CN115449709A - Thick-specification high-strength high-toughness L485M pipeline steel and production method thereof - Google Patents

Thick-specification high-strength high-toughness L485M pipeline steel and production method thereof Download PDF

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CN115449709A
CN115449709A CN202211052972.6A CN202211052972A CN115449709A CN 115449709 A CN115449709 A CN 115449709A CN 202211052972 A CN202211052972 A CN 202211052972A CN 115449709 A CN115449709 A CN 115449709A
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CN115449709B (en
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王杨
孔祥磊
黄国建
黄明浩
张英慧
张瑜
刘干
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Angang Steel Co Ltd
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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    • C—CHEMISTRY; METALLURGY
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
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    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
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    • C22C33/00—Making ferrous alloys
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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Abstract

The invention relates to thick-specification high-strength-toughness L485M pipeline steel and a production method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.05 to 0.07%, si:0.15% -0.25%, mn:1.60% -1.80%, nb:0.060% -0.078%, ti:0.026% -0.032%, mo: 0.12-0.16%, cr: 0.16-0.20%, ni:0.11% -0.18%, als: 0.015-0.045%, P less than or equal to 0.02%, S less than or equal to 0.005%, N less than or equal to 0.005%, and the balance of iron and impurities. The invention adopts the design of C-Mn-Nb-Mo-Cr series alloy, adds a proper amount of Ni and Ti elements, combines two-stage rolling and cooling processes to obtain fine and uniform acicular ferrite tissues, ensures that the pipeline steel has excellent obdurability, and simultaneously realizes the purpose of producing the thick-specification high-obdurability L485M pipeline steel hot-rolled coil by adopting medium and thin slab continuous casting and rolling.

Description

Thick high-strength high-toughness L485M pipeline steel and production method thereof
Technical Field
The invention relates to the technical field of pipeline steel production, in particular to thick-specification high-strength-toughness L485M pipeline steel and a production method thereof.
Background
Pipeline transportation is the most economical transportation mode for transporting oil and natural gas for long distance, and the transportation pressure is gradually increased along with the increase of global oil and natural gas demand. In order to ensure the safety and stability of oil and gas pipeline transportation, the requirements on the thickness specification and the toughness of pipeline steel are gradually improved, and the L485M pipeline steel is taken as the most mainstream steel grade in the pipeline transportation main lines at home and abroad at present, and the improvement on the toughness is paid much attention.
The thickness of the continuous casting billet used in hot rolling in domestic steel mills is generally more than 200mm at present, but the thickness of the continuous casting billet adopted by the invention is 170mm, and the compression ratio is small, so that the production of the thick L485M hot-rolled coil has certain difficulty, the basic requirement of API 5L can only be met by producing the coil according to the conventional process, but the toughness index cannot meet the requirement of actual engineering.
The Chinese patent application with the application number of 200410066297.8 discloses a needle-shaped ferrite X70 pipeline steel with high crack arrest toughness and a manufacturing method thereof, wherein the components of the pipeline steel comprise 0.02-0.06 percent of C, 0.10-0.50 percent of Si, 1.45-1.75 percent of Mn, less than or equal to 0.002 percent of S, 0.004-0.012 percent of P, 0.050-0.080 percent of Nb, 0.010-0.060 percent of V, 0.005-0.025 percent of Ti, 0.10-0.30 percent of Mo, less than or equal to 0.30 percent of Cu, less than or equal to 0.30 percent of Ni, less than or equal to 0.008 percent of N and 0.015-0.045 percent of Al. The S content in the components is low, and the steel-making cost is high; in addition, V and Cu are added, the upper limit of Mo and Ni is higher, and the alloy cost is higher.
Chinese patent application with application number CN200810013479.7 discloses 'a thick high-toughness X70 acicular ferrite pipeline steel and a manufacturing method thereof', the pipeline steel comprises the following components (weight percentage): 0.03 to 0.06 percent of C, 0.15 to 0.25 percent of Si, 1.55 to 1.75 percent of Mn, 0.012 to 0.020 percent of P, less than or equal to 0.003 percent of S, 0.2 to 0.35 percent of Cu, 0.20 to 0.35 percent of Cr, 0.06 to 0.08 percent of Nb, 0.01 to 0.02 percent of Ti, less than or equal to 0.05 percent of Als and 0.20 to 0.30 percent of Mo. The S content is controlled to be low, and the steel-making cost is high; the components contain Cu, and the addition amounts of Cr and Mo are large, so that the alloy cost is high. The impact test temperature is-20 ℃, the DWTT test temperature is-15 ℃, the toughness index requirement is loose, and in addition, the thickness specification of the finished product is more than 14mm, and the thickness of the finished product has a certain difference with the thickness of the pipeline steel.
Chinese patent application with application number CN201310407627.4 discloses 'a 485MPa pipeline steel hot-rolled coil and a manufacturing method thereof', which comprises the following chemical components in percentage by weight: 0.040-0.070% of C, 0.10-0.35% of Si, 1.76-1.95% of Mn, 0.040-0.080% of Nb, 0.20-0.35% of Cr, 0.030-0.060% of V, 0.005-0.025% of Ti, 0.015-0.045% of Als, less than or equal to 0.018% of P, less than or equal to 0.003% of S, and the balance of Fe and inevitable impurities. The alloy contains V, is different from the alloy system of the invention, has higher Cr content, does not add noble metals such as Mo, ni and the like, but has a finish rolling reduction rate of more than or equal to 75 percent and higher rolling mill load, and is not beneficial to production; in addition, the temperature of the impact test is-25 ℃, the temperature of the DWTT test is-20 ℃, and the requirement on toughness index is also loose.
Chinese patent application with application number CN201710283378.0 discloses X70 pipeline steel with excellent low-temperature dynamic tearing resistance and a manufacturing method thereof, wherein the pipeline steel comprises the following components in percentage by weight: 0.025 to 0.08 percent of C, 0.1 to 0.4 percent of Si, 1.1 to 1.6 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.2 percent of Cu, 0.31 to 0.50 percent of Ni, less than or equal to 0.2 percent of Cr, less than or equal to 0.2 percent of Mo, 0.04 to 0.08 percent of Nb, 0.005 to 0.02 percent of Ti, ca:0.001 to 0.005 percent of Al, 0.02 to 0.05 percent of B, less than or equal to 0.0005 percent of B, 0.001 to 0.006 percent of N, less than or equal to 0.005 percent of O, and the balance of Fe and impurities; moreover, the ratio of (C + Mn/6) is more than or equal to 0.25 percent and less than or equal to 0.33 percent, and the ratio of (Mo + Cr) is more than or equal to 0.10 percent and less than or equal to 0.40 percent. The S content in the components is low, and the steel-making cost is high; the contents of Mo, cr and Cu are wide, and the performance fluctuation of a finished product is easily caused; the Ni content is higher, and the overall alloy cost of the product is higher; the thickness of the casting blank is 200-230 mm, the compression ratio is obviously higher than that of the invention, and the production difficulty is lower than that of the invention; in addition, the toughness index is excellent, but the strength index only meets API 5L, the requirement is low, and the toughness and the matching of the product are poor.
Chinese patent application with application number CN201110179851.3 discloses 'acid-resistant low-manganese X70 pipeline steel and a production method thereof', wherein the chemical components of the pipeline steel comprise 0.05-0.07% of C, 0.10-0.25% of Si and 1.05-1.25% of Mn; 0 percent to 0.019 percent of P; 0 to 0.006 percent of S; nb 0.06-0.09%; 0.010 percent to 0.020 percent of Ti; 0.20 to 0.30 percent of Mo; 0.05 to 0.30 percent of Ni; 0.05 to 0.30 percent of Cu; 0.015 to 0.040 percent of Alsoul, and the balance of iron and inevitable impurities. The low Mn design is adopted, but Mo, cr and Ni are added more, and the alloy cost is higher; and the total reduction of finish rolling is more than 80 percent, the finish rolling mill has heavy load and is not beneficial to plate shape control, and the toughness of the finished product is not specifically described.
Chinese patent application with application number CN200910013129.5 discloses a method for producing thick-wall X70 pipeline steel coils with low cost, which comprises the following chemical components in percentage by mass: 0.04 to 0.08 percent of C, 0.10 to 0.20 percent of Si, 1.58 to 1.68 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.003 percent of S, 0.04 to 0.08 percent of Nb, 0.006 to 0.018 percent of Ti, 0.05 to 0.30 percent of Mo, less than or equal to 0.20 percent of Ni, less than or equal to 0.25 percent of Cu, less than or equal to 0.050 percent of Alsoul, less than or equal to 0.0060 percent of N, and the balance of iron and inevitable impurities. The S content in the components is low, and the steel-making cost is high; cu is added, the upper limits of Ni and Mo are higher, and the alloy cost is higher; in addition, the temperature of the impact test is-20 ℃, the temperature of the DWTT test is-15 ℃, and the requirement on toughness index is loose.
In the paper "research on the structural properties of ultra-thick X70 pipeline hot rolled coils" (written in great waves, austin, and the like, published in the tenth annual meeting of steel in china), the chemical components of pipeline steel are as follows: 0.055 percent of C, 0.20 percent of Si, 1.60 percent of Mn, less than or equal to 0.001 percent of P, less than or equal to 0.0012 percent of S, 0.035 percent of Alt, 0.07 percent to 0.09 percent of Nb, 0.015 percent of Ti, and the like. The S content is low, and the steel-making cost is high; the thickness of the continuous casting slab is 250mm, the total rolling reduction is large, the control difficulty is low, and the production difficulty is lower than that of the invention.
In the alloy design of the L485M steel grade pipeline steel disclosed in the above documents, the S content in other pipeline steels except the low-manganese X70 pipeline steel is basically controlled below 0.003 percent, which results in higher steel-making cost; based on Nb microalloyed C-Mn steel as a whole, the synergistic effect of all or part of elements of Cr, mo, ni and Cu is comprehensively utilized, ni, mo and Cu are added in a large amount in part of pipeline steel, and the product economy is poor. Some pipeline steel is produced by adopting a casting blank of 170mm, but the thickness of the finished product is smaller; some casting blanks with the thickness of more than 200mm are adopted, the toughness index is excellent, but the strength index only meets the API 5L standard, and the requirement is wide; some precision rolling has higher total rolling reduction, and the control difficulty of the finished plate type is increased; some have higher cooling speed and are easy to generate supercooled tissues.
In summary, no production method for the L485M hot rolled coil of the pipeline steel, which can simultaneously meet the requirements of thick specification and high strength and toughness, exists in the prior art.
Disclosure of Invention
The invention provides thick-specification high-strength and toughness L485M pipeline steel and a production method thereof, wherein a C-Mn-Nb-Mo-Cr series alloy design is adopted, a proper amount of Ni and Ti elements are added, and a precisely controlled two-stage rolling and cooling process is combined to obtain fine and uniform Acicular Ferrite (AF) tissues, so that the pipeline steel is ensured to have excellent strength and toughness, and meanwhile, the aim of producing a thick-specification high-strength and toughness L485M pipeline steel hot-rolled coil plate by adopting medium-thin slab continuous casting and rolling is fulfilled.
In order to achieve the purpose, the invention adopts the following technical scheme:
the thick-specification high-strength-toughness L485M pipeline steel comprises the following chemical components in percentage by weight: 0.05 to 0.07%, si:0.15% -0.25%, mn:1.60% -1.80%, nb:0.060% -0.078%, ti:0.026% -0.032%, mo: 0.12-0.16%, cr: 0.16-0.20%, ni:0.11% -0.18%, als: 0.015-0.045%, P less than or equal to 0.02%, S less than or equal to 0.005%, N less than or equal to 0.005%, and the balance of iron and inevitable impurities.
A production method of thick-specification high-strength-toughness L485M pipeline steel comprises the following production process flows: the method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, plate blank heating, rolling, cooling and coiling; wherein:
1) An external refining process: RH vacuum treatment and LF furnace treatment are adopted, calcium wire feeding treatment is carried out, the wire feeding speed is more than or equal to 3.6m/s, the net argon blowing time is more than or equal to 5min, and the calming time is more than or equal to 10min;
2) And (3) a continuous casting process: adopting a dynamic light pressing mode, wherein the reduction is 1.5-2 mm, and the thickness of the obtained casting blank is less than or equal to 170mm;
3) A rolling procedure: heating the continuous casting plate blank to 1140-1180 ℃, and performing controlled rolling in two stages of rough rolling and finish rolling, wherein the finish rolling temperature of the rough rolling is more than or equal to 980 ℃, and the total reduction rate of the rough rolling is 64.71-69.41%; the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the finish rolling temperature of finish rolling is 760-810 ℃, and the total reduction rate of finish rolling is more than 66.35-70.83%;
4) A cooling process: the method adopts a mode of combining ultra-fast cooling and laminar cooling, wherein the water temperature of the ultra-fast cooling is 17-20 ℃, and the water temperature of the laminar cooling is 23-28 ℃; the cooling speed of the cooling process is 20.58-24.60 ℃/s, and the steel wire is finally cooled to 400-450 ℃ for coiling.
The properties of the produced hot rolled coil are as follows: the yield strength is 517-593 MPa, the tensile strength is 641-695 MPa, and the elongation after fracture is more than or equal to 34 percent; the average value of the Charpy impact energy Akv at-60 ℃ of 3 samples is more than or equal to 270J, and the average value of the shearing area SA of the average drop hammer tear test at-60 ℃ of 2 samples is more than or equal to 88 percent; hardness HV 10 Less than or equal to 236, d =2a,180 degrees cold bending is qualified.
The thickness of the produced hot-rolled coil plate is 17-20 mm.
Compared with the prior art, the invention has the beneficial effects that:
(1) Creatively adopts the inclusion effect of Ti modified sulfide to deprive S in MnS to form Ti 4 C 2 S 2 Spherical Ti not easy to deform during rolling 4 C 2 S 2 MnS which is easy to deform and elongate in the rolling process is completely replaced, so that the structural uniformity of the product can be obviously improved, and the obdurability index of the product is obviously improved;
(2) The C-Mn-Nb-Cr-Mo alloy design is adopted, the alloy design is economic and reasonable, the process route is simple, the execution is easy, the process control stability is strong, and the obtained tissue is fine and uniform through the precise controlled rolling and cooling technology, so that the product has excellent obdurability matching;
(3) The product has excellent obdurability matching, rt0.5 is 517-593MPa, rm is 641-695MPa, and A50 is more than or equal to 34 percent; the Charpy impact energy (3 samples) Akv at-60 ℃ is more than or equal to 270J, and the average drop-weight tear test shear area (2 samples) SA at-60 ℃ is more than or equal to 88 percent;
(4) The short-flow continuous casting and rolling production process of medium and thin slabs (the thickness of the casting blank is less than or equal to 170 mm) is adopted to roll the L485M coil with the thick specification (17-20 mm), thereby achieving the aims of obviously saving energy, reducing consumption, reducing production cost and improving production efficiency.
Drawings
FIG. 1 is a metallographic structure photograph of thick gauge high toughness L485M pipeline steel produced in example 1 of the present invention.
Detailed Description
The invention relates to thick-specification high-strength-toughness L485M pipeline steel, which comprises the following chemical components in percentage by weight: 0.05 to 0.07 percent of Si:0.15% -0.25%, mn:1.60% -1.80%, nb:0.060% -0.078% of Ti:0.026% -0.032%, mo: 0.12-0.16%, cr: 0.16-0.20%, ni:0.11% -0.18%, als:0.015 to 0.045 percent, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of iron and inevitable impurities.
A production method of thick-specification high-strength-toughness L485M pipeline steel comprises the following production process flows: the method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab heating, rolling, cooling and coiling; wherein:
1) An external refining process: adopting RH vacuum treatment and LF furnace treatment, and then performing calcium wire feeding treatment, wherein the wire feeding speed is more than or equal to 3.6m/s, the net argon blowing time is more than or equal to 5min, and the sedation time is more than or equal to 10min;
2) And (3) continuous casting process: adopting a dynamic light pressing mode, wherein the reduction is 1.5-2 mm, and the thickness of the obtained casting blank is less than or equal to 170mm;
3) A rolling procedure: heating a continuous casting plate blank to 1140-1180 ℃, and performing two-stage controlled rolling of rough rolling and finish rolling, wherein the finish rolling temperature of the rough rolling is more than or equal to 980 ℃, and the total reduction rate of the rough rolling is 64.71-69.41%; the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the finish rolling temperature of finish rolling is 760-810 ℃, and the total reduction rate of finish rolling is more than 66.35-70.83%;
4) A cooling process: the method adopts a mode of combining ultra-fast cooling and laminar cooling, wherein the water temperature of the ultra-fast cooling is 17-20 ℃, and the water temperature of the laminar cooling is 23-28 ℃; the cooling speed of the cooling process is 20.58-24.60 ℃/s, and the steel wire is finally cooled to 400-450 ℃ for coiling.
The properties of the produced hot rolled coil are as follows: the yield strength is 517-593 MPa, the tensile strength is 641-695 MPa, and the elongation after fracture is more than or equal to 34 percent; the average value of-60 ℃ Charpy impact energy Akv of 3 samples is more than or equal to 270J, and the average value of-60 ℃ average drop hammer tear test shearing area SA of 2 samples is more than or equal to 88%; hardness HV 10 Not less than 236, d =2a, and 180 degrees cold bending is qualified.
The thickness of the produced hot-rolled coil plate is 17-20 mm.
The main elements in the thick high-strength high-toughness L485M pipeline steel have the following functions and selection reasons:
c: the steel is the most main element next to iron in steel, which directly influences the strength, plasticity, toughness, welding performance and the like of steel, C can obviously improve the strength of the steel through solid solution strengthening and precipitation strengthening, but the toughness and weldability of the steel gradually become worse along with the increase of C content, so the low-carbon design is the basic guarantee that the pipeline steel has excellent toughness and good welding performance. Therefore, the content of C is controlled to be 0.05-0.07 percent.
Si: is an important reducing agent and deoxidizing agent in the steel-making process, and many carbon steels contain less than 0.5 percent of Si which is generally taken in as the reducing agent and the deoxidizing agent in the steel-making process, and in addition, the Si can be dissolved in ferrite and austenite in a solid manner to improve the strength of the steel, but simultaneously the plasticity and the toughness are lost. Therefore, the Si content of the invention is controlled between 0.15 percent and 0.25 percent.
Mn: manganese has a solid solution strengthening effect, can also reduce the gamma-alpha phase transition temperature so as to refine ferrite grains, and simultaneously, mn is the most main and economic strengthening element for compensating strength loss caused by reduced C content in pipeline steel. However, too high a manganese content causes serious segregation. Therefore, the invention controls the manganese content to be 1.60-1.80%.
Nb: the steel is the most main element for realizing the control rolling of modern microalloyed pipeline steel, nbC strain-induced precipitation hinders the recovery and recrystallization of deformed austenite, the phase transition temperature is reduced, the rolling process window of a recrystallization zone can be enlarged, the formation of an acicular ferrite structure and an M-A island is promoted, and the effect of refining grains is achieved. Nb can also improve the performance of the steel through various strengthening mechanisms such as precipitation strengthening, phase change strengthening and the like, but Nb is a precious element and the strengthening effect is not obvious after Nb is added to a certain amount. Therefore, the content of Nb is controlled to be 0.060-0.078 percent in the invention.
Ti: the high-temperature stable and fine TiN particles can effectively prevent austenite from growing in the reheating process of a casting blank on one hand, and can improve the impact toughness of a welding heat affected zone on the other hand; in addition, ti has much greater binding capacity to S than Mn, so Ti can "abstract" S from MnS to form Ti 4 C 2 S 2 Spherical Ti not easy to deform in rolling process 4 C 2 S 2 MnS which is easy to elongate in the rolling process is completely replaced, the tissue uniformity of the product can be obviously improved, and the toughness index is greatly improved; in the present invention, the amount of Ti added is such that Ti is produced in the entirety of S at the upper limit (0.005%) in consideration of the S content 4 C 2 S 2 The amount of Ti to be added is 0.25%, and it is also considered that a predetermined amount of Nb and Ti is formedThe carbonitride is used for improving the toughness of the finished product, so that the Ti content of the invention is controlled between 0.026 percent and 0.032 percent.
Mo: the hardenability of the steel can be effectively improved, the effect is stronger than that of Cr, and the steel plate has a certain effect of improving the structure uniformity of thick steel plates; further, when the Mo content exceeds 0.12%, mo and Nb are compositely added to form (NbMo) 4 C 3 The number of the precipitated phase is higher than that of pure NbC, so that the nucleation core number, the dislocation density and the precipitation hardening capacity can be improved, the formation of an acicular ferrite structure is promoted, a structure with finer and more uniform crystal grains is formed, and the toughness of the material is improved. However, mo belongs to noble metals, and excessive addition can obviously increase the alloy cost, so that the Mo content of the invention is controlled to be 0.12-0.16%.
Cr: the hardenability can be effectively improved, and the tissue uniformity of thick products in the thickness direction can be improved; the composition is matched with more than 0.12 percent of Mo and more than 0.11 percent of Ni for use, so that the formation of the Malao island (M/A) can be promoted, and the strength loss in the pipe manufacturing process is reduced; in addition, cr is combined with rapid cooling after rolling, so that the formation of Acicular Ferrite (AF) is promoted, and the toughness of the product is improved. And Cr is less expensive than Mo. Therefore, the Cr content of the invention is controlled to be 0.16-0.20%.
Ni: the austenite stabilizing element can prevent the growth of grains at high temperature, can maintain a fine grain structure, and is a guarantee that fine original austenite grains exist in the product structure; ni can promote the cross slip of dislocation, so the impact toughness of the product can be effectively improved; in addition, ni can play a certain role in solid solution strengthening and has certain contribution to the strength index of the product. However, the Ni alloy has higher cost and is not suitable to be added too much so as not to influence the economical efficiency of the product. Therefore, the Ni content of the invention is controlled between 0.11 percent and 0.18 percent.
And Als: the deoxidation element is added with a proper amount of aluminum to form fine and dispersed AlN particles, which is beneficial to refining crystal grains and improving the toughness of the steel; when the solid-solution Al content exceeds 0.015%, the steel material can obtain a fine austenite grain structure upon reheating for welding, thereby improving weldability. Therefore, the Als content of the invention is controlled to be 0.015-0.045%.
P: the P is easy to be highly segregated when molten steel is solidified to form a banded F-P structure, the benefit of reducing C in the pipeline steel is greatly reduced, and the toughness of the steel is lost, so that the content of the P serving as a harmful element in the pipeline steel is as small as possible, but the production cost is increased when the content is too low. Therefore, the P content of the invention is controlled below 0.02%.
S: is an inevitable impurity element in steel, the lower the content of the impurity element, the better the content of the impurity element, the lower the requirement of the S content in high-grade pipeline steel, generally below 0.003 percent, but the lower the requirement, the production cost is increased, the S content is more widely controlled in the invention, and Ti is formed mainly by adding Ti 4 C 2 S 2 And the harmful influence of the strip MnS on the mechanical property, particularly the toughness of the steel is reduced. Therefore, the S of the invention is less than or equal to 0.005 percent.
N: the increase in the nitrogen content results in a significant increase in the strength of the steel, but the plasticity, in particular the toughness, is also significantly reduced, the weldability is poor and the cold shortness is increased, so that P is present as a harmful element in the steel, the lower the content the better. In the invention, N is less than or equal to 0.005 percent.
The invention discloses a production method of thick-specification high-strength high-toughness L485M pipeline steel, which comprises the following production process flows: the method comprises the steps of molten iron pretreatment, converter smelting, external refining (RH + LF + calcium treatment), continuous casting, slab heating, rolling, ultrafast cooling, laminar cooling and coiling. The main control process is as follows:
the smelting-continuous casting process comprises the following steps: after the molten iron is pretreated, converter smelting adopts top blowing or top-bottom combined blowing; the external refining adopts RH vacuum treatment and LF furnace treatment, then calcium wire feeding treatment is carried out, the wire feeding speed is more than or equal to 3.6m/s, the net argon blowing time is more than or equal to 5min, and the calming time is more than or equal to 10min, so as to ensure the spheroidization of sulfide and oxide inclusions; the continuous casting adopts a dynamic light pressing mode, the reduction is 1.5-2 mm, the center segregation of the casting blank is reduced, and the thickness of the obtained casting blank is less than or equal to 170mm;
the rolling process comprises the following steps: heating the continuous casting plate blank to 1140-1180 ℃ by a stepping heating furnace, and then performing two-stage controlled rolling by a rough rolling unit and a finishing rolling unit, wherein the rough rolling finishing temperature is more than or equal to 980 ℃, and the rough rolling total reduction rate is 64.71-69.41%; the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the finish rolling temperature of finish rolling is 760-810 ℃, and the total reduction rate of finish rolling is more than 66.35-70.83%;
the cooling process comprises the following steps: the method adopts a mode of combining ultra-fast cooling and laminar cooling, wherein the water temperature of the ultra-fast cooling is 17-20 ℃, and the water temperature of the laminar cooling is 23-28 ℃; the cooling speed of the cooling process is 20.58-24.60 ℃/s, and the steel wire is finally cooled to 400-450 ℃ for coiling.
The L485M steel-grade hot rolled plate coil produced by the invention has excellent obdurability, the yield strength is 517-593 MPa, the tensile strength is 641-695 MPa, and the elongation after fracture is more than or equal to 34 percent; the Charpy impact energy (3 samples) Akv at-60 ℃ is more than or equal to 270J, and the average drop-weight tear test shear area (2 samples) SA at-60 ℃ is more than or equal to 88 percent; hardness HV 10 The cold bending is less than or equal to 236 and qualified.
The following examples are carried out on the premise of the technical scheme of the invention, and detailed embodiments and specific operation procedures are given, but the scope of the invention is not limited to the following examples.
[ examples ] A
In the present example, the chemical composition of the steel is shown in table 1, the rolling process parameters are shown in table 2, and the main mechanical properties of the steel are shown in table 3.
TABLE 1 chemical composition of steel (wt%)
Examples C Si Mn P S Nb Ti Mo Cr Ni Als N
1 0.052 0.16 1.80 0.016 0.005 0.078 0.032 0.16 0.19 0.17 0.028 0.005
2 0.050 0.20 1.66 0.013 0.004 0.072 0.031 0.13 0.18 0.18 0.033 0.005
3 0.057 0.17 1.60 0.014 0.003 0.076 0.026 0.14 0.16 0.15 0.045 0.004
4 0.065 0.15 1.63 0.002 0.004 0.063 0.028 0.12 0.16 0.11 0.022 0.004
5 0.060 0.25 1.76 0.011 0.005 0.060 0.030 0.14 0.20 0.12 0.015 0.005
6 0.070 0.22 1.72 0.018 0.004 0.068 0.027 0.15 0.20 0.17 0.020 0.004
7 0.063 0.18 1.78 0.002 0.0048 0.073 0.030 0.16 0.19 0.13 0.042 0.005
8 0.059 0.24 1.75 0.0019 0.0043 0.071 0.027 0.15 0.17 0.14 0.038 0.005
TABLE 2 Rolling Process parameters of the steels
Figure BDA0003824464850000081
TABLE 3 Main mechanical Properties of the steels
Figure BDA0003824464850000082
In Table 3, R t0.5 For yield strength, R m For tensile strength, A 50mm Is elongation after fracture; in the cold bend test, a is the nominal thickness and d is the bend diameter.
As can be seen from Table 3, the cost of steel-making and desulfurization can be reduced by the creative use of Ti element, and the product has extremely excellent obdurability ratio by adopting an economical and reasonable alloy design and a precise controlled rolling and cooling process.
FIG. 1 is a photograph of the metallographic structure of thick high toughness L485M pipeline steel produced in example 1, and it can be seen that the metallographic structure is fine and uniform Acicular Ferrite (AF) structure, which can ensure excellent toughness of the pipeline steel.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (4)

1. The thick-specification high-strength-toughness L485M pipeline steel is characterized in that the steel comprises the following chemical components in percentage by weight: 0.05 to 0.07 percent of Si:0.15% -0.25%, mn:1.60% -1.80%, nb:0.060% -0.078% of Ti:0.026% -0.032%, mo: 0.12-0.16%, cr:0.16% -0.20%, ni:0.11% -0.18%, als:0.015 to 0.045 percent, less than or equal to 0.02 percent of P, less than or equal to 0.005 percent of S, less than or equal to 0.005 percent of N, and the balance of iron and inevitable impurities.
2. The production method of the thick-gauge high-strength and toughness L485M pipeline steel as claimed in claim 1, wherein the production process flow comprises the following steps: the method comprises the following steps of molten iron pretreatment, converter smelting, external refining, continuous casting, plate blank heating, rolling, cooling and coiling; wherein:
1) An external refining process: adopting RH vacuum treatment and LF furnace treatment, and then performing calcium wire feeding treatment, wherein the wire feeding speed is more than or equal to 3.6m/s, the net argon blowing time is more than or equal to 5min, and the sedation time is more than or equal to 10min;
2) And (3) continuous casting process: adopting a dynamic light pressing mode, wherein the reduction is 1.5-2 mm, and the thickness of the obtained casting blank is less than or equal to 170mm;
3) A rolling procedure: heating the continuous casting plate blank to 1140-1180 ℃, and performing controlled rolling in two stages of rough rolling and finish rolling, wherein the finish rolling temperature of the rough rolling is more than or equal to 980 ℃, and the total reduction rate of the rough rolling is 64.71-69.41%; the initial rolling temperature of finish rolling is less than or equal to 960 ℃, the finish rolling temperature of finish rolling is 760-810 ℃, and the total reduction rate of finish rolling is more than 66.35-70.83%;
4) A cooling process: the method adopts a mode of combining ultra-fast cooling and laminar cooling, wherein the water temperature of the ultra-fast cooling is 17-20 ℃, and the water temperature of the laminar cooling is 23-28 ℃; the cooling speed of the cooling process is 20.58-24.60 ℃/s, and the steel wire is finally cooled to 400-450 ℃ for coiling.
3. The production method of the thick-gauge high-strength-toughness L485M pipeline steel as claimed in claim 2, wherein the properties of the produced hot-rolled coil are as follows: the yield strength is 517-593 MPa, the tensile strength is 641-695 MPa, and the elongation after fracture is more than or equal to 34 percent; the average value of-60 ℃ Charpy impact energy Akv of 3 samples is more than or equal to 270J, and the average value of-60 ℃ average drop hammer tear test shearing area SA of 2 samples is more than or equal to 88%; hardness HV 10 Less than or equal to 236, d =2a,180 degrees cold bending is qualified.
4. The method for producing the thick-gauge high-strength-toughness L485M pipeline steel according to claim 2, wherein the thickness of the produced hot-rolled coil plate is 17-20 mm.
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