CN109881086B - High-strength high-quality steel plate Q550EZ35 with thickness of 300mm and production method thereof - Google Patents
High-strength high-quality steel plate Q550EZ35 with thickness of 300mm and production method thereof Download PDFInfo
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Abstract
The invention particularly relates to an extra-thick high-strength tempered steel Q550EZ35 for a hydropower station with the thickness of 300mm and a production method thereof. The steel plate is combined and matched with basic elements such as C, Mn, Si, P, S, AlS and the like and alloy elements such as Cr, Mo, V, Ni, Nb, Ti, B, Cu and the like, so that the low-temperature impact toughness and the welding performance of the steel plate are improved on the premise of ensuring the strength of the steel plate. By adopting the water-cooling ingot for casting, the solidification speed of the molten steel is accelerated, the defects of looseness, segregation and the like are favorably reduced, and the component deviation of the head and the tail of the steel plate is reduced. The steel plate is rolled at low speed and high pressure and tempered at high temperature after rolling, so that the internal stress of the steel plate is released, the hydrogen content is reduced, the flaw detection quality of the steel plate is improved, and the requirements of NB/T47013.3-2015I level are met. Through normalizing the uniform organization in advance, carry out the quenching and tempering again, be favorable to the promotion of whole board performance homogeneity of steel sheet, through control cooling rate, and the low temperature long-time tempering after the quenching and tempering, be favorable to guaranteeing the low temperature impact toughness and the intensity matching of steel sheet, the stable performance easily realizes batch production.
Description
Technical Field
The invention belongs to the technical field of production of super-thick quenched and tempered steel plates, and particularly relates to super-thick high-strength tempered steel Q550EZ35 with the thickness of 300mm and a production method thereof.
Background
The fixed guide vane is one of the most important casting and forging pieces in the water guide mechanism of the water turbine generator set, and the manufacturing of the fixed guide vane is a big problem facing the manufacturing of large-scale water turbine generator sets. It is generally processed and manufactured by sand casting, electroslag casting, forging and the like. The sand casting production is adopted, the internal quality of the casting is unstable, and the common casting defects such as shrinkage porosity, shrinkage cavity, air holes, impurities, cracks and the like are easy to generate. Compared with the conventional sand casting and forging guide vane, the electroslag casting guide vane has the advantages that the comprehensive quality is greatly improved, but the production cost is high.
Disclosure of Invention
The invention adopts a water-cooled steel ingot as a raw material, produces a high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm in a four-high rolling mill rolling mode, and manufactures the fixed guide vane by mechanical processing. The performance of the high-strength high.
The invention successfully obtains the ultra-thick high-strength high-quality steel plate Q550EZ35 for the hydropower station with the thickness of 300mm and the production process thereof through experimental groping and large-scale production application practice, and the ultra-thick high-strength high-quality steel plate is finally used for processing and manufacturing the fixed guide vane in the water guide mechanism of the water turbine generator set, thereby completing the invention.
Therefore, the invention aims to provide a high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm and a production method thereof.
In order to achieve the purpose, the invention adopts the technical scheme that: a high-strength textured steel plate Q550EZ35 with the thickness of 300mm comprises the following chemical components: c: 0.10 to 0.14%, Si: less than or equal to 0.20 percent, Mn: 1.00-1.60%, P: less than or equal to 0.015%, S: less than or equal to 0.005 percent, Nb: 0.030-0.055%, V: 0.050-0.070%, Ti: not more than 0.010%, Mo in an amount of 0.35-0.60%, Ni: 0.90 to 1.50%, 0.50 to 0.80% of Cr, Als: 0.040 to 0.060%, B: less than or equal to 0.00040%, Cu: less than or equal to 0.020%, and the balance of Fe and residual elements; in addition, the total amount of the key element combinations needs to be controlled: cr + Mo + V is less than or equal to 1.2%, Ni + Nb is less than or equal to 1.45%, and carbon equivalent CEV is less than or equal to 0.64.
In order to obtain the high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm, the production process flow is as follows: casting a large steel ingot, treating the surface of the steel ingot, heating, rolling, tempering at high temperature, stacking and cooling, tempering, cutting, leveling with temperature, inspecting appearance and warehousing. The specific production steps are as follows:
(1) casting a large steel ingot: producing a water-cooled steel ingot, and adjusting the thickness of the large steel ingot according to a compression ratio, wherein the compression ratio is 2-3; the components of the molten steel are strictly controlled before pouring to meet the design requirements, and meanwhile, the hydrogen content needs to be detected and controlled within 1.3PPm after VD vacuum treatment; after the molten steel is qualified, rotating the die to cast, wherein the casting temperature is 1550-1555 ℃, the casting time is controlled within 23-25 min, and the casting residual is more than 8 tons; after the pouring is finished, carrying out heat preservation treatment on the cap opening to slow down the riser solidification time;
(2) steel ingot surface treatment: the method needs to thoroughly clean the surface cracks, indentation, riser flash, residual refractory material, cap opening line folding and other harmful defects of the steel ingot body;
(3) heating a water-cooled steel ingot: the method needs four stages of preheating, temperature rising, heat preservation and the like. Preheating temperature is less than 500 ℃, and preheating time is about 0.5 min/mm; in the temperature rise stage, the temperature rise speed needs to be controlled to be less than 70 ℃/h, the heat preservation temperature is 1290 +/-20 ℃, and the heat preservation time is 1.1-1.5 min/mm. The temperature of the steel ingot body is measured before tapping, and is not lower than 1270 ℃ so as to facilitate high-temperature rolling;
(4) rolling: the initial rolling temperature is higher than 960 ℃, the steel is hot rolled at low speed and high pressure, the pass reduction is enough to be 50-80 mm, the central part of the steel ingot can be fully deformed, and high-pressure water is used for removing residual iron sheets on the surface when the steel advances from a machine to a machine in the rolling process;
(5) high-temperature tempering: after rolling, the steel plate is quickly lifted to a trolley furnace for tempering, the temperature of the steel plate entering the furnace is higher than 650 ℃, the heat preservation temperature is 700 +/-10 ℃, and the heat preservation time is 2.0-2.5 min/mm. After the heat preservation is finished, the steel plates are lifted out of the stack for slow cooling, a protection plate is covered, and the steel plates can be spread and cooled to room temperature after the temperature is reduced to be below 150 ℃;
(6) tempering: and (3) carrying out heat treatment by adopting a quenching and tempering process, wherein the steel plate is subjected to pre-normalizing treatment before quenching and tempering, the normalizing temperature is 910 +/-10 ℃, and the heat preservation time is 1.5-1.8 min/mm. In the quenching and tempering process, the quenching heat preservation temperature is 860 +/-10 ℃, the heat preservation time is 2.0-2.5 min/mm, the steel plate is cooled in a water cooling mode after heat preservation, the steel plate needs to move back and forth in the cooling process, and the water temperature is controlled to be less than 25 ℃ so as to stabilize the cooling speed; the heat preservation temperature in the tempering process after quenching is 650 +/-10 ℃, the heat preservation time is 4.0-4.5 min/mm, and the temperature uniformity needs to be controlled during the heat preservation period.
According to the invention, the basic elements such as C, Mn, Si, P, S, AlS and the like and the alloy elements such as Cr, Mo, V, Ni, Nb, Ti, B, Cu and the like are combined and matched, so that the low-temperature impact toughness and the welding performance of the steel plate are improved on the premise of ensuring the strength of the steel plate. By adopting the water-cooling ingot for casting, the solidification speed of the molten steel is accelerated, the defects of looseness, segregation and the like are favorably reduced, and the component deviation of the head and the tail of the steel plate is reduced. Through high-temperature tempering after rolling, the internal stress of the steel plate is released, the hydrogen content is reduced, and the flaw detection quality of the steel plate is improved. Through normalizing the uniform organization in advance, carry out the quenching and tempering again, be favorable to the promotion of whole board performance homogeneity of steel sheet, through control cooling rate, and the low temperature long-time tempering after the quenching and tempering, be favorable to guaranteeing the low temperature impact toughness and the intensity matching of steel sheet, the stable performance easily realizes batch production.
Drawings
FIG. 1 is a metallographic phase diagram (metallographic microscope, x 200) of a tempered structure according to an example of the invention.
FIG. 2 shows a metallographic image (SEM, magnification 1000) of a tempered structure according to an example of the present invention.
FIG. 3 shows the macro-topography (SEM, x 15) of a Z-direction tensile sample according to an embodiment of the present invention.
FIG. 4 shows the microstructure of a Z-direction tensile specimen (scanning electron microscope,. times.200) according to an embodiment of the present invention.
Detailed Description
The present invention is described in further detail below with reference to examples.
The steel grade of this example, No. Q550EZ35, produced 300mm thick, 23.4t steel sheet basis weight. The paint comprises the following chemical components: c: 0.12%, Si: 0.16%, Mn: 1.14%, P: 0.009%, S: 0.003%, Als: 0.053%, V: 0.056%, Ti: 0.007%, Cr 0.62%, Ni: 1.34%, Mo: 0.44%, Nb: 0.037%, Cu: 0.014%, B: 0.00017%, wherein Cr + Mo + V =1.116%, Ni + Nb =1.377%, CEV =0.62, and the others are Fe and residual elements.
The production steps of the high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm in the embodiment example are as follows:
(1) casting a large steel ingot: the thickness of the water-cooled steel ingot is 700mm, and the compression ratio is 2.7; after VD vacuum degassing treatment, the hydrogen content is 1.2 PPm; the casting temperature is 1554 ℃, the total casting time is 23min, wherein the body casting time is 18min, the riser casting time is 5min, and 9 tons of residual casting are left after casting;
(2) steel ingot surface treatment: after the steel ingot is demoulded and slowly cooled, carrying out visual inspection on the surface of the steel ingot body, wherein fine longitudinal cracks exist in the central area of the width, completely cleaning the whole surface, completely cleaning the longitudinal cracks and subcutaneous cracks, and cleaning and smoothing the area of a cap opening line;
(3) heating a water-cooled steel ingot: the charging temperature is 350 ℃, the preheating time is 6 hours, the heating rate is 53 ℃/h, the heat preservation temperature is 1300 ℃, the steel is tapped after the heat preservation time is 15 hours, the temperature of the steel ingot body is 1290 ℃, and the rolling condition is met;
(4) rolling: the initial rolling temperature is 1130 ℃, the hot rolling is carried out under low speed and large reduction, the reduction of each pass is enough to be 70mm, high pressure water is used for removing surface iron sheets in each pass in the rolling process, and the rolling is carried out for the next pass after the red returning is carried out for 40S;
(5) high-temperature tempering: after rolling, the steel plate is quickly lifted to a trolley furnace for tempering, the time from rolling to furnace entry is 25 minutes, the temperature of the steel plate entering the furnace is 680 ℃, heat preservation is carried out according to 700 ℃, and the heat preservation is carried out for 24 hours. After the heat preservation is finished, lifting the steel plates out of the stack for slow cooling, and spreading and cooling the steel plates to room temperature after the temperature is reduced to be below 150 ℃;
(6) and (3) heat treatment: the pre-normalizing temperature is 910 +/-10 ℃, and the heat preservation time is 1.5-1.8 min/mm. In the quenching and tempering process, the quenching heat preservation temperature is 860 +/-10 ℃, the heat preservation time is 2.0-2.5 min/mm, the steel plate is cooled in a water cooling mode after heat preservation, the steel plate needs to move back and forth in the cooling process, and the water temperature is controlled to be less than 25 ℃ so as to stabilize the cooling speed; the heat preservation temperature in the tempering process after quenching is 650 +/-10 ℃, the heat preservation time is 4.0-4.5 min/mm, and the temperature uniformity needs to be controlled during the heat preservation period.
The quality of the high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm in the embodiment example is as follows:
(1) mechanical property detection
The sampling position and the preparation of the mechanical property test piece of the steel plate are carried out according to the GB/T2975 standard and the GB/T5313 regulation, the low-temperature impact toughness test is carried out according to the GB/T229 standard, and the tensile property test is carried out according to the GB/T228 standard. Simulating a postweld heat treatment system: keeping the temperature at 580 ℃ for 12 hours, and cooling along with the furnace. The results of the mechanical property tests are shown in the following table:
(2) metallographic structure detection
The metallographic structure is evaluated according to the standard of GB/T13299 steel microstructure evaluation method and GB/T6394 metal average grain size determination method, the matrix structure is mainly tempered bainite, the grain size is 10-11 grades, and the appearance is shown in figures 1 and 2. The Z-direction tensile fracture is macroscopically cup-cone-shaped, mainly comprises a central fiber area and a shearing lip on the periphery, is mainly a dimple-shaped fracture with better plasticity under a scanning electron microscope, and has the structure morphology shown in figures 3 and 4.
(3) Inclusion detection
The inclusion rating is carried out according to GB/T10561 microscopic examination method of determination standard rating chart of the content of non-metallic inclusions in steel, and the detection results are shown in the following table:
(4) nondestructive inspection
According to NB/T47013.3-2015' third part of nondestructive testing of pressure bearing equipment: the ultrasonic detection standard is used for nondestructive inspection, and the grade I is combined.
According to the above test results, the high-strength high-tensile strength steel sheet Q550EZ35 produced in the present example and having a thickness of 300mm was excellent in flaw detection quality: the whole inclusion content of the steel plate is low, and the flaw detection meets NB/T47013.3-2015I level; the steel plate has the advantages of uniform and fine grain structure, high lamellar tearing resistance, stable reduction of area over 60 percent, high head and tail strength, high elongation, high-20 ℃ low-temperature impact toughness and other performance enrichment, and is mainly prepared from tempered bainite, and the quality use requirement of the steel for the hydroelectric generating set is completely met.
Claims (2)
1. A production method of a high-strength high-quality steel plate Q550EZ35 with the thickness of 300mm is characterized in that: the steel plate comprises the following chemical components: c: 0.10 to 0.14%, Si: less than or equal to 0.20 percent, Mn: 1.00-1.60%, P: less than or equal to 0.015%, S: less than or equal to 0.005 percent, Nb: 0.030-0.055%, V: 0.050-0.070%, Ti: not more than 0.010%, Mo in an amount of 0.35-0.60%, Ni: 0.90 to 1.50%, 0.50 to 0.80% of Cr, Als: 0.040 to 0.060%, B: less than or equal to 0.00040%, Cu: less than or equal to 0.020%, and the balance of Fe and residual elements; in addition, the total amount of the key element combinations needs to be controlled: cr + Mo + V is less than or equal to 1.2%, Ni + Nb is less than or equal to 1.45%, and carbon equivalent CEV is less than or equal to 0.64;
the production process flow adopted by the steel plate is as follows: large steel ingot casting, steel ingot surface treatment, heating, rolling, high-temperature tempering, stacking cooling, tempering, cutting, leveling with temperature, appearance inspection and warehousing, specifically,
(1) casting a large steel ingot: producing a water-cooled steel ingot, and adjusting the thickness of the large steel ingot according to a compression ratio, wherein the compression ratio is 2-3; the components of the molten steel are strictly controlled before pouring to meet the design requirements, and meanwhile, the hydrogen content needs to be detected and controlled within 1.3PPm after VD vacuum treatment; after the molten steel is qualified, rotating the die to cast, wherein the casting temperature is 1550-1555 ℃, the casting time is controlled within 23-25 min, and the casting residual is more than 8 tons; after the pouring is finished, carrying out heat preservation treatment on the cap opening to slow down the riser solidification time;
(2) steel ingot surface treatment: the method needs to thoroughly clean the surface cracks, pressure pits, riser flashes, residual refractory materials and the folding hazardous defects of the cap opening line of the steel ingot body;
(3) heating a water-cooled steel ingot: the method comprises three stages of preheating, heating and heat preservation, wherein the preheating temperature is less than 500 ℃, and the preheating time is 0.5 min/mm; in the temperature rising stage, the temperature rising speed is controlled to be less than 70 ℃/h, the heat preservation temperature is 1290 +/-20 ℃, the heat preservation time is 1.1-1.5 min/mm, the temperature of a steel ingot body needs to be measured before steel tapping, and the temperature is not lower than 1270 ℃ so as to facilitate high-temperature rolling;
(4) rolling: the initial rolling temperature is higher than 960 ℃, the steel is hot rolled at low speed and high pressure, the pass reduction is enough to be 50-80 mm, the central part of the steel ingot can be fully deformed, and high-pressure water is used for removing residual iron sheets on the surface when the steel advances from a machine to a machine in the rolling process;
(5) high-temperature tempering: after rolling, quickly lifting the steel plates to a trolley furnace for tempering, wherein the temperature of the steel plates entering the furnace is higher than 650 ℃, the heat preservation temperature is 700 +/-10 ℃, the heat preservation time is 2.0-2.5 min/mm, after the heat preservation is finished, the steel plates are lifted out of the stack for slow cooling, and protective plates are covered, and the steel plates can be spread out and cooled to the room temperature after the temperature is reduced to below 150 ℃;
(6) tempering: carrying out thermal treatment by adopting a quenching and tempering process, carrying out pre-normalizing treatment on a steel plate before quenching and tempering, wherein the normalizing temperature is 910 +/-10 ℃, the heat preservation time is 1.5-1.8 min/mm, the quenching heat preservation temperature is 860 +/-10 ℃ and the heat preservation time is 2.0-2.5 min/mm in the quenching and tempering process, cooling by adopting a water cooling mode after heat preservation, moving the steel plate back and forth in the cooling process, and controlling the water temperature to be less than 25 ℃ so as to stabilize the cooling speed; the heat preservation temperature in the tempering process after quenching is 650 +/-10 ℃, the heat preservation time is 4.0-4.5 min/mm, and the temperature uniformity needs to be controlled during the heat preservation period.
2. A high-strength textured steel plate Q550EZ35 with the thickness of 300mm, which is characterized in that: prepared by the production method of claim 1.
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| CN112725707A (en) * | 2020-12-22 | 2021-04-30 | 南阳汉冶特钢有限公司 | Production method for producing steel plate with thickness of 350mm for water turbine seat ring by rolling instead of forging |
| CN112828043B (en) * | 2020-12-24 | 2023-05-23 | 舞阳钢铁有限责任公司 | Production method of large-thickness ultra-wide low-Si alloy steel plate |
| CN114427065A (en) * | 2021-12-28 | 2022-05-03 | 南阳汉冶特钢有限公司 | Production method of 250-400mm thick high-quality low-cost plastic mold steel 1.2738 |
| CN114164322A (en) * | 2022-02-11 | 2022-03-11 | 杭州汽轮铸锻有限公司 | Tower connecting node, heat treatment method thereof and lightning-protection tower for power transmission and transformation |
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