CN114622073A - Method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching - Google Patents
Method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 56
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- 238000000034 method Methods 0.000 title claims abstract description 42
- 229910052796 boron Inorganic materials 0.000 title claims abstract description 20
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 title claims abstract description 18
- 238000005496 tempering Methods 0.000 claims abstract description 30
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 5
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- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 4
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- 238000009489 vacuum treatment Methods 0.000 claims description 4
- 229910000604 Ferrochrome Inorganic materials 0.000 claims description 2
- 229910001309 Ferromolybdenum Inorganic materials 0.000 claims description 2
- 229910000592 Ferroniobium Inorganic materials 0.000 claims description 2
- 238000003723 Smelting Methods 0.000 claims description 2
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- 238000007872 degassing Methods 0.000 claims description 2
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- 239000007789 gas Substances 0.000 claims description 2
- 238000000265 homogenisation Methods 0.000 claims description 2
- 239000012535 impurity Substances 0.000 claims description 2
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- 229910052759 nickel Inorganic materials 0.000 claims description 2
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- 230000008520 organization Effects 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 239000006104 solid solution Substances 0.000 claims description 2
- 238000003756 stirring Methods 0.000 claims description 2
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- 238000009849 vacuum degassing Methods 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 230000000052 comparative effect Effects 0.000 description 12
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C33/00—Making ferrous alloys
- C22C33/04—Making ferrous alloys by melting
- C22C33/06—Making ferrous alloys by melting using master alloys
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
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- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/009—Pearlite
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
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Abstract
The invention discloses a method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching, which mainly solves the technical problems of improving the low-temperature impact toughness and the stability of the boron-containing steel, namely adding a sub-temperature quenching process on the basis of a conventional quenching and tempering (quenching and high-temperature tempering) process to improve the low-temperature impact toughness of a steel plate, wherein the steel plate produced by adopting the method has excellent low-temperature impact toughness and transverse impact energy at-40 ℃: 181J to 225J, meets the technical requirements of users, and improves the stability of the impact performance.
Description
Technical Field
The invention relates to the technical field of metallurgical plate production, in particular to a method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching.
Background
Hydroelectric power generation is used as clean energy, has the characteristics of reproducibility, no pollution, low operating cost, convenience in carrying out electric power peak regulation and the like, and is favorable for improving the resource utilization rate. Under the condition that the traditional energy is increasingly tense, all countries in the world have high priority to develop water and electricity and utilize water resources. With the rapid development of national large hydropower engineering and the increasing numerical values of installed capacity, water head and the like of hydropower stations, the special hydropower steel for manufacturing pressure pipelines, rib plates, branch pipes, volutes and the like of the large hydropower stations develops towards the direction of high strength and large thickness, and for the purpose of enabling the performance of steel plates to be uniform and stable, each large steel mill basically adopts a quenching and tempering process to produce the hydropower steel, the hardenability of the steel plates is gradually weakened along with the increase of the thickness of the steel plates, and the strength of the steel plates cannot meet the standard requirements easily. In order to improve the hardenability of the thick steel sheet, a trace amount of boron is generally added to improve the hardenability. With the addition of the boron element, the strength of the steel plate is greatly improved, but the low-temperature impact toughness is obviously reduced, and even the standard requirement is not met. How to improve the low-temperature impact toughness of boron-containing steel is urgently needed to be solved. And (3) performing sub-temperature quenching, namely, performing quenching on the steel plate at the temperature of a two-phase region for a proper time, wherein the structure after quenching is martensite and a small amount of ferrite.
Disclosure of Invention
The invention aims to provide a method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching, which is characterized in that the sub-temperature quenching process is added on the basis of the conventional quenching and tempering (quenching and high-temperature tempering) process to improve the low-temperature impact toughness of the steel plate.
In order to solve the technical problems, the invention adopts the following technical scheme:
the invention relates to a method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching, which comprises the following steps:
(1) firstly, carrying out desulfurization pretreatment on incoming molten iron, slagging off after desulfurization, ensuring that the molten iron is carried with slag as little as possible after desulfurization, and ensuring that the S content is less than or equal to 0.005% after pretreatment;
(2) smelting in a converter, namely adopting self-produced low-sulfur scrap steel, adding nickel plate alloy along with the scrap steel, and adopting a full-process argon blowing mode for converter bottom blowing gas to ensure that the tapping temperature is more than or equal to 1620 ℃;
(3) LF external refining and RH vacuum degassing, wherein LF refining ensures the formation time of white slag, and ferrocolumbium, ferrochromium and ferromolybdenum are added after the white slag is adjusted to target components; in the RH refining stage, molten steel is mainly degassed to promote inclusion floating, pure degassing time is ensured to be more than 5 minutes, vacuum treatment is carried out after vacuum treatment is carried out for 20 minutes, vacuum is restored to break vacuum to carry out calcium treatment, and after the calcium treatment is finished, soft blowing time is ensured to be more than or equal to 10 minutes;
(4) continuously casting the plate blank, controlling the drawing speed at 0.80-1.2 m/min, and ensuring the quality of the casting blank by adopting electromagnetic stirring and soft reduction;
(5) heating the plate blank, strictly controlling the time of the plate blank in a furnace, the soaking time and the tapping temperature, ensuring the homogenization of austenite and the full solid solution of alloy components, and simultaneously avoiding the excessive growth of crystal grains; the in-furnace time is 240-300 min, the soaking time is 30-60 min, and the out-furnace temperature is 1200 +/-20 ℃;
(6) primary dephosphorization, rolling and cooling are carried out, primary dephosphorization is carried out after the plate blank is taken out of the furnace, the high-pressure water nozzle is ensured to be normally opened without blockage, and the dephosphorization pressure is not less than 20 MPa; the rough rolling completes broadening in as few passes as possible, the relative reduction rate of at least 2 passes of a single pass is controlled to be more than 14 percent, the rough rolling ensures the rolling in a recrystallization zone, austenite crystal grains are fully refined, and the final rolling temperature is not less than 1050 ℃; the initial rolling temperature of finish rolling is not more than 950 ℃, the relative reduction rate of at least 2 passes is more than 14%, the rolling in a non-recrystallization area is ensured, organization and energy preparation is carried out for subsequent phase change, and the final rolling temperature of the finish rolling is set to be 810-850 ℃; the cooling mode adopts a second-level system self-learning calculation result, and the final cooling temperature is 630-650 ℃;
(7) the conventional quenching and tempering heat treatment process comprises the following steps: the quenching temperature is 910-920 ℃, and the heat preservation time is 20 min; tempering temperature is 600-620 ℃, and the heat preservation time is 20-40 min;
(8) adding a sub-temperature quenching heat treatment process, namely adding sub-temperature quenching in the conventional quenching, and then carrying out high-temperature tempering: the quenching temperature is 910-920 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 865-875 ℃, and the heat preservation time is 20 min; the tempering temperature is 600-620 ℃, and the heat preservation time is 20-40 min.
Further, the chemical components of the boron-containing steel are calculated as C: less than or equal to 0.08 percent, Si: less than or equal to 0.30 percent, Mn: less than or equal to 1.50 percent, P: not more than 0.010 percent, not more than 0.005 percent of S, Alt: 0.020-0.040%, Nb is less than or equal to 0.060%, Ti is less than or equal to 0.030%, V: less than or equal to 0.050 percent, Cr is less than or equal to 0.50 percent, Mo: less than or equal to 0.50 percent, Ni: less than or equal to 0.6 percent, less than or equal to 0.5 percent of Cu, less than or equal to 0.0030 percent of B, and the balance of Fe and inevitable impurities.
Further, the thickness of the steel plate finished product is 20.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 865 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 20 min.
Further, the thickness of the finished steel plate is 56.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 870 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 30 min.
Further, the thickness of the finished steel plate is 70.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 920 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 875 ℃, the heat preservation time is 20min, the tempering temperature is 600 ℃, and the heat preservation time is 30 min.
Compared with the prior art, the invention has the beneficial technical effects that:
the steel plate produced by the method has uniform and fine structure, the grain size is about 13 grades, the microstructure is tempered sorbite, a small amount of ferrite and trace residual austenite, the steel plate has excellent low-temperature impact toughness, and all properties meet the technical requirements of users. The steel plate prepared by the method can meet the requirements of hydroelectric steel with higher strength and larger thickness, and has wide market prospect.
Drawings
The invention is further illustrated in the following description with reference to the drawings.
FIG. 1 is a comparative example impact fracture morphology;
FIG. 2 is the impact fracture morphology of example 2.
Detailed Description
The present invention is described in more detail below by way of specific comparative examples and examples. The examples are merely illustrative of the best mode of carrying out the invention and do not limit the scope of the invention in any way.
The invention aims to improve the low-temperature impact toughness of the steel plate by adding a sub-temperature quenching process on the basis of the conventional quenching and tempering (quenching and high-temperature tempering) process, so the chemical components of the steel plates of the comparative example and the embodiment of the invention are the same, and the specific formula is shown in Table 1. Meanwhile, the process route of the comparative example is basically consistent with that of the embodiment before quenching and tempering heat treatment, so that the detailed description is omitted, and only the quenching and tempering process and the sub-temperature increasing quenching process are described below.
Comparative example
The thickness of the steel plate finished product is 38.0mm, and the technological parameters of quenching and tempering heat treatment are as follows: the quenching temperature is 910 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 30 min. (mechanical properties were measured by sampling at a plate thickness of 1/4).
Example 1
The thickness of the steel plate finished product is 20.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 865 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 20 min. (sampling the full thickness of the steel plate for mechanical property detection).
Example 2
The thickness of the finished steel plate is 56.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 870 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 30 min. (mechanical properties were measured by sampling at a plate thickness of 1/4).
Example 3
The thickness of the finished product is 70.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 920 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 875 ℃, the heat preservation time is 20min, the tempering temperature is 600 ℃, and the heat preservation time is 30 min. (mechanical properties were measured by sampling at a plate thickness of 1/4).
TABLE 1 chemical composition (wt%) of comparative and example of the present invention
| C | Si | Mn | P | S | Alt | Nb | Ti | V | Cr | Mo | Ni | Cu | B |
| 0.075 | 0.25 | 1.34 | 0.008 | 0.005 | 0.045 | 0.040 | 0.019 | 0.045 | 0.45 | 0.36 | 0.50 | 0.19 | 0.0015 |
The steel sheets of the comparative example and the inventive example were subjected to mechanical property tests, and the test results are shown in table 2.
TABLE 2 mechanical Properties of comparative and examples of the invention
As can be seen from the data in Table 2, the yield strength, tensile strength, elongation and 180 ℃ cold bending performance indexes of the comparative example and the example can meet the technical requirements of users. But the impact energy at the transverse low temperature of-40 ℃ in the comparative example is lower, the standard requirement cannot be met, and the numerical stability of the impact energy is poor; the steel plate produced by the method (embodiment 1-3) has high transverse low-temperature impact energy at-40 ℃, meets the technical requirements, and has good impact energy value stability.
FIGS. 1 and 2 are respectively the appearance of the impact fracture of the steel plates of the comparative example and the example 2, and it can be seen that the impact fracture of the comparative example is in a cleavage shape, and is brittle fracture, and the impact work is low; example 2 the impact fracture is dimple-shaped, belonging to ductile fracture and having higher impact energy.
The invention aims to solve the technical problem of improving the low-temperature impact toughness and the stability of boron-containing steel, namely, adding a one-time sub-temperature quenching process on the basis of the conventional quenching and tempering (quenching and high-temperature tempering) process to improve the low-temperature impact toughness of the steel plate. The steel plate produced by the invention has excellent low-temperature impact toughness, and the transverse impact energy at minus 40 ℃ is as follows: 181J to 225J, meets the technical requirements of users, and improves the stability of the impact performance.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (5)
1. A method for improving low-temperature impact toughness of boron-containing steel by using sub-temperature quenching is characterized by comprising the following steps:
(1) firstly, carrying out desulfurization pretreatment on incoming molten iron, slagging off after desulfurization, ensuring that the molten iron is carried with slag as little as possible after desulfurization, and ensuring that the S content is less than or equal to 0.005% after pretreatment;
(2) smelting in a converter, namely adopting self-produced low-sulfur scrap steel, adding nickel plate alloy along with the scrap steel, and adopting a full-process argon blowing mode for converter bottom blowing gas to ensure that the tapping temperature is more than or equal to 1620 ℃;
(3) LF external refining and RH vacuum degassing, wherein LF refining ensures the formation time of white slag, and ferrocolumbium, ferrochromium and ferromolybdenum are added after the white slag is adjusted to target components; in the RH refining stage, molten steel is mainly degassed to promote inclusion floating, pure degassing time is ensured to be more than 5 minutes, vacuum treatment is carried out after vacuum treatment is carried out for 20 minutes, vacuum is restored to break vacuum to carry out calcium treatment, and after the calcium treatment is finished, soft blowing time is ensured to be more than or equal to 10 minutes;
(4) continuously casting the plate blank, controlling the drawing speed at 0.80-1.2 m/min, and ensuring the quality of the casting blank by adopting electromagnetic stirring and soft reduction;
(5) heating the plate blank, strictly controlling the time of the plate blank in the furnace, the soaking time and the tapping temperature, ensuring the homogenization of austenite and the full solid solution of alloy components, and simultaneously avoiding the excessive growth of crystal grains; the in-furnace time is 240-300 min, the soaking time is 30-60 min, and the out-furnace temperature is 1200 +/-20 ℃;
(6) primary dephosphorization, rolling and cooling are carried out, primary dephosphorization is carried out after the plate blank is taken out of the furnace, the high-pressure water nozzle is ensured to be normally opened without blockage, and the dephosphorization pressure is not less than 20 MPa; the rough rolling completes broadening in as few passes as possible, the relative reduction rate of at least 2 passes of a single pass is controlled to be more than 14 percent, the rough rolling ensures the rolling in a recrystallization zone, austenite crystal grains are fully refined, and the final rolling temperature is not less than 1050 ℃; the initial rolling temperature of finish rolling is not more than 950 ℃, the relative reduction rate of at least 2 passes is more than 14%, the rolling in a non-recrystallization area is ensured, organization and energy preparation is carried out for subsequent phase change, and the final rolling temperature of the finish rolling is set to be 810-850 ℃; the cooling mode adopts a second-level system self-learning calculation result, and the final cooling temperature is 630-650 ℃;
(7) the conventional quenching and tempering heat treatment process comprises the following steps: the quenching temperature is 910-920 ℃, and the heat preservation time is 20 min; tempering temperature is 600-620 ℃, and the heat preservation time is 20-40 min;
(8) adding a sub-temperature quenching heat treatment process, namely adding sub-temperature quenching in the conventional quenching, and then carrying out high-temperature tempering: the quenching temperature is 910-920 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 865-875 ℃, and the heat preservation time is 20 min; the tempering temperature is 600-620 ℃, and the heat preservation time is 20-40 min.
2. The method for improving the low-temperature impact toughness of the boron-containing steel by using the sub-temperature quenching as claimed in claim 1, wherein the chemical composition of the boron-containing steel is C: less than or equal to 0.08 percent, Si: less than or equal to 0.30 percent, Mn: less than or equal to 1.50 percent, P: not more than 0.010 percent, not more than 0.005 percent of S, Alt: 0.020-0.040%, Nb is less than or equal to 0.060%, Ti is less than or equal to 0.030%, V: less than or equal to 0.050 percent, Cr is less than or equal to 0.50 percent, Mo: less than or equal to 0.50 percent, Ni: less than or equal to 0.6 percent, less than or equal to 0.5 percent of Cu, less than or equal to 0.0030 percent of B, and the balance of Fe and inevitable impurities.
3. The method for improving the low-temperature impact toughness of the boron-containing steel by using the sub-temperature quenching as claimed in claim 1, wherein the thickness of the finished steel plate is 20.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 865 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 20 min.
4. The method for improving the low-temperature impact toughness of the boron-containing steel by using the sub-temperature quenching as claimed in claim 1, wherein the thickness of the finished steel plate is 56.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 910 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 870 ℃, the heat preservation time is 20min, the tempering temperature is 620 ℃, and the heat preservation time is 30 min.
5. The method for improving the low-temperature impact toughness of the boron-containing steel by using the sub-temperature quenching as claimed in claim 1, wherein the thickness of the finished steel plate is 70.0mm, and the heat treatment process comprises the following steps: the quenching temperature is 920 ℃, the heat preservation time is 20min, the sub-temperature quenching temperature is 875 ℃, the heat preservation time is 20min, the tempering temperature is 600 ℃, and the heat preservation time is 30 min.
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