Method for improving mechanical property of steel slag ingot and application thereof
By controlling the alkalinity of the steel slag and regulating the cooling rate in stages, the problem of cracking during the cooling process of steel slag ingots was solved, its mechanical properties were improved, and the requirements of sensible heat recovery and carbon fixation modification processes were met.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-03-10
AI Technical Summary
In existing technologies, steel slag castings are prone to cracking during the cooling process, which leads to a decrease in mechanical properties and fails to meet the requirements of sensible heat recovery and carbon fixation modification processes.
By controlling the basicity of the steel slag and regulating its cooling rate in stages, the internal microstructure can be optimized. Specifically, the basicity can be adjusted by adding CaO or SiO2 to the tempering furnace, and the cooling rate can be controlled in stages. First, the slag is cooled to 800-900℃ at a rate of less than 25℃/min in a temperature-controlled furnace, then cooled to 400-500℃ at a rate of less than 15℃/min, and finally cooled naturally to room temperature.
It significantly improves the compressive strength and drop strength of steel slag castings, meets the performance requirements of high-strength materials for sensible heat recovery and carbon fixation modification processes, avoids cracking and breakage, and reduces equipment maintenance costs.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of comprehensive utilization technology of metallurgical solid waste resources, and more specifically, relates to a method and its application for improving the mechanical properties of steel slag castings based on cooling rate regulation. Background Technology
[0002] Steel slag, a major industrial solid waste generated during steelmaking, accounts for approximately 10%-15% of crude steel production. With the rapid development of the steel industry, the accumulated stockpile of steel slag has reached hundreds of millions of tons. This not only occupies valuable land resources but also easily causes multiple forms of pollution to the soil, water, and atmosphere through infiltration and dust generation, exacerbating ecological and environmental pressures. At the same time, steel slag contains extremely high sensible heat energy value. Molten steel slag typically exceeds 1500℃, and calculations show that each ton of steel slag contains energy equivalent to approximately 41 kg of standard coal, possessing significant energy recovery potential. However, due to limitations such as insufficient maturity of existing sensible heat recovery technologies and poor process stability, this considerable heat energy in steel slag has not been fully developed and utilized, leading to serious energy waste. Therefore, how to overcome technological bottlenecks and achieve efficient value-added utilization of steel slag has become one of the core challenges in promoting the steel industry's transformation towards a green and low-carbon direction.
[0003] According to the search, the patent document with publication number CN118239702A (publication date: June 25, 2024) is entitled "A process for sensible heat recovery and carbon fixation modification of steel slag". The technical solution proposed in this patent is as follows: Molten steel slag is cast into a high-temperature steel slag block using a casting device, resulting in a block with a "solid outer shell and liquid inner core." The block is then fed into the reactor from the top inlet of a vertical reactor, while metallurgical flue gas is introduced from the bottom inlet pipe. During the flue gas flow, it exchanges heat with the high-temperature steel slag block, forming high-temperature flue gas. Simultaneously, the high-temperature steel slag block reacts chemically with CO2 in the flue gas, achieving carbon fixation modification and forming carbon-modified steel slag blocks. After the heat exchange reaction is complete, the high-temperature flue gas is discharged through the top pipe of the vertical reactor, undergoes dust removal, and then enters a heat exchanger for secondary heat exchange. Finally, the heat-exchanged flue gas is discharged from the chimney. The carbon-modified steel slag blocks are then crushed, separated, and graded for use in the preparation of high-value-added steel slag products. Although this patent effectively achieves the synergistic recovery of sensible heat of steel slag and carbon fixation process through the convective heat transfer between flue gas and steel slag ingots in a vertical heat exchange reactor, there are certain problems in practical applications: a large amount of glass phase is easily generated when the steel slag melt is placed directly in the air for natural cooling after being cast into the mold, which leads to frequent cracking of the final cast steel slag ingot. Not only is the surface quality poor, but its mechanical properties and strength are also difficult to meet the working conditions of the subsequent vertical reactor.
[0004] Therefore, the present invention provides a method for improving the mechanical properties of steel slag castings to solve the above-mentioned technical problems. Summary of the Invention
[0005] The purpose of this invention is to solve the problem that in the existing technology, steel slag ingots are easily cracked when directly cast from high-temperature molten steel slag, resulting in a decrease in the mechanical properties of the steel slag ingots. This invention provides a method to improve the mechanical properties of steel slag ingots. By controlling the cooling rate of the steel slag during the cooling stage and adjusting the basicity of the steel slag, the internal microstructure is optimized, thereby effectively improving the mechanical properties of the steel slag ingots and meeting the requirements of steel slag sensible heat recovery and carbon fixation modification processes.
[0006] Furthermore, the present invention also provides steel slag ingots produced by the above method, which have significantly improved compressive strength and drop strength, thereby better meeting the performance requirements of high-strength materials for steel slag sensible heat recovery and carbon fixation modification processes.
[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for improving the mechanical properties of steel slag ingots. During the slag removal process, a tempering furnace is used to receive molten steel slag, and then the basicity of the molten steel slag is controlled. The basicity of common converter slag is between 2.5 and 4. The basicity of the steel slag can be controlled within the preferred range of 3 to 3.5 by adding CaO or SiO2. The molten steel slag is cooled using the following strategy: First, after preheating the mold, the molten steel slag is poured into the mold and cooled to 1200-1300°C. Then, the mold is pushed into a temperature-controlled furnace preheated to 1200-1300°C. The steel slag is cooled to 800-900°C in the temperature-controlled furnace at a first cooling rate. Then, the steel slag is cooled to 400-500°C in the temperature-controlled furnace at a second cooling rate. Finally, the steel slag is pushed into the air for natural cooling to room temperature to form steel slag ingots. The first cooling rate is no higher than 25°C / min, and the second cooling rate is no higher than 15°C / min.
[0008] It should be noted that in steel slag sensible heat recovery or carbon fixation modification processes, steel slag ingots are pushed into a vertical reactor for processing. Inside the reactor, the steel slag ingots are in a "stacking state," with the lower layer bearing the weight of the upper layer. If the compressive strength of the steel slag ingots is insufficient, they will be crushed into fragments, disrupting the stacking structure and easily breaking into smaller pieces or even powder. This can clog the reactor inlet, outlet, and discharge port, leading to process interruption and increased equipment maintenance costs. This invention proposes a solution that, by controlling the basicity of the steel slag and the cooling rate, improves the compressive strength of the steel slag ingots, effectively preventing cracking and breakage during waste heat recovery or carbon fixation modification.
[0009] Specifically, the method of the present invention includes the following steps: Step 1: Slag is discharged from the converter and collected in the quenching and tempering furnace. The basicity of the steel slag is changed by adding CaO or SiO2 in the quenching and tempering furnace. Step 2: The components are uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a preheated mold pushed out of the temperature-controlled furnace and cooled in the air to 1200~1300℃. Step 3: Push the mold along with the molten steel slag into a temperature-controlled furnace preheated to 1200~1300℃, and control the cooling rate of the molten steel slag in stages; including: First stage cooling: Cool the steel slag at 1200~1300℃ to 800~900℃ at the first cooling rate, with the first cooling rate not exceeding 25℃ / min; Second stage cooling: The steel slag at 800~900℃ is cooled to 400~500℃ at a second cooling rate, which is no higher than 15℃ / min; The third stage of cooling: The steel slag at 400~500℃ is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air to form steel slag ingots.
[0010] In one possible implementation of the first aspect of this invention, after casting molten steel slag into a preheated mold, the subsequent cooling rate of the steel slag needs to be controlled when it is cooled to 1200-1300°C. If the temperature at which the steel slag finishes cooling in air after casting is below 1200°C, the large temperature difference will generate huge thermal stress inside the ingot. At this point, slow cooling can partially eliminate the stress, but the initial stress may have already caused microcracks, which are irreversible. Excessive cooling inhibits the full growth of beneficial phases such as C3S and C2S. Even with subsequent slow cooling, the crystals are unlikely to continue to grow significantly, resulting in poor strength framework development. If the cooling temperature at the end is above 1300°C, it is equivalent to prolonging the slow cooling time in the high-temperature range, which may provide a time window for some high-temperature harmful reactions (such as the decomposition of C3S). At the same time, this conflicts with the economics of the process. Starting slow cooling from an excessively high temperature (such as 1400°C) will extend the entire cooling cycle, resulting in high energy consumption and being uneconomical.
[0011] In one possible embodiment of the first aspect of the present invention, the first cooling rate is 15~25°C. Controlling the cooling rate of the steel slag within this range during the first stage of cooling preserves high-strength oxide phases such as C3S, C2S, and calcium ferrite, allowing them to fully nucleate and grow into a robust and dense crystal framework without becoming excessively large. Simultaneously, preventing excessively rapid cooling leads to the formation of a high content of glassy phase, which would also inhibit the formation of high-strength oxide phases such as C3S, C2S, and calcium ferrite, resulting in a decrease in the falling strength of the steel slag ingot. Furthermore, excessive glassy phase may encapsulate some components that we wish to separate (such as metallic iron particles), affecting subsequent recovery efficiency. However, if the cooling rate is too slow during this stage, C3S decomposes and C2S undergoes a crystal transformation. Under slow cooling, C3S decomposes into C2S and f-CaO, leading to a decrease in C3S content and an increase in C2S and f-CaO content. The introduced f-CaO is a harmful phase. The phase transition from β-C2S to γ-C2S can cause expansion and pulverization of the steel slag ingot, affecting its strength. Furthermore, the purpose of cooling to 800-900℃ at this stage is to ensure sufficient growth of the C3S / C2S crystals while reserving a sufficient window for controlling the more dangerous phase transition later. During this temperature range, the steel slag temperature is higher than the C2S phase transition temperature but lower than the temperature for large-scale atomic diffusion; at this point, the crystal framework is basically formed. If the cooling temperature at the end of this stage is higher (e.g., above 900℃), the slower cooling rate in the next stage will lead to a longer residence time in the phase transition region, increasing the degree of the β-C2S to γ-C2S phase transition. If the cooling temperature at the end of this stage is lower (below 800℃), it will approach or even begin to enter the C2S phase transition region. At this point, switching to slow cooling is too late and cannot effectively suppress the β-C2S→γ-C2S transformation.
[0012] As one possible embodiment of the first aspect of the present invention, the second cooling rate is 5~15℃ / min. Controlling the cooling rate of the steel slag within this range during the second stage of cooling effectively promotes stress release, maximizes the elimination of internal stress, and makes the crystal structure more stable. This prevents excessively rapid cooling from causing some residual internal stress to remain in the steel slag, which would reduce the strength of the steel slag ingot upon drop. Simultaneously, the β-C2S → γ-C2S transformation is sufficiently suppressed, and the β-C2S content is almost completely retained, ensuring the strength of the ingot. However, if the cooling rate is too slow during this stage, a C2S crystal transformation will occur. The β-C2S to γ-C2S phase transformation may cause the steel slag ingot to expand and pulverize, affecting its strength. Slower cooling also increases energy consumption. While a rapid cooling rate maximizes the retention of β-C2S, thermal stress may also lead to cracks, physically damaging the ingot structure. The sole purpose of cooling at this stage is to pass through the C2S phase transformation danger zone (~675℃) at the safest rate, thereby preserving the high-strength β-C2S to room temperature. Controlling the cooling temperature at this stage to 400-500℃, far below the phase transformation temperature, means the danger has completely passed. Ending this cooling stage at a higher temperature (above 500℃, such as 600℃) means the subsequent cooling rate of the ingot (from 600℃ to room temperature) is uncontrollable air cooling. If this rate happens to fall within the unsafe range, β-C2S may still transform into γ-C2S, causing the ingot to pulverize after cooling to room temperature. Since the cooling ends below 400℃ at this stage, the phase transformation risk is eliminated, and continuing slow cooling will only increase energy consumption and time costs, without improving the microstructure.
[0013] In one possible implementation of the first aspect of this invention, slag is discharged from the converter and received in the tempering furnace. The basicity of the steel slag is altered in the tempering furnace by adding CaO or SiO2, controlling the basicity of the steel slag within a preferred range of 3 to 3.5. When the basicity is low (low CaO / SiO2 ratio), SiO2 is relatively excessive in the melt. This tends to generate the silicon-rich silicate mineral calcium silicate (Ca3Si2O7). Calcium silicate itself has low strength and cannot form a robust framework, thus the compressive strength of the ingot is relatively low. Within the optimal basicity range (3.0 to 3.5), tricalcium silicate (C3S) and dicalcium silicate (C2S) are generated in large quantities. Simultaneously, the generated calcium ferroate (CaFeO2) effectively fills the gaps in the C3S and C2S crystal framework, providing excellent bonding and making the entire structure more compact. The synergistic effect of these phases causes the compressive strength of the ingot to reach its peak within this range. The basicity of steel slag is in the high basicity range (>3.5, close to 4). Excess CaO cannot be completely combined into C3S and C2S, and will precipitate separately as free calcium oxide (f-CaO). At room temperature, f-CaO undergoes a slow hydration reaction with moisture in the air, causing volume instability. This hydration expansion generates huge internal stresses within the ingot, leading to the generation and propagation of microcracks. These microcracks are stress concentration points, which severely weaken the overall integrity of the material. Even if the C3S skeleton remains strong at this point, the ubiquitous microcrack network makes the ingot extremely vulnerable to failure at these weak points under pressure, resulting in a decrease in macroscopic compressive strength.
[0014] In one possible embodiment of the first aspect of the present invention, in step two, the composition is homogenized by mechanical stirring in a tempering furnace, and then the molten steel slag is poured into a mold and cooled to 1200~1300°C. Furthermore, the mold is preheated in a temperature-controlled furnace beforehand. Preheating the mold reduces the initial cooling rate of the steel slag, making the cooling process inside and outside the ingot, as well as the surface and interior, more synchronized, thereby minimizing the generation of thermal stress. This effectively prevents cracks from forming in the ingot during cooling, while avoiding or greatly reducing the formation of amorphous or extremely fine-grained regions on the surface.
[0015] As one possible embodiment of the first aspect of the present invention, the steel slag casting block simultaneously meets the following requirements: compressive strength ≥ 5KN, free fall from a height of 0.5m, and fracture after ≥ 30 falls.
[0016] In a second aspect, the present invention provides an application of steel slag ingots for use in steel slag sensible heat recovery or steel slag carbonization modification processes.
[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention promotes the formation of a high-strength phase and a fine, uniform, and dense crystal structure inside the steel slag by precisely controlling the alkalinity of the steel slag and staged cooling during the cooling process. At the same time, it effectively inhibits the formation of the glass phase and crack propagation, thereby enhancing the overall structural stability of the steel slag ingot.
[0018] The steel slag ingots prepared by the method of the present invention have significantly improved compressive strength and drop strength, thus better meeting the performance requirements of the steel slag sensible heat recovery and carbon fixation modification process for material strength. Detailed Implementation
[0019] The steel slag used in this embodiment specifically includes: The composition is as follows: CaO 39.91%, SiO2 12.72%, Al2O3 1.74%, MgO 3.69%, Fe2O3 31.31%, P2O5 2.87%, with the remainder being unavoidable impurities. Its alkalinity is 3.14.
[0020] The present invention will be further described below with reference to specific embodiments.
[0021] Example 1 The method for improving the mechanical properties of steel slag castings based on cooling rate regulation in this embodiment includes the following specific steps: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0022] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1200℃; the mold is then pushed into the temperature-controlled furnace preheated to 1200℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the temperature control furnace cooling rate regulation stage, includes: 1) First stage cooling: After the temperature of the steel slag drops to 1200℃, it is cooled to 900℃ at a cooling rate of 20℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 900℃, it is cooled to 400℃ at a cooling rate of 10℃ / min; 3) Third stage cooling: When the temperature of the steel slag drops to 400℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air to obtain steel slag ingots.
[0023] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1.
[0024] Example 2 The method for improving the mechanical properties of steel slag castings based on cooling rate regulation in this embodiment includes the following specific steps: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0025] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1300℃; the mold is then pushed into the temperature-controlled furnace preheated to 1300℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the temperature control furnace cooling rate regulation stage, includes: 1) First stage cooling: After the temperature of the steel slag drops to 1300℃, it is cooled to 850℃ at a cooling rate of 15℃ / min. 2) Second stage cooling: When the temperature of the steel slag drops to 850℃, it is cooled to 450℃ at a cooling rate of 10℃ / min; 3) Third stage of cooling: When the temperature of the steel slag drops to 450℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0026] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1.
[0027] Example 3 The method for improving the mechanical properties of steel slag castings based on cooling rate regulation in this embodiment includes the following specific steps: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0028] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1250℃; the mold is then pushed into the temperature-controlled furnace preheated to 1250℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the temperature control furnace cooling rate regulation stage, includes: 1) First stage cooling: After the temperature of the steel slag drops to 1250℃, it is cooled to 800℃ at a cooling rate of 25℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 800℃, it is cooled to 500℃ at a cooling rate of 5℃ / min; 3) Third stage of cooling: When the temperature of the steel slag drops to 500℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0029] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1.
[0030] Example 4 The method for improving the mechanical properties of steel slag castings based on cooling rate regulation in this embodiment includes the following specific steps: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0031] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1200℃; the mold is then pushed into the temperature-controlled furnace preheated to 1200℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the temperature control furnace cooling rate regulation stage, includes: 1) First stage cooling: After the temperature of the steel slag drops to 1200℃, it is cooled to 800℃ at a cooling rate of 15℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 800℃, it is cooled to 400℃ at a cooling rate of 5℃ / min; 3) Third stage of cooling: When the temperature of the steel slag drops to 400℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0032] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1.
[0033] Comparative Example 1 The specific steps of the method for improving the mechanical properties of steel slag castings in this comparative example are as follows: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0034] Step 2: The components are uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and placed directly in the air to cool naturally to room temperature; Mechanical property testing: The cooled steel slag was removed from the mold, and the compressive strength and drop strength of the steel slag ingot were tested. The test results are shown in Table 1. The comparison clearly shows that the steel slag ingot treated by the method of this invention has significant advantages in mechanical properties.
[0035] Comparative Example 2 The specific steps of the method for improving the mechanical properties of steel slag castings in this comparative example are as follows: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0036] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1100℃; the mold is then pushed into the temperature-controlled furnace preheated to 1100℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the temperature control furnace cooling rate regulation stage, includes: 1) First stage cooling: After the temperature of the steel slag drops to 1100℃, it is cooled to 900℃ at a cooling rate of 10℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 900℃, it is cooled to 400℃ at a cooling rate of 5℃ / min; 3) Third stage of cooling: When the temperature of the steel slag drops to 400℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0037] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1. The comparison clearly shows that the steel slag ingot treated by the method of this invention has significant advantages in mechanical properties.
[0038] Comparative Example 3 The specific steps of the method for improving the mechanical properties of steel slag castings in this comparative example are as follows: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0039] Step 2: The components are uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 1000℃; the mold is then pushed into the temperature-controlled furnace preheated to 1000℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3: Temperature control furnace cooling rate regulation stage: 1) First stage cooling: After the temperature of the steel slag drops to 1000℃, it is cooled to 800℃ at a cooling rate of 30℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 800℃, it is cooled to 400℃ at a cooling rate of 5℃ / min; 3) Third stage of cooling: When the temperature of the steel slag drops to 400℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0040] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1. The comparison clearly shows that the steel slag ingot treated by the method of this invention has significant advantages in mechanical properties.
[0041] Comparative Example 4 The specific steps of the method for improving the mechanical properties of steel slag castings in this comparative example are as follows: Step 1: Slag is discharged from the converter and slag is received in the conditioning furnace.
[0042] Step 2: The composition is uniformly stirred by mechanical stirring in the tempering furnace, and then the molten steel slag is poured into a mold pushed out of the temperature-controlled furnace and allowed to cool from 1500℃ to 800℃; the mold is then pushed into the temperature-controlled furnace preheated to 800℃, and the cooling rate of the molten steel slag is controlled in stages. Step 3, the cooling rate control stage, includes: 1) First stage cooling: When the temperature of the steel slag drops to 800℃, it is cooled to 400℃ at a cooling rate of 10℃ / min; 2) Second stage cooling: When the temperature of the steel slag drops to 400℃, the steel slag is pushed out of the temperature-controlled furnace and allowed to cool naturally to room temperature in the air.
[0043] Mechanical property testing: The cooled steel slag ingot was removed from the mold, and its compressive strength and drop strength were tested. The test results are shown in Table 1. The comparison clearly shows that the steel slag ingot treated by the method of this invention has significant advantages in mechanical properties.
[0044] Comparative Example 5 The method for improving the mechanical properties of steel slag castings in this embodiment has the same specific steps as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step one, the basicity of the steel slag is adjusted to 2.5.
[0045] Comparative Example 6 The method for improving the mechanical properties of steel slag castings in this embodiment has the same specific steps as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step one, the basicity of the steel slag is adjusted to 4.
[0046] Example 5 The method for improving the mechanical properties of steel slag castings in this embodiment has the same specific steps as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step one, the basicity of the steel slag is adjusted to 3.
[0047] Example 6 The method for improving the mechanical properties of steel slag castings in this embodiment has the same specific steps as in Embodiment 1. The difference between this embodiment and Embodiment 1 is that in step one, the basicity of the steel slag is adjusted to 3.5.
[0048] The specific testing methods used for the steel slag ingots obtained in this embodiment and comparative example are as follows: 1) Compressive strength of steel slag ingots: Place the ingot sample to be tested between two parallel plates of a universal testing machine, and apply axial pressure to the ingot at a constant speed of 2 mm / min until the ingot fractures. Record the maximum pressure value at which the ingot fractures; this value is the compressive strength of the ingot.
[0049] 2) Drop strength of steel slag ingots: The ingot sample to be tested is dropped from a height of 0.5m in a free fall manner, and the number of drops after breaking is recorded as the last drop.
[0050] Table 1. Test results of mechanical properties of steel slag ingots obtained in Examples 1-6 and Comparative Examples 1-6
[0051] As shown in Table 1, when implementing the same cooling rate strategy, the compressive strength of steel slag ingots increases and then decreases with increasing basicity when the basicity is controlled between 2.5 and 4. The compressive strength is best when the basicity is between 3 and 3.5. However, when the basicity is too high, the compressive strength of SiO2 and Al2O3 decreases. ³ When acidic oxides are insufficient, excess CaO cannot be completely solidified into silicate minerals and exists as free calcium oxide, leading to decreased casting stability and strength. When alkalinity is too low, the content of calcium silicate phase and Al-Fe-Si intermetallic compounds decreases, further reducing the strength of the steel slag casting. Under the same alkalinity conditions, the cooling rate of the steel slag needs to be strictly controlled. Using the four-stage cooling control strategy of this invention, the compressive strength and drop strength of the steel slag can be simultaneously guaranteed to meet the operating requirements of the subsequent vertical reactor. As shown in the table, both excessively high and low cooling rates negatively impact the compressive strength of the steel slag casting. Alkalinity and cooling rate jointly affect the mechanical properties of the steel slag casting; neither is dispensable. More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, such as combinations between various embodiments, adaptive changes, and / or substitutions, as would be apparent to those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly as used in the language of the claims and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, which should be considered non-exclusive. Any step listed in any method or process claim may be performed in any order and is not limited to the order set forth in the claims. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given above.
[0052] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail. When a rate, pressure, temperature, time, or other value or parameter is expressed as a range, preferred range, or a range defined by a series of upper and lower preferred values, this shall be understood to specifically disclose all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether such range is disclosed individually. For example, the range 1-50 should be understood to include any number, combination of numbers, or subrange selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all decimal values between the integers mentioned above, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Regarding subranges, specifically consider "nested subranges" extending from any endpoint of the range. For example, nested sub-ranges of the exemplary range 1-50 may include 1-10, 1-20, 1-30 and 1-40 in one direction, or 50-40, 50-30, 50-20 and 50-10 in another direction.
Claims
1. A method for improving the mechanical properties of a steel slag ingot, characterized in that, After the converter slagging, the steel slag basicity is regulated to 3.0-3.5, and after the molten steel slag is cooled to 1200-1300℃, a segmented cooling strategy is adopted for cooling, which includes: cooling the steel slag at 1200-1300℃ to 800-900℃ at a first cooling rate; cooling the steel slag at 800-900℃ to 400-500℃ at a second cooling rate; naturally cooling the steel slag at 400-500℃ in air to room temperature to form a steel slag block; the second cooling rate is not higher than the first cooling rate.
2. The method for improving the mechanical properties of a steel slag ingot according to claim 1, characterized in that, the first cooling rate is not higher than 25℃ / min.
3. The method for improving the mechanical properties of a lifted steel slag block according to claim 2, characterized in that, the first cooling rate is 15-25℃ / min.
4. The method for improving the mechanical properties of a steel slag ingot according to claim 1, characterized in that, the second cooling rate is not higher than 15℃ / min.
5. The method for improving the mechanical properties of a lifted steel slag block according to claim 4, characterized in that, the second cooling rate is 5-15℃ / min.
6. The method for improving the mechanical properties of a steel slag ingot according to any one of claims 1 to 5, characterized in that, Specifically includes the following steps: Step one, converter slagging, the conditioning furnace receives the molten steel slag, and the steel slag basicity is adjusted to 3.0-3.5; Step two, after the conditioning is uniform, the steel slag is cast into a preheated mold and naturally cooled to 1200-1300℃, and then the steel slag is sent into a temperature control furnace for segmented cooling, which includes: cooling the steel slag at 1200-1300℃ to 800-900℃ at a cooling rate of 15-25℃ / min, and cooling the steel slag at 800-900℃ to 400-500℃ at a cooling rate of 5-15℃ / min; Step three, the steel slag at 400-500℃ is pushed out of the temperature control furnace and naturally cooled in air to room temperature to form a steel slag block.
7. The method for improving the mechanical properties of a lifted steel slag block according to claim 6, characterized in that, In the step one, the steel slag basicity is regulated by adding CaO or SiO2.
8. The method for improving the mechanical properties of a lifted steel slag block according to claim 6, characterized in that, In the step three, the obtained steel slag block has mechanical properties that simultaneously satisfy: compressive strength ≥5 KN, free fall at a height of 0.5m, and the number of falls ≥30 before starting to break.
9. Use of a steel slag ingot, characterized in that: The steel slag block is treated by the method of any one of claims 1-8, and the steel slag block is used for steel slag sensible heat recovery or steel slag carbon sequestration modification process.
Citation Information
Patent Citations
Steel slag sensible heat recovery and carbon sequestration modification process
CN118239702A