High alloy steel continuous casting wide and thick plate blank and manufacturing method thereof

Abstract

The invention relates to a high alloy steel continuous casting wide and thick plate blank which is characterized by comprising the following chemical components: 0.09%-0.11% of C, 0.20%-0.50% of Si, 0.40%-0.50% of Mn and Plt, 0.015%, Slt; the invention discloses a high-strength and high-temperature fatigue-resistant steel and a preparation method thereof, the high-strength and high-temperature fatigue-resistant steel and the preparation method thereof, the high-strength and high-temperature fatigue-resistant steel and the preparation method thereof comprise the following steps: molten iron pretreatment, converter steelmaking, LF refining, RH vacuum treatment, continuous casting and blank slow cooling treatment, and the high-strength and high-temperature fatigue-resistant steel and the preparation method thereof are excellent in mechanical property, high in heat resistance and high in high-temperature fatigue resistance.

Description

Technical Field

[0001] This invention relates to a high-alloy steel continuously cast thick slab and its manufacturing method, belonging to the field of metal material manufacturing technology. Background Technology

[0002] As the global energy system undergoes a profound transformation towards higher efficiency and lower carbon emissions, ultra-supercritical (USC) coal-fired power generation technology, with its groundbreaking thermal efficiency (≥45%) and significant CO2 emission reduction benefits, has become the most strategically valuable development direction in the thermal power generation field. Against this backdrop, the extreme operating conditions of power units (steam temperature ≥600℃, pressure ≥25MPa) pose unprecedented challenges to key high-temperature structural materials—traditional low-alloy steels face prominent bottlenecks such as insufficient creep resistance and high-temperature oxidation failure during long-term service. To solve this major technical problem, ferritic heat-resistant steel SA-1017Gr92 (ASME Grade 92) based on a 9%Cr system stands out due to its superior comprehensive performance: while maintaining cost advantages, this material exhibits excellent high-temperature creep strength, outstanding creep resistance, and good oxidation resistance, thus being established as the preferred material for core components of ultra-supercritical boilers (including superheaters, reheaters, main steam pipes, and pipe support systems).

[0003] Currently, the industrial production of SA-1017Gr92 billets still follows the traditional process route: electric furnace primary refining → AOD refining → ladle refining (LF / VOD) → continuous casting / in-mold casting → slow cooling treatment. This process suffers from problems such as cumbersome procedures, high costs, insufficient stability in the continuous casting process, and high defect rates in subsequent processing. Specifically, this manifests as: insufficient matching of electromagnetic stirring parameters during continuous casting, fluctuations in crystallizer cooling efficiency, and difficulties in billet cutting; defects such as cutting marks, burrs, and cracks easily appearing on the surface of the billet after it leaves the production line; poor adaptability of slow cooling process parameters to actual production conditions, resulting in insufficient consistency in billet quality; and high production costs and large quality fluctuations. Especially driven by the "three 80 million" strategic goals in the power industry, the demand for SA-1017Gr92 materials from new power plant projects and unit renovation projects is showing exponential growth. To address these issues, there is an urgent need to develop a SA-1017Gr92 billet manufacturing technology with precise control of chemical composition, innovative production processes, and high production efficiency, achieving a synergistic improvement in material performance and production efficiency. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a high-alloy steel continuous casting wide and thick slab and its manufacturing method, which has excellent mechanical properties, high thermal strength and high temperature fatigue resistance, while solving the problems of cumbersome processes and high production costs in traditional production processes, and realizing the ability for large-scale industrial production.

[0005] The technical solution of this invention to solve the above technical problems is as follows: A high-alloy steel continuously cast wide and thick slab is provided, characterized by the following chemical composition: C: 0.09%-0.11%, Si: 0.20%-0.50%, Mn: 0.40%-0.50%, P<0.015%, S<0.005%, Cr: 8.60%-9.00%, Ni: 0.10-0.20%, Mo: 0.35%-0.45%, Cu≤0.10%, Nb: 0.05%-0.08%, V: 0.16%-0.20%, Ti≤0.01%, Alt≤0.015%, N: 0.035%-0.065%, W: 1.55%-1.80%, B: 0.0015%-0.0040%, Zr≤0.010%, with the balance being iron and unavoidable impurities.

[0006] This invention also provides a method for manufacturing high-alloy steel continuous casting thick slabs, the specific steps of which are as follows: S1: Hot metal pretreatment: Hot metal is sent to the KR desulfurization station for pretreatment. By adding desulfurizing agents such as lime and calcium carbide, the sulfur content of the hot metal is reduced to below 0.003%. S1: Converter smelting: Mo and W alloys are initially added in the converter process, and the tapping temperature is guaranteed to be ≥1680℃; S2: LF Refining: After confirming the cleanliness of the ladle at the LF process, aluminum wire is added for deoxidation. The target amount of aluminum wire added is based on the converter CAS sample. The deoxidation target is 0.020%. After the alloying of Cr, W, V, Mn, Ni, Mo and other components is completed, the carbon and silicon components are adjusted. S3: RH refining: After RH alloying, maintain a high vacuum of ≤5.0mbar for ≥20min. After RH is completed, feed 150-200 meters of seamless pure calcium wire per furnace. After feeding the wire, stir for ≥20min. Feed silicon nitride wire according to the nitrogen content. Add ferroboron after the nitrogen content is qualified. S4: Pre-treatment of the middle bread: Baking time of the middle bread ≥260 minutes, baking temperature ≥1231℃; S5: Continuous casting: Peritectic steel continuous casting protective slag is used, the liquidus temperature is 1504℃, the superheat is controlled at 10-35℃, the continuous casting speed is 0.65~1.10m / min, the electromagnetic stirring is set to a target of 420A / 6Hz, and the billet exit temperature is ≥600℃. S6: Billet Cutting: After the billet comes off the production line, a flame cutter is used, along with an oxygen blowing pipe and edge wire for combustion assistance, to ensure a smooth cut surface; after cutting, the surface cutting nodules and burrs are initially cleaned. S7: Slow cooling of billet: After the billet comes off the production line, it is immediately transferred to the heat preservation pit for heat preservation. The furnace temperature is controlled at 300-600℃ and the heat preservation time is ≥72 hours. S8: Surface treatment: After the billet has been cooled, a surface inspection is performed. Billets with cutting nodules, burrs or slight cracks are mechanically ground to ensure that the surface is free of defects before rolling.

[0007] The technical solution further defined in this invention is as follows: Preferably, KR desulfurization is used in S1, the amount of desulfurizing agent added is 1500±100kg / furnace, the number of slag removals is ≥5 times, there is no residue on the surface of molten iron after slag removal, and the S content of the steel tapped from the converter is ≤0.010%.

[0008] Preferably, the lime addition in the S2 converter is 5800-6500 kg / furnace. During the smelting process, the lance position is adjusted according to the slag formation, controlled at 1.8-2.2 m, and the oxygen flow rate is 38000-42000 Nm³. 3 / h; tapping temperature ≥1690℃ to ensure full melting of Mo and W alloys; P≤0.013% and carbon≤0.04% at tapping.

[0009] Preferably, in S3, after RH alloying, the high vacuum degree ≤3.0mbar is maintained for ≥22min; 180±10 meters / furnace of seamless pure calcium wire is fed in for calcium treatment, and the static stirring time is ≥22min; after breaking the vacuum, carbonized rice husks are added to cover the slag surface, the bottom blowing flow rate is controlled at 150-200NL / min, and silicon nitride alloy is added. After 10 minutes, a sample is taken to confirm the nitrogen content of the molten steel. After sampling, the bottom blowing flow rate is maintained at 100-150NL / min to confirm that the molten steel is not exposed, and silicon nitride wire is added according to the nitrogen content of the molten steel.

[0010] Preferably, in the S5 continuous casting, a type I covering agent + carbonized rice husk protective casting is used. After the tundish starts casting, the covering agent is added when the tundish reaches 15 tons. After the covering agent is added, 10 bags of carbonized rice husk are added at the sleeve position. No protective slag is added at the stopper rod position. The superheat is controlled at 22±3℃.

[0011] Preferably, the S7 slow cooling curve is as follows: first, maintain the temperature at 800±10℃ for 8 to 9 hours, then lower the temperature to 600±10℃ and maintain the temperature for 5 to 6 hours, and finally cool it with the furnace to below 300℃ and then air cool it to reduce the generation of cracks. Beneficial effects

[0012] (1) Short-process and efficient production: This invention replaces electric furnace primary refining with converter, utilizes the converter's efficient decarburization capability, combines hot iron pretreatment for desulfurization and dephosphorization, and initially adds Mo and W alloys in the converter process, supplemented in the subsequent refining process, which greatly shortens the smelting cycle, improves production efficiency, and reduces energy consumption. At the same time, the refining process adopts LF+RH, with the LF furnace responsible for fine-tuning of composition, desulfurization and temperature control, to ensure the accurate addition of alloying elements (Cr, Mo, V, W, Nb, etc.); through RH vacuum refining for deep degassing, the N content is accurately controlled, avoiding the nitrogen content fluctuation problem caused by traditional AOD refining; the continuous casting process adopts low superheat constant casting speed casting + electromagnetic stirring to increase the proportion of equiaxed crystals, reduce center segregation, and improve the high-temperature plasticity of the billet. (2) Multi-furnace continuous casting technology: adopting double LF+RH synergistic refining matching high-efficiency continuous casting, controlling the production rhythm, it can achieve 8-furnace continuous casting, improving production efficiency while reducing head and tail billet losses; (3) Precise control of components: Mo and W are precisely added by LF, and C and N contents are precisely adjusted by RH vacuum treatment to achieve precise control of chemical components.

[0013] (4) Cost and environmental advantages: Eliminating the AOD / VOD process reduces refining time by more than 30%, and the cost per ton of steel is reduced by about 10% to 15%. The converter smelting adopts a high proportion of molten iron (≥80%), reducing reliance on scrap steel and reducing CO2 emissions. Detailed Implementation Example 1

[0014] This embodiment provides a method for manufacturing SA-1017Gr92 high-alloy steel continuously cast thick slabs, including the following steps for steelmaking raw materials: hot metal pretreatment → converter steelmaking → LF refining → RH vacuum treatment → continuous casting → billet slow cooling treatment, to obtain a continuously cast slab with specifications of 320×2070mm. The chemical composition of the continuously cast slab is as follows: C: 0.10%, Si: 0.33%, Mn: 0.43%, P: 0.012%, S: 0.002%, Cr: 8.8%, Ni: 0.15%, Cu: 0.02%, Mo: 0.36%, V: 0.17%, Nb: 0.06%, Ti: 0.0019%, Al: 0.008%, W: 1.59%, B: 0.0019%, Zr: 0.0039%, N: 444ppm, with the balance being Fe and unavoidable impurities. Example 2

[0015] This embodiment provides a method for manufacturing SA-1017Gr92 high-alloy steel continuously cast thick slabs, including the following steps for steelmaking raw materials: hot metal pretreatment → converter steelmaking → LF refining → RH vacuum treatment → continuous casting → billet slow cooling treatment, to obtain a continuously cast slab with specifications of 320×2070mm. The chemical composition of the continuously cast slab is as follows: C: 0.10%, Si: 0.32%, Mn: 0.43%, P: 0.009%, S: 0.001%, Cr: 8.8%, Ni: 0.16%, Cu: 0.02%, Mo: 0.35%, V: 0.17%, Nb: 0.06%, Ti: 0.0016%, Al: 0.009%, W: 1.58%, B: 0.0023%, Zr: 0.0037%, N: 487ppm, with the balance being Fe and unavoidable impurities. Example 3

[0016] A method for manufacturing SA-1017Gr92 high-alloy steel continuously cast thick slabs includes the following steps for steelmaking raw materials: hot metal pretreatment → converter steelmaking → LF refining → RH vacuum treatment → continuous casting → slow cooling treatment of the billet, to obtain continuously cast slabs with specifications of 320×2070mm. The chemical composition of the continuously cast slabs is as follows: C: 0.10%, Si: 0.32%, Mn: 0.43%, P: 0.009%, S: 0.001%, Cr: 8.8%, Ni: 0.16%, Cu: 0.02%, Mo: 0.35%, V: 0.17%, Nb: 0.06%, Ti: 0.0016%, Al: 0.009%, W: 1.58%, B: 0.0023%, Zr: 0.0037%, N: 487ppm, with the balance being Fe and unavoidable impurities.

[0017] The manufacturing method of the above embodiments 1-3 specifically includes the following steps: S1: Hot metal pretreatment: KR desulfurization is used, with 1500±100kg / furnace of KR desulfurizing agent added. After desulfurization, the sulfur content of the hot metal is ≤0.002%. The slag removal effect is enhanced, with ≥5 slag removal operations before the slag removal is completed. After slag removal, there is no residue on the surface of the hot metal, and the sulfur content of the steel tapped from the converter is ≤0.010%. S2: Converter smelting: The amount of lime added to the converter is 5800-6500 kg / furnace. During the smelting process, the lance position is adjusted according to the slag formation, and the lance position is controlled at 1.8-2.2 m. The oxygen flow rate is 38000-42000 Nm³. 3 / h, add appropriate pellets to adjust the temperature, TSC target temperature 1620℃, carbon content 0.25%; dynamically adjust carbon temperature balance according to TSC measurement results, TSO target temperature ≥1690℃, carbon ≤0.04%; tap steel in equal samples to ensure that the tapped steel meets the conditions of P≤0.013% and temperature ≥1680℃, and add some Mo and W alloys in the converter process; LF Refining: Upon arrival of molten steel, confirm the ladle's empty space, bottom blowing effect, and observe for alloy agglomerates on the slag surface. For molten steel entering the station, the power supply level should be 10⁻⁶. Slag melting operation should last ≥2 minutes. After slag melting, confirm the slag condition and add lime to adjust it. The target lime addition amount is 300±50 kg. Add aluminum wire for deoxidation, with the target aluminum wire addition amount adjusted to 0.020% based on the converter CAS sample. When the molten steel temperature is ≥1550℃, take samples to confirm the residual element content. After confirming the residual elements are qualified, proceed with alloying: ≤2 tons of micro-carbon ferrochrome from the silo per batch, added at 3-minute intervals, at a temperature ≥1600℃. After the total alloy addition reaches 20 tons, the ladle car departs to confirm the molten steel volume. If the 1 vertical and 3 horizontal alignment is not met, coordinate to avoid molten steel. Subsequent alloying operations are performed according to the chromium composition until qualified. After alloying of chromium, tungsten, vanadium, manganese, etc., the carbon and silicon compositions are adjusted. RH refining: After RH alloying, maintain a high vacuum of ≤3.0 mbar for ≥20 min. After breaking the vacuum, add carbonized rice husks to cover the slag surface. Control the bottom blowing flow rate at 150-200 NL / min and add silicon nitride alloy. Take a sample after 10 minutes to confirm the nitrogen content of the molten steel. After sampling, maintain the bottom blowing flow rate at 100-150 NL / min to ensure that the molten steel is not exposed. Feed silicon nitride wire according to the nitrogen content of the molten steel. After the nitrogen content is qualified, add ferroboron, and then perform calcium treatment (at 160±10 meters). After calcium treatment, perform static stirring for ≥20 min. Continuous casting: Type I covering agent + carbonized rice husk (protective casting) is used. After the tundish starts casting, the covering agent is added when the tundish reaches 15 tons. After the covering agent is added, 10 bags of carbonized rice husk are added at the casing position. No covering agent is added at the stopper rod position. Peritectic steel continuous casting protective slag is used. The liquidus temperature is 1504℃, the superheat is controlled at 10-35℃, the continuous casting speed is 0.65~1.10m / min, the electromagnetic stirring is 420A / 6Hz, and the billet exit temperature is ≥600℃. The casting speed of the three embodiments is shown in the table below: type Slab specifications / mm Continuous casting speed (m / min) Example 1 220×2070 1.0 Example 2 260×2070 0.8 Example 3 320×2070 0.65 Slow cooling of billet: The heat preservation pit is ignited the day before production, and the temperature is maintained at 300-400℃. After the billet comes off the production line, it is immediately transferred to the heat preservation pit and heated to 800℃ at a rate of 60-80℃ / h. It is then held for 8 hours, then cooled to 600±10℃ at a rate of 60-80℃ / h and held for 5 hours. Finally, it is cooled with the furnace to below 300℃ and then removed from the furnace for air cooling.

[0018] In summary, this invention, by employing a converter-LF-RH-continuous casting production process, successfully overcomes the technical bottlenecks in production efficiency, energy consumption, and production costs of existing SA1017Gr92 high-alloy heat-resistant steel. It simplifies the process flow, shortens smelting time, reduces production costs, and enables mass production. This technology not only provides a solution for the production of SA1017Gr92 high-alloy continuously cast slabs but also offers new ideas and process models for the research and development of similar 9-12%Cr series alloy steels, possessing significant engineering application value and industry promotion significance.

[0019] In addition to the above embodiments, the present invention may have other implementation methods. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A high-alloy steel continuously cast wide and thick slab, characterized in that, Its chemical composition is as follows: C: 0.09%-0.11%, Si: 0.20%-0.50%, Mn: 0.40%-0.50%, P<0.015%, S<0.005%, Cr: 8.60%-9.00%, Ni: 0.10-0.20%, Mo: 0.35%-0.45%, Cu≤0.10%, Nb: 0.05%-0.08%, V: 0.16%-0.20%, Ti≤0.01%, Alt≤0.015%, N: 0.035%-0.065%, W: 1.55%-1.80%, B: 0.0015%-0.0040%, Zr≤0.010%, with the balance being iron and unavoidable impurities.

2. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 1, characterized in that: The specific steps are as follows: S1: Hot metal pretreatment: Hot metal is sent to the KR desulfurization station for pretreatment. By adding desulfurizing agents such as lime and calcium carbide, the sulfur content of the hot metal is reduced to below 0.003%. S1: Converter smelting: Mo and W alloys are initially added in the converter process, and the tapping temperature is guaranteed to be ≥1680℃; S2: LF Refining: After confirming the cleanliness of the ladle at the LF process, aluminum wire is added for deoxidation. The target amount of aluminum wire added is based on the converter CAS sample. The deoxidation target is 0.020%. After the alloying of Cr, W, V, Mn, Ni, Mo and other components is completed, the carbon and silicon components are adjusted. S3: RH refining: After RH alloying, maintain a high vacuum of ≤5.0mbar for ≥20min. After RH is completed, feed 150-200 meters of seamless pure calcium wire per furnace. After feeding the wire, stir for ≥20min. Feed silicon nitride wire according to the nitrogen content. Add ferroboron after the nitrogen content is qualified. S4: Pre-treatment of the middle bread: Baking time of the middle bread ≥260 minutes, baking temperature ≥1231℃; S5: Continuous casting: Peritectic steel continuous casting protective slag is used, the liquidus temperature is 1504℃, the superheat is controlled at 10-35℃, the continuous casting speed is 0.65~1.10m / min, the electromagnetic stirring is set to a target of 420A / 6Hz, and the billet exit temperature is ≥600℃. S6: Billet Cutting: After the billet comes off the production line, a flame cutter is used, along with an oxygen blowing pipe and edge wire for combustion assistance, to ensure a smooth cut surface; after cutting, the surface cutting nodules and burrs are initially cleaned. S7: Slow cooling of billet: After the billet comes off the production line, it is immediately transferred to the heat preservation pit for heat preservation. The furnace temperature is controlled at 300-600℃ and the heat preservation time is ≥72 hours. S8: Surface treatment: After the billet has been cooled, a surface inspection is performed. Billets with cutting nodules, burrs or slight cracks are mechanically ground to ensure that the surface is free of defects before rolling.

3. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 2, characterized in that: In the S1 process, KR desulfurization is used, with a desulfurizing agent addition of 1500±100kg / furnace, and the number of slag removals is ≥5 times. After slag removal, there is no residue on the surface of the molten iron, and the S content of the steel tapped from the converter is ≤0.010%.

4. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 2, characterized in that: The lime addition rate in the S2 converter is 5800-6500 kg / furnace. During the smelting process, the lance position is adjusted according to the slag formation, controlled at 1.8-2.2 m, and the oxygen flow rate is 38000-42000 Nm³. 3 / h; tapping temperature ≥1690℃ to ensure full melting of Mo and W alloys; P≤0.013% and carbon≤0.04% at tapping.

5. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 2, characterized in that: After RH alloying in S3, the high vacuum degree ≤3.0mbar is maintained for ≥22min; 180±10m / furnace of seamless pure calcium wire is fed in for calcium treatment, and the static stirring time is ≥22min; after breaking the void, carbonized rice husks are added to cover the slag surface, the bottom blowing flow rate is controlled at 150-200NL / min, and silicon nitride alloy is added. After 10 minutes, a sample is taken to confirm the nitrogen content of the molten steel. After sampling, the bottom blowing flow rate is maintained at 100-150NL / min to confirm that the molten steel is not exposed, and silicon nitride wire is added according to the nitrogen content of the molten steel.

6. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 2, characterized in that: In the S5 continuous casting, a type I covering agent + carbonized rice husk protective casting is used. After the tundish starts casting, the covering agent is added when the tundish reaches 15 tons. After the covering agent is added, 10 bags of carbonized rice husk are added at the sleeve position. No covering agent is added at the stopper rod position. Peritectic steel continuous casting protective slag is used. The superheat is controlled at 22±3℃.

7. The method for manufacturing a high-alloy steel continuous casting thick slab according to claim 2, characterized in that: The optimal S7 slow cooling curve is as follows: first, maintain the temperature at 800±10℃ for 8 to 9 hours, then lower the temperature to 600±10℃ and maintain it for 5 to 6 hours, and finally cool it with the furnace to below 300℃ before air cooling to reduce the generation of cracks.