CN111996448A - L485MS pipeline steel with excellent SSCC (stress induced cracking) resistance under high loading stress and manufacturing method thereof - Google Patents

L485MS pipeline steel with excellent SSCC (stress induced cracking) resistance under high loading stress and manufacturing method thereof Download PDF

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CN111996448A
CN111996448A CN202010765872.2A CN202010765872A CN111996448A CN 111996448 A CN111996448 A CN 111996448A CN 202010765872 A CN202010765872 A CN 202010765872A CN 111996448 A CN111996448 A CN 111996448A
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孔祥磊
黄国建
黄明浩
张英慧
王杨
周敬
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Angang Steel Co Ltd
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    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • 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
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • 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
    • C22C38/06—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
    • 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
    • C22C38/50—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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  • Crystallography & Structural Chemistry (AREA)
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Abstract

The invention provides L485MS pipeline steel with excellent SSCC resistance under high loading stress and a manufacturing method thereof, wherein the pipeline steel comprises the following components in percentage by weight: 0.04 to 0.06 percent of C, 0.15 to 0.25 percent of Si, 1.61 to 1.70 percent of Mn, 0.066 to 0.080 percent of Nb, 0.008 to 0.025 percent of Ti, 0.12 to 0.18 percent of Mo, 0.15 to 0.25 percent of Cr, 0.10 to 0.20 percent of Ni, 0.015 to 0.045 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.001 percent of S, less than or equal to 0.004 percent of N, less than or equal to 0.0001 percent of H, less than or equal to 0.001 percent of O, and the balance of Fe and inevitable impurities. The manufacturing method comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab cleaning, slab heating, rolling, ultrafast cooling, laminar cooling and coiling; the invention can meet the requirements of HIC resistance and SSCC resistance under increasingly upgraded high stress loading, and the fracture shear area is more than or equal to 95 percent at the temperature of-30 ℃; the Charpy impact power is more than or equal to 350J at the temperature of minus 40 ℃; the method meets the development trend and the requirement of the current acidic oil and gas field, and has outstanding economic benefit and good social benefit.

Description

L485MS pipeline steel with excellent SSCC (stress induced cracking) resistance under high loading stress and manufacturing method thereof
Technical Field
The invention belongs to the field of metal materials, and particularly relates to L485MS pipeline steel with excellent SSCC (stress induced cracking) resistance under high loading stress and a manufacturing method thereof.
Background
With the improvement of cognition and the technical progress, the corrosion resistance problem of long-distance oil and gas pipelines is increasingly emphasized, and particularly, the pipelines are rich in H2S and other acidic oil gas resources of corrosive media continuously permeate into steel through H atoms generated in the conveying process, H molecules are gathered at defect positions such as inclusions and banded structures to expand and expand, and the H atoms interact with stress borne by the steel pipe to cause pipeline breakage and failure, so that major accidents are caused. It is now common in the industry to use H in the medium being transported through a pipeline2When the S partial pressure is more than 300Pa, an acid-resistant pipe is needed.
In the current international universal standard API SPEC 5L or ISO 3183.3 for pipeline steel, the acid resistance test for acidic service pipeline steel includes 2 items: hydrogen Induced Cracking (HIC) and Sulfide Stress Corrosion Cracking (SSCC). Wherein SSCC adopts a four-point bending test sample, loads 0.72 times of stress value of specified minimum yield strength of the steel pipe, and continuously introduces H2The saturated acidic solution of the S gas was immersed for 720 hours, and the sample was taken out to observe whether or not the surface of the sample was cracked or cracked.
At present, the main steel grade developed and applied internationally is BMS-L450MS, the highest steel grade is L485MS, the higher the steel grade is, the thicker the specification is, the higher the sensitivity of HIC and SSCC is, and the greater the development difficulty is.
In published domestic and foreign documents, the SSCC-resistant test loading stress generally adopts a stress value of 0.72 time or 0.80 time of the specified minimum yield strength of a steel pipe. However, as the research on the corrosion problem progresses, the SSCC resistance test loaded with a stress value of 0.80 times or more the actual yield strength is more in line with the development trend.
The following are related documents at home and abroad which are closer to the invention:
1) the invention relates to an acid-resistant X70MS steel-grade spiral welded pipe and a manufacturing method thereof (application number: CN201110331254.8) was designed to: 0.02 to 0.05 percent of C, 0.10 to 0.20 percent of Si, 1.10 to 1.40 percent of Mn, less than or equal to 0.0013 percent of S, less than or equal to 0.013 percent of P, 0.020 to 0.060 percent of Nb, 0.030 to 0.060 percent of V, 0.010 to 0.020 percent of Ti, 0.05 to 0.15 percent of Mo, 0.10 to 0.25 percent of Cr, 0.10 to 0.25 percent of Ni, 0.10 to 0.25 percent of Cu, less than or equal to 0.005 percent of N, less than or equal to 0.0005 percent of B, 0.0020 to 0.0050 percent of Ca, more than or equal to 2.0 percent of Ca/S and the balance of. The invention adopts low-carbon low-manganese design, contains a large amount of noble elements such as Nb, V, Cr, Mo, Ni, Cu and the like, has high alloy cost, and introduces a tube making process instead of a plate coil production method.
2) The invention relates to an acid corrosion resistant X70MS pipeline steel hot rolled coil and a manufacturing method thereof (application number: CN201811020840.9) was designed to: 0.03 to 0.10 percent of C, 0.10 to 0.20 percent of Si, 1.10 to 1.40 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.0020 percent of S, 0.15 to 0.55 percent of Cr, 0.15 to 0.45 percent of Mo, 0.050 to 0.080 percent of Nb, 0.020 to 0.040 percent of V, 0.15 to 0.30 percent of Ni, less than or equal to 0.0002 percent of B, less than or equal to 0.006 percent of N, less than or equal to 0.0018 percent of O, less than or equal to 0.0005 percent of H, and the balance. The invention adopts the low manganese design, the content of noble alloy elements is high, and the cost is high; in addition, the impurity elements in the product design are generally controlled, impurities and banded structures are not different from the requirements of common pipelines, the acid resistance is general, the HIC resistance test is only met, and the SSCC resistance test performance is not involved.
3) The invention relates to an X65MS/X70MS spiral submerged arc welded pipe with excellent SSCC stress corrosion resistance and a manufacturing method thereof (application number: CN201310470450.2) discloses welded tube alloy design: less than or equal to 0.05 percent of C, 0.10 to 0.30 percent of Si, less than or equal to 1.20 percent of Mn, less than or equal to 0.008 percent of P, less than or equal to 0.001 percent of S, less than or equal to 0.25 percent of Cu, less than or equal to 0.25 percent of Ni, less than or equal to 0.1 percent of Cr, less than or equal to 0.10 percent of Nb, less than or equal to 0.05 percent of V, less than or equal to 0.06 percent of Ti, less than or equal to 0.30 percent of Mo, less than or equal. Firstly, the invention introduces the manufacturing process of the X65MS/X70MS steel tube, and does not relate to the production process of the plate coil; secondly, it relates to the product specification is thin (10 mm at the thickest), and the structure and performance are easily controlled, adopts low manganese design in addition, need add more precious alloy element and compensate the loss in intensity, and the alloy cost is high.
4) The invention relates to an ERW welded pipe of X70MS with excellent SSCC stress corrosion resistance and a manufacturing method thereof (application number: CN201310469618.8) discloses welded tube alloy design: less than or equal to 0.04 percent of C, 0.10 to 0.20 percent of Si, less than or equal to 1.20 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.001 percent of S, less than or equal to 0.15 percent of Cu, less than or equal to 0.15 percent of Ni, less than or equal to 0.10 percent of Cr, less than or equal to 0.05 percent of Nb, less than or equal to 0.02 percent of V, less than or equal to 0.02 percent of Ti, less than or equal to 0.10 percent of Mo, less than or equal. Firstly, the invention introduces an ERW welded pipe and a manufacturing method thereof, and does not relate to a coil production process. The ERW welded pipe is thin in plate coil specification and low in strength (generally lower by one steel grade than a spiral welded pipe), and in addition, the ERW welded pipe adopts a low-carbon and low-manganese design, so that more precious alloy elements are required to be added to make up for the loss in strength, and the alloy cost is high.
5) The invention relates to a hydrogen sulfide corrosion resistant high-strength X70MS longitudinal submerged arc welded pipe and a manufacturing method thereof (application number: CN201310198848.5) discloses welded tube alloy design: 0.03 to 0.04 percent of C, 0.25 to 0.35 percent of Si, less than or equal to 1.20 percent of Mn, less than or equal to 0.008 percent of P, less than or equal to 0.001 percent of S, 0.10 to 0.20 percent of Cu, 0.10 to 0.20 percent of Ni, less than or equal to 0.15 percent of Cr, 0.05 to 0.10 percent of Nb, less than or equal to 0.06 percent of V, 0.15 to 0.20 percent of Ti, 0.01 to 0.02 percent of Mo, 0.04 to 0.10 percent of Al, less than or equal to 0.0005 percent of B, less than or equal to 0.0002 percent of Ca, and. Firstly, the invention introduces an ERW welded pipe and a manufacturing method thereof, which do not relate to a coil production process; the required ranges of C, Ti, Mo and the like in the components are too narrow, the production practicability is poor, the straight welded pipe is low in strength (the test direction is transverse, and is generally lower than a spiral welded pipe with an oblique test direction by one steel grade due to the anisotropy of pipeline steel), and in addition, the low-carbon low-manganese design is adopted, more precious alloy elements are required to be added to make up the loss in strength, and the alloy cost is high.
6) The invention discloses a hot-rolled coil alloy design disclosed in application No. (CN200910187515.6) of a low-cost acid-resistant pipeline steel hot-rolled coil and a manufacturing method thereof: 0.04 to 0.10 percent of C, 0.05 to 0.50 percent of Si, 1.00 to 1.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, less than or equal to 0.08 percent of Nb, 0.005 to 0.030 percent of Ti, less than or equal to 0.006 percent of N, less than or equal to 0.002 percent of H, less than or equal to 0.0010 percent of O, 0.010 to 0.050 percent of Als, 0.001 to 0.004 percent of Ca, and the balance of Fe and inevitable impurities. The invention does not add any effective corrosion-resistant alloy elements, can meet the requirements of low SSCC (0.72 time of the specified minimum yield strength of the steel pipe) loading stress resistance value and thin specification (the maximum thickness is 12.5 mm).
7) The article, the research and development of the H2S acid corrosion resistant X70MS pipeline steel, the 2014 national steel rolling production technical conference, 107 + 113. The article introduces a production method of a pipeline steel flat plate produced on a production line of a Qin 4300mm wide and thick plate, which is obviously different from a process of a pipeline steel coiled plate produced by a hot rolling strip steel production line; in addition, the low-carbon low-manganese design is adopted, other main alloy elements are not noted, the main alloy elements comprise noble elements such as Cr, Ni and Cu, the inferred cost is higher, and the SSCC loading stress resistance value of the product is low.
The low-carbon low-manganese alloy design is mostly adopted in the alloy design of the documents, more precious alloy elements are required to be added to compensate the loss of the strength in order to compensate the strength, the alloy cost is high, the corrosion resistance of some documents is general, the SSCC (stress cracking resistance test) test loading stress value is low, the specification is thin, the control is easy, and the documents are pipeline flat plate production methods and ERW (electric resistance welding) or straight welded pipe production methods which are obviously different from the invention, and the creativity and the novelty of the invention are not influenced.
Disclosure of Invention
The invention aims to overcome the problems and the defects and provide L485MS pipeline steel with low cost and excellent SSCC resistance under high loading stress with the thickness of more than or equal to 14mm and a manufacturing method thereof.
The purpose of the invention is realized as follows:
l485MS pipeline steel with excellent SSCC resistance under high loading stress comprises the following components in percentage by weight: 0.04 to 0.06 percent of C, 0.15 to 0.25 percent of Si, 1.61 to 1.70 percent of Mn, 0.066 to 0.080 percent of Nb, 0.008 to 0.025 percent of Ti, 0.12 to 0.18 percent of Mo, 0.15 to 0.25 percent of Cr, 0.10 to 0.20 percent of Ni, 0.015 to 0.045 percent of Als, less than or equal to 0.010 percent of P, less than or equal to 0.001 percent of S, less than or equal to 0.004 percent of N, less than or equal to 0.0001 percent of H, less than or equal to 0.001 percent of O, and the balance of Fe and inevitable impurities.
The microstructure of the pipeline steel is fine acicular ferrite, and the thickness of the pipeline steel is more than or equal to 14 mm.
The components of the L485MS pipeline steel are designed by adopting a C-Mn-Nb-Mo-Cr system, and meanwhile, fine acicular ferrite tissues are obtained by adopting micro Ti treatment and combining a thermomechanical control rolling production process, so that the excellent comprehensive performance of the product is ensured.
The invention has the following design reasons:
c: is the most economic, basic and effective strengthening element in steel, but C is the element which is most easy to cause continuous casting billet segregation, and the content of C is too high, so that the HIC resistance capability is rapidly reduced, and the crack rate is suddenly increased. The carbon content of the invention is 0.04-0.06%.
Si: deoxidizing element, which is solid-dissolved in ferrite to improve the strength of steel, but loses plasticity and toughness, and the Si content of the invention is 0.15-0.25%.
Mn: manganese has a solid solution strengthening effect, and can also reduce the gamma-alpha phase transition temperature, further refine ferrite grains and compensate main strengthening elements of strength loss caused by reduced content of C. However, in the medium and low strength ferrite-pearlite pipeline steel, the band-shaped structure generated by Mn segregation forms a low temperature transformation hard structure band sensitive to HIC during hot rolling, and promotes the increase of HIC and SSCC sensitivity. The manganese content of the invention is 1.61-1.70%.
Nb: the steel is the most main element for controlled rolling in modern microalloyed pipeline steel, NbC strain induced precipitation hinders recovery and recrystallization of deformed austenite, phase transition temperature is reduced, and formation of acicular ferrite structure and M-A island is promoted. Nb can improve the performance of steel through multiple strengthening mechanisms such as fine grain strengthening, 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, so the content of Nb in the invention is 0.066-0.080%.
Ti: is a strong nitrogen-fixing element, and the stoichiometric ratio of Ti/N is 3.42. When about 0.015 percent of Ti is added, a high-temperature stable fine TiN precipitated phase can be formed during slab continuous casting, the precipitated phase can effectively prevent austenite grains of a continuous casting billet from growing in the heating process, and meanwhile, the precipitated phase has an obvious effect of improving the fracture toughness of a heat affected zone during steel welding. The Ti content of the invention is controlled between 0.008 percent and 0.025 percent.
Mo: the element is a strong hardenability element, inhibits the generation of a pearlite structure zone, is a main element for ensuring the structure uniformity of thick products, and simultaneously improves the precipitation strengthening effect of Nb (C, N), so that Mo can reduce the ductile-brittle transition temperature and improve the HIC resistance of the steel while improving the strength of the steel. The molybdenum content of the invention is 0.12-0.18%.
Cr: the element with medium hardenability can make up the shortage of hardenability (the price of Cr is about one sixth of Mo) caused by reducing Mo, and Cr and Mo are both elements forming strong carbides, have higher affinity with C, can strongly prevent the diffusion of C element to reduce the segregation of C, and have better composite addition effect of the two elements. In addition, Cr is a corrosion resistant element and can obviously slow down H2And S corrosion. The chromium content of the invention is 0.15-0.25%.
Ni: the nickel can improve the strength of the steel through solid solution strengthening, simultaneously can reduce the ductile-brittle transition temperature of the steel, greatly improves the toughness of the steel and is beneficial to slowing down H2And S corrosion. The nickel content of the invention is 0.10-0.20%.
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 steel, and the content of Als is controlled to be 0.015-0.045%.
S: is an extremely harmful element in acid-resistant pipeline steel, and the HIC and SSCC sensitivity is improved sharply. MnS inclusions formed by S and Mn are the most easily nucleated positions of HIC, and MnS can become scattered spheroids through calcium treatment, so that the formation of HIC can be inhibited, and the crack sensitivity is obviously reduced. The S content of the invention is less than or equal to 0.0001 percent.
P: is an inevitable impurity element in steel, is an easily segregated element, causes nonuniformity of components and tissues, and increases crack sensitivity. The P content of the invention is less than or equal to 0.010 percent.
N, O, H: are inevitable impurity elements in the steel, and reduce the toughness and corrosion resistance of the steel. The invention has N less than or equal to 0.004%, H less than or equal to 0.0001% and O less than or equal to 0.001%.
The second technical scheme of the invention is to provide a manufacturing method of L485MS pipeline steel with excellent SSCC resistance under high loading stress, which comprises the steps of molten iron pretreatment, converter smelting, external refining (RH + LF + calcium treatment), continuous casting, slab cleaning, slab heating, rolling, ultrafast cooling and laminar cooling, and coiling;
(1) smelting and continuous casting: carrying out deep desulfurization on the molten iron in a pretreatment manner, and simultaneously completely removing molten iron desulfurization slag; the top and bottom of the converter are blown compositely to avoid rephosphorization of molten steel in the converter, and 85-100m is adopted in the initial stage and the final stage of smelting3Argon bottom blowing stirring at the intensity of/h, tapping at double slag stops, and adding synthetic slag in the tapping process to reduce molten steel rephosphorization in the LF treatment process; adopting RH + LF vacuum refining treatment, wherein the total amount of P, S, O, N, H and other impurities is less than or equal to 150ppm, the alkalinity of steel slag in an LF furnace is kept at 3.8-4.5, deep desulfurization treatment is carried out again, meanwhile, calcium treatment is carried out on molten steel after external refining, the complete spheroidization of inclusions in the steel is ensured, the grades of all the inclusions are all lower than 2 grades, and the sum is not more than 5 grades; the superheat degree of the molten steel of the tundish is less than or equal to 25 ℃, the casting is protected in the whole process, dynamic soft reduction is required to be put in, the center segregation and center porosity of the continuous casting billet are strictly controlled, and the quality of the continuous casting billet is ensured; the thickness of the casting blank is less than 200mm so as to ensure that the solidification cooling rate of the casting blank is greater than that of the traditional thick plate blank. The continuous casting plate blank needs to be subjected to offline inspection and cleaning, and the edge and surface quality is ensured.
(2) The rolling process comprises the following steps: reheating the cleaned continuous casting slab at 1160-1200 ℃, and then performing controlled rolling in two stages of a rough rolling unit and a finishing rolling unit, wherein the finish rolling temperature of rough rolling is 980-1050 ℃, the finish rolling start temperature is not more than 960 ℃, and the finish rolling temperature is 780-820 ℃; reheating the cleaned continuous casting plate blank by a stepping heating furnace;
then the coiled plate is cooled by adopting ultra-fast cooling and laminar cooling, the front 2 groups of the cooling unit are subjected to ultra-fast cooling at the cooling speed of over 40 ℃/s, then laminar cooling is carried out at the cooling speed of 20-30 ℃/s, and then coiling is carried out at the coiling temperature of 450-.
The invention has the beneficial effects that:
1) the alloy is simple and economical in design, adopts C-Mn-Nb-Mo-Cr system design and micro Ti treatment, reasonably utilizes the composite hardenability effect of Mo and Cr elements, and can still obtain uniform and consistent product structure under the condition that the plate thickness is more than or equal to 14 mm.
2) The pure steel smelting continuous casting and TMCP process is adopted for production, the purity of steel, the content and the shape of impurities, the edge and surface quality of a casting blank, the grain refinement and the homogenization control of a whole-flow structure are strictly controlled, and the product performance and the quality are ensured.
3) By adopting the ultra-fast cooling and laminar cooling sectional cooling process, the steel plate is quickly cooled and the crystal grains are refined in the phase change stage, and the uniform cooling in the thickness direction of the plate coil can be ensured, so that the organization of the product in the thickness direction is more uniform and consistent.
4) The effect of microalloy elements, particularly the composite effect of Mo and Cr elements, is fully exerted, and the coil produced by combining the pure steel smelting continuous casting and TMCP process can meet the increasingly upgraded HIC and SSCC (stress loaded with 0.85 times of actual yield strength value) resistance test requirement, and the fracture shear area is more than or equal to 95 percent at the temperature of minus 30 ℃; the Charpy impact power is more than or equal to 350J at the temperature of minus 40 ℃; the method meets the development trend and the requirement of the current acidic oil and gas field, and has outstanding economic benefit and good social benefit.
Detailed Description
The present invention is further illustrated by the following examples.
According to the component proportion of the technical scheme, the embodiment of the invention carries out molten iron pretreatment, converter smelting, external refining, continuous casting, slab cleaning, slab heating, rolling, ultra-fast cooling, laminar cooling and coiling;
(1) smelting and continuous casting: carrying out deep desulfurization on the molten iron in a pretreatment manner, and simultaneously completely removing molten iron desulfurization slag; the top and bottom of the converter are blown compositely, and the initial stage and the final stage of the smelting adopt 85-100m3Argon bottom blowing stirring at the intensity of/h, tapping at double slag stops, and adding synthetic slag in the tapping process; adopting RH + LF vacuum refining treatment, wherein the total amount of P, S, O, N, H and other impurities is less than or equal to 150ppm, the alkalinity of steel slag in an LF furnace is kept at 3.8-4.5, deep desulfurization treatment is carried out again, meanwhile, calcium treatment is carried out on molten steel after external refining, the complete spheroidization of inclusions in the steel is ensured, the grades of all the inclusions are all lower than 2 grades, and the sum is not more than 5 grades; the superheat degree of the molten steel in the tundish is less than or equal to 25 ℃, and the whole processProtection pouring is carried out, and dynamic soft pressing is carried out; the thickness of the continuous casting billet is less than 200 mm;
(2) the rolling process comprises the following steps: reheating temperature of the cleaned continuous casting slab is 1160-1200 ℃, then rolling is controlled by two stages of a rough rolling unit and a finishing rolling unit, the finishing rolling temperature of rough rolling is 980-1050 ℃, the finishing rolling temperature is not more than 960 ℃, and the finishing rolling temperature of finishing rolling is 780-820 ℃;
(3) and (3) cooling: then, ultrafast cooling and laminar cooling are adopted, the first 2 groups of the cooling units are subjected to ultrafast cooling at the cooling speed of over 40 ℃/s, then laminar cooling is carried out at the cooling speed of 20-30 ℃/s, and then coiling is carried out, wherein the coiling temperature is 450 ℃ and 500 ℃.
The compositions of the steels of the examples of the invention are shown in table 1. The main process parameters of the steel of the embodiment of the invention are shown in Table 2. The mechanical properties of the steels of the examples of the invention are shown in Table 3. The HIC resistance of the steel of the examples of the present invention is shown in Table 4. The SSCC resistance of the steel of the examples of the present invention is shown in Table 5.
TABLE 1 composition (wt%) of steels of examples of the present invention
Numbering C Si Mn P S Nb Ti Mo Cr Als N H O
Example 1 0.055 0.18 1.63 0.009 0.0008 0.075 0.015 0.13 0.17 0.015 0.003 0.00009 0.0009
Example 2 0.060 0.15 1.61 0.0010 0.0009 0.068 0.012 0.18 0.21 0.034 0.002 0.00008 0.0006
Example 3 0.045 0.22 1.69 0.008 0.0008 0.066 0.019 0.15 0.25 0.045 0.004 0.00010 0.0009
Example 4 0.040 0.18 1.66 0.007 0.0010 0.077 0.025 0.14 0.15 0.035 0.003 0.00007 0.0008
Example 5 0.047 0.25 1.63 0.006 0.0009 0.069 0.008 0.12 0.18 0.030 0.003 0.00009 0.0007
Example 6 0.052 0.20 1.67 0.008 0.0007 0.080 0.016 0.17 0.19 0.025 0.004 0.00008 0.00010
TABLE 2 Main Process parameters of the steels of the examples of the invention
Figure BDA0002614571040000111
TABLE 3 Main continuous casting Process parameters for the steels of the examples of the invention
Figure BDA0002614571040000112
TABLE 4 Inclusion control of steels of the examples of the invention
Figure BDA0002614571040000113
TABLE 5 mechanical Properties of steels of examples of the invention
Figure BDA0002614571040000121
Note: the sampling directions of the tensile test, Charpy impact test and Drop Weight Tear Test (DWTT) samples were all 30 ° to the rolling direction.
TABLE 6 HIC resistance of steels of examples of the invention
Figure BDA0002614571040000122
Note: no hydrogen bubbles were present on the surface of the samples.
TABLE 5 SSCC resistance of steels according to the examples of the invention
Figure BDA0002614571040000131
In order to describe the present invention, the above embodiments are properly and fully described by way of examples, and the above embodiments are only used for illustrating the present invention and not for limiting the present invention, and those skilled in the relevant art can make various changes and modifications without departing from the spirit and scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made by the persons skilled in the relevant art should be included in the protection scope of the present invention, and the protection scope of the present invention should be defined by the claims.

Claims (3)

1. The L485MS pipeline steel with excellent SSCC resistance under high loading stress is characterized by comprising 0.04-0.06% of C, 0.15-0.25% of Si, 1.61-1.70% of Mn, 0.066-0.080% of Nb, 0.008-0.025% of Ti, 0.12-0.18% of Mo, 0.15-0.25% of Cr, 0.10-0.20% of Ni, 0.015-0.045% of Als, less than or equal to 0.010% of P, less than or equal to 0.001% of S, less than or equal to 0.004% of N, less than or equal to 0.0001% of H, less than or equal to 0.001% of O, and the balance of Fe and inevitable impurities.
2. The L485MS pipeline steel with excellent SSCC resistance under high loading stress as claimed in claim 1, wherein the microstructure of the pipeline steel is fine acicular ferrite, and the thickness of the pipeline steel plate is not less than 14 mm.
3. A manufacturing method of the L485MS pipeline steel with excellent SSCC resistance under high loading stress as claimed in claim 1 or 2, which comprises the steps of molten iron pretreatment, converter smelting, external refining, continuous casting, slab cleaning, slab heating, rolling, ultra-fast cooling, laminar cooling and coiling; the method is characterized in that:
(1) smelting and continuous casting: carrying out deep desulfurization on the molten iron in a pretreatment manner, and simultaneously completely removing molten iron desulfurization slag; the top and bottom of the converter are blown compositely, and the initial stage and the final stage of the smelting adopt 85-100m3Argon bottom blowing stirring at the intensity of/h, tapping at double slag stops, and adding synthetic slag in the tapping process; adopting RH + LF vacuum refining treatment, wherein the total amount of P, S, O, N, H and other impurities is less than or equal to 150ppm, the alkalinity of steel slag in an LF furnace is kept at 3.8-4.5, deep desulfurization treatment is carried out again, meanwhile, calcium treatment is carried out on molten steel after external refining, the complete spheroidization of inclusions in the steel is ensured, the grades of all the inclusions are all lower than 2 grades, and the sum is not more than 5 grades; the superheat degree of the molten steel of the tundish is less than or equal to 25 ℃, the whole process is protected and poured, and dynamic soft reduction is carried out; the thickness of the continuous casting billet is less than 200 mm;
(2) the rolling process comprises the following steps: reheating the cleaned continuous casting slab at 1160-1200 ℃, and then performing controlled rolling in two stages of a rough rolling unit and a finishing rolling unit, wherein the finish rolling temperature of rough rolling is 980-1050 ℃, the finish rolling start temperature is not more than 960 ℃, and the finish rolling temperature is 780-820 ℃;
(3) and (3) cooling: then, ultra-fast cooling and laminar cooling are adopted for cooling, the front 1-2 groups of the cooling unit are ultra-fast cooling, the cooling speed is more than 40 ℃/s, then laminar cooling is carried out, the cooling speed is 20-30 ℃/s, then coiling is carried out, and the coiling temperature is 450-.
CN202010765872.2A 2020-08-03 2020-08-03 L485MS pipeline steel with excellent SSCC (stress induced cracking) resistance under high loading stress and manufacturing method thereof Pending CN111996448A (en)

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