CN111705266B - 300 MPa-grade hot-rolled smooth round refractory steel bar and manufacturing method thereof - Google Patents
300 MPa-grade hot-rolled smooth round refractory steel bar and manufacturing method thereof Download PDFInfo
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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
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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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/065—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires 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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
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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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- C—CHEMISTRY; METALLURGY
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- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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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
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
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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
- C21D2211/002—Bainite
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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
- C21D2211/005—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
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention provides a 300 MPa-grade hot rolled plain round refractory steel bar and a manufacturing method thereof, wherein the hot rolled plain round refractory steel bar comprises the following chemical components in percentage by weight: c: 0.16% -0.22%, Si: 0.20-0.50%, Mn: 0.30% -0.60%, P: less than or equal to 0.03%, S: less than or equal to 0.03 percent, Cr: less than or equal to 0.35 percent, Mo: 0.20 to 0.40 percent of the total weight of the alloy, and the balance of Fe and inevitable residual elements; the specific manufacturing method comprises the following steps: smelting molten steel, continuous casting, heating continuous casting billets and rolling reinforcing steel bars. The method produces the high-strength steel bar with fire resistance, the yield strength of which is not lower than the room-temperature yield strength 2/3 at 600 ℃ through component optimization design and optimization of steel making, refining, continuous casting and steel rolling processes.
Description
Technical Field
The invention belongs to the technical field of steel preparation, and particularly relates to a 300 MPa-grade hot rolled plain round refractory steel bar and a manufacturing method thereof.
Background
At present, the development of super high-rise buildings in China starts from 1990, 1990-2007 is the starting period of the super high-rise buildings, 2008-2012 is the rapid development period of the super high-rise buildings, and 2013-2018 is the prosperity period of the super high-rise buildings. Based on the height, the super high-rise building is divided into the following 4 sections: 250 to 300m, 300 to 400m, 400 to 500m and more than 500 m. Before 2012, 94 super high-rise buildings are built in China, and the number of the super high-rise buildings of 250-300 m is the largest and accounts for about 59% of the total number of the buildings; only one super high-rise building with the height of more than 500m is built; the number of the super high-rise buildings in hong Kong and Australia is 18 in total, and the total number of the super high-rise buildings is about 20%. In 2013-2018, the number of super high-rise buildings with the height of more than 250m built in China is 164 in total, and the number of the super high-rise buildings with the height of 300-400 m is increased remarkably and accounts for about 43% of the total number. The number of the super high-rise buildings in hong Kong and Australia is 2, and the total number of the super high-rise buildings is about 1.2%. The total number of the super high-rise buildings above 250m is 258. Foreign high-rise and super high-rise buildings mainly have pure steel structures, and China mostly has steel-concrete mixed structures. The steel-concrete hybrid structure has been greatly developed because it can effectively combine steel and concrete members, and has the technical advantages of a steel structure and the characteristic of relatively low cost of concrete construction. High-rise and super high-rise buildings have a series of advantages, but once a fire occurs, the consequences of the high-rise and super high-rise buildings are catastrophic. Therefore, fire protection problems in high-rise and super high-rise buildings have attracted much attention. When the temperature of the common construction steel is increased to be more than 350 ℃, the yield strength is reduced to 2/3 of the room-temperature strength or even lower; when the temperature reaches 600 ℃, the yield strength is obviously reduced, and is only about 1/3 of the yield strength at room temperature; when the temperature is increased to about 700 ℃, the yield strength is reduced by about 50MPa, and the fire resistance of the building can not be met.
The hot-rolled smooth steel bar is mainly used for a reinforced concrete structure, is used as a stirrup, a wall reinforcement, a floor reinforcement and secondary deep processing, and has the diameter specification of phi 6-phi 22mm and the strength level of 300 MPa. Aiming at the reinforced concrete structure of high-rise and super high-rise buildings, the problem of the fire resistance of the steel bar for the main reinforcement is solved, and the problem of the fire resistance of the hot rolled smooth steel bar which is also used for the stirrup, particularly used as a floor slab reinforcement is also solved. Therefore, the hot rolled plain round refractory steel bar is also required to have a fire resistance performance under a high temperature condition of 600 ℃ in which the high temperature yield strength is maintained at or above 2/3 of the room temperature strength. Because hot rolled plain steel bar mainly supplies in order to coil, its mode of production is different with straight bar reinforcing bar, and hot rolled plain steel bar intensity level is mainly 300MPa in addition, and hot rolled plain steel bar all is blank at home and abroad at present, therefore development hot rolled plain steel bar production technology is very necessary.
The development of hot rolled smooth round refractory steel bars needs to solve the following aspects: 1) room temperature mechanical properties of hot rolled polished round refractory reinforcing steel bars; 2) the yield strength of the hot rolled smooth round refractory steel bar is not lower than the room temperature yield strength 2/3 at 600 ℃; 3) the processing performance is good; 4) the welding material has certain weldability, and the mechanical property of the welding point is equivalent to that of a base material; 5) the requirement on the air-cooled wire controlled cooling condition is high, and the performance index fluctuation between the heads and the tails of the same batch and between different batches of steel is small; 6) the manufacturing cost is relatively low.
Because elements such as Cr, Mo and the like of the refractory steel bars have stronger hardenability, the cooling rate after rolling brings very adverse effect on the plastic index of the steel bars, and therefore, the production process of the hot rolled smooth round refractory steel bars can not be carried out by referring to common steel bars.
Disclosure of Invention
The invention provides a manufacturing method of a 300 MPa-grade hot rolled plain round refractory steel bar in view of the blank problem of the prior domestic hot rolled plain round refractory steel bar production process, and the method is used for producing the high-strength steel bar with the fire resistance of which the yield strength is not lower than 2/3 at room temperature at 600 ℃ through component optimization design and optimization of steel making, refining, continuous casting and steel rolling processes.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a 300 MPa-grade hot rolled plain round refractory steel bar which comprises the following chemical components in percentage by weight: c: 0.16% -0.22%, Si: 0.20-0.50%, Mn: 0.30% -0.60%, P: less than or equal to 0.03%, S: less than or equal to 0.03 percent, Cr: less than or equal to 0.35 percent, Mo: 0.20 to 0.40 percent, and the balance of Fe and inevitable residual elements.
The 300 MPa-grade hot-rolled smooth round refractory steel bar comprises the following chemical components in percentage by weight: c: 0.2%, Si: 0.40%, Mn: 0.50%, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, Cr: less than or equal to 0.35 percent, Mo: 0.30%, the balance being Fe and unavoidable residual elements.
The invention also provides a manufacturing method of the 300 MPa-grade hot rolled plain round refractory steel bar, which comprises the following steps:
s1 molten steel smelting
Smelting molten iron and/or scrap steel materials by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1670 to 1680 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and steel is tapped; during tapping, adding Si iron, Mn iron, Si-Mn alloy, Cr iron and Mo iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon through LF, adding alloy bulk materials to adjust the contents of C, Si and Mn elements in the molten steel;
or smelting the molten iron and/or the scrap steel material by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1640-1655 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and tapping is carried out; during tapping, adding Si iron, Mn iron, Si-Mn alloy and Cr iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon by LF, and adding Mo iron alloy and other alloy bulk materials to adjust the contents of C, Si and Mn elements in molten steel;
s2 continuous casting
The LF refined qualified molten steel is continuously cast in a whole-process protection mode, the temperature of a tundish is 1515-1535 ℃, the drawing speed is 2.0-2.6 m/s, D-type inclusions in the produced continuous casting square billet steel are less than or equal to 2.0 grade, and Ds-type inclusions are less than or equal to 2.0 grade; the loosening and cracking grade is less than or equal to 1.5 grade, and the macroscopic defect meets the requirement of a qualified continuous casting billet;
s3 continuous casting billet heating
The continuous casting billet is hot-charged at the temperature of 1100-1140 ℃ in a heating soaking section of a steel rolling heating furnace, and the heating time is 60-90 min; or the continuous casting billet is cold-packed at the temperature of 1120-1160 ℃ in the heating soaking section of the steel rolling heating furnace, and the heating time is cold-packed for 80-110 min;
s4 Rolling reinforcing bar
And continuously rolling the heated continuous casting blank, controlling the initial rolling temperature to be 980-1020 ℃, obtaining the rolled steel bar according to the dimension specification of the wire rod and the final rolling temperature to be 960-1000 ℃, and blowing and cooling the rolled steel bar in the air by a fan to obtain the 300 MPa-grade hot rolled plain round refractory steel bar.
According to the manufacturing method of the 300 MPa-level hot rolled polished round refractory steel bar, the 300 MPa-level hot rolled polished round refractory steel bar prepared by the method has the mechanical properties of yield strength of 320-380 MPa at room temperature, tensile strength of 500-580 MPa, elongation after fracture of more than or equal to 25 percent and maximum total elongation of more than or equal to 10 percent; the structure is ferrite F, pearlite P and a small amount of bainite B, and the grain size is as follows: 8.5-10.5 grades.
According to the manufacturing method of the 300 MPa-grade hot rolled polished round refractory steel bar, the 300 MPa-grade hot rolled polished round refractory steel bar prepared by the method has the mechanical property yield strength of 210 MPa-300 MPa at 600 ℃, the tensile strength of 310 MPa-4000 MPa and the elongation after fracture of more than or equal to 30 percent, and meets the requirement that the thermal mechanical property yield strength of the hot rolled polished round refractory steel bar is more than or equal to 200MPa at 600 ℃.
Compared with the prior art, the invention has the following beneficial effects:
1. because the hot rolled smooth round refractory steel bars used in the method have few strength levels, mainly have the room temperature yield strength of 300MPa, and adopt low-Si and low-Mn components; since Mo and Cr are the most effective alloy elements for improving the high-temperature strength of steel, but the price is high, the components should be optimized as much as possible to reduce the cost. Aiming at the precipitation strengthening effect of the Mo element, the precipitates mainly comprise MoC and Mo2C, Mo2C is relatively coarse in steel and has small effect on the strength of the steel, and fine MoC obviously contributes to the high-temperature strength of the steel. Cr can effectively improve the high-temperature oxidation resistance and creep resistance of the steel and can effectively improve the high-temperature strength of the steel. However, elements such as Cr, Mo and the like have stronger hardenability and have adverse effect on plasticity indexes, so the requirement on controlled cooling after rolling is higher.
2. According to the invention, the process routes of converter smelting, LF furnace refining, square billet continuous casting and high-speed wire rolling are selected, and the LF furnace refining plays a role in fine adjustment of components, reduction of inclusion content and improvement of purity of steel, so that the high-strength steel bar with the fire resistance of which the yield strength is not lower than room-temperature yield strength 2/3 at 600 ℃ is produced.
Detailed Description
The technical solution of the present invention is further illustrated by the following examples, but the scope of the present invention is not limited thereto.
Example (b):
the invention provides a 300 MPa-grade hot rolled plain round refractory steel bar which comprises the following chemical components in percentage by weight: c: 0.16% -0.22%, Si: 0.20-0.50%, Mn: 0.30% -0.60%, P: less than or equal to 0.03%, S: less than or equal to 0.03 percent, Cr: less than or equal to 0.35 percent, Mo: 0.20 to 0.40 percent, and the balance of Fe and inevitable residual elements.
The manufacturing method of the 300 MPa-grade hot rolled smooth round refractory steel bar comprises the following steps:
s1 molten steel smelting
Smelting molten iron and/or scrap steel materials by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1670 to 1680 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and steel is tapped; during tapping, adding Si iron, Mn iron, Si-Mn alloy, Cr iron and Mo iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon through LF, adding alloy bulk materials to adjust the contents of C, Si and Mn elements in the molten steel;
or smelting the molten iron and/or the scrap steel material by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1640-1655 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and tapping is carried out; during tapping, adding Si iron, Mn iron, Si-Mn alloy and Cr iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon by LF, and adding Mo iron alloy and other alloy bulk materials to adjust the contents of C, Si and Mn elements in molten steel;
1) the blast furnace molten iron is required to satisfy the conditions of table 1.
TABLE 1 molten iron conditions
Iron alloy: adding alloy of silicomanganese, ferrosilicon, silicoaluminoferrite, ferromolybdenum, ferrochromium and the like, and requiring clean and dry materials.
Deoxidizing agent: Si-Al-Ba, Si-Ca-Ba, etc.
Lime: CaO is more than or equal to 88 percent.
2) Converter charging and converting
The total charge amount is controlled to be +/-2 tons of furnace volume, the scrap steel ratio is controlled to be below 35 percent, and otherwise, the information is informed to the furnace length of the converter to adjust the cold ball addition amount. Adopts PLC automatic control mode bottom blowing control and variable pressure variable lance position operation oxygen supply.
A slagging system: the lime addition in the converting process is calculated according to the following formula:
lime addition 2.14 × [ Si ] molten iron × basicity × molten iron charge/(CaO lime-basicity × SiO2 lime)
The addition amount and the final composition of the lime in the last furnace can be properly adjusted.
The converter requires accurate control of end point carbon, avoids molten steel peroxidation, and strictly controls the post blowing frequency not more than 2 times.
End point components: c is less than or equal to 0.06 percent, P is less than or equal to 0.020 percent, S is less than or equal to 0.025 percent, and if the end point carbon content does not meet the control requirement, point blowing treatment is carried out; and if the content of the end point P, S does not meet the control requirement, adding lime for point blowing treatment.
End point temperature: the end point temperature is controlled to be more than 1650 ℃, otherwise, the point blowing treatment is carried out.
The final slag components: the final slag alkalinity R is more than or equal to 3.0, MgO is 6-10%, and TFe is less than or equal to 20%.
3) Tapping from converter
Tapping temperature: 1670 to 1680 ℃;
slag stopping and tapping are needed during tapping, and the slag thickness is controlled to be less than or equal to 50 mm;
and opening the bottom for blowing before tapping, and controlling the blowing diameter of the ladle to be 300-500 mm.
The deoxidizer is added manually before 1/4 steel tapping, other alloys are added when 1/4 steel tapping, and the deoxidizer is added when 3/4 steel tapping so as to perform deoxidation alloying. The converter determines the alloy adding amount according to the molten steel amount, the molten steel oxidability, the alloy components and other conditions.
1/3 silico-alumino-ferrite was added when the amount of molten steel in the ladle was 1/10, and alloys were added in the order of "silicon carbide → silico-manganese → carburant → ferrosilicon → 2/3 silico-alumino-ferrite → ferrochrome → ferromolybdenum → fluorite → lime" when the amount of molten steel in the ladle was 1/4. And if the addition process of the alloy or the top slag is abnormal, informing the refining furnace of the abnormal information.
The addition amount of the deoxidizer is determined according to the end point oxidability, and the addition amount of the recarburizing agent is determined according to the tapping carbon content.
The alloy addition is calculated according to the following formula:
alloy addition (kg) ═ molten steel residual component (middle limit of component control in refining furnace)/(alloy grade x alloy absorption) x tap quantity (t)
4) Argon blowing station control
Pre-argon temperature control references are as follows: a first furnace 1630-1650 ℃, a continuous casting furnace: 1600 ℃ to 1620 ℃.
Argon blowing time control: the argon blowing time is not less than 5 minutes.
If alloy is supplemented or argon blowing time is not less than 2 minutes after temperature adjustment.
Post-argon temperature control references are as follows: the first furnace 1595-1605 ℃, and the continuous casting furnace 1575-1585 ℃.
5) Refining in LF furnace
Sampling and measuring the temperature after transmitting power for 8min, wherein the power transmission time for refining the molten steel is more than 15min, and the station time of an LF furnace is more than or equal to 38 min.
Preparing alloy bulk materials, and finely adjusting the contents of [ C ], [ Si ] and [ Mn ] in the molten steel according to internal control standards.
When the LF furnace is out of the station, SiCa or SiCaBa is fed in a line which is more than or equal to 150 meters, and soft argon blowing is carried out for more than or equal to 3 minutes.
The composition of the molten steel discharged from the LF furnace is required to enter an internal control range.
The addition of the alloy is adjusted according to the requirements of internal control components, and the specific addition is according to the following formula:
and (4) determining whether to continue adjusting according to the analysis of the molten steel after each alloy addition, if the alloy addition is lower than the lower limit of the internal control requirement, continuing to adjust, and if the alloy addition is higher than the upper limit of the internal control requirement, continuing to normally process.
S2 continuous casting
The LF refined qualified molten steel is continuously cast in a whole-process protection mode, the temperature of a tundish is 1515-1535 ℃, the drawing speed is 2.0-2.6 m/s, D-type inclusions in the produced continuous casting square billet steel are less than or equal to 2.0 grade, and Ds-type inclusions are less than or equal to 2.0 grade; the loosening and cracking grade is less than or equal to 1.5 grade, and the macroscopic defect meets the requirement of a qualified continuous casting billet;
the long nozzle is used for protecting pouring and the pouring is not allowed to be opened.
The molten steel in the tundish is not exposed, so that the liquid level of the tundish is not red.
The drawing speed must be carried out according to a drawing curve, generally the drawing speed is 2.0-2.6 m/min, and the drawing speed is not frequently changed greatly.
The crystallizer covering slag is plain carbon steel covering slag and is kept dry.
The liquidus temperature of the steel grade is 1505 ℃, and the typical temperature of the tundish is less than or equal to 1535 ℃.
The surface quality of the casting blank is as YB/T2011-2014 (continuous casting square and rectangular steel blanks).
S3 continuous casting billet heating
The continuous casting billet is hot-charged at the temperature of 1100-1140 ℃ in a heating soaking section of a steel rolling heating furnace, and the heating time is 60-90 min; or the continuous casting billet is cold-packed at the temperature of 1120-1160 ℃ in the heating soaking section of the steel rolling heating furnace, and the heating time is cold-packed for 80-110 min; the heating furnace is a walking beam type side-in side-out three-section heating furnace, and the temperatures of the preheating section, the heating section and the soaking section in the hearth are all automatically controlled and adjusted by a computer.
A heating system: the soaking temperature of the steel billet is controlled to be 1100-1140 ℃ when the hot billet is charged, and the soaking temperature of the cold billet is controlled to be 1120-1160 ℃.
A heating process: heating time of hot charging blank is 60-90 min, and heating time of cold blank is as follows: 80-110 min.
S4 Rolling reinforcing bar
And continuously rolling the heated continuous casting blank, controlling the initial rolling temperature to be 980-1020 ℃, obtaining the rolled steel bar according to the dimension specification of the wire rod and the final rolling temperature to be 960-1000 ℃, and blowing and cooling the rolled steel bar in the air by a fan to obtain the 300 MPa-grade hot rolled plain round refractory steel bar.
According to the requirements of the performance of the wire rod, the initial rolling temperature, the finish rolling temperature and the finish rolling temperature are respectively set to 1050 +/-20 ℃, 980-1020 ℃ and 980-1020 ℃; controlling the spinning temperature to be 960-1000 ℃ according to different specifications, starting a fan, and turning off the rest.
The smelting composition of the hot rolled plain round refractory steel bar of HPB300FR in this example is shown in Table 2.
TABLE 2 chemical composition/% of hot rolled plain refractory steel wire rod
Through the smelting component design, the refractory steel bar smelting and steel rolling tests are carried out on site, and the site tests respectively carry out converter steelmaking and LF furnace refining. The specification of the continuous casting billet after converter steelmaking refining is 160mm multiplied by 160mm square billet. Rolling HPB300FR grade smooth round refractory steel bar wire rods with the diameter of 6mm and the diameter of 10mm, heating the steel bar wire rods at the temperature of 1120 ℃, the heating time of 90min, the initial rolling temperature of 1040 ℃, the spinning temperature of 980 ℃, and the cold-controlled linear fan is completely closed, wherein the room-temperature mechanical properties after sampling are shown in Table 3.
TABLE 3 Hot-rolled plain-round refractory steel wire rod tensile mechanical properties at room temperature
From the results in table 3, the average value of the yield strength at room temperature of the phi 6mm smooth round refractory steel wire rod is 374MPa, and the average value of the tensile strength is 569MPa, so that the HPB300FR grade requirement is met; the average value of the yield ratio is 1.52, which is much higher than the requirement of 1.25; the average elongation after fracture is 28.2 percent which is higher than the requirement and is not less than 25 percent; the average value of the total extension of the maximum force is 13.5 percent which is not less than 10 percent higher than the requirement. The average yield strength of the phi 10mm smooth round refractory steel wire rod at room temperature is 364MPa, the average tensile strength is 540MPa, and the requirements of HPB300FR grade are met; the average value of the yield ratio is 1.48, which is much higher than the requirement of 1.25; the average elongation after fracture is 29.7 percent which is higher than the requirement and is not less than 25 percent; the average value of the total extension of the maximum force is 15.8 percent which is not less than 10 percent higher than the requirement. The microstructure of the hot-rolled smooth round refractory steel bar consists of ferrite, pearlite and bainite.
The tensile mechanical property results of the hot-rolled polished round refractory steel bar wire rod at the high temperature of 600 ℃ are shown in table 4.
TABLE 4 Hot-rolled plain round refractory steel wire rod 600 deg.C high-temp. tensile mechanical property
As can be seen from Table 4, the average value of the 600 ℃ high-temperature tensile yield strength of the phi 6mm plain steel wire rod is 263MPa, and the requirement that the HPB300FR grade is greater than or equal to 200MPa is met; elongation after break averaged 38.7%. The average value of the tensile yield strength of the phi 10mm plain round steel wire rod at the high temperature of 600 ℃ is 267MPa, and the requirement that the HPB300FR grade is greater than or equal to 200MPa is met; elongation after break averaged 33.2%.
From the results of the field test HPB300FR, the room temperature performance and the high temperature performance at 600 ℃ of the hot rolled plain round refractory steel bar meet the requirements, and the components of the hot rolled plain round refractory steel bar are further optimized for products with different specifications.
Claims (5)
1. The 300 MPa-grade hot rolled polished round refractory steel bar is characterized in that the 300 MPa-grade hot rolled polished round refractory steel bar has the room-temperature mechanical property yield strength of 320 MPa-380 MPa, the tensile strength of 500 MPa-580 MPa, the elongation after fracture is more than or equal to 25 percent, and the maximum force total elongation is more than or equal to 10 percent; the structure is ferrite F, pearlite P and a small amount of bainite B, and the grain size is as follows: 8.5-10.5 grade;
the 300 MPa-level hot rolled polished round refractory steel bar has the mechanical property yield strength of 210 MPa-300 MPa at 600 ℃, the tensile strength of 310 MPa-400 MPa and the elongation after fracture of more than or equal to 30 percent, and meets the requirement that the thermal mechanical property yield strength of the hot rolled polished round refractory steel bar at 600 ℃ is more than or equal to 200 MPa; the weight percentage and chemical components are as follows:
c: 0.16% -0.22%, Si: 0.20% -0.50%, Mn: 0.30% -0.60%, P: less than or equal to 0.03%, S: less than or equal to 0.03 percent, Cr: less than or equal to 0.35 percent, Mo: 0.20-0.40%, and the balance of Fe and unavoidable residual elements.
2. The 300MPa grade hot rolled smooth round refractory steel bar according to claim 1, wherein: the weight percentage and chemical components are as follows:
c: 0.2%, Si: 0.40%, Mn: 0.50%, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, Cr: less than or equal to 0.35 percent, Mo: 0.30%, the balance being Fe and unavoidable residual elements.
3. The method for manufacturing 300MPa hot rolled round refractory steel bar according to claim 1, characterized in that it comprises the following steps:
s1 molten steel smelting
Smelting molten iron and/or scrap steel materials by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1670 to 1680 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and steel is tapped; during tapping, adding Si iron, Mn iron, Si-Mn alloy, Cr iron and Mo iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon through LF, adding alloy bulk materials to adjust the contents of C, Si and Mn elements in the molten steel;
or smelting the molten iron and/or the scrap steel material by a converter or an electric furnace to obtain molten steel; when the condition is satisfied: the temperature is 1640-1655 ℃, the mass fraction of C is less than or equal to 0.06 percent, the mass fraction of P is less than or equal to 0.02 percent, the mass fraction of sulfur is less than or equal to 0.025 percent, and tapping is carried out; during tapping, adding Si iron, Mn iron, Si-Mn alloy and Cr iron, after tapping, according to chemical components of 300 MPa-level hot rolling plain round refractory steel bars, blowing argon by LF, and adding Mo iron alloy and other alloy bulk materials to adjust the contents of C, Si and Mn elements in molten steel;
s2 continuous casting
The LF refined qualified molten steel is continuously cast in a whole-process protection mode, the temperature of a tundish is 1515-1535 ℃, the drawing speed is 2.0-2.6 m/s, D-type inclusions in the produced continuous casting square billet steel are less than or equal to 2.0 grade, and Ds-type inclusions are less than or equal to 2.0 grade; the loosening and cracking grade is less than or equal to 1.5 grade, and the macroscopic defect meets the requirement of a qualified continuous casting billet;
s3 continuous casting billet heating
The continuous casting billet is hot-charged at the temperature of 1100-1140 ℃ in a heating soaking section of a steel rolling heating furnace, and the heating time is 60-90 min; or the continuous casting billet is cold-packed at the temperature of 1120-1160 ℃ in the heating soaking section of the steel rolling heating furnace, and the heating time is cold-packed for 80-110 min;
s4 Rolling reinforcing bar
And continuously rolling the heated continuous casting blank, controlling the initial rolling temperature to be 980-1020 ℃, obtaining the rolled steel bar according to the dimension specification of the wire rod and the final rolling temperature to be 960-1000 ℃, and blowing and cooling the rolled steel bar in the air by a fan to obtain the 300 MPa-grade hot rolled plain round refractory steel bar.
4. The method for manufacturing 300 MPa-grade hot rolled smooth round refractory steel bar according to claim 3, wherein the method comprises the following steps: the 300 MPa-grade hot rolled plain round refractory steel bar prepared by the method has the mechanical properties of room temperature yield strength of 320-380 MPa, tensile strength of 500-580 MPa, elongation after fracture of more than or equal to 25 percent and maximum force total elongation of more than or equal to 10 percent; the structure is ferrite F, pearlite P and a small amount of bainite B, and the grain size is as follows: 8.5-10.5 grades.
5. The method for manufacturing 300 MPa-grade hot rolled smooth round refractory steel bar according to claim 3, wherein the method comprises the following steps: the 300 MPa-grade hot rolled polished round refractory steel bar prepared by the method has the mechanical property yield strength of 210 MPa-300 MPa at 600 ℃, the tensile strength of 310 MPa-400 MPa and the elongation after fracture of more than or equal to 30 percent, and meets the requirement that the thermal mechanical property yield strength of the hot rolled polished round refractory steel bar is more than or equal to 200MPa at 600 ℃.
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