Preparation method of 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip

Abstract

The application discloses a preparation method of 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip, which comprises the following steps: molten iron pretreatment, converter composite blowing, LF refining, RH, continuous casting, slab heating, hot continuous rolling, laminar flow cooling and coiling, and heat preservation slow cooling; the chemical components of the heat-resistant alloy steel are as follows in percentage by weight: C: 0.12-0.18%, Si: 0.15-0.40%, Mn: 0.40-0.70%, P: ≤0.030%, S: ≤0.030%, Cr: 0.80-1.10%, Mo: 0.40-0.55%, and Ce: ≤0.0030%. The application aims at adding reasonable Mn, Cr, Mo and Ce and controlling the content of gas elements, matching reasonable controlled rolling and controlled cooling process, and adopting heat preservation slow cooling measures after rolling, so that the product has uniform and small organization, stable performance and good plate shape.

Description

TECHNICAL FIELD

[0001] The application is mainly applied to the industrial fields of boiler heat-resistant structural parts, high-temperature pipelines, high-temperature flanges and ship desulfurization towers, and particularly relates to a preparation method of 3.0-20.0 mm thick rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip. BACKGROUND

[0002] With the fierce competition in the steel market and the rapid development of the domestic and foreign steel industry, the demand for 15CrMo coiled sheets is increasing, and in combination with the application requirements of the product in the petroleum, aerospace and energy fields, the toughness and oxidation resistance and weldability of the product are required, and the product serving in the atmospheric corrosion environment, such as in the power and chemical enterprise construction engineering, the 15CrMo steel is a pearlite heat-resistant steel, which has significant thermal strength and oxidation resistance in a high-temperature environment, and exhibits certain hydrogen corrosion resistance. These outstanding performances are mainly due to the high content of Cr, C and other alloy elements in the steel.

[0003] In order to meet the production and market demand, the 15CrMo hot-rolled coiled sheet meeting the market requirements is developed, the advanced 2250 mm rolling equipment and the rolling process special for the product are used, the performance indexes of the product are good, and the product is well received by the customers.

[0004] Deng Jianjun et al. (Deng Jianjun et al., Rolling method of low-alloy 15CrMo steel plate, accepted for patent, December 21, 2018) study a rolling method of low-alloy 15CrMo steel plate, which includes two-stage controlled rolling of continuous casting billet and post-rolling controlled cooling process, the thickness of the produced steel plate is 20-50 mm, and the performance meets: yield strength ≥ 300 MPa, tensile strength Rm: 470-590 MPa; elongation ≥ 20%, 0℃ transverse impact energy is greater than 80J, the produced product meets the requirements of the customers, and the deficiencies are that the product is designed as a medium plate, and the CVC technology is not used to adjust the flatness of the steel strip, and the composition of the steel strip and the rolling production situation are not introduced.

[0005] Yang Hua et al. (Yang Hua et al., Heat treatment-free 15CrMo heat-resistant alloy steel hot continuous rolling coiled sheet and CSP process production method thereof, accepted for patent, February 27, 2024) introduce a heat treatment-free 15CrMo heat-resistant alloy steel hot continuous rolling coiled sheet and a CSP process production method thereof, and the deficiencies are that the thickness of the continuous casting slab is 60-70 mm, the compression ratio is small when rolling compared with the slab 230 mm in this patent, the metallographic structure size and grain size are larger and non-uniform compared with the 2250 mm rolling mill rolled steel strip, and the cost is high, and the rare earth element is not added.

[0006] Nie Xinlei et al. (Nie Xinlei et al., A heat-resistant steel 15CrMo welding process, accepted patent, September 29, 2023) introduces a heat-resistant steel 15CrMo welding process, which belongs to the field of welding technology. Based on the adoption of GTAW+SMAW hybrid welding process test, and the adoption of preheating, interlayer temperature control, post-heating and holding slow cooling, reasonable matching of welding materials, low heat input welding parameters and other welding processes, excellent welding joints are obtained. The disadvantage is that it does not specify the 15CrMo product production process control in detail, and does not add rare earth elements.

[0007] In summary, the above-mentioned patents have studied the production and welding process of heat-resistant alloy steel produced by 15CrMo medium plate production line, and have not specified the detailed production of 3-20mm thickness heat-resistant alloy steel products in 2250mm production line and the organization and performance of the products. SUMMARY

[0008] The purpose of the present application is to provide a preparation method of 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip, by adding reasonable Mn, Cr, Mo, Ce and controlling the content of gas elements (H, O, N), matching the reasonable controlled rolling and controlled cooling process, adopting holding slow cooling measures after rolling, the product organization is uniform and fine, the performance is stable, the plate shape is good, and the customer feedback application effect is good.

[0009] The product thickness of the hot-rolled coil is 3.0-20.0mm, the plate shape quality is good after slow cooling by the holding cover, the organization is uniform, the performance is stable, especially the strength and toughness, weldability and oxidation resistance.

[0010] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0011] The present application is a preparation method of 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip, which comprises the following steps: molten iron pretreatment, converter composite blowing, LF refining, RH, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling, holding slow cooling; the hot continuous rolling comprises a heating furnace, rough rolling and finish rolling; wherein:

[0012] The continuous casting blank heating temperature is controlled at 1190-1250℃, the soaking temperature is 1190-1240℃, the out-of-furnace temperature is controlled at 1220±20℃ when the thickness is ≤6mm, the out-of-furnace temperature is controlled at 1210±20℃ when the thickness is 6.01-12.00mm, the furnace temperature is controlled at 1200±20℃ when the thickness is 12.01-20.00mm, and the slab in-furnace time is controlled within 180-240min;

[0013] The rough rolling adopts 3+5 mode, and the rough rolling opening temperature is 980-1120℃;

[0014] The finishing rolling open rolling thickness is 3.0-12.00mm, the intermediate blank thickness is 40-55mm, and the finish rolling temperature is 870-1010℃; the intermediate blank thickness is 55-65mm, and the finish rolling temperature is 850-870℃ for thickness 12.0-20.00mm;

[0015] In the cooling and coiling step:

[0016] The thickness is 3.0-12.0mm, the cooling adopts laminar flow cooling mode of "29" mode, is after dispersion, the cooling mode is every other one, the cooling speed control is 30-50℃ / s, and the coiling temperature is 650-690℃;

[0017] The thickness is 12.0-16.0mm, the cooling adopts laminar flow cooling mode of "12" mode, is before dispersion, the cooling mode is every other two, the cooling speed control is 25-45℃ / s, and the coiling temperature is 630-670℃;

[0018] The thickness is 16.0-20.0mm, the cooling adopts laminar flow cooling mode of "11" mode, is before dispersion, the cooling mode is every other one, the cooling speed control is 20-40℃ / s, and the coiling temperature is 610-650℃.

[0019] Further, the finishing rolling adopts 7-stand continuous variable crown mill finishing rolling, and the open rolling temperature of the finishing rolling is 980-1120℃.

[0020] Further, the chemical composition of the heat-resistant alloy steel is C: 0.12-0.18%, Si: 0.15-0.40%, Mn: 0.40-0.70%, P: ≤0.030%, S: ≤0.030%, Cr: 0.80-1.10%, Mo: 0.40-0.55%, Ce ≤0.0030%, and the balance is Fe and inevitable impurities.

[0021] Further, the chemical composition of the heat-resistant alloy steel is C: 0.13-0.15%, Si: 0.20-0.30%, Mn: 0.40-0.55%, P: ≤0.015%, S: ≤0.01%, Cr: 0.90-1.10%, Mo: 0.40-0.50%, Ce: 0.0010-0.0025%, and the balance is Fe and inevitable impurities.

[0022] Further, the metallographic structure of the heat-resistant alloy steel is ferrite+pearlite, and the grain size is ≥11 levels.

[0023] Furthermore, the heat-resistant alloy steel meets the following requirements: tensile strength ≥ 450 MPa, yield strength ≥ 295 MPa, elongation ≥ 19%, and 180° cold bending test.

[0024] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0025] This invention is based on an alloy design system using C, Mn, Cr, and Mo as the base elements, 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, 15CrMo, 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.

[0026] This invention, through a rationally designed composition system, produces a hot-rolled steel strip containing 0.90-1.00% Cr, 0.40-0.50% Mo, and 0.0010-0.0030% Ce, all corrosion-resistant elements. The microstructure is ferrite + pearlite, with a grain size of approximately grade 12. It possesses high strength, oxidation resistance, and corrosion resistance, making it suitable for high-temperature pipeline applications. The mechanical and technological properties meet the following requirements: tensile strength ≥ 450 MPa, yield strength ≥ 295 MPa, and elongation ≥ 19%. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings.

[0028] Figure 1 Metallographic structure diagram of the steel strip at 1 / 4 of its longitudinal direction in this invention;

[0029] Figure 2 Application diagram for customers. Detailed Implementation

[0030] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0031] Example 1

[0032] A method for preparing 3.0-20.0 mm thick rare earth heat-resistant alloy steel 15CrMo hot-rolled strip:

[0033] The molten iron is desulfurized pretreated, the converter adopts top and bottom combined blowing smelting technology, manganese iron, copper plate and chromium iron alloy are added in the converter for deoxidization and alloying, the composition is adjusted to meet the tapping requirements, and the converter tapping temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment, according to the composition of the molten steel, manganese iron, silicon iron, chromium iron, aluminum iron, molybdenum iron and other alloys are added to adjust to the target composition. The molten steel is transported to the RH vacuum treatment, the composition and temperature are adjusted during the period, the vacuum degree is required to be ≤2.6mbar, the vacuum time is ≥10min, and the circulating pure degassing time is more than 7min. After vacuum treatment, calcium treatment is carried out, the soft blowing time is ensured to be more than 8min after wire feeding, the argon flow is adjusted before the steel is put into the soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab is continuously cast with a superheating degree of 33℃. Then the slab is cleaned, slowly cooled and the continuous casting blank quality is checked. The slab heating temperature is 1230℃, the soaking temperature is 1220℃, the discharge temperature is 1210℃, and the heating time is 210min. The heated slab is subjected to high-pressure water phosphorus removal. The width is fixed by a fixed-width press, 2 roughing mills and 7 CVC finishing mills are used. The intermediate blank thickness is 45.0mm, and the finishing temperature is 890℃. The laminar cooling adopts the rear dispersion cooling mode "29" (the upper and lower nozzles are opened one by one), the cooling speed is 38℃ / s, the coiling temperature is 690℃, the finished product thickness is 5.7mm, and the mechanical property detection results of the steel strip prepared in the example are shown in Table 2.

[0034] Example 2

[0035] A method for preparing a 3.0-20.0mm thick rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip:

[0036] The molten iron is desulfurized pretreated, the converter adopts top and bottom combined blowing smelting technology, manganese iron, copper plate and chromium iron alloy are added in the converter for deoxidization and alloying, the composition is adjusted to meet the tapping requirements, and the converter tapping temperature is ≥1620℃. The molten steel after converter smelting is lifted to the LF refining process for treatment, according to the composition of the molten steel, manganese iron, silicon iron, chromium iron, aluminum iron, molybdenum iron and other alloys are added to adjust to the target composition. The molten steel is transported to the RH vacuum treatment, the composition and temperature are adjusted during the period, the vacuum degree is required to be ≤2.6mbar, the vacuum time is ≥10min, and the circulating pure degassing time is more than 7min. After vacuum treatment, calcium treatment is carried out, the soft blowing time is ensured to be more than 8min after wire feeding, the argon flow is adjusted before the steel is put into the soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab continuous casting superheat is 31℃. Then the slab is cleaned, slowly cooled and the continuous casting blank quality is checked. The slab heating temperature is 1220℃, the soaking temperature is 1210℃, the discharge temperature is 1200℃, and the heating time is 216min. The heated slab is subjected to high-pressure water phosphorus removal. The width is fixed by a fixed-width press, 2 roughing mills and 7 CVC finishing mills are used. The intermediate blank thickness is 45.0mm, and the finishing temperature is 890℃. The laminar cooling adopts the rear dispersion cooling mode "29" (the upper and lower nozzles are opened one by one), the cooling speed is 44℃ / s, the coiling temperature is 673℃, the finished product thickness is 9.8mm, and the mechanical property detection results of the steel strip prepared in the example are shown in Table 2.

[0037] Example 3

[0038] A preparation method of a 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip:

[0039] The molten iron is desulfurized pretreated, the converter adopts top and bottom combined blowing smelting technology, manganese iron, copper plate and chromium iron alloy are added in the converter for deoxidization and alloying, the composition is adjusted to meet the tapping requirements, and the converter tapping temperature is ≥1620℃. The molten steel after converter smelting is lifted to the LF refining process for treatment, according to the composition of the molten steel, manganese iron, silicon iron, chromium iron, aluminum iron, molybdenum iron and other alloys are added to adjust to the target composition. The molten steel is transported to the RH vacuum treatment, the composition and temperature are adjusted during the period, the vacuum degree is required to be ≤2.6mbar, the vacuum time is ≥10min, and the circulating pure degassing time is more than 7min. After vacuum treatment, calcium treatment is carried out, the soft blowing time is ensured to be more than 8min after wire feeding, the argon flow is adjusted before the steel is put into the soft blowing state to prevent the molten steel from being exposed. According to the chemical composition shown in Table 1, the slab is continuously cast with a superheating degree of 30℃. Then the slab is cleaned, slowly cooled and the continuous casting blank quality is checked. The slab heating temperature is 1210℃, the soaking temperature is 1200℃, the discharge temperature is 1190℃, and the heating time is 220min. The heated slab is subjected to high-pressure water phosphorus removal. The width is fixed by a fixed-width press, 2 roughing mills and 7 CVC finishing mills are used. The intermediate blank thickness is 57.0mm, and the finishing temperature is 864℃. The laminar cooling adopts the front and rear cooling mode "12" (the upper and lower nozzles are separated by two), the cooling speed is 46℃ / s, the coiling temperature is 655℃, the finished product thickness is 15.75mm, and the mechanical property detection results of the steel strip prepared in the example are shown in Table 2.

[0040] Example 4

[0041] A preparation method of a 3.0-20.0mm thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip:

[0042] The molten iron is desulfurized pretreated, the converter adopts top and bottom combined blowing smelting technology, manganese iron, copper plate and chromium iron alloy are added in the converter for deoxidization and alloying, the composition is adjusted to meet the tapping requirements, and the converter tapping temperature is ≥1620℃. The molten steel after converter smelting is hoisted to the LF refining process for treatment, and according to the composition of the molten steel, manganese iron, silicon iron, chromium iron, aluminum iron, molybdenum iron and other alloys are added to adjust to the target composition. The molten steel is transported to the RH vacuum treatment, the composition and temperature are adjusted during the period, the vacuum degree is required to be ≤2.6mbar, the vacuum time is required to be ≥10min, and the circulating pure degassing time is required to be more than 7min. After vacuum treatment, calcium treatment is carried out, the soft blowing time is ensured to be more than 8min after wire feeding, the argon flow is adjusted before the molten steel is charged to make the molten steel in a soft blowing state, and the molten steel is prevented from being exposed. The chemical composition is smelted according to Table 1, and the slab continuous casting superheat is 32℃. Then the slab is cleaned, slowly cooled and the continuous casting blank quality is checked. The slab heating temperature is 1211℃, the soaking temperature is 1208℃, the discharge temperature is 1193℃, and the heating time is 220min. The phosphorus of the heated slab is removed by high-pressure water. The width is fixed by a fixed-width press, 2 roughing mills and 7 CVC finishing mills are used. The intermediate blank thickness is 60.0mm, and the finishing temperature is 850℃. The laminar cooling adopts the front and rear cooling mode "11" (the upper and lower nozzles are opened one by one), the cooling speed is 53℃ / s, the coiling temperature is 631℃, the finished product thickness is 19.8mm, and the mechanical property detection results of the steel strip prepared in the embodiment are shown in Table 2.

[0043] In order to improve the uniformity of the steel coil and reduce the stress of the steel strip, all the steel coils of the specification are slowly cooled after rolling, the steel coil slow cooling time is not less than 48 hours, and the steel coils are not stacked near the ventilation port.

[0044] Figure 1 The typical microstructure diagram of the steel strip prepared in this embodiment is shown in the figure, from which it can be known that the microstructure is ferrite and a small amount of pearlite, and the grain size is about 12 levels. The mechanical property detection results of the steel strip prepared in this embodiment are shown in Table 2.

[0045] Table 1 Chemical composition (wt%) of the embodiments 1-3 of the present application

[0046] Embodiments C Si Mn P S Mo Cr Ce 1 0.13 0.25 0.45 0.011 0.005 0.44 0.93 0.0020 2 0.14 0.26 0.44 0.012 0.003 0.43 0.95 0.0017 3 0.13 0.22 0.46 0.010 0.001 0.43 0.96 0.0015

[0047] Table 2 Mechanical property and corrosion resistance detection results of the steel strip prepared in the embodiments 1-3 of the present application

[0048]

[0049] From the data in Table 2, it can be known that:

[0050] The mechanical properties and process properties meet: yield strength ≥295MPa, tensile strength ≥450MPa, elongation A ≥19%, and cold bending d=3a.

[0051] From the above embodiment results, the heat-resistant alloy steel strip for boiler and pipeline has excellent mechanical properties, welding performance, corrosion resistance and other characteristics.

[0052] The above-described embodiments are only to describe the preferred modes of the present application, and are not intended to limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for producing a hot-rolled steel strip of rare earth heat-resistant alloy steel 15CrMo having a thickness of 3.0-20.0 mm, characterized in that: It comprises the following steps: hot metal pretreatment, combined blowing in converter, LF refining, RH, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling, and holding and slow cooling; the hot continuous rolling comprises a heating furnace, rough rolling, and finish rolling; wherein: The heating temperature of the continuous casting slab is controlled to be 1190-1250℃, the soaking temperature is controlled to be 1190-1240℃, the out-of-furnace temperature is controlled to be 1220±20℃ when the thickness is less than or equal to 6mm, the out-of-furnace temperature is controlled to be 1210±20℃ when the thickness is 6.01-12.00mm, the out-of-furnace temperature is controlled to be 1200±20℃ when the thickness is 12.01-20.00mm, and the slab time in the furnace is controlled to be within 180-240min; The rough rolling adopts a 3+5 mode, and the rough rolling starting temperature is 980-1120℃; The finish rolling starting thickness is 3.0-12.00mm, the intermediate slab thickness is 40-55mm, and the finish rolling temperature is 870-1010℃; the intermediate slab thickness is 55-65mm when the thickness is 12.0-20.00mm, and the finish rolling temperature is 850-870℃; In the cooling and coiling step: 3.0mm 12.0mm 16.0mm The chemical composition of the heat-resistant alloy steel, by weight percentage, is C: 0.13-0.15%, Si: 0.20-0.30%, Mn: 0.40-0.55%, P: ≤0.015%, S: ≤0.01%, Cr: 0.90-1.10%, Mo: 0.40-0.50%, Ce: 0.0010-0.0025%, and the balance is Fe and inevitable impurities.

2. A method of producing a 3.0-20.0 mm thick rare earth heat resistant alloy steel 15CrMo hot-rolled steel strip according to claim 1, characterized by: The finish rolling adopts a 7-stand continuous variable crown mill finish rolling, and the finish rolling starting temperature is 980-1120℃.

3. A method of producing a 3.0-20.0 mm thick 15CrMo hot-rolled steel strip of a rare earth heat-resistant alloy steel according to claim 1, characterized in that: The metallographic structure of the heat-resistant alloy steel is ferrite+pearlite, and the grain size is greater than or equal to 11 levels.

4. A method of producing a 3.0-20.0 mm thick 15CrMo hot-rolled steel strip of rare earth heat-resistant alloy steel as claimed in claim 1, characterized in that: The heat-resistant alloy steel satisfies: tensile strength ≥450MPa, yield strength ≥295MPa, elongation ≥19%, and 180° cold bending test.

Images