Ti microalloyed q355nh steel plate and preparation method thereof

Abstract

A Ti microalloyed Q355NH steel plate and its preparation method are disclosed, comprising the following components: C≤0.12%; Si: 0.20~0.35%; Mn: 1.0~1.2%; Ni≤0.30%; Cr: 0.40~0.60%; Cu: 0.25~0.35%; Ti≤0.03%; P≤0.02%; S≤0.01%. The beneficial effects of this invention are: by employing Ti microalloying technology, a trace amount of Ti is added to Q355NH steel, which combines with C and N to form fine titanium carbonitride particles, effectively refining the grains and producing a significant precipitation strengthening effect. Thus, while reducing the amount of microalloying elements such as Nb added, the strength, toughness, and weldability of the steel plate can still be guaranteed or even improved, reducing production costs. Simultaneously, these fine titanium carbonitride particles can pin grain boundaries, inhibiting grain coarsening in the weld heat-affected zone, further improving the weldability of the steel plate. Furthermore, the combination of this Ti microalloying technology with controlled rolling and controlled cooling processes can effectively refine and homogenize the microstructure of steel plates, significantly improving their comprehensive mechanical properties and atmospheric corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a Ti microalloyed Q355NH steel plate and its preparation method. Background Technology

[0002] Q355NH is a low-alloy high-strength weathering steel that is widely used in outdoor structures such as bridges, buildings, and towers due to its excellent resistance to atmospheric corrosion. Its corrosion resistance mainly comes from alloying elements such as Cu, Cr, and Ni added to the steel. These elements promote the formation of a dense and stable protective rust layer on the steel surface, thus providing long-term protection for the structure.

[0003] To improve the mechanical properties of Q355NH, patent CN117344221A (A Low-Cost, High-Toughness Q355NH Hot-Rolled Steel Strip and Its Preparation Method) proposes a process combining Nb microalloying with "thermomechanical rolling + laminar flow cooling". This process can produce hot-rolled steel strips with a yield strength ≥355MPa, tensile strength ≥490MPa, and elongation after fracture ≥25%. However, the addition of Nb microalloying elements increases costs.

[0004] To reduce reliance on Nb microalloying elements, this invention employs Ti, a lower-cost element, for microalloying. Ti has a strong affinity for N and C, and theoretically, its strength can be improved through grain refinement and precipitation strengthening. However, Ti is chemically reactive and readily reacts with O and N during smelting to form coarse inclusions, resulting in low and unstable Ti yields, severely impacting the consistency of mechanical properties. Furthermore, coarse inclusions can fracture the matrix, deteriorate low-temperature toughness, and affect the surface quality of the steel plate. Existing processes lack precise control over the entire process, further limiting the effectiveness of Ti microalloying. Therefore, existing Ti microalloying technologies often face problems such as large performance fluctuations, poor strength-toughness matching, and low yield in practical applications, making it difficult to achieve significant cost optimization while ensuring overall performance, thus hindering their large-scale application.

[0005] Therefore, developing a new method that can stably prepare high-performance Ti microalloyed Q355NH steel plates by synergistic matching of composition design and process flow has become a technical challenge that the industry urgently needs to overcome. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings and defects of the existing technology by providing a Ti microalloyed Q355NH steel plate and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a Ti microalloyed Q355NH steel plate and its preparation method, comprising the following components: C≤0.12%; Si: 0.20~0.35%; Mn: 1.0~1.2%; Ni≤0.30%; Cr: 0.40~0.60%; Cu: 0.25~0.35%; Ti≤0.03%; P≤0.02%; S≤0.01%; the remainder being Fe and unavoidable impurities.

[0008] A Ti microalloyed Q355NH steel plate and its preparation method include the following steps: smelting, refining, and continuously casting C, Si, Mn, Ni, Cr, Cu, Ti, P, S, and Fe components in a converter; heating, rough rolling, and finish rolling the continuously cast billet; and controlling cooling, straightening, shearing, and finishing the rolled product.

[0009] Furthermore, the converter smelting process specifically includes: charging system: 89t of molten iron and 18t of pure scrap steel; deoxidation of steel: 5kg / t of aluminum-manganese steel.

[0010] Furthermore, the refining process specifically involves: the white slag stabilization time being ≥20 minutes, and obtaining the target slag system through slag formation control: CaO: 50~60%; Al2O3: 25~35%; SiO2≤10%; MgO: 6~8%; FeO+MnO≤1%; after the white slag stabilizes, other alloys are first prepared, and then titanium is prepared using ferrotitanium, and stirred for 1~2 minutes after titanium preparation.

[0011] Furthermore, the continuous casting process specifically includes: a liquidus temperature of 1513℃, a tundish start-up temperature of 1585±5℃; a continuous casting furnace temperature of 1565±5℃; a start-up superheat target of 30-45℃, a tundish superheat target of 26±6℃, protective casting, the use of slab-bound steel protective slag, an argon flushing pressure of 0.1~0.2 MPa for more than 2 minutes, the addition of heat-insulating covering agent, and a casting speed controlled at 0.90~1.15 m / min.

[0012] Furthermore, the heating process specifically includes: a first heating stage with a temperature ≥950℃ and a target temperature of 1050℃; a second heating stage with a target temperature of 1180±20℃ and a homogenization temperature of 1200±20℃; and heating control to ensure that the temperature after high-pressure water descaling is ≥1080℃, ensuring that the billet is thoroughly heated, the temperature is uniform, and the temperature difference between points is <30℃.

[0013] Furthermore, in the roughing process, specifically: before roughing, the billet needs to undergo 1-2 descaling processes to ensure descaling quality; during roughing, descaling is performed 3-4 times, and descaling must be thorough. When the steel temperature is high or the surface quality of the steel plate is poor, one additional descaling can be performed. During the roughing stage, the rolling mill capacity should be fully utilized to increase the reduction per pass. For steel plates with a finished thickness ≤70mm, a reduction rate of ≥20% must be ensured for 2 or more passes. The initial rolling temperature for roughing is 1040~1150℃, and the target temperature is 1070℃.

[0014] Furthermore, in the finishing rolling process: depending on the thickness of the finished product, the initial rolling temperature is 790~930℃, and the final rolling temperature is 780~850℃.

[0015] Furthermore, the relevant processes of controlled cooling, straightening, and shearing are as follows: In the controlled cooling process: steel plates with a finished thickness ≥ 8 mm adopt controlled cooling technology, and are quickly sent to the controlled cooling zone for controlled cooling after rolling. The appropriate number of controlled cooling manifolds to be opened is selected according to the final rolling temperature, and the red-hot temperature is 600~670℃; In the straightening process: for steel plates with a finished thickness < 16 mm, the reduction is controlled at 3.2±0.5 mm; for steel plates with a finished thickness < 16 mm and < 30 mm, the reduction is controlled at 3±0.5 mm; for steel plates with a finished thickness ≥ 30 mm, the reduction is controlled at 2.7±0.5 mm; In the shearing process: for steel plates with a thickness < 20 mm, the shearing temperature is less than 200℃; for steel plates with a thickness ≤ 26 mm, online shearing and sampling are performed; for steel plates with a thickness > 26 mm, the plates are removed from the line and enter the intermediate warehouse, where they are manually flame-cut and sampled.

[0016] The beneficial effects of this invention after adopting the above technical solution are as follows: By using Ti microalloying technology, a trace amount of Ti is added to Q355NH steel, which combines with C and N to form fine titanium carbonitride (TiC, TiN) particles. This effectively refines the grains and produces a significant precipitation strengthening effect. Thus, even with reduced addition of microalloying elements such as Nb, the strength, toughness, and weldability of the steel plate can still be guaranteed or even improved, reducing production costs. Simultaneously, these fine titanium carbonitride (TiC, TiN) particles can pin grain boundaries, inhibiting grain coarsening in the weld heat-affected zone, further improving the weldability of the steel plate. Furthermore, the combination of this Ti microalloying technology with controlled rolling and controlled cooling processes can effectively refine and homogenize the microstructure of the steel plate, significantly improving its comprehensive mechanical properties (such as strength, toughness, and plasticity) and atmospheric corrosion resistance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a metallographic microstructure diagram of Example 1 in this invention.

[0019] Figure 2 This is a metallographic microstructure diagram of Example 2 in this invention.

[0020] Figure 3 The tensile properties of the experimental steels in Examples 1 and 2 of this invention are shown in the diagram. Detailed Implementation

[0021] The technical solution adopted in this specific embodiment is: a Ti microalloyed Q355NH steel plate and its preparation method, which includes the following components by mass percentage: C≤0.12%; Si: 0.20~0.35%; Mn: 1.0~1.2%; Ni≤0.30%; Cr: 0.40~0.60%; Cu: 0.25~0.35%; Ti≤0.03%; P≤0.02%; S≤0.01%; the remainder is Fe and unavoidable impurities.

[0022] A Ti microalloyed Q355NH steel plate and its preparation method, comprising the following steps: S1. The components C, Si, Mn, Ni, Cr, Cu, Ti, P, S, and Fe are smelted, refined, and continuously cast in a converter. In the converter smelting process, the charging regime is: 89t of molten iron and 18t of pure scrap steel; the deoxidation at tapping is: 5kg / t of aluminum-manganese.

[0023] In the refining process, the white slag stabilization time is ≥20 minutes. The target slag system is obtained by controlling the slag formation: CaO: 50~60%; Al2O3: 25~35%; SiO2≤10%; MgO: 6~8%; (FeO+MnO)≤1%. After the white slag stabilizes, other alloys are prepared first, and then titanium is prepared by ferrotitanium. After preparing titanium, the mixture is stirred for 1~2 minutes.

[0024] In the continuous casting process, the liquidus temperature is 1513℃, the tundish start-up temperature is 1585±5℃, the continuous casting furnace temperature is 1565±5℃, the start-up superheat target is 30-45℃, the tundish superheat target is 26±6℃, protective casting is adopted, slab peritectic steel protective slag is used, the tundish argon flushing pressure is between 0.1~0.2Mpa, the time is greater than 2 minutes, heat preservation covering agent is added, and the casting speed is controlled between 0.90~1.15m / min.

[0025] S2. The continuously cast billet is heated, rough rolled, and finish rolled. The first heating stage has a temperature ≥950℃, with a target of 1050℃; the second heating stage has a target temperature of 1180±20℃, and a soaking temperature of 1200±20℃; the heating is controlled to ensure that the temperature after high-pressure water descaling is ≥1080℃, ensuring that the billet is thoroughly heated, the temperature is uniform, and the temperature difference between all points is <30℃.

[0026] In the roughing process, specifically: before roughing, the billet needs to undergo 1-2 descaling processes to ensure the quality of descaling; during the roughing process, descaling is performed 3-4 times, and the descaling must be thorough. When the steel temperature is high or the surface quality of the steel plate is poor, an additional descaling can be performed. During the roughing stage, the rolling mill capacity should be fully utilized to increase the reduction per pass. For steel plates with a finished thickness ≤70mm, at least 2 passes with a reduction rate ≥20% are required. The initial rolling temperature for roughing is 1040~1150℃, and the target temperature is 1070℃.

[0027] In the finishing rolling process: depending on the thickness of the finished product, the initial rolling temperature is 790~930℃, and the final rolling temperature is 780~850℃.

[0028] S3. The rolled finished product undergoes controlled cooling, straightening, shearing, and finishing. In the controlled cooling process: steel plates with a thickness ≥ 8mm are processed using controlled cooling technology. After rolling, the plates are quickly sent to the controlled cooling zone for controlled cooling. The appropriate number of controlled cooling manifolds is selected based on the final rolling temperature, and the reheat temperature is 600~670℃.

[0029] In the straightening process: for steel plates with a finished thickness < 16mm, the reduction amount is controlled at 3.2±0.5mm; for steel plates with a finished thickness < 16mm and < 30mm, the reduction amount is controlled at 3±0.5mm; for steel plates with a finished thickness ≥ 30mm, the reduction amount is controlled at 2.7±0.5mm. In the shearing process: steel plates with a thickness of <20mm are sheared at a temperature of less than 200℃; steel plates with a thickness of ≤26mm are sheared and sampled online; steel plates with a thickness of >26mm are removed from the line and sent to the intermediate warehouse, where they are manually flame-cut and sampled.

[0030] The following are relevant embodiments of the present invention. Example 1

[0031] See Figure 1 and Figure 3 As shown, the Ti microalloyed Q355NH steel plate provided in this embodiment has a finished thickness of 12mm. Its chemical composition by mass percentage is as follows: C: 0.12%; Si: 0.25%; Mn: 1.1%; Ni: 0.09%; Cr: 0.45%; Cu: 0.27%; Ti: 0.017%; P: 0.019%; S: 0.004%; the remainder being Fe and unavoidable impurities. The specific manufacturing steps are as follows: (1) After the Q355NH steel plate is smelted, refined and continuously cast according to the composition as described above, a continuously cast billet with a thickness of 220mm is obtained. (2) The continuously cast billet is heated, rough rolled and finished rolled: In the heating process, the first heating temperature is 1025℃, the second heating temperature is 1190℃, and the soaking temperature is 1200℃. In the rough rolling process, the rough rolling start temperature is 1100℃; in the finish rolling process, the finish rolling start temperature is 915℃ and the finish rolling temperature is 796℃.

[0032] (3) Control the cooling of the rolled finished product: the reddening temperature is 625℃.

[0033] (4) The steel plate after controlled cooling is straightened, sheared and finished to finally obtain Ti microalloyed Q355NH steel plate with a yield strength of 399MPa, a tensile strength of 499MPa and an elongation of 32%. Example 2

[0034] See Figure 2 and Figure 3 As shown, the Ti microalloyed Q355NH steel plate provided in this embodiment has a finished thickness of 20mm. Its chemical composition by mass percentage is as follows: C: 0.12%; Si: 0.25%; Mn: 1.05%; Ni: 0.011%; Cr: 0.49%; Cu: 0.28%; Ti: 0.014%; P: 0.011%; S: 0.004%; the remainder being Fe and unavoidable impurities. The specific manufacturing steps are as follows: (1) After the Q355NH steel plate is smelted, refined and continuously cast according to the composition as described above, a continuously cast billet with a thickness of 220mm is obtained. (2) The continuously cast billet is heated, rough rolled and finished rolled: In the heating process, the first heating temperature is 1040℃, the second heating temperature is 1190℃, and the soaking temperature is 1200℃. In the rough rolling process, the rough rolling start temperature is 1085℃; in the finish rolling process, the finish rolling start temperature is 861℃ and the finish rolling temperature is 795℃.

[0035] (3) Control the cooling of the rolled finished product: the reddening temperature is 630℃.

[0036] (4) The steel plate after controlled cooling is straightened, sheared and finished to finally obtain Ti microalloyed Q355NH steel plate with a yield strength of 378MPa, a tensile strength of 490MPa and an elongation of 33%.

[0037] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solution of the present invention, as long as they do not depart from the spirit and scope of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A Ti microalloyed Q355NH steel plate, characterized in that: It includes the following components: C≤0.12%; Si: 0.20~0.35%; Mn: 1.0~1.2%; Ni≤0.30%; Cr: 0.40~0.60%; Cu: 0.25~0.35%; Ti≤0.03%; P≤0.02%; S≤0.01%; the remainder is Fe and unavoidable impurities.

2. A Ti microalloyed Q355NH steel plate and its preparation method, comprising the following steps: S1. The components C, Si, Mn, Ni, Cr, Cu, Ti, P, S, and Fe are smelted, refined, and continuously cast in a converter. S2. The continuously cast billet is heated, rough rolled, and finish rolled; S3. Controlled cooling, straightening, shearing and finishing of the rolled finished product.

3. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: The converter smelting process in step S1 is specifically as follows: Loading procedure: 89t molten iron, 18t pure scrap steel; Deoxidation at tapping: 5kg / t of aluminum-manganese steel.

4. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: The refining process in step S1 specifically includes: The white slag stabilization time is ≥20 minutes. The target slag system is obtained through slag formation control: CaO: 50~60%; Al2O3: 25~35%; SiO2≤10%; MgO: 6~8%; FeO+MnO≤1%. After the white slag stabilizes, other alloys are prepared first, and then titanium is prepared by titanium-iron alloy. After preparing titanium, the mixture is stirred for 1~2 minutes.

5. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: The continuous casting process in step S1 specifically includes: The liquidus temperature is 1513℃, and the tundish start-up temperature is 1585±5℃; continuous casting furnace: 1565±5℃; the target superheat at start-up is 30-45℃, and the target superheat in the tundish is 26±6℃. Protective casting is adopted, using slab-bound crystallizing steel protective slag. The argon flushing pressure in the tundish is between 0.1 and 0.2 MPa, and the time is greater than 2 minutes. Insulating covering agent is added, and the casting speed is controlled between 0.90 and 1.15 m / min.

6. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: The heating process in step S2 specifically includes: The first heating stage has a temperature of ≥950℃, with a target of 1050℃; the second heating stage has a target temperature of 1180±20℃, and a target temperature of 1200±20℃ for heat homogenization; heating is controlled to ensure that the temperature after high-pressure water descaling is ≥1080℃, ensuring that the billet is thoroughly heated, the temperature is uniform, and the temperature difference between points is <30℃.

7. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: In step S2, the roughing process specifically includes: Before rough rolling, the billet needs to undergo 1-2 descaling processes to ensure descaling quality. During rough rolling, descaling is performed 3-4 times, and the descaling must be thorough. If the steel temperature is high or the surface quality of the steel plate is poor, an additional descaling process can be performed. During the rough rolling stage, the mill capacity should be fully utilized to increase the reduction per pass. For steel plates with a finished thickness ≤70mm, at least 2 passes with a reduction rate ≥20% are required. The initial rolling temperature for rough rolling is 1040~1150℃, and the target temperature is 1070℃.

8. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: In the finishing rolling process of step S2: depending on the thickness of the finished product, the initial rolling temperature is 790~930℃ and the final rolling temperature is 780~850℃.

9. The Ti microalloyed Q355NH steel plate and its preparation method according to claim 2, characterized in that: The relevant processes for controlled cooling, straightening, and shearing in step S3 are as follows: In the controlled cooling process: steel plates with a finished thickness of ≥8mm are subjected to controlled cooling process. After rolling, they are quickly sent to the controlled cooling zone for controlled cooling. The appropriate number of controlled cooling manifolds to be opened is selected according to the final rolling temperature. The red-hot temperature is 600~670℃. In the straightening process: for steel plates with a finished thickness < 16mm, the reduction amount is controlled at 3.2±0.5mm; for steel plates with a finished thickness < 16mm and < 30mm, the reduction amount is controlled at 3±0.5mm; for steel plates with a finished thickness ≥ 30mm, the reduction amount is controlled at 2.7±0.5mm. In the shearing process: steel plates with a thickness of <20mm are sheared at a temperature of less than 200℃; steel plates with a thickness of ≤26mm are sheared and sampled online; steel plates with a thickness of >26mm are removed from the line and sent to the intermediate warehouse, where they are manually flame-cut and sampled.

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