Titanium-vanadium composite microalloyed low-carbon high-strength steel and preparation method thereof

Abstract

The invention relates to the field of steel production and manufacturing, in particular to titanium-vanadium composite microalloyed low-carbon high-strength steel and a preparation method thereof. The titanium-vanadium microalloyed low-carbon high-strength steel comprises the following chemical components in percentage by mass: 0.05 to 0.09 percent of C, 0.10 to 0.25 percent of Si, 1.85 to 2.2 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, 0.06 to 0.18 percent of Ti, 0.06 to 0.18 percent of V, less than or equal to 0.005 percent of N, 0.25 to 0.32 percent of Cr and the balance of Fe and inevitable impurities. The preparation method comprises the following steps: casting molten steel to obtain a plate blank, reheating the plate blank, sequentially carrying out rough rolling, finish rolling, cooling and curling, and tempering at 590-610 DEG C after curling to obtain a product, wherein the secondary heating and tapping temperature ranges from 1200 DEG C to 1250 DEG C, and the heating time ranges from 90 min to 120 min. The composition design is reasonable, the process is simple and controllable, the product performance is excellent, and industrial application is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of iron and steel production and manufacturing, and particularly to a titanium-vanadium complex microalloyed low-carbon high-strength steel and a preparation method thereof. Background Art

[0002] In order to achieve the lightweight of equipment such as automobiles, high-strength steel has been more and more widely used. Microalloyed steel refers to a type of steel in which a small amount of strong carbide-forming elements such as Ti, V, and Nb are added to the steel to favorably improve the properties of the steel. Commonly used microalloying elements include V, Nb, Ti, etc. Adding them alone or in combination can form relatively stable nitrides, carbides or carbonitrides in the steel. These precipitates will simultaneously play a role in the fine grain strengthening, dislocation strengthening and second-phase strengthening of the steel. At present, Ti microalloying technology is generally used in industrial production of high-strength steel. Ti is easy to combine with C and N atoms to form TiN and TiC. The precipitation strengthening effect of TiC is the largest. TiC particles can prevent the growth of austenite during hot working and welding, thereby reducing the austenite grain size. However, Ti microalloying also has obvious deficiencies. For example, Ti is easy to combine with [O], [N], and [S] in the steel at high temperature to form large inclusions. These inclusions can neither play a role in refining grains nor play a precipitation strengthening role, resulting in a low utilization rate of Ti; the precipitation of TiC is highly sensitive to temperature, which easily causes fluctuations in the performance of the steel plate. The element with the highest solubility in steel is V, which is also one of the most effective precipitation strengthening elements in microalloyed steel. V is a strong carbide-forming element. V(C,N) formed by V and carbon and nitrogen exists inside the grain matrix and at the grain boundaries, which can not only inhibit grain growth but also have a precipitation strengthening effect. The solubility of V carbide is significantly higher than that of nitride, and its solubility in ferrite drops significantly. V precipitates in a large amount in the ferrite temperature range, and the precipitation strengthening effect is obvious. Adding 0.10wt% of V to the steel can increase the strength by more than 200MPa. The addition of V mainly plays a precipitation strengthening effect, and the fine grain strengthening effect is weak. It is difficult to achieve the ideal effect by adding V alone. It can be seen from this that single-element microalloying has its own advantages and disadvantages. Using the composite microalloying technology can effectively make up for the disadvantages of the two elements, and the performance stability of the product will be greatly improved compared with the performance stability of the product with Ti added alone.

[0003] Patent CN103911552B discloses a vanadium-titanium microalloyed hot-rolled low-carbon bainitic steel strip and a production method thereof. This method does not require Nb microalloying, and adopts low-carbon, vanadium + titanium microalloying, which greatly reduces the cost. In its chemical composition, the C content is 0.10%-0.20%, the Ti content is 0.035%-0.050%, the V content is 0.06%-0.10%, and the tensile strength of the obtained product is about 700MPa.

[0004] Patent CN105624382A discloses a hot rolling method for V and Ti microalloyed steel, which includes the following steps: casting slab - heating - descaling with high-pressure water - rough rolling - coiling in a hot coil box - finish rolling - cooling - coiling. Its heating furnace outlet temperature is 1150°C to 1200°C, the finish rolling starting temperature is 900 to 950°C, and the finishing temperature is 800°C to 850°C. The strength of the obtained product is only 450 to 480 MPa. Patent CN104213024A discloses an extra-low carbon high-strength steel produced by bell-type annealing and its production method. It uses Ti alloying to remove interstitial atoms in the steel. In its chemical composition, C ≤ 0.0050%, and the addition amount of Ti is: Ti = 3.42N + 4C + 1.5S + (0.02 to 0.04). The yield strength of the obtained product is above 180 MPa. Summary of the Invention

[0005] In order to further improve the mechanical properties of microalloyed high-strength steel, the present invention provides a Ti-V microalloyed low-carbon high-strength steel and its preparation method.

[0006] The present invention discloses a low-carbon high-strength steel without rare earth.

[0007] To achieve the above object, on the one hand, the present invention provides a titanium-vanadium composite microalloyed low-carbon high-strength steel. Based on the total mass of the titanium-vanadium microalloyed low-carbon high-strength steel, the mass fractions of its chemical components are: C: 0.05 to 0.09%, Si: 0.10 to 0.25%, Mn: 1.85 to 2.2%, P: ≤ 0.01%, S ≤ 0.01%, Ti: 0.06 to 0.18%, V: 0.06 to 0.18%, N: ≤ 0.005%, Cr: 0.25 to 0.32%, and the balance is Fe and unavoidable impurities. The titanium-vanadium microalloyed low-carbon high-strength steel is a tempered product obtained after hot rolling, coiling and tempering at 590 to 610°C.

[0008] Preferably, the mass fractions of the chemical components of a titanium-vanadium composite microalloyed low-carbon high-strength steel are: C: 0.05 to 0.07%, Si: 0.13 to 0.22%, Mn: 1.85 to 2.0%, P: ≤ 0.008%, S ≤ 0.005%, Ti: 0.07 to 0.14%, V: 0.07 to 0.14%, N: ≤ 0.004%, Cr: 0.27 to 0.30%, and the balance is Fe and unavoidable impurities.

[0009] Further preferably, the mass fractions of the chemical components of the above-mentioned titanium-vanadium complex microalloyed low-carbon high-strength steel are as follows: C: 0.065 - 0.07%, Si: 0.13 - 0.14%, Mn: 1.9 - 1.95%, P: ≤0.007%, S ≤0.0035%, Ti: 0.07 - 0.08%, V: 0.07 - 0.075%, N: ≤0.0036%, Cr: 0.27 - 0.28%, and the balance is iron and inevitable impurities. Under this group, combined with the rolling, coiling and tempering processes of the present invention, the strength of the product can be much higher than that in the rolled state and the elongation can also be slightly enhanced.

[0010] On the other hand, the present invention also provides a preparation method of titanium-vanadium complex microalloyed low-carbon high-strength steel. The method includes: casting molten steel to obtain a slab, reheating the slab again, and then successively performing rough rolling, finish rolling, cooling and coiling. After coiling is completed, tempering is carried out at 590 - 610°C to obtain the product. Among them, in the above production method of titanium-vanadium microalloyed high-strength steel, the reheating furnace outlet temperature is 1200°C - 1250°C, and the heating time is 90 - 120 min.

[0011] Among them, in the preparation method of the above-mentioned titanium-vanadium complex microalloyed low-carbon high-strength steel, the finish rolling start rolling temperature is 1050°C - 1100°C, the finish rolling end rolling temperature is 800°C - 850°C, and the total reduction is 80 - 85%.

[0012] Among them, in the production method of the above-mentioned titanium-vanadium complex microalloyed low-carbon high-strength steel, the coiling temperature is 600 - 650°C.

[0013] After coiling is completed, it is cooled to room temperature, and then heated to 595 - 605°C and tempered for 25 - 35 min.

[0014] In the present invention, when the mass fractions of the chemical components of the titanium-vanadium complex microalloyed low-carbon high-strength steel are: C: 0.07%, Si: 0.13%, Mn: 1.9%, P: ≤0.0066%, S ≤0.0033%, Ti: 0.075%, V: 0.073%, N: ≤0.0036%, Cr: 0.27%, and the balance is iron. After obtaining the casting blank, the casting blank is heated to 1250°C, and 5 passes of rough rolling are carried out. The rough rolling end rolling temperature is 1050°C, and then 7 passes of finish rolling are carried out. The finish rolling end rolling temperature is 845°C; after finish rolling, it undergoes laminar flow cooling and coiling. The coiling temperature is 573°C, and finally a hot-rolled sheet with a thickness of 6.40 mm is obtained; the total reduction ratio is 80%; the hot-rolled sheet is cooled to room temperature, and then heated to 600°C at a rate of 10°C / min and held for 30 min for tempering to obtain a tempered product; the maximum tensile strength of the tempered product is 960 MPa, the yield strength is 901 MPa, and the elongation is 12.5%.

[0015] In the present invention, appropriate amounts of Ti and V can inhibit the growth of austenite grains by forming carbides (such as TiC and VC) or nitrides (such as TiN and VN), and play a significant role in grain refinement during the hot deformation process. The carbides and nitrides of Ti and V will precipitate in the form of dispersed phases, hindering the movement of dislocations, thereby producing a precipitation strengthening effect and improving the strength of the steel.

[0016] For the low-carbon high-strength steel obtained by the technology developed in the present invention, its yield strength is far superior to that of existing products.

[0017] The advantages and beneficial effects of the present invention are:

[0018] The composition design of the present invention adopts low carbon and Ti-V complex microalloying, as well as the addition of appropriate components such as Si, Mn, and Cr. Through the combined strengthening effect of Ti and V, without the need for rare earths, and in combination with an appropriate preparation process, the mechanical properties of the microalloyed steel are greatly improved. In the present invention, by reasonably formulating the rolling process, controlling the precipitation of the carbonitrides of Ti and V, and refining the size of the matrix structure, the microalloyed steel has high strength properties. Then, tempering is carried out at 590-610 °C, which greatly increases the precipitation amount of the carbonitrides of Ti and V in the Ti-V complex microalloyed high-strength steel, thereby further improving the strength of the product. Brief Description of the Drawings

[0019] Figure 1 It is the microstructure diagram of the hot-rolled sheet obtained in Example 1 before tempering; Figure 2 It is the microstructure diagram of the hot-rolled sheet obtained in Example 2 before tempering; Figure 3 It is the microstructure diagram of the hot-rolled sheet obtained in Example 3 before tempering; Figure 4 It is the microstructure diagram of the hot-rolled sheet obtained in Comparative Example 1 before tempering; Figure 5 It is the microstructure diagram of the hot-rolled sheet obtained in Comparative Example 2 before tempering; Figure 6 It is the microstructure diagram at a tempering temperature of 600 °C in Example 3; Detailed Description of the Invention

[0020] Example 1

[0021] This embodiment provides a Ti-V microalloyed low-carbon hot-rolled high-strength steel and its preparation method. The specific steps of the preparation method of the high-strength steel are as follows: After desulfurizing the blast furnace hot metal, it is poured into a 150t converter for smelting, then refined by a 150t LF furnace, and cast into slabs by continuous casting. The mass fractions of the chemical components of the cast slabs are: C: 0.07%, Si: 0.18%, Mn: 1.90%, P: ≤0.007%, S ≤0.0030%, Ti: 0.088%, V: 0.13%, N: ≤0.0037%, Cr: 0.30%.

[0022] The cast slabs are heated to 1250°C and subjected to 5 passes of rough rolling. The final rolling temperature of the rough rolling is 1053°C, and then 7 passes of finish rolling are carried out. The final rolling temperature of the finish rolling is 852°C. After finish rolling, laminar cooling and coiling are carried out, and the coiling temperature is 570°C, and finally a hot-rolled sheet with a thickness of 6.1 mm is obtained. The total reduction ratio is 83%.

[0023] Properties of the hot-rolled sheet: The tensile strength is 771 MPa, the yield strength is 517 MPa, and the elongation is 15%.

[0024] The hot-rolled sheet is cooled to room temperature, then heated to 600°C at a rate of 10°C / min and held for 30 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 927 MPa, the yield strength is 841 MPa, and the elongation is 11.5%.

[0025] Example 2

[0026] This embodiment provides a Ti-V microalloyed low-carbon hot-rolled high-strength steel and its preparation method. The specific steps of the preparation method of the high-strength steel are as follows: After desulfurizing the blast furnace hot metal, it is poured into a 150t converter for smelting, then refined by a 150t LF furnace, and cast into slabs by continuous casting. The mass fractions of the chemical components of the cast slabs are: C: 0.05%, Si: 0.22%, Mn: 2.0%, P: ≤0.007%, S ≤0.0032%, Ti: 0.075%, V: 0.073%, N: ≤0.0030%, Cr: 0.27%.

[0027] The cast slabs are heated to 1250°C and subjected to 5 passes of rough rolling. The final rolling temperature of the rough rolling is 1048°C, and then 7 passes of finish rolling are carried out. The final rolling temperature of the finish rolling is 848°C. After finish rolling, laminar cooling and coiling are carried out, and the coiling temperature is 568°C, and finally a hot-rolled sheet with a thickness of 6.30 mm is obtained. The total reduction ratio is 81%.

[0028] Properties of the hot-rolled sheet: The tensile strength is 721 MPa, the yield strength is 501 MPa, and the elongation is 14%.

[0029] The hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 30 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 890 MPa, the yield strength is 811 MPa, and the elongation is 11.3%.

[0030] Example 3

[0031] This example provides a Ti-V microalloyed low-carbon hot-rolled high-strength steel and its preparation method. The specific steps of the preparation method of the high-strength steel are as follows: The blast furnace hot metal is desulfurized and then poured into a 150 t converter for smelting, then refined by a 150 t LF furnace, and cast into slabs by continuous casting. The mass fractions of the chemical components of the cast slabs are: C: 0.07%, Si: 0.13%, Mn: 1.9%, P: ≤0.0066%, S ≤0.0033%, Ti: 0.13%, V: 0.073%, N: ≤0.0036%, Cr: 0.27%, and the balance is iron.

[0032] The cast slabs are heated to 1250 °C, subjected to 5 passes of rough rolling, the rough rolling finishing temperature is 1050 °C, then subjected to 7 passes of finish rolling, and the finish rolling finishing temperature is 845 °C. After finish rolling, laminar cooling and coiling are carried out, the coiling temperature is 573 °C, and finally a hot-rolled plate with a thickness of 6.40 mm is obtained. The total reduction ratio is 80%.

[0033] Properties of the hot-rolled plate: The tensile strength is 781 MPa, the yield strength is 617 MPa, and the elongation is 16%.

[0034] The hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 30 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 960 MPa, the yield strength is 901 MPa, and the elongation is 12.5%.

[0035] Example 4

[0036] Other conditions are the same as those in Example 3, the difference is that: the tempering temperature is 590 °C, the maximum tensile strength of the tempered product is 939 MPa, the yield strength is 875 MPa, and the elongation is 13.1%.

[0037] Example 5

[0038] Other conditions are the same as those in Example 3, the difference is that: the tempering temperature is 610 °C, the maximum tensile strength of the tempered product is 913 MPa, the yield strength is 844 MPa, and the elongation is 13.5%.

[0039] Example 6

[0040] Other conditions are the same as those in Example 3, except that: the hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 15 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 914 MPa, the yield strength is 894 MPa, and the elongation is 13.7%.

[0041] Example 7

[0042] Other conditions are the same as those in Example 3, except that: the hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 45 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 927 MPa, the yield strength is 889 MPa, and the elongation is 13.8%.

[0043] Example 8

[0044] Other conditions are the same as those in Example 3, except that: the hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 60 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 890 MPa, the yield strength is 811 MPa, and the elongation is 14.5%.

[0045] Comparative Example 1

[0046] This example presents a Ti-V microalloyed low-carbon hot-rolled high-strength steel and its preparation method. The specific steps of the preparation method of the high-strength steel are as follows: After desulfurizing the blast furnace hot metal, it is poured into a 150 t converter for smelting, then refined by a 150 t LF furnace, and cast into slabs by continuous casting. The mass fractions of the chemical components of the cast slabs are: C: 0.06%, Si: 0.11%, Mn: 1.9%, P: ≤0.0069%, S ≤0.0036%, Ti: 0.059%, N: ≤0.0035%, Cr: 0.27%.

[0047] The cast slabs are heated to 1250 °C, subjected to 5 passes of rough rolling, the rough rolling finishing temperature is 1047 °C, then subjected to 7 passes of finish rolling, and the finish rolling finishing temperature is 847 °C. After finish rolling, it undergoes laminar cooling and coiling, and the coiling temperature is 578 °C, finally obtaining a hot-rolled plate with a thickness of 6.30 mm. The total reduction ratio is 80%.

[0048] Properties of the hot-rolled plate: The tensile strength is 620 MPa, the yield strength is 436 MPa, and the elongation is 19%.

[0049] The hot-rolled plate is cooled to room temperature, then heated to 600 °C at a rate of 10 °C / min and held for 30 min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 781 MPa, the yield strength is 615 MPa, and the elongation is 16%.

[0050] Comparative Example 2

[0051] This example provides a Ti-V microalloyed low-carbon hot-rolled high-strength steel and its preparation method. The specific steps of the preparation method of the high-strength steel are as follows: After desulfurization treatment of blast furnace hot metal, it is poured into a 150t converter for smelting, then refined by a 150t LF furnace, and cast into slabs by continuous casting. The mass fractions of the chemical components of the cast slabs are: C: 0.06%, Si: 0.12%, Mn: 1.84%, P: ≤0.0076%, S ≤0.0031%, V: 0.076%, N: ≤0.0035%, Cr: 0.27%.

[0052] The cast slabs are heated to 1250°C, rough rolled in 5 passes, the rough rolling finishing temperature is 1045°C, then finish rolled in 7 passes, and the finish rolling finishing temperature is 844°C. After finish rolling, it undergoes laminar cooling and coiling, and the coiling temperature is 565°C, finally obtaining a 6.0mm thick hot-rolled plate. The total reduction ratio is 83%.

[0053] Properties of the hot-rolled plate: The tensile strength is 516MPa, the yield strength is 318MPa, and the elongation is 28%.

[0054] The hot-rolled plate is cooled to room temperature, then heated to 550°C at a rate of 10°C / min and held for 30min for tempering to obtain a tempered product. The maximum tensile strength of the tempered product is 704MPa, the yield strength is 527MPa, and the elongation is 18%.

[0055] Comparative Example 3

[0056] Other conditions are the same as those in Example 3, the difference is that: the tempering temperature is 700°C; the maximum tensile strength of the tempered product is 878MPa, the yield strength is 802MPa, and the elongation is 14.1%.

Claims

1. A titanium-vanadium complex microalloyed low-carbon high-strength steel, characterized in that, The mass fractions of the chemical components contained in the titanium-vanadium complex microalloyed low-carbon high-strength steel are as follows: C: 0.05 - 0.09%, Si: 0.10 - 0.25%, Mn: 1.85 - 2.2%, P: ≤0.01%, S ≤0.01%, Ti: 0.06 - 0.18%, V: 0.06 - 0.18%, N: ≤0.005%, Cr: 0.25 - 0.32%, and the balance is Fe and inevitable impurities. The titanium-vanadium microalloyed low-carbon high-strength steel is a tempered product obtained by hot rolling, coiling and then tempering at 590 - 610°C.

2. The low-carbon high-strength steel with titanium-vanadium complex microalloying according to claim 1, wherein: The mass fractions of the chemical components of the titanium-vanadium complex microalloyed low-carbon high-strength steel are as follows: C: 0.05 - 0.07%, Si: 0.13 - 0.22%, Mn: 1.85 - 2.0%, P: ≤0.008%, S ≤0.005%, Ti: 0.07 - 0.14%, V: 0.07 - 0.14%, N: ≤0.004%, Cr: 0.27 - 0.30%, and the balance is Fe and inevitable impurities.

3. The titanium-vanadium complex microalloyed low-carbon high-strength steel according to claim 2, characterized in that: The mass fractions of the chemical components of the titanium-vanadium complex microalloyed low-carbon high-strength steel are as follows: C: 0.065 - 0.07%, Si: 0.13 - 0.14%, Mn: 1.9 - 1.95%, P: ≤0.007%, S ≤0.0035%, Ti: 0.07 - 0.08%, V: 0.07 - 0.075%, N: ≤0.0036%, Cr: 0.27 - 0.28%, and the balance is iron and inevitable impurities.

4. A preparation method of the titanium-vanadium microalloyed low-carbon high-strength steel according to any one of claims 1-3; characterized in that: The molten steel is cast into a slab, the slab is reheated, and then rough rolling, finish rolling, cooling and coiling are carried out in sequence. After coiling is completed, it is tempered at 590 - 610°C to obtain the product; among them, the reheat furnace outlet temperature is 1200°C - 1250°C, and the heating time is 90 - 120 min.

5. The preparation method of a titanium-vanadium complex microalloyed low-carbon high-strength steel according to claim 4, characterized in that: The finish rolling start rolling temperature is 1050°C - 1100°C, the finish rolling temperature is 800°C - 850°C, and the total reduction is 80 - 85%.

6. The preparation method of a titanium-vanadium complex microalloyed low-carbon high-strength steel according to claim 4, characterized in that: The coiling temperature is 600 - 650°C.

7. The preparation method of a titanium-vanadium complex microalloyed low-carbon high-strength steel according to claim 4, characterized in that: After coiling is completed, it is cooled to room temperature, and then heated to 595 - 605°C and tempered for 25 - 35 min.

8. The preparation method of a titanium-vanadium complex microalloyed low-carbon high-strength steel according to claim 4, characterized in that: When the mass fractions of the chemical components of the titanium-vanadium complex microalloyed low-carbon high-strength steel are as follows: C: 0.07%, Si: 0.13%, Mn: 1.9%, P: ≤0.0066%, S ≤0.0033%, Ti: 0.075%, V: 0.073%, N: ≤0.0036%, Cr: 0.27%, and the balance is iron. After obtaining the continuous casting billet, the continuous casting billet is heated to 1250°C, and undergoes 5 passes of rough rolling. The finishing temperature of the rough rolling is 1050°C, and then undergoes 7 passes of finish rolling. The finishing temperature of the finish rolling is 845°C; after finish rolling, it undergoes laminar cooling and coiling. The coiling temperature is 573°C, and finally a hot-rolled sheet with a thickness of 6.40 mm is obtained; the total reduction ratio is 80%; the hot-rolled sheet is cooled to room temperature, and then heated to 600°C at a rate of 10°C / min and held for 30 min for tempering to obtain a tempered product; the maximum tensile strength of the tempered product is 960 MPa, the yield strength is 901 MPa, and the elongation is 12.5%.

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