Weather-resistant heavy special-shaped blank and preparation method thereof

Abstract

The invention discloses a weather-resistant heavy special-shaped blank and a preparation method thereof, and belongs to the technical field of steel, and the weather-resistant heavy special-shaped blank comprises the following chemical components in percentage by weight: 0.05%-0.10% of C, 0.20%-0.80% of Si, 0.30%-0.90% of Mn, 0.06%-0.12% of P, less than or equal to 0.005% of S, 0.005%-0.050% of Alt, 0.05%-0.15% of Ni, 0.15%-0.35% of Cu, 0.2%-0.8% of Cr, 0.01%-0.03% of Nb, 0.01%-0.05% of V, 0.02%-0.06% of Ti, less than or equal to 0.0050% of N, less than or equal to 0.0008% of B, less than or equal to 0.0002% of H and the balance of Fe and inevitable impurities The low-C, low-Mn, low-N and C-P-Mn-Cr-Cu-Ni-Ti component collaborative design is adopted, the P content and the Ti content are increased, the Ni content, the Cr content and the Cu content are reduced, the weather resistance of the heavy special-shaped blank and the casting blank quality are guaranteed, and meanwhile the comprehensive cost of alloy, steel materials, slag materials and the like is greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of steel technology, specifically relating to a weather-resistant heavy-duty shaped billet and its preparation method. Background Technology

[0002] Weathering steel is short for atmospheric corrosion resistant steel. It is a low-alloy steel with high corrosion resistance and toughness. It can form a dense oxide layer in natural environment, which can effectively block oxygen, moisture or salt in the atmosphere or sea breeze from penetrating into the steel matrix, significantly improving the ability to resist atmospheric corrosion. Its corrosion resistance can reach 2 to 8 times that of ordinary carbon steel. It is widely used in structural components such as bridges, buildings, railway vehicles, and offshore oil platforms.

[0003] With the rapid development of my country's economy, large-scale construction projects such as high-speed railways, cross-sea bridges, and offshore oil drilling platforms are increasing, leading to higher quality requirements for weather-resistant structural steel. Due to the foreign monopoly on the heavy H-beam market, domestic large-scale weather-resistant structural steel is typically produced using steel plate welding and riveting processes. This requires processes such as leveling, shearing, flame cutting, bending, and welding (riveting) before being used in large structural components. During use, problems such as cracking, poor low-temperature toughness, and warping after flame cutting can occur, not only increasing steel consumption but also potentially affecting the stability and safety of the structure.

[0004] Heavy-duty hot-rolled H-beam weathering steel is an economical and efficient profile with a more optimized cross-sectional area distribution and a more reasonable strength-to-weight ratio. Its unique honeycomb beam characteristics allow it to be combined into various cross-sectional forms, largely meeting the needs of engineering design and manufacturing. The economical and reasonable cross-sectional shape of H-beams gives them advantages over ordinary steel, such as a larger section modulus and metal savings, effectively saving about 20% of steel used in large structures and reducing internal forces in structural design. The parallel inner and outer sides of the H-beam legs make it easy to assemble into components, resulting in low cost and high precision. Compared with other steels, it can save about 25% of welding and riveting work and about 30% of steel costs.

[0005] Steel used in large structural components such as bridges and drilling platforms bears almost the entire weight of the bridge or drilling platform and is the main load-bearing component. It is exposed to high salinity and high water vapor sea winds, sun and rain, and seasonal temperature changes for a long time, which puts forward higher requirements for the quality of weather-resistant structural steel. On the one hand, it requires the development of large-scale and high-strength steel; on the other hand, it requires excellent corrosion resistance, toughness, fatigue resistance and weldability.

[0006] Chinese Patent CN 117867363 A discloses a method for producing thick-gauge weather-resistant H-beams with niobium-vanadium composite microalloying. The billet has dimensions of 555mm×440mm×105mm and a chemical composition by mass percentage of C: 0.07%~0.15%, Si: 0.50%~0.80%, Mn: 0.09%~1.65%, P≤0.025%, S≤0.015%, Cr: 0.30%~0.35%, Cu: 0.40%~0.45%, Ni: 0.25%~0.30%, V: 0.09%~0.12%, Nb: 0.01%~0.05%, with the remainder being Fe and unavoidable impurities. In the aforementioned continuous casting and billet cooling process for irregularly shaped billets, protective casting is used throughout the process, with superheat ≤30℃. A weak cooling regime is adopted. Before entering the straightening machine, the target temperature of the billet web is ≥900℃ and the target temperature of the billet flange is ≥800℃. Constant casting speed operation is adopted, with the casting speed controlled between 0.7 m / min and 0.9 m / min. After the continuous casting billet is cut, it is promptly removed from the line. First, the continuous casting billet is cooled to 400-500℃ at a cooling rate of 2-3℃ / s, and then stacked for slow cooling for more than 48 hours. This patent is limited to the production of irregularly shaped billets with small sections. As the width and flange height of the irregularly shaped billet increase, the stress increases significantly during solidification and shrinkage, and the shear force increases significantly during straightening, making it more prone to cracking. Heavy irregularly shaped billets for weather-resistant structures have relatively low drawing speeds, which exacerbate the cooling of the flange legs, resulting in the straightening temperature not being able to reach above 800℃. The above requirements are not applicable when producing heavy irregularly shaped billets for thick and heavy weather-resistant structures, and the casting billet is prone to transverse cracks at the flange top.

[0007] Chinese Patent CN 117904534 A discloses a special-shaped billet for weather-resistant hot-rolled H-beams and its production process. The billet has dimensions of 750×450×120mm and its chemical composition by mass percentage is as follows: C: 0.08%~0.14%, Si: 0.45%~0.65%, Mn: 1.40%~1.55%, P≤0.030%, S≤0.015%, Cu: 0.20%~0.30%, Ni: 0.20%~0.30%, Cr: 0.20%~0.30%, V: 0.10%~0.14%, [Ni] / [Cu]≥1, with the remainder being Fe and unavoidable impurities. The special-shaped billet for weather-resistant hot-rolled H-beams described in this patent also has a conventional cross-section, and the Cu, P, and Cr elements that play a major role in weather resistance are relatively low in the composition design, resulting in a low atmospheric corrosion resistance index value and general resistance to marine atmospheric corrosion. In addition, the C and Mn contents are relatively high, which is detrimental to the low-temperature toughness and weldability of the billet.

[0008] Chinese Patent CN 105886961 A discloses a high-performance hot-rolled H-beam resistant to marine atmospheric corrosion and its preparation method. The chemical composition of the H-beam, by mass percentage, is as follows: C: 0.015%–0.075%, Si: 0.20%–0.65%, Mn: 0.40%–1.60%, Ni: 0.90%–3.50%, Cu: 0.30%–1.20%, Mo: 0.20%–0.70%, Sb: 0.035%–0.10%, Als: 0.015%–0.07%, P≤0.025%, S≤0.010%, Nb: 0.015%–0.10%, Ti: 0.01%–0.05%, with the remainder being Fe and unavoidable impurities. This H-beam exhibits good toughness and plasticity, as well as excellent resistance to marine atmospheric corrosion and weldability. However, the patent uses high levels of precious alloying elements such as Ni, Cu, and Mo, and also adds elements such as Sb or rare earth elements RE, resulting in high alloy production costs and complex processes, which is not conducive to reducing manufacturing costs. Summary of the Invention

[0009] To address the aforementioned technical problems, this invention provides a weather-resistant heavy-duty shaped billet and its preparation method. It employs a synergistic design of low C, low Mn, low N, and CP-Mn-Cr-Cu-Ni-Ti compositions to increase P and Ti content while reducing Ni, Cr, and Cu content. This significantly reduces the overall cost of alloys, steel materials, and slag materials while ensuring the weather resistance and billet quality of the heavy-duty shaped billet.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] This invention provides a weather-resistant heavy-duty shaped billet, which comprises the following chemical composition by weight percentage: C: 0.05%~0.10%, Si: 0.20%~0.80%, Mn: 0.30%~0.90%, P: 0.06%~0.12%, S≤0.005%, Alt: 0.005%~0.050%, Ni: 0.05%~0.15%, Cu: 0.15%~0.35%, Cr: 0.2%~0.8%, Nb: 0.01%~0.03%, V: 0.01%~0.05%, Ti: 0.02%~0.06%, N≤0.0050%, B≤0.0008%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

[0012] The specifications of the weather-resistant heavy-duty shaped billet are: height × width × web thickness × flange thickness = 1300mm × 510mm × 140mm × 180mm. It is one of the largest heavy-duty shaped billets in China, with large size, high strength, high weather resistance, good mechanical properties and surface quality, which can effectively improve the quality of engineering projects and service life.

[0013] Furthermore, the chemical composition of the weather-resistant heavy-duty shaped billet satisfies:

[0014] C = 0.21 - 0.218Mn - 0.387P;

[0015] And / or, 0.8≤(Ni+3.5Ti) / Cu≤1.1;

[0016] And / or, 1.6≤(7Ni+3P+2Cr) / 4Cu≤2.5;

[0017] And / or, 20≤(Nb+ V+ Ti) / N≤25; In the above formulas, the value of each component is its content in steel ×100.

[0018] The atmospheric corrosion resistance index I of the weather-resistant heavy-duty shaped billet is ≥7.0.

[0019] The atmospheric corrosion resistance index I is calculated according to the modified Legault-Leckie formula in ASTM G101-01: I = 26.01 (%Cu) + 3.88 (%Ni) + 1.20 (%Cr) + 1.49 (%Si) + 17.28 (%P) - 7.29 (%Cu) × (%Ni) - 9.10 (%Ni) × (%P) - 33.39 (%Cu) 2 .

[0020] The present invention also provides a method for preparing the weather-resistant heavy-duty shaped billet, the method comprising the following steps:

[0021] 1) KR molten iron pretreatment and desulfurization;

[0022] 2) Converter smelting;

[0023] 3) Deoxidation and alloying of the steel;

[0024] 4) Argon blowing at the argon station;

[0025] 5) LF furnace refining;

[0026] 6) VD furnace refining;

[0027] 7) Heavy-duty irregular billet continuous casting.

[0028] In step 1), the target S content of the desulfurized molten iron is ≤0.010%, and the slag removal bright surface is ≥80%.

[0029] In step 2), the steel plant’s self-circulating scrap copper, nickel pig iron and scrap steel are loaded into the converter for preheating. The amount of self-circulating scrap copper added is 2.4~3.2 kg / t and the amount of nickel pig iron added is 6.2~14.4 kg / t. Then, molten iron is added and smelted.

[0030] Furthermore, the steel plant's self-circulating scrap copper includes scrap copper tubes from crystallizers, scrap copper plates, scrap tuyere sleeves from blast furnaces, scrap cables, etc., with a Cu percentage content ≥90wt%, and the remainder being unavoidable impurities.

[0031] The elemental mass percentages in the nickel pig iron are: Ni: 9~12%, C: 1.5~3%, P≤0.05%, S≤0.3%, with the remainder being unavoidable impurities.

[0032] In step 2), the oxygen lance position is controlled at 1.0~1.4 m, the oxygen pressure at 0.85~0.95 MPa, and the oxygen flow rate at 22000~26000 Nm³. 3 / h, bottom-blown argon flow rate is 300~500 Nm 3 / h.

[0033] In step 2), lime and dolomite are used for slag formation, and the initial slag basicity R is controlled to be 1.2~1.8. If the initial slag basicity R < 1.2, the slag will cause greater erosion of the furnace lining and is prone to splashing. If R > 1.8, the basic slag will deplete more phosphorus at low temperatures, resulting in a lower phosphorus content in the molten steel. The final slag basicity R of the converter is 2.0~2.5, the MgO content is 15%~19%, and the TFe content in the slag is 10%~13%. The converter adopts a circulating slag retention operation, with a slag retention amount of 50~70 kg / t. The final converter temperature is controlled at 1640 ℃~1680 ℃. The converter smelting produces low-basicity, high-magnesium oxide, and low-TFe slag, while the circulating slag retention enriches P2O5 in the slag, ensuring that the final P content of the converter is ≥0.050%.

[0034] Furthermore, 3 kg / t of lime is added to molten iron with a silicon content of 0.1%; and 7-10 kg / t of dolomite is added to molten iron with a silicon content of 0.1%.

[0035] Furthermore, for every 0.1% silicon content in molten iron, the amount of dolomite added is k. 白云石 The relationship between the silicon content and the iron content satisfies k 白云石 =(12.51w[Si] 2 -17.38w[Si]+12.95).

[0036] In step 3), alloys and auxiliary materials such as ferroaluminum, ferrosilicon, low-carbon ferromanganese, ferrovanadium, low-carbon ferrochrome, ferroniobium balls, ferrophosphorus, environmentally friendly pre-melted refining slag, and metallurgical lime are added during the steel tapping process. The ferroniobium balls contain the following elemental mass percentages: Nb ≥ 42%, C ≤ 0.4%, P: 4.0~6.0%, S ≤ 0.1%, with the remainder being unavoidable impurities.

[0037] In step 4), the bottom argon blowing begins during the converter tapping process. The temperature of the molten steel is measured after it enters the argon blowing station, and the argon blowing time is required to be ≥3min.

[0038] In step 5), the heating process controls the arc voltage to 260~320 V, the arc current to 35kA~40 kA, the argon flow rate to 100~200 NL / min, and the dust removal fan speed to 225~375 r / min. This maintains a slightly positive pressure atmosphere inside the ladle furnace, reduces nitrogen addition during the refining process, and controls the final LF refining endpoint Alt to be 0.005%~0.020%, S≤0.005%, B≤0.0008%, and N≤0.0060%. The remaining steel composition and temperature meet the design requirements before leaving the station.

[0039] In step 6), the vacuum degree is ≤133 Pa, the vacuum argon flow rate is 40~150 NL / min, and the vacuum holding time is 9~20 min. After the vacuum is completed, hydrogen is determined, and the H percentage content is ≤0.00015%. After the hydrogen determination, 0.4~1.0 kg / t ferrotitanium is added, and 50~150 meters of pure calcium wire is fed in to modify the inclusions in the steel. The soft argon blowing time after feeding the wire is ≥8 min.

[0040] Furthermore, in step 6), the vacuum degree P 真 When the pressure is ≤67 Pa, the argon flow rate during the vacuum process is 40~80 NL / min, and the vacuum holding time is t. 真 9 min; 67 Pa < P 真 At ≤133 Pa, the argon blowing flow rate during the vacuum process is 80~150 NL / min, and the vacuum holding time is... , the unit is min.

[0041] In step 7), argon gas is used for protection throughout the continuous casting process; the continuous casting speed is 0.45~0.65 m / min; a scoop-type water blower is added at the end of the fan-shaped section, and the gas is blown across the entire surface using a slit-type air outlet to blow the water accumulated in the web into the water collection hopper and discharge it outside the billet; a water-blocking device is added to the top of the fan-shaped section, and a drainage groove is added at the lower flange of each fan-shaped section.

[0042] In step 7), the temperature of the billet at the top of the front flange of the straightening machine is ≥700 ℃.

[0043] The functions and controls of each component in the weather-resistant heavy-duty shaped billet provided by this invention are as follows:

[0044] Carbon (C): Increased C content leads to higher strength and hardness in steel, but lower plasticity and toughness. Therefore, reducing C content while maintaining strength is beneficial for improving the toughness and cold-working properties of steel. The heavy-duty shaped billet for weathering structures provided by this invention achieves a balance of strength and low-temperature toughness. The C content is designed to be 0.05%~0.10%, with precise adjustment based on the linkage between P and Mn content, i.e., C = 0.21-0.218Mn-0.387P. This avoids large fluctuations in the mechanical properties of the billet, which could affect the strength and toughness of the steel matrix.

[0045] Silicon (Si): Si promotes the formation of a dense protective rust layer on the surface of steel, thereby improving its resistance to atmospheric corrosion; Si also promotes the formation of ferrite structure, dissolving in ferrite to increase its strength. However, excessive Si content will reduce the weldability of steel and affect surface quality. The Si content designed in this invention is 0.20%~0.80%.

[0046] Manganese (Mn) is an important alloying element for improving the strength and toughness of heavy H-beams. It can be infinitely dissolved in Fe, thus increasing steel strength while having a relatively small impact on plasticity. However, excessively high Mn content not only increases manufacturing costs but also expands the austenite phase region, increasing the stability of supercooled austenite. During cooling, this causes some supercooled austenite to transform into bainite, reducing ferrite content and affecting low-temperature toughness. Therefore, this invention designs the Mn content to be 0.30%~0.90%.

[0047] Phosphorus (P): P is the most economical element for improving the weather resistance of steel. It readily reacts with oxygen and water in the air to form insoluble, dense phosphates that uniformly cover the steel matrix surface, preventing oxygen and water from penetrating into the matrix, thereby improving the steel's resistance to atmospheric corrosion. It also has a strong solid solution strengthening effect. However, P tends to segregate at grain boundaries, reducing the steel's low-temperature toughness and increasing its susceptibility to welding cracks. In this invention, the P content is designed to be 0.060%~0.12%. P improves atmospheric corrosion resistance, and by using converter slag recycling, P2O5 is enriched in the slag, creating low-basicity, high-magnesium-oxide, and low-oxidizing slag. This ensures that the P content of the molten steel at the converter endpoint is ≥0.050%, reducing the cost of converter steel and slag materials, and significantly reducing the manufacturing cost of heavy-duty special-shaped billets for weather-resistant structures.

[0048] Sulfur (S): Sulfur is a harmful residual element in steel. It easily forms sulfide inclusions in steel, and its presence promotes hot brittleness and rusting, deteriorating the steel's resistance to atmospheric corrosion. Therefore, the sulfur content of heavy H-beams should be ≤0.015%, and the sulfur content of heavy special-shaped billets used in large weathering structures such as bridges and drilling platforms with high design service life requirements should be ≤0.005%.

[0049] Alt (aluminum): An appropriate aluminum content can reduce inclusions and AlN in steel, ensuring the effectiveness of calcium treatment, while also refining grains and improving the performance of heavy H-beams. Excessive or insufficient aluminum content will increase the total amount of inclusions, reducing the low-temperature toughness of the steel and the quality of the cast billet. This invention designs the Alt content to be 0.005%~0.050%.

[0050] Ni (Ni): Ni can increase the self-corrosion potential of steel, reduce its corrosion tendency, and improve its resistance to atmospheric corrosion. Ni can also react with Cu to form a high-melting-point Cu-Ni binary alloy phase, effectively preventing copper embrittlement caused by Cu. It can also improve the low-temperature toughness of materials. However, Ni is a precious metal element, and excessively high content significantly increases manufacturing costs. The heavy-duty special-shaped billet for weather-resistant structures provided by this invention adopts a low nickel-copper ratio composition, with a Ni content designed to be 0.05%~0.15%. Furthermore, it uses inexpensive nickel pig iron in a converter instead of pure nickel plates or nickel-iron alloys for smelting, further reducing alloy costs.

[0051] Cu (copper): It can significantly improve the atmospheric corrosion resistance of steel, and the effect is even better when added in combination with Cr. Cu can also precipitate fine second-phase particles during cooling to improve the strength of steel. However, Cu has a melting point of only 1083℃. If the content is too high, it can easily cause cracks in the steel billet during hot rolling. Therefore, the Cu content is designed to be 0.15%~0.35%, and copper plates are replaced with recycled copper from the steel mill to reduce the cost of the alloy.

[0052] Cr (chromium): Cr enrichment in the rust layer promotes the formation of stable and dense α-FeOOH, facilitates anodic passivation, and improves the atmospheric corrosion resistance of steel. Cr can also increase the hardenability of steel, promote bainite formation, reduce the volume fraction of ferrite, and is detrimental to improving material toughness. The Cr content in this invention is designed to be 0.2%~0.8%.

[0053] Niobium (Nb): Nb is a strong carbonitride forming element that inhibits the recrystallization of deformed austenite, expands the non-recrystallized region, and enhances the grain refinement effect during rolling by controlling the non-recrystallized region. During cooling, it precipitates nanoscale second-phase particles, exhibiting significant grain refinement and precipitation strengthening effects, thus improving the strength and toughness of the material. However, excessively high Nb content significantly increases the manufacturing cost of steel; therefore, this invention designs its content to be between 0.01% and 0.03%.

[0054] Vanadium (V): Most of V is dissolved in the matrix and can form fine carbonitride particles with C and N, inhibiting austenite grain growth and playing a role in grain refinement and precipitation strengthening, thus improving strength and low-temperature toughness. Furthermore, the fine V(CN) particles have good stability at high temperatures, preventing grain boundary movement, delaying crack propagation, and improving high-temperature performance. However, excessively high V content results in more V dissolved in the matrix, which is detrimental to low-temperature toughness and increases steel manufacturing costs. The content in this invention is designed to be 0.01%–0.05%.

[0055] Titanium (Ti): Titanium is a strong C and N compound forming element, forming stable compounds such as TiC or Ti(CN), which can effectively prevent excessive grain growth, refine the grain structure, and improve the strength and toughness of steel. Titanium can also inhibit the formation of cementite (Fe3C) in steel, prevent the micro-cell effect of ferrite-cementite during corrosion, and increase the self-corrosion potential of steel, which is beneficial to the steel's resistance to marine atmospheric corrosion. Ti can also improve the weldability of weathering steel by reducing the embrittlement tendency of the weld heat-affected zone. However, when the Ti content is too high, it is easy to form coarse square TiN particles with N in the steel. When stress is concentrated near the TiN particles, it will form a growth source of microcracks, reducing the fatigue performance of the steel. In this invention, its content is designed to be 0.02%~0.06%.

[0056] Nb, V, and Ti are all microalloying elements that can significantly refine grains. Nb, V, and Ti not only individually play roles in solid solution strengthening, precipitation strengthening, and grain refinement, but also exhibit a synergistic strengthening effect. The solid solution strengthening of Nb and V can improve the strength of steel, while the precipitation strengthening of Ti can further improve the impact toughness of steel. The synergistic effect of Nb, V, and Ti gives the heavy-duty special-shaped billet for weathering structures provided by this invention higher comprehensive performance. Therefore, this invention limits the Nb content to 0.01%~0.03%, V to 0.01%~0.05%, and Ti to 0.02%~0.06%, and restricts 20≤(Nb+V+Ti) / N≤25. The total addition of Nb+V+Ti is precisely adjusted according to the nitrogen content of the molten steel to fully utilize the grain refinement, strength, and toughness-improving effects of Nb, V, and Ti, while avoiding the adverse effects of excessive microalloying, such as increased ductile-brittle transition temperature, reduced low-temperature toughness, and increased cost.

[0057] Boron (B): Boron significantly increases the cold cracking sensitivity index of steel, thus worsening its weldability. Excessive boron content also reduces the toughness of steel, increasing the risk of brittle fracture. This invention limits its content to ≤0.0008%.

[0058] Nitrogen (N): As the nitrogen content increases, the strength of steel increases significantly, but its plasticity, especially its toughness, decreases significantly, its weldability deteriorates, and its cold brittleness intensifies; it also increases the tendency to age and reduces weldability. This invention limits its content to N ≤ 0.0050%.

[0059] Hydrogen (H): The most harmful element in steel. Dissolved hydrogen in steel can cause defects such as hydrogen embrittlement and white spots. Like oxygen and nitrogen, hydrogen has extremely low solubility in solid steel. At high temperatures, it dissolves into molten steel, and upon cooling, it cannot escape in time, accumulating in the microstructure to form high-pressure micropores. This drastically reduces the steel's plasticity, toughness, and fatigue strength, and in severe cases, can cause cracks and brittle fracture. This invention limits its content to H ≤ 0.0002%.

[0060] To ensure the control of N and H in the steel, a VD furnace vacuum treatment process is adopted to ensure sufficient vacuum holding time and meet the product quality requirements of heavy-duty special-shaped billets for weather-resistant structures.

[0061] At the same time, the above chemical components must also satisfy the following relationship:

[0062] 0.8≤(Ni+3.5Ti) / Cu≤1.1, 1.6≤(7Ni+3P+2Cr) / 4Cu≤2.5.

[0063] When (Ni+3.5Ti) / Cu < 0.8, copper accumulates at the interface of the steel matrix during solidification, weakening the austenite grain boundaries and significantly impacting grain boundary cracks, thus increasing the risk of copper embrittlement. When (Ni+3.5Ti) / Cu > 1.1, manufacturing costs increase, and low-temperature toughness is also negatively affected. When (7Ni+3P+2Cr) / 4Cu < 1.6, the weather resistance of heavy-duty shaped billets for weather-resistant structures cannot be guaranteed. When (7Ni+3P+2Cr) / 4Cu > 2.5, the low-temperature toughness of heavy-duty shaped billets for weather-resistant structures decreases, and alloy costs increase.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] This invention employs a synergistic design of low C, low Mn, low N, and CP-Mn-Cr-Cu-Ni-Ti compositions to increase P and Ti content while reducing Ni, Cr, and Cu content. The converter utilizes recycled copper and nickel pig iron from the steel plant to create low-basicity, low-oxidizing slag and low-slag smelting. The recycled slag enriches P2O5 in the slag, controlling the P content of the molten steel at the converter endpoint to ≥0.050%. The tapped steel uses inexpensive niobium-iron balls for alloying, ensuring an atmospheric corrosion resistance index (I) ≥7.0. Simultaneously, it significantly reduces the overall cost of alloys, steel materials, and slag materials for weather-resistant structural heavy H-beams.

[0066] Low C and low Mn content can increase ferrite content, shrink the austenite phase region, promote the transformation of supercooled austenite to proeutectoid ferrite, increase the ferrite volume fraction, and precisely adjust the C content based on the linkage of P and Mn content to improve the strength and toughness of the steel matrix and avoid large fluctuations in the mechanical properties of the billet.

[0067] By controlling the N content in the steel to a low level and precisely controlling the addition of Nb, V, and Ti, the fine-grain strengthening, precipitation strengthening, phase transformation strengthening, and deformation penetration control of Nb, V, and Ti are utilized to form dispersed carbonitride microparticles. These particles can inhibit austenite grain coarsening during billet heating and rolling, further refining the grains and improving the low-temperature toughness of heavy H-beams. This greatly expands the size range of hot-rolled heavy H-beam weathering steel, resulting in heavy special-shaped billets of weathering structural steel with large dimensions, high strength, high weather resistance, good mechanical properties, and good surface quality.

[0068] The weather-resistant heavy-duty shaped billet provided by this invention, after undergoing processes such as heating furnace, hot rolling, controlled cooling, and finishing, yields a heavy H-beam product whose mechanical properties reach the yield strength R. eL Not less than 385 MPa, tensile strength R m With a strength of not less than 500 MPa, an elongation A of not less than 25%, and a KV2 of not less than 120 J at -40℃, the product possesses excellent surface quality, mechanical properties, and weather resistance, and its quality meets design requirements. Attached Figure Description

[0069] Figure 1 This is a low-magnification photograph of the heavy irregular blank with dimensions of 1300mm×510mm×140mm×80mm in Example 1. Detailed Implementation

[0070] The present invention will now be described in detail with reference to the embodiments.

[0071] This invention provides a weather-resistant heavy-duty shaped billet with dimensions of height × width × web thickness × flange thickness = 1300mm × 510mm × 140mm × 180mm. Its main chemical composition and weight percentages are: C: 0.05%~0.10%, Si: 0.20%~0.80%, Mn: 0.30%~0.90%, P: 0.06%~0.12%, S≤0.005%, Alt: 0.005%~ 0.050%, Ni: 0.05%~0.15%, Cu: 0.15%~0.35%, Cr: 0.2%~0.8%, Nb: 0.01%~0.03%, V: 0.01%~0.05%, Ti: 0.02%~0.06%, N≤0.0050%, B≤0.0008%, H≤0.0002%, with the balance being Fe and unavoidable impurities; simultaneously, its chemical composition satisfies:

[0072] C = 0.21 - 0.218Mn - 0.387P;

[0073] And / or, 0.8≤(Ni+3.5Ti) / Cu≤1.1;

[0074] And / or, 1.6≤(7Ni+3P+2Cr) / 4Cu≤2.5;

[0075] And / or, 20≤(Nb+V+Ti) / N≤25; In the above formulas, the values ​​of each component are their content in steel ×100.

[0076] The atmospheric corrosion resistance index I of the weather-resistant heavy-duty shaped billet is ≥7.0.

[0077] The method for preparing the weather-resistant heavy-duty shaped billet includes the following steps:

[0078] 1) KR molten iron pretreatment and desulfurization: Molten iron undergoes pretreatment at the KR desulfurization station before being poured into the converter. The target S content of the desulfurized molten iron is ≤0.010%, and the slag removal bright surface is ≥80%.

[0079] 2) Converter smelting: Steel mill self-circulating scrap copper, nickel pig iron, and scrap steel are preheated together in the converter. The amount of self-circulating scrap copper added is 2.4~3.2 kg / t, and the amount of nickel pig iron added is 6.2~14.4 kg / t. This is then mixed with molten iron for blowing. The converter uses a circulating slag retention operation, with a slag retention amount of 50~70 kg / t. The oxygen lance position is controlled at 1.0~1.4 m, the oxygen pressure at 0.85~0.95 MPa, and the oxygen flow rate at 22000~26000 Nm³. 3 / h, bottom-blown argon flow rate is 300~500 Nm 3 / h; Lime and dolomite are used for slag formation. The lime addition is 3 kg / t of lime per ton of molten iron with a silicon content of 0.1%, and the dolomite addition is 7-10 kg / t of dolomite per ton of molten iron with a silicon content of 0.1%. The amount of dolomite added per ton of molten iron with a silicon content of 0.1% is k. 白云石 The relationship between the silicon content and the iron content satisfies k 白云石 =(12.51w[Si] 2 -17.38w[Si]+12.95); 60 seconds after successful ignition, the first batch of slag is added. The first batch of slag includes all the lime and 60% dolomite. The initial slag basicity R is controlled at 1.2~1.8. If the initial slag basicity R < 1.2, the slag will corrode the furnace lining more and easily cause splashing. If R > 1.8, the basic slag will deplete more P at low temperature, and the P content of the molten steel will be lower. The second batch of slag is the remaining 40% dolomite. The second batch of dolomite is added in small batches and multiple times, and is controlled to be added 120 seconds before the end of blowing. The final slag basicity R of the converter is 2.0~2.5, the MgO content is 15%~19%, and the TFe content in the slag is 10%~13%.

[0080] 3) Deoxidation and alloying at tapping: The final converter temperature is controlled at 1640℃~1680℃. During tapping, alloys and auxiliary materials such as ferroaluminum, ferrosilicon, low-carbon ferromanganese, ferrovanadium, low-carbon ferrochrome, ferroniobium balls, ferrophosphorus, environmentally friendly pre-melted refining slag, and metallurgical lime are added. The ferroniobium balls contain the following elemental mass percentages: Nb≥42%, C≤0.4%, P: 4.0%~6.0%, S≤0.1%, with the remainder being unavoidable impurities.

[0081] 4) Argon Station: Argon is blown from the bottom at the beginning of the converter tapping process. The temperature of the molten steel is measured after it enters the argon blowing station. The argon blowing time is required to be ≥3min. Before leaving the station, a sample is taken to measure the composition of the initial smelting steel.

[0082] 5) LF furnace refining: A low-alumina slag-forming process is adopted. During the refining process, environmentally friendly pre-melted refining slag, refined lime, and aluminum granules are added for slag formation. During the heating process, the arc voltage is controlled at 260~320 V, the arc current at 35 kA~40 kA, the argon flow rate at 100~200 NL / min, and the dust removal fan speed at 225~375 r / min. A slightly positive pressure atmosphere is maintained in the ladle furnace to reduce nitrogen addition during the refining process. The final LF refining parameters Alt can be controlled to be 0.005%~0.020%, S≤0.005%, B≤0.0008%, and N≤0.0060%. The remaining steel composition and temperature meet the design requirements before leaving the station.

[0083] 6) VD furnace refining: Vacuum degree ≤133 Pa, argon blowing flow rate during vacuum process 40~150 NL / min, vacuum holding time 9~20 min. Vacuum degree P 真 When the pressure is ≤67 Pa, the argon flow rate during the vacuum process is 40~80 NL / min, and the vacuum holding time is t. 真 9 min; 67 Pa < P 真 At ≤133 Pa, the argon blowing flow rate during the vacuum process is 80~150 NL / min, and the vacuum holding time is... After vacuuming, determine the hydrogen content (H) with a percentage of ≤0.00015%. After hydrogen determination, add 0.4~1.0 kg / t ferrotitanium according to the steel composition. Feed 50~150 meters of pure calcium wire to modify the inclusions in the steel. After feeding the wire, the soft blowing argon time is ≥8 min, and temperature is measured and samples are taken.

[0084] 7) Heavy-duty shaped billet continuous casting: Argon blowing protection during ladle transfer; argon blowing protection in the tundish of the heavy-duty shaped billet continuous casting machine before pouring to quickly raise the molten steel level in the tundish to ≥12 t before pouring; argon blowing protection at the ladle nozzle during pouring. The continuous casting speed range of the heavy-duty shaped billet continuous casting machine is 0.45 m / min~0.65 m / min; the superheat of the molten steel in the tundish is 15~35 ℃; the vibration polarization of the crystallizer is ≤0.3 mm; the secondary cooling water ratio is 0.4~0.6 L / kg; a scoop-type blower is added at the end of the fan-shaped section, using a slit-type air outlet to form gas purging across the entire surface, blowing the water accumulated in the web into the water receiving hopper and discharging it outside the billet; the height between the blower and the web surface of the billet is ≤5 mm; a water-blocking device is added to the top of the fan-shaped section; a drainage groove is added at the lower flange of each fan-shaped section; the temperature of the top of the flange before the billet enters the straightening machine is ≥700 ℃. After fire cutting, a heavy special-shaped billet for weathering structures with a cross-section of 1300 mm (height) × 510 mm (width) × 140 mm (web thickness) × 180 mm (flange thickness) is obtained. It is the largest cross-section heavy special-shaped billet for weathering structures in China.

[0085] The present invention is further verified through examples and comparative examples.

[0086] The composition control of Examples 1 to 4 and Comparative Examples 1 to 4 in this invention is shown in Table 1. The converter production process parameters and control results are shown in Table 2. The production process parameters and control results of LF furnace and VD furnace are shown in Table 3. The alloy addition amount and alloy cost of heavy special-shaped billets for weather-resistant structures are shown in Table 4. The continuous casting production process parameters are controlled in Table 5. The billet quality is shown in Table 6.

[0087] Table 1. Composition control (wt%) of heavy-duty profiled preforms for weather-resistant structures

[0088]

[0089] Table 2 Control of Converter Production Process Parameters

[0090]

[0091] Table 3. Control of process parameters for LF furnace and VD furnace

[0092]

[0093] Table 4 Alloy Addition Amount and Alloy Cost for Heavy Shaped Billets for Weather-Resistant Structures

[0094]

[0095] Table 5 Control of Continuous Casting Process Parameters

[0096]

[0097] Table 6 Billet Quality

[0098]

[0099] The weather-resistant heavy-duty shaped billets produced in Examples 1 to 4 above adopt a low-C, low-Mn, low-N, and CP-Mn-Cr-Cu-Ni-Ti composition synergistic design to increase P and Ti content and reduce Ni, Cr, and Cu content. The converter uses steel plant self-circulating waste copper and nickel pig iron to create low-basicity, low-oxidizing slag and low-slag smelting. The recycled slag enriches P2O5 in the slag, and the P content of the molten steel at the converter endpoint is controlled to be ≥0.050%. The steel is alloyed using inexpensive niobium iron balls. The atmospheric corrosion resistance index meets the requirement of I≥7.0, with an average I value of 7.60. The alloy cost is reduced by an average of 251.1 yuan / ton of steel compared to Comparative Examples 1-4, a reduction of about 35.2%. While ensuring high weather resistance, the alloy cost of weather-resistant heavy-duty shaped billets is significantly reduced.

[0100] As can be seen from Table 6, the heavy-duty special-shaped billets for weathering structures produced in Examples 1 to 4 are of excellent quality and have good surface. Low-magnification analysis shows that: the porosity at the center of the web is ≤1.0, the segregation at the center of the web is ≤0.5, the crack in the middle of the web is ≤0.5, the porosity at the center of the R-angle is ≤1.0, the segregation at the center of the R-angle is ≤0.5, the crack in the middle of the R-angle is ≤0.5, the crack in the center of the R-angle is ≤0.5, the crack in the middle of the narrow face is ≤0.5, and there are no quality problems such as subcutaneous cracks, flange end cracks, non-metallic inclusions, and subcutaneous bubbles.

[0101] The heavy-duty special-shaped blanks for weathering structures produced using the above comparative examples 1 to 4 have generally poor surface quality. Low-magnification analysis shows that the central porosity of the web is ≤1.5, the central segregation of the web is ≤1.0, the middle crack of the web is ≤1.0, the central crack of the web is ≤1.0, the central porosity of the R-angle is ≤1.5, the central segregation of the R-angle is ≤1.0, the middle crack of the R-angle is ≤1.0, the central crack of the R-angle is ≤1.0, and the middle crack of the narrow face is ≤1.0.

[0102] The weather-resistant heavy-duty shaped billets in the above embodiments and comparative examples were heated in a heating furnace at 1180~1300℃, rough rolled for 13 passes, and then finished with universal finishing for 13 passes to obtain heavy-duty H-beams. Their properties are shown in Table 7.

[0103] Table 7 Properties of Heavy H-beams Produced from Cast Billets

[0104]

[0105] As can be seen from Table 7, the finished heavy H-beams produced using the billets manufactured according to this invention have a yield of R. eL Not less than 385 MPa, tensile strength R mThe yield strength of the heavy H-beam produced from the cast billet manufactured using the comparative model is not less than 500 MPa, the elongation A is not less than 25%, and the KV2 is not less than 125 J at -40℃. eL Not less than 385 MPa, tensile strength R m The KV2 is 89.5J~111.7J under conditions of not less than 500MPa, elongation A not less than 20%, and -40℃.

[0106] The heavy-duty shaped billet for weathering structures produced in Comparative Example 1 has a higher nickel-copper ratio and a (7Ni+3P+2Cr) / 4Cu ratio, resulting in higher alloy costs, insufficient vacuum holding time, higher H and N content in the billet, and good surface quality.

[0107] The heavy-duty special-shaped billet for weathering structure produced in Comparative Example 2 has a high Ti content, a low Ni content and a low (7Ni+3P+2Cr) / 4Cu ratio, a low atmospheric corrosion resistance index, and does not meet the requirement of I≥7.0. It did not use VD refining for vacuum degassing, and the billet has a high H and N content, poor surface quality, and poor low-temperature toughness.

[0108] The heavy-duty special-shaped billets for weathering structures produced by Comparative Examples 3 and 4 have a higher C content, with C located in the peritectic region. The addition of Nb+V+Ti is relatively high, resulting in a higher (Nb+V+Ti) / N value. The billets have higher strength, poorer low-temperature toughness, higher alloy cost, and better surface quality.

[0109] The above detailed description of a weather-resistant heavy-duty shaped billet and its preparation method, with reference to the embodiments, is illustrative rather than limiting. Several embodiments can be listed according to the defined scope. Therefore, variations and modifications without departing from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A weather-resistant heavy-duty irregular-shaped billet, characterized in that, The weather-resistant heavy-duty shaped billet comprises the following chemical composition by weight percentage: C: 0.05%~0.10%, Si: 0.20%~0.80%, Mn: 0.30%~0.90%, P: 0.06%~0.12%, S≤0.005%, Alt: 0.005%~0.050%, Ni: 0.05%~0.15%, Cu: 0.15%~0.35%, Cr: 0.2%~0.8%, Nb: 0.01%~0.03%, V: 0.01%~0.05%, Ti: 0.02%~0.06%, N≤0.0050%, B≤0.0008%, H≤0.0002%, with the balance being Fe and unavoidable impurities; the chemical composition of the weather-resistant heavy-duty shaped billet satisfies: C = 0.21 - 0.218Mn - 0.387P; And / or, 0.8≤(Ni+3.5Ti) / Cu≤1.1; And / or, 1.6≤(7Ni+3P+2Cr) / 4Cu≤2.5; And / or, 20≤(Nb+V+Ti) / N≤25.

2. The weather-resistant heavy-duty shaped billet according to claim 1, characterized in that, The atmospheric corrosion resistance index I of the weather-resistant heavy-duty shaped billet is ≥7.

0.

3. A method for preparing a weather-resistant heavy-duty shaped billet as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: 1) KR molten iron pretreatment and desulfurization; 2) Converter smelting; 3) Deoxidation and alloying of the steel; 4) Argon blowing at the argon station; 5) LF furnace refining; 6) VD furnace refining; 7) Heavy-duty irregular billet continuous casting.

4. The preparation method according to claim 3, characterized in that, In step 1), the target S content of the desulfurized molten iron is ≤0.010%, and the slag removal bright surface is ≥80%.

5. The preparation method according to claim 3, characterized in that, In step 2), lime and dolomite are used to make slag, and the initial slag basicity R is controlled to be 1.2~1.8; the final slag basicity R of the converter is 2.0~2.5, the MgO content is 15%~19%, and the TFe content in the slag is 10%~13%; the converter adopts a circulating slag retention operation, and the slag retention amount is 50~70 kg / t.

6. The preparation method according to claim 3, characterized in that, In step 2), the converter endpoint temperature is controlled at 1640℃~1680℃; the P content at the converter endpoint is ≥0.050%.

7. The preparation method according to any one of claims 3-5, characterized in that, For every 0.1% silicon content in molten iron, add 3 kg / t of lime; for every 0.1% silicon content in molten iron, add 7-10 kg / t of dolomite, and the amount of dolomite added for every 0.1% silicon content in molten iron is... k 白云石 The relationship between the silicon content and the iron content is satisfied k 白云石 =(12.51 w [Si] 2 -17.38 w [Si]+12.95).

8. The preparation method according to any one of claims 3-5, characterized in that, In step 5), the heating process controls the arc voltage to 260~320 V, the arc current to 35 kA~40 kA, the argon flow rate to 100~200 NL / min, and the dust removal fan speed to 225~375 r / min.

9. The preparation method according to any one of claims 3-5, characterized in that, In step 6), the vacuum degree is ≤133Pa, the vacuum argon flow rate is 40~150 NL / min, and the vacuum holding time is 9~20 min. After the vacuum is completed, hydrogen is determined, and the H percentage content is ≤0.00015%. After the hydrogen determination, 0.4~1.0 kg / t ferrotitanium is added, and 50~150 meters of pure calcium wire is fed in to modify the inclusions in the steel. The soft argon blowing time after feeding the wire is ≥8 min.

10. The preparation method according to any one of claims 3-5, characterized in that, In step 7), argon gas is used for protection throughout the continuous casting process; the continuous casting speed is 0.45 ~ 0.65 m / min; a scoop-type water blower is added at the end of the fan-shaped section, a water-blocking device is added to the top of the fan-shaped section, and a drainage groove is added to the lower flange of each fan-shaped section.

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