Method for improving performance stability of titanium microalloyed steel

Abstract

The invention discloses a method for improving the performance stability of titanium microalloyed steel, and belongs to the technical field of steelmaking. The method for improving the performance stability of the titanium microalloyed steel is provided for improving the mechanical performance stability of the titanium microalloyed steel, and the control precision of chemical components of the titanium microalloyed steel is optimized as follows: the content of C is + / -0.01%, the content of Si is + / -0.03%, the content of Mn is + / -0.05%, the content of Nb is + / -0.005%, the content of Ti is + / -0.005%, N is smaller than or equal to 0.0040%, and O is smaller than or equal to 0.0020%. And the working procedures of smelting, slab heating, controlled rolling and controlled cooling, coiling and slow cooling are optimized, so that the performance stability of the titanium microalloyed steel is remarkably improved, the proportion of the tensile strength fluctuation range of + / -30 MPa is not lower than 95%, and the yield is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking, and in particular relates to a method for improving the performance stability of titanium microalloyed steel. Background Art

[0002] With the development of microalloying technology, pure steel smelting technology, and precise chemical composition control technology, microalloying elements such as Nb, V, and Ti are increasingly widely used in hot-rolled high-strength steel. Among them, Ti is favored by domestic and foreign steel companies for its relatively low alloy price and high second phase precipitation efficiency. At the same time, since Ti is easily combined with impurity elements such as N and S to form liquid precipitation TiN and Ti4S2C2 inclusions during the smelting process, the yield of Ti alloy elements is relatively unstable; moreover, Ti is easy to precipitate in each hot rolling process, such as forming deformation-induced precipitation, interphase precipitation, ferrite supersaturation precipitation, etc. in the rolling, laminar cooling, and coiling stages, respectively. The sizes of the above-mentioned precipitated phases differ greatly, so the precipitation behavior of the Ti element is greatly affected by the stability of the hot rolling process. For this reason, the present invention proposes a Ti microalloyed steel smelting process and a hot rolling process stability control technology through industrial research to improve the stability of mechanical properties and promote the stable application of Ti microalloyed hot-rolled high-strength steel.

[0003] CN114395728B discloses a microalloy hot-rolled high-strength steel coil and a preparation method thereof, wherein the chemical composition of the steel is as follows by mass percentage: C 0.05-0.12%, Mn 1.50-2.00%, Si 0.05-0.30%, P≤0.015%, S≤0.005%, Nb 0.01-0.06%, Ti 0.02-0.20%, Mo≤0.25%, Cr≤0.20%, V≤0.20%, N≤0.0050%, Als 0.015-0.050%, and the remainder is Fe and unavoidable impurities. The invention solves the problem of insufficient microalloy precipitation and poor uniformity of the through-rolling performance of the steel coil in the prior art. The method comprises the following steps: rolling and laminar cooling the continuous casting billet of microalloy hot-rolled steel, controlling the final rolling temperature to be 850°C to 870°C, induction heating the rolled steel plate to maintain the temperature of the rolled steel plate at 610°C to 630°C; coiling the induction heated steel plate, and placing the steel coil to be cooled in a slow cooling pit for cooling.

[0004] CN113020256B discloses a production method suitable for hot-rolled wide steel strip containing titanium, which specifically involves four process parameters in the heating furnace: the total furnace time of the ingot, the soaking time, the soaking temperature, and the target furnace discharge temperature; the invention provides a heating furnace process scheme that varies with the thickness of the ingot, the [Ti%]*[C%] solubility product, and the Ti content. The calculation formula in the scheme accurately calculates the heating furnace process conditions and operating points for completely dissolving large-sized TiC particles in the ingot and fully diffusing the dissolved Ti element based on a combination of theoretical reasoning and production experience, thereby solving the mixed crystal problem caused by the uneven distribution of titanium in titanium-containing steel.

[0005] CN114182167B discloses that the present invention provides a hot-rolled steel bar with stable aging performance and a production method thereof, wherein the production method of the hot-rolled steel bar with stable aging performance comprises: a steel bar component formula, according to mass fraction Wt%, is: C: 0.21-0.25, Si: 0.40-0.60, Mn: 1.30-1.45, Nb: 0.023-0.035, B: 0.0008-0.0018, P and S are both not greater than 0.040, and the rest are Fe and inevitable impurities. The steel bar obtained by the present invention has extremely low residual stress, and the yield strength of the steel bar changes very little after natural aging, thereby ensuring high stability of the steel bar strength during normal use.

[0006] From the above, it can be seen that the above methods have partial process control for final rolling and coiling temperature, slab heating system, etc. to improve performance stability, but there are no systematic control measures for titanium microalloyed steel, including chemical composition control accuracy, temperature control accuracy, steel coil cooling method, etc. Summary of the invention

[0007] The purpose of the present invention is to study the smelting process of Ti microalloyed steel and the stable control technology of hot rolling process, to optimize the preparation process of titanium microalloyed steel, to improve its performance stability, to ensure the yield, and to promote the stable application of titanium microalloyed hot-rolled high-strength steel.

[0008] To achieve the above-mentioned purpose, the present invention provides a method for improving the performance stability of titanium microalloyed steel. The production process of the titanium microalloyed steel is: converter smelting-refining-continuous casting-slab heating-rough rolling-finishing rolling-laminar cooling-coiling-slow cooling. The chemical composition control accuracy of the titanium microalloyed steel is, by weight percentage, as follows: C content ±0.01%, Si content ±0.03%, Mn content ±0.05%, Nb content ±0.005%, Ti content ±0.005%, N≤0.0040%, O≤0.0020%.

[0009] Wherein, in the above method for improving the performance stability of titanium microalloyed steel, the tensile strength level of the titanium microalloyed steel is 500MPa, 600MPa, 700MPa or 800MPa; when the tensile strength level of the microalloyed steel is 500MPa, its chemical composition is calculated by weight percentage as follows: C 0.06% to 0.08%, Si 0.12% to 0.18%, Mn 1.15%-1.25%, Nb0.015%-0.025%, Ti 0.010%-0.020%; when the tensile strength level of the microalloyed steel is 600MPa, its chemical composition is calculated by weight percentage as follows: C 0.06% to 0.08%, Si 0.12% to 0.18%, Mn 1.45%-1.55%, Nb0.035%-0.045%, Ti 0.025%-0.035%; when the tensile strength level of the micro-alloyed steel is 700MPa, its chemical composition is calculated by weight percentage: C 0.05%-0.07%, Si 0.04%-0.10%, Mn1.60%-1.70%, Nb0.035%-0.045%, Ti 0.080%-0.090%; when the tensile strength level of the micro-alloyed steel is 800MPa, its chemical composition is calculated by weight percentage: C 0.03%-0.05%, Si 0.04%-0.10%, Mn1.70%-1.80%, Nb0.035%-0.045%, Ti 0.090%-0.100%.

[0010] Among them, the above method for improving the performance stability of titanium microalloyed steel is that in the converter process, the oxygen blowing time is 15min to 17min. At the same time, in the refining process, considering that the average carbon increase amount of LF electrode heating is 0.0291% / (t·h), the factors affecting the C content in smelting and refining are comprehensively controlled to achieve the C content control within the range of ±0.01%.

[0011] Among them, the above-mentioned method for improving the performance stability of titanium microalloyed steel, in the refining process, compares and corrects the calculated theoretical refined molten steel entering the station composition with the actual refined entering station composition, and then compares it with the finished steel composition requirements, and calculates the alloy addition amounts of ferrosilicon, metallic manganese, ferroniobium, ferrotitanium, etc., so as to achieve Si content control within ±0.03%, Mn content control within ±0.05%, Nb content control within ±0.005%, and Ti content control within ±0.005%.

[0012] Among them, the above method for improving the performance stability of titanium microalloyed steel adopts a bottom blowing gas supply mode in the refining process, and the blowing argon flow rate is 50-80m 3 / h, add 3-5 kg ​​of refined slag / ton of steel on the surface of the ladle to reduce the nitrogen increase during the process, so that the nitrogen in the molten steel is controlled within the range of ≤0.0040%.

[0013] Among them, in the above method for improving the performance stability of titanium microalloyed steel, in the refining process, the refining slag used has, by weight percentage, (FeO+MnO)<2.0%, SiO2<10.0%, and CaO / Al2O3:1.5~2.0, so that the O in the molten steel is controlled in the range of ≤0.0020%.

[0014] Among them, in the above-mentioned method for improving the performance stability of titanium microalloyed steel, when the tensile strength level of the titanium microalloyed steel is 500MPa or 600MPa, in the slab heating process, the slab heating temperature is 1190-1210°C, and the soaking time is 30-50min; when the tensile strength level of the titanium microalloyed steel is 700MPa or 800MPa, in the slab heating process, the slab heating temperature is 1220-1240°C, and the soaking time is 30-50min.

[0015] Wherein, in the above method for improving the performance stability of titanium microalloyed steel, in the finishing rolling process, the finishing rolling temperature is 860-890°C.

[0016] Among them, in the above method for improving the performance stability of titanium microalloyed steel, in the coiling process, the coiling temperature of the head and middle of the steel coil is 590-620°C, and the coiling temperature of the tail of the steel coil is 640-670°C.

[0017] Among them, in the above method for improving the performance stability of titanium microalloyed steel, after coiling, when the temperature of the tail of the steel coil is not less than 580°C, the steel coil is sent to a slow cooling pit for slow cooling for 72 to 96 hours.

[0018] Wherein, in the above method for improving the performance stability of titanium microalloyed steel, the proportion of the titanium microalloyed steel within the tensile strength fluctuation range of ±30MPa is not less than 95%.

[0019] In the present invention, the operations or parameters in the steps not specially marked, such as smelting, continuous casting, rough rolling and the like, are all based on conventional methods in the art.

[0020] In the present invention, the head, middle and tail of the steel coil each account for 1 / 3 of the total length of the steel coil.

[0021] Beneficial effects of the present invention:

[0022] The present invention systematically proposes a control method for performance stability from the processes of smelting, refining, rolling, etc., accurately controls the fluctuations in the contents of C, Si, Mn, Nb, and Ti to reduce the strength fluctuations of the steel; at the same time, in-depth research is conducted on the factors affecting the contents of N and O, and the refining process, refining slag, etc. are optimized to achieve precise control of impurity elements such as oxygen and nitrogen. In addition, the present invention combines the optimization technology of smelting, slab heating, controlled rolling and controlled cooling, coiling, and slow cooling processes to improve the performance stability of titanium microalloyed steel, ensure the yield, promote the stable application of titanium microalloyed hot-rolled high-strength steel, and provide a new idea for the industrial preparation of titanium microalloyed high-strength steel, which is technologically advanced, operable, and scalable. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the tensile strength distribution diagram of the steel described in Example 1.

[0024] Figure 2 This is the tensile strength distribution diagram of the steel described in Example 2.

[0025] Figure 3 This is the tensile strength distribution diagram of the steel described in Example 3. DETAILED DESCRIPTION

[0026] Specifically, the present invention provides a method for improving the stability of mechanical properties of titanium microalloyed steel. The reasons for limiting the control accuracy of the main chemical components and the smelting process requirements in the steel of the present invention are explained below.

[0027] C can play the role of interstitial solid solution in steel, and C can also combine with Ti to form TiC second phase precipitation, which plays the role of precipitation strengthening. Therefore, the fluctuation of C element content will cause the strength fluctuation of steel. The present invention limits the control accuracy of C content to ±0.01% to reduce the strength fluctuation of steel. In the present invention, in the converter process, the oxygen blowing time is 15min to 17min; at the same time, in the refining process, considering that the average carbon increase amount of LF electrode heating is 0.0291% / (t·h), the factors affecting the C content in smelting and refining are comprehensively regulated to achieve the control of C content within the range of ±0.01%.

[0028] Si plays a role of solid solution strengthening in steel. At the same time, Si can also increase the activity of C, promote the diffusion of C from austenite, and promote the formation of cementite. The content of cementite has a significant effect on the strength of steel. Therefore, the present invention limits the control accuracy of Si content to ±0.03% to reduce the strength fluctuation of steel.

[0029] Mn plays a role in solid solution strengthening in steel, as well as expanding the austenite region and improving toughness. Therefore, fluctuations in the Mn element content will cause fluctuations in the strength of the steel. The present invention limits the control accuracy of the Mn content to ±0.05% to reduce fluctuations in the strength of the steel.

[0030] Nb and Ti are strong carbide elements, which can form second phase precipitation such as NbC and TiC with C, and play a role of precipitation strengthening. At the same time, Nb can play a role of pinning the original austenite grain boundary in the solid solution state and promote grain refinement. Therefore, Nb and Ti elements can affect the strength of steel through fine grain strengthening and precipitation strengthening. Therefore, the present invention limits the control accuracy of Nb content to ±0.005%, and the control accuracy of Ti content to ±0.005%, so as to reduce the strength fluctuation of steel.

[0031] In the present invention, in the refining process, the calculated theoretical refined molten steel inlet composition is compared and corrected with the actual refined inlet composition, and then compared with the finished steel composition requirements, and the addition amounts of alloys such as ferrosilicon, metallic manganese, ferroniobium, and ferrotitanium are calculated to achieve Si content control within ±0.03%, Mn content control within ±0.05%, Nb content control within ±0.005%, and Ti content control within ±0.005%.

[0032] The reasons for the production process limitations of the titanium microalloyed steel of the present invention are explained below.

[0033] First, in terms of smelting process. After the refined molten steel is finally cast, titanium microalloyed steel is obtained, and the N and O contents in the molten steel are the N and O contents in the titanium microalloyed steel; the present invention realizes the control of the N content in the refined molten steel by blowing argon and protecting the refined slag in the refining process; and realizes the control of the O content in the refined molten steel by controlling the components of oxides (FeO, MnO, etc.) in the refined slag. First, the oxidizability of the molten steel will be affected by the oxidizability of the slag. With the increase of the (FeO+MnO) and SiO2 contents in the final refined slag, the O activity in the molten steel will increase; the present invention controls the CaO / Al2O3 ratio in the refined slag in the range of 1.5 to 2.0. This is because when the ratio is too low or too high, it will lead to a higher O activity in the molten steel, which is easy to cause the generation of inclusions and reduce the yield of the Ti content in the steel, thereby affecting the precipitation strengthening effect of TiC in the later stage and causing the strength fluctuation of the steel. Secondly, the high N content in the steel will also combine with Ti to form liquid TiN, which will eventually reduce the precipitation ratio of TiC in the finished steel and cause the strength fluctuation of the steel. Therefore, the present invention makes the following restrictions on the refining process to reduce the N content in the steel to ≤0.0040%: 1) adopting the bottom blowing gas supply mode to take away the N element in the steel through tiny Ar bubbles, 2) reducing the nitrogen increase in the process, adding 3 to 5 kg of refined slag / ton of steel on the surface of the ladle.

[0034] Second, in terms of slab heating process. Since the slab heating temperature, soaking time, etc. directly affect the solid solution of micro-alloying elements such as Nb and Ti, the fluctuations of heating temperature, soaking time, etc. will affect the solid solution of Nb and Ti in steel, and then affect the second phase precipitation content in the finished steel, thereby causing the strength fluctuation of the steel. Therefore, the present invention limits the fluctuation of the slab heating temperature to ±10°C, and the fluctuation of the soaking time to ±10min, specifically: for steel with a tensile strength level of 500MPa or 600MPa, the slab heating temperature is 1190-1210°C, and the soaking time is 30-50min; for steel with a tensile strength level of 700MPa or 800MPa, the slab heating temperature is 1220-1240°C, and the soaking time is 30-50min. At this time, a higher heating temperature is used to promote the solid solution of Nb and Ti elements, so as to achieve the effect of increasing the precipitation strengthening increment and improving the strength of the steel.

[0035] Third, in terms of controlled rolling and controlled cooling technology. The present invention limits the final rolling temperature to 860-890°C, the coiling temperature at the head and middle of the coil to 590-620°C, and the coiling temperature at the tail of the coil to 640-670°C. The above temperature fluctuation ranges are all limited to ±15°C. By improving the temperature control accuracy, the microstructure size, second phase precipitation, and stable control of mechanical properties can be achieved.

[0036] At the same time, the final rolling temperature is set at 860-890℃ because this temperature range is higher than the phase transformation temperature, which is conducive to the stable ferrite pearlite transformation in the laminar cooling process. If the final rolling temperature is too low, it may cause the final stand of the finishing rolling to roll in the two-phase region, forming a mixed crystal structure, affecting the uniformity of the steel structure. If the final rolling temperature is too low, it may cause the original austenite grains to be coarse, resulting in coarse finished steel structure. The coiling temperature at the head and middle of the steel coil is set at 590-620℃ because this temperature range is close to the nose point temperature of TiC precipitation. The coiling temperature is set in this temperature range, which is conducive to the full precipitation of Ti elements during the coiling process. The coiling temperature setting value at the tail of the steel coil is 50℃ higher than that at the head and middle. This is because the temperature of the tail of the steel coil drops faster when the steel coil is transported on the roller after coiling. In order to ensure that the temperature of the tail of the steel coil entering the slow cooling pit can still reach 580℃, the temperature of the tail of the steel coil is controlled in a higher range.

[0037] Finally, the present invention requires that the coiled steel coil be sent to a slow cooling pit for slow cooling for 72 to 96 hours in order to promote the full precipitation of TiC from the steel coil in the slow cooling pit and improve the strength of the steel.

[0038] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0039] Example 1

[0040] The steel billet having the chemical composition shown in Table 1 was prepared by the converter-refining-continuous casting process, and the chemical composition control accuracy met the following requirements: C content ±0.01%, Si content ±0.03%, Mn content ±0.05%, Nb content ±0.005%, Ti content ±0.005%, N content ≤0.0040%, and O content ≤0.0020%.

[0041] The oxygen blowing time in the steel converter process is 16 minutes. In the refining process, the (FeO+MnO) content in the final slag is 1.8%, SiO2 is 9.2%, and the CaO / Al2O3 ratio is 1.8. At the same time, bottom argon is blown during refining, and the argon flow rate is 65m 3 / h, add 4.2kg slag / ton steel on the surface of the ladle. The slab heating temperature is 1201℃, the soaking time is 41min, the final rolling temperature is 874℃, the coiling temperature is 603℃, the coiling temperature at the tail of the steel coil is 655℃, and the tail temperature of the steel coil before it is sent into the slow cooling pit is 593℃. After slow cooling in the slow cooling pit for 80h, the steel coil is taken out and air cooled to room temperature.

[0042] The steel prepared by the above composition process has a tensile strength in the range of 520 MPa to 580 MPa, that is, the tensile strength fluctuation range is ±30 MPa, which accounts for 95.9%.

[0043] Table 1 Chemical composition of the steel described in Example 1 (wt%)

[0044] element Test requirements Minimum Maximum average value Pass rate / % C 0.06-0.08 0.06 0.08 0.07 100 Si 0.12-0.18 0.13 0.18 0.16 99.6 Mn 1.15-1.25 1.17 1.23 1.21 100 P ≤0.015 0.006 0.015 0.012 100 S ≤0.005 0.001 0.005 0.004 100 Nb 0.015-0.025 0.015 0.027 0.019 98.5 Ti 0.010-0.020 0.010 0.020 0.016 100 N ≤0.0040％ 0.0022 0.0040 0.0031 100 O ≤0.0020％ 0.0008 0.0016 0.0013 100

[0045] Example 2

[0046] The steel billet having the chemical composition shown in Table 2 was prepared by the converter-refining-continuous casting process, and the chemical composition control accuracy met the following requirements: C content ±0.01%, Si content ±0.03%, Mn content ±0.05%, Nb content ±0.005%, Ti content ±0.005%, N content ≤0.0040%, and O content ≤0.0020%.

[0047] The oxygen blowing time in the converter process is 17 minutes. In the refining process, the (FeO+MnO) content in the final slag is 1.6%, SiO2 is 9.5%, and the CaO / Al2O3 ratio is 1.6. At the same time, bottom argon is blown during refining, and the argon flow rate is 72m 3 / h, add 4.8kg slag / ton steel on the surface of the ladle. The slab heating temperature is 1206℃, the soaking time is 44min, the final rolling temperature is 876℃, the coiling temperature is 598℃, the coiling temperature at the tail of the steel coil is 647℃, and the tail temperature of the steel coil before it is sent into the slow cooling pit is 584℃. After slow cooling in the slow cooling pit for 88h, the steel coil is taken out and air cooled to room temperature.

[0048] The steel prepared by the above composition process has a tensile strength of 620MPa to 680MPa, that is, the tensile strength fluctuation range of ±30MPa is 95.3%, see Figure 2 .

[0049] Table 2 Chemical composition of the steel described in Example 2 (wt%)

[0050]

[0051]

[0052] Example 3

[0053] The steel billet having the chemical composition shown in Table 3 was prepared by the converter-refining-continuous casting process, and the chemical composition control accuracy met the following requirements: C content ±0.01%, Si content ±0.03%, Mn content ±0.05%, Nb content ±0.005%, Ti content ±0.005%, N content ≤0.0040%, and O content ≤0.0020%.

[0054] The oxygen blowing time in the steel converter process is 15 minutes. In the refining process, the (FeO+MnO) content in the final slag is 1.9%, SiO2 is 9.8%, and the CaO / Al2O3 ratio is 1.6. At the same time, bottom argon is blown during refining, and the argon flow rate is 72m 3 / h, add 3.8kg slag / ton steel on the surface of the ladle. The slab heating temperature is 1232℃, the soaking time is 38min, the final rolling temperature is 871℃, the coiling temperature is 607℃, the coiling temperature at the tail of the steel coil is 665℃, and the tail temperature of the steel coil before it is sent into the slow cooling pit is 601℃. After slow cooling in the slow cooling pit for 75h, the steel coil is taken out and air cooled to room temperature.

[0055] The steel prepared by the above composition process has a tensile strength of 800MPa to 880MPa, and the tensile strength fluctuation range is ±30MPa, which accounts for 95%. Figure 3 .

[0056] Table 3 Chemical composition of the steel described in Example 3 (wt%)

[0057] element Test requirements Minimum Maximum average value Pass rate / % C 0.03-0.05 0.03 0.04 0.04 100 Si 0.04-0.10 0.07 0.10 0.08 100 Mn 1.70-1.80 1.69 1.76 1.73 99.6 P ≤0.015 0.006 0.012 0.008 100 S ≤0.004 0.002 0.004 0.003 100 Nb 0.035-0.045 0.032 0.041 0.036 100 Ti 0.090-0.100 0.091 0.100 0.096 100 N ≤0.0040％ 0.0023 0.0039 0.0030 100 O ≤0.0020％ 0.0008 0.0012 0.0010 100

Claims

1. A method for improving the performance stability of titanium microalloyed steel, wherein the production process of the titanium microalloyed steel is: converter smelting - refining - continuous casting - slab heating - rough rolling - finishing rolling - laminar cooling - coiling - slow cooling, characterized in that: The chemical composition control accuracy of the titanium microalloyed steel is, by weight percentage, as follows: C content ±0.01%, Si content ±0.03%, Mn content ±0.05%, Nb content ±0.005%, Ti content ±0.005%, N≤0.0040%, O≤0.0020%.

2. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: The tensile strength level of the titanium microalloyed steel is 500MPa, 600MPa, 700MPa or 800MPa; When the tensile strength level of the microalloyed steel is 500 MPa, the chemical composition thereof is as follows by weight percentage: C 0.06% to 0.08%, Si 0.12% to 0.18%, Mn 1.15% to 1.25%, Nb 0.015% to 0.025%, Ti 0.010% to 0.020%; When the tensile strength level of the microalloyed steel is 600 MPa, the chemical composition thereof is as follows by weight percentage: C 0.06% to 0.08%, Si 0.12% to 0.18%, Mn 1.45% to 1.55%, Nb 0.035% to 0.045%, Ti 0.025% to 0.035%; When the tensile strength level of the microalloyed steel is 700 MPa, the chemical composition thereof is as follows by weight percentage: C 0.05% to 0.07%, Si 0.04% to 0.10%, Mn 1.60% to 1.70%, Nb 0.035% to 0.045%, Ti 0.080% to 0.090%; When the tensile strength level of the microalloyed steel is 800 MPa, the chemical composition thereof is as follows by weight percentage: C 0.03%-0.05%, Si 0.04%-0.10%, Mn 1.70%-1.80%, Nb 0.035%-0.045%, and Ti 0.090%-0.100%.

3. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: In the converter process, the oxygen blowing time is 15min to 17min.

4. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: In the refining process, the bottom blowing gas supply mode is adopted, and the blowing argon flow rate is 50~80m 3 / h, add 3-5 kg ​​of refined slag / ton of steel on the surface of the ladle to make N ≤ 0.0040% in the molten steel.

5. The method for improving the performance stability of titanium microalloyed steel according to claim 1 or 4, characterized in that: In the refining process, the refining slag used has the following weight percentages: (FeO+MnO)<2.0%, SiO2<10.0%, and CaO / Al2O3:1.5~2.0, so that O in the molten steel is ≤0.0020%.

6. The method for improving the performance stability of titanium microalloyed steel according to claim 2, characterized in that: When the tensile strength level of titanium microalloyed steel is 500MPa or 600MPa, in the slab heating process, the slab heating temperature is 1190-1210°C, and the soaking time is 30-50min; when the tensile strength level of titanium microalloyed steel is 700MPa or 800MPa, in the slab heating process, the slab heating temperature is 1220-1240°C, and the soaking time is 30-50min.

7. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: In the finishing rolling process, the finishing rolling temperature is 860-890°C.

8. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: In the coiling process, the coiling temperature at the head and middle of the steel coil is 590-620°C, and the coiling temperature at the tail of the steel coil is 640-670°C.

9. The method for improving the performance stability of titanium microalloyed steel according to claim 1, characterized in that: After coiling, when the temperature of the tail of the steel coil is not less than 580℃, the steel coil is sent to the slow cooling pit for slow cooling for 72 to 96 hours.

10. The method for improving the performance stability of titanium microalloyed steel according to any one of claims 1 to 9, characterized in that: The proportion of the titanium microalloyed steel within the tensile strength fluctuation range of ±30 MPa is not less than 95%.

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