Production and preparation method of rare earth heat-resistant alloy steel 12Cr1MoVRE hot rolled steel strip with thickness of 2.5-25.0 mm

Abstract

The invention discloses a production and preparation method of a rare earth heat-resistant alloy steel 12Cr1MoVRE hot rolled steel strip with the thickness of 2.5-25.0 mm. The production and preparation method comprises the steps of molten iron pretreatment, converter combined blowing, LF refining and slab continuous casting to form a continuous casting slab, and the continuous casting slab comprises, by weight, 0.08%-0.15% of C, 0.15%-0.40% of Si, 0.40%-0.70% of Mn, smaller than or equal to 0.030% of P, smaller than or equal to 0.030% of S, 0.90%-1.10% of Cr, 0.25%-0.35% of Mo, 0.15%-0.30% of V and smaller than or equal to 0.0025% of Ce; heating the casting blank; hot rolling; and cooling and coiling. Reasonable Mn, Cr, Mo and Ce are added, a reasonable controlled rolling and controlled cooling process is matched, and stacking heat preservation and slow cooling measures are adopted after rolling, so that a product is uniform and fine in structure, stable in performance, good in plate shape and good in customer feedback application effect.

Description

Technical Field

[0001] This invention belongs to the field of hot-rolled steel strip production technology, and particularly relates to a method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip. Background Technology

[0002] As modern industry develops towards higher temperatures and pressures, the performance requirements for materials are becoming increasingly stringent. In industries such as power and petrochemicals, equipment such as boilers, pressure vessels, and steam pipelines need to operate stably for extended periods under high temperatures and pressures, requirements that ordinary steel cannot meet. 12Cr1MoV was developed to address this need. Inheriting the excellent properties of chromium-molybdenum steel, it further enhances these properties through a specific alloying element ratio, exhibiting superior oxidation resistance, thermal strength, and high-temperature mechanical properties. It effectively resists oxidation and corrosion in harsh environments, maintaining good mechanical properties and creep resistance. Furthermore, the addition of rare earth elements further improves the heat resistance and corrosion resistance of the steel plate, better meeting user requirements.

[0003] To meet production and market demands, we developed 12Cr1MoVRE hot-rolled coils that meet market requirements. Utilizing advanced 2250mm rolling equipment and rolling processes tailored to specific product needs, the product exhibits excellent performance indicators and has received positive feedback from customers.

[0004] Sun Changyu et al. (Sun Changyu et al., A Production Method of Thin-Gauge High-Toughness 12Cr1MoVR Pressure Vessel Steel Plate, Patent Application Received, August 5, 2022) researched a production method for thin-gauge high-toughness 12Cr1MoVR pressure vessel steel plates. The production process includes KR desulfurization → converter smelting → LF refining → RH refining → continuous casting → slow cooling in the heat preservation pit → heating → rolling → cooling → hot straightening → shearing → flaw detection → normalizing → tempering. The produced steel plates have a thickness of 10-40mm. The produced products have stable processes, excellent performance, and high toughness in thin gauges with good surface quality and impact toughness, meeting customer requirements. This method provides controlled rolling delivery of 3.0-20mm thick hot-rolled coils. Compared with the above patent, it does not involve the RH process, but the various performance indicators of the products are well controlled.

[0005] Tan Fengliang et al. (Tan Fengliang et al., A 12Cr1MoV Low Alloy Heat-Resistant Steel and Its Production Process, Authorized Patent, November 15, 2019) introduced a low alloy heat-resistant steel and its production process. The product thickness is 6.0~8.0mm. The production process adopts controlled rolling-relaxation-online low temperature tempering. The product has a low hourly output and only adds conventional alloy components without adding rare earth elements.

[0006] Deng Jianjun et al. (Deng Jianjun et al., A low-alloy 12Cr1MoV steel plate and its production method, patent application accepted, August 29, 2017) introduced a low-cost steel plate with good strength and toughness. The production method of the invented steel plate includes smelting, continuous casting, heating, rolling and tempering processes. The shortcoming is that rare earth elements are not added to its composition and the production process route is not consistent.

[0007] In summary, the aforementioned patents describe the production and welding processes of heat-resistant alloy steel produced on a 12Cr1MoVRE medium-thick plate production line, but fail to provide detailed specifications for the production of 2.5-25.00mm thick heat-resistant alloy steel products on a 2250mm production line, as well as the product's microstructure and properties. Summary of the Invention

[0008] The purpose of this invention is to provide a production method for 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip. By adding appropriate amounts of Mn, Cr, Mo, and Ce, and matching them with a reasonable controlled rolling and cooling process, and by adopting stacking insulation and slow cooling measures after rolling, the product has a uniform and fine microstructure, stable performance, good plate shape, and good application results according to customer feedback.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0010] This invention discloses a method for producing hot-rolled rare-earth heat-resistant alloy steel 12Cr1MoVRE strip with a thickness of 2.5~25.0mm, comprising:

[0011] The hot metal is pretreated, combined with converter blowing, and refined by LF. The slab is then continuously cast to form a continuously cast billet. The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08~0.15%, Si: 0.15~0.40%, Mn: 0.40~0.70%, P: ≤0.030%, S: ≤0.030%, Cr: 0.90~1.10%, Mo: 0.25~0.35%, V: 0.15~0.30%, Ce≤0.0025%, with the balance being Fe and unavoidable impurities.

[0012] For slabs with a thickness of 2.5-6mm, the heating temperature is controlled at 1210-1260℃, the soaking temperature at 1200-1250℃, and the furnace exit temperature at 1230±20℃; for slabs with a thickness of 6.01-12.00mm, the heating temperature is controlled at 1200-1230℃, the soaking temperature at 1210-1240℃, and the furnace exit temperature at 1220±20℃; for slabs with a thickness of 12.01-25.00mm, the heating temperature is controlled at 1190-1230℃, the soaking temperature at 1190-1220℃, and the furnace temperature at 1200±20℃. Hot charging is used for the slabs, and the furnace time is controlled within 170-250 minutes.

[0013] Hot rolling employs a two-stage controlled rolling process: roughing and finishing. Roughing uses a 3+5 pattern with an initial rolling temperature of 980–1130℃. Finishing involves an initial rolling thickness of 2.5–12.00 mm for intermediate slabs of 40–55 mm and a final rolling temperature of 870–1010℃; for intermediate slabs of 12.01–20.00 mm, the thickness is 55–65 mm and the final rolling temperature is 860–1000℃; and for intermediate slabs of 20.01–25.00 mm, the thickness is 55–65 mm and the final rolling temperature is 850–890℃. Finishing is achieved using a 7-stand continuous variable crown mill with an initial rolling temperature of 980–1120℃.

[0014] Cooling and winding: For thicknesses of 3.0~6.00mm, the cooling adopts a "15" mode laminar flow cooling method, which is a post-dispersion cooling method, with a cooling interval of two to one, and the cooling rate is controlled at 22~43℃ / s. The winding temperature is 720~760℃. For thicknesses of 6.01~12.0mm, the cooling adopts a "15" mode laminar flow cooling method, which is a pre-dispersion cooling method, with a cooling interval of two to one, and the cooling rate is controlled at 22~43℃ / s. The winding temperature is 710~760℃. 50℃; thickness 12.01~20.00mm, cooling adopts "15" mode laminar flow cooling method, which is post-dispersion, cooling method is two-on-one, cooling speed is controlled at 20~40℃ / s, and winding temperature is 700~740℃; thickness 20.01~25.00mm, cooling adopts "15" mode laminar flow cooling method, which is post-dispersion, cooling method is two-on-one, cooling speed is controlled at 20~40℃ / s, and winding temperature is 690~730℃.

[0015] Furthermore, the chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08~0.10%, Si: 0.15~0.25%, Mn: 0.40~0.55%, P: ≤0.015%, S: ≤0.005%, Cr: 0.90~1.00%, Mo: 0.25~0.35%, V: 0.15~0.25%, Ce: ≤0.0020%, with the balance being Fe and unavoidable impurities.

[0016] Furthermore, the chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08%, Si: 0.17%, Mn: 0.45%, P: 0.011%, S: 0.005%, Cr: 0.93%, Mo: 0.26%, V: 0.16%, Ce: 0.0018%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.09%, Si: 0.18%, Mn: 0.44%, P: 0.012%, S: 0.003%, Cr: 0.95%, Mo: 0.27%, V: 0.15%, Ce: 0.0017%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08%, Si: 0.16%, Mn: 0.46%, P: 0.010%, S: 0.001%, Cr: 0.96%, Mo: 0.26%, V: 0.17%, Ce: 0.0015%, with the balance being Fe and unavoidable impurities.

[0019] Furthermore, the mechanical properties meet the following requirements: yield strength ≥ 520 MPa, tensile strength ≥ 610 MPa.

[0020] Furthermore, the mechanical properties meet the following requirements: elongation ≥ 23.5%.

[0021] Furthermore, the metallographic structure of this rare earth heat-resistant alloy steel is ferrite + pearlite, with a grain size ≥11.5.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] This invention is based on an alloy design system using C, Mn, Cr, Mo, and V, supplemented by Ce microalloying. By controlling various corrosion-resistant and strengthening elements, the produced products exhibit excellent corrosion resistance, weldability, strength, and toughness. The inventors have discovered that by using the raw material composition and mass ratio provided in this invention, combined with controlled rolling and cooling processes, a rare-earth heat-resistant alloy steel, 12Cr1MoVRE, has been developed using a 2250mm hot rolling production line. This steel possesses excellent corrosion resistance, strength, toughness, and weldability, and has been successfully applied to pipeline steel systems in metallurgical, power, and chemical industries, offering the following beneficial effects:

[0024] This invention provides a 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip and its production method. Through a reasonable composition system design, the microstructure is ferrite + pearlite with a grain size of approximately 11.5. It possesses high strength, oxidation resistance, and corrosion resistance, making it suitable for high-temperature pipeline applications. The mechanical and technological properties meet the requirements of tensile strength ≥610MPa, yield strength ≥520MPa, and elongation ≥23.5%. Detailed Implementation

[0025] Example 1: A 2.5~25.0 mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip and its production method

[0026] The molten iron undergoes desulfurization pretreatment. The converter employs top-and-bottom blowing smelting technology, adding ferromanganese, copper plates, and ferrochrome alloys for deoxidation and alloying. The composition is adjusted to meet steelmaking requirements, with a converter tapping temperature ≥1620℃. The molten steel after converter smelting is then transferred to the LF refining process for further treatment. Ferromanganese, ferrosilicon, ferrochrome, ferroaluminum, and ferromolybdenum alloys are added to adjust the composition to the target level. The molten steel is then transported for RH vacuum treatment, during which the composition and temperature are fine-tuned. The vacuum level is required to be ≤2.6 mbar, maintained for ≥10 min, and a pure degassing time of at least 7 min is ensured. After vacuum treatment, calcium treatment is performed. After wire feeding, a soft blowing time of at least 8 min is ensured. Before steel loading, the argon flow rate is adjusted to maintain the molten steel in a soft blowing state to prevent exposed steel. Smelting is carried out according to the chemical composition shown in Table 1, with a slab superheat of 30℃ for continuous casting. Following this, the slab is cleaned, slowly cooled, and the continuous casting slab quality is inspected. The slab was heated to 1230℃, the soaking temperature was 1220℃, the exit temperature was 1210℃, and the heating time was 210 min. The heated slab was then subjected to high-pressure water descaling. Width was determined using a width-fixing press, and a 2-stand roughing mill and a 7-stand CVC finishing mill were used. The intermediate slab thickness was 44.0 mm, and the finishing rolling temperature was 895℃. Laminar flow cooling employed a post-dispersion cooling mode "15" (two upper and one lower nozzle), with a cooling rate of 33℃ / s. The coiling temperature was 741℃, and the finished product thickness was 2.75 mm. The mechanical property test results of the steel strip prepared in this example are shown in Table 2.

[0027] Example 2: A 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip and its production method

[0028] The molten iron undergoes desulfurization pretreatment. The converter employs top-and-bottom blowing smelting technology, adding ferromanganese, copper plates, and ferrochrome alloys for deoxidation and alloying. The composition is adjusted to meet steelmaking requirements, with a converter tapping temperature ≥1620℃. The molten steel after converter smelting is then transferred to the LF refining process for further treatment. Ferromanganese, ferrosilicon, ferrochrome, ferroaluminum, and ferromolybdenum alloys are added to adjust the composition to the target level. The molten steel is then transported for RH vacuum treatment, during which the composition and temperature are fine-tuned. The vacuum level is required to be ≤2.6 mbar, maintained for ≥10 min, and a pure degassing time of at least 7 min is ensured. After vacuum treatment, calcium treatment is performed. After wire feeding, a soft blowing time of at least 8 min is ensured. Before steel loading, the argon flow rate is adjusted to maintain the molten steel in a soft blowing state to prevent exposed steel. Smelting is carried out according to the chemical composition shown in Table 1, with a slab superheat of 29℃ for continuous casting. Afterwards, slab cleaning, slow cooling, and continuous casting slab quality inspection are performed. The slab was heated to 1220℃, the soaking temperature was 1215℃, the exit temperature was 1220℃, and the heating time was 215 minutes. The heated slab was then subjected to high-pressure water descaling. Width was determined using a width-fixing press, and a 2-stand roughing mill and a 7-stand CVC finishing mill were employed. The intermediate slab thickness was 48.0 mm, and the finishing rolling temperature was 890℃. Laminar flow cooling adopted a post-dispersion cooling mode "15" (two upper and one lower nozzle), with a cooling rate of 35℃ / s. The coiling temperature was 731℃, and the finished product thickness was 9.8 mm. The mechanical property test results of the steel strip prepared in this example are shown in Table 2.

[0029] Example 3: A 2.5~25.0 mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip and its production method

[0030] The molten iron undergoes desulfurization pretreatment. The converter employs top-and-bottom blowing smelting technology, adding ferromanganese, copper plates, and ferrochrome alloys for deoxidation and alloying. The composition is adjusted to meet steelmaking requirements, with a converter tapping temperature ≥1620℃. The molten steel after converter smelting is then transferred to the LF refining process for further treatment. Ferromanganese, ferrosilicon, ferrochrome, ferroaluminum, and ferromolybdenum alloys are added to adjust the composition to the target level. The molten steel is then transported for RH vacuum treatment, during which the composition and temperature are fine-tuned. The vacuum level is required to be ≤2.6 mbar, maintained for ≥10 min, and a pure degassing time of at least 7 min is ensured. After vacuum treatment, calcium treatment is performed. After wire feeding, a soft blowing time of at least 8 min is ensured. Before steel loading, the argon flow rate is adjusted to maintain the molten steel in a soft blowing state to prevent exposed steel. Smelting is carried out according to the chemical composition shown in Table 1, with a slab superheat of 30℃ for continuous casting. Following this, the slab is cleaned, slowly cooled, and the continuous casting slab quality is inspected. The slab was heated to 1210℃, the soaking temperature was 1200℃, the exit temperature was 1198℃, and the heating time was 220 min. The heated slab was then subjected to high-pressure water descaling. Width was determined using a width-fixing press, and a 2-stand roughing mill and a 7-stand CVC finishing mill were employed. The intermediate slab thickness was 56.0 mm, and the finishing rolling temperature was 864℃. Laminar flow cooling was used in a rear-front diffused cooling mode "15" (two nozzles on top and one on the bottom), with a cooling rate of 38℃ / s. The coiling temperature was 719℃, and the finished product thickness was 19.8 mm. The mechanical property test results of the steel strip prepared in this example are shown in Table 2.

[0031] To improve the uniformity of the steel coil structure and reduce the stress in the steel strip, all specifications of steel coils were slowly cooled in an insulation hood after rolling. The slow cooling time for the steel coils was no less than 48 hours, and none of them were piled up near the ventilation openings.

[0032] The typical microstructure of the steel strip prepared in this embodiment is ferrite and a small amount of pearlite, with a grain size of approximately 11.5. The mechanical property test results of the steel strip prepared in this embodiment are shown in Table 2.

[0033] Table 1. Chemical composition (wt%) of Examples 1-3 of the present invention

[0034] Example C Si Mn P S Mo V Cr Ce 1 0.08 0.17 0.45 0.011 0.005 0.26 0.16 0.93 0.0018 2 0.09 0.18 0.44 0.012 0.003 0.27 0.15 0.95 0.0017 3 0.08 0.16 0.46 0.010 0.001 0.26 0.17 0.96 0.0015

[0035] Table 2. Test results of mechanical properties and corrosion resistance of the steel strips prepared in Examples 1-3 of this invention.

[0036] Example Finished product thickness (mm) Yield strength (MPa) Tensile strength (MPa) Elongation A (%) 180° cold bending test 1 2.75 535 627 27.5 qualified 2 9.8 540 610 25.5 qualified 3 19.8 520 625 23.5 qualified Standard requirements ~ ≥245 ≥440 ≥19 d=3a

[0037] Table 2 shows the data for a 2.5~25.0 mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip and its production preparation method.

[0038] The mechanical and technological properties meet the following requirements: yield strength ≥ 520 MPa, tensile strength ≥ 610 MPa, elongation A ≥ 23.5%, and cold bending d = 3a.

[0039] As can be seen from the results of the above embodiments, the heat-resistant alloy steel strip for boilers and pipelines of the present invention has excellent mechanical properties, weldability, corrosion resistance and other characteristics.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing a 2.5~25.0 mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip, characterized in that: include: The hot metal is pretreated, combined with converter blowing, and refined by LF. The slab is then continuously cast to form a continuously cast billet. The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08~0.15%, Si: 0.15~0.40%, Mn: 0.40~0.70%, P: ≤0.030%, S: ≤0.030%, Cr: 0.90~1.10%, Mo: 0.25~0.35%, V: 0.15~0.30%, Ce≤0.0025%, with the balance being Fe and unavoidable impurities. For slabs with a thickness of 2.5-6mm, the heating temperature is controlled at 1210-1260℃, the soaking temperature at 1200-1250℃, and the furnace exit temperature at 1230±20℃; for slabs with a thickness of 6.01-12.00mm, the heating temperature is controlled at 1200-1230℃, the soaking temperature at 1210-1240℃, and the furnace exit temperature at 1220±20℃; for slabs with a thickness of 12.01-25.00mm, the heating temperature is controlled at 1190-1230℃, the soaking temperature at 1190-1220℃, and the furnace temperature at 1200±20℃. Hot charging is used for the slabs, and the furnace time is controlled within 170-250 minutes. Hot rolling employs a two-stage controlled rolling process: roughing and finishing. Roughing uses a 3+5 pattern with an initial rolling temperature of 980–1130℃. Finishing involves an initial rolling thickness of 2.5–12.00 mm for intermediate slabs of 40–55 mm and a final rolling temperature of 870–1010℃; for intermediate slabs of 12.01–20.00 mm, the thickness is 55–65 mm and the final rolling temperature is 860–1000℃; and for intermediate slabs of 20.01–25.00 mm, the thickness is 55–65 mm and the final rolling temperature is 850–890℃. Finishing is achieved using a 7-stand continuous variable crown mill with an initial rolling temperature of 980–1120℃. Cooling and winding: For thicknesses of 3.0~6.00mm, the cooling adopts a "15" mode laminar flow cooling method, which is a post-dispersion cooling method, with a cooling interval of two parts and one part open, and the cooling rate is controlled at 22~43℃ / s. The winding temperature is 720~760℃. For thicknesses of 6.01~12.0mm, the cooling adopts a "15" mode laminar flow cooling method, which is a pre-dispersion cooling method, with a cooling interval of two parts and one part open, and the cooling rate is controlled at 22~43℃ / s. The winding temperature is 710~760℃. 50℃; thickness 12.01~20.00mm, cooling adopts "15" mode laminar flow cooling method, which is post-dispersion, cooling method is two-on-one, cooling speed is controlled at 20~40℃ / s, and winding temperature is 700~740℃; thickness 20.01~25.00mm, cooling adopts "15" mode laminar flow cooling method, which is post-dispersion, cooling method is two-on-one, cooling speed is controlled at 20~40℃ / s, and winding temperature is 690~730℃.

2. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 1, characterized in that: The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08~0.10%, Si: 0.15~0.25%, Mn: 0.40~0.55%, P: ≤0.015%, S: ≤0.005%, Cr: 0.90~1.00%, Mo: 0.25~0.35%, V: 0.15~0.25%, Ce: ≤0.0020%, with the balance being Fe and unavoidable impurities.

3. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 2, characterized in that: The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08%, Si: 0.17%, Mn: 0.45%, P: 0.011%, S: 0.005%, Cr: 0.93%, Mo: 0.26%, V: 0.16%, Ce: 0.0018%, with the balance being Fe and unavoidable impurities.

4. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 2, characterized in that: The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.09%, Si: 0.18%, Mn: 0.44%, P: 0.012%, S: 0.003%, Cr: 0.95%, Mo: 0.27%, V: 0.15%, Ce: 0.0017%, with the balance being Fe and unavoidable impurities.

5. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 2, characterized in that: The chemical composition and weight percentage of the continuously cast billet are as follows: C: 0.08%, Si: 0.16%, Mn: 0.46%, P: 0.010%, S: 0.001%, Cr: 0.96%, Mo: 0.26%, V: 0.17%, Ce: 0.0015%, with the balance being Fe and unavoidable impurities.

6. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 2, characterized in that: Mechanical properties must meet the following requirements: yield strength ≥ 520 MPa, tensile strength ≥ 610 MPa.

7. The method for producing 2.5~25.0mm thick rare earth heat-resistant alloy steel 12Cr1MoVRE hot-rolled steel strip according to claim 2, characterized in that: Mechanical properties must meet the following requirement: elongation ≥ 23.5%.