CN115181882A - 500 MPa-grade refractory deformed steel bar and production method thereof - Google Patents

500 MPa-grade refractory deformed steel bar and production method thereof Download PDF

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CN115181882A
CN115181882A CN202211102114.8A CN202211102114A CN115181882A CN 115181882 A CN115181882 A CN 115181882A CN 202211102114 A CN202211102114 A CN 202211102114A CN 115181882 A CN115181882 A CN 115181882A
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steel bar
percent
deformed steel
equal
temperature
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CN115181882B (en
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周云
杨晓伟
陈焕德
张宇
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Jiangsu Shagang Group Co Ltd
Jiangsu Shagang Iron and Steel Research Institute Co Ltd
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Jiangsu Shagang Group Co Ltd
Jiangsu Shagang Iron and Steel Research Institute 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
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • 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
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • 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
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • 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
    • 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
    • C21D2211/008—Martensite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention provides 500 MPa-level fireproof deformed steel bar and a production method thereof, and relates to the technical field of alloys, wherein in the aspect of component design, the deformed steel bar is alloyed by C, cr, mo, nb, V, N and W, wherein the content of Mo is 0.10 to 0.24 percent, mo/(5N + C) is limited to 1.1 to 2.0, the influence of each element on normal temperature performance and high temperature performance is comprehensively considered, and the deformed steel bar is ensured to have excellent high temperature resistance and lower yield ratio under the condition of lower Mo component design. On the basis of component design, the deformed steel bar with the microstructure of bainite, martensite and ferrite is obtained by controlling the technological parameters of subsequent rolling treatment and cooling treatment, the normal-temperature yield strength of the steel is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75, so that the comprehensive refractory requirement of the deformed steel bar is met.

Description

500 MPa-grade refractory deformed steel bar and production method thereof
Technical Field
The invention relates to the technical field of alloys, in particular to 500 MPa-level refractory deformed steel bar and a production method thereof.
Background
With the increase of high-rise, large-span, earthquake-resistant, low-temperature-resistant and fire-resistant building structures and the like, the performance of the reinforcing steel bar for the building becomes an important index for judging whether the building is safe and reliable or not and whether the design life can be ensured or not. In the existing deformed steel bar products with fire resistance, more Mo elements are usually added into deformed steel bars with fire resistance, the Mo price is high, the cost of the steel is difficult to control due to the addition of more Mo, and the conventional fire-resistant deformed steel bars have high yield ratio at normal temperature and high temperature and insufficient safety performance. For example, patent CN114134413A discloses an HRB400FR refractory steel bar and a production process thereof, wherein the content of Mo is 0.30 to 0.50%, the normal-temperature yield strength of the steel bar is 420 to 505mpa, the requirement of a higher-level wire rod deformed steel bar cannot be met, the 600 ℃ yield ratio is 0.95 to 0.98, and an excessively high yield ratio is not favorable for the safety of a building at high temperature. The patent CN114032459A discloses a 400MPa hot-rolled refractory reinforcing steel bar and a manufacturing method thereof, wherein the Mo content is 0.25 to 0.45 percent, the microstructure of the reinforcing steel bar is ferrite, pearlite and a small amount of bainite, the strength of the microstructure is lower, the difference between the strength of soft-phase ferrite and the strength of hard-phase pearlite is small, the yield ratio is higher, the normal-temperature yield strength of the reinforcing steel bar is 420 to 490MPa, the comprehensive performance requirement of a higher-level construction reinforcing steel bar cannot be met, the yield ratio at 600 ℃ is 0.81 to 0.82, and the yield ratio is also higher.
Disclosure of Invention
The invention aims to provide 500 MPa-grade refractory deformed steel bar and a production method thereof.
The invention provides a production method of 500 MPa-level refractory deformed steel bar, which comprises the following chemical components in percentage by mass: 0.1 to 0.15 percent of C, 0.6 to 0.8 percent of Si, 1.0 to 1.2 percent of Mn, 0.1 to 0.5 percent of Cr, 0.10 to 0.24 percent of Mo, 0.012 to 0.048 percent of Nb, 0.012 to 0.035 percent of V, 0.01 to 0.035 percent of N, 0.1 to 0.2 percent of W, and the balance of Fe and inevitable impurities;
and Mo/(5N + C) is more than or equal to 1.1 and less than or equal to 2.0, wherein the symbol of the element is the mass percent of the corresponding element;
the production method comprises the following steps:
smelting and casting according to the chemical component proportion to obtain a casting blank;
heating the casting blank until alloy elements are fully dissolved in the solid solution, and rolling the casting blank within the temperature range of an austenite non-recrystallization zone to obtain deformed steel bar;
and cooling the deformed steel bar, and controlling the cooling speed to enable the deformed steel bar to form a microstructure comprising bainite, martensite and ferrite.
As a further improvement of the present invention, the heating the casting slab until the alloying elements are sufficiently dissolved includes:
and heating the casting blank, wherein the heating temperature range is controlled to be 1200-1220 ℃, and the heat preservation time is controlled to be 50-60min.
As a further improvement of the present invention, the rolling of the cast slab in the austenite non-recrystallization region temperature range to obtain the deformed steel bar specifically comprises:
controlling the initial rolling temperature to be 1080 to 1100 ℃, and carrying out rough rolling on the casting blank through a rough rolling mill to obtain an intermediate blank;
and controlling the inlet temperature of finish rolling to be 960-1000 ℃, carrying out finish rolling on the intermediate blank by a finish rolling machine, and then sending the intermediate blank into a wire laying head to obtain the threaded steel, wherein the outlet temperature of the finish rolling is controlled to be 1060-1080 ℃, and the wire laying temperature is controlled to be 1000-1020 ℃.
As a further improvement of the present invention, the cooling treatment of the deformed steel bar and the control of the cooling speed enable the deformed steel bar to form a microstructure including bainite, martensite and ferrite, specifically includes:
uniformly distributing the deformed steel bar on a Stelmor roller way for cooling, closing a heat preservation cover at a 1~3 section of the roller way, and controlling the speed of the roller way to be 0.4-0.8m/s; opening a heat insulation cover at a 4~6 section of a roller way, opening a fan for 60 to 80 percent, and controlling the speed of the roller way to be 0.9 to 1.2m/s; starting a fan at sections 7 to 12 of a roller way for 80 to 90 percent, and controlling the speed of the roller way to be 1.3 to 1.6m/s;
and rolling and cooling to enable the deformed steel bar to form a microstructure comprising bainite, martensite and ferrite, wherein the quantity of the bainite is 70-85%, the quantity of the martensite is 5-15% and the quantity of the ferrite is 5-15% in percentage by volume.
As a further improvement of the invention, the smelting and casting according to the chemical component proportion to obtain the casting blank specifically comprises the following steps:
and sequentially carrying out a converter smelting process, an LF refining process and a continuous casting process according to the chemical component ratio to obtain the casting blank.
As a further improvement of the invention, the converter smelting process specifically comprises the following steps:
feeding the molten iron into a converter for oxygen blowing smelting, wherein the C content is controlled to be less than or equal to 0.06 percent and the P content is controlled to be less than or equal to 0.010 percent at the smelting end point, and the tapping temperature of the converter is controlled to be 1615 to 1645 ℃;
when the steel tapping amount reaches 1/4, low-carbon ferrochrome, ferromolybdenum, silicomanganese, ferrosilicon, ferroniobium and tungsten oxide are sequentially added for preliminary alloying.
As a further improvement of the present invention, the LF refining process specifically includes:
sending the molten steel smelted by the converter into an LF refining furnace, and adding 5.5-6.7 kg/t of lime and 1.6-2.4 kg/t of fluorite whitening slag;
adding ferrocolumbium and ferrovanadium core-spun yarns for alloying after refining white slag for 4min, blowing argon for 300-450L/min, sampling after heating, adding alloy adjusting components according to results, and blowing argon for 150-250L/min;
the LF tapping temperature is controlled to be 1575-1605 ℃, and the free oxygen range in the molten steel is 30-50ppm during tapping.
As a further improvement of the present invention, the continuous casting process specifically includes:
sending molten steel into a continuous casting machine for continuous casting after LF refining, controlling the temperature of a tundish of the continuous casting machine to be 1515-1555 ℃, blowing argon into a ladle long nozzle of the continuous casting machine to realize argon sealing, adopting an alkaline covering agent in the tundish of the continuous casting machine, and carrying out full-protection casting at an immersion nozzle of the continuous casting machine;
continuously casting to obtain a small square billet with the size of 140 multiplied by 140mm, wherein the continuous casting drawing speed is controlled to be 2.8-3.0 m/min, and the secondary cooling specific water amount is controlled to be 2.1-2.4L/kg.
The invention also provides 500 MPa-level fire-resistant deformed steel bar which is manufactured by adopting the production method of the 500 MPa-level fire-resistant deformed steel bar, wherein the normal-temperature yield strength of the deformed steel bar is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75.
The invention also provides 500 MPa-grade refractory deformed steel bar, which comprises the following chemical components in percentage by mass: 0.1 to 0.15 percent of C, 0.6 to 0.8 percent of Si, 1.0 to 1.2 percent of Mn, 0.1 to 0.5 percent of Cr, 0.10 to 0.24 percent of Mo, 0.012 to 0.048 percent of Nb, 0.012 to 0.035 percent of V, 0.01 to 0.035 percent of N, 0.1 to 0.2 percent of W, and the balance of Fe and inevitable impurities;
and Mo/(5N + C) is more than or equal to 1.1 and less than or equal to 2.0, wherein the symbol of the element is the mass percent of the corresponding element;
the normal-temperature yield strength of the deformed steel bar is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75.
As a further improvement of the invention, the microstructure of the deformed steel bar comprises bainite, martensite and ferrite, wherein the quantity of the bainite is 70-85%, the quantity of the martensite is 5-15%, and the quantity of the ferrite is 5-15% in percentage by volume.
The invention has the beneficial effects that: in the component design, the 500 MPa-level refractory deformed steel bar provided by the embodiment is alloyed by C, cr, mo, nb, V, N and W, mo/(5N + C) is limited to be 1.1-2.0, the influence of each element on normal temperature performance and high temperature performance is comprehensively considered, the corresponding relation of the components on high temperature strength and high temperature yield ratio is established, and the deformed steel bar is ensured to have excellent high temperature resistance and lower yield ratio under the condition of lower Mo component design. On the basis of component design, the deformed steel bar with the microstructure of bainite, martensite and ferrite is obtained by controlling the subsequent rolling treatment and cooling treatment process parameters, the normal-temperature yield strength of the steel is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, the yield ratio is less than or equal to 0.75, and the comprehensive refractory requirement of the deformed steel bar is met.
Drawings
FIG. 1 is a schematic flow chart of a production method of 500 MPa-grade refractory deformed steel bar according to an embodiment of the invention.
FIG. 2 is a schematic view of the rolling process in the production method of 500MPa grade refractory deformed steel bar according to one embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail and completely with reference to the following detailed description of the invention and the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
Compared with the existing refractory deformed steel bar, the embodiment adopts lower Mo element content, the steel still obtains higher yield strength and lower yield ratio, meets the comprehensive performance requirement of the refractory wire rod deformed steel bar, and can improve the safety level of a high-rise building structure when the refractory wire rod deformed steel bar is used as the constructional deformed steel bar.
The chemical components of the thread steel provided by the embodiment comprise the following components in percentage by mass: 0.1 to 0.15 percent of C, 0.6 to 0.8 percent of Si, 1.0 to 1.2 percent of Mn, 0.1 to 0.5 percent of Cr, 0.10 to 0.24 percent of Mo, 0.012 to 0.048 percent of Nb, 0.012 to 0.035 percent of V, 0.01 to 0.035 percent of N, 0.1 to 0.2 percent of W, and the balance of Fe and inevitable impurities.
And Mo/(5N + C) is more than or equal to 1.1 and less than or equal to 2.0, wherein the symbol of the element is the mass percent of the corresponding element.
The core idea of the design of the chemical components of the steel plate is that a proper amount of Mo, V, nb and other alloy elements capable of improving the thermal stability and the thermal strength are added on the basis of carbon steel, the Mo content in the alloy elements is controlled, the production cost of the deformed steel bar is reduced, and the deformed steel bar has higher yield strength and lower yield ratio under the high-temperature condition by matching with the subsequent process parameter regulation and control of the production process.
Specifically, the design principle of the chemical composition of the steel sheet is explained as follows:
c: c is one of important alloy elements in the steel, and the content of C can obviously influence the structure of the steel and the performance of the steel. C dissolved in the steel effectively improves the yield strength and the tensile strength of the steel, thereby directly improving the strength grade of the deformed steel bar. In addition, C can be combined with V, mo in steel to form carbonitride, which can play a good role in precipitation strengthening, thereby improving the normal-temperature strength and the high-temperature strength of a steel matrix. Therefore, the content of C has a remarkable influence on the strength of the deformed steel bar, and the lower content of C is not beneficial to improving the strength. A higher C content results in a deterioration in the plasticity, toughness and weldability of the steel. Considering the structure and performance design of the deformed steel bar comprehensively, the content of C is controlled to be 0.1-0.15% in the embodiment.
Si: si plays a role in deoxidation in steel and has a strong solid solution strengthening effect, and can be dissolved in ferrite and austenite, so that the hardness and strength of the steel are improved, the strengthening effect on the ferrite is obvious, and the yield strength of steel can be obviously improved. Meanwhile, si can inhibit the growth of cementite, thereby improving the high-temperature strength of the steel. If the amount of Si is too large, the yield ratio of the steel material is not reduced, and martensite-retained austenite islands (M-a islands) are formed in a large amount, which adversely affects the plasticity, toughness and weldability of the steel material. Considering the structural and performance design of the deformed steel bar comprehensively, the Si content is controlled to be 0.6 to 0.8 percent in the embodiment.
Mn: mn is a main strengthening element in steel, and improves hardenability of steel, thereby improving strength thereof. In addition, mn can refine the pearlite structure of the steel material, so that the Mn has a more obvious effect on tensile strength relative to yield strength, and is beneficial to reducing the yield ratio of the steel material. When the content of Mn is higher, excessive Mn can aggravate the segregation of P, sb, sn and other elements, and the Mn is combined with MnS, so that the segregation tendency of a casting blank is increased, and the low-temperature toughness and the welding performance of the core of the steel plate are deteriorated. Considering the structure and performance design of the deformed steel bar comprehensively, the Mn content is controlled to be 1.0 to 1.2 percent in the embodiment.
Mo: mo is a main strengthening element in the refractory deformed steel bar, the diffusion speed of Mo at high temperature is low, the dissolved Mo is easy to be segregated in a grain boundary, and the difference between the atomic radius of Mo and the atomic radius of Fe is large, so that strong interaction can be generated between the dissolved Mo and dislocation, the dislocation movement is hindered by high lattice friction strength, and the high-temperature yield strength and creep strength of the steel are obviously improved. Mo also has excellent precipitation strengthening effect in steel, and fine Mo (C, N) in the precipitates has outstanding contribution to high-temperature yield and tensile strength of the steel. In addition, mo can strongly suppress pearlite transformation, thereby contributing to obtaining a bainite structure with high density dislocation and outstanding high-temperature performance. However, the high-temperature yield strength is increased obviously after excessive Mo is added into the steel, so that the yield ratio is increased, and the price of Mo is very high. The Mo content is controlled to be 0.1 to 0.24 percent by comprehensively considering the structure, the performance design and the cost factors of the deformed steel bar.
Cr: cr can effectively improve the high-temperature oxidation resistance and creep resistance of the steel, and has obvious effect of improving the high-temperature strength of the steel. Meanwhile, the composite action of Cr and Mo obviously contributes to the high-temperature resistance of the steel. However, too high Cr content reduces the plasticity of the material. The structure and performance design of the deformed steel bar are comprehensively considered, and the Cr content is controlled to be 0.1 to 0.5 percent.
Nb: the Nb precipitate has good high-temperature stability, and can effectively improve the high-temperature strength of the steel. Nb has a fine-grain strengthening effect, and can realize bainite second phase strengthening by matching with process parameters, so that the steel has excellent toughness comprehensive performance, in addition, a small amount of Mo can improve the solid solubility of Nb in austenite, thereby increasing the precipitation amount of Nb (C, N) in ferrite, and Mo can form a segregation layer at the interface between Nb (C, N) and a ferrite matrix, so that the pulling and coarsening of Nb (C, N) grains are inhibited, the Nb (C, N) precipitates are more in number and smaller in size, and a better precipitation strengthening effect is achieved, therefore, nb and Mo are added in a compounding manner, and the high-temperature strength of Mo steel can be obviously improved. However, if Nb is excessively added, the toughness of the steel and the toughness of the weld heat affected zone are impaired. The structure and performance design of the deformed steel bar are comprehensively considered, and the Nb content is controlled to be 0.012 to 0.048%.
V: similar to Nb, V precipitates have good high-temperature stability, and can effectively improve the high-temperature strength of steel. The V (C, N) precipitates formed by adding V are dispersed in the steel, so that nanoscale V (C, N) compounds can be precipitated in the rolling process, the ferrite nucleation point is increased, the growth of ferrite grains is prevented, the obvious precipitation strengthening effect is achieved, the strength is improved, meanwhile, the growth of austenite grains in a welding heat affected zone can be effectively prevented, and the toughness of the steel is improved. In addition, nb and V are added in combination, and Nb can enhance the effect of strengthening VN precipitation. Excessive addition results in increased susceptibility of the steel to weld cracking. The structure and performance design of the deformed steel bar are comprehensively considered, and the content of V is controlled to be 0.012 to 0.035%.
W: w can effectively improve the high-temperature strength and the oxidation resistance of steel, and if the content is too high, the toughness and the plasticity of the steel bar are adversely affected. The structure and performance design of the deformed steel bar are comprehensively considered, and the W content is controlled to be 0.1 to 0.2 percent.
N: the excessively low content of N makes Nb, V and Mo insufficiently precipitated at normal temperature and high temperature, and influences the precipitation strengthening effect of the Nb, V and Mo. Too high content of N can be combined with part of alloy elements to form a large-size N-containing precipitated phase in steel, and the ductility and toughness are influenced. The structure and performance design of the deformed steel bar are comprehensively considered, and the content of N is controlled to be 0.01 to 0.035%.
Further, for Mo, N and C element contents, 1.1. Ltoreq. Mo/(5N + C). Ltoreq.2.0 is defined, and this coefficient is used to guide the high temperature yield strength and yield ratio, and if the ratio is higher or lower, the added Mo cannot form enough precipitates to pin the grain boundaries. Under the action of high temperature, the yield strength and the tensile strength are both obviously reduced, and the tensile strength is more obviously reduced, which is not beneficial to reducing the yield ratio. Comprehensively, the coefficient is limited to be 1.1 to 2.0.
As shown in figure 1, the production method of the 500 MPa-grade refractory deformed steel bar comprises the following steps:
s1: smelting and casting according to the chemical component proportion to obtain a casting blank.
S2: and heating the casting blank until alloy elements are fully dissolved in the solution, and rolling the casting blank within the temperature range of an austenite non-recrystallization zone to obtain the deformed steel bar.
S3: the deformed steel bar is cooled, and the cooling speed is controlled to form a microstructure comprising bainite, martensite and ferrite.
In step S1, it specifically includes: and sequentially carrying out a converter smelting process, an LF refining process and a continuous casting process according to the chemical component ratio to obtain a casting blank.
Specifically, the converter smelting process comprises the following steps:
feeding the molten iron into a converter for oxygen blowing smelting, controlling the C content at the smelting end point to be less than or equal to 0.06 percent, controlling the P content to be less than or equal to 0.010 percent, and controlling the tapping temperature of the converter to be 1615-1645 ℃.
When the steel tapping amount reaches 1/4, low-carbon ferrochrome, ferromolybdenum, silicomanganese, ferrosilicon, ferroniobium and tungsten oxide are sequentially added for preliminary alloying.
Specifically, the LF refining process includes:
and (3) sending the molten steel smelted by the converter into an LF refining furnace, and adding 5.5-6.7 kg/t of lime and 1.6-2.4 kg/t of fluorite whitening slag.
And (3) refining the white slag for 4min, adding ferroniobium and ferrovanadium cored wires for alloying, blowing argon for 300-450L/min, sampling after heating, adding alloy adjusting components according to results, and blowing argon for 150-250L/min.
The LF tapping temperature is controlled to be 1575-1605 ℃, and the free oxygen range in the molten steel is 30-50ppm during tapping. The free oxygen range in the tapping process is controlled, molten steel splashing caused by alloy addition can be reduced, and fine field control is performed.
Specifically, the continuous casting process comprises the following steps:
and after LF refining, sending the molten steel into a continuous casting machine for continuous casting, controlling the temperature of a tundish of the continuous casting machine to be 1515-1555 ℃, blowing argon into a long nozzle of a ladle of the continuous casting machine to realize argon sealing, and carrying out full-protection pouring on an immersion nozzle of the continuous casting machine by adopting an alkaline covering agent in the tundish of the continuous casting machine.
In the embodiment, a billet with the size of 140 multiplied by 140mm is obtained by continuous casting, the continuous casting drawing speed is controlled to be 2.8 to 3.0m/min, and the secondary cooling specific water amount is controlled to be 2.1 to 2.4L/kg.
Because the molten steel is added with more alloy elements such as Cr, mo and W and the like and has poorer liquidity, compared with the conventional steel production process, the tundish temperature is set to be higher, so that the molten steel has good liquidity and is convenient to cast while the uniformity of the alloy elements in the molten steel is ensured.
During the continuous casting process, the argon sealing is carried out on the ladle long nozzle, so that the molten steel can be prevented from being secondarily oxidized, and the inclusions in the steel can be reduced. The alkaline covering agent can prevent the molten steel from being secondarily oxidized and can effectively absorb and purify the inclusions. The submerged nozzle carries out full-protection pouring, and low-carbon covering slag is adopted to further isolate air, insulate heat and preserve heat, prevent secondary oxidation and absorb impurities. Through the design of the steps, the inclusion is effectively reduced, molten steel is purified, and the quality of the surface and the core of a casting blank is ensured, so that the strength performance of the deformed steel bar obtained by subsequent rolling and spinning is improved, and the defects caused by the inclusion are reduced.
In other embodiments of the invention, billets with other sizes can be obtained by continuous casting, and the continuous casting drawing speed and the secondary cooling specific water amount are correspondingly adjusted.
In step S2, it specifically includes:
s21: and heating the casting blank, wherein the heating temperature range is controlled to be 1200-1220 ℃, and the heat preservation time is controlled to be 50-60min.
S22: controlling the initial rolling temperature to be 1080-1100 ℃, and carrying out rough rolling on a casting blank by a rough rolling mill to obtain an intermediate blank; and controlling the inlet temperature of finish rolling to be 960-1000 ℃, carrying out finish rolling on the intermediate billet by a finish rolling mill, and then sending the intermediate billet into a wire laying head to obtain the threaded steel, wherein the outlet temperature of the finish rolling is controlled to be 1060-1080 ℃, and the wire laying temperature is controlled to be 1000-1020 ℃.
In step S21, the heating temperature used in the present embodiment is higher than the temperature used in conventional steel, and the use of a higher soaking temperature can ensure that the alloy elements can be fully dissolved in the solution, so that the alloy elements such as Mo, V, nb, etc. are formed in the subsequent process steps to precipitate the phase strengthening, so that the steel obtains excellent high-temperature strength. In addition, the higher soaking temperature can make the austenite grain size in the casting blank microstructure larger, thereby reducing the yield ratio of the steel.
In step S22, the start rolling temperature and finish rolling temperature used in the present embodiment are also higher than those used for conventional steel materials, thereby ensuring that the steel material is rolled in the austenite high-temperature non-recrystallization region. By rolling in the non-recrystallization zone, a finer ferrite grain structure can be obtained, so that the toughness and the strength of the steel are improved to a greater extent. Further, the rolling in the non-recrystallization region can produce deformation-induced precipitation, and the precipitation temperature of the precipitates is increased by the driving of the deformation, so that the precipitation rate is increased, the function of strengthening the precipitated phase of the alloy elements such as Mo, V, nb and the like is further ensured, and the precipitates precipitated in the non-recrystallization region can prevent the growth of grains and refine ferrite, thereby effectively improving the toughness and strength of the steel.
In step S3, it specifically includes:
uniformly distributing the deformed steel bar on a Stelmor roller way for cooling, closing a heat preservation cover at a 1~3 section of the roller way, and controlling the speed of the roller way to be 0.4-0.8m/s; opening a heat preservation cover at the stage 4~6 of the roller way, opening a fan for 60 to 80 percent, and controlling the speed of the roller way to be 0.9 to 1.2m/s; and (4) opening the fan for 80-90% in sections 7-12 of the roller way, and controlling the speed of the roller way to be 1.3-1.6 m/s.
And rolling and cooling to form a microstructure comprising bainite, martensite and ferrite, wherein the quantity of the bainite is 70-85%, the quantity of the martensite is 5-15% and the quantity of the ferrite is 5-15% in percentage by volume.
The microstructure of the deformed steel bar after rolling and cooling treatment is mainly bainite and contains a small amount of martensite and ferrite. Because alloying elements such as Mo and V are dissolved into austenite in the high-temperature heating process to delay pearlite transformation, after the pearlite transformation is inhibited, the steel mainly forms bainite and a small amount of martensite, so that the steel has higher strength, and the ferrite enables the steel to have higher toughness.
And the cooled deformed steel bar enters a coil collecting barrel at the tail end of the roller way for coil collection, is suspended and transported by utilizing a C-shaped hook, and is bundled, weighed and warehoused.
The embodiment also provides 500 MPa-grade refractory deformed steel bar which is manufactured by adopting the production method of the 500 MPa-grade refractory deformed steel bar.
The normal temperature yield strength of the deformed steel bar is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high temperature yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75.
Mo precipitated in Mo (C, N) after the deformed steel bar is stretched at a high temperature accounts for 10 to 15 percent of the total amount of Mo element.
In summary, in the component design of the 500 MPa-level refractory deformed steel bar provided in the embodiment, C, cr, mo, nb, V, N, and W are alloyed, mo/(5 + N + C) is limited to 1.1 to 2.0, and the influence of each element on the normal temperature performance and the high temperature performance is comprehensively considered, so that the corresponding relationship between the components and the high temperature strength and the high temperature yield ratio is established, and the deformed steel bar is ensured to have excellent high temperature resistance and a low yield ratio under the condition of a low Mo component design. On the basis of component design, the deformed steel bar with the microstructure of bainite, martensite and ferrite is obtained by controlling the subsequent rolling treatment and cooling treatment process parameters, the normal-temperature yield strength of the steel is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, the yield ratio is less than or equal to 0.75, and the comprehensive refractory requirement of the deformed steel bar is met.
The following further describes embodiments of the invention by means of 6 examples and 2 comparative examples.
Chemical compositions of example 1~6 and comparative examples 1 and 2 are shown in table 1, and the ratio of Mo precipitation, normal temperature properties and high temperature properties measured after sampling in example 1~6 and comparative examples 1 and 2 were produced by the above-described production method are shown in table 2. The embodiment 1~6 meets the requirements in performance, the embodiment with high yield strength at normal temperature reaches about 600MPa, and the embodiment with high yield strength at 600 ℃ reaches about 400 MPa.
Figure 922848DEST_PATH_IMAGE001
Figure 167884DEST_PATH_IMAGE002
It should be understood that although the specification describes embodiments, not every embodiment includes only a single embodiment, and such description is for clarity purposes only, and it will be appreciated by those skilled in the art that the specification as a whole may be appropriately combined to form other embodiments as will be apparent to those skilled in the art.
The above-listed detailed description is only a specific description of a possible embodiment of the present invention and is not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention are included in the scope of the present invention.

Claims (11)

1. A production method of 500 MPa-level refractory deformed steel bar is characterized by comprising the following steps:
the deformed steel bar comprises the following chemical components in percentage by mass: 0.1 to 0.15 percent of C, 0.6 to 0.8 percent of Si, 1.0 to 1.2 percent of Mn, 0.1 to 0.5 percent of Cr, 0.10 to 0.24 percent of Mo, 0.012 to 0.048 percent of Nb, 0.012 to 0.035 percent of V, 0.01 to 0.035 percent of N, 0.1 to 0.2 percent of W, and the balance of Fe and inevitable impurities;
and Mo/(5N + C) is more than or equal to 1.1 and less than or equal to 2.0, wherein the symbol of the element is the mass percent of the corresponding element;
the production method comprises the following steps:
smelting and casting according to the chemical component proportion to obtain a casting blank;
heating the casting blank until alloy elements are fully dissolved in the solid solution, and rolling the casting blank within the temperature range of an austenite non-recrystallization zone to obtain deformed steel bar;
and cooling the deformed steel bar, and controlling the cooling speed to enable the deformed steel bar to form a microstructure comprising bainite, martensite and ferrite.
2. The production method of the 500 MPa-level refractory deformed steel bar according to claim 1, wherein the heating of the casting blank until the alloying elements are sufficiently dissolved in solution specifically comprises:
and heating the casting blank, wherein the heating temperature range is controlled to be 1200-1220 ℃, and the heat preservation time is controlled to be 50-60min.
3. The production method of the 500MPa grade refractory deformed steel bar according to claim 1, wherein the rolling of the casting blank in the temperature range of the austenite non-recrystallization zone to obtain the deformed steel bar specifically comprises the following steps:
controlling the initial rolling temperature to be 1080-1100 ℃, and carrying out rough rolling on the casting blank by a rough rolling mill to obtain an intermediate blank;
and controlling the inlet temperature of finish rolling to be 960-1000 ℃, carrying out finish rolling on the intermediate blank by a finish rolling machine, and then sending the intermediate blank into a wire laying head to obtain the threaded steel, wherein the outlet temperature of the finish rolling is controlled to be 1060-1080 ℃, and the wire laying temperature is controlled to be 1000-1020 ℃.
4. The production method of the 500MPa grade fire-resistant deformed steel bar according to claim 1, wherein the cooling treatment is performed on the deformed steel bar, and the cooling speed is controlled to form the deformed steel bar into a microstructure comprising bainite, martensite and ferrite, and the method comprises the following specific steps:
uniformly distributing the deformed steel bar on a Stelmor roller way for cooling, closing a heat preservation cover at a 1~3 section of the roller way, and controlling the speed of the roller way to be 0.4-0.8m/s; opening a heat insulation cover at a 4~6 section of a roller way, opening a fan for 60 to 80 percent, and controlling the speed of the roller way to be 0.9 to 1.2m/s; starting a fan at sections 7 to 12 of a roller way for 80 to 90 percent, and controlling the speed of the roller way to be 1.3 to 1.6m/s;
and rolling and cooling to enable the deformed steel bar to form a microstructure comprising bainite, martensite and ferrite, wherein the quantity of the bainite is 70-85%, the quantity of the martensite is 5-15% and the quantity of the ferrite is 5-15% in percentage by volume.
5. The production method of the 500 MPa-level refractory deformed steel bar according to claim 4, wherein the smelting and casting according to the chemical component proportion to obtain a casting blank specifically comprises the following steps:
and sequentially carrying out a converter smelting process, an LF refining process and a continuous casting process according to the chemical component ratio to obtain the casting blank.
6. The production method of the 500 MPa-level refractory deformed steel bar according to claim 5, wherein the converter smelting process specifically comprises the following steps:
feeding the molten iron into a converter for oxygen blowing smelting, wherein the C content is controlled to be less than or equal to 0.06 percent and the P content is controlled to be less than or equal to 0.010 percent at the smelting end point, and the tapping temperature of the converter is controlled to be 1615 to 1645 ℃;
when the steel tapping amount reaches 1/4, low-carbon ferrochrome, ferromolybdenum, silicomanganese, ferrosilicon, ferroniobium and tungsten oxide are sequentially added for preliminary alloying.
7. The production method of the 500MPa grade refractory deformed steel bar according to claim 5, wherein the LF refining process specifically comprises:
sending the molten steel smelted by the converter into an LF refining furnace, and adding 5.5-6.7 kg/t of lime and 1.6-2.4 kg/t of fluorite whitening slag;
adding ferrocolumbium and ferrovanadium core-spun yarns for alloying after refining white slag for 4min, blowing argon for 300-450L/min, sampling after heating, adding alloy adjusting components according to results, and blowing argon for 150-250L/min;
the LF tapping temperature is controlled to be 1575-1605 ℃, and the free oxygen range in the molten steel is 30-50ppm during tapping.
8. The production method of the 500 MPa-grade refractory deformed steel bar according to claim 5, wherein the continuous casting process specifically comprises the following steps:
sending molten steel into a continuous casting machine for continuous casting after LF refining, controlling the temperature of a tundish of the continuous casting machine to be 1515-1555 ℃, blowing argon into a ladle long nozzle of the continuous casting machine to realize argon sealing, adopting an alkaline covering agent in the tundish of the continuous casting machine, and carrying out full-protection casting at an immersion nozzle of the continuous casting machine;
continuously casting to obtain a small square billet with the size of 140 multiplied by 140mm, wherein the continuous casting drawing speed is controlled to be 2.8-3.0 m/min, and the secondary cooling specific water amount is controlled to be 2.1-2.4L/kg.
9. The 500 MPa-level refractory deformed steel bar is characterized by being manufactured by the production method of the 500 MPa-level refractory deformed steel bar of any one of 1~8, wherein the yield strength of the deformed steel bar at normal temperature is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75.
10. The 500 MPa-grade refractory deformed steel bar is characterized by comprising the following chemical components in percentage by mass: 0.1 to 0.15 percent of C, 0.6 to 0.8 percent of Si, 1.0 to 1.2 percent of Mn, 0.1 to 0.5 percent of Cr, 0.10 to 0.24 percent of Mo, 0.012 to 0.048 percent of Nb, 0.012 to 0.035 percent of V, 0.01 to 0.035 percent of N, 0.1 to 0.2 percent of W, and the balance of Fe and inevitable impurities;
and Mo/(5N + C) is more than or equal to 1.1 and less than or equal to 2.0, wherein the symbol of the element is the mass percent of the corresponding element;
the normal-temperature yield strength of the deformed steel bar is more than or equal to 500MPa, the yield ratio is less than or equal to 0.60, the high-temperature yield strength at 600 ℃ is more than or equal to 330MPa, and the yield ratio is less than or equal to 0.75.
11. The 500 MPa-grade refractory threaded steel according to claim 10, wherein the microstructure of the threaded steel comprises 70-85% of bainite, 5-15% of martensite and 5-15% of ferrite by volume percentage.
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