CN114164374A - 850 MPa-grade high-strength high-toughness easy-welding nano steel with thickness of 5-60 mm and preparation method thereof - Google Patents
850 MPa-grade high-strength high-toughness easy-welding nano steel with thickness of 5-60 mm and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a 850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm and a preparation method thereof, wherein the nano steel comprises the following components: according to the mass percentage of alloy elements, C: 0.02 to 0.08, Si: 0.1 to 0.4, Mn: 0.5-1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, Cu: 1.0 to 1.5, Ni: 2.5-4.0, Cr: 0.2 to 0.8, Mo: 0.3 to 0.6, Nb: 0.02-0.1, Ti: 0.01 to 0.05, Al: 0.005 to 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-continuous casting or die casting-rolling-heat treatment. The yield strength of the nano steel is more than or equal to 850MPa, the Charpy V notch impact energy at-80 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%.
Description
Technical Field
The invention belongs to the field of alloy steel, and particularly relates to 850 MPa-grade high-strength high-toughness easy-welding steel with the thickness of 5-60 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
With the rapid development of the manufacturing industry, people have higher and higher requirements on the performance of the steel materials. The strengthening mechanism of conventional high strength steels comes from their martensitic or lower bainite microstructure with a high carbon content. In order to ensure sufficient hardenability of thick gauge steel sheets, high contents of alloying elements such as C, Ni, Cr, Mo, etc. are added to the steel. The higher the strength grade requirements of the steel, the higher the content of the added alloying elements, which inevitably leads to a loss of other properties of the steel, such as ductility, fracture toughness, weldability, and workability, etc. In addition, with the continuous increase of the strength, the carbon equivalent of the steel is also greatly increased, which can significantly increase the welding difficulty of the material and increase the welding processing cost. Therefore, the conventional steel reinforcing method must be reformed and innovated.
In the early stage of the 20 th century and the 80 th year, people begin to explore high-strength low-alloy steel, the hardenability and the number of precipitated phases of the material are further improved by adding precipitated phase forming elements such as Cu and Ni on the basis of the original material, and the precipitation of the precipitated phases can be promoted by reducing the grain boundary through the addition of Ni, so that the plasticity and the toughness of the material are improved and the hot brittleness of the material is reduced while the strength of the material is improved. In the subsequent studies, the strength level was further improved by optimizing the thermo-mechanical treatment and hot working process.
At present, the low alloy steel strengthened by Cu-containing precipitated phase published at home and abroad is difficult to ensure better low-temperature toughness when the strength level is more than 800 MPa.
Patent document CN108004475B discloses a 900 MPa-level hot-rolled precipitation-strengthened high-strength and high-toughness steel and a manufacturing method thereof, wherein the yield strength is more than 800MPa, but the carbon content is higher than 0.1%, the steel is not easy to weld, and the impact energy at-40 ℃ is less than 100J.
Patent document No. CN110229999A discloses a 900MPa grade precipitation-strengthened high-toughness steel sheet and a method for producing the same, wherein the yield strength of martensitic steel obtained by copper-rich precipitation phase strengthening is greater than 900 MPa. Because the content of the nickel element is not high, vanadium, boron and more chromium are required to be added to improve the hardenability, but the low-temperature toughness of the steel is still less than 80J at minus 80 ℃, and the high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm and the thickness of 850MPa can be used under a severer condition.
In the patent document with the publication number of CN106636961A, a Cu precipitated phase strengthened easy-welding steel and a preparation method are disclosed, wherein the preparation of steel with the thickness of less than 15mm is only carried out, and the preparation method is not explained for steel plates with the thickness of more than 15 mm.
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 purpose of the invention is as follows: the invention aims to provide 850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 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 yield strength of the steel plate is more than or equal to 850MPa, the Charpy V notch impact energy at minus 84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15 percent 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 850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm comprises the following steps:
(1) smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen for dephosphorization and decarbonization, performing 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: 0.02 to 0.08, Si: 0.1 to 0.4, Mn: 0.5-1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, Cu: 1.0 to 1.5, Ni: 2.5-4.0, Cr: 0.2 to 0.8, Mo: 0.3 to 0.6, Nb: 0.02-0.1, Ti: 0.01 to 0.05, Al: 0.005-0.05, and the balance of Fe and inevitable impurities, adjusting the components to target components, and then performing dehydrogenation and deoxidation in a VD vacuum furnace;
(2) continuous casting or die casting: continuous casting is adopted for converter smelting, a die casting mode is adopted for electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
(3) rolling: heating the casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron scale with high-pressure water before rolling, removing phosphorus with high-pressure water during rolling, carrying out continuous rolling including rough rolling and finish rolling, and controlling the rough rolling temperature to be 1000-1150 ℃; the finish rolling initial rolling temperature is 950-1050 ℃, the finish rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled;
(4) and (3) heat treatment: after the steel plate is subjected to heat preservation at 800-950 ℃ for 30-90 minutes, water-cooling quenching to room temperature; then tempering at 550-700 ℃ for 50-120 minutes, and air cooling to room temperature.
A850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm is disclosed, and a microstructure of the steel consists of an ultra-low carbon lath martensite structure and a flaky inversion austenite.
Furthermore, the yield strength of the nano steel is more than or equal to 850MPa, the Charpy V notch impact energy at-84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the 850 MPa-grade high-strength high-toughness easy-welding steel with the thickness of 5-60 mm, the copper-rich nano precipitated phase strengthening with the hierarchical structure is used for replacing the traditional precipitation strengthening and carbon strengthening, the carbon content is low, and the welding performance is good; meanwhile, the content of alloy elements is low, and the cost is low.
2. The preparation method of the 850MPa grade high-strength high-toughness easy-welding steel with the thickness of 5-60 mm is simple, the process controllability is strong, and the industrial production is easy to realize.
3. The yield strength of the 5-60 mm thick 850MPa grade high-strength high-toughness easy-welding steel is more than or equal to 850MPa, the Charpy V notch impact energy at-84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%. Has the characteristics of excellent obdurability matching, high plasticity, easy welding and the like.
Drawings
FIG. 1 is a structural view of a 20mm thick steel plate of example 1;
FIG. 2 is a structural view of a 25mm thick steel plate of example 2;
FIG. 3 is a structural view of a 30mm thick steel plate of example 3;
fig. 4 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 850MPa grade high-strength high-toughness easy-welding steel with the thickness of 5-60 mm and a preparation method thereof, and the high-strength steel comprises the following components: c, according to mass percent: 0.02 to 0.05, Si: 0.1 to 0.3, Mn: 0.5-1.0, P is less than or equal to 0.01, S is less than or equal to 0.0015, Cu: 1.0 to 1.5, Ni: 2.5-3.2, Cr: 0.2 to 0.5, Mo: 0.3 to 0.5, Nb: 0.02-0.1, Ti: 0.01 to 0.05, Al: 0.005 to 0.05, and the balance of Fe and inevitable impurities.
The invention principle and the component design basis of the 850MPa grade high-strength high-toughness easy-welding steel are as follows:
the invention principle is as follows: the microstructure of the 850 MPa-grade high-strength high-toughness easy-welding steel with the thickness of 5-60 mm is lath martensite, copper-rich nickel-aluminum composite nano precipitated phase and reversed austenite. The high strength of steel comes mainly from four aspects: the method comprises the steps of precipitation strengthening of a copper-rich nano phase, fine crystal strengthening of lath martensite, dislocation strengthening and solid solution strengthening of alloy elements. 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 form a composite nano phase with the size of below 10 nanometers, so that the dislocation motion is hindered to play a strengthening role. 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. The solid solution strengthening results from strengthening by the addition of various alloy elements.
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. According to the invention, the traditional carbon strengthening is replaced by the nanophase strengthening, so that the carbon content is controlled to be 0.02-0.05%.
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 to be 1.0-1.5%.
Ni: nickel is one of main elements formed by a nanometer precipitated phase, a B2 ordered structure is formed to wrap the surface of a precipitated phase formed by copper, the thermal stability of the precipitated phase can be increased, meanwhile, the nickel can strengthen a matrix, the low-temperature toughness is obviously improved, and the content of the nickel is controlled to be 2.5-3.2%.
Mn: manganese is one of main constituent elements of the nano precipitated phase, crystal grains can be refined, the strength and the low-temperature toughness of steel are improved, casting blank segregation, large structural stress, reduced welding performance and the like are easily caused by excessively high content, and the content of manganese is controlled to be 0.5-1.0%.
Al: aluminum is a strong deoxidizing element in the steelmaking 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. The chromium content of the invention is controlled to be 0.2-0.5%.
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. The content of molybdenum in the invention is controlled to be 0.3-0.5%.
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 content of niobium in the invention is controlled to be 0.02-0.1%.
Ti: titanium can form carbonitride pinning grain boundaries to refine grains. The content of niobium in the invention is controlled to be 0.01-0.05%
The invention relates to 850MPa 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 → continuous casting or die casting → casting blank heating → 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) continuous casting or die casting: continuous casting is adopted for converter smelting, a die casting mode is adopted for electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
3) rolling: heating the casting blank to 1160-1200 ℃, 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 continuous rolling comprises rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1000-1150 ℃; and the finish rolling temperature is 950-1050 ℃, the finish rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled.
4) And (3) heat treatment: after the steel plate is subjected to heat preservation at 800-950 ℃ for 30-90 minutes, water-cooling quenching to room temperature; then tempering at 550-700 ℃ for 50-120 minutes, and air cooling to room temperature.
The chemical compositions 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 | 0.042 | 0.25 | 0.85 | 0.007 | 0.0012 | 1.21 | 2.7 | 0.50 | 0.50 | 0.040 | 0.014 | 0.025 |
| Example 2 | 0.048 | 0.25 | 0.88 | 0.005 | 0.0007 | 1.28 | 3.1 | 0.55 | 0.49 | 0.038 | 0.013 | 0.034 |
| Example 3 | 0.052 | 0.32 | 0.95 | 0.005 | 0.0006 | 1.36 | 3.6 | 0.79 | 0.56 | 0.048 | 0.023 | 0.044 |
In each embodiment, electric furnace smelting is adopted, oxygen blowing, dephosphorization and decarburization are carried out, aluminum deoxidation is carried out, then the steel ladle furnace is carried out for refining, deep desulfurization, heating, refining treatment and component adjustment are carried out to target components, argon is blown into molten steel from a gas permeable brick at the bottom of a steel 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 inclusions are fully removed, the purity of the molten steel is ensured, finally, the molten steel is cast into steel billets, and stacking and slow cooling are carried out for 48 hours;
heating the casting blank to 1160-1200 ℃, 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 rough rolling temperature is controlled to be 1000-1150 ℃; and the finish rolling temperature is 950-1050 ℃, the finish rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled.
After the steel plate is subjected to heat preservation at 800-950 ℃ for 30-90 minutes, water-cooling quenching to room temperature; then tempering at 550-700 ℃ for 50-120 minutes, and air cooling to room temperature.
Table 2 shows the main rolling process parameters of each example.
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
The test steel plate of the invention has excellent strength, impact toughness and elongation performance, large allowance, and excellent low-temperature toughness and plasticity.
FIG. 1 is a structural diagram showing a structure of a 20mm thick steel plate in example 1, wherein the structure is lath martensite. The structure not only ensures that the steel has better obdurability, but also ensures better elongation.
FIG. 2 shows the tensile curve of the 20mm thick steel plate 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 850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm and a preparation method thereof, and the high-strength high-toughness easy-welding nano steel comprises the following components: according to the mass percentage of alloy elements, C: 0.02 to 0.08, Si: 0.1 to 0.4, Mn: 0.5-1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, Cu: 1.0 to 1.5, Ni: 2.5-4.0, Cr: 0.2 to 0.8, Mo: 0.3 to 0.6, Nb: 0.02-0.1, Ti: 0.01 to 0.05, Al: 0.005 to 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-continuous casting or die casting-rolling-heat treatment. The high-strength high-toughness easy-welding steel disclosed 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, and meanwhile, the plasticity and low-temperature toughness are optimized by controlling the shape, distribution and volume fraction of inverted austenite, the yield strength is more than or equal to 850MPa, the Charpy V notch impact power at-80 ℃ is more than or equal to 200J, the elongation is more than or equal to 15%, and the high-strength high-toughness easy-welding steel has the characteristics of high strength, high toughness, high plasticity and easy 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 850 MPa-grade high-strength high-toughness easy-welding nano steel with the thickness of 5-60 mm 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, performing 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: 0.02 to 0.08, Si: 0.1 to 0.4, Mn: 0.5-1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, Cu: 1.0 to 1.5, Ni: 2.5-4.0, Cr: 0.2 to 0.8, Mo: 0.3 to 0.6, Nb: 0.02-0.1, Ti: 0.01 to 0.05, Al: 0.005-0.05, and the balance of Fe and inevitable impurities, adjusting the components to target components, and then performing dehydrogenation and deoxidation in a VD vacuum furnace;
(2) continuous casting or die casting: continuous casting is adopted for converter smelting, a die casting mode is adopted for electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
(3) rolling: heating the casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron scale with high-pressure water before rolling, removing phosphorus with high-pressure water during rolling, carrying out continuous rolling including rough rolling and finish rolling, and controlling the rough rolling temperature to be 1000-1150 ℃; the finish rolling initial rolling temperature is 950-1050 ℃, the finish rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled;
(4) and (3) heat treatment: after the steel plate is subjected to heat preservation at 800-950 ℃ for 30-90 minutes, water-cooling quenching to room temperature; then tempering at 550-700 ℃ for 50-120 minutes, and air cooling to room temperature.
2. The nano-steel produced according to the method of claim 1, wherein the microstructure consists of an ultra-low carbon lath martensite structure and a sheet-like reversed austenite.
3. The nano-steel according to claim 2, wherein the yield strength is not less than 850MPa, the charpy V-notch impact energy at-84 ℃ is not less than 200J, and the elongation is not less than 15%.
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