Production method of rare earth 15CrMo heat-resistant alloy structural steel plate

Abstract

The invention discloses a production method of a rare earth 15CrMo heat-resistant alloy structural steel plate. The steel plate comprises the following chemical components in percentage by weight: 0.12 to 0.15 percent of C, 0.20 to 0.35 percent of Si, 0.40 to 0.65 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.005 percent of S, 0.80 to 0.90 percent of Cr, 0.40 to 0.50 percent of Mo, 0.020 to 0.035 percent of Als, 0.0005 to 0.0020 percent of rare earth Ce and the balance of Fe and inevitable impurities. Meanwhile, the invention discloses main process and parameter setting. The mechanical properties of the rare earth 15CrMo heat-resistant alloy structural steel plate meet the technical requirements that the yield strength is larger than or equal to 300 MPa, the tensile strength is larger than or equal to 450 MPa, the percentage elongation after fracture is larger than or equal to 19%, the impact energy at 0 DEG C is larger than or equal to 60 J, and meanwhile the rare earth 15CrMo heat-resistant alloy structural steel plate has the characteristics of low yield ratio, heat resistance and the like; and the actual performance is better.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat-resistant alloy steel, and particularly relates to a production method of a rare earth 15CrMo heat-resistant alloy structural steel plate. BACKGROUND

[0002] The 15CrMo steel plate is a low-alloy medium-temperature pressure vessel steel plate, which is commonly used in the fields of petroleum and chemical industry, coal chemical industry and electric power, and the steel plate has harsh use conditions and is long-term used under high-temperature, high-pressure and hydrogen conditions. The traditional 15CrMoR steel plate adopts a production process of normalizing + tempering, and the production cost of the user pressure vessel body is also high. Directly used for manufacturing heat-resistant structural parts increases the construction cost. It is urgent to develop an alloy steel plate which can meet the requirements of heat-resistant working conditions and reduce the manufacturing cost.

[0003] Chinese patent CN 115652053 B discloses a production method of a 15CrMo steel plate with low brittle-ductile transition temperature and low yield ratio. The production method comprises the steps of electric furnace smelting, continuous casting, heating and rolling process. In the rolling process, the 15CrMo steel plate with low brittle-ductile transition temperature and low yield ratio is produced by adopting the hot rolling + water cooling control redness + stacking process. The disadvantage is that the electric furnace production is adopted, and the production process is complex.

[0004] Chinese patent CN 105861924 A discloses a low-alloy 15CrMo steel plate and a production method thereof. The production method adopts the production process of converter smelting, refining, continuous casting blank heating, controlled rolling and tempering heat treatment. The produced steel plate has good strength and toughness matching, greatly reduces the production cost, and completely meets the standard requirements. The disadvantages are as follows: first, the valuable metal nickel is added, which increases the manufacturing cost. Second, the rolling process is strict and is not suitable for other steel plants. Third, the tempering heat treatment is needed, which increases the manufacturing cost.

[0005] Chinese patent CN 118957402 A discloses a preparation method of a 3.0-20.0mm-thickness rare earth heat-resistant alloy steel 15CrMo hot-rolled steel strip. The 3.0-20.0mm-thickness rare earth heat-resistant alloy steel strip is produced by adopting the processes of molten iron pretreatment, converter composite blowing, LF refining, RH, continuous casting, slab heating, hot continuous rolling, laminar cooling and coiling, heat preservation and slow cooling and the like. The disadvantage is that the method is only suitable for hot-rolled steel strips, and the thickness of the steel plate is 3-20mm, which is not suitable for medium-thick plates. SUMMARY

[0006] The purpose of the present application is to provide a production method of a rare earth 15CrMo heat-resistant alloy structural steel plate, which has the mechanical properties meeting the technical requirements of yield strength ≥ 300MPa, tensile strength ≥ 450MPa, elongation after fracture ≥ 19%, 0℃ impact energy ≥ 60J, low yield ratio, heat resistance and the like, and the actual performance is better.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for producing rare earth 15CrMo heat-resistant alloy structural steel plates, comprising:

[0009] S1 molten iron pretreatment: After desulfurization and dephosphorization by KR stirring method, the molten iron is guaranteed to have S≤0.005% and P≤0.015%;

[0010] S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The molten iron temperature is ≥1260℃. After smelting, the phosphorus and carbon content is reduced to ensure that the molten steel has P≤0.010% and S≤0.004%.

[0011] S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, and adds chromium and molybdenum alloying elements to ensure that the content meets the design requirements; it further reduces non-metallic inclusions and harmful impurities in the steel, with S≤0.004%, and improves the purity of the steel;

[0012] S4 RH Vacuum Treatment: This treatment mode significantly reduces the content of hydrogen, oxygen, and nitrogen gases in molten steel, minimizing the adverse effects of harmful gases on the steel quality; the vacuum degree is less than 80 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is greater than 15 minutes, the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6 ppm, the oxygen content is ≤30 ppm, and the nitrogen content is ≤50 ppm.

[0013] S5 slab continuous casting: Dynamic light reduction is used during continuous casting, with light reduction positions at sections 8 and 9, and a total reduction of 7.5-8mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at the outlet of section 3 and the inlet of section 4, the electromagnetic stirring frequency is 5Hz, and the current is 350A; protective casting is used, with the long nozzle sealing argon pressure greater than 0.4MPa; the tundish immersion nozzle sealing argon pressure greater than 0.3MPa; protective casting is used throughout the continuous casting process, using special protective slag, the continuous casting superheat is 20-30℃, and the tundish liquid level is not less than 30 tons when changing ladles; constant casting speed is used, with the casting speed stabilized at 0.9m / min; the billet straightening temperature is 950-1000℃, and the temperature difference along the width of the billet must not exceed 40℃; finally, 250mm and 300mm thick continuously cast billets are produced, and the low-magnification center segregation of the billet is controlled below Class C 3.0. After the billets are removed from the line, they are placed in a heat preservation pit for more than 36 hours;

[0014] S6 heating: The slab is heated in a walking beam furnace with strict control of the furnace atmosphere to ensure the heating temperature and time of the slab. The heating temperature is 1210℃~1250℃; the total time in the furnace is greater than 230min, of which the heating section is greater than 120min and the soaking section is greater than 30min, to ensure the full solid solution of alloying elements and uniform slab temperature.

[0015] S7 Rolling and Cooling: Rolling adopts two-stage controlled rolling. The roughing rolling temperature is above 1170℃, and the relative reduction rate of a single pass is controlled at least 15% for at least two passes. During finishing rolling, the deformation of each pass is strictly controlled. The finishing rolling temperature is ≤930℃ and the finishing rolling temperature is ≤830℃. After the steel plate is rolled, it is air-cooled and then placed in a slow cooling hood for 36 hours.

[0016] The chemical composition of the steel plate, by weight percentage, is: C: 0.12-0.15%, Si: 0.20-0.35%, Mn: 0.40-0.65%, P: ≤0.015%, S: ≤0.005%, Cr: 0.80-0.90%, Mo: 0.40-0.50%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.13%, Si: 0.22%, Mn: 0.44%, P: 0.011%, S: 0.002%, Cr: 0.83%, Mo: 0.41%, Als: 0.021%, rare earth Ce: 0.00015%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.13%, Si: 0.25%, Mn: 0.53%, P: 0.012%, S: 0.001%, Cr: 0.85%, Mo: 0.42%, Als: 0.021%, rare earth Ce: 0.00014%, with the balance being Fe and unavoidable impurities.

[0019] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.14%, Si: 0.26%, Mn: 0.57%, P: 0.012%, S: 0.003%, Cr: 0.90%, Mo: 0.43%, Als: 0.020%, rare earth Ce: 0.00013%, with the balance being Fe and unavoidable impurities.

[0020] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.14%, Si: 0.25%, Mn: 0.58%, P: 0.012%, S: 0.002%, Cr: 0.90%, Mo: 0.45%, Als: 0.022%, rare earth Ce: 0.00014%, with the balance being Fe and unavoidable impurities.

[0021] Furthermore, the chemical composition of the steel plate by weight percentage is C: 0.15%, Si: 0.28%, Mn: 0.55%, P: 0.011%, S: 0.002%, Cr: 0.86%, Mo: 0.43%, Als: 0.022%, rare earth Ce: 0.00013%, with the balance being Fe and unavoidable impurities.

[0022] Furthermore, its mechanical properties meet the technical requirements: yield strength ≥300MPa, tensile strength ≥450MPa, elongation after fracture ≥19%, impact energy at 0℃ ≥60J, and it also has a low yield strength ratio and heat resistance.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0024] This invention produces rare earth 15CrMo heat-resistant alloy structural steel plates with a thickness of 10-50mm based on C, Mn, Cr, and Mo, supplemented by Ce micro-alloying alloy design system. The plates have a yield strength ≥300MPa, tensile strength ≥450MPa, elongation after fracture ≥19%, and impact energy at 0℃ ≥60J. They also have low yield strength ratio and heat resistance.

[0025] This invention improves billet segregation, reduces the harm of banded structures, avoids the accumulation of harmful elements and hard phases in the core, and improves the product's flaw detection pass rate by using electromagnetic stirring and dynamic light pressure.

[0026] This invention employs air cooling and a thermal insulation cover for slow cooling, which reduces the strength of the steel plate, improves its plasticity and toughness, effectively improves the shape of the steel plate, and solves the problem of uneven internal stress in the product.

[0027] This invention uses hot rolling process instead of normalizing + tempering process, reducing manufacturing cost by more than 350 yuan per ton of steel. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 Metallographic structure of the steel plate in Example 3;

[0030] Figure 2 The macroscopic morphology of the impact fracture surface of the steel plate at -40℃ in Example 3;

[0031] Figure 3 The microstructure of the impact fracture surface of the steel plate at -40℃ in Example 3 is shown.

[0032] Figure 4 The images show the morphology of the steel plates after bending in Examples 1 and 2. Detailed Implementation

[0033] The present invention will now be described in more detail with reference to the accompanying drawings and specific embodiments. These embodiments are merely descriptions of the preferred embodiments of the invention and do not limit the scope of the invention in any way.

[0034] The chemical composition of the steel plate of this invention, by weight percentage, is: C: 0.12-0.15%, Si: 0.20-0.35%, Mn: 0.40-0.65%, P: ≤0.015%, S: ≤0.005%, Cr: 0.80-0.90%, Mo: 0.40-0.50%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, with the balance being Fe and unavoidable impurities.

[0035] Furthermore, this invention also provides a method for manufacturing steel plates. The main steps and process parameters are as follows:

[0036] Hot metal pretreatment—converter top and bottom re-blowing smelting—LF ladle refining—RH vacuum degassing—slab continuous casting (electromagnetic stirring, light reduction)—slab slow cooling in the heat preservation pit—slab heating—descaling—rough rolling—finish rolling—air cooling—straightening—steel plate placed in a slow cooling hood for 36 hours after finishing line—shearing—flaw detection—sampling inspection—finished product warehousing.

[0037] S1 molten iron pretreatment: After desulfurization and dephosphorization by KR stirring method, the molten iron is guaranteed to have S≤0.005% and P≤0.015%;

[0038] S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The temperature of the molten iron is ≥1260℃. After smelting, the phosphorus and carbon content is reduced to ensure that the molten steel has P≤0.010% and S≤0.004%.

[0039] S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, and adds chromium and molybdenum alloying elements to ensure their content meets design requirements. This further reduces non-metallic inclusions and harmful impurities in the steel, achieving S≤0.004% and improving steel purity.

[0040] S4 RH Vacuum Treatment: This treatment method significantly reduces the hydrogen, oxygen, and nitrogen content in molten steel, minimizing the adverse effects of harmful gases on the steel quality. The vacuum level is less than 80 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is greater than 15 minutes, and the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content in the molten steel is ≤1.6 ppm, the oxygen content is ≤30 ppm, and the nitrogen content is ≤50 ppm.

[0041] S5 slab continuous casting: Dynamic light reduction is used during continuous casting, with light reduction positions at sections 8 and 9, and a total reduction of 7.5-8mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at the outlet at section 3 and the inlet at section 4, the electromagnetic stirring frequency at 5Hz, and the current at 350A; protective casting is used, with the long nozzle sealing argon pressure greater than 0.4MPa; the tundish immersion nozzle sealing argon pressure greater than 0.3MPa; protective casting is used throughout the continuous casting process, using special protective slag; the continuous casting superheat is 20-30℃, and the tundish liquid level is not less than 30 tons during ladle changes; constant casting speed is used, with the casting speed stabilized at 0.9m / min; the slab straightening temperature is 950-1000℃, and the temperature difference along the width of the slab must not exceed 40℃. Finally, 250mm and 300mm thick continuously cast slabs are produced, with low-magnification center segregation controlled below Class C 3.0, and the slabs are placed in a heat preservation pit for more than 36 hours after casting.

[0042] S6 Heating: The slab is heated in a walking beam furnace with strict control of the furnace atmosphere to ensure the heating temperature and time of the slab. The heating temperature is 1210℃~1250℃. The total furnace time is greater than 230min, of which the heating period is greater than 120min and the soaking period is greater than 30min, to ensure the full solidification of alloying elements and uniform slab temperature.

[0043] S7 Rolling and Cooling: Rolling adopts a two-stage controlled rolling process. The roughing rolling temperature is above 1170℃, and the relative reduction rate per pass is controlled at least 15% for at least two passes. During finishing rolling, the deformation amount of each pass is strictly controlled, with the finishing rolling temperature ≤930℃ and the finishing rolling temperature ≤830℃. After rolling, the steel plate is air-cooled and then placed in a slow cooling hood for 36 hours.

[0044] The present invention will now be described in detail with reference to actual embodiments.

[0045] Table 1 lists the chemical composition of the examples, and Table 2 lists the rolling process parameters of the examples.

[0046] Table 1 Chemical composition (wt%) of the embodiments of the present invention

[0047] Example C Si Mn P S Cr Mo Als Ce 1 0.13 0.22 0.44 0.011 0.002 0.83 0.41 0.021 0.0015 2 0.13 0.25 0.53 0.012 0.001 0.85 0.42 0.021 0.0014 3 0.14 0.26 0.57 0.012 0.003 0.90 0.43 0.020 0.0013 4 0.14 0.25 0.58 0.012 0.002 0.90 0.45 0.022 0.0014 5 0.15 0.28 0.55 0.011 0.002 0.86 0.43 0.022 0.0013

[0048] Table 2 Rolling process parameters of the embodiments of the present invention

[0049] Example Steel plate thickness mm Coarse rolling start temperature / °C Finish rolling start temperature / °C Finish rolling finish temperature / °C Start cooling temperature / °C Finish cooling temperature / °C Muffle slow cooling 1 10 1182 921 793 / Air cooling 36 hours 2 20 1201 894 801 / Air cooling 36 hours 3 30 1205 905 799 / Air cooling 36 hours 4 40 1193 902 798 / Air cooling 36 hours 5 50 1194 889 798 / Air cooling 36 hours

[0050] The mechanical properties, low-temperature impact properties, and cold bending properties of the steel plate in the embodiment of the present invention were tested, and the results are shown in Table 3.

[0051] Table 3 Mechanical properties of the steel plates in the embodiments of the present invention

[0052] Example Thickness (mm) Yield strength (MPa) Tensile strength (MPa) Yield ratio Elongation (%) 0°C transverse impact energy value (J) Cold bending performance 1 10 437 578 0.75 22.5 124、100、174 Pass 2 20 421 578 0.73 23.5 198、178、187 Pass 3 30 414 555 0.75 22.5 126、130、135 Pass 4 40 410 589 0.70 22.5 146、138、137 Pass 5 50 411 551 0.75 22.5 178、174、195 Pass Technical requirement ≥300 ≥450 / ≥19 ≥60 180° D = 3a

[0053] Table 4. High-temperature heat resistance of steel plates in the embodiments of the present invention at 350℃

[0054] Example Thickness (mm) Yield strength (MPa) Tensile strength (MPa) Elongation (%) 1 10 256 465 26.5 2 20 257 482 24.5 3 30 255 474 25.0 4 40 233 477 24.5 5 50 251 468 26.5 Technical requirement ≥200

[0055] This invention produces rare earth 15CrMo heat-resistant alloy structural steel plates using a reasonable chemical composition and a specific process. The plates have a yield strength ≥300MPa, tensile strength ≥450MPa, elongation after fracture ≥19%, and impact energy at 0℃ ≥60J. They also have characteristics such as low yield strength ratio and heat resistance.

[0056] 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 rare earth 15CrMo heat-resistant alloy structural steel plate, characterized in that, include: S1 molten iron pretreatment: After desulfurization and dephosphorization by KR stirring method, the molten iron is guaranteed to have S≤0.005% and P≤0.015%; S2 converter smelting: The converter smelting stage uses desulfurized pretreated molten iron and high-quality scrap steel as raw materials. The molten iron temperature is ≥1260℃. After smelting, the phosphorus and carbon content is reduced to ensure that the molten steel has P≤0.010% and S≤0.004%. S3 LF Ladle Refining: The ladle refining stage precisely controls the steel composition, deoxidizes and alloys, and adds chromium and molybdenum alloying elements to ensure that the content meets the design requirements; it further reduces non-metallic inclusions and harmful impurities in the steel, with S≤0.004%, and improves the purity of the steel; S4 RH Vacuum Treatment: This treatment mode significantly reduces the content of hydrogen, oxygen, and nitrogen gases in molten steel, minimizing the adverse effects of harmful gases on the steel quality; the vacuum degree is less than 80 Pa, the vacuum time is maintained for more than 15 minutes, the pure degassing time is greater than 15 minutes, the soft blowing time is greater than 15 minutes, ensuring that the hydrogen content of the molten steel is ≤1.6 ppm, the oxygen content is ≤30 ppm, and the nitrogen content is ≤50 ppm. S5 slab continuous casting: Dynamic light reduction is used during continuous casting, with light reduction positions at sections 8 and 9, and a total reduction of 7.5-8mm; electromagnetic stirring is used during continuous casting, with electromagnetic stirring positions at the outlet of section 3 and the inlet of section 4, the electromagnetic stirring frequency is 5Hz, and the current is 350A; protective casting is used, with the long nozzle sealing argon pressure greater than 0.4MPa; the tundish immersion nozzle sealing argon pressure greater than 0.3MPa; protective casting is used throughout the continuous casting process, using special protective slag; the continuous casting superheat is 20-30℃, and the tundish liquid level is not less than 30 tons when changing ladles; constant casting speed is used, with the casting speed stabilized at 0.9m / min; the billet straightening temperature is 950-1000℃, and the temperature difference along the width of the billet must not exceed 40℃; finally, 250mm and 300mm thick continuously cast billets are produced, and the low-magnification center segregation of the billet is controlled below Class C 3.

0. After the billets are removed from the line, they are placed in a heat preservation pit for more than 36 hours; S6 heating: The slab is heated in a walking beam furnace with strict control of the furnace atmosphere to ensure the heating temperature and time of the slab. The heating temperature is 1210℃~1250℃; the total time in the furnace is greater than 230min, of which the heating section is greater than 120min and the soaking section is greater than 30min, to ensure the full solid solution of alloying elements and uniform slab temperature. S7 Rolling and Cooling: Rolling adopts two-stage controlled rolling. The roughing rolling temperature is above 1170℃, and the relative reduction rate of a single pass is controlled at least 15% for at least two passes. During finishing rolling, the deformation of each pass is strictly controlled. The finishing rolling temperature is ≤930℃ and the finishing rolling temperature is ≤830℃. After the steel plate is rolled, it is air-cooled and then placed in a slow cooling hood for 36 hours. The chemical composition of the steel plate, by weight percentage, is: C: 0.12-0.15%, Si: 0.20-0.35%, Mn: 0.40-0.65%, P: ≤0.015%, S: ≤0.005%, Cr: 0.80-0.90%, Mo: 0.40-0.50%, Als: 0.020-0.035%, rare earth Ce: 0.0005-0.0020%, with the balance being Fe and unavoidable impurities.

2. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.13%, Si: 0.22%, Mn: 0.44%, P: 0.011%, S: 0.002%, Cr: 0.83%, Mo: 0.41%, Als: 0.021%, rare earth Ce: 0.00015%, with the balance being Fe and unavoidable impurities.

3. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.13%, Si: 0.25%, Mn: 0.53%, P: 0.012%, S: 0.001%, Cr: 0.85%, Mo: 0.42%, Als: 0.021%, rare earth Ce: 0.00014%, with the balance being Fe and unavoidable impurities.

4. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.14%, Si: 0.26%, Mn: 0.57%, P: 0.012%, S: 0.003%, Cr: 0.90%, Mo: 0.43%, Als: 0.020%, rare earth Ce: 0.00013%, with the balance being Fe and unavoidable impurities.

5. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.14%, Si: 0.25%, Mn: 0.58%, P: 0.012%, S: 0.002%, Cr: 0.90%, Mo: 0.45%, Als: 0.022%, rare earth Ce: 0.00014%, with the balance being Fe and unavoidable impurities.

6. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, The chemical composition of the steel plate by weight percentage is C: 0.15%, Si: 0.28%, Mn: 0.55%, P: 0.011%, S: 0.002%, Cr: 0.86%, Mo: 0.43%, Als: 0.022%, rare earth Ce: 0.00013%, with the balance being Fe and unavoidable impurities.

7. The method for producing rare earth 15CrMo heat-resistant alloy structural steel plate according to claim 1, characterized in that, Its mechanical properties meet the technical requirements: yield strength ≥300MPa, tensile strength ≥450MPa, elongation after fracture ≥19%, impact energy at 0℃ ≥60J, and it also has low yield strength ratio and heat resistance.

Images