CN115491591A - Low-cost Q345B steel produced by using over-RH vacuum refining furnace and production method thereof - Google Patents
Low-cost Q345B steel produced by using over-RH vacuum refining furnace and production method thereof Download PDFInfo
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Abstract
The invention discloses low-cost Q345B steel produced by using an RH vacuum refining furnace and a production method thereof, belonging to the technical field of ferrous metallurgy. The molten steel comprises the following chemical components in percentage by mass: c:0.060% to 0.080%, si: less than or equal to 0.060 percent, mn:0.40% -0.60%, P: less than or equal to 0.020%, S: less than or equal to 0.006 percent, als:0.03 to 0.06 percent, ti:0.043% -0.058%, N: less than or equal to 0.0040 percent; the balance of iron and unavoidable impurities. Aiming at the defects in the prior art, the invention aims to provide the low-cost Q345B steel produced by using the over-RH vacuum refining furnace and the production method thereof, and the over-RH process route is adopted, so that the content of N and the content of effective Ti in molten steel are stably controlled, and the stability of the hot rolling performance of the finished coil is favorably improved.
Description
Technical Field
The invention relates to the technical field of ferrous metallurgy, in particular to low-cost Q345B steel produced by an RH vacuum refining furnace and a production method thereof.
Background
The hot-rolled structural steel Q345B has the advantages of high strength, good impact toughness, light self weight, long service life and the like, and is widely applied to the fields of bridges, vehicles, ships, buildings, pressure vessels and the like. At present, two methods for producing Q345B are available in China, most steel mills adopt a C-Mn component design system to produce hot-rolled structural steel Q345B, the carbon content in the steel is 0.14% -0.17%, the steel is in the range of peritectic steel (w (C) =0.08% -0.16% in the steel), L + delta → gamma occurs in the solidification process, the volume shrinkage rate is large at the moment, and the casting blank is easy to crack; the manganese content in the steel is 1.1-1.5%, and the high manganese content easily causes MnS segregation, so that the strip structure is aggravated, and the steel is subjected to cold bending cracking.
In recent years, some steel mills produce Q345B by refining in an LF furnace and microalloying titanium, and Ti element is added into steel to combine with [ C ] and [ N ] to produce carbide, nitride and carbonitride, and the carbide, nitride and carbonitride are dissolved at high temperature and precipitated at low temperature to play roles in inhibiting grain growth (namely refining grains) and strengthening precipitation. The nitrogen content control of the LF furnace refining process is unstable, so that the performance fluctuation of the hot rolled coil is large. Therefore, a low-cost Q345B steel produced by using an RH vacuum refining furnace and a production method thereof need to be designed urgently, an RH process path is adopted, so that the N content and the effective Ti content in molten steel are stably controlled, and the stability of the hot rolling performance of a finished coil is improved.
Through retrieval, relevant patents related to the production technology of Q345B steel are disclosed, for example, a Chinese patent with the publication number of CN201610191782.0 discloses a method for producing Q345B microalloyed steel, which is applied to rolling Q345B with the thickness of 9-20mm, titanium microalloying reduces the production cost and improves the mechanical property of a hot-rolled coil. The microalloyed Q345B composition is as follows: 0.13 to 0.18 percent of C; si is less than or equal to 0.25 percent; 0.35 to 0.50 percent of Mn; p is less than or equal to 0.020%; s is less than or equal to 0.010 percent; al is more than or equal to 0.010 percent; 0.045-0.065% of Ti. In the invention, the C content does not completely avoid a crystal covering region, and the risk of corner crack of the casting blank is large; the external refining is LF refining, the difficulty of controlling the N content is high, the stability of controlling the Ti content is poor, the performance fluctuation of a finished product roll is large, and the stable production is not facilitated.
Also, for example, in chinese patent publication No. CN201510805917.3, a preparation process for reducing the Q345B band-shaped structure is disclosed, wherein a large amount of manganese (about 0.80%) is replaced with trace titanium (about 0.040%) through the procedures of molten iron pretreatment, converter, argon station, continuous casting, and the like, and solid solution strengthening is replaced with fine grain strengthening, and the finished band-shaped structure is reduced by matching with hot rolling, and cooling. The C content is 0.17%, the elongation and impact performance of a finished coil are affected by the high carbon content, the effective Ti content in molten steel is affected by the N content and the S content, and the Q345B hot rolled coil produced by the process has large N content fluctuation and large S content control difficulty, so that the effective Ti content in the steel is affected, and the performance of the finished coil is affected.
Disclosure of Invention
1. Technical problems to be solved by the invention
Aiming at the defects in the prior art, the invention aims to provide the low-cost Q345B steel produced by using the over-RH vacuum refining furnace and the production method thereof, and the over-RH process route is adopted, so that the content of N and the content of effective Ti in molten steel are stably controlled, and the stability of the hot rolling performance of the finished coil is favorably improved.
2. Technical scheme
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
the invention relates to low-cost Q345B steel produced by an RH vacuum refining furnace, which comprises the following chemical components in percentage by mass: c:0.060% to 0.080%, si: less than or equal to 0.060%, mn: 0.40-0.60%, P: less than or equal to 0.020%, S: less than or equal to 0.006 percent, als: 0.03-0.06%, ti:0.043% -0.058%, N: less than or equal to 0.0040 percent; the balance of iron and unavoidable impurities.
As a further improvement of the invention, the effective Ti = (Ti%) -3.42 (N%) -1.5 (S%), and the effective Ti content satisfies 0.027% to 0.042%.
As a further improvement of the invention, the thickness of the Q345B steel hot rolled coil is 2-12 mm, the yield strength is more than or equal to 345MPa, the tensile strength is 470-630 MPa, the elongation A after fracture is more than or equal to 21 percent, and the impact energy is more than or equal to 34KV/J.
The invention relates to a production method of low-cost Q345B steel produced by using an RH vacuum refining furnace, which comprises the following production steps:
(1) Pretreating molten iron;
(2) A converter;
(3) An argon blowing station;
(4) RH refining: adopting a deep processing mode, wherein the vacuum processing time is more than or equal to 15min, if chemical temperature rise is needed, the time interval from the oxygen blowing end to the alloying is more than or equal to 3min, and the net cycle time before breaking is more than or equal to 6min;
(5) Continuous casting;
(6) And (4) hot rolling.
As a further improvement of the invention, the bright surface of the molten iron is more than or equal to 90 percent after controlling slag skimming in the step of pretreating the molten iron, and the content of [ S ] is less than or equal to 0.003 percent after treating the molten iron.
As a further improvement of the invention, the adding amount of the scrap steel in the step (2) is controlled to be less than or equal to 60 tons, and a strong bottom blowing mode is adopted in the later stage of converter blowing, so that the slag discharging amount of the converter is strictly controlled.
As a further improvement of the invention, in the step (2), aluminum particles are added firstly, then medium carbon ferromanganese is added, and finally slag is added in the tapping process.
As a further improvement of the invention, the station entering temperature of the molten steel of the argon blowing station in the step (3) is 1623-1640 ℃, and the tapping temperature is 1595-1612 ℃.
As a further improvement of the invention, argon is filled in the step (5) before casting, and a protective casting mode is adopted in the casting process.
As a further improvement of the invention, the finishing temperature in the hot rolling step is 872-889 ℃, and the coiling temperature of the steel coil is 609-631 ℃.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:
(1) The invention relates to low-cost Q345B steel produced by an over-RH vacuum refining furnace, which changes the solid solution strengthening effect of C and Mn elements in the traditional molten steel design into the precipitation strengthening of a new component TiC by mainly reducing the contents of C and Mn and increasing the contents of Si and Ti, and the C element in the molten steel avoids a peritectic reaction zone, and when the C element in the molten steel is in the range of 0.08-0.15%, the peritectic reaction is easy to occur, so that the crack sensitivity of a casting blank is effectively reduced, and the constant crack defect of the corner of the casting blank is eliminated. The production process design ensures that the effective titanium content meets the range of 0.027-0.042% according to the principle of S control and N control.
(2) According to the production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace, the adding amount of the scrap steel is controlled to be less than or equal to 60 tons in the converter steelmaking process, so that the influence of the scrap steel S is reduced; a strong bottom blowing mode is adopted in the later stage of converter blowing to enhance molten pool stirring; the slag discharge amount of the converter is strictly controlled. The charging sequence in the tapping process is as follows: pre-deoxidizing carbon powder-aluminum particles-medium carbon ferromanganese-slag charge, and ensuring the alloy yield.
(3) According to the production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace, a deep treatment mode is adopted in the RH refining process, the vacuum treatment time is more than or equal to 15min, and the degassing effect is ensured; if chemical temperature rise is needed, the chemical temperature rise is carried out before alloying, the time interval from the end of oxygen blowing to the alloying is more than or equal to 3min, the Ti yield is stabilized, and the N content is stably controlled; the net circulation time before air break is more than or equal to 6min, so that the component temperature of the molten steel is more uniform, and impurities can float upwards. The proper heating temperature ensures that Ti is fully dissolved in the furnace and austenite grains cannot excessively grow, and is combined with actual production, so the tapping temperature is set to be 1240 ℃, and the furnace time is more than 180 min.
(4) According to the production method of the low-cost Q345B steel produced by using the over-RH vacuum refining furnace, the Q345B produced by using the over-RH process route is adopted, and because nitrogen is increased in the heating and temperature rising process of the LF furnace and the effect of removing nitrogen is achieved in the vacuum treatment process of the RH furnace, the nitrogen content can be stably controlled to be lower, so that the effective Ti control is more stable than the over-LF furnace process; effective Ti and performance are in direct proportion, so that the Q345B performance dispersion produced by the RH process is small, and the stability of the hot rolling performance of the finished coil is improved.
Drawings
FIG. 1 is a process capability trend graph of the N content in Q345B steel produced by an LF process in the present invention;
FIG. 2 is a process capability trend graph of N content in Q345B steel produced by the RH process of the present invention;
FIG. 3 is a process capability trend graph of the effective Ti content in Q345B steel produced by an LF process in accordance with the present invention;
FIG. 4 is a process capability trend plot of the effective Ti content in Q345B steel produced by the RH process of the present invention.
Detailed Description
For a further understanding of the invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The present invention will be further described with reference to the following examples.
Example 1
In the low-cost Q345B steel produced by using the RH vacuum refining furnace, the molten steel comprises the following chemical components in percentage by mass: c:0.060% to 0.080%, si: less than or equal to 0.060 percent, mn:0.40% -0.60%, P: less than or equal to 0.020%, S: less than or equal to 0.006 percent, als:0.03 to 0.06 percent, ti:0.043% -0.058%, N: less than or equal to 0.004 percent; the balance of iron and unavoidable impurities. Wherein the effective Ti is = (Ti%) -3.42 (N%) -1.5 (S%), and the effective Ti content satisfies 0.027% -0.042%. In the embodiment, the solid solution strengthening effect of C and Mn elements in the traditional molten steel design is changed into the precipitation strengthening of new component TiC by reducing the contents of C and Mn and increasing the contents of Si and Ti, the C element in the molten steel avoids a peritectic reaction zone, and when the C element in the molten steel is in the range of 0.08-0.15%, the peritectic reaction is easy to occur, so that the crack sensitivity of a casting blank is effectively reduced, and the constant crack defect of the corner of the casting blank is eliminated. The production process design ensures that the effective titanium content meets the range of 0.027-0.042% according to the principle of S control and N control.
In the embodiment, the thickness of the hot rolled coil of the Q345B steel is 2-12 mm, the yield strength is more than or equal to 345MPa, the tensile strength is 470-630 MPa, the elongation A after fracture is more than or equal to 21 percent, and the impact energy is more than or equal to 34KV/J.
The production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace comprises the following production steps:
(1) Pretreating molten iron: the bright surface of the molten iron is more than or equal to 90% after slag skimming is controlled in the molten iron pretreatment step, the [ S ] content is guaranteed to be less than or equal to 0.003% after the molten iron is treated, the requirement of controlling S is met, and the effective Ti content can be improved by lowering the S content.
(2) Converter steelmaking: the adding amount of the scrap steel is controlled to be less than or equal to 60 tons, and the influence of the scrap steel S is reduced; a strong bottom blowing mode is adopted in the later stage of converter blowing to enhance molten pool stirring; the slag discharge amount of the converter is strictly controlled. The charging sequence in the tapping process is as follows: pre-deoxidation carbon powder-aluminum particles-medium carbon ferromanganese-slag charge, so as to ensure the yield of the alloy. The end point temperature of the converter is 1651-1671 ℃, the end point oxygen is 384-681 ppm, the end point carbon is 0.033-0.079%, and the end point sulfur is 0.0031-0.0065%.
(3) An argon blowing station; the molten steel entering temperature of the argon blowing station is 1623-1640 ℃, the tapping temperature is 1595-1612 ℃, and the average tapping temperature drop is 28 ℃.
(4) RH refining: a deep processing mode is adopted, the vacuum processing time is more than or equal to 15min, and the degassing effect is ensured; if chemical heating is needed to be carried out before alloying, the time interval from the end of oxygen blowing to alloying is more than or equal to 3min, the Ti yield is stabilized, the N content is stably controlled at a lower level, and the effective Ti content can be improved; the net circulation time before air break is more than or equal to 6min, so that the component temperature of the molten steel is more uniform, and impurities can float upwards.
The proper heating temperature ensures that Ti is fully precipitated in the furnace and austenite grains cannot excessively grow, and the tapping temperature is set to be 1240 ℃ in combination with actual production, and the time in the furnace is more than 180 min.
In the embodiment, the molten steel at the RH refining end point comprises the following components in percentage by mass: c:0.061% -0.078%, si: 0.0076-0.0164%, mn:0.48% -0.52%, P:0.010% -0.016%, S: 0.0035-0.0065%, als: 0.044-0.076%, ti:0.052% -0.060%, N:0.0022% -0.0032%, O:0.0013 to 0.0038 percent
(5) Continuous casting; and (5) filling argon into the tundish before casting, and adopting a protective casting mode in the casting process to reduce nitrogen increase in the continuous casting process, ensure stable control of nitrogen content in steel and reduce the performance dispersion difference of the Q345B finished product coil. In the embodiment, the molten steel of the continuous casting tundish comprises the following components in percentage by mass: c:0.060% -0.081%, si:0.009% -0.018%, mn:0.49% -0.51%, P: 0.010-0.015%, S:0.0035% -0.0065%, als:0.040% -0.067%, ti:0.050% -0.058%, N:0.0025 to 0.0034 percent
(6) And (3) hot rolling, wherein the finishing temperature in the hot rolling step is 872-889 ℃, and the coiling temperature of the steel coil is 609-631 ℃.
The Q345B produced by adopting the RH process route has the advantages that nitrogen is increased in the heating process of the LF furnace, the RH furnace has the effect of removing nitrogen in the vacuum treatment process, and the nitrogen content can be stably controlled at a lower content, so that the control of effective Ti (effective Ti = (% Ti) -3.42 (% N) -1.5 (% S)) is more stable than the process of passing the LF furnace; effective Ti and performance are in direct proportion, so that the Q345B performance dispersion produced by the RH process is small, and the stability of the hot rolling performance of the finished coil is improved.
In this embodiment, a casting time 6 furnace Q345B is taken as an example:
specifically, in the low-cost Q345B steel produced by using the RH vacuum refining furnace according to the present embodiment, the molten steel comprises the following chemical components by mass percent: c:0.060%, si:0.060%, mn:0.40%, P:0.020%, S:0.006%, als:0.03%, ti:0.043%, N:0.0040%; the balance of iron and unavoidable impurities.
Wherein the effective Ti = (Ti%) -3.42 (N%) -1.5 (S%) =0.043% -3.42 0.0040% -1.5% 0.006% =0.40732%, and the effective Ti content is in the range of 0.027% -0.042%.
The production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace comprises the following production steps:
(1) Pretreatment of molten iron: the S content after KR treatment is 0.001%, and then slag skimming is performed to obtain a bright surface of 91%;
(2) Converter steelmaking: adding 30 tons of scrap steel and 270 tons of molten iron; the bottom blowing mode is enhanced in the later stage of converter blowing, and the stirring of a molten pool is enhanced; the slag discharge amount is strictly controlled in the converter tapping process; the charging sequence in the tapping process is as follows: pre-deoxidizing carbon powder-aluminum particles-medium carbon ferromanganese-slag charge; the end point temperature of the converter is 1651 ℃, the end point oxygen is 384ppm, the end point carbon is 0.033% and the end point sulfur is 0031%;
(3) And (3) argon blowing station: the station-entering temperature of the argon blowing station is 1623 ℃, and the average tapping temperature drop is 28 ℃;
(4) RH refining: adopting a deep processing mode, wherein the vacuum processing time is 15min; the net circulation time before breaking is 6min; single open exit temperature: 1583 deg.C, and the continuous casting leaving temperature is 1576 deg.C; the casting is carried out by blowing oxygen in the 1 st furnace, the 4 th furnace and the 5 th furnace and heating, and the time interval from the oxygen blowing to the alloying is 3min.
RH end point C in this example: 0.061%, si:0.0076%, mn:0.48%, P:0.010%, S:0.0035%, als:0.044%, ti:0.052%, N:0.0022 percent, 0.0013 percent of O; the RH average ferrotitanium yield is 99.5 percent;
(5) Continuous casting: in the continuous casting process, the argon filling of the tundish before casting and the protective casting in the casting process are well carried out; the continuous casting tundish comprises the following components: c:0.060%, si:0.009%, mn:0.49%, P:0.010%, S:0.0035%, als:0.040%, ti:0.050%, N:0.0025 percent;
(6) Hot rolling: the tapping temperature is set to be 1240 ℃, the furnace time is 203min, the tapping temperature is 1235 ℃, the rough rolling is 3+5 passes, the finish rolling is 7 passes, the final rolling temperature is 872 ℃, and the coiling temperature is 609 ℃.
(7) Hot rolling of coils: the thickness of the hot rolled coil is 2mm, the yield strength is 392 MPa-519 MPa, the tensile strength is 498 MPa-608 MPa, the elongation A range after fracture is 23-32%, and the impact energy range is 70-96 KV/J. The yield strength, tensile strength, elongation and impact energy performance of the finished hot rolled coil in the embodiment all meet the national standard, and the cold bending performance is qualified.
Comparison of LF and RH process routes: the N content control, effective Ti content control and hot-rolled coil performance conditions of the LF and RH process paths are compared, and the statistical results are shown in Table 1. Compared with the effective Ti process capability of the LF and RH process paths, the N content control of the RH process is better, and the effective Ti control is more stable; compared with the LF path production Q345B, the calculation of the thickness specification is divided, the performance dispersion of the RH process production Q345B is small, and the performance is more stable.
TABLE 1 LF and RH route production Q345B Hot-coil Performance comparison
Example 2
The basic steps of the method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace in the embodiment are the same as those of the embodiment 1, and the difference is that the low-cost Q345B steel produced by using the over-RH vacuum refining furnace in the embodiment comprises the following chemical components in percentage by mass: c:0.070%, si:0.050%, mn:0.50%, P:0.010%, S:0.005%, als:0.04%, ti:0.050%, N:0.003%; the balance of iron and unavoidable impurities. Wherein the effective Ti = (Ti%) -3.42 (N%) -1.5 (S%) =0.050% -3.42 × 0.0030% -1.5 × 0.005% =0.03224%, and the effective Ti content is in the range of 0.027% -0.042%.
The production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace comprises the following production steps:
(1) Pretreatment of molten iron: after KR treatment, the S content is 0.002%, and the post-skimming bright surface is 92%;
(2) Converter steelmaking: adding 40 tons of scrap steel and adding 285 tons of molten iron; the bottom blowing mode is enhanced at the later stage of converter blowing, and the stirring of a molten pool is enhanced; the slag discharge amount is strictly controlled in the converter tapping process; the charging sequence in the tapping process is as follows: pre-deoxidizing carbon powder-aluminum particles-medium carbon ferromanganese-slag charge; the end point temperature of the converter is 1660 ℃, the end point oxygen is 450ppm, the end point carbon is 0.045%, and the end point sulfur is 004%;
(3) An argon blowing station: the station-entering temperature of the argon blowing station is 1633 ℃, and the average tapping temperature drop is 28 ℃;
(4) RH refining: adopting a deep processing mode, wherein the vacuum processing time is 16min; the net circulation time before breaking is 7min; single open exit temperature: 1585 ℃, and the continuous casting outlet temperature is 1580 ℃; the casting is carried out by blowing oxygen in the 1 st furnace, the 4 th furnace and the 5 th furnace and heating, and the time interval from the end of oxygen blowing to alloying is 4min.
RH end point C in this example: 0.071%, si:0.0088%, mn:0.50%, P:0.013%, S:0.0046%, als:0.055%, ti:0.055%, N:0.0028 percent and 0.0022 percent of O.
(5) Continuous casting: in the continuous casting process, the argon filling of the tundish before casting and the protective casting in the casting process are well carried out; the continuous casting tundish comprises the following components: c:0.072%, si:0.012%, mn:0.50%, P:0.013%, S:0.0044%, als:0.054%, ti:0.053%, N:0.0029%;
(6) Hot rolling: the tapping temperature is set to be 1240 ℃, the tapping time is 180min, the tapping temperature is 1235 ℃, the rough rolling is carried out for 3+5 passes, the finish rolling is carried out for 7 passes, the final rolling temperature is 880 ℃, and the coiling temperature is 615 ℃.
(7) Hot rolling: the thickness of the hot rolled coil is 8mm, the yield strength is 381Mpa to 430Mpa, the tensile strength is 482Mpa to 525Mpa, the elongation A range after fracture is 25.5 percent to 31 percent, and the impact energy range is 64KV/J to 115KV/J. The yield strength, tensile strength, elongation and impact energy performance of the finished hot rolled coil in the embodiment all meet the national standard, and the cold bending performance is qualified.
Example 3
The basic steps of the method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace in the embodiment are the same as those of the embodiment 1, and the difference is that the low-cost Q345B steel produced by using the over-RH vacuum refining furnace in the embodiment comprises the following chemical components in percentage by mass: c:0.080%, si:0.060%, mn:0.60%, P:0.020%, S:0.005%, als:0.06%, ti:0.058%, N:0.004%; the balance of iron and unavoidable impurities. Wherein the effective Ti = (Ti%) -3.42 (N%) -1.5 (S%) =0.058% -3.42 0.004% -1.5% 0.005% =0.03682%, and the effective Ti content is in the range of 0.027% -0.042%.
The production method of the low-cost Q345B steel produced by using the RH vacuum refining furnace comprises the following production steps:
(1) Pretreating molten iron: after KR treatment, the S content is 0.001%, and the post-skimming bright surface is 93%;
(2) Converter steelmaking: adding 55 tons of scrap steel and adding 300 tons of molten iron; the bottom blowing mode is enhanced at the later stage of converter blowing, and the stirring of a molten pool is enhanced; the slag discharge amount is strictly controlled in the converter tapping process; the charging sequence in the tapping process is as follows: pre-deoxidizing carbon powder-aluminum particles-medium carbon ferromanganese-slag charge; the end point temperature of the converter is 1671 ℃, the end point oxygen is 681ppm, the end point carbon is 0.079 percent, and the end point sulfur is 0.0065 percent;
(3) And (3) argon blowing station: the station-entering temperature of the argon blowing station is 1640 ℃, and the average tapping temperature drop is 28 ℃;
(4) RH refining: a deep processing mode is adopted, and the vacuum processing time is 16min; the net circulation time before breaking is 6min; single-start outlet temperature: 1583 ℃, and the continuous casting outlet temperature is 1581 ℃; the casting is carried out in the 1 st, 4 th and 5 th furnaces for oxygen blowing and temperature rise, and the time interval from the oxygen blowing to the alloying is 5min.
RH end point C in this example: 0.078%, si:0.0164%, mn:0.52%, P:0.016%, S:0.0065%, als:0.076%, ti:0.060%, N:0.0032%, O:0.0038 percent.
(5) Continuous casting: in the continuous casting process, well performing the argon filling of the tundish before casting and the protective casting in the casting process; the continuous casting tundish comprises the following components: c:0.081%, si:0.018%, mn:0.51%, P:0.015%, S:0.0065%, als:0.067%, ti:0.058%, N:0.0034%;
(6) Hot rolling: the tapping temperature is set to be 1240 ℃, the tapping time is 210min, the tapping temperature is 1245 ℃, the rough rolling is carried out for 3+5 passes, the finish rolling is carried out for 7 passes, the final rolling temperature is 889 ℃, and the coiling temperature is 631 ℃.
(7) Hot rolling: the thickness of the hot rolled coil is 12mm, the yield strength is 375 Mpa-424 Mpa, the tensile strength is 492 Mpa-526 Mpa, the range of the elongation A after fracture is 24.5% -33%, and the range of the impact energy is 110 KV/J-224 KV/J. The yield strength, tensile strength, elongation and impact energy performance of the finished hot rolled coil in the embodiment all meet the national standard, and the cold bending performance is qualified.
Comparative example 1
The LF process is adopted to produce the Q345B steel in the comparative example, the thickness of the hot rolled coil in the comparative example is 2mm, the yield strength is 348-550 Mpa, the tensile strength is 470-593 Mpa, the range of the elongation A after fracture is 21-39%, and the range of the impact power is 65 KV/J-262 KV/J.
Comparative example 2
The LF process is adopted to produce the Q345B steel in the comparative example, the thickness of the hot rolled coil in the comparative example is 8mm, the yield strength is 350-479 Mpa, the tensile strength is 475-599 Mpa, the range of the elongation A after fracture is 23.5-30.5%, and the range of the impact work is 63-128 KV/J.
Comparative example 3
The comparative example adopts the LF process to produce the Q345B steel, the thickness of the hot rolled coil in the comparative example is 2mm, the yield strength is 355 Mpa-495 Mpa, the tensile strength is 481 Mpa-590 Mpa, the range of the elongation A after fracture is 23.5% -29.5%, and the range of the impact energy is 98 KV/J-205 KV/J.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.
Claims (10)
1. The low-cost Q345B steel produced by using the RH vacuum refining furnace is characterized in that: the molten steel comprises the following chemical components in percentage by mass: c:0.060% to 0.080%, si: less than or equal to 0.060 percent, mn:0.40% -0.60%, P: less than or equal to 0.020%, S: less than or equal to 0.006 percent, als: 0.03-0.06%, ti: 0.043-0.058%, N: less than or equal to 0.0040 percent; the balance of iron and unavoidable impurities.
2. The low-cost Q345B steel produced by using the over-RH vacuum refining furnace as set forth in claim 1, wherein: effective Ti = (Ti%) -3.42 (N%) -1.5 (S%), and the effective Ti content satisfies 0.027% -0.042%.
3. The low-cost Q345B steel produced by using the over-RH vacuum refining furnace as set forth in claim 2, wherein: the thickness of the Q345B steel hot rolled coil is 2-12 mm, the yield strength is more than or equal to 345MPa, the tensile strength is 470-630 MPa, the elongation A after fracture is more than or equal to 21 percent, and the impact energy is more than or equal to 34KV/J.
4. A method for producing a low cost Q345B steel using a super RH vacuum refining furnace according to any one of claims 1 to 3, wherein: comprises the following production steps:
(1) Pretreating molten iron;
(2) A converter;
(3) An argon blowing station;
(4) RH refining: adopting a deep processing mode, wherein the vacuum processing time is more than or equal to 15min, if chemical temperature rise is needed, the time interval from the oxygen blowing end to the alloying is more than or equal to 3min, and the net cycle time before breaking is more than or equal to 6min;
(5) Continuous casting;
(6) And (4) hot rolling.
5. The method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace as claimed in claim 4, wherein the method comprises the following steps: the bright surface of the molten iron is more than or equal to 90 percent after slagging-off is controlled in the step of molten iron pretreatment, and the content of [ S ] is less than or equal to 0.003 percent after the molten iron is treated.
6. The method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace as claimed in claim 5, wherein the method comprises the following steps: in the step (2), the adding amount of the scrap steel is controlled to be less than or equal to 60 tons, a strong bottom blowing mode is adopted in the later stage of converter blowing, and the slag discharging amount of the converter is strictly controlled.
7. The method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace as claimed in claim 6, wherein the method comprises the following steps: in the step (2), aluminum particles are added firstly, then medium carbon ferromanganese is added, and finally slag charge is added in the tapping process.
8. The method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace as claimed in claim 7, wherein the method comprises the following steps: the station entering temperature of the molten steel of the argon blowing station in the step (3) is 1623-1640 ℃, and the tapping temperature is 1595-1612 ℃.
9. A method for producing a low cost Q345B steel using a super RH vacuum refining furnace according to any one of claims 4 to 8, wherein: and (5) filling argon in the tundish before casting, and adopting a protective casting mode in the casting process.
10. The method for producing the low-cost Q345B steel by using the over-RH vacuum refining furnace as claimed in claim 9, wherein the method comprises the following steps: the final rolling temperature in the hot rolling step is 872-889 ℃, and the coiling temperature of the steel coil is 609-631 ℃.
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