CN109161791B - 690 MPa-grade ship and ocean engineering steel with excellent low-temperature toughness and manufacturing method thereof - Google Patents
690 MPa-grade ship and ocean engineering steel with excellent low-temperature toughness and manufacturing method thereof Download PDFInfo
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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Abstract
690MPa grade ship and ocean engineering steel with excellent low-temperature toughness and a manufacturing method thereof are disclosed, wherein the steel comprises the following components in percentage by weight: 0.06 to 0.13 percent of C, 0.05 to 0.30 percent of Si, 0.70 to 1.30 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.0040 percent of S, 0.15 to 0.50 percent of Cr, 1.0 to 2.5 percent of Ni, 0.10 to 0.40 percent of Mo, less than or equal to 0.50 percent of Cu, 0.01 to 0.06 percent of Al, 0.005 to 0.05 percent of Ti, 0.01 to 0.05 percent of V, less than or equal to 0.0025 percent of B, less than or equal to 0.0045 percent of Ca, and the balance of Fe and inevitable impurities,
Description
Technical Field
The invention relates to the field of manufacturing of high-strength low-alloy steel, in particular to 690 MPa-grade ship and ocean engineering steel with excellent low-temperature toughness and a manufacturing method thereof.
Background
In recent years, rapid development of world economy aggravates energy consumption, exploitation of energy such as petroleum and natural gas gradually extends from land to offshore and deep sea, and as a necessary device for sea energy development, various ocean drilling, production and living platforms such as self-elevating type and semi-submersible type are rapidly developed, and continuous progress of steel for ocean platforms is promoted.
Steel for ocean platforms is developed on the basis of hull structural steel, and initially constructed steel platforms are all made of hull structural steel. With the progress of science and technology and the vigorous development of marine development, the number of ocean platform construction is continuously increased and the types are also increased day by day; meanwhile, energy exploitation is developed from shallow sea to deep sea and from warm sea areas to low-temperature sea areas, so that the ocean platform is subjected to attack of various weather conditions and wind waves and corrosion of seawater, and the working conditions are very harsh; in addition, the large-scale trend of the ocean platform is obvious, the structure is complex, the welding workload is large, and the stress concentration degree is high. Therefore, the requirements for the properties of the steel for the ocean platform are more and more strict, namely the strict requirements of large thickness, high strength, excellent low-temperature toughness, weldability and good corrosion resistance.
Chinese patent publication No. CN101418418A discloses a "690 MPa grade yield strength low crack sensitivity steel plate and a manufacturing method thereof", which adopts an alloy design of ultralow C, higher Mn content, Cr, Mo and B alloying, Nb, V and Ti micro alloying, and no Ni and Cu elements are added, and Pcm is less than or equal to 0.20%. The thickness of the finished steel plate is less than or equal to 60mm by adopting controlled rolling and cooling processes. The yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 770MPa, and the impact energy at-20 ℃ is more than or equal to 150J.
Chinese patent publication No. CN102226255A discloses a "high strength and toughness steel plate with yield strength of 690MPa and its preparation process", which adopts lower C, Mn, Cr, Ni, Mo, Cu alloying, Nb, Ti microalloying, does not add V, B component design, and adopts controlled rolling, controlled cooling, and quenching and tempering heat treatment processes. The thickness of the finished steel plate is 50-100mm, the yield strength is more than or equal to 690MPa, the tensile strength is more than or equal to 750MPa, and the impact energy at minus 80 ℃ is more than or equal to 90J.
Chinese patent publication No. CN102260823A discloses an economical high-strength steel plate with yield strength of 690MPa grade and a manufacturing method thereof, which adopts micro-alloying of ultra-low C, high Mn, Nb and Ti, adds B, does not contain the component design of Cr, Ni, Mo and Cu, and requires Pcm not more than 0.18 percent. It adopts controlled rolling, controlled cooling and tempering heat treatment process, and its microstructure is bainite. The yield strength of the steel plate is more than or equal to 690MPa, the tensile strength is more than or equal to 770MPa, and the impact energy at 40 ℃ is more than or equal to 100J.
Chinese patent publication No. CN103343285A discloses 'a 690-grade ultrahigh-strength steel plate for ocean engineering and a production method thereof', which adopts the component design of higher C content, medium Mn content, Nb, V and Ti microalloying and no addition of Cr, Ni, Mo, Cu and B. It adopts controlled rolling, controlled cooling, quenching and tempering heat treatment. The thickness of the finished steel plate is less than or equal to 80 mm. The yield strength of the steel plate is 695 minus 760MPa, and the tensile strength is 780 minus 920 MPa.
Chinese patent publication No. CN102345045A discloses 'A514 GrQ steel plate for ocean platform rack and production method thereof', which adopts medium C, medium Mn, Cr + Ni + Mo + B alloying, Nb + V + Ti microalloying component design. The thickness of the finished steel plate is 120-150mm by using controlled rolling and normalizing heat treatment processes. The yield strength of the steel plate is 720-760MPa, the tensile strength is 830-880MPa, and the impact energy is 90-150J at the temperature of minus 40 ℃.
Disclosure of Invention
The invention aims to provide 690MPa grade steel with excellent low-temperature toughness for ships and ocean engineering and a manufacturing method thereof, wherein the steel can be used for steel plates for ships and ocean engineering structures, particularly key structural components of ocean engineering structures, can be used in different sea areas, and is particularly suitable for low-temperature sea areas such as the North sea.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention adopts low C, low Mn, Cr-Ni-Mo-Cu-B alloying and V, Ti microalloying component system. Through the manufacturing procedures of converter smelting, LF + RH vacuum smelting, continuous casting, controlled rolling, heat treatment and the like, the microstructure is tempered sorbite and a small amount of bainite structure (the tempered sorbite is more than or equal to 90 percent), and the steel for ships and ocean engineering with the yield strength of more than or equal to 690MPa, the impact energy of more than or equal to 140J at-60 ℃, the NDT (nickel-hardness Transition Temperature) Temperature of less than or equal to-65 ℃ and high strength and excellent low-Temperature impact toughness can be manufactured.
Specifically, the 690MPa grade steel with excellent low-temperature toughness for ships and ocean engineering comprises the following chemical components in percentage by weight: 0.06 to 0.13 percent of C, 0.05 to 0.30 percent of Si, 0.70 to 1.30 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.0040 percent of S, 0.15 to 0.50 percent of Cr, 1.0 to 2.5 percent of Ni, 0.10 to 0.40 percent of Mo, less than or equal to 0.50 percent of Cu, 0.01 to 0.07 percent of Alt, 0.005 to 0.05 percent of Ti, 0.01 to 0.05 percent of V, less than or equal to 0.0025 percent of B, less than or equal to 0.0045 percent of Ca,
the balance being Fe and unavoidable impurities.
The microstructure of the steel for ships and ocean engineering is tempered sorbite and a small amount of bainite structure, and the tempered sorbite is more than or equal to 90 percent, so that the steel has good obdurability matching.
The yield strength of the steel for ships and ocean engineering is more than or equal to 690MPa, the impact energy at minus 60 ℃ is more than or equal to 140J, and the NDT temperature is less than or equal to minus 65 ℃.
In the chemical composition of the steel of the invention:
c, carbon C: the most basic strengthening elements. C dissolves in steel to form an interstitial solid solution, which acts as solid solution strengthening, and forms carbide precipitates with a strong carbide-forming element, which acts as precipitation strengthening, and C can improve the hardenability of steel. However, too high C is disadvantageous in ductility, toughness, crack arrest property and weldability of steel, and also reduces solid solution of micro-alloying elements such as Nb, V, etc., affecting precipitation strengthening effect and also reducing hardenability effect of B. Therefore, C is controlled to be 0.06% -0.13%.
Manganese Mn: is the most basic alloy element of low-alloy high-strength steel, and the strength of the steel is improved through solid solution strengthening so as to compensate the strength loss caused by the reduction of the content of C in the steel. Mn is also an element for expanding a gamma phase region, can reduce the gamma → alpha phase transition temperature of the steel, is beneficial to obtaining a fine phase transition product, and can improve the toughness and the crack arrest performance of the steel. When the Mn content is too high, segregation tends to occur at the center of the steel sheet in the case of an extremely thick steel grade, and the low-temperature toughness at the center is reduced. Therefore, the Mn content of the steel grade is 0.70-1.30%.
S sulfur, P phosphorus: inevitable harmful impurity elements in the steel, easily forming segregation, inclusion and other defects, and deteriorating the welding performance, impact toughness and HIC resistance of the steel sheet. Therefore, in the steel for the thick-specification ocean platform and the production method thereof, P is controlled to be less than or equal to 0.015 percent and S is controlled to be less than or equal to 0.0040 percent, and the inclusions are spheroidized and uniformly distributed by a Ca treatment inclusion modification technology, so that the influence of the inclusions on toughness and corrosivity is reduced.
Titanium Ti: is a strong solid N element, has a Ti/N stoichiometric ratio of 3.42, can fix less than 60ppm of N in steel by about 0.02% of Ti, and can form a fine high-temperature stable TiN precipitated phase during slab continuous casting. Such fine TiN particles can effectively inhibit austenite grain growth during slab reheating, and contribute to improvement in the solid solubility of Nb in austenite. For the ultra-thick steel plate, the proper Ti content is beneficial to forming stable TiN particles, and plays a role in inhibiting the grain growth of a heat affected zone and improving the impact toughness of the welding heat affected zone during welding. In the present invention, the Ti content is limited to 0.005 to 0.05%.
V, V: v contributes to the strengthening of steel by forming VN or V (cn) fine precipitated particles with C and N. Meanwhile, V is beneficial to improving the stability of hardness after tempering. However, if the content is too high, the cost increases significantly. Therefore, the content is controlled to be 0.01-0.05%.
Chromium Cr: since an important element for enhancing hardenability of steel, it is necessary to add high Cr to a steel sheet of an extra-thick gauge to enhance hardenability so as to compensate for a loss of strength due to thickness, enhance strength of steel, and improve uniformity of properties in the thickness direction. Cr can suppress transformation of proeutectoid ferrite and pearlite, and is advantageous for obtaining an acicular ferrite structure. However, the addition of Cr and Mn, which are too high, to the steel at the same time results in the formation of low-melting Cr-Mn complex oxides, the formation of surface cracks during hot working, and the severe deterioration of weldability. Therefore, the Cr content in the invention should be limited to 0.15% -0.50%.
Molybdenum Mo: the element for improving hardenability has the second action to Mn, so that the strength can be effectively improved; mo suppresses transformation of pro-eutectoid ferrite and pearlite and contributes to obtaining an acicular ferrite structure. However, as the Mo content increases, the yield strength of the steel increases, and therefore too high Mo impairs plasticity. The content of Mo in the invention is 0.10-0.40%.
Nickel Ni: improving the low-temperature toughness of the material. The addition of a proper amount of Ni element reduces the dislocation energy of the crystal, is beneficial to the slippage movement of dislocation, improves the impact toughness of the material, especially the impact toughness of the central part of the extra-thick plate, and can improve the crack arrest performance of the steel plate. Ni can improve the hardenability effect of Mo. However, when the Ni content is too high, the surface of the plate blank is easy to generate iron scale with high viscosity, and the iron scale is difficult to remove, so that the surface quality and the fatigue performance of the steel plate are influenced; meanwhile, too high Ni content is not beneficial to welding of extra-thick plates. Therefore, the Ni content is limited to be 1.0-2.5 percent.
Copper Cu: the hardenability of the steel is properly improved, and the atmospheric corrosion resistance of the steel can be improved. However, too high Cu deteriorates the weldability of steel, so the present invention limits the Cu content to 0.50% or less.
B, boron B: and B is mainly used for improving the hardenability of the steel and ensuring the mechanical property of the steel. It is generally considered that the effect is best when the B content is less than 0.0025%. Further, it is necessary to be solid-soluble in steel as a precondition for its action, and the addition of Mo and Ti contributes to the improvement of the hardenability effect of B. Therefore, in order to obtain a good hardenability effect, the present invention defines the B content to be 0.0025% or less.
Al and Al: the elements in the steel are added for deoxidation, and after the deoxidation is completed, the O content in the material is reduced, and the aging performance is improved; in addition, a proper amount of Al is beneficial to refining crystal grains and improving the toughness of steel. The Al content is limited to 0.01-0.07%.
Calcium (Ca): the Ca treatment can control the form of sulfide, improve the anisotropy of the steel plate and improve the low-temperature toughness, and the content of the Ca treatment is not effective when the content is less than 0.001 percent, while the content of the Ca treatment exceeds 0.006 percent, a great amount of CaO and CaS are generated, large-scale inclusions are formed, the toughness of the steel is damaged, and the welding performance of the steel is even affected. Therefore, the content of Ca is defined to be less than or equal to 0.0045 percent.
Furthermore, the chemical composition should meet the following requirements:
the method mainly aims to keep balance among refined grain elements of Al, Ti and V, and further avoid the condition that the total quantity of the refined grain elements is enough, but excessive addition of Ti and V can cause coarse precipitates to increase and deteriorate toughness;
mainly aims to ensure that the distribution proportion of the element with small red hardenability of the microstructure is suitable to ensure that C, Mn and B uniform carbide structures are formed at grain boundaries, but not to cause the concentrated aggregation of certain structures to further destroy the integral uniformity of the structures, especially for large-thickness steel plates;
sufficient additions of Mn and Ni are ensured but do not account for large alloy proportions, otherwise it is difficult to ensure an overall balance of alloying element contents, otherwise a good strength and toughness match is difficult to obtain.
The invention relates to a method for manufacturing 690 MPa-grade ship and ocean engineering steel with excellent low-temperature toughness, which comprises the following steps:
1) smelting, refining outside a furnace and casting;
smelting and continuously casting the components into a plate blank;
2) heating of slabs to a heating temperature
Unit degree C;
3) controlling the rolling and the air cooling,
the initial rolling temperature is (Tr-100) to (Tr-50) in unit ℃;
the accumulated reduction is more than or equal to 60 percent;
4) heat treatment, including quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering;
wherein the content of the first and second substances,
the tempering temperature before quenching is 580-600 ℃;
the tempering temperature after quenching is 620-640 ℃.
In the manufacturing method of the present invention:
slab reheating temperature (. degree. C.)
Wherein the alloy elements are in percentage by mass. The slab reheating temperature is set to ensure sufficient solid solution and homogenization of alloy and microalloy elements, to precipitate carbonitrides or to form a desired phase in the subsequent rolling process, and to improve the hardenability of steel.
Initial rolling temperature (DEG C): (Tr-100) to (Tr-50). This is mainly to ensure that the steel sheet starts rolling in the recrystallization zone to be sufficiently recrystallized and to refine the crystal grains.
The accumulated rolling reduction is more than or equal to 60 percent. This is mainly to sufficiently deform the steel sheet and refine the crystal grains, and particularly to ensure sufficient deformation of the core of the steel sheet and to obtain a uniform structure.
Tempering temperature before quenching: tempering prior to quenching is primarily to eliminate internal stresses, so that good plate shape is maintained during the continued quenching. Therefore, the tempering temperature before quenching is set to 580 to 600 ℃.
Tempering temperature after quenching: 620 ℃ and 640 ℃. After quenching, tempering heat treatment is required. But the tempering temperature cannot be too high to avoid too much strength reduction, and at the same time, the tempering temperature cannot be too low to avoid insufficient low-temperature toughness of the steel. Therefore, the tempering temperature is set to 620-640 ℃, so that sorbite with small grain size and a small amount of bainite structure can be obtained, and the steel has good toughness.
The difference between the invention and the prior art is that:
compared with the Chinese patent publication No. CN101418418A, the invention adopts higher C content, lower Mn content and higher Ni content, adds Ni and Cu but not Nb, and has special requirements among different components. The tempered sorbite and a small amount of bainite tissue are obtained by adopting the special controlled rolling and heat treatment process technology, and the tempered sorbite and bainite tissue has high strength (the yield strength is more than or equal to 690MPa) and very excellent low-temperature toughness (the impact energy is more than or equal to 140J at the temperature of minus 60 ℃ and the NDT temperature is less than or equal to minus 65 ℃).
Compared with Chinese patent publication No. CN102226255A, the invention adopts a higher C, Ni content, a lower Cu content, a component design of V, B but no Nb, and different element contents have strict requirements. The tempered sorbite and a small amount of bainite tissue are obtained by adopting the special controlled rolling and heat treatment process technology, and the tempered sorbite and bainite tissue has high strength (the yield strength is more than or equal to 690MPa) and very excellent low-temperature toughness (the impact energy is more than or equal to 140J at the temperature of minus 60 ℃ and the NDT temperature is less than or equal to minus 65 ℃).
Compared with the Chinese patent publication No. CN102260823A, the invention adopts the lower Mn content, adds Cr, Ni, Mo, Cu and V, but does not add Nb, and has strict requirements on the contents of different elements. The special controlled rolling and heat treatment technology (quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering) are adopted to obtain a tempered sorbite and a small amount of bainite tissues, so that the tempered sorbite has high strength (the yield strength is more than or equal to 690MPa), and has very good low-temperature toughness (the impact energy at minus 60 ℃ is more than or equal to 140J, and the NDT temperature is less than or equal to minus 65 ℃).
Compared with the Chinese patent publication No. CN103343285A, the invention adopts lower C content, adds Cr, Ni, Mo, Cu and B, but does not add Nb, and has strict requirements on different element contents. The special controlled rolling and heat treatment technology (quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering) are adopted to obtain a tempered sorbite and a small amount of bainite tissues, so that the tempered sorbite has high strength (the yield strength is more than or equal to 690MPa), and has very good low-temperature toughness (the impact energy at minus 60 ℃ is more than or equal to 140J, and the NDT temperature is less than or equal to minus 65 ℃).
Compared with the Chinese patent publication No. CN10234504A, the invention adopts the lower C content, does not add Nb, and has strict special requirements on different element contents. The special controlled rolling and heat treatment technology (quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering) are adopted to obtain a tempered sorbite and a small amount of bainite tissues, so that the tempered sorbite has high strength (the yield strength is more than or equal to 690MPa), and has very good low-temperature toughness (the impact energy at minus 60 ℃ is more than or equal to 140J, and the NDT temperature is less than or equal to minus 65 ℃).
Compared with foreign and domestic patents, the steel plate with high strength, good low-temperature impact toughness and good weldability can be produced by adopting a unique component design method and a unique manufacturing process technology, and has great difference in structure, components and process design compared with the existing patents.
The invention has the beneficial effects that:
the invention can manufacture the steel plate with the thickness less than or equal to 90mm, high strength and excellent low-temperature toughness, and the mechanical properties are as follows: the yield strength is more than or equal to 690MPa, the impact energy is more than or equal to 140J at the Temperature of minus 60 ℃, and the NDT Temperature (Nil-hardness Transition Temperature) is more than or equal to minus 65 ℃.
The steel has Ceq less than or equal to 0.70 percent, Pcm less than or equal to 0.30 percent, excellent welding performance and better cuttability; wherein Ceq is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15; pcm is C + Si/30+ (Mn + Cu + Cr)/20+ Ni/60+ Mo/15+ V/10+ 5B.
The steel of the invention can be used for manufacturing ship and ocean engineering structures.
Detailed Description
The present invention will be further described with reference to the following examples.
The chemical components of the steel of the embodiment of the invention are shown in table 1, the implementation process is shown in table 2, 6 different chemical components are designed, and the steel plates with different thickness specifications are manufactured by combining the proper production process.
Controlled rolling and controlled cooling are carried out by adopting the different implementation processes, and bar-shaped stretching is carried out on the finished plate
Or sheet drawing, Charpy V-notch impact, NDT property test (the NDT property is an important index for measuring the crack resistance of a steel sheet), and the obtained property results are shown in Table 3.
Therefore, the steel plate manufactured by the invention has high strength, excellent low-temperature toughness, proper carbon equivalent and better weldability.
Compared with the prior patents, the invention adopts unique chemical components and process design, and can produce the steel plate with the thickness specification of less than or equal to 90mm for the ship and ocean engineering structure. The thick steel plate produced by the invention can be used for key components of ship and ocean engineering structures, meets the current development requirements of China on steel for ship and ocean engineering equipment, and has wide application prospect.
Claims (7)
1. 690MPa grade ship and ocean engineering steel with excellent low-temperature toughness comprises the following chemical components in percentage by weight: 0.06 to 0.13 percent of C, 0.05 to 0.30 percent of Si, 0.70 to 1.30 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.0040 percent of S, 0.15 to 0.50 percent of Cr, 1.0 to 2.5 percent of Ni, 0.10 to 0.40 percent of Mo, less than or equal to 0.50 percent of Cu, 0.01 to 0.07 percent of Alt, 0.005 to 0.05 percent of Ti, 0.01 to 0.05 percent of V, less than or equal to 0.0025 percent of B, less than or equal to 0.0045 percent of Ca,
the balance of Fe and inevitable impurities; wherein Ceq is C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15; the steel for ship and ocean engineering is obtained by adopting the following process, and comprises the following steps:
1) smelting, refining outside a furnace and casting;
smelting and continuously casting the components into a plate blank;
2) heating of slabs to a heating temperature
Unit degree C;
3) controlling rolling and air cooling;
the initial rolling temperature is (Tr-100) to (Tr-50) in unit ℃;
the accumulated reduction is more than or equal to 60 percent;
4) heat treatment, including quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering;
wherein the content of the first and second substances,
the tempering temperature before quenching is 580-600 ℃;
the tempering temperature after quenching is 620-640 ℃.
2. The steel for ships and ocean engineering of 690MPa grade having excellent low-temperature toughness of claim 1, wherein the microstructure of the steel for ships and ocean engineering is tempered sorbite + a small amount of bainite structure, and the tempered sorbite is not less than 90%.
3. The steel for ships and ocean engineering with excellent low temperature toughness of 690MPa grade according to claim 1 or 2, wherein the steel for ships and ocean engineering has yield strength of 690MPa or more, -60 ℃ impact energy of 140J or more, and NDT temperature of 65 ℃ or less.
4. The method for manufacturing steel for ships and oceanographic engineering of 690MPa grade having excellent low-temperature toughness according to claim 1, comprising the steps of:
1) smelting, refining outside a furnace and casting;
smelting and continuously casting the components of claim 1 into a slab;
2) heating of slabs to a heating temperature
Unit degree C;
3) controlling rolling and air cooling;
the initial rolling temperature is (Tr-100) to (Tr-50) in unit ℃;
the accumulated reduction is more than or equal to 60 percent;
4) heat treatment, including quenching and tempering, or normalizing, quenching and tempering, or tempering, quenching and tempering;
wherein the content of the first and second substances,
the tempering temperature before quenching is 580-600 ℃;
the tempering temperature after quenching is 620-640 ℃.
5. The method for producing 690MPa grade steel for ships and oceanographic engineering having excellent low temperature toughness according to claim 4, wherein the smelting is carried out in an electric furnace or a converter, and the external refining is carried out by RH vacuum degassing and LF desulfurization.
6. The method for manufacturing 690MPa grade steel for ships and oceanographic engineering having excellent low-temperature toughness of claim 4, wherein the microstructure of the steel for ships and oceanographic engineering is tempered sorbite + a small amount of bainite structure, and the tempered sorbite is not less than 90%.
7. The method for manufacturing steel for ships and ocean engineering of 690MPa grade having excellent low-temperature toughness as claimed in claim 4 or 6, wherein the steel for ships and ocean engineering has yield strength of 690MPa or more, -60 ℃ impact energy of 140J or more, and NDT temperature of-65 ℃ or less.
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