500MPa-grade low-carbon low-cost anti-seismic fire-resistant steel plate and preparation method thereof

Abstract

The invention discloses a 500MPa-grade low-cost anti-seismic fire-resistant steel plate and a preparation method thereof, and the steel plate comprises the following chemical components in percentage by weight: 0.02 to 0.10 percent of C, 0.1 to 0.3 percent of Si, 1.2 to 1.6 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.006 percent of S, 0.15 to 0.35 percent of Mo, 0.01 to 0.06 percent of Nb, 0.16 to 0.20 percent of V, 0.040 to 0.045 percent of Ti, 0.0014 to 0.0018 percent of B, 0.002 to 0.003 percent of N and the balance of Fe and inevitable impurities. The preparation method comprises the procedures of blast furnace ironmaking, converter steelmaking, continuous casting and rolling. The low-cost anti-seismic fire-resistant steel plate is manufactured by accurately controlling the content of alloy elements and controlling parameters of rolling and cooling processes, so that the requirements of the building industry on high-performance building materials are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory metal materials, and particularly relates to a 500MPa grade low-carbon, low-cost earthquake-resistant refractory steel plate and a preparation method thereof. Background Art

[0002] Steel structures have the advantages of light self-weight, short construction period, large structural span, good earthquake resistance performance, and recyclable resources, and are widely used in modern super high-rise buildings, large-span space structure buildings and industrial fields. With the development trend of buildings towards high-rise and complex, people have higher and higher requirements for the fire resistance, earthquake resistance, corrosion resistance and other properties of construction steel. The yield strength of refractory steel after being kept at 600°C for 1 - 3 hours remains not less than 2 / 3 of the room temperature yield strength, thereby enhancing the fire resistance ability of buildings, improving safety, and providing sufficient time for personnel evacuation and property transfer. At the same time, refractory steel also needs to meet the requirements of other properties of buildings, such as good earthquake resistance, ductility, weldability, corrosion resistance, etc.

[0003] At present, ordinary carbon steel and low-alloy structural steel have poor fire resistance. The bare steel structure without protection under high-temperature conditions will quickly lose its bearing capacity. The yield strength will suddenly decrease by 1 / 3 compared with the room temperature condition above 350°C, and the yield strength at 600°C is only 1 / 3 of the room temperature yield strength. In case of a fire, the safety of buildings cannot be guaranteed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a 500MPa grade low-carbon, low-cost earthquake-resistant refractory steel plate and a preparation method thereof. By precisely controlling the content of alloying elements and optimizing the parameters of the rolling process, a low-cost earthquake-resistant refractory steel plate is manufactured to meet the needs of the construction industry for high-performance building materials.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a 500MPa grade low-carbon, low-cost earthquake-resistant refractory steel plate, the chemical composition of the steel plate by weight percentage: C: 0.02 - 0.10%, Si: 0.1 - 0.3%, Mn: 1.2 - 1.6%, P≤0.01%, S≤0.006%, Mo: 0.15 - 0.35%, Nb: 0.01 - 0.06%, V: 0.16 - 0.20%, Ti: 0.040 - 0.045%, B: 0.0014 - 0.0018%, N: 0.002 - 0.003%, and the rest is Fe and unavoidable impurities.

[0006] The yield strength of the steel plate of the present invention is ≥500MPa, the tensile strength is ≥600MPa, the yield ratio is ≤0.84, and the elongation after fracture is ≥20%; the total elongation at maximum force is ≥8%, and the impact energy at -40°C is 47KV2 / J; the thickness specification of the steel plate is 3 - 14mm.

[0007] The mechanical properties of the steel plate according to the present invention at 600 °C: the tensile strength ≥ 400 MPa, Rp 0.2 -600 °C ≥ 335 MPa, Rp 0.2 -600 °C / Rp 0.2 -25 °C ≥ 0.67, the elongation after fracture ≥ 18%, and the reduction of area ≥ 40%.

[0008] Another object of the present invention is to further provide a method for preparing the above-mentioned 500 MPa grade low-carbon low-cost earthquake-resistant and fire-resistant steel plate, comprising the following steps: S1: Blast furnace ironmaking. Add iron ore, coke and flux into the blast furnace according to the configured ratio, and control the temperature and air permeability in the furnace by blowing hot air and injecting pulverized coal to obtain hot metal with a C content between 3.5% and 4.0% and an S content < 0.06%; S2: Converter steelmaking. The hot metal obtained in the process of S1 is subjected to desiliconization, dephosphorization and desulfurization treatment through the hot metal pretreatment process and then added into the converter. Remove impurities by blowing, control the converter end point by the high-pull supplementary blowing method, and then add the molten steel and the alloy materials configured in proportion into the pre-baked and heated ladle for in-ladle deoxidation alloying; Use the LF refining furnace to deeply deoxidize the molten steel and make fine adjustments to the composition, take steel samples and measure the temperature to obtain molten steel meeting the chemical composition ratio; S3: Continuous casting process. Feed the molten steel obtained in the process of S2 into the continuous casting mold through the tundish and the submerged nozzle, and obtain a continuous casting slab with the required width for rolling after solidification and cooling; S4: Rolling process. Feed the qualified continuous casting slab obtained in the process of S3 into the heating furnace, heat it in the heating furnace for a certain time, control the heating time within 120 - 220 min, control the heating temperature within 1200 - 1240 °C, subject the red-hot slab to high-pressure descaling and then enter the roughing mill for rolling, and control the temperature of the slab after roughing within 1040 - 1080 °C.

[0009] In the processes of S2 and S3 of the present invention, the chemical composition weight percentages of the molten steel after refining are: C: 0.02 - 0.10%, Si: 0.1 - 0.3%, Mn: 1.2 - 1.6%, P ≤ 0.01%, S ≤ 0.006%, Mo: 0.15 - 0.35%, Nb: 0.01 - 0.06%, V: 0.16 - 0.20%, Ti: 0.040 - 0.045%, B: 0.0014 - 0.0018%, N: 0.002 - 0.003%, and the rest are Fe and inevitable impurities.

[0010] In the process of S4 of the present invention, the control requirements for heating and heat preservation are: the heating temperature is 1200 - 1240 °C, and the heating time is 120 - 220 min.

[0011] In the S4 process of the present invention, the compression ratio controlled by the last set of finishing stands is ≥12%, the temperature after finishing is controlled at 860 - 900°C, forced cooling is adopted after rolling, coiling is carried out at 520 - 560°C, and then air cooling is carried out to room temperature.

[0012] In the S2 and S3 processes of the present invention, the chemical composition weight percentages of the molten steel after refining are as follows: C: 0.02 - 0.10%, Si: 0.1 - 0.3%, Mn: 1.2 - 1.6%, P ≤ 0.01%, S ≤ 0.006%, Mo: 0.15 - 0.35%, Nb: 0.01 - 0.06%, V: 0.16 - 0.20%, Ti: 0.040 - 0.045%, B: 0.0014 - 0.0018%, N: 0.002 - 0.003%, and the rest are Fe and inevitable impurities.

[0013] In the S4 process of the present invention, controlling the heating temperature and time is to ensure that the inside of the steel billet is completely transformed into austenite. By controlling the rough rolling, finishing temperatures and the compression ratio of the last set of finishing stands ≥12%, it is ensured that the structure between the finishing stands is austenite and the structure does not recrystallize. Rapid cooling after finishing causes the deformed austenite to rapidly transform into ferrite. During the process, carbides of Mo, Nb, and V in the steel will precipitate, pin the grain boundaries, inhibit grain growth, and form a tissue morphology with coexisting polygonal ferrite, ultra-fine granular bainite, and lath / needle-shaped martensite, which can effectively guarantee the strength of the steel plate.

[0014] In the S4 process of the present invention, coiling starts when the steel is cooled to 520 - 560°C, and then air cooling is carried out.

[0015] The chemical composition and action mechanism of the present invention are as follows: Carbon: C is an indispensable component in steelmaking and coexists with iron during steelmaking. The higher the C content, the higher the hardness and the better the wear resistance, but the toughness and corrosion resistance will decrease with the increase of the C content. Most of the C will form cementite or carbides and exist in the steel. C can increase the hardenability of the steel, making it easier to generate bainite and martensite during the structure transformation process in the steel. In the present invention, the set mass percentage content of C is 0.02 - 0.10%.

[0016] Silicon: Si is an important heat-generating element. When the Si content in the hot metal is high, the slag amount increases, which is beneficial to dephosphorization and desulfurization. However, too high a silicon content will increase the slag material and consumption, reduce the metal yield, and prolong the blowing time. In the present invention, the set mass percentage content of Si is 0.1 - 0.3%.

[0017] Phosphorus: P is a high heat-generating element and is a harmful element for earthquake-resistant refractory steel. Therefore, it is required that the P content in molten iron be as low as possible. The lower the P content in molten iron, the simpler the steelmaking process, which is beneficial to improving various technical and economic indicators. In the present invention, the mass percentage content of P is set to ≤0.01%.

[0018] Sulfur: S is a harmful element, and it is required that the S content in steel be as low as possible. In the present invention, the mass percentage content of S is set to ≤0.006%.

[0019] Molybdenum: Mo is a core element in refractory steel. Mo has two strengthening effects in refractory steel: solid solution strengthening and precipitation strengthening. Among them, solid solution strengthening is the direct and main strengthening effect. The influence of the solid solution strengthening effect of Mo on the high-temperature strength of refractory steel is significantly greater than that of the precipitation strengthening effect of Mo. Mo has a relatively high promotion effect on the high-temperature yield strength of the steel plate because Mo has a strengthening effect on the ferrite matrix of refractory steel, is prone to segregation at grain boundaries, improves the bonding force of grain boundaries at high temperatures, prevents the annihilation of dislocations at high temperatures, and maintains the effect of dislocation strengthening, which can avoid the rapid decline of the strength of refractory steel at high temperatures and cause the steel to fail. Mo also has a certain precipitation strengthening effect. In the steel, it forms MoC or Mo2C with C, which can promote the precipitation of Nb and V, and is prone to segregation around NbC and VC. The microalloying effect of Mo, Nb, and V improves the high-temperature strength of the steel through precipitation strengthening. After adding elements such as Nb and V, Mo promotes the formation of MC precipitation phases, which have higher stability, are not easy to aggregate and grow at high temperatures, have finer sizes, and higher dispersion degrees, thereby improving the high-temperature yield strength of the steel. Adding Mo can not only improve the high-temperature performance of the steel but also improve the earthquake resistance performance. However, too high a Mo content will affect the hardenability of the steel, making the weldability and toughness-brittle property of the steel worse; at the same time, the price of Mo element is expensive, and excessive addition will increase the cost of the steel. In the present invention, the mass percentage content of Mo is set to 0.15 - 0.35%.

[0020] Vanadium: V has two strengthening methods in steel, namely fine grain strengthening and precipitation strengthening. Fine grain strengthening: During the heating and holding process of austenite, it will coarsen. The V solute atoms and their fine and dispersed carbonitrides have a fixing effect on grain boundaries, can hinder the migration of austenite grain boundaries, and inhibit the growth of austenite grains. Precipitation strengthening: The more the content of solute elements, the more the precipitation amount during cooling, and the more obvious the strengthening effect. For V microalloying, a small amount of nitrogen needs to be added. The nitride precipitation rate of V is fast, the dispersion degree is small, the precipitation temperature is low, the precipitation particles are fine, and it is not easy to aggregate and grow, and the strengthening effect is obvious. The precipitated VC is fine, which can improve the strength of the material without reducing its plasticity. In the present invention, the mass percentage content of V is set to 0.16 - 0.20%.

[0021] Niobium: Nb also has two strengthening methods in steel, namely fine grain strengthening and precipitation strengthening. Fine grain strengthening: During the heating and holding process, austenite will coarsen. The Nb solid solution atoms and their fine and dispersed carbonitrides have a fixing effect on the grain boundaries, which can hinder the migration of austenite grain boundaries and inhibit the growth of austenite grains. During hot rolling, the dissolved Nb has a dragging effect on the grain boundaries, significantly inhibiting the dynamic recrystallization of austenite, increasing the recrystallization temperature of the steel, enabling the steel to enter the rolling in the non-recrystallized zone at high temperatures in advance, and thus significantly refining the grains. Precipitation strengthening: The more the content of the dissolved element, the more the precipitation amount during cooling, and the more obvious the strengthening effect. The precipitation temperature is low, the precipitate particles are fine, and they are not easy to aggregate and grow, so the strengthening effect is obvious. Compared with the Nb-free steel, the precipitates in the Nb-containing steel increase significantly, the precipitate particle size is small, and they are mainly M(C,N) particles. In the present invention, the mass percentage content of Nb is set to be 0.01 - 0.06%.

[0022] Titanium: Ti can combine with C and N in steel to form carbonitrides, inhibiting grain growth and coarsening. However, too much Ti will generate some inclusions, reducing the plasticity and toughness of the steel. In the present invention, the mass percentage content of Ti is set to be 0.040 - 0.045%.

[0023] Nitrogen: N can form MN with other alloying elements, and a small amount of nitrogen needs to be added for microalloying. The nitride precipitation rate is fast, the dispersion degree is small, the precipitation temperature is low, the precipitate particles are fine, and they are not easy to aggregate and grow, so the strengthening effect is obvious. In the present invention, the mass percentage content of N is set to be 0.002 - 0.003%.

[0024] Boron: The main function of B in steel is to increase the hardenability of the steel, which can effectively save other more expensive rare metals, such as Mo used in the present invention. In the present invention, the mass percentage content of B is set to be 0.0014 - 0.0018%.

[0025] The beneficial effects of adopting the above technical solutions are as follows: 1. The core element in the refractory steel of the present invention is Mo, but it is a precious metal element, and a high content in the refractory steel will result in a high cost. In the present invention, a low Mo element is adopted, and its chemical composition is 0.15 - 0.35% by weight percentage. On the premise of ensuring the performance of the refractory steel, the dosage of the Mo element is reduced, and at the same time, three elements of Nb, V, and Ti are used to strengthen the performance of the 500MPa grade earthquake-resistant refractory steel plate. 2. The heating temperature of the continuous casting billet in the present invention is 1200 - 1240°C, the holding time is not less than 120 - 220min, the rough rolling temperature is 1040 - 1080°C, the finish rolling temperature is 860 - 900°C, and it is air-cooled to room temperature after rolling. The reasonable temperature control is conducive to the phase transformation of the bainite structure in the refractory steel; the long holding time is conducive to the full solution, uniform distribution, and pinning of the Mo element at the grain boundaries to play a role in refining the grains, thereby improving the strength of the refractory steel plate and obtaining a building refractory steel plate with high strength, light self-weight, excellent earthquake resistance performance, simple construction, energy conservation, and environmental protection. Description of the Drawings

[0026] Figure 1 It is a physical diagram of Example 1; Figure 2 It is a physical diagram of Example 2; Figure 3 It is a physical diagram of Example 3; Figure 4 It is a physical diagram of Example 4; Figure 5 It is a physical diagram of Example 5; Figure 6 It is a metallographic structure diagram of Example 1 under 500×; Figure 7 It is a metallographic structure diagram of Example 2 under 500×; Figure 8 It is a metallographic structure diagram of Example 3 under 500×; Figure 9 It is a metallographic structure diagram of Example 4 under 500×; Figure 10 It is a metallographic structure diagram of Example 5 under 500×. Detailed Description of the Invention

[0027] The following further describes the present invention in detail in conjunction with the specific embodiments.

[0028] Examples 1 - 5 A preparation method of a 500 MPa grade low - carbon and low - cost earthquake - resistant and fire - resistant steel plate, comprising the following steps: S1: Ironmaking in a blast furnace. Add iron ore, coke and flux in the configured proportion in the blast furnace, control the temperature and air permeability in the furnace by blowing hot air and injecting pulverized coal, and obtain hot metal with a C content between 3.5% and 4.0% and an S content < 0.06%; S2: Steelmaking in a converter. The hot metal obtained in the S1 process is subjected to desiliconization, dephosphorization and desulfurization treatments through the hot metal pretreatment process and then added to the converter. Remove impurities by blowing, control the converter end point by the high - pull supplementary blowing method, and then add the molten steel and the alloy materials configured in proportion to a pre - baked and heated ladle for in - ladle deoxidation alloying; Use an LF refining furnace to deeply deoxidize the molten steel and make fine adjustments to the composition, take a steel sample and measure the temperature to obtain molten steel meeting the chemical composition ratio (the same as the chemical composition of the steel plate); S3: Continuous casting process. Feed the molten steel obtained in the S2 process into the continuous casting mold through a tundish and an immersion nozzle, and obtain a continuous casting slab with the required width for rolling after solidification and cooling.

[0029] S4: Rolling process. Feed the qualified continuous casting slab obtained in the S3 process into the heating furnace, heat it in the heating furnace for a certain period of time, control the heating time within 120 - 220 min, and control the heating temperature within 1200 - 1240 °C. After descaling the red-hot slab under high pressure, feed it into the rough rolling mill for rolling. Control the temperature of the slab after rough rolling within 1040 - 1080 °C. For finish rolling, control the reduction ratio of the last finishing mill unit to be not less than 12%. Control the temperature after finish rolling within 860 - 900 °C. After finish rolling, quickly cool it to 520 °C to 560 °C and coil it into a coil. After coiling, air cool it to room temperature.

[0030] The chemical compositions of the steel plates in each example are shown in Table 1, the rolling process parameters of each example are shown in Table 2, the mechanical properties of the steel plates at room temperature in each example are shown in Table 3, and the mechanical properties of the steel plates at 600 °C in each example are shown in Table 4.

[0031] Table 1 Chemical compositions of the steel plates in each example (wt, %)

[0032] Table 2 Rolling process parameters of each example

[0033] Table 3 Mechanical properties of the steel plates at room temperature in each example

[0034] Table 4 Mechanical properties of the steel plates at 600 °C in each example

[0035] From the above data, it can be seen that the room temperature and high temperature properties of the 5 examples in the present invention all meet the requirements of the Q500FR standard fire-resistant steel plate.

[0036] The above examples are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above examples, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the present invention without departing from the spirit and scope of the present invention, and any modification or partial replacement.

Claims

1. A 500MPa grade low-carbon low-cost earthquake-resistant fire-resistant steel plate, characterized in that: The chemical composition of the steel plate in weight percentage is as follows: C: 0.02-0.10%, Si: 0.1-0.3%, Mn: 1.2-1.6%, P≤0.01%, S≤0.006%, Mo: 0.15-0.35%, Nb: 0.01-0.06%, V: 0.16-0.20%, Ti: 0.040-0.045%, B: 0.0014-0.0018%, N: 0.002-0.003%, and the rest is Fe and unavoidable impurities.

2. A 500MPa grade low-carbon, low-cost, earthquake-resistant and fire-resistant steel plate according to claim 1, characterized in that: The steel plate has a yield strength of ≥500MPa, a tensile strength of ≥600MPa, a yield strength ratio of ≤0.84, and an elongation after fracture of ≥20%; a total elongation under maximum force of ≥8%, and an impact energy of 47KV2 / J at -40°C; and a steel plate thickness specification of 3-14mm.

3. The 500MPa low-carbon, low-cost, earthquake-resistant and fire-resistant steel plate according to claim 1, characterized in that: Mechanical properties of the steel plate at 600°C: tensile strength ≥ 400 MPa, Rp 0.2 -600℃≥335MPa, Rp 0.2 -600℃ / Rp 0.2 -25℃≥0.67, elongation after break≥18%, section shrinkage≥40%.

4. A method for preparing a 500MPa grade low-carbon, low-cost, earthquake-resistant and fire-resistant steel plate according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1: Blast furnace ironmaking, in which iron ore, coke and flux are added in a certain proportion, and the temperature and air permeability in the furnace are controlled by blowing hot air and injecting pulverized coal to obtain molten iron with a C content of 3.5-4.0% and an S content of <0.06%; S2: Converter steelmaking, the molten iron obtained in the S1 process is desiliconized, dephosphorized and desulfurized through the molten iron pretreatment process and then added to the converter, impurities are removed by blowing, and the converter end point is controlled by the high-draw supplementary blowing method, and then the molten steel and the alloy materials configured in proportion are added to the pre-baked and heated ladle for deoxidation and alloying in the ladle; the molten steel is deeply deoxidized using the LF refining furnace, and the composition is fine-tuned, steel samples are taken, and the temperature is measured to obtain molten steel that meets the chemical composition ratio; S3: continuous casting process, the molten steel obtained in the S2 process is sent into the continuous casting crystallizer through the tundish and the submerged nozzle, and after solidification and cooling, a continuous casting slab with the required width for rolling is obtained; S4: rolling process, the qualified continuous casting slab obtained in the S3 process is sent to the heating furnace, and heated in the heating furnace for a certain time, the heating time is controlled at 120-220 minutes, the heating temperature is controlled at 1200-1240°C, the red-hot slab is dephosphorized under high pressure and then sent to the rough rolling mill for rolling, and the slab temperature after rough rolling is controlled at 1040-1080°C.

5. The method for preparing a 500MPa grade low-carbon, low-cost earthquake-resistant and fire-resistant steel plate according to claim 4, characterized in that: In the S2 and S3 processes, the chemical composition weight percentage of the refined molten steel is as follows: C: 0.02-0.10%, Si: 0.1-0.3%, Mn: 1.2-1.6%, P≤0.01%, S≤0.006%, Mo: 0.15-0.35%, Nb: 0.01-0.06%, V: 0.16-0.20%, Ti: 0.040-0.045%, B: 0.0014-0.0018%, N: 0.002-0.003%, and the rest is Fe and unavoidable impurities.

6. The method for preparing a 500MPa grade low-carbon low-cost earthquake-resistant fire-resistant steel plate according to claim 4, characterized in that: In the S4 process, the control requirements for heating and heat preservation are: heating temperature is 1200-1240° C., and heating time is 120-220 min.

7. A method for preparing a 500MPa grade low-carbon, low-cost, earthquake-resistant and fire-resistant steel plate according to claims 4-6, characterized in that: In the S4 process, the compression ratio of the last set of stands for finishing rolling is controlled to be ≥12%, the temperature after finishing rolling is controlled to be 860-900°C, forced cooling is adopted after rolling, the temperature is controlled to be 520-560°C for coiling, and then air-cooling is performed to room temperature.

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