CN113789476B - Low-temperature Hi-B steel and production method capable of enhancing inherent AlN inhibition capacity - Google Patents

Low-temperature Hi-B steel and production method capable of enhancing inherent AlN inhibition capacity Download PDF

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CN113789476B
CN113789476B CN202111083172.6A CN202111083172A CN113789476B CN 113789476 B CN113789476 B CN 113789476B CN 202111083172 A CN202111083172 A CN 202111083172A CN 113789476 B CN113789476 B CN 113789476B
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CN113789476A (en
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庞树芳
游清雷
罗理
贾志伟
张海利
张静
李莉
蒋奇武
于宁
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Angang Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • 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
    • 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
    • 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
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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
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1261—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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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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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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Abstract

The low-temperature Hi-B steel and the production method capable of enhancing the inhibition capability of the innate AlN comprise the following chemical components in percentage by weight: 0.020-0.085% of C, 2.620-3.700% of Si, 0.0010-0.080% of Mn, 0.001-0.010% of S, 0.001-0.020% of P, 0.008-0.020% of Als0.001-0.007% of N, 0.005-0.200% of Cu and the balance of Fe inevitable impurities. The invention ensures that the heating temperature of the casting blank cannot be too high through the content of inhibitor forming elements; according to the transformation rule of austenite phase content along with temperature and the transformation speed of AlN solid solution precipitation, the normalizing heating temperature and the rapid cooling temperature after normalizing air cooling are adjusted, alN is dispersed and precipitated in a large amount in a normalizing plate, and the inhibition capability of the innate AlN in the steel is enhanced.

Description

Low-temperature Hi-B steel and production method capable of enhancing inherent AlN inhibition capacity
Technical Field
The invention relates to the field of cold-rolled oriented silicon steel production, in particular to low-temperature Hi-B steel and a production method capable of enhancing the inhibition capacity of innate AlN.
Background
The oriented silicon steel is 3-percent Si-Fe soft magnetic material with {110} <001> texture, namely Goss texture, and the inhibitor inhibits normal growth of primary crystal grains in a high-temperature annealing process, so that primary crystal grains with {110} <001> orientation, namely secondary crystal nuclei, can engulf other surrounding primary crystal grains to generate abnormal growth, namely secondary recrystallization is generated, and perfect single {110} <001> texture is obtained. Because the <001> direction of the iron single crystal is an easy magnetization direction and the <111> direction is a hard magnetization direction, the oriented silicon steel is widely used for manufacturing transformer cores and stator cores of large generators, and therefore, the oriented silicon steel with a single {110} <001> texture has excellent magnetism along the rolling direction.
In recent years, in order to overcome the disadvantages of high energy consumption, more slag, low yield and the like of the traditional high-temperature slab heating technology, a low-temperature slab heating technology is developed. At present, the Hi-B steel generally adopts A1N and Cu with the solid solution temperature much lower than that of MnS in the early stage 2 S is used as an inherent inhibitor or a small amount of Sn is added as an auxiliary to improve the inhibition effect of the S and the Sn, so that the heating temperature of the plate blank is reduced to 1150-1250 ℃, and a gaseous nitriding method is adopted in the process immediately after the heating, namely the plate blank is subjected to NH before secondary recrystallization annealing 3 Nitriding under atmosphere to form nitride of (A1, si) as supplementary inhibitor to offset the defect caused by insufficient inhibition ability.
The choice of the early inhibitor technique is generally critical because it severely affects the late nitriding temperature. AlN, which is an inhibitor for the production of Hi-B steel, preferentially grows secondary grains during decarburization annealing and initiation of secondary recrystallization, and serves to "adjust" or "control" the texture of secondary recrystallization, which MnS and other inhibitor particles do not possess. Therefore, the research on the solid solution and precipitation behaviors of A1N particles in the production of oriented silicon steel, particularly Hi-B steel, has important effects on improving the strength of the oriented silicon steel and reducing the iron loss.
According to the invention, the heating temperature of the casting blank cannot be too high by designing the content of inhibitor forming elements in the Hi-B steel component; meanwhile, the solid solubility of AlN in the austenite phase is 9 times that of AlN in ferrite, so that the normalizing heating temperature and the temperature for starting rapid cooling after normalizing air cooling are adjusted according to the transformation rule of the austenite phase content along with the temperature and the transformation speed of AlN solid solution precipitation, alN is dispersed and precipitated in a large amount in a normalizing plate, and the inhibition capability of the innate AlN in the Hi-B steel is greatly enhanced.
Disclosure of Invention
The invention aims to provide a low-temperature Hi-B steel and a production method capable of enhancing the inhibition capacity of innate AlN, wherein the heating temperature of a casting blank cannot be too high by designing the content of inhibitor forming elements in the components of the Hi-B steel; according to the transformation rule of austenite phase content along with temperature and the transformation speed of AlN solid solution precipitation, the normalizing heating temperature and the temperature for starting rapid cooling after normalizing air cooling are adjusted, alN is dispersed and precipitated in a large amount in a normalizing plate, and the inhibition capability of the innate AlN in the Hi-B steel is greatly enhanced.
In order to achieve the purpose, the invention adopts the following technical scheme:
the low-temperature Hi-B steel comprises the following chemical components in percentage by weight: 0.020-0.085% of C, 2.620-3.700% of Si, 0.0010-0.080% of Mn, 0.001-0.010% of S, 0.001-0.020% of P, 0.008-0.020% of Als, 0.001-0.007% of N, 0.005-0.200% of Cu, and the balance of Fe and inevitable impurities.
Mn and S mainly form an inhibitor MnS, al and N mainly form an inhibitor AlN, and Cu is added to form an inhibitor Cu2S; controlling the contents of Mn and S to ensure that the heating temperature of the casting blank cannot be too high; the Al and N contents are controlled to make the AlN inhibitor content as large as possible.
A production method capable of enhancing the inhibition ability of innate AlN is used for producing Hi-B steel at low temperature; the method comprises the following steps:
1) The hot rolling process comprises the following steps:
combining the solid solution precipitation transition temperature of the inhibitor AlN and MnS, designing the heating temperature of the casting blank to be 1200-1250 ℃, and the heating time to be 120-140 min;
the rough rolling temperature is not specifically required, the heat preservation cover and the edge heater are used for ensuring that the rough rolling temperature is as high as possible, the first pass of rough rolling adopts rolling with the reduction rate of more than or equal to 33 percent, and the rough rolling reduction rates of other passes are evenly distributed;
the initial rolling temperature of finish rolling is 1150-1170 ℃, the finish rolling is carried out for 7 times by adopting a seven-rack four-rod continuous rolling mill, the finish rolling time is controlled within 180s, and the finish rolling temperature of the finish rolling is 970 +/-20 ℃;
2) A normalizing process:
calculated using Thermo-Calc software: variation of austenite phase content with temperature; calculating the solid solution precipitation transformation speed of the AlN phase at different temperatures, and designing a normalizing process of the hot rolled plate;
the normalizing heating temperature is the temperature corresponding to the maximum austenite phase content, the heat preservation time is 1-5 min, alN is fully dissolved in solution, and then air cooling is started;
air cooling to a certain temperature and starting quick cooling: according to the solid solution precipitation transformation speed of the AlN phase at different temperatures, the temperature corresponding to the moment that the solid solution precipitation transformation speed of the AlN phase is reduced by one order of magnitude is selected as the starting rapid cooling temperature, the AlN phase is rapidly cooled in quenching water, and the water temperature is 90-100 ℃.
If the aluminum alloy is quenched in water at the temperature of not higher than 20 ℃ immediately after normalizing and heat preservation, the dissolved AlN is still in a solid solution state, and the quantity of the fine AlN is small; air cooling is carried out all the time after the normalizing heat preservation, and coarse AlN is separated out; therefore, in order to start rapid cooling by air cooling to a certain temperature after the temperature keeping for normalization, the selection of the start rapid cooling temperature is very important for controlling the AlN size.
The adopted smelting process comprises the following steps: adopting converter smelting, RH refining, argon blowing in the whole process, and controlling the rear end point of the converter: c is less than or equal to 0.062%; p is less than or equal to 0.015 percent; s is less than or equal to 0.025 percent; mn is less than or equal to 0.035%; the alkalinity of the slag in the blowing process is 2.8-3.4; the thickness of the slag is less than or equal to 75mm; and (5) slag stopping and tapping.
The adopted continuous casting process comprises the following steps: calculating the liquidus temperature of the molten steel, pouring the molten steel when the superheat degree is less than 25 ℃, keeping a constant speed in the pouring process, and controlling the casting blank pulling speed to be 0.40-0.80 m/min; electromagnetic stirring is added in the continuous casting process, and the casting blank is hot-fed after continuous casting.
The thickness of the continuous casting billet is 180-230 mm.
The thickness of the intermediate blank is 48 +/-4 mm.
The target thickness of the hot rolled plate after finish rolling is 2.00-2.50 mm
Compared with the prior art, the invention has the beneficial effects that:
1) The heating temperature of the casting blank is ensured to be lower than 1250 ℃ by designing the content of inhibitor forming elements in the Hi-B steel components, so that the energy is greatly saved;
2) According to the transformation rule of the austenite phase content along with the temperature, the heating temperature of the normalizing process is designed, so that AlN can be fully dissolved in a solid solution;
3) Designing the cooling temperature after the normalizing heating and heat preservation according to the solid solution precipitation transformation speed of the AlN at different temperatures, so that the AlN is precipitated in a large amount before growing;
4) The invention adopts a method of combining component design and normalizing process design, doubly enhances the inhibition capability of the innate AlN in the Hi-B steel, improves the yield of the Hi-B steel and has obvious economic benefit.
Drawings
FIG. 1 is a graph of the austenite phase content versus temperature for example 1;
FIG. 2 is the solid-solution precipitation transition rates of the AlN phase of example 1 at different temperatures;
FIG. 3 is a graph of the austenite phase content as a function of temperature for example 2;
FIG. 4 is the solid-solution precipitation transition rate of the AlN phase of example 2 at different temperatures;
FIG. 5 is a graph of the austenite phase content as a function of temperature for example 3;
FIG. 6 shows the solid-solution precipitation transition rates of the AlN phase of example 3 at different temperatures.
Detailed Description
The following examples are intended to illustrate the invention in detail, and are intended to be a general description of the invention, and not to limit the invention.
Example 1:
the steel grade comprises the following components: the element contents of the Hi-B steel are designed as follows: 0.052 percent of C, 3.10 percent of Si, 0.060 percent of Mn, 0.006 percent of S, 0.011 percent of P, 0.018 percent of Als, 0.005 percent of N, 0.150 percent of Cu, and the balance of Fe and impurities.
The preparation method comprises the following steps:
1) Smelting: smelting by adopting a converter, RH refining, argon blowing in the whole process, and controlling the rear end point of the converter: 0.042% by weight of C;0.010P%;0.022% S;0.035% Mn; the alkalinity of the slag in the blowing process is 3.0; the slag thickness is 55mm; and (5) stopping slag when tapping is finished.
2) Continuous casting: calculating the liquidus temperature of the molten steel to be 1490 ℃, selecting the superheat degree of the molten steel to be 20 ℃, pouring the molten steel at 1510 ℃, keeping the constant speed in the pouring process, and controlling the casting blank pulling speed to be 0.60m/min; electromagnetic stirring is put into the continuous casting process, a casting blank is hot-fed after continuous casting, and the thickness of the continuous casting blank is 210mm.
3) Hot rolling:
the calculated solid solution precipitation transition temperatures of the AlN and MnS inhibitors are 1220 ℃ and 1189 ℃, the heating temperature of the designed casting blank is 1230 ℃, and the heating time is 120min.
The rough rolling temperature is not specifically required, the rough rolling temperature is ensured to be as high as possible by using a heat preservation cover and an edge heater, the first pass of rough rolling adopts high-speed rolling with the reduction rate of 40%, the rough rolling reduction rates of 2 nd, 3 rd and 4 th passes are uniformly distributed with the reduction rate of 28%, and the thickness of a rough rolling blank is 47mm.
The initial rolling temperature of the finish rolling is 1160 ℃, the finish rolling is carried out for 7 times by adopting a seven-rack four-rod continuous rolling mill, the finish rolling time is controlled to be 170s, the final rolling temperature is 985 ℃, and the target thickness of the hot rolled plate is 2.30mm.
4) A normalizing process:
the variation of the austenite phase content with the temperature is calculated as shown in fig. 1, and from fig. 1, the temperature corresponding to the maximum austenite phase content is 1160 ℃; the solid solution precipitation transition rates of the AlN phase at different temperatures are shown in FIG. 2, and it is understood from FIG. 2 that the AlN phase has the highest rate at the time of precipitation, and the solid solution precipitation rate decreases with a decrease in temperature. The AlN solid solution precipitation transformation speed is selected to be 10 -7 Down to 10 -8 Namely, the temperature 923-928 ℃ corresponding to one order of magnitude of reduction is used as the temperature for starting rapid cooling after the normalizing heat preservation.
Selecting the temperature 1160 ℃ corresponding to the maximum austenite phase content as the normalizing heating temperature, keeping the temperature for 3min to fully dissolve AlN, and then starting air cooling.
The temperature 923-928 ℃ corresponding to the reduction of the AlN solid solution precipitation transition speed by one order of magnitude is selected as the temperature for starting the quick cooling after the air cooling process is finished, and the quick cooling mode is quenching into 100 ℃ water.
Finally, cold rolling and subsequent processes are carried out to prepare a finished product.
Example 2:
the steel grade comprises the following components: the element content of the Hi-B steel is designed as follows: 0.065% of C, 3.19% of Si, 0.074% of Mn, 0.005% of S, 0.008% of P, 0.016% of Als, 0.006% of N, 0.100% of Cu and the balance of Fe and impurities.
The preparation method comprises the following steps:
1) Smelting: adopting converter smelting, RH refining, argon blowing in the whole process, and controlling the rear end point of the converter: 0.046% by weight of C;0.008P%; 0.021%; 0.040% of Mn; the alkalinity of slag in the converting process is 3.0; the slag thickness is 55mm; and (5) stopping slag when tapping is finished.
2) Continuous casting: calculating the liquidus temperature of the molten steel to be 1488 ℃, selecting the superheat degree of the molten steel to be 20 ℃, pouring the molten steel at 1508 ℃, keeping a constant speed in the pouring process, and controlling the casting blank pulling speed to be 0.60m/min; electromagnetic stirring is put into the continuous casting process, a casting blank is hot-fed after continuous casting, and the thickness of the continuous casting blank is 210mm.
3) Hot rolling:
the solid solution precipitation transition temperatures of the AlN and MnS inhibitors are respectively 1226 ℃ and 1192 ℃ and are calculated, the temperature for fully dissolving the AlN and MnS inhibitors is selected as the heating temperature of the casting blank within the temperature range of 1200-1250 ℃, 1246 ℃ and the heating time is 120min.
The rough rolling temperature is not specifically required, the rough rolling temperature is ensured to be as high as possible by using a heat preservation cover and an edge heater, the first pass of rough rolling adopts high-speed rolling with the reduction rate of 40%, the rough rolling reduction rates of 2 nd, 3 rd and 4 th passes are uniformly distributed with the reduction rate of 28%, and the thickness of a rough rolling blank is 47mm.
The initial rolling temperature of finish rolling is 1170 ℃, the finish rolling is carried out for 7 times by adopting a seven-rack four-rod continuous rolling mill, the finish rolling time is controlled to be 170s, the final rolling temperature is 995 ℃, and the target thickness of the hot rolled plate is 2.30mm.
4) A normalizing process:
the calculated change of the austenite phase content with temperature is shown in FIG. 3, it can be known from FIG. 3 that the temperature corresponding to the maximum austenite phase content is 1167 deg.C, the solid solution precipitation transformation speed of AlN phase at different temperatures is shown in FIG. 4, it can be known from FIG. 4 that the AlN phase has the maximum speed at the beginning of precipitation, and the solid solution precipitation transformation speed is reduced with temperatureThe precipitation rate decreases. The AlN solid solution precipitation transition rate is selected to be 10 -7 Down to 10 -8 Namely, the temperature 894-898 ℃ corresponding to one order of magnitude of reduction is used as the temperature for starting rapid cooling.
Selecting the temperature 1167 ℃ corresponding to the maximum austenite phase content as the normalizing heating temperature, keeping the temperature for 3min to fully dissolve AlN, and then starting air cooling.
The temperature 894-898 ℃ corresponding to the reduction of the AlN solid solution precipitation transformation speed by one order of magnitude is selected as the temperature for starting the quick cooling after the air cooling process is finished, and the quick cooling mode is that the quick cooling is carried out by quenching into 100 ℃ water.
Finally, cold rolling and subsequent processes are carried out to prepare a finished product.
Example 3:
the steel comprises the following components: the element contents of the Hi-B steel are designed as follows: 0.054% of C, 3.3% of Si, 0.065% of Mn, 0.006% of S, 0.015% of P, 0.017% of Als, 0.0040% of N, 0.130% of Cu and the balance of Fe and impurities.
The preparation method comprises the following steps:
1) Smelting: smelting by adopting a converter, RH refining, argon blowing in the whole process, and controlling the rear end point of the converter: 0.052% of C;0.013 percent of P; 0.022% S;0.037% Mn; the alkalinity of slag in the converting process is 3.0; the thickness of the slag is 55mm; and (5) stopping slag when tapping is finished.
2) Continuous casting: calculating the liquidus temperature of the molten steel to be 1487 ℃, selecting the superheat degree of the molten steel to be 20 ℃, pouring the molten steel at the temperature of 1507 ℃, keeping a constant speed in the pouring process, and controlling the casting blank pulling speed to be 0.60m/min; electromagnetic stirring is put into the continuous casting process, a casting blank is subjected to hot delivery after continuous casting, and the thickness of the continuous casting blank is 210mm.
3) Hot rolling:
the solid solution precipitation transition temperatures of the inhibitors AlN and MnS are respectively 1204 ℃ and 1195 ℃ and are calculated, the temperature for fully dissolving the inhibitors AlN and MnS is selected as the heating temperature of the casting blank within the temperature range of 1200-1250 ℃, 1234 ℃ is selected, and the heating time is 120min.
The rough rolling temperature is not specifically required, the rough rolling temperature is ensured to be as high as possible by using a heat preservation cover and an edge heater, the first pass of rough rolling adopts high-speed rolling with the reduction rate of 40%, the rough rolling reduction rates of 2 nd, 3 rd and 4 th passes are uniformly distributed with the reduction rate of 28%, and the thickness of a rough rolling blank is 47mm.
The initial rolling temperature of finish rolling is 1150 ℃, the finish rolling is carried out for 7 times by adopting a seven-frame four-rod continuous rolling mill, the finish rolling time is controlled to be 170s, the final rolling temperature is 975 ℃, and the target thickness of a hot rolled plate is 2.30mm.
4) A normalizing process:
the temperature-dependent change of the austenite phase content was calculated as shown in FIG. 5, and it is understood from FIG. 5 that the temperature corresponding to the maximum austenite phase content was 1148 ℃ and the solid solution precipitation transition rate of the AlN phase at different temperatures is shown in FIG. 6, and it is understood from FIG. 6 that the AlN phase has the maximum speed at the start of precipitation and the solid solution precipitation rate decreases as the temperature decreases. The AlN solid solution precipitation transition rate is selected to be 10 -7 Down to 10 -8 Namely, when the temperature is reduced by one order of magnitude, the corresponding temperature 933-937 ℃ is taken as the temperature for starting quick cooling.
Selecting the temperature 1148 ℃ corresponding to the maximum austenite phase content as the normalizing heating temperature, keeping the temperature for 3min to fully dissolve AlN, and then starting air cooling.
And selecting the temperature of 933-937 ℃ corresponding to the reduction of the AlN solid solution precipitation transition speed by one order of magnitude as the temperature for starting quick cooling after the air cooling process is finished, wherein the quick cooling mode is to quench into 100 ℃ water.
Finally, cold rolling and subsequent processes are carried out to prepare a finished product.
The examples summarize:
in order to clarify the amount and size distribution of AlN precipitates in the normalized plate, the precipitates were collected by taking photographs continuously by the extraction replica method, and the results of counting the size and distribution of AlN in combination with EDS analysis are shown in table 1. It can be seen that the precipitates AlN each had an average size of 50nm or less, functioned well as an inhibitor, and were present in a sufficient number.
Table 1 examples the amount and size of AlN in the normalized plates
Example number Example 1 Example 2 Example 3
Heating temperature of 1240 1246 1234
Normalizing temperature of low DEG C 1160 1167 1148
Onset of Rapid Cooling temperature,. Degree.C 923～928 894～898 933～937
AlN average size, nm 36.17 34.15 36.91
AlN areal density, units/mm 2 5.52 7.83 5.56
。

Claims (6)

1. The low-temperature Hi-B steel is characterized by comprising the following chemical components in percentage by weight: 0.020-0.085% of C, 2.620-3.700% of Si, 0.0010-0.074% of Mn, 0.001-0.010% of S, 0.001-0.020% of P, 0.008-0.020% of Als, 0.001-0.006% of N, 0.005-0.200% of Cu, and the balance of Fe and inevitable impurities;
a production method of low-temperature Hi-B steel can enhance the inhibition capability of innate AlN, and comprises the processes of smelting, continuous casting, hot rolling and normalizing, wherein:
1) The hot rolling process comprises the following steps:
the heating temperature of the casting blank is 1230-1250 ℃, and the heating time is 120-140 min;
the first rough rolling pass is rolled by adopting a reduction rate of more than or equal to 33 percent, and the rough rolling reduction rates of other passes are distributed evenly;
the initial rolling temperature of finish rolling is 1150-1170 ℃, the finish rolling time is controlled within 180s, and the finish rolling temperature of finish rolling is 970 +/-20 ℃;
2) A normalizing process:
calculating the change of the austenite phase content with the temperature; calculating the solid solution precipitation transformation speed of the AlN phase at different temperatures, and designing a normalizing process of the hot rolled plate;
the normalizing heating temperature is the temperature corresponding to the maximum austenite phase content, the heat preservation time is 1-5 min, and then air cooling is started;
air cooling to a certain temperature and starting rapid cooling: according to the solid solution precipitation transformation speed of the AlN phase at different temperatures, the temperature corresponding to the moment that the solid solution precipitation transformation speed of the AlN phase is reduced by one order of magnitude is selected as the starting rapid cooling temperature, the AlN phase is rapidly cooled in quenching water, and the water temperature is 90-100 ℃.
2. The low-temperature Hi-B steel as claimed in claim 1, wherein the adopted smelting process is as follows: smelting by adopting a converter, RH refining, argon blowing in the whole process, and controlling the rear end point of the converter: c is less than or equal to 0.062 percent; p is less than or equal to 0.015 percent; s is less than or equal to 0.025 percent; mn is less than or equal to 0.035%; the alkalinity of the slag in the converting process is 2.8-3.4; the slag thickness is less than or equal to 75mm; and (5) slag stopping and tapping.
3. A low temperature Hi-B steel according to claim 1, characterised in that the continuous casting process used is: the molten steel is poured when the superheat degree is less than 25 ℃, and the casting blank pulling speed is controlled to be 0.40-0.80 m/min.
4. A low temperature Hi-B steel according to claim 3 wherein the slab thickness is 180 to 230mm.
5. A low temperature Hi-B steel according to claim 1, characterised in that the thickness of the intermediate blank is 48 ± 4mm.
6. The low-temperature Hi-B steel according to claim 1, wherein the target thickness of the hot-rolled sheet after the finish rolling in the step 1) is 2.00 to 2.50mm.
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