CN115747657B - HY950CF steel plate for high-strength hydroelectric engineering and production method thereof - Google Patents
HY950CF steel plate for high-strength hydroelectric engineering and production method thereof Download PDFInfo
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Abstract
The invention belongs to the field of medium plate production, and particularly relates to an HY950CF steel plate for high-strength hydroelectric engineering and a production method thereof, wherein the steel plate comprises C, si, mn, P, S, als, nb, V, cr, ni, cu, mo, RE, fe and residual elements, and the addition of rare earth elements is beneficial to the purification of molten steel and the modification of inclusions and the low-temperature impact toughness of steel; reasonably controlling the addition amount of the hardenability elements, and obtaining 100% bainite tempered structure after heat treatment; adopting large-thickness steel ingot production, improving rolling compression ratio, improving steel ingot heating rolling process, realizing replacing forging with rolling; the heat treatment link refines austenite grains through quenching for multiple times, ensures hardenability, and improves the uniformity of the mechanical property of the whole plate through tempering. The obtained steel plate has high strength, high toughness, fatigue resistance, lamellar tearing resistance, good weldability and corrosion resistance, and can meet the long-term service requirement of pressure steel pipes in large-scale high-water-head power stations.
Description
Technical Field
The invention belongs to the field of medium plate production, and particularly relates to an HY950CF steel plate for high-strength hydropower engineering and a production method thereof.
Background
At present, the number of large-scale high-water-head power station projects of the Yangtze river upstream main current, jinsha river and large-scale ferry river which are already or are to be built is 33, and hydropower stations with more than 500 ten thousand kW have directed domestic dams, stream Ludu, white crane beaches, wu Dongde, dragon disk gorges and the like. The highest water head of the existing pressure steel pipe reaches 1200m, the wall thickness of the high-strength steel pipe reaches 90mm, the crescent rib thickness of the high-strength steel pipe reaches 150mm, and the HD value (H refers to the internal pressure water head born by the volute, D refers to the diameter of the section of the inlet of the volute) exceeds 4700m2. The corresponding materials applied to engineering are updated continuously, 800MPa high-strength steel is widely used in the hydropower field, and the research and development of new 1000MPa materials are urgent and significant. The 1000MPa high-strength steel material is used in engineering, the wall thickness is reduced, the weight of the component is reduced, the construction difficulty is reduced, the material consumption is reduced, and the energy-saving and emission-reduction effects are achieved.
Chinese patent CN 114395731A discloses a low welding crack-susceptibility crack-arresting steel HY950CF for hydroelectric engineering, the thickness of the steel sheet is 20-100 mm, the structure is tempered sorbite structure retaining martensite orientation, comprising the following chemical components in percentage by mass (unit, wt%): 0.06-0.15% of C, less than or equal to 0.20% of Si, 0.7-1.5% of Mn, less than or equal to 0.008% of P, less than or equal to 0.001% of S, 0.015-0.060% of Als, less than or equal to 0.05% of V, 0.5-0.8% of Cr, 1.5-4.0% of Ni, 0.4-0.8% of Mo, less than or equal to 0.04% of Nb, 0.0008-0.0015% of B, and the balance of Fe and residual elements; and the delivery state of the steel plate is quenched and tempered, namely on-line quenching and tempering treatment. The invention has the advantages that reasonable component proportion is adopted to realize the strength and toughness matching of the steel plate, the steel plate is thin, and continuous casting is adopted, but the thickness and strength level of the steel plate can not meet the use requirement at present along with the continuous construction of a large hydropower station project with a high water head.
Chinese patent CN 105925887A discloses 980 MPa-grade hot-rolled ferrite-bainite dual-phase steel, which comprises the following chemical components in percentage by weight: c: 0.15-0.30%, si 0.8-2.0%, mn:1.0 to 2.0 percent, P is less than or equal to 0.02 percent, S is less than or equal to 0.005 percent, O is less than or equal to 0.003 percent, al is 0.5 to 1.0 percent, N is less than or equal to 0.006 percent, and Nb:0.01 to 0.06 percent, ti:0.01 to 0.05 percent, and the balance of Fe and unavoidable impurities, and the elements simultaneously need to satisfy the following relation: nb+Ti is more than or equal to 0.05% and less than or equal to 0.10%, al/C is more than or equal to 2.5 and less than or equal to 5.0. The invention is characterized in that the design of high carbon and high manganese components is adopted, the thickness of the steel plate is 3-6mm, and the invention has the defects of higher carbon equivalent and poor weldability.
Disclosure of Invention
In order to solve the technical defects, the invention aims to provide the HY950CF steel plate for the high-strength hydroelectric engineering and the production method thereof, and the steel plate obtained according to the scheme has high strength, high toughness, fatigue resistance, lamellar tearing resistance, good weldability and corrosion resistance, and can meet the long-term service use requirements of pressure steel pipes in large-scale high-water-head power stations.
The invention further aims to provide a production method of the HY950CF steel plate for high-strength hydroelectric engineering.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: the HY950CF steel plate for the high-strength hydroelectric engineering has the thickness of 50-120mm and comprises the following chemical components in percentage by mass (unit, wt%): c:0.09 to 0.12, si:0.15 to 0.25, mn:0.30 to 0.60, P is less than or equal to 0.010, S is less than or equal to 0.003, als:0.020 to 0.040, nb:0.02 to 0.03, V:0.04-0.1, cr:1.2-1.6, ni:2.4-2.8, cu:0.8-1.0, mo:0.2 to 0.3, RE:0.0015 to 0.0025, and the balance of Fe and residual elements, wherein the carbon equivalent Ceq is less than 0.7, the structure is a bainite tempered structure, and the longitudinal and transverse V-shaped impact energy at minus 60 ℃ is more than or equal to 127J.
Regarding the composition design, in order to ensure the special requirements of high strength, high low-temperature impact toughness, weldability, corrosion resistance and the like of the HY950CF, the scheme adopts Nb, V, cu, cr, ni, mo multi-element microalloying. Wherein, the increase of the nickel content can not only strongly improve the strength of the extra-thick plate steel plate, but also promote the toughness to be kept at a higher level; chromium carbide is the smallest of various carbides, can be uniformly distributed in a steel body, and the improvement of Cr content makes a prominent contribution to the improvement of strength, hardness and wear resistance; the low-carbon design is beneficial to improving the low-temperature impact toughness; micro-alloy elements such as Nb, V, ti and the like are critical to toughness, strength and weldability, and promote the formation of various M (C, N) nano precipitated phases in a heat treatment process; the addition of trace rare earth elements has the functions of purifying molten steel and deteriorating inclusions, and can improve the low-temperature impact toughness of the rare earth steel.
The production method of the steel plate comprises the following steps: casting steel ingot, primary heating, cogging and rolling, secondary heating, rolling and heat treatment, and the concrete steps are as follows:
a. casting steel ingot, wherein the thickness of the steel ingot body is 960-990mm, the casting temperature is controlled according to 1555-1560 ℃, RE wire is added into a middle injection pipe in the casting process to improve the internal quality, the wire feeding speed is 15m/min, and rare earth elements are added into molten steel to facilitate the modification of inclusions and the purification of molten steel;
b. the primary heating process is that when the steel is filled, the temperature of a hearth is less than or equal to 750 ℃, the steel is stewed for 2 to 4 hours to reduce the temperature difference between the furnace temperature and the steel ingot, the stress caused by the temperature difference between the inside and the outside of the steel ingot is reduced, the target heat preservation temperature of a high temperature section is 1220 to 1240 ℃, the heat preservation time is 16 to 18 hours, and the total heating time is 15min/cm; in order to effectively exert the effects of Ni and Mo alloy elements, the alloy elements are required to be fully dissolved at a high enough heating temperature, but the heating temperature is too high to promote austenite grains to grow, ferrite grains are coarsened, and the comprehensive performance of the coarse ferrite structure is reduced, so that the ingot-shaped characteristics of the steel ingot are combined, and the primary heating process is adopted; meanwhile, the steel is turned before tapping to ensure uniform and thorough burning of the steel ingot and easy removal of surface iron scales;
c. the cogging rolling process adopts high temperature, low speed and large rolling reduction, the initial rolling temperature is 1050-1100 ℃, the pass rolling reduction is 60-70 mm, the internal loose and effective welding is promoted, the cast structure is fully broken, the steel plate crystal grains are uniformly refined, the cogging is carried out to 400mm thick, and the temperature of the steel plate after rolling is controlled at 950-980 ℃;
d. the secondary heating and rolling process is carried out, a soaking pit is arranged after the intermediate blank is cut, the target temperature of the high temperature section is 1220-1240 ℃, the total heat preservation time is 5-6 hours, the secondary rolling is carried out without stretching again, the secondary rolling is directly carried out until the thickness of the finished product is reached, the pass reduction is more than or equal to 30+/-5 mm, the deformation penetration is ensured to the 1/2 position of the thickness, and the further refinement of crystal grains is promoted; the initial rolling temperature is more than or equal to 1020 ℃, the final rolling temperature is less than or equal to 950 ℃, high-pressure water is used for cooling in the rolling process, rolling can be started after the surface of the steel plate is fully reddened, the total rolling time is controlled to be 3-4 minutes, ACC is started to be cooled by water after rolling is finished, the surface and the core temperature of the steel plate are quickly reduced to a non-recrystallized region after the ACC is cooled by water, the water inlet temperature is 900-950 ℃, the reddened temperature is 800-830 ℃, the quick cooling is beneficial to reducing the temperature difference between the thickness central region and the surface of the steel plate, inhibiting austenite grains from growing and recrystallizing, and promoting grain refinement and grain uniformity;
e. the heat treatment process adopts high-temperature quenching, critical quenching and tempering heat treatment, wherein the first quenching heating temperature is 920-940 ℃, the heating time is 2.4min/mm, and the quenching machine cools to normal temperature after the hot steel plate is discharged from the furnace, and the water temperature is 15-18 ℃; the second quenching heating temperature is 860-870 ℃, the heating time is 2.4min/mm, the quenching machine cools to normal temperature after the hot steel plate is discharged from the furnace, and the water temperature is 15-18 ℃; quenching, tempering at 650+ -20deg.C, and air cooling to normal temperature.
It is to be noted that, the single structure obtained by single-phase austempering of the high-strength steel has obvious effects of improving strength and toughness, the quenching degree is ensured by complete austempering in the heat treatment process, the influence of excessive growth of crystal grains on low-temperature impact toughness is avoided, the quenching temperature is increased by the first quenching, the sufficient austempering of carbide and alloy elements is ensured, the foundation is laid for tissue homogenization, the quenching is the critical zone quenching, the excessive growth of crystal grains is prevented while austempering is ensured, and finally, the stress is eliminated by high-temperature tempering, so that the bainite tempered structure with uniform and fine structure is obtained, and the impact toughness and the strength uniformity of the whole plate are improved.
The invention has the beneficial effects that: a brand new component design is adopted, and 100% bainite tempered structure is obtained after heat treatment by reasonably controlling the addition amount of hardenability elements; a brand new rare earth element adding process is adopted to realize molten steel purification and modification of inclusions, so that the low-temperature impact toughness of the rare earth steel is effectively improved; adopting a brand new steel plate forming process, increasing the thickness of steel ingots, improving the rolling compression ratio, improving the steel ingot heating rolling process, ensuring the internal quality of the steel plates to reach the forging level, and realizing replacing forging by rolling; the heat treatment link ensures the hardenability and refines austenite grains through multiple times of quenching by high and low matching, and improves the uniformity of the mechanical property of the whole plate through improved tempering.
Drawings
FIG. 1 is a schematic diagram of a metallographic structure (metallographic microscope, X100) of a section of a 120mm thick steel plate according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a metallographic structure (metallographic microscope, X200) of a section of a 120mm thick steel plate according to an embodiment of the present invention.
FIG. 3 is a schematic diagram of a metallographic structure (metallographic microscope, X500) of a section of a 120mm thick steel plate according to the embodiment of the invention.
Detailed Description
The technical features of the present invention will be further described with reference to the accompanying drawings and examples.
The production method of the 50-120mm thick high-strength water-electricity HY950CF steel plate comprises the following chemical components in percentage by mass (unit, wt%): c:0.09 to 0.12, si:0.15 to 0.25, mn:0.30 to 0.60, P is less than or equal to 0.010, S is less than or equal to 0.003, als:0.020 to 0.040, nb:0.02 to 0.03, V:0.04-0.1, cr:1.2-1.6, ni:2.4-2.8, cu:0.8-1.0, mo:0.2 to 0.3, RE:0.0015 to 0.0025, the others being Fe and residual elements.
The production method comprises the following process flows: KR molten iron pretreatment, converter smelting, argon blowing treatment, VD decarburization, LF refining, VD refining, casting technology, steel ingot cleaning and coating, cogging heating and rolling, secondary heating and rolling and heat treatment. The method comprises the following steps:
1) The KR molten iron pretreatment process comprises the following steps: before molten iron is stopped, slag must be scraped clean, the thickness of a slag layer at the liquid level is ensured to be less than or equal to 25mm, the sulfur content of the molten iron after KR treatment is controlled to be less than 0.005%, and the desulfurization temperature is reduced to be less than or equal to 25 ℃;
2) Smelting in a converter: the molten iron S is less than or equal to 0.005 percent, the P is less than or equal to 0.050 percent, the molten iron temperature is more than or equal to 1280 ℃, the added scrap steel of the converter is required to be dried high-quality leftover materials and nickel-containing special scrap steel, the converter loading amount is controlled according to 6-8 tons of casting steel, the tapping temperature is more than or equal to 1600 ℃, C is more than or equal to 0.04 percent and less than or equal to 0.07 percent, and P is less than or equal to 0.007 percent, the tapping is finished by adopting a slag blocking cone to block slag, if slag blocking fails, the converter must be lifted in advance, the slag thickness of the converter is controlled below 20mm, and the slag returning P is avoided;
3) Argon blowing treatment: after the molten steel reaches the argon station, alloy, aluminum wires or auxiliary materials are forbidden to be added into the molten steel, and argon blowing is also forbidden. Directly hoisting molten steel to a VD furnace for vacuum treatment, and controlling the leaving temperature according to the temperature of more than or equal to 1560 ℃;
4) And (3) VD decarburization: ensuring that the temperature of molten steel reaches the VD temperature of more than or equal to 1540 ℃, properly adding carbon powder according to the content of steel C after the molten steel is located in a VD furnace, then covering a cover to perform vacuum operation, and fully realizing vacuum decarburization by increasing the argon gas quantity of the molten steel in the vacuum stage of the VD furnace, wherein the pressure maintaining time is more than or equal to 10min, and the leaving temperature is more than or equal to 1535 ℃;
5) LF refining: slagging according to a large slag amount process standard, wherein the addition amount of lime is 1000-1200 Kg, the alkalinity is controlled according to 4.5-6.5, 50Kg of calcium carbide is firstly added after heating for 3min, 20-40Kg of aluminum particles are then added, and then 2-4 shovel aluminum particles are added into a ladle every 2min to ensure that slag turns white; adding 10-30Kg of calcium carbide each time according to the submerged arc effect, and simultaneously adding 1-3 shovel aluminum particles into the steel ladle every 2min by using a shovel to ensure that white slag is maintained in the whole secondary heating process; adding a three-heating deoxidizer according to the color of slag, and maintaining white slag; the white slag is required to be kept for 25-35 minutes in the refining process;
6) And (3) VD refining: the VD dwell time is controlled according to the value of more than or equal to 18min, the molten steel rising effect in the dwell process is good under the vacuum degree of 67Pa, and the H content is required to be less than or equal to 1.0PPm; after the air break, adding rice hulls in time for soft blowing for 5-8min, and then preparing a hanging bag to leave a station, wherein the temperature of leaving the station is controlled to be about 1578-1583 ℃;
7) The casting process comprises the following steps: the temperature of the heat-insulating cap on line is higher than 160 ℃, a 45-ton water-cooling ingot mould with fixed thickness and width is used, the thickness of a steel ingot body is 960-990mm, the width is 2150mm, the height is 2730mm, the mould arranging process must ensure that all auxiliary materials are dry, and ensure that a pouring system is dry and clean, the water-cooling mould must ensure taper (30 mm) and simultaneously is provided with an extrusion mechanism on the side edge, the wide edge of the ingot is extruded in the later stage of solidification, compact tissues are formed by high-efficiency laminating and cooling, an effective heat-insulating measure is adopted at the mouth of the steel ingot cap, and a large-up and small-down feeding channel is formed inside the steel ingot in the solidification process; the casting temperature is controlled according to 1555-1560 ℃; after the molten steel arrives at the station, the temperature is proper (at the standard upper limit-upper limit +3℃), and after sedation and temperature measurement confirm that the casting requirements are met, casting is started; if the arrival temperature of the molten steel does not meet the standard, immediately carrying out soft argon blowing, and after the argon blowing is finished, requiring sedation for 5min, starting casting, and adding a feeding model RECE-48 into a middle casting pipe in the casting process, wherein the wire feeding speed is 15m/min. After the pouring is finished, the heat preservation effect of the cap opening must be ensured.
8) Steel ingot cleaning and coating: after the steel ingot is demolded, cleaning is completed within 24 hours, the cleaning temperature is more than or equal to 200 ℃, and after cleaning, stacking is slowly cooled to 50-100 ℃ in a slow cooling pit, and the spraying of antioxidant coating is started.
9) Cogging, heating and rolling: the total heating time of the steel ingot is 15min/cm, the temperature of a hearth is less than or equal to 750 ℃ when the steel is filled, the steel is stewed for 2 to 4 hours to reduce the temperature difference between the furnace temperature and the steel ingot, the stress difference caused by the temperature difference between the inside and outside of the steel ingot is reduced, and the target heat preservation temperature of a high temperature section is 1220 to 1240 ℃ and the heat preservation time is 16 to 18 hours; the rolling process adopts high temperature, low speed and large reduction, the initial rolling temperature is 1050-1100 ℃, the advantage of large rolling force of a 3800mm rolling mill is fully exerted, the single pass reduction is controlled to be 60-70 mm, deformation penetration to the position with the thickness of 1/2 is ensured, loose and effective welding inside the steel ingot is realized, the cast structure is fully crushed, the uniform refinement of steel plate crystal grains is promoted, the cogging specification is 400 multiplied by 2200 multiplied by Lmm, the rolling thickness is discharged when the rolling thickness is 400mm, and the rolling finishing temperature is 950-980 ℃;
10 Secondary heating and rolling: after the intermediate billet is cut, a soaking pit is arranged, the target temperature of a high temperature section is 1220-1240 ℃, the total heat preservation time is 5-6 hours, the rolling is directly carried out to the thickness of a finished product without stretching again during secondary rolling, the pass reduction is more than or equal to 30+/-5 mm, the starting rolling temperature is more than or equal to 1020 ℃, the finishing rolling temperature is less than or equal to 950 ℃, high-pressure water is used for cooling in the rolling process, rolling can be started after the surface of the steel plate is fully reddened, the total rolling time is controlled to 3-4 minutes, the ACC is started to be cooled twice after the rolling is finished, the surface and the core temperature of the steel plate are quickly reduced to an unrecrystallized area, the water inlet temperature is 900-950 ℃, and the reddening temperature is 800-830 ℃;
11 Heat treatment: in order to effectively improve the strength and ensure the low-temperature impact toughness, a two-time quenching and tempering heat treatment process is adopted, the first quenching heating temperature of a quenching furnace is 920-940 ℃, the heating time=the solid thickness of the steel plate is x2.4min/mm, and a quenching machine is cooled to normal temperature after the hot steel plate is discharged, and the water temperature is 15-18 ℃; the second quenching heating temperature is 860-870 ℃, the heating time=the solid thickness of the steel plate is 2.4min/mm, the quenching machine cools to normal temperature after the hot steel plate is discharged, and the water temperature is 15-18 ℃; after quenching, the steel is put into a quenching furnace for tempering at 650+/-20 ℃, air cooling is carried out to normal temperature, sampling and detection are carried out, and the following table shows the detection results:
detection and analysis: the chemical composition, mechanical property test piece sampling position and sample preparation of the steel plate are carried out according to the standard GB/T2975 mechanical property test sampling position and sample preparation regulation. The low-temperature impact toughness test is carried out according to the GB/T229 standard, the tensile property test is carried out according to the GB/T228 standard, and all mechanical properties and metallographic structures of the steel plate in the supply state are comprehensively checked.
From the data, the 1/4 part and 1/2 part of the steel plate have moderate strength margin and good low-temperature impact toughness, and all performance indexes meet the requirements of the high-strength hydroelectric HY950CF steel. Metallographic detection results: (1) the level of the inclusion A+B+D is less than or equal to 2.0; (2) organization: and (3) a bainite tempered structure.
External inspection and flaw detection: the external inspection quality rate of the developed steel plate is 100%, and the final steel plate flaw detection meets the I-level flaw detection requirement of GB/T2970 super-inspection method for thick steel plates.
The above description is only of the preferred embodiments of the present invention, and the above embodiments are not intended to limit the present invention, and those skilled in the art may make modifications, adaptations or equivalent substitutions according to the above description, which fall within the scope of the present invention.
Claims (1)
1. A production method of an HY950CF steel plate for high-strength hydroelectric engineering is characterized by comprising the following steps: the thickness of the steel plate is 50-120mm, and the steel plate comprises the following chemical components in percentage by mass (unit, wt%): c:0.09 to 0.12, si:0.15 to 0.25, mn:0.30 to 0.60, P is less than or equal to 0.010, S is less than or equal to 0.003, als:0.020 to 0.040, nb:0.02 to 0.03, V:0.04-0.1, cr:1.2-1.6, ni:2.4-2.8, cu:0.8-1.0, mo:0.2 to 0.3, RE:0.0015 to 0.0025, and the balance of Fe and residual elements, wherein the carbon equivalent Ceq is less than 0.7, the structure is a bainite tempered structure, and the longitudinal and transverse V-shaped impact energy at minus 60 ℃ is more than or equal to 127J;
the production method of the steel plate comprises the following steps: casting steel ingot, primary heating, cogging and rolling, secondary heating and rolling, and heat treatment, specifically,
a. casting steel ingot, wherein the thickness of the steel ingot body is 960-990mm, the casting temperature is controlled according to 1555-1560 ℃, RE wire is added into a middle injection pipe in the casting process to improve the internal quality, and the wire feeding speed is 15m/min;
b. the primary heating process is that when the steel is filled, the temperature of a hearth is less than or equal to 750 ℃, the steel is stewed for 2 to 4 hours to reduce the temperature difference between the furnace temperature and the steel ingot, the stress caused by the temperature difference between the inside and the outside of the steel ingot is reduced, the target heat preservation temperature of a high temperature section is 1220 to 1240 ℃, the heat preservation time is 16 to 18 hours, and the total heating time is 15min/cm;
c. the cogging rolling process adopts high temperature, low speed and large reduction, the initial rolling temperature is 1050-1100 ℃, the pass reduction is 60-70 mm, cogging is carried out until the thickness is 400mm, and the temperature of the rolled steel plate is controlled at 950-980 ℃;
d. the secondary heating and rolling process includes four steps of cutting an intermediate blank, installing a soaking pit, setting the target temperature of a high-temperature section at 1220-1240 ℃ and the total heat preservation time at 5-6 hours, directly expanding to the thickness of a finished product without stretching again during secondary rolling, setting the pass reduction at 30+/-5 mm, setting the initial rolling temperature at 1020 ℃ and the final rolling temperature at 950 ℃, using high-pressure water for cooling during rolling, starting rolling after the surface of a steel plate is fully reddened, controlling the total rolling time at 3-4 minutes, starting ACC water cooling for two times after rolling is finished, quickly reducing the surface and core temperature of the steel plate to a non-recrystallized region, setting the water inlet temperature at 900-950 ℃ and the reddening temperature at 800-830 ℃;
e. the heat treatment process adopts high-temperature quenching, critical quenching and tempering heat treatment, wherein the first quenching heating temperature is 920-940 ℃, the heating time is 2.4min/mm, and the quenching machine cools to normal temperature after the hot steel plate is discharged from the furnace, and the water temperature is 15-18 ℃; the second quenching heating temperature is 860-870 ℃, the heating time is 2.4min/mm, the quenching machine cools to normal temperature after the hot steel plate is discharged from the furnace, and the water temperature is 15-18 ℃; quenching, tempering at 650+ -20deg.C, and air cooling to normal temperature.
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