heating and holding temperature of the second quenching treatment is not lower than 780℃, and the total quenching heating and holding time does not exceed 300 seconds, so as to ensure that the metallographic structure of the steel to be treated is completely austenitized. Water quenching: The steel to be treated is subjected to water quenching, and the temperature of the cooling water is not higher than 45°C; Tempering treatment: The steel to be treated is subjected to continuous tempering treatment. The heating and holding temperature of the first tempering treatment is 520-580℃, the heating and holding temperature of the second tempering treatment is 520-580℃, and the heating and holding temperature of the third tempering treatment is 520-580℃. The total tempering heating and holding time is the minimum time required to completely austenitize the metallographic structure of the steel to be treated, and the maximum time required to ensure that the austenite grain size is not coarse than grade 8. Cooling yields high-strength, high-toughness steel.

[0008] Optionally, the heating and holding temperature of the first quenching treatment is 780-820℃, and the heating and holding temperature of the second quenching treatment is 870-910℃.

[0009] Optionally, the temperature of the water used for water quenching is 35-45℃.

[0010] Optionally, the heating and holding temperature of the first tempering treatment is 520-580℃, the heating and holding temperature of the second tempering treatment is 520-580℃, and the heating and holding temperature of the third tempering treatment is 520-580℃.

[0011] Optionally, in the quenching step, the current frequency is 2600-3200Hz, and the quenching heating and holding time is 180-220 seconds; in the tempering step, the current frequency is 1200-1800Hz.

[0012] Optionally, in the tempering process, the total tempering heating and holding time is 570-620 seconds.

[0013] Optionally, the heat treatment equipment is a continuous medium-frequency induction heating tempering line, which includes a quenching induction heating zone, a water-cooled quenching zone, and a tempering induction heating zone.

[0014] Optionally, the steel comprises the following components by mass percentage: C: 0.30-0.45%, Si: 0.15-0.35%, Mn: 0.30-0.60%, P: ≤0.010%, S: ≤0.005%, Cr: 0.50-1.20%, Mo: 0.45-0.65%, Cu: ≤0.30%, Ni: 0.15-1.00%, V: 0.10%-0.45%, Nb: 0.02%-0.10%, Ti: 0.01%-0.03%, Al: 0.02-0.05%, H: ≤0.0002%, with the remainder being Fe.

[0015] Secondly, this application provides a high-strength, high-toughness steel, which is obtained by the heat treatment process described above.

[0016] Thirdly, this application provides a stud, wherein the stud is made of high-strength, high-toughness steel obtained by the heat treatment process described above or high-strength, high-toughness, fatigue-resistant steel as described above.

[0017] The beneficial effects of this application are: The heat treatment process for high-strength and high-toughness steel provided in the first aspect of this application employs a two-stage continuous quenching process at a temperature not lower than 780℃, combined with a short-term heating and holding time not exceeding 300 seconds. This ensures complete austenitization of the steel while effectively suppressing grain coarsening. A water-cooling quench at a temperature not higher than 45℃ is then performed to obtain a fine and uniform martensitic structure. Subsequently, a three-stage continuous tempering process at 520-580℃ is carried out within a strictly controlled time window to achieve a sufficient but not overheated tempering transformation, allowing carbides to precipitate diffusely and eliminating residual stress. This significantly improves low-temperature toughness and fatigue resistance while maintaining an ultra-high strength of 14.9 grade, fundamentally solving the problems of strength-toughness mismatch and insufficient fatigue life in existing high-strength steels.

[0018] The high-strength and high-toughness steel provided in the second aspect of this application achieves uniform refinement of the microstructure and full release of stress through the above-mentioned heat treatment process on a continuous quenching and tempering line. This effectively avoids the problems of grain coarsening, uneven microstructure and imbalance of strength and toughness that are prone to occur in traditional heat treatment. It has the characteristics of high strength, excellent low-temperature toughness and fatigue resistance, as well as high production efficiency and good quality stability.

[0019] The stud provided in the third aspect of this application not only has a strength grade of not less than 12.9, but also has excellent low-temperature impact toughness and fatigue resistance. Attached Figure Description

[0020] Figure 1 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 1 of this application; Figure 2Metallographic image of the high-strength, high-toughness steel provided in Embodiment 1 of this application; Figure 3 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 2 of this application; Figure 4 Metallographic image of the high-strength, high-toughness steel provided in Embodiment 2 of this application; Figure 5 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 3 of this application; Figure 6 Metallographic image of the high-strength, high-toughness steel provided in Embodiment 3 of this application; Figure 7 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 4 of this application; Figure 8 Metallographic image of the high-strength, high-toughness steel provided in Example 4 of this application; Figure 9 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 5 of this application; Figure 10 Metallographic image of the high-strength, high-toughness steel provided in Embodiment 5 of this application; Figure 11 This is a tensile property test diagram of the high-strength and high-toughness steel provided in Embodiment 6 of this application; Figure 12 Metallographic image of the high-strength, high-toughness steel provided in Embodiment 6 of this application. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0022] The first aspect of this application provides a heat treatment process for high-strength and high-toughness steel, comprising the following steps: Quenching treatment: The steel to be treated is subjected to continuous quenching treatment. The heating and holding temperature of the first quenching treatment is not lower than 780℃, the heating and holding temperature of the second quenching treatment is not lower than 780℃, and the total quenching heating and holding time does not exceed 300 seconds to ensure that the metallographic structure of the steel to be treated is completely austenitized. Water quenching: The steel to be treated is subjected to water quenching, and the temperature of the cooling water is not higher than 45℃; Tempering treatment: The steel to be treated is subjected to continuous tempering treatment. The heating and holding temperature of the first tempering treatment is 520-580℃, the heating and holding temperature of the second tempering treatment is 520-580℃, and the heating and holding temperature of the third tempering treatment is 520-580℃. The total tempering heating and holding time is the minimum time required to completely austenitize the metallographic structure of the steel to be treated, and the maximum time required to ensure that the austenite grain size is not coarse than grade 8. Cooling yields high-strength, high-toughness steel.

[0023] The heat treatment process for high-strength and high-toughness steel provided in the first aspect of this application employs a two-stage continuous quenching process at a temperature not lower than 780℃, combined with a short-term heating and holding time not exceeding 300 seconds. This ensures complete austenitization of the steel while effectively suppressing grain coarsening. A water-cooling quench at a temperature not higher than 45℃ is then performed to obtain a fine and uniform martensitic structure. Subsequently, a three-stage continuous tempering process at 520-580℃ is carried out within a strictly controlled time window to achieve a sufficient but not overheated tempering transformation, allowing carbides to precipitate diffusely and eliminating residual stress. This significantly improves low-temperature toughness and fatigue resistance while maintaining an ultra-high strength of 14.9 grade, fundamentally solving the problems of strength-toughness mismatch and insufficient fatigue life in existing high-strength steels.

[0024] In some possible implementations, the heating and holding temperature of the first quenching treatment is 780-820℃, and the heating and holding temperature of the second quenching treatment is 870-910℃. For example, the heating and holding temperature of the first quenching treatment can be any typical but non-limiting value such as 780℃, 790℃, 800℃, 810℃, or 820℃, or any value between any two such values; the heating and holding temperature of the second quenching treatment can be any typical but non-limiting value such as 870℃, 880℃, 890℃, 900℃, or 910℃, or any value between any two such values. In this approach, the steel undergoes initial austenitization at a lower temperature while retaining some undissolved carbides to pin grain boundaries and inhibit grain growth. Subsequently, at a higher temperature, the alloying elements are fully dissolved and the microstructure is homogenized. This ensures complete austenitization while avoiding grain coarsening caused by single high-temperature heating, thus laying the microstructure foundation for subsequent water-cooled quenching to obtain fine martensite and for the synergistic improvement in strength and toughness after three-stage tempering.

[0025] In some possible implementations, the cooling water temperature for water quenching is 35-45℃. For example, the cooling water temperature for water quenching can be any typical but non-limiting value such as 25℃, 30℃, 35℃, 40℃, or 45℃, or any value between any two points. In this case, sufficient cooling rate is ensured to obtain a fully martensitic structure, avoiding the reduction in strength and toughness caused by non-martensitic transformation products. It also effectively prevents quenching cracks and excessive residual stress caused by excessively rapid cooling due to excessively low water temperature. To a certain extent, this improves the low-temperature toughness and fatigue resistance of the steel, providing a stable and reliable microstructure prerequisite for achieving a strength-toughness balance in the subsequent three-stage tempering process.

[0026] In some possible implementations, the heating and holding temperatures for the first tempering treatment are 520-580℃, the second tempering treatment is 520-560℃, and the third tempering treatment is 520-580℃. For example, the heating and holding temperatures for the first, second, and third tempering treatments can be independent of typical but not limiting values ​​such as 530℃, 540℃, 550℃, and 560℃, or any value between any two points. In this case, by precisely controlling the three consecutive tempering temperatures, the quenched martensite can complete the dispersed precipitation of carbides, the full transformation of retained austenite, and the gradual release of internal stress in stages, while avoiding overheating and coarsening. This ensures both the uniformity and fineness of the tempered microstructure and a grain size no coarser than grade 8, while effectively avoiding the strength loss caused by single high-temperature tempering or the insufficient toughness caused by low-temperature tempering. Thus, it is possible to improve the low-temperature toughness and fatigue resistance of the steel while maintaining ultra-high strength, achieving synergistic optimization of strength, toughness, and fatigue life.

[0027] In some possible implementations, the current frequency in the quenching step is 2600-3200Hz, and the quenching heating and holding time is 180-220 seconds; the current frequency in the tempering step is 1200-1800Hz. For example, in the quenching step, the current frequency can be any typical but non-limiting value such as 2600Hz, 2700Hz, 2800Hz, 2900Hz, 3000Hz, 3100Hz, 3200Hz, or any value between any two such values; the quenching heating and holding time can be any typical but non-limiting value such as 180 seconds, 190 seconds, 200 seconds, 210 seconds, 220 seconds, or any value between any two such values; the current frequency in the tempering step can be 1200Hz, 1300Hz, 1400Hz, 1500Hz, 1600Hz, 1700Hz, etc. Typical but not limiting values ​​such as 1800Hz, or values ​​between any two points, allow for uniform and rapid heating of the steel from the surface in a suitable depth of penetration at this frequency. This ensures complete austenitization and fine, uniform grains in a short time, while avoiding energy waste caused by excessive heating at low frequencies or uneven microstructure caused by excessive skin effect at high frequencies. At the same time, the same frequency is used in the tempering stage to ensure stable heat transfer. Combined with three-stage temperature-controlled tempering, carbide dispersion and full stress release are achieved without grain coarsening. This improves low-temperature toughness and fatigue resistance while ensuring ultra-high strength.

[0028] In some possible implementations, the total tempering heating and holding time in the tempering process is 560-630 seconds. For example, the total tempering heating and holding time in the tempering process can be any typical but non-limiting value, such as 570 seconds, 580 seconds, 590 seconds, 600 seconds, 610 seconds, or 620 seconds, or any value between any two points. In this case, combined with the rapid heat penetration characteristics of 1200-1800Hz medium-frequency induction heating, the quenched martensite completes carbide dispersion precipitation, retained austenite transformation, and internal stress release in stages within a precise short heat treatment window. This avoids insufficient microstructure transformation and insufficient toughness caused by excessively short tempering times, while also preventing carbide coarsening and strength loss caused by excessively long tempering times. Thus, while ensuring a grain size no coarser than grade 8, it achieves a synergistic improvement in ultra-high strength, excellent low-temperature toughness, and fatigue resistance, providing stable and reliable comprehensive mechanical performance assurance for large wind turbine blade root studs.

[0029] In some possible implementations, the heat treatment equipment is a continuous medium-frequency induction heating tempering line, which includes a quenching induction heating zone, a water-cooled quenching zone, and a tempering induction heating zone. This achieves fully automated continuous production of steel from austenitization and water-cooled quenching to three-stage tempering.

[0030] In some possible implementations, the steel comprises the following components by mass percentage: C: 0.30-0.45%, Si: 0.15-0.35%, Mn: 0.30-0.60%, P: ≤0.010%, S: ≤0.005%, Cr: 0.50-1.20%, Mo: 0.45-0.65%, Cu: ≤0.30%, Ni: 0.15-1.00%, V: 0.10%-0.45%, Nb: 0.02%-0.10%, Ti: 0.01%-0.03%, Al: 0.02-0.05%, H: ≤0.0002%, with the remainder being Fe.

[0031] In some possible implementations, the steel comprises the following components by mass percentage: C: 0.40%, Si: 0.26%, Mn: 0.54%, P: 0.007%, S: 0.002%, Cr: 1.10%, Mo: 0.56%, Cu: 0.10%, Ni: 0.73%, V: 0.12%, Nb: 0.022%, Ti: 0.015%, Al: 0.035%, H: 0.00005%, with the remainder being Fe.

[0032] The second aspect of this application provides a high-strength, high-toughness steel, which is obtained by the heat treatment process described above.

[0033] The high-strength and high-toughness steel provided in the second aspect of this application achieves uniform refinement of the microstructure and full release of stress through the above-mentioned heat treatment process on a continuous quenching and tempering line. This effectively avoids the problems of grain coarsening, uneven microstructure and imbalance of strength and toughness that are prone to occur in traditional heat treatment. It has the characteristics of high strength, excellent low-temperature toughness and fatigue resistance, as well as high production efficiency and good quality stability.

[0034] The third aspect of this application provides a stud, the stud being made of high-strength, high-toughness steel obtained by the heat treatment process described above, or high-strength, high-toughness, fatigue-resistant steel as described above.

[0035] The stud provided in the third aspect of this application not only has a strength grade of not less than 12.9, but also has excellent low-temperature impact toughness and fatigue resistance.

[0036] To ensure that the above-described implementation details and operations of this application can be clearly understood by those skilled in the art, and to highlight the significant improvements in the performance of the high-strength, high-toughness steel and its heat treatment process, as well as the studs, the following examples illustrate the above technical solutions. Specifically: Experimental materials: The hot-rolled black suede material, made of 42CrMoVNb with a diameter of φ34×9000mm, has the following chemical composition (mass percentage): The composition is as follows: C: 0.40%, Si: 0.26%, Mn: 0.54%, P: 0.007%, S: 0.002%, Cr: 1.10%, Mo: 0.56%, Cu: 0.10%, Ni: 0.73%, V: 0.12%, Nb: 0.022%, Ti: 0.015%, Al: 0.035%, H: 0.00005%, with the remainder being Fe.

[0037] Using a continuous medium-frequency induction heating tempering line, and following the heat treatment method described in this application, parameters such as quenching, water-cooled quenching, and tempering were adjusted to obtain Examples 1-6.

[0038] Table 1

[0039]

[0040] As shown in Table 1, as the quenching temperature in Zone 1 gradually increased from 759℃ to 850℃, the tensile strength and yield strength of the steel decreased from 1500 / 1411 MPa to 1356 / 1278 MPa, respectively, and the core hardness also decreased from 459.4 HV10 to 401.5 HV10. This is mainly due to the weakening effect of precipitation strengthening caused by the growth of austenite grains and the coarsening of tempering carbides. At the same time, the elongation and reduction of area increased from 14% and 49% to 17% and 54.5%, respectively, and the impact energy at -20℃ increased significantly from 27 J to 60 J. This indicates that although the strength decreased, the plasticity and low-temperature toughness of the material were significantly improved due to the more complete dissolution of alloying elements and the increased degree of matrix alloying, showing a typical inverse relationship between strength and plasticity.

[0041] Considering all performance indicators, Example 3 is the optimal process scheme, with a tensile strength of 1437 MPa, a yield strength of 1342 MPa, an elongation of 16%, a reduction of area of ​​53%, an impact energy of 46.1 J at -20℃, a core hardness of 434.3 HV10, a core-to-surface hardness difference of only 5.9 HV10, and a martensite content of 95%. All indicators meet the technical requirements of grade 14.9 bolts, achieving the best balance of strength, plasticity, toughness, and hardness. In contrast, Examples 1 and 2 have insufficient austenitization due to the low quenching temperature in zone 1, resulting in high strength but insufficient low-temperature toughness. Examples 4-6 have decreased strength due to the high quenching temperature in zone 1. Among them, the tensile strength and yield strength of Example 6 are lower than the minimum requirements of ≥1400 MPa and ≥1300 MPa for grade 14.9 bolts, respectively, so none of them are ideal choices.

[0042] Example A below uses the raw materials prepared in Examples 1-3 above, which are peeled (φ34 is processed into φ33.23), tumbled, blanked, chamfered, bored, extruded, precision turned, laser marked, thread rolled, cleaned, magnetic particle tested, cleaned, shot blasted, and Dacromet tested to produce screw products. Comparative Example B uses 42CrMoA material and Comparative Example C uses 40CrNiMoA material. Three screws with the same characteristics as in Example A are produced. The performance is shown in Table 2 below.

[0043] Table 2

[0044] As can be seen from Table 2, the screw product prepared using the material of the present invention (Example A) has a significantly better fatigue cycle count than the workpieces of 42CrMoA (Comparative Example B) and 40CrNiMoA (Comparative Example C).

[0045] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0046] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A heat treatment process for high-strength and high-toughness steel, characterized in that, Includes the following steps: Quenching treatment: The steel to be treated is subjected to continuous quenching treatment. The heating and holding temperature of the first quenching treatment is not lower than 780℃, the heating and holding temperature of the second quenching treatment is not lower than 780℃, and the total quenching heating and holding time does not exceed 300 seconds, so as to ensure that the metallographic structure of the steel to be treated is completely austenitized. Water quenching: The steel to be treated is subjected to water quenching, and the temperature of the cooling water is not higher than 45°C; Tempering treatment: The steel to be treated is subjected to continuous tempering treatment. The heating and holding temperature of the first tempering treatment is 520-580℃, the heating and holding temperature of the second tempering treatment is 520-580℃, and the heating and holding temperature of the third tempering treatment is 520-580℃. The total tempering heating and holding time is the minimum time required to completely austenitize the metallographic structure of the steel to be treated, and the maximum time required to ensure that the austenite grain size is not coarse than grade 8. Cooling yields high-strength, high-toughness steel.

2. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, The heating and holding temperature of the first quenching treatment is 780-820℃, and the heating and holding temperature of the second quenching treatment is 870-910℃.

3. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, The water temperature for water quenching is 35-45℃.

4. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, The heating and holding temperature of the first tempering treatment is 530-560℃, the heating and holding temperature of the second tempering treatment is 520-560℃, and the heating and holding temperature of the third tempering treatment is 520-560℃.

5. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, In the quenching process, the current frequency is 2600-3200Hz, and the quenching heating and holding time is 180-220 seconds; in the tempering process, the current frequency is 1200-1800Hz.

6. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, In the tempering process, the total tempering heating and holding time is 570-620 seconds.

7. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, The equipment used for heat treatment is a continuous medium-frequency induction heating tempering line, which includes a quenching induction heating zone, a water-cooled quenching zone, and a tempering induction heating zone.

8. The heat treatment process for high-strength and high-toughness steel according to claim 1, characterized in that, The steel comprises the following components by mass percentage: C: 0.30-0.45%, Si: 0.15-0.35%, Mn: 0.30-0.60%, P: ≤0.010%, S: ≤0.005%, Cr: 0.50-1.20%, Mo: 0.45-0.65%, Cu: ≤0.30%, Ni: 0.15-1.00%, V: 0.10%-0.45%, Nb: 0.02%-0.10%, Ti: 0.01%-0.03%, Al: 0.02-0.05%, H: ≤0.0002%, with the remainder being Fe.

9. A high-strength, high-toughness steel, characterized in that, It is obtained by heat treatment process as described in any one of claims 1-8.

10. A stud, characterized in that, The stud is made of high-strength, high-toughness steel obtained by the heat treatment process described in any one of claims 1-8, or high-strength, high-toughness, fatigue-resistant steel as described in claim 9.

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