Production method of marine environment corrosion resistant deformed steel bar

Abstract

The invention belongs to the technical field of steel smelting, and relates to a production method of marine environment corrosion resistant deformed steel bar which comprises the following components: 0.04%-0.08% of C, 0.20%-0.40% of Si, 1.60%-2.00% of Mn, 7.0%-9.0% of Cr, 0.6%-2.0% of Mo, less than or equal to 0.030% of P, less than or equal to 0.030% of S, 0.03%-0.10% of V, 0.0080%-0.0150% of N, 0.02%-0.06% of Al and the balance of Fe and inevitable impurities. The corrosion resistance of the material is improved through high Cr and Mo elements, and a proper amount of Al and N are added to refine crystals. And the quality of a casting blank is ensured by reasonably optimizing the superheat degree, the pulling speed and tail end electromagnetic stirring parameters in the continuous casting process. And the structure is homogenized through a high-temperature diffusion process in the rolling process. And compared with common deformed steel bars with the same strength level, the corrosion resistance is improved by 80%.

Description

Technical Field

[0001] The present invention belongs to the technical field of steel smelting and relates to a production method of corrosion-resistant ribbed steel bars for marine environments. Background Art

[0002] Due to characteristics such as high salt spray, high humidity, and chloride ion enrichment in marine environments, metal materials are extremely corrosive. As a key structural material for marine engineering (such as cross-sea bridges, undersea tunnels, and offshore wind power platforms), ribbed steel bars are prone to local corrosion, pitting corrosion, and stress corrosion cracking when exposed to such environments for a long time. According to statistics, the economic losses caused by steel structure failure accidents due to marine corrosion worldwide reach up to hundreds of billions of US dollars annually. Traditional ribbed steel bars (such as HRB400, HRB500) mainly rely on carbon-manganese system design. Although the cost is relatively low, their corrosion resistance is seriously insufficient, and the annual corrosion rate in marine environments can reach 0.3 - 0.5 mm / a, resulting in a shortening of the structure life by more than 50%, and frequent maintenance causing huge waste of resources.

[0003] In the prior art, conventional means to improve the corrosion resistance of steel include: 1) single addition of Cr element (such as 12% Cr in stainless steel). Although a passivation film can be formed, when the Cr content exceeds 10%, the material cost increases significantly, and brittle σ phase is easily precipitated in high-Cr steel, leading to deterioration of processing performance; 2) surface treatment technologies such as epoxy coating or galvanizing, but the coating is easily damaged during transportation and construction, and the accelerated local corrosion instead increases the overall failure risk; 3) microalloying combined with controlled rolling process (such as addition of Cu, Ni). Although it has certain effects, the passivation film stability is insufficient in high Cl- environments, and the alloy cost is high. In addition, in traditional production processes, center segregation (C-class segregation ≥ 2.5 grades) is prone to occur in continuous casting billets, the structure after rolling is uneven, the grain size is only 6 - 7 grades, and the high hydrogen content ([H] ≥ 3 ppm) increases the hydrogen embrittlement sensitivity, further reducing the material reliability.

[0004] In recent years, domestic and foreign research has focused on the development of low-cost weathering steels, but most solutions still have bottlenecks. Therefore, there is an urgent need for a ribbed steel solution that takes into account the matching of corrosion resistance, strength and plasticity, and process feasibility to meet the requirements of long life and low maintenance of marine infrastructure. Summary of the Invention

[0005] To achieve the above object, the present invention provides a production method of corrosion-resistant ribbed steel bars for marine environments, which solves the problems existing in the prior art.

[0006] The technical solution adopted by the present invention is a production method of marine environment corrosion-resistant ribbed steel. The chemical composition of the steel by weight percentage is: C: 0.04% - 0.08%, Si: 0.20% - 0.40%, Mn: 1.60 - 2.00%, Cr: 7.0% - 9.0%, Mo: 0.6% - 2.0%, P ≤ 0.030%, S ≤ 0.030%, V: 0.03% - 0.10%, N: 0.0080% - 0.0150%, Al: 0.02% - 0.06%, and the rest is Fe and inevitable impurities; the key production steps include:

[0007] Step (1) Smelting: In the converter, the ratio of hot metal to scrap charged into the furnace is controlled at 6:4, and the target composition of the molten steel at the end is controlled: C ≤ 0.05%, P ≤ 0.025%. Slag tapping is prohibited. During the tapping process, part of Si, Mn, Cr, and V alloys are added.

[0008] Step (2) Refining: During the LF smelting process, part of Si, Mn, Cr, and V alloys are added. The added alloys are baked at a high temperature not lower than 600 degrees. The basicity of the refining slag is controlled at 6.0 - 8.0. Before the end of the LF furnace refining, aluminum wire is fed. After 6 minutes of soft blowing, nitrogen wire is fed. Before tapping, calcium wire is fed to perform calcium treatment on the molten steel, and then a covering agent is added to protect the molten steel. The RH is evacuated to below 67 Pa, and the vacuum is maintained for 15 minutes and then broken to determine the hydrogen content of the molten steel, and the hydrogen content is controlled ≤ 1.0 ppm. The RH is opened for circulating nitrogen addition. Before tapping, the soft blowing time is 25 - 35 minutes. Samples are taken for gas detection at 5 minutes of soft blowing, and nitrogen manganese wire is fed to adjust the nitrogen component according to the nitrogen content.

[0009] Step (3) Continuous casting: Weak cooling is adopted, the specific water volume is 0.20 - 0.25 L / KG, the target value of the superheat in the tundish is 15℃ - 25℃, the casting speed is 0.8 - 1.2 m / min, the current of the final electromagnetic stirring is 300 - 500 A, the frequency is 3 - 8 Hz. The continuous casting final soft reduction process is adopted. The size of the slab is 150*150*mm*12.0 m, and the slab is put into a slow cooling pit for slow cooling for 72 h.

[0010] Step (4) Rolling: The slab is subjected to high-temperature diffusion at 1200 - 1250℃ for 2 - 4 h. The steel billet is taken out of the furnace and descaled with high-pressure water. The descaling pressure is not less than 20 Mpa. The reduction ratio of the first pass and the second pass is greater than 60%. The rough rolling temperature is 950 - 1100℃, and the finish rolling temperature is 800 - 900℃.

[0011] Step (5) Slow cooling after rolling: After rolling, it is put on a cooling bed for slow cooling. The cooling bed is covered with a heat preservation cover. The cooling bed is closely arranged for slow cooling. After taking out of the cover, it is bundled and put into a slow cooling pit.

[0012] Step (6) Annealing: After the ribbed steel bars are put into the pit, they are annealed in a continuous annealing furnace within 24 hours, kept at 650 - 720°C for 2 - 3 hours, slowly cooled to 250°C and then taken out of the furnace for air cooling.

[0013] Further, in step (1), the scrap steel used for smelting is scrap steel containing Mo element, and ferromolybdenum alloy is added before converter smelting.

[0014] Further, in step (2), when refining, feeding aluminum wire adjusts the aluminum in the molten steel to 0.050% - 0.080%, and feeding nitrogen wire adjusts the N in the molten steel to 0.0090% - 0.0120%.

[0015] Further, in step (2), during continuous casting, the feeding amount of calcium wire for the first furnace is 180 meters, and the feeding amount for continuous casting furnaces is 150 meters.

[0016] Further, in step (3), during continuous casting, the reduction amount of light reduction at the end is 10 - 12 mm.

[0017] The beneficial effects of the present invention are as follows:

[0018] (1) A production method of ribbed steel bars resistant to marine environment corrosion provided by the present invention reduces the consumption of precious metal resources through composition optimization (the Cr content is reduced by 30% compared with traditional stainless steel), and no additional coating treatment is required in the whole process, reducing production energy consumption and environmental pollution.

[0019] (2) Through the collaborative design of multiple elements of Cr - Mo - Al - N, on the premise of controlling costs, a dense and self - repairing composite passivation film (mainly composed of Cr2O3, with MoO3 filling defects) is constructed, significantly inhibiting the penetration of Cl -, with the target that the salt spray corrosion rate ≤ 0.05 mm / a, which is more than 80% higher than that of ordinary ribbed steel bars.

[0020] (3) Utilizing the precipitation strengthening and fine - grain strengthening mechanisms of V and N, while ensuring that the yield strength ≥ 500 MPa, the elongation rate ≥ 15%, avoiding the brittleness problem caused by high alloying, and meeting the seismic and anti - impact requirements of ocean engineering.

[0021] (4) Through RH vacuum dehydrogenation ([H] ≤ 1.5 ppm) and electromagnetic stirring at the end of continuous casting (segregation index ≤ 1.2), the risk of hydrogen embrittlement is eliminated and the homogeneity of the billet is improved; by adopting high - temperature diffusion (1200 - 1250°C) and two - stage controlled rolling (rough rolling + finish rolling), the original as - cast structure is fully homogenized, and the final grain size ≥ 8 grades; an innovative annealing process (holding at 650 - 720°C) eliminates rolling stress and avoids excessive grain growth.

[0022] (5) The present invention provides a special marine engineering ribbed steel with low life-cycle cost, strong process adaptability (which can be realized by upgrading existing steel plant production lines), and comprehensive performance indicators superior to existing products, providing material guarantee for improving the durability of infrastructure. Detailed implementation manners

[0023] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] A production method of ribbed steel resistant to marine environment corrosion, which uses higher Cr and Mo elements to improve the corrosion resistance of the material, and adds appropriate amounts of Al and N to refine the crystal grains. In the smelting process, H removal control is strengthened, and in the continuous casting process, the quality of the cast billet is ensured by reasonably optimizing the superheat degree, drawing speed and end electromagnetic stirring parameters. In the rolling process, the structure is homogenized through a high-temperature diffusion process, and good finished product quality is obtained through a controlled rolling and controlled cooling process. Subsequently, the final product performance is achieved through an annealing process. The steel has good strength and plasticity, and has good corrosion resistance in the marine environment. The corrosion resistance is increased by 80% compared with ordinary ribbed steel of the same strength level.

[0025] The ribbed steel resistant to marine environment corrosion has the following components by weight percentage: C: 0.04% - 0.08%, Si: 0.20% - 0.40%, Mn: 1.60 - 2.00%, Cr: 7.0% - 9.0%, Mo: 0.6% - 2.0%, P≤0.030%, S≤0.030%, V: 0.03% - 0.10%, N: 0.0080% - 0.0150%, Al: 0.02% - 0.06%, and the rest are Fe and inevitable impurities.

[0026] The specific production process and technical parameters are as follows:

[0027] (1) Smelting: The ratio of hot metal to scrap steel charged into the converter is controlled at 6:4; the scrap steel used is scrap steel containing Mo element, and the Fe-Mo alloy is added before converter smelting. Control the target composition of the molten steel at the end point: C≤0.05%, P≤0.025%, slagging is prohibited, and part of Si, Mn, Cr, and V alloys are added during the tapping process.

[0028] (2) Refining: Add some alloys during the LF smelting process. Bake the added alloys at a high temperature, and the baking temperature is not lower than 600 °C. Control the basicity of the refining slag at 6.0 - 8.0. Feed aluminum wire before the end of the LF furnace refining to adjust the aluminum in the molten steel to 0.050% - 0.080%. Feed nitrogen wire 6 minutes after soft blowing for 6 minutes to adjust the N in the molten steel to 0.0090% - 0.0120%. Feed calcium wire for calcium treatment of the molten steel before tapping. The feeding amount of calcium wire for the first continuous casting furnace is 180 m, and the feeding amount for continuous casting furnaces is 150 m. Then add a covering agent to protect the molten steel. Vacuumize the RH to below 67 Pa, maintain the vacuum for 15 min, then break the vacuum to determine the hydrogen content in the molten steel, and control the hydrogen content ≤ 1.0 ppm. Turn on the circulation in the RH to increase nitrogen. The soft blowing time before tapping is 25 - 35 minutes. Take a sample for gas detection at the 5th minute of soft blowing, and adjust the nitrogen component by feeding nitrogen-manganese wire according to the nitrogen content.

[0029] (3) Continuous casting: Adopt weak cooling, with the specific water consumption of 0.20 - 0.25 L / KG, the target value of the tundish superheat of 15 °C - 25 °C, the casting speed of 0.8 - 1.2 m / min, the current of the final electromagnetic stirring of 300 - 500 A, and the frequency of 3 - 8 Hz. Adopt the final soft reduction process in continuous casting with a reduction amount of 10 - 12 mm. The size of the billet is 150 * 150 * mm * 12.0 m, and the billet is put into a slow cooling pit for slow cooling for 72 h.

[0030] (4) Rolling: The billet is subjected to high-temperature diffusion at 1200 - 1250 °C for 2 - 4 h. The steel billet is de-scaled by high-pressure water when it comes out of the furnace, and the de-scaling pressure is not less than 20 Mpa. The reduction rate of the first pass and the second pass is greater than 60%. The rough rolling temperature is 950 - 1100 °C, and water-cooling controlled rolling is carried out. The finish rolling temperature is 800 - 900 °C.

[0031] (5) Slow cooling after rolling: After rolling, put it on the cooling bed for slow cooling, and cover the cooling bed with a heat preservation cover. The cooling bed is closely arranged for slow cooling, and it is bundled and put into the slow cooling pit after coming out of the cover.

[0032] (6) Annealing: The deformed steel bars are put into a continuous annealing furnace for annealing within 24 hours after entering the pit, kept at 650 - 720 °C for 2 - 3 h, slowly cooled to 250 °C and then taken out of the furnace for air cooling.

[0033] Example 1

[0034] Production is carried out according to the technological processes such as converter - refining - continuous casting - rolling - annealing.

[0035] (1) The chemical composition of the corrosion-resistant deformed steel bars suitable for the marine environment obtained by smelting is shown in Table 1;

[0036] The rest is Fe and inevitable impurities;

[0037] (2) The C content at the end of the converter is 0.04%.

[0038] (3) The final basicity of the refining slag in the LF furnace is 6.9; the RH is kept under vacuum for 16 minutes, the RH soft blowing is 30 minutes, and the fixed H at tapping is 1.1 ppm.

[0039] (4) The secondary cooling water ratio in continuous casting is 0.20 L / KG, the superheat in the tundish is 24 °C, the casting speed is 1.0 m / min, the current of the electromagnetic stirring at the end is 350 A, and the frequency is 5 Hz; the light reduction at the end is 10 mm, and the cast slab is put into the slow cooling pit for slow cooling for 72 h.

[0040] (5) The temperature in the high-temperature section of the slab heating is controlled at 1220 °C, the time in the high-temperature section is 3 h, and the finishing rolling temperature is 900 °C.

[0041] (6) After rolling, a heat preservation cover is covered on the cooling bed. The cooling bed is closely arranged for slow cooling, and it is bundled and put into the slow cooling pit. After 20 hours of entering the pit, it enters the continuous annealing furnace for annealing, is kept at 700 °C for 3 h, and is slowly cooled to 250 °C and then taken out of the furnace for air cooling.

[0042] The mechanical properties and relative corrosion rates of the deformed steel bars prepared through the above embodiments are shown in Table 2.

[0043] Example 2

[0044] Production is carried out according to the technological processes such as converter - refining - continuous casting - rolling - annealing.

[0045] (1) The chemical composition of the corrosion-resistant deformed steel bars suitable for the marine environment obtained by smelting is shown in Table 1;

[0046] The rest is Fe and inevitable impurities;

[0047] (2) The C content at the end of the converter is 0.04%.

[0048] (3) The final basicity of the refining slag in the LF furnace is 6.6; the RH is kept under vacuum for 17 minutes, the RH soft blowing is 28 minutes, and the fixed H at tapping is 0.9 ppm.

[0049] (4) The secondary cooling water ratio in continuous casting is 0.20 L / KG, the superheat in the tundish is 23 °C, the casting speed is 1.0 m / min, the current of the electromagnetic stirring at the end is 350 A, and the frequency is 5 Hz; the light reduction at the end is 10 mm, and the cast slab is put into the slow cooling pit for slow cooling for 72 h.

[0050] (5) The temperature in the high-temperature section of the slab heating is controlled at 1230 °C, the time in the high-temperature section is 3 h, and the finishing rolling temperature is 890 °C.

[0051] (6) After rolling, a heat preservation cover is covered on the cooling bed. The cooling bed is closely arranged for slow cooling, and it is bundled and put into the slow cooling pit. After 22 hours of entering the pit, it enters the continuous annealing furnace for annealing, is kept at 700 °C for 3 h, and is slowly cooled to 250 °C and then taken out of the furnace for air cooling.

[0052] The mechanical properties and relative corrosion rates of the deformed steel bars prepared through the above embodiments are shown in Table 2.

[0053] Table 1 Chemical composition / %

[0054] Serial number Si Mn P S <![CDATA[Al T > Cr Mo V N C Example 1 0.25 1.95 0.021 0.005 0.035 7.45 0.90 0.05 0.0098 0.05 Example 2 0.24 1.90 0.018 0.006 0.032 7.58 0.88 0.05 0.0095 0.06

[0055] Corrosion resistance test method for corrosion-resistant ribbed steel bars:

[0056] The corrosion test of ribbed steel bars is carried out by salt spray test, referring to "GB / T 10125-2021 Artificial Atmosphere Corrosion Test Salt Spray Test". This test adopts an intermittent spray corrosion method, with a cycle period (1 day) of spraying for 4 hours and intermittent for 20 hours, and the corrosion test period is 21 days. The solution is 5% NaCl solution, with a pH value of 6.7 - 7.1 and a temperature of (35 ± 2) °C. After the corresponding corrosion time ends, the ribbed steel bars are taken out, placed in the natural condition to dry, the corrosion products on the surface of the ribbed steel bars are cleaned with an acid solution, rinsed with pure water until clean, and the rinsed ribbed steel bars are dried by blowing with high-pressure air. After rust removal and drying of the ribbed steel bars, they are weighed. The weight loss of the ordinary ribbed steel bars in the control group is 8.51 g, the weight loss of the ribbed steel bars in Example 1 is 1.56 g, and the weight loss of the ribbed steel bars in Example 2 is 1.62 g. The greater the weight loss, the more corrosion products there are, and the worse the corrosion resistance of the steel.

[0057] Table 2 Mechanical properties and relative corrosion rate of corrosion-resistant ribbed steel bars

[0058] Specimen number Tensile strength, MPa Yield strength, MPa Elongation, % Relative corrosion rate compared with ordinary HRB500 Example 1 700 545 18 18.3％ Example 2 695 535 19 19.1％

[0059] In summary, the method for preparing ribbed steel bars provided by the present invention, through the collaborative design of multiple elements of Cr-Mo-Al-N, constructs a dense and self-repairing composite passivation film on the premise of controlling costs, significantly inhibits the penetration of Cl-, with the target of making the salt spray corrosion rate ≤ 0.05 mm / a, which is more than 80% higher than that of ordinary ribbed steel bars, and enhances the corrosion resistance of the steel.

[0060] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A production method of marine environment corrosion-resistant ribbed steel bars, characterized in that, The chemical composition of the steel by weight percentage is as follows: C: 0.04% - 0.08%, Si: 0.20% - 0.40%, Mn: 1.60 - 2.00%, Cr: 7.0% - 9.0%, Mo: 0.6% - 2.0%, P ≤ 0.030%, S ≤ 0.030%, V: 0.03% - 0.10%, N: 0.0080% - 0.0150%, Al: 0.02% - 0.06%, and the rest is Fe and unavoidable impurities; The key production steps include: Step (1) Smelting: In the converter, control the ratio of hot metal to scrap charged into the furnace to be 6:4, and control the target composition of the molten steel at the end: C ≤ 0.05%, P ≤ 0.025%. Prohibit slagging. Add some Si, Mn, Cr, and V alloys during the tapping process; Step (2) Refining: Add some Si, Mn, Cr, and V alloys during the LF smelting process. Bake the added alloys at a high temperature not lower than 600 degrees. Control the basicity of the refining slag at 6.0 - 8.

0. Feed aluminum wire before the end of the LF furnace refining. Feed the nitrogen wire 6 minutes after soft blowing. Feed the calcium wire before tapping to perform calcium treatment on the molten steel, and then add a covering agent to protect the molten steel. Vacuumize the RH to below 67 Pa, keep the vacuum for 15 minutes, then break the vacuum to determine the hydrogen content in the molten steel, and control the hydrogen content ≤ 1.0 ppm. Turn on the circulation in the RH to increase nitrogen. The soft blowing time before tapping is 25 - 35 minutes. Take a sample for gas detection 5 minutes after soft blowing, and adjust the nitrogen component by feeding nitrogen-manganese wire according to the nitrogen content; Step (3) Continuous casting: Adopt weak cooling, with a specific water volume of 0.20 - 0.25 L / KG. The target value of the superheat in the tundish is 15°C - 25°C. The casting speed is 0.8 - 1.2 m / min. The current of the final electromagnetic stirring is 300 - 500 A, and the frequency is 3 - 8 Hz. Adopt the final soft reduction process for continuous casting. The size of the slab is 150*150*mm*12.0 m. The slab enters the slow cooling pit for slow cooling for 72 h; Step (4) Rolling: The slab undergoes high-temperature diffusion at 1200 - 1250°C for 2 - 4 h. The steel billet is de-scaled with high-pressure water when it leaves the furnace. The de-scaling pressure is not less than 20 Mpa. The reduction rate of the first pass and the second pass is greater than 60%. The rough rolling temperature is 950 - 1100°C, and the finish rolling temperature is 800 - 900°C; Step (5) Slow cooling after rolling: After rolling, the steel goes onto the cooling bed for slow cooling. Cover the cooling bed with a heat preservation cover. The cooling bed is closely arranged for slow cooling. After leaving the cover, it is bundled and sent into the slow cooling pit; Step (6) Annealing: The deformed steel bars enter the continuous annealing furnace for annealing within 24 hours after entering the pit. Keep the temperature at 650 - 720°C for 2 - 3 h, slowly cool to 250°C, and then leave the furnace for air cooling.

2. The production method of a marine environment corrosion-resistant ribbed steel bar according to claim 1, characterized in that, For the scrap used in step (1) smelting, use scrap containing Mo element, and add ferromolybdenum alloy before converter smelting.

3. The production method of a marine environment corrosion-resistant ribbed steel bar according to claim 1, characterized in that, In step (2) refining, feeding aluminum wire adjusts the aluminum in the molten steel to 0.050% - 0.080%, and feeding the nitrogen wire adjusts the N in the molten steel to 0.0090% - 0.0120%.

4. The production method of a marine environment corrosion-resistant ribbed steel bar according to claim 1, characterized in that In step (2) refining, for the first furnace of continuous casting, the feeding amount of calcium wire is 180 m, and for continuous casting furnaces, the feeding amount is 150 m.

5. The production method of a marine environment corrosion-resistant ribbed steel bar according to claim 1, characterized in that, In step (3) continuous casting, the reduction amount of the final soft reduction is 10 - 12 mm.