Controlled rolling and controlled cooling process for improving ultralow-temperature impact toughness of high-building steel and structure optimization method

Abstract

The invention discloses a controlled rolling and controlled cooling process for improving ultralow-temperature impact toughness of high building steel and a structure optimization method, and relates to the technical field of alloy preparation. Comprising the following steps: preparing a high-rise building steel billet, and heating the billet to a recrystallization temperature interval; the heated steel billet is always in a coupling field of an electromagnetic field and an ultrasonic field in the whole rolling process before rolling, during rolling and after rolling; the pre-finished product steel is sequentially subjected to ultralow-temperature aging treatment and gradient tempering treatment; the macroscopic deformation resistance is reduced through the electromagnetic field, the microcosmic strain distribution is refined through the ultrasonic waves, and the grain refinement limit is broken through synergistically.

Description

TECHNICAL FIELD

[0001] The present application relates to the alloy preparation technical field, especially relates to a kind of high building steel ultra-low temperature impact toughness promotion's controlled rolling and controlled cooling process and organization optimization method. BACKGROUND

[0002] With the rapid development of high-end fields such as aerospace, deep-sea exploration, more stringent requirements are put forward for the comprehensive performance of high building steel, especially the impact toughness in ultra-low temperature environment. There are two major problems with traditional high building steel: first, the ultra-low temperature toughness is insufficient, such as the existing 09MnNiDR steel, the impact energy at -70℃ is only 25J, even after normalizing + tempering treatment, the impact energy can only be increased to ≥50J, which is difficult to meet the use requirements in extreme ultra-low temperature environment such as -196℃; second, the preparation process has defects, the traditional rolling process needs high temperature heating or long time subsequent heat treatment to reduce the deformation resistance of the material, which leads to high energy consumption, long production cycle, and in the rolling process, brittle intermetallic compounds such as Fe-Al, Ti-Fe are easily generated, and composition segregation phenomena such as pores, cracks and carbide aggregation are easily generated inside the material, which seriously weakens the interface bonding strength, reduces the hardness, wear resistance and fatigue resistance of the material.

[0003] In the prior art, a single grain refinement method or heat treatment process cannot simultaneously solve the problems of deformation resistance control, grain refinement limit breakthrough and ultra-low temperature toughness improvement, and a new type of controlled rolling and controlled cooling process and organization optimization method is urgently needed to significantly improve the ultra-low temperature impact toughness of high building steel, while improving the energy consumption and efficiency problems in the preparation process. SUMMARY

[0004] In view of the technical problems of insufficient ultra-low temperature impact toughness of existing high building steel, high energy consumption of traditional rolling process, limited grain refinement effect and easy generation of internal defects, the present application provides a controlled rolling and controlled cooling process and organization optimization method for improving the ultra-low temperature impact toughness of high building steel, which breaks through the grain refinement limit, reduces the production energy consumption, and significantly improves the impact toughness and comprehensive mechanical properties of high building steel in ultra-low temperature environment through the synergistic design of electromagnetic field and ultrasonic field coupling, gradient cooling and gradient tempering.

[0005] To achieve the above purpose, the present application provides the following technical scheme: a controlled rolling and controlled cooling process and organization optimization method for improving the ultra-low temperature impact toughness of high building steel, comprising the following steps: Preparation of high building steel billet, heating the billet to the recrystallization temperature range; The heated billet is in the coupling field of electromagnetic field and ultrasonic field before, during and after rolling throughout the rolling process; The pre-product steel is sequentially subjected to ultra-low temperature aging treatment and gradient tempering treatment.

[0006] Further, the frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, and the vibration amplitude is 1-10 μm.

[0007] Further, the electromagnetic field is a high-frequency pulsed magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0008] Further, the total deformation of the multi-pass rolling is 30-40%.

[0009] Further, it further comprises gradient cooling before the ultra-low temperature aging treatment, and the gradient cooling comprises surface layer rapid cooling and core slow cooling. The cooling speed of the surface layer rapid cooling is > 500℃ / s, and the speed of the core slow cooling is < 10℃ / s.

[0010] Further, the surface layer rapid cooling is cooled by liquid nitrogen jet cooling, and the core slow cooling is cooled by gas mist cooling.

[0011] Further, the temperature of the ultra-low temperature aging treatment is -80—-120℃, and the aging treatment time is 0.5-1h.

[0012] Further, the gradient tempering comprises surface layer high-temperature tempering and core low-temperature tempering. The temperature of the surface layer high-temperature tempering is 200-300℃, the temperature of the core low-temperature tempering is 150-200℃, and the tempering time is 0.5-2h.

[0013] Further, the application further provides a high constructional steel with improved ultra-low temperature impact toughness, which is prepared according to the preparation method.

[0014] Further, the application further provides application of the high constructional steel with improved ultra-low temperature impact toughness, and the high constructional steel is prepared according to the preparation method.

[0015] Compared with the prior art, the application has the following beneficial effects: 1. The application can reduce the rolling pressure by 30%-50% through the coupling effect of the electromagnetic field and the ultrasonic field, and the production cycle is shortened, and the energy consumption is reduced without high-temperature heating or long-time subsequent heat treatment. 2. The application can reduce the rolling pressure by 30%-50% through the coupling effect of the electromagnetic field and the ultrasonic field, and the production cycle is shortened, and the energy consumption is reduced without high-temperature heating or long-time subsequent heat treatment. 3.The application disperses local stress concentration by ultrasonic cavitation, homogenizes plastic flow by electromagnetic field, reduces pores, cracks and composition segregation; meanwhile, inhibits the generation of brittle intermetallic compounds, purifies grain boundaries, reduces impurity segregation, and improves interface bonding strength, so that the prepared high construction steel has a tensile strength of ≥870MPa and a yield strength of ≥670MPa, and has high strength and high toughness, which meets the strict requirements of high-end fields such as aerospace and deep-sea equipment. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments.

[0017] The technical solutions provided by the embodiments of the application are as follows: a high construction steel ultralow-temperature impact toughness improvement controlled rolling and controlled cooling process and microstructure optimization method, comprising the following steps: Preparation of high construction steel billets, heating the billets to the recrystallization temperature range; The heated billets are in the coupling field of the electromagnetic field and the ultrasonic field throughout the rolling process before, during and after rolling; The pre-product steel is sequentially subjected to ultralow-temperature aging treatment and gradient tempering treatment.

[0018] In further embodiments of the present application, the frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, and the vibration amplitude is 1-10 μm.

[0019] In further embodiments of the present application, the electromagnetic field is a high-frequency pulsed magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0020] In further embodiments of the present application, the total deformation of the multi-pass rolling is 30-40%.

[0021] In further embodiments of the present application, gradient cooling before ultralow-temperature aging treatment is further included, and the gradient cooling comprises surface layer rapid cooling and core slow cooling. The cooling speed of the surface layer rapid cooling is >500℃ / s, and the cooling speed of the core slow cooling is <10℃ / s.

[0022] In further embodiments of the present application, the surface layer rapid cooling is cooled by liquid nitrogen jet cooling, and the core slow cooling is cooled by gas mist cooling.

[0023] In further embodiments of the present application, the temperature of the ultralow-temperature aging treatment is -80—-120℃, and the aging treatment time is 0.5-1h.

[0024] In a further implementation form of the embodiment, the gradient tempering includes a surface high-temperature tempering and a core low-temperature tempering. The surface high-temperature tempering has a temperature of 200-300 DEG C, and the core low-temperature tempering has a temperature of 150-200 DEG C, and the tempering time is 0.5-2 hours.

[0025] Further, the embodiment of the present application also provides a high constructional steel with improved ultra-low-temperature impact toughness, which is prepared according to the preparation method.

[0026] In another aspect, the embodiment of the present application also provides an application of the high constructional steel with improved ultra-low-temperature impact toughness, which is characterized by the application of the high constructional steel prepared according to the preparation method in high-end fields such as aerospace and deep-sea equipment.

[0027] It should be noted that the high-frequency vibration of the ultrasonic vibration under the condition of 20-30 kHz induces a local transient temperature rise of the steel billet by about 200-500 DEG C, promotes the dynamic recrystallization inside the steel billet, and makes the grain refinement to a sub-micron level of 0.5-2 microns; the ultrasonic vibration is different from the traditional longitudinal wave / transverse wave, and the Stoneley surface wave generated by the ultrasonic tool head propagates along the rolling interface to induce high-frequency vibration of atoms with an amplitude of 1-10 microns, which can reduce the dislocation movement resistance, promote the dynamic recrystallization effect, and the micro-area high pressure of >100 MPa generated by the ultrasonic cavitation can make the local temperature rise of the steel billet soft, so as to reduce the rolling pressure by 30%-50% in the rolling process.

[0028] The electromagnetic field preferably adopts a rotating pulse magnetic field, generates eddy current through the alternating magnetic field, accelerates the dislocation movement and grain boundary migration inside the steel billet to inhibit grain coarsening, and further forms a uniform nano bainite / martensite mixed structure, the pulse magnetic field induces metal internal eddy current to generate dynamic Lorentz force, refines the initial grain and regulates the phase transformation path, such as inhibiting pearlite formation and promoting bainite transformation, the electromagnetic stirring reduces the segregation of impurities such as sulfur and phosphorus at the grain boundary, and improves the grain boundary purity.

[0029] The coupling phase transformation of the ultrasonic field and the electromagnetic field, the electromagnetic field inhibits the coarsening of carbides, the ultrasonic vibration promotes the transformation of austenite to ultrafine bainite, while retaining 5%-15% residual austenite, absorbs impact energy by using TRIP effect, the ultrasonic vibration and the electromagnetic field synergistically act, break through the grain refinement limit of a single energy field, realize nano-level structure regulation, the electromagnetic field reduces the macro deformation resistance, the ultrasonic wave refines the micro strain distribution, and avoids crack initiation caused by local stress concentration. Embodiment

[0030] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0031] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 30%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. Meanwhile, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -80℃.

[0032] After the ultra-low temperature aging treatment at -80℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 200℃, the tempering temperature of the core is controlled to be 150℃, and the tempering treatment is performed for 0.5 h. Example

[0033] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0034] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. Meanwhile, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -80℃.

[0035] After the ultra-low temperature aging treatment at -80℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 200℃, the tempering temperature of the core is controlled to be 150℃, and the tempering treatment is performed for 0.5 h. Example

[0036] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0037] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 40%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -80℃.

[0038] After the ultra-low temperature aging treatment at -80℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 200℃, and the tempering temperature of the core is controlled to be 150℃, and the tempering treatment is performed for 0.5 h. Example

[0039] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0040] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -90℃.

[0041] After the ultra-low temperature aging treatment at -90℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 200℃, and the tempering temperature of the core is controlled to be 150℃, and the tempering treatment is performed for 0.5 h. Example

[0042] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, and the vibration amplitude is 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the frequency of the magnetic field is 1-10 kHz.

[0043] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -100℃.

[0044] After the ultra-low temperature aging treatment at -100℃ for 0.5 h, the steel billet is heated and tempered after slowly warming to room temperature. The tempering temperature of the surface layer is controlled to be 200℃, and the tempering temperature of the core is controlled to be 150℃. The tempering treatment is performed for 0.5 h. Example

[0045] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, and the vibration amplitude is 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the frequency of the magnetic field is 1-10 kHz.

[0046] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -110℃.

[0047] After the ultra-low temperature aging treatment at -110℃ for 0.5 h, the steel billet is heated and tempered after slowly warming to room temperature. The tempering temperature of the surface layer is controlled to be 200℃, and the tempering temperature of the core is controlled to be 150℃. The tempering treatment is performed for 0.5 h. Example

[0048] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of the rolling mill. The ultrasonic field and the rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, the vibration amplitude is 1-10 μm, and the electromagnetic field is a high-frequency pulse magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0049] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -120℃.

[0050] The steel billet is subjected to ultra-low temperature aging treatment at -120℃ for 0.5 h, and then slowly heated to room temperature. The steel billet is subjected to heating tempering, the tempering temperature of the surface layer is controlled to be 200℃, the tempering temperature of the core is controlled to be 150℃, and the tempering treatment is performed for 0.5 h. Embodiment

[0051] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of the rolling mill. The ultrasonic field and the rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, the vibration amplitude is 1-10 μm, and the electromagnetic field is a high-frequency pulse magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0052] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -100℃.

[0053] The steel billet is subjected to ultra-low temperature aging treatment at -100℃ for 0.5 h, and then slowly heated to room temperature. The steel billet is subjected to heating tempering, the tempering temperature of the surface layer is controlled to be 220℃, the tempering temperature of the core is controlled to be 160℃, and the tempering treatment is performed for 0.5 h. Embodiment

[0054] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0055] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -80℃.

[0056] The steel billet is subjected to ultra-low temperature aging treatment at -80℃ for 0.5 h, and then slowly heated to room temperature. The steel billet is subjected to heating tempering, the tempering temperature of the surface layer is controlled to be 240℃, and the tempering temperature of the core is controlled to be 170℃. The tempering treatment is performed for 0.5 h. Embodiment

[0057] The A1106-Mn25 steel billet is heated to the crystallization temperature interval, i.e. 850-950℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The ultrasonic field has a frequency of 20-30 kHz, a power of 8000-10000 W and a vibration amplitude of 1-10 μm. The electromagnetic field is a high-frequency pulse magnetic field, and the magnetic field has a frequency of 1-10 kHz.

[0058] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10℃ / s, and the whole steel billet is cooled to -80℃.

[0059] The steel billet is subjected to ultra-low temperature aging treatment at -80℃ for 0.5 h, and then slowly heated to room temperature. The steel billet is subjected to heating tempering, the tempering temperature of the surface layer is controlled to be 260℃, and the tempering temperature of the core is controlled to be 180℃. The tempering treatment is performed for 0.5 h. Embodiment

[0060] The A1106-Mn25 steel billet is heated to the crystallization temperature range, i.e. 850-950 ℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, the vibration amplitude is 1-10 μm, and the electromagnetic field is a high-frequency pulse magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0061] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500 ℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10 ℃ / s, and the whole steel billet is cooled to -80 ℃.

[0062] After the ultra-low temperature aging treatment at -80 ℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 280 ℃, the tempering temperature of the core is controlled to be 190 ℃, and the tempering treatment is performed for 0.5 h. Example

[0063] The A1106-Mn25 steel billet is heated to the crystallization temperature range, i.e. 850-950 ℃, and the heated steel billet is placed at the inlet end of a rolling mill. An ultrasonic field and a rotating pulse electromagnetic field are arranged at the inlet section, the rolling region and the outlet section of the rolling mill. The frequency of the ultrasonic field is 20-30 kHz, the power is 8000-10000 W, the vibration amplitude is 1-10 μm, and the electromagnetic field is a high-frequency pulse magnetic field, wherein the frequency of the magnetic field is 1-10 kHz.

[0064] The steel billet is subjected to multi-pass rolling in the rolling mill, and the total deformation is 35%. After rolling, the surface layer is subjected to ultrafast cooling by liquid nitrogen spraying, and the cooling speed of the surface layer is controlled to be greater than 500 ℃ / s. At the same time, the core is subjected to air mist cooling, and the cooling speed of the core is controlled to be less than 10 ℃ / s, and the whole steel billet is cooled to -80 ℃.

[0065] After the ultra-low temperature aging treatment at -80 ℃ for 0.5 h, the steel billet is slowly heated to room temperature and then tempered, the tempering temperature of the surface layer is controlled to be 300 ℃, the tempering temperature of the core is controlled to be 200 ℃, and the tempering treatment is performed for 0.5 h.

[0066] Comparative Example 1 The traditional hot rolling process is adopted, no electromagnetic field and ultrasonic field are assisted, and the steel billet is naturally cooled after rolling. No ultra-low temperature aging and gradient tempering treatment is performed. The grain size is 20-50 μm, and the impact energy at -196 ℃ is 109 J.

[0067] Comparative Example 2 The grain size is 10-20 mu m, and the impact energy at-196 DEG C is 71 J by using normalizing + tempering process without coupling field assistance and gradient cooling.

[0068] The above examples 1-12 and comparative examples 1 and 2 are sampled to conduct the HB 5278-1984 metal low temperature impact test and detect the grain size range.

[0069] The steel material with accurate size of 300±2 mm, width of 20±1 mm and thickness of 20±1 mm is cut respectively to conduct the experiment, the impact testing machine (range 0-200 J, precision 1 J) and the ultra-low temperature environment box (minimum-196 DEG C) are used, the sample is kept at low temperature at-50 DEG C and-196 DEG C for more than 3 hours, the temperature is ensured to be uniform, the impact test is completed within 2 minutes after taking out, the back temperature is avoided to affect the result, and the experimental results are shown in the following table 1.

[0070] Table 1

[0071] From the above table 1, it can be seen that the high construction steel prepared by examples 1-12 has grain size of 0.5-5 mu m, impact energy at-196 DEG C of 146-186 J, tensile strength of greater than or equal to 870 MPa, and yield strength of greater than or equal to 670 MPa, wherein the total deformation amount of example 9 is 35%, the ultra-low temperature aging is-80 DEG C, the surface tempering is 240 DEG C, and the core tempering is 170 DEG C, and the total deformation amount of example 10 is 35%, the ultra-low temperature aging is-80 DEG C, the surface tempering is 260 DEG C, and the core tempering is 180 DEG C, which are the optimal examples, and have excellent ultra-low temperature toughness and cost performance.

[0072] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all aspects as illustrative and not restrictive, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended to encompass all changes falling within the meaning and range of equivalents of the claims.

Claims

1. A controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel, characterized in that, Includes the following steps: To prepare high-strength structural steel billets, the billets are heated to the recrystallization temperature range of 850-950℃. The heated steel billet is continuously exposed to the coupled field of electromagnetic and ultrasonic fields throughout the entire rolling process, including before, during, and after rolling. The rolled pre-finished steel is subjected to ultra-low temperature aging treatment and gradient tempering treatment in sequence.

2. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, The ultrasonic field has a frequency of 20-30kHz, a power of 8000-10000W, and a vibration amplitude of 1-10μm.

3. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, The electromagnetic field is a high-frequency pulsed magnetic field, wherein the frequency of the magnetic field is 1-10kHz.

4. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, The total deformation of the multi-pass rolling is 30-40%.

5. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, It also includes gradient cooling prior to cryogenic aging treatment, wherein the gradient cooling includes rapid surface cooling and slow core cooling; The surface layer undergoes rapid cooling at a rate of >500℃ / s, while the core layer undergoes slow cooling at a rate of <10℃ / s.

6. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 5, characterized in that, The surface layer is rapidly cooled by liquid nitrogen injection, while the core is slowly cooled by aerosol cooling.

7. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, The ultra-low temperature aging treatment is performed at a temperature of -80 to -120°C for a duration of 0.5 to 1 hour.

8. The controlled rolling and cooling process and microstructure optimization method for improving the ultra-low temperature impact toughness of high-strength structural steel according to claim 1, characterized in that, The gradient tempering includes high-temperature tempering of the surface layer and low-temperature tempering of the core. The surface high-temperature tempering temperature is 200-300℃, the core low-temperature tempering temperature is 150-200℃, and the tempering time is 0.5-2h.

9. A high-strength structural steel with improved impact toughness at ultra-low temperatures, characterized in that, The high-strength steel prepared according to any one of claims 1-8 has a grain size of 0.5-5 μm, an impact energy of ≥146 J at -196℃, a tensile strength of ≥870 MPa, and a yield strength of ≥670 MPa.

10. An application of high-strength structural steel with improved impact toughness at ultra-low temperatures, characterized in that, Applications of high-strength structural steel prepared according to any one of claims 1-8 in high-end fields of aerospace and deep-sea equipment.

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