CN114164315B - 1000 MPa-grade high-strength high-toughness easy-welding nano steel with thickness of 60-120 mm and preparation method thereof - Google Patents
1000 MPa-grade high-strength high-toughness easy-welding nano steel with thickness of 60-120 mm and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a 1000MPa grade high-strength high-toughness easy-welding nano steel with the thickness of 60-120 mm and a preparation method thereof, which comprises the following components: according to the mass percentage of alloy elements, C:0.04 to 0.08, si:0.1 to 0.6, mn: 0.8-1.5, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.5 to 2.5, ni:7.0 to 9.0, cr:0.7 to 1.5, mo:0.5 to 1.0, nb:0.02 to 0.1, ti:0.01 to 0.05, al:0.005 to 0.05, and the balance of Fe and inevitable impurities, comprising the steps of: smelting and refining-casting-rolling-heat treatment; the yield strength of the nano steel is more than or equal to 1000MPa, the Charpy V notch impact energy at-84 ℃ can reach more than 100J, the elongation is more than or equal to 15%, and the nano steel has the characteristics of high strength, high toughness and easiness in welding.
Description
Technical Field
The invention belongs to the field of alloy steel, and particularly relates to 1000 MPa-grade high-strength high-toughness easy-welding steel with the thickness of 60-120 mm and a manufacturing method thereof, which can be used in the fields of ships, ocean engineering equipment, pipelines, heavy mechanical equipment and the like.
Background
In China, the steel plate with the thickness of more than 60mm is generally called an extra-thick plate, and the extra-thick plate can be widely used in the fields of ocean engineering equipment, high-rise buildings, pressure containers, chemical reaction synthetic towers, bridges, armors and the like. The strengthening mechanism of the traditional extra-thick high-strength steel is mainly a martensite or lower bainite structure with higher carbon content. In order to ensure sufficient hardenability, high contents of alloying elements such as C, ni, cr, mo and the like are generally added, so that the ductility and toughness of the material are deteriorated, and the welding performance is also deteriorated due to the increase of the carbon equivalent.
The nano-phase strengthening is a strengthening method which effectively improves the strength and does not lose the plasticity and toughness, the traditional carbon strengthening is replaced by the Cu nano precipitated phase strengthening, the good strengthening effect can be achieved in the center of the extra-thick plate, and meanwhile, the better welding performance can be achieved due to the ultra-low carbon content. At present, high-strength steel of more than 1000MPa is mostly designed by adopting components of low-carbon and micro-alloy elements, and the toughness and welding performance are not ideal due to higher carbon content.
Patent document No. CN108359897B discloses precipitation-strengthened ferritic steel with yield strength of 1000MPa grade, which is greater than 1000MPa but has high carbon content and is not easy to weld, and a production method thereof.
The patent document with the publication number of CN112143958A discloses a 1000 MPa-grade steel plate with super-thick, ultrahigh toughness and excellent weldability and a manufacturing method thereof, wherein the yield strength is more than 890MPa, a rolling process of a non-recrystallization zone is adopted to obtain smaller grain size, a TMCP + offline modulation process is used, vanadium and boron are required to be added to improve hardenability, the carbon content is higher than 0.08%, and only the impact property of minus 60 ℃ is characterized.
In patent document CN106544590A, a 1000MPa grade high-toughness high-performance uniform easy-welding super-thick steel plate and its manufacturing method are disclosed, the steel plate thickness reaches 180mm while the yield strength is kept to be more than 1000MPa, but the carbon content is higher than 0.1%, and the impact energy is less than 100J at-40 ℃.
In patent document CN106636961A, a Cu nanophase reinforced easy-to-weld steel and a preparation method thereof are disclosed, which has a relatively high aluminum content, and only the preparation of steel with a thickness of less than 15mm is performed, and for steel plates with a thickness of more than 15mm is not described, the invention controls the aluminum element at a lower level, and simultaneously adopts secondary refining and a post-rolling slow cooling process, so that steel plates with a larger thickness can be produced.
In summary, there is no steel material that can satisfy high strength, high toughness and good welding performance at the same time, which is a great challenge for the traditional tissue design idea and heat treatment process.
Disclosure of Invention
The invention aims to: the invention aims to provide 1000MPa grade high-strength high-toughness easy-welding steel with the thickness of 60-120 mm and a preparation method thereof, which can meet the requirements of high strength, high toughness and good welding performance of a steel plate, and the steel plate has the yield strength of more than or equal to 1000MPa, the elongation of more than or equal to 15 percent and the Charpy V notch impact energy of more than or equal to 100J at the temperature of minus 84 ℃ through a two-step heat treatment process of solution treatment and aging treatment.
The technical scheme of the invention is as follows:
a preparation method of 1000MPa grade high-strength high-toughness easy-welding nano steel with the thickness of 60-120 mm comprises the following steps:
(1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen to dephosphorize and decarbonize, performing aluminum deoxidation, then transferring into a ladle furnace for refining, and simultaneously adding alloy materials, wherein the mass percentages are as follows: 0.04 to 0.08, si:0.1 to 0.6, mn: 0.8-1.5, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.5 to 2.5, ni:7.0 to 9.0, cr:0.7 to 1.5, mo:0.5 to 1.0, nb:0.02 to 0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and inevitable impurities, and the components are adjusted to target components and then are dehydrogenated and deoxidized in a VD vacuum furnace;
(2) Casting into steel ingots: pouring the smelted molten iron into steel ingots;
(3) Cogging: heating the steel ingot at 1150-1200 ℃ for 18-24 h, performing hot rolling cogging after heating, and performing high-temperature large-reduction rolling for ensuring the strength of the extra-thick plate, wherein the reduction amount is more than 45mm for at least 3 times, and the final rolling temperature is higher than 900 ℃; rolling: heating the billet to 1150-1200 ℃, preserving heat for 2-6 hours, removing iron scale with high-pressure water before rolling, and removing phosphorus with high-pressure water during rolling; the rolling comprises rough rolling and finish rolling, and the rough rolling temperature is controlled to be 1150-1100 ℃; the initial rolling temperature of finish rolling is 1050-950 ℃, the finishing rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 60-120 mm is rolled;
(4) And (3) heat treatment: after the steel plate is subjected to heat preservation for 60-300 minutes at 750-950 ℃, ultra-fast quenching is carried out to room temperature, and the quenching retention time is t Quenching maintenance =30+ (H-10) × 1.5 in min, and H is the thickness of the finished steel plate in mm; then tempering for 120-540 minutes at 550-600 ℃, air cooling to room temperature, and tempering for holding time t Temper retention And (4) the unit is min for 60+ (H-10) multiplied by 2.5, and the unit is the thickness of the finished steel plate and the unit is mm.
A high-strength high-toughness easily welded nano steel with thickness of 60-120 mm and high strength at 1000MPa has a microstructure composed of ultralow-carbon lath martensite or lower bainite structure and flaky reverse austenite.
The yield strength of the nano steel is more than or equal to 1000MPa, the Charpy V notch impact energy at-84 ℃ is more than or equal to 100J, and the elongation is more than or equal to 15%.
Compared with the prior art, the invention has the following beneficial effects:
1. the 1000 MPa-grade high-strength high-toughness easy-welding steel with the thickness of 60-120 mm replaces the traditional carbon reinforcement by copper-rich nano precipitated phase reinforcement, and has lower carbon content and good welding performance; meanwhile, the content of the alloy elements is low, and the cost is low. The high obdurability improves the safety stability of a heavy steel structure, the good weldability saves the manufacturing cost of components, especially for ultrahigh-strength steel plates, the welding cold crack sensitivity is greatly reduced, the welding preheating, the post-heating temperature reduction, the heat input and output range are wider, and the cost is greatly reduced.
2. The preparation method of the 1000MPa grade high-strength high-toughness easy-welding steel with the thickness of 60-120 mm is simple, the process controllability is strong, and the industrial production is easy to realize.
3. The high-strength high-toughness easy-welding steel with the thickness of 60-120 mm and the thickness of 1000MPa fully exerts the potential of full hardenability of alloy elements through regulating and controlling rolling and heat treatment processes, effectively refines the sizes of prior austenite and martensite lath bundles, ensures a high-density large-angle crystal boundary, and obtains excellent performances of the yield strength being more than or equal to 1000MPa, the elongation being more than or equal to 15 percent, and the Charpy V-notch impact energy being more than or equal to 100J at minus 84 ℃.
Drawings
FIG. 1 photo of optical microscope of example 1;
fig. 2 engineering stress strain curves for example 1.
Detailed Description
The invention is further described in the following with reference to the following figures and examples:
the invention relates to a high-strength high-toughness easy-welding steel with the thickness of 60-120 mm and the thickness of 1000MPa and a preparation method thereof, wherein the high-strength steel comprises the following components: c:0.04 to 0.08, si:0.1 to 0.6, mn: 0.8-1.5, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.5 to 2.5, ni:7.0 to 9.0, cr:0.7 to 1.5, mo:0.5 to 1.0, nb:0.02 to 0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and inevitable impurities.
The invention principles and the component design of the 1000 MPa-grade high-strength high-toughness easy-welding steel are as follows:
the invention principle is as follows: the microstructure of the 1000MPa grade high-strength high-toughness easy-welding steel with the thickness of 60-120 mm is lath martensite, copper, nickel, aluminum and manganese elements, and has a nano precipitated phase and an inverted austenite of a hierarchical structure. The high strength of the steel of the invention mainly comes from four aspects: the method comprises the steps of precipitation strengthening of a copper-rich nano phase, solid solution strengthening of alloy elements, fine crystal strengthening of lath martensite and dislocation strengthening. The precipitation strengthening mainly comes from the precipitation of copper, nickel and manganese elements added in the alloy in the aging process, and the elements are uniformly distributed in a matrix phase to block dislocation motion to play a strengthening role, and the strengthening effect of over 300MPa can be achieved in the core part and the surface simultaneously. The uniform distribution of alloy components can be ensured through LF ladle refining, so that the effects of precipitation strengthening and solid solution strengthening are ensured, and the two strengthening modes can play the same role in the core and the surface of the medium plate. The fine grain strengthening brings great strength contribution because the compound of Nb and the like pins grain boundaries in the recrystallization rough rolling stage and further refines austenite grain size in the subsequent finish rolling stage in a non-crystallization area, and because the effective grain size of lath martensite is the size of lath bundles, and the size of the lath bundles is only a fraction of the size of original austenite. The dislocation strengthening is mainly from the high density of dislocations in the lath martensite.
In order to ensure that enough lath martensite can be obtained after quenching, the invention adopts the ideal critical diameter DI to simulate and calculate the hardenability of different alloy components, and DI is larger than 1.5 times of the thickness of the steel plate by adjusting the alloy components to ensure that the core part of the medium plate also has enough proportion of martensite to provide fine grain strengthening and dislocation strengthening, thereby ensuring the strength of the material.
The parameters of the ideal critical diameter DI formula adopted by the invention are summarized by the series of high-strength steel experiments, the ideal critical diameter DI is more consistent with the type of steel, and the ideal critical diameter DI is calculated according to the factors of carbon and alloy elements.
D I ＝25.4·f C ·f Mn ·f si ·f Ni ·f Cr ·f Mo ·f Cu (mm)
The toughness of the steel mainly comes from the inhibition effect of lath martensite on crack propagation, the inhibition of crack initiation and propagation by reversing austenite passivation crack tips, and the control of the content of impurity elements such as phosphorus, sulfur and the like and inclusions. The quantity density of lath martensite in the steel core of the medium-thickness plate is controlled by regulating and controlling the ideal critical diameter DI of the alloy, and the contents of impurity elements and inclusions are controlled by VD vacuum degassing, so that the toughness of the steel core of the medium-thickness plate can reach a higher level.
The basis of component design is as follows:
c: carbon is an element that is solid-solution strengthened and plays an important role in enhancing strength. The traditional steel materials are improved in strength mainly through solid solution strengthening of carbon, but excessive carbon can form massive brittle cementite in the tempering process and seriously affect toughness, and meanwhile, the increase of high carbon content can affect weldability. The invention replaces the traditional carbon strengthening by using the nano-phase strengthening, so the carbon content is controlled to be 0.04-0.08%.
Cu: copper is the most main forming element of a precipitated phase, can improve the strength without losing ductility and toughness by forming a nano-scale precipitated phase, and has the effect of refining grains. Too low a copper content affects the strengthening effect, and too high a copper content easily causes hot shortness, which affects welding and hot working. Therefore, the copper content of the invention is controlled between 1.5 and 2.5 percent.
Ni: nickel is one of main elements formed by a nanometer precipitated phase, and a B2 ordered structure is formed to wrap the surface of a precipitated phase formed by copper elements, so that the thermal stability of the precipitated phase can be improved; meanwhile, nickel is used as an austenite stabilizing element, so that the size of the martensite lath bundle can be refined, and the low-temperature toughness is obviously improved; the nickel in the copper-containing steel can also eliminate the phenomenon of copper brittleness and reduce intergranular cracking in the hot rolling process; for extra thick plates a sufficient nickel content is necessary to increase hardenability. Therefore, the nickel content of the invention is controlled between 7.0 and 9.0 percent.
Mn: manganese is one of main constituent elements of the nano precipitated phase, and can also refine grains, so that the strength and the low-temperature toughness of steel are improved, but the excessive content easily causes casting blank segregation, large structural stress, reduced welding performance and the like, and the manganese content is controlled to be 0.8-1.5%.
Al: aluminum is a strong deoxidizing element in the steel making process, can play a role in refining grains, but promotes the graphitization tendency of carbon in steel when the content is too high, and reduces the effect of refining grains, and the content of aluminum is controlled to be 0.005-0.05%.
Cr: chromium may increase the corrosion resistance of the steel, while increasing the hardenability and improving the tempering stability of the steel. Because the steel plate of the invention has thicker thickness, the chromium content is controlled between 0.7 and 1.5 percent.
Mo: molybdenum can increase the hardenability of steel, refine grains, form carbide and improve strength, and has a promoting effect on nucleation of a nano precipitated phase. Because the thickness of the steel plate is thicker, the content of molybdenum is controlled to be 0.5-1.0%.
Nb: niobium can form carbonitride to pin austenite grain boundary, prevent grain growth, and simultaneously play a role in strengthening precipitation to improve strength. The niobium content of the invention is controlled between 0.02 and 0.1 percent.
Ti: titanium can form carbonitride pinning grain boundaries to refine grains. The niobium content of the invention is controlled between 0.01 and 0.05 percent
The invention relates to 1000MPa grade high-strength high-toughness easy-welding steel and a preparation method thereof, which comprises the following steps:
smelting molten iron in a converter or an electric furnace → oxygen blowing dephosphorization and decarburization → LF ladle refining → VD vacuum furnace treatment → casting → cogging → rolling → quenching → tempering → flaw detection → performance inspection;
the main process comprises the following specific operations:
1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen to dephosphorize and decarbonize, deoxidizing aluminum, transferring into a ladle furnace for refining, simultaneously adding alloy materials, adjusting components to target components, and then performing dehydrogenation and deoxidation in a VD vacuum furnace;
2) Casting into steel ingots: pouring the smelted molten iron into steel ingots;
3) Cogging: heating the steel ingot at 1150-1200 ℃ for 18-24 h, performing hot rolling cogging after heating, and performing high-temperature large-reduction rolling at least 3 times with the reduction amount larger than 45mm and the final rolling temperature higher than 900 ℃ in order to ensure the strength of the extra-thick plate.
3) Rolling: heating the billet to 1150-1200 ℃, preserving heat for 2-6 hours, removing the iron scale with high-pressure water before rolling, and removing phosphorus with high-pressure water during rolling.
The rolling comprises rough rolling and finish rolling, and the rough rolling temperature is controlled to be 1150-1100 ℃; the initial rolling temperature of the finish rolling is 1050-950 ℃, the final rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 60-120 mm is rolled.
And (3) heat treatment: after the steel plate is subjected to heat preservation at 750-950 ℃ for 60-300 minutes, carrying out ultra-fast cold quenching to room temperature, wherein the quenching retention time is t quenching retention =30+ (H-10) multiplied by 1.5, the unit is min, and H is the thickness of the finished steel plate, and the unit is mm; and tempering at 550-600 ℃ for 120-540 minutes, and air-cooling to room temperature, wherein the tempering retention time is t tempering retention =60+ (H-10). Times.2.5, the unit is min, and H is the thickness of the finished steel plate, and the unit is mm.
The chemical components of the examples of the present invention are shown in table 1 (mass%), and the balance is Fe and inevitable impurities.
TABLE 1
| C | Si | Mn | P | S | Cu | Ni | Cr | Mo | Nb | Ti | Als | |
| Example 1 | 0.070 | 0.45 | 1.20 | 0.003 | 0.0004 | 2.28 | 6.8 | 0.95 | 0.79 | 0.06 | 0.031 | 0.021 |
In the embodiment, electric furnace smelting, oxygen blowing, dephosphorization and decarburization, aluminum deoxidation, ladle furnace refining is carried out, deep desulfurization, heating, refining treatment and component adjustment are carried out to target components, argon is blown into molten steel from an air brick at the bottom of a ladle for stirring to ensure that the components are uniform, then refining treatment such as degassing, inclusion removal and the like is carried out in a VD vacuum furnace, gas and the inclusion are fully removed, the purity of the molten steel is ensured, finally, the molten steel is cast into steel ingots, and stacking and slow cooling are carried out for 48 hours;
heating the steel ingot at 1150-1200 ℃ for 18-24 h, hot rolling for cogging after heating, rolling at high temperature and high pressure for ensuring the strength of the extra-thick plate, wherein the rolling reduction is more than 45mm in at least 3 times, and the finishing temperature is more than 900 ℃.
Then reheating the billet to 1160-1200 ℃, preserving the heat for 2-6 hours, and rolling. Removing the iron scale with high-pressure water before rolling, and removing phosphorus with high-pressure water during rolling. The rolling comprises two steps of rough rolling and finish rolling, and the rough rolling temperature is controlled to be 1000-1150 ℃; the initial rolling temperature of the finish rolling is 950-1050 ℃, the finishing rolling temperature is higher than 900 ℃, and the steel plate is rolled.
After the steel plate is subjected to heat preservation for 60-300 minutes at 800-950 ℃, ultrafast water-cooling quenching is carried out to the room temperature; then tempering for 120-540 minutes at 550-700 ℃, and cooling to room temperature in air. Table 2 shows the main rolling process parameters of the examples.
TABLE 2
Table 3 shows the heat treatment process parameters.
TABLE 3
The heat-treated steel plate was subjected to transverse sampling to prepare tensile and impact test specimens, and mechanical property tests were carried out, the results of which are shown in Table 4.
TABLE 4
FIG. 1 is an optical micrograph of a steel sheet of example 1 showing a lath martensite structure. The structure not only ensures that the steel has better obdurability, but also ensures better elongation.
FIG. 2 shows the tensile curve of the steel sheet of example 1.
The invention has wide application and can be applied to key structures of ships, ocean engineering, aerospace engineering and the like.
The invention discloses a 1000MPa grade high-strength high-toughness easy-welding nano steel with the thickness of 60-120 mm and a preparation method thereof, and the high-strength high-toughness easy-welding nano steel comprises the following components: according to the mass percent of alloy elements, C:0.04 to 0.08, si:0.1 to 0.6, mn: 0.8-1.5, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.5 to 2.5, ni:7.0 to 9.0, cr:0.7 to 1.5, mo:0.5 to 1.0, nb:0.02 to 0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and inevitable impurities. The preparation method of the high-strength high-toughness easy-welding steel comprises the following steps: smelting and refining-casting-rolling-heat treatment. The ultra-thick plate steel provided by the invention has the characteristics that under the condition of ultralow carbon content, a large amount of nano precipitated phases are separated out to improve the strength by adjusting the content of elements forming the nano precipitated phases and a thermal mechanical treatment process, the plasticity and low-temperature toughness are optimized by controlling the shape, distribution and volume fraction of inverted austenite, the Charpy V notch impact power of the yield strength of more than or equal to 1000MPa at-84 ℃ can be more than 100J, the elongation of more than or equal to 15%, and the ultra-thick plate steel has high strength, high toughness, high plasticity and easiness in welding. The high-strength high-toughness easy-welding steel can be widely applied to key structures of ships, ocean engineering, engineering machinery, bridges, oil pipelines, aerospace engineering and the like.
It should be noted that the above examples are only specific embodiments of the present invention, and it is obvious that the present invention is not limited to the above embodiments, but many similar variations are possible as needed. All modifications which would occur to one skilled in the art and which are, therefore, directly derivable or suggested by the disclosure herein are to be included within the scope of the present invention.
Claims (3)
1. A preparation method of 1000 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 60 to 120mm is characterized by comprising the following steps of:
(1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen for dephosphorization and decarbonization, carrying out aluminum deoxidization, then transferring into a ladle furnace for refining, and simultaneously adding alloy materials, wherein the alloy materials comprise the following components in percentage by mass: 0.07 to 0.08, si:0.45 to 0.6, mn:0.8 to 1.5, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.5 to 2.5, ni:7.0 to 9.0, cr:0.7 to 1.5, mo:0.5 to 1.0, nb:0.02 to 0.1, ti:0.01 to 0.05, als:0.005 to 0.021, and the balance of Fe and inevitable impurities, adjusting the components to the target components, and then carrying out dehydrogenation and deoxidation in a VD vacuum furnace;
(2) Casting into steel ingots: pouring the smelted molten iron into steel ingots;
(3) Cogging: heating the steel ingot at 1150-1200 ℃ for 18-24h, performing hot rolling for cogging after heating, and performing high-temperature high-reduction rolling for ensuring the strength of the extra-thick plate, wherein the reduction amount is more than 45mm in at least 3 passes, and the final rolling temperature is higher than 900 ℃; rolling: heating the billet to 1150-1200 ℃, preserving heat for 2-6 hours, removing the scale with high-pressure water before rolling, and removing phosphorus with high-pressure water in the rolling process; the rolling comprises rough rolling and finish rolling, and the rough rolling temperature is controlled to be 1150-1100 ℃; the finish rolling initial rolling temperature is 1050 to 950 ℃, the finish rolling temperature is higher than 900 ℃, and the steel plate is rolled into a steel plate with the thickness of 60 to 120mm;
(4) And (3) heat treatment: after the steel plate is subjected to heat preservation at 750-950 ℃ for 60-300 minutes, carrying out ultra-fast cold quenching to room temperature, wherein the quenching retention time is t quenching retention =30+ (H-10) multiplied by 1.5, the unit is min, and H is the thickness of the finished steel plate, and the unit is mm; then tempering at 550 to 600 ℃ for 120 to 540 minutes, air-cooling to room temperature, wherein the tempering retention time is t tempering retention =60+ (H-10) multiplied by 2.5, the unit is min, and H is the thickness of a finished steel plate, and the unit is mm;
the microstructure of the nano steel consists of an ultra-low carbon lath martensite or lower bainite structure and a flaky reverse austenite.
2. A nano-steel produced by the method of claim 1, wherein the microstructure consists of ultra-low carbon lath martensite or lower bainite structure and plate-like reversed austenite.
3. The nano-steel according to claim 2, wherein the yield strength is not less than 1000MPa, the charpy V-notch impact energy at-84 ℃ is not less than 100J, and the elongation is not less than 15%.
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