Acid-resistant pipeline steel and manufacturing method therefor

Abstract

The present invention relates to the field of metal materials and provides acid-resistant pipeline steel and a manufacturing method therefor. The chemical components of the acid-resistant pipeline steel comprise, in percentage by weight: 0.02-0.06% of C, 0.10-0.30% of Si, 0.80-1.10% of Mn, 0.02-0.08% of Nb, 0.06-0.12% of V, 0.20-0.30% of Ni, Mo ≤ 0.08%, 0.03-0.06% of Al, 0.0005-0.0030% of Ca, P ≤ 0.008%, S ≤ 0.002%, 0.004-0.006% of [N], [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the balance being Fe and inevitable impurities. The acid-resistant pipeline steel is obtained by sequentially carrying out KR pre-desulfurization, BOF top-bottom combined blowing smelting, LF refining, RH refining, continuous casting with stack cooling, heating, steel rolling, rapid water cooling, and heat treatment on blast furnace molten iron. By means of the synergistic effect of composition design and process optimization, the present invention solves the problems of poor low-temperature drop-weight tear test performance and large strength variation across the same plate in acid-resistant pipeline steel.

Description

An acid-resistant pipeline steel and a manufacturing method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of metal materials, in particular to an acid-resistant pipeline steel and a manufacturing method thereof. BACKGROUND

[0002] The HIC / SSC-resistant pipeline steel is a special steel developed to address the hydrogen embrittlement and stress corrosion problems in high-strength oil and gas pipeline systems. In addition to meeting the tensile, impact, drop hammer and other performance requirements of conventional pipelines, the acid-resistant pipeline steel must also meet the hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC) performance requirements in the American Corrosion Engineers Association NACE TM 0177 and TM 0284 standards.

[0003] The HIC / SSC resistance, strength, drop hammer, and yield ratio are mutually restrictive, which is a difficulty in the production of acid-resistant pipeline steel. In order to obtain good HIC / SSC resistance, a low C (≤0.05wt.%) and low Mn (≤1.2wt.%) composition design is usually adopted; the inclusions are reduced by clean steel smelting process and changing the morphology of inclusions; by adding trace amounts of Nb, V, Ti and other micro-alloying elements, as well as a small amount of Mo, Cu, Ni and other elements, combined with a specific TMCP process, the microstructure of the pipeline steel is finely controlled and significantly refined, and finally the mechanical properties are ensured; however, the refinement of the overall microstructure of the pipeline steel, the increase of the strength, and the application of large heat input welding technology make the softening problem of the heat-affected zone of high-grade pipeline steel increasingly prominent; the appearance of the softening zone leads to a serious mismatch between the performance of the heat-affected zone and the base material, becoming the weakest part of the entire welded joint, seriously affecting the service safety and service life of the welded structure.

[0004] Research has found that low C and Mn content can weaken the center segregation, but leads to an increase in phase transition temperature and grain recovery and growth, and the grain growth leads to a decrease in drop hammer performance; at the same time, low C and Mn content weakens the solid solution strengthening effect, which easily leads to a high yield ratio; the inclusion morphology is controlled by controlling the Ca / S ratio, but because Ca is a active metal, the steelmaking control is extremely difficult; the thermomechanical control process (TMCP) obtains fine-grained structure by controlling the rolling and cooling of the steel plate, but leads to uneven performance of the head, middle and tail of the plate, thereby hiding potential hazards for subsequent pipe manufacturing. In recent years, in order to ensure the stability and safety of the process, the steel plant usually requires that the strength difference of different batches and the head, middle and tail of the steel plate be within 50MPa, which increases the difficulty of production control of the steel plant, leading to the phenomenon of downgrading or even scrapping of the steel plate.

[0005] CN 116790978 A discloses an acid corrosion resistant pipeline steel plate and a preparation method thereof. In order to reduce the influence of center segregation on the hydrogen-induced cracking resistance of the steel plate, the content of Mn is only 0.15-0.30%; in order to ensure the strength of the steel plate, the content of Cr reaches 0.90-1.20%; therefore, the Cr element will expand the formation range of granular bainite during the cooling and phase change process during welding, resulting in a large amount of granular bainite structure in the weld, increasing the number of M / A components and increasing the particle size, thereby reducing the impact toughness of the weld, which is not conducive to welding.

[0006] CN 114836683 B discloses a high-strength and high-toughness low-yield ratio pipeline steel plate suitable for a wet hydrogen sulfide environment. The patent adopts a low-carbon and medium-manganese design, and requires Ca / S to be greater than or equal to 2 in order to control the inclusion morphology. High Mn content and Ca / S ratio will bring great difficulty to the steelmaking process, which is not conducive to the stable control of acid resistance. SUMMARY

[0007] The present application aims to provide an acid-resistant pipeline steel and a manufacturing method thereof. The scheme solves the problems of poor low-temperature drop hammer performance and large strength difference of the same plate of the high-strength double-resistant pipeline steel through component design and process optimization, and improves the softening problem of the welding heat affected zone.

[0008] To achieve the above-mentioned purpose, the present application proposes the following technical scheme:

[0009] In a first aspect, an acid-resistant pipeline steel is provided. The chemical composition of the acid-resistant pipeline steel includes, by weight percentage, C: 0.02-0.06%, Si: 0.10-0.30%, Mn: 0.80-1.10%, Nb: 0.02-0.08%, V: 0.06-0.12%, Ni: 0.20-0.30%, Mo≤0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the remainder is Fe and unavoidable impurities.

[0010] The center segregation of the acid-resistant pipeline steel is not higher than C0.5 level, and the center porosity is not higher than 0.5 level.

[0011] Further, when the steel plate thickness D of the acid-resistant pipeline steel is 8mm ≤ D < 16mm, the chemical components of the acid-resistant pipeline steel include, in weight percentage, C: 0.02 ~ 0.04%, Si: 0.10 ~ 0.30%, Mn: 0.80 ~ 0.90%, Nb: 0.02 ~ 0.04%, V: 0.06 ~ 0.08%, Ni: 0.20 ~ 0.30%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0012] Further, when the steel plate thickness D of the acid-resistant pipeline steel is 8mm ≤ D < 16mm, the chemical components of the acid-resistant pipeline steel include, in weight percentage, C: 0.02 ~ 0.04%, Si: 0.10 ~ 0.30%, Mn: 0.80 ~ 0.90%, Nb: 0.02 ~ 0.04%, V: 0.06 ~ 0.08%, Ni: 0.20 ~ 0.30%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0013] Further, when the steel plate thickness D of the acid-resistant pipeline steel is 8mm ≤ D < 16mm, the chemical components of the acid-resistant pipeline steel include, in weight percentage, C: 0.02 ~ 0.04%, Si: 0.10 ~ 0.30%, Mn: 0.80 ~ 0.90%, Nb: 0.02 ~ 0.04%, V: 0.06 ~ 0.08%, Ni: 0.20 ~ 0.30%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0014] Further, when the thickness D of the steel plate of the acid-resistant pipeline steel is 32mm≤D≤40mm, the chemical composition of the acid-resistant pipeline steel includes, by weight percentage, C: 0.04-0.06%, Si: 0.10-0.30%, Mn: 1.0-1.1%, Nb: 0.07-0.08%, V: 0.10-0.12%, Ni: 0.20-0.30%, Mo: 0.05-0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities.

[0015] In a second aspect, a manufacturing method of an acid-resistant pipeline steel is provided, comprising the following steps:

[0016] S1: blast furnace smelting, the chemical composition of the molten steel at the end of smelting includes, by weight percentage, Si: 0.30-0.60%, Mn≤0.40%, S≤0.040%, P≤0.120%;

[0017] S2: KR pre-desulphurization, the temperature of the molten steel after desulphurization is not lower than 1300℃, and the weight percentage of S in the molten steel after desulphurization is not more than 0.002%;

[0018] S3: 180-ton BOF top and bottom combined blowing smelting, scrap steel is added to the molten steel during smelting to adjust the composition of the molten steel; the tapping temperature at the end of smelting is 1640℃±30℃, and metal manganese, ferrosilicon and aluminum ingot are added to the molten steel at the time of tapping to adjust the composition of the molten steel and to deoxidize the molten steel, the chemical composition of the molten steel at the end of smelting includes, by weight percentage, P≤0.010%, S≤0.005%, 0.02%≤C≤0.05%; the oxygen lance position is 1.5m-1.8m, the bottom blowing flow rate is 574m 3 / h-604m 3 / h, and the top blowing flow rate is 35000m 3 / h-38000m 3 / h.

[0019] S4: LF refining, argon is blown throughout the refining process to prevent oxidation of the molten steel, and slag is melted and adjusted during the heating process to perform white slag treatment, and niobium iron is added after the white slag treatment to ensure stable recovery of the Nb element after static holding for 10min-20min;

[0020] S5: RH refining, the vacuum degree of the RH refining process is controlled to be less than 2 mBar, the degassing time is greater than 15 min, after adding vanadium iron according to the weight percentage, the net circulation time is ensured to be 5-10 min; then seamless silicon calcium wire is added according to the weight percentage, soft stirring is carried out for 12-18 min after wire feeding, the slag surface appears fluctuation during the soft stirring process, but the molten steel is not exposed to prevent oxidation of the molten steel; the chemical composition of the molten steel after the RH refining according to the weight percentage includes C: 0.02-0.06%, Si: 0.10-0.30%, Mn: 0.80-1.10%, Nb: 0.02-0.08%, V: 0.06-0.12%, Ni: 0.20-0.30%, Mo≤0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities;

[0021] S6: continuous casting and cold storage: a continuous casting billet with a thickness of not less than 320 mm is obtained through electromagnetic stirring and light pressing at the end of continuous casting, the continuous casting billet is cold stored and is treated for hydrogen evolution for not less than 72 h, and then the continuous casting billet is unpacked;

[0022] S7: furnace charging and heating, the continuous casting billet is heated to 1160℃±20℃, and the holding time is 250 min-300 min;

[0023] S8: single-stage rolling in the unrecrystallization zone: the continuous casting billet after heating is discharged and is measured for temperature, when the temperature of the continuous casting billet is not higher than the unrecrystallization temperature, the continuous casting billet is opened and rolled by using a multi-pass hot rolling process, high-temperature fast rolling is carried out with large reduction, and the finish rolling temperature is 800℃-840℃; wherein, the reduction of at least three passes in the rolling process is not less than 22%;

[0024] S9: MULPIC rapid water cooling, the steel plate after rolling is rapidly water cooled, the cooling speed is 25℃ / s-35℃ / s, and the final cooling temperature is controlled to be not more than 300℃;

[0025] S10: heat treatment: the steel plate after water cooling is subjected to heat treatment, the furnace gas temperature of the heating furnace is controlled to be 450±10℃, and the holding time is 30 min; and the steel plate is cooled after being discharged from the furnace to obtain an acid-resistant pipeline steel.

[0026] Further, the center segregation of the continuous casting billet obtained in step S6 is not higher than C0.5 level, the center porosity is not higher than 0.5 level, and the A, B, C and D type inclusions in the continuous casting billet are all not higher than 1 level.

[0027] Further, the unrecrystallization temperature Tnr in step S8 is calculated by using an empirical formula, and the specific formula is as follows:

[0028] Tnr(℃) = 887 + 464*[C] + (6445*[Nb] - 644*sqrt[Nb]) + ((1732*[V] - 230*sqrt[V]) + 890*[Ti]) + 363*[Al] - 357*[Si], [C], [Nb], [V], [Ti], [Al], [Si] are weight percentages of each element in the acid-resistant pipeline steel, sqrt is an arithmetic square root function;

[0029] The step S8 is rolling the steel plate, and the flattened grain in the steel plate is not higher than 5 microns.

[0030] Further, the step S9 is fast water cooling the steel plate, and the microstructure of the steel plate is an initial structure of ferrite, bainite and martensite and austenite island, and the proportion of each initial structure is 75%-85%, 10%-25% and 5%-8% respectively.

[0031] Further, the step S10 is preparing the acid-resistant pipeline steel, and the strength difference of the head, middle and tail of the acid-resistant pipeline steel is not more than 30 MPa.

[0032] From the above technical solutions, the technical solutions of the present application have the following beneficial effects:

[0033] The acid-resistant pipeline steel and the manufacturing method thereof disclosed by the present application, wherein the acid-resistant pipeline steel comprises, in terms of weight percentage, C: 0.02-0.06%, Si: 0.10-0.30%, Mn: 0.80-1.10%, Nb: 0.02-0.08%, V: 0.06-0.12%, Ni: 0.20-0.30%, Mo≤0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities; in the manufacturing process, the blast furnace molten iron is obtained by blast furnace smelting, the blast furnace molten iron is sequentially subjected to KR pre-desulfurization, BOF top and bottom combined blowing smelting, LF refining, RH refining, continuous casting and cold pile, heating, rolling, MULPIC fast water cooling and heat treatment, and the acid-resistant pipeline steel is obtained, the center segregation of the steel is not higher than C0.5 level, and the center porosity is not higher than 0.5 level; the present application solves the problem of poor low-temperature drop hammer performance of the large-thickness high-strength double-acid-resistant pipeline steel plate through the synergistic effect of component design and process optimization, and simultaneously improves the softening problem of the welding heat affected zone.

[0034] Specifically, the acid-resistant pipeline steel prepared by the present application has stable and safe component proportion and preparation process, effectively solves the problem of large strength difference of the same plate, realizes the control of the strength difference of the head, middle and tail of the steel plate within 30 MPa, and stabilizes the grade and acid-resistant performance of the steel plate.

[0035] It should be appreciated that all combinations of the foregoing concepts and additional concepts described in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter. For example, a specific embodiment of a particular concept can be combined with an embodiment of another concept, even though such a combination is not expressly disclosed in the present description.

[0036] The foregoing and other aspects, embodiments and features of the present teachings can be better understood from the following description of the present teachings when considered in connection with the accompanying drawings. The accompanying drawings, which are incorporated herein and illustrate example embodiments of the present teachings, provide a further understanding of the principles of the present teachings and the description serves to explain the features and advantages thereof. BRIEF DESCRIPTION OF DRAWINGS

[0037] The drawings are not drawn to scale. In the drawings, each identical, or nearly identical, component that is illustrated in various figures is represented with a like numeral. For purposes of clarity, not every component is called out in every drawing. There is no implied relationship or dependency between components that are illustrated in different figures. Embodiments of various aspects of the present teachings will now be described, by way of example only, with reference to the accompanying drawings in which:

[0038] Figure 1 is the Vickers hardness test data for the samples prepared in Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0039] In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below with reference to the drawings of the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application. Unless otherwise defined, the technical terms or scientific terms used herein should be understood as the common meanings thereof by those skilled in the art.

[0040] The terms "comprise", "comprising", "include", "including", "contain", "containing", "have", "having", "carry", "carrying", "comprised of", "comprising of", "including of", "include of", "contain of", "containing of", "have of", "having of", "carry of", "carrying of", and the like used herein are used in their open-ended, conventional sense and can be used in conjunction with the term "consisting of", "consisting essentially of", or "consisting of", and / or can be used in the place of the term "comprising" or "including", and / or the like.

[0041] In the prior art method for preparing the anti-HIC / SSC pipeline steel, the content of the easily-segregated elements C and Mn is reduced to ensure the quality of the casting blank, and meanwhile, the precious metal elements such as Cr, Mo and Cu are used to compensate for the strength, which results in the reduction of the welding performance of the steel plate and the increase of the cost; in addition, the method of improving the inclusion morphology by controlling the Ca / S ratio greatly increases the difficulty of steelmaking; in addition, when the TMCP process is used to prepare the anti-acid pipeline steel, the inherent characteristics of the method result in the uneven performance of the head and tail of the steel plate and the obvious softening of the welding heat affected zone, which causes hidden troubles for the subsequent welding pipe making and use. Therefore, the present application aims to provide an anti-acid pipeline steel and a manufacturing method thereof, which can not only solve the problems of poor low-temperature drop hammer performance and large strength difference of the same plate of the double anti-pipeline steel, but also can improve the softening problem of the welding heat affected zone.

[0042] Specifically, an anti-acid pipeline steel, by weight percentage, the chemical composition includes C: 0.02-0.06%, Si: 0.10-0.30%, Mn: 0.80-1.10%, Nb: 0.02-0.08%, V: 0.06-0.12%, Ni: 0.20-0.30%, Mo≤0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities; the center segregation of the anti-acid pipeline steel is not higher than C0.5 level, and the center porosity is not higher than 0.5 level.

[0043] When the thickness D of the steel plate of the anti-acid pipeline steel is 8mm≤D<16mm, by weight percentage, the chemical composition of the anti-acid pipeline steel preferably includes C: 0.02-0.04%, Si: 0.10-0.30%, Mn: 0.80-0.90%, Nb: 0.02-0.04%, V: 0.06-0.08%, Ni: 0.20-0.30%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities.

[0044] When the steel plate thickness D of the acid-resistant pipeline steel is 16mm ≤ D < 26mm, the chemical composition of the acid-resistant pipeline steel preferably includes, by weight percentage, C: 0.02 ~ 0.04%, Si: 0.10 ~ 0.30%, Mn: 0.90 ~ 1.0%, Nb: 0.035 ~ 0.055%, V: 0.08 ~ 0.10%, Ni: 0.20 ~ 0.30%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0045] When the steel plate thickness D of the acid-resistant pipeline steel is 26mm ≤ D < 32mm, the chemical composition of the acid-resistant pipeline steel preferably includes, by weight percentage, C: 0.04 ~ 0.06%, Si: 0.10 ~ 0.30%, Mn: 0.90 ~ 1.0%, Nb: 0.055 ~ 0.065%, V: 0.08 ~ 0.10%, Ni: 0.20 ~ 0.30%, Mo: 0.03 ~ 0.06%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0046] When the steel plate thickness D of the acid-resistant pipeline steel is 32mm ≤ D ≤ 40mm, the chemical composition of the acid-resistant pipeline steel preferably includes, by weight percentage, C: 0.04 ~ 0.06%, Si: 0.10 ~ 0.30%, Mn: 1.0 ~ 1.1%, Nb: 0.07 ~ 0.08%, V: 0.10 ~ 0.12%, Ni: 0.20 ~ 0.30%, Mo: 0.05 ~ 0.08%, Al: 0.03 ~ 0.06%, Ca: 0.0005 ~ 0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004 ~ 0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest is Fe and inevitable impurities.

[0047] The above-mentioned acid-resistant pipeline steel has different effects of each component in the steel material, and the effects of the core components are introduced as follows:

[0048] C is one of the most common alloying elements in steel, is a stable austenite element, is conducive to expanding the process window; C can significantly increase the hardness and strength of the steel by forming solid solution and precipitating eutectic structure; too low C will lead to a substantial increase in the cost of pipeline steel strength increment, while too high C will aggravate the center segregation, reduce the acid resistance and drop hammer performance of the pipeline steel; C: 0.02-0.06% is selected in the scheme for cost, acid resistance and other aspects.

[0049] Si can increase the hardness and strength of the steel by forming solid solution and precipitating dispersed particles, thereby improving the tensile strength and impact resistance, and is also an important alloying element for deoxidation in the smelting process; however, too high Si content will lead to difficulty in removing phosphorus from the surface of the steel plate; considering the above reasons, Si: 0.10-0.30% is designed in the scheme.

[0050] Mn and C elements can improve the strength of the steel through solid solution strengthening, and Mn can also reduce the austenite transformation temperature, which is conducive to obtaining fine phase transformation products and improving toughness; however, due to the large variation of Mn solubility in steel, when the temperature decreases during steel solidification, Mn will precipitate from the solution and segregate to the crystal growth center area, leading to weakening of the grain boundary, local mechanical properties and acid resistance; in order to ensure the strength and acid resistance of the steel, Mn: 0.80-1.10% is selected in the scheme.

[0051] V plays an important role in the formula, which can refine the grain, stabilize the austenite, improve the strength and improve the softening problem of the welding heat affected zone, at the same time, the generated VC can become an irreversible trap for hydrogen, which is conducive to improving the acid resistance; VN generated by V and N can play a dragging role at high temperature, effectively refining the austenite grain; however, the precipitation of V during tempering will lead to an increase in yield ratio and increase the cost of alloy; considering the above factors, V: 0.06-0.12% is selected in the scheme.

[0052] Nb is a strong grain refining element, reasonable Nb can increase the stability of austenite, refine the grain, increase the unrecrystallization temperature and effectively improve the process window, which plays an important role in improving the drop hammer performance; compared with using Nb or V alone, the strengthening effect is more obvious when Nb and V are used together; however, too high Nb content will lead to a decrease in impact toughness at the welding joint during large heat input welding, so Nb: 0.02-0.08% is selected in the scheme.

[0053] Mo can improve the hardenability of the material, for low C, low Mn and large thickness acid-resistant pipeline steel, in order to ensure the uniformity of the thickness direction organization, a certain amount of Mo alloy needs to be added; uniform organization is conducive to improving the strength and toughness of the pipeline steel; however, too high Mo will increase the size of the martensite structure and reduce the drop hammer performance; therefore, Mo≤0.08% is selected in the scheme.

[0054] Ni is a stable austenite element, which improves the strength of the steel through solid solution strengthening and can reduce the stacking fault energy to improve the toughness, and can effectively improve the low temperature toughness of the pipeline steel, and is a beneficial element; Ni is a precious metal, and excessive content will greatly increase the total cost; considering the above reasons, the content of Ni in the present application is 0.20-0.30%.

[0055] N is a harmful element, and excessive content is easy to cause stress concentration phenomenon of coarse TiN in continuous casting billet, so as to cause intergranular fracture, and the crack arrest performance of the material will be obviously damaged; N is difficult to completely remove in steelmaking, and when the content is lower than 0.004%, the smelting cost will be greatly increased; considering the above factors, the harm of N can be effectively reduced by adding V to fix nitrogen, and a fine grain effect is also achieved. Therefore, the content of [N] in the present application is 0.004-0.006%.

[0056] Al is a strong deoxidizing element, and high Al content will increase inclusions; on the basis of ensuring the deoxidizing effect, the content of Al should be as low as possible, and the content of Al in the present application is controlled to be 0.03-0.06%.

[0057] Ca mainly plays a role in modifying inclusions, and in order to ensure the modification of inclusions, Ca is added in the present application, and the content of Ca is 0.0005-0.0030%.

[0058] The manufacturing method of the acid-resistant pipeline steel disclosed in the present application will be further specifically introduced in combination with specific examples; in the examples, 180t converter is used for smelting, and the molten steel is 150-160 tons.

[0059] Example 1

[0060] S1: blast furnace smelting, the chemical composition in the molten steel at the end of smelting includes Si: 0.38%, Mn: 0.16%, S: 0.034%, P: 0.08% by weight percentage;

[0061] S2: KR pre-desulfurization, the temperature of the molten steel after desulfurization is 1340℃, and the weight percentage of S in the molten steel after desulfurization is 0.0018%; too high S and too low temperature will both increase the desulfurization time of LF in the subsequent process, and the N content will exceed the standard, so the content of S should be strictly controlled according to the scheme.

[0062] S3: BOF top and bottom combined blowing smelting, scrap steel is added to the molten steel during smelting to adjust the composition of the molten steel; the tapping temperature at the end of smelting is 1633℃, and metal manganese, ferrosilicon and aluminum ingot are added to the molten steel according to weight percentage to adjust the composition of the molten steel and carry out desulfurization of the molten steel; the chemical composition in the molten steel at the end of smelting includes P: 0.008%, S: 0.0022%, C: 0.035% by weight percentage; the oxygen lance position is 1.8m, and the bottom blowing flow is 590m3 / h, the top blowing flow rate is 36500 m 3 / h. Too high tapping temperature will cause excessive oxidation of the alloy, resulting in waste of resources, and too low tapping temperature will increase the burden of LF refining, resulting in power consumption and electrode loss.

[0063] S4: LF refining, argon blowing throughout the refining process to prevent oxidation of the molten steel, and slag melting, slag adjusting, and white slag making during temperature rising, static holding for 15 min after white slag making treatment, and then adding niobium iron to ensure stable recovery of Nb element;

[0064] S5: RH refining, the vacuum degree during RH refining process is controlled to be 1 mBar, the degassing time is 25 min, after adding vanadium iron according to the weight percentage, the net circulation time is ensured to be 10 min; then seamless silicon-calcium wire is added according to the weight percentage, soft stirring is performed for 15 min after wire feeding, the slag surface appears fluctuation during soft stirring process, but the molten steel is not exposed, to prevent oxidation of the molten steel; the chemical composition of the molten steel after the RH refining, according to the weight percentage, includes C: 0.32%, Si: 0.20%, Mn: 0.88%, Nb: 0.035%, V: 0.065%, Ni: 0.25%, Mo: 0.006%, Al: 0.035%, Ca: 0.0018%, P: 0.008%, S: 0.0012%, [N]: 0.005%, [O]: 0.0018%, [H]: 0.0012%, B: 0.0003%, and the rest is Fe and inevitable impurities; the molten steel is 160 tons;

[0065] S6: continuous casting and cold stacking: a continuous casting billet with a thickness of 320 mm is obtained through electromagnetic stirring and light pressing at the end of continuous casting, the center segregation of the continuous casting billet is C0.5 level, the center porosity is 0.5 level, and the A, B, C, and D type inclusions in the continuous casting billet are 0.5 level, 0.5 level, 0 level, and 0 level respectively; the continuous casting billet is treated by hydrogen precipitation through cold stacking, and the treatment time is 72 h;

[0066] S7: furnace charging and heating, the continuous casting billet is heated to 1140℃, and the holding time is 250 min; the NbC and VC are completely solid-solved, and the NbN and VN are not solid-solved during the furnace charging and heating process, the complete solid-solution of NbC and VC can effectively play a precipitation strengthening role, and the unsolved NbN and VN play a dragging role, which, combined with the heating time, prevents the austenite grains from growing too much.

[0067] S8: Single stage rolling in non-recrystallization zone: After the heated continuous casting billet is discharged, the temperature is measured, and when the temperature of the continuous casting billet is not higher than the non-recrystallization temperature, multi-pass hot rolling process is adopted for rough rolling, high-temperature fast rolling and large reduction, the rough rolling temperature is 920°C, and the finish rolling temperature is 822°C; wherein, the rolling is a total of 16 passes, the reduction of the 8th-10th pass and the 12th pass is 27.3%, 25%, 33.3% and 30% respectively, to ensure that the deformation is fully penetrated to the core, the grain flattening height is 5μm after flattening, and the low-temperature drop hammer performance is improved; in addition, the non-recrystallization temperature Tnr is calculated by using an empirical formula, and the calculation result is 937°C; the thickness of the steel plate obtained by rolling is 8mm.

[0068] S9: MULPIC fast water cooling, the steel plate after rolling is subjected to fast water cooling, the cooling speed is 30°C / s, and the final cooling temperature is controlled at 220°C; the microstructure of the steel plate after fast water cooling is the initial structure of ferrite, bainite and martensite-austenite island, and the proportion of each initial structure is 82%, 13% and 5% respectively.

[0069] S10: Heat treatment: the steel plate after water cooling is subjected to heat treatment, the furnace gas temperature of the heating furnace is controlled at 440°C, and the holding time is 30min, and the anti-acid pipeline steel is obtained after the steel plate is discharged and cooled; by heating, the purpose of decomposing the martensite carbide in the martensite-austenite island is achieved, and the merging and growing of bainite laths does not occur.

[0070] Table 1 Chemical composition data of examples 1-4 and comparative examples 1-4

[0071] The continuous casting billets with a thickness of 320mm are first prepared by the component design and smelting process of examples 1-4 and comparative examples 1-4, and then anti-acid pipeline steels with different thicknesses are prepared, wherein the manufacturing processes of examples 2-4 and comparative examples 1-4 are the same as that of example 1, the difference lies in the actual smelting components and process parameters, as shown in tables 2 and 3, the parameters not marked in the tables are the same as those of example 1 and remain unchanged; table 1 above is the chemical composition results of the continuous casting billets prepared in each example. Table 2 is the process parameters of steps S1-S5 before the continuous casting billets are prepared in each example, table 3 is the process parameters of steps S6-S10 for preparing anti-acid pipeline steel from the continuous casting billets in each example, and table 4 is the proportion of each phase of the microstructure of the steel plate after water cooling in each example.

[0072] Table 2 Process parameters for preparing continuous casting billets in examples 1-4 and comparative examples 1-4

[0073] Table 3 Process parameters for preparing anti-acid pipeline steel from continuous casting billets in examples 1-4 and comparative examples 1-4

[0074] Table 4 Proportion of each phase of the microstructure of the steel plate after rolling in examples 1-4 and comparative examples 1-4

[0075] In combination with Table 5, Examples 1-4 and Comparative Examples 1-4 respectively correspond to the influence of changing the content of Mn, C, V and Nb single components on the non-recrystallization temperature Tnr and center porosity and center segregation of the steel material; the continuous casting billets obtained from each example are sampled for macroscopic observation; from Table 4, it can be seen that after increasing the element C or element Mn, the center segregation of the continuous casting billet is aggravated, and the center porosity is 0.5 level; the Nb element has a greater influence on the non-recrystallization temperature, and other elements have little influence.

[0076] Table 5 is the non-recrystallization temperature, center segregation level and inclusion data of Examples 1-4 and Comparative Examples 1-4

[0077] The performance of the steel plates obtained from the above Examples 1-4 and Comparative Examples 1-4 is further tested in combination with double resistance tests and the like; the standards and test results are shown in Table 6 as follows:

[0078] Double resistance test: according to NACE TM0284 standard, HIC resistance test is carried out, the test solution is NACE TM0284-A solution, no stress, test for 96 hours, crack length sensitivity CLR% = 0, crack thickness sensitivity CTR% = 0, crack sensitivity CSR% = 0; according to NACE TM0177 standard, SSCC resistance experiment is carried out in A solution by method B, the load is 90% of the minimum nominal yield strength, and there is no crack.

[0079] Vickers hardness test: test standard ASTM E92-17, HV10 test.

[0080] Tensile test and charpy impact test: test standard ASTM A370-20.

[0081] Drop weight tear test (DWTT): API RP 5L3-2014, full thickness sample.

[0082] Physical performance: yield strength ≥ 460 MPa, tensile strength ≥ 550 MPa, elongation A50 after fracture ≥ 40%; DWTT toughness tear area at -40℃ ≥ 85%.

[0083] Crack length sensitivity (CLR): 0, crack thickness sensitivity (CTR): 0, crack sensitivity (CSR): 0, SSC resistance performance: no crack.

[0084] Table 6 is the performance data of Examples 1-4 and Comparative Examples 1-4 of the acid-resistant pipeline steel

[0085] From Table 6, it can be found from Comparative Examples 1 and 2 that the increase of C and Mn contents results in the decrease of the HIC resistance of the steel plate, and the length crack sensitive rate of Comparative Example 2 even reaches 25.27%; Comparative Example 3 does not add V element, and the softening of the heat affected zone is obvious; Comparative Example 4 does not add Nb element, and the low-temperature drop performance is obviously decreased.

[0086] Figure 1 is the Vickers hardness test of the acid pipeline steel samples of Example 3 and Comparative Example 3 after welding according to ASTM E92; as can be seen from Figure 1, the compositions of the samples of Example 3 and Comparative Example 3 are similar, except that the composition of Example 3 increases the V element by 0.085%, and the softening of the heat affected zone of the sample of Example 3 after welding is obviously weaker than that of the sample of Comparative Example 3.

[0087] Example 5 is produced in the same heat as Example 4, and the smelting process and composition are the same, except that the thickness of the steel plate is 35 mm, and the rolling process also has some differences; Comparative Examples 5-8 and Example 5 are divided from the same steel plate, except for the heat treatment temperature and time, and whether heat treatment is performed; the process parameters are shown in Table 7, and the performance parameters are shown in Table 8.

[0088] Table 7 Process parameters for producing acid pipeline steel from continuous casting billets of Example 5 and Comparative Examples 5-7

[0089] Table 8 Performance data of acid pipeline steel of Example 5 and Comparative Examples 5-8

[0090] In combination with the process data in Table 7 and the performance data in Table 8, the steel plate of Comparative Example 6 is in the TMCP state, and the yield strength is only 415 MPa; after tempering at 460℃ for 30 min, the yield strength of Example 5 increases to 475 MPa, and the tensile strength does not decrease significantly, which is 580 MPa. With the extension of the heat treatment temperature, the tensile strength of Comparative Example 5 decreases to 520 MPa; the tensile strength decreases to 520 MPa; with the decrease of the heat treatment temperature, the tensile strength of Comparative Example 7 decreases slightly; with the increase of the heat treatment temperature, the tensile and yield strengths of Comparative Example 8 are obviously decreased compared with those of Example 5. The double resistance performance is as follows: crack length sensitive rate (CLR): 0, crack thickness sensitive rate (CTR): 0, crack sensitive rate (CSR): 0, and SSC resistance performance: no crack.

[0091] In combination with the above data, when the TMCP process is used to control the performance of the steel plate, the strength difference of the head, middle and tail of the steel plate exceeds 50 MPa, but after the preparation process disclosed by the present application, the performance stability of the steel plate is obviously improved, and the strength difference of the head, middle and tail is controlled within 30 MPa.

[0092] While the application has been described by way of example with reference to preferred embodiments, it is to be understood that this application is not limited to the embodiments disclosed, but is intended to cover modifications and variations within the spirit and scope of the application. Therefore, the scope of the application is defined not by the detailed description of the application but by the following claims, wherein reference to an alternative embodiment includes reference to all features describing that embodiment.

Claims

1. A method of manufacturing an anti-acid line pipe steel, characterized by, It comprises the following steps: S1: blast furnace smelting, the chemical composition in the molten steel at the end of smelting comprises Si: 0.30-0.60%, Mn≤0.40%, S≤0.040%, P≤0.120% by weight percentage; S2: KR pre-desulphurization, the temperature of the molten steel after desulphurization is not less than 1300 DEG C, and the weight percentage of chemical composition S in the molten steel after desulphurization is not more than 0.002%; S3: BOF top and bottom combined blowing smelting, scrap steel is added to molten steel to adjust the composition of molten steel during smelting; the tapping temperature at the end of smelting is 1640℃±30℃, metal manganese, ferrosilicon, aluminum ingot are added according to the weight percentage to adjust the composition of molten steel and to deoxidize molten steel when tapping, the chemical composition of molten steel at the end of smelting includes P≤0.010%, S≤0.005%, 0.02%≤C≤0.05% according to the weight percentage; the oxygen lance position is 1.5-1.8m, the bottom blowing flow is 574m 3 / h-604m 3 / h, the top blowing flow is 35000m 3 / h-38000m 3 / h; S4: LF refining, argon is blown throughout the refining process to prevent oxidation of the molten steel, and slag is melted and adjusted during the temperature rising process, white slag treatment is carried out, and after the white slag treatment, niobium iron is added after static keeping for 10-20 min to ensure stable recovery of Nb element; S5: RH refining, the vacuum degree during the RH refining process is controlled to be less than 2 mBar, the degassing time is greater than 15 min, after adding vanadium iron by weight percentage, the net circulation time is ensured to be 5-10 min; then seamless silicon-calcium wire is added by weight percentage, soft stirring is carried out for 12-18 min after wire feeding, the slag surface appears fluctuation during the soft stirring process, but the molten steel is not exposed to prevent oxidation of the molten steel; the chemical composition of the molten steel after the RH refining comprises C: 0.02-0.06%, Si: 0.10-0.30%, Mn: 0.80-1.10%, Nb: 0.02-0.08%, V: 0.06-0.12%, Ni: 0.20-0.30%, Mo≤0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008% by weight percentage, and the rest is Fe and inevitable impurities; S6: continuous casting billet stack cooling: a continuous casting billet with a thickness of not less than 320 mm is obtained through electromagnetic stirring and light pressing at the end of continuous casting, and the continuous casting billet is subjected to hydrogen precipitation treatment during stack slow cooling, and the treatment time is not less than 72 h before the stack is disassembled; S7: furnace charging and heating, the heated continuous casting billet is heated to 1160 DEG C±20 DEG C, and the holding time is 250-300 min; S8: single-stage rolling in the unrecrystallization zone: the heated continuous casting billet is discharged from the furnace to measure the temperature, and when the temperature of the continuous casting billet is not higher than the unrecrystallization temperature, the continuous casting billet is rolled by using a multi-pass hot rolling process, high-temperature fast rolling is carried out with large reduction, and the finish rolling temperature is 800-840 DEG C; wherein, the reduction of at least three passes during rolling is not less than 22%; S9: MULPIC rapid water cooling, the rolled steel plate is subjected to rapid water cooling, the cooling speed is 25-35 DEG C / s, and the final cooling temperature is controlled to be not more than 300 DEG C; S10: heat treatment: the steel plate after water cooling is subjected to heat treatment, the furnace gas temperature of the heating furnace is controlled to be 450±10 DEG C, and the holding time is 30 min; the steel plate is cooled after being discharged from the furnace to obtain an acid-resistant pipeline steel.

2. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, When the steel plate thickness D of the acid-resistant pipeline steel prepared in step S10 is 8mm ≤ D < 16mm, the chemical composition of the molten steel after RH refining described in step S5 is controlled to include, in terms of weight percentage, C: 0.02-0.04%, Si: 0.10-0.30%, Mn: 0.80-0.90%, Nb: 0.02-0.04%, V: 0.06-0.08%, Ni: 0.20-0.30%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004-0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest Fe and inevitable impurities.

3. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, When the steel plate thickness D of the acid-resistant pipeline steel prepared in step S10 is 8mm ≤ D < 16mm, the chemical composition of the molten steel after RH refining described in step S5 is controlled to include, in terms of weight percentage, C: 0.02-0.04%, Si: 0.10-0.30%, Mn: 0.80-0.90%, Nb: 0.02-0.04%, V: 0.06-0.08%, Ni: 0.20-0.30%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004-0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest Fe and inevitable impurities.

4. The method of producing an anti-acid line steel according to claim 1, characterized by, When the steel plate thickness D of the acid-resistant pipeline steel prepared in step S10 is 8mm ≤ D < 16mm, the chemical composition of the molten steel after RH refining described in step S5 is controlled to include, in terms of weight percentage, C: 0.02-0.04%, Si: 0.10-0.30%, Mn: 0.80-0.90%, Nb: 0.02-0.04%, V: 0.06-0.08%, Ni: 0.20-0.30%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P ≤ 0.008%, S ≤ 0.002%, [N]: 0.004-0.006%, [O] ≤ 0.002%, [H] ≤ 0.0015%, B ≤ 0.0008%, and the rest Fe and inevitable impurities.

5. The method of producing an anti-acid line steel according to claim 1, characterized by, When the thickness D of the anti-acid pipeline steel plate prepared in step S10 is 32mm≤D≤40mm, the chemical composition of the molten steel after RH refining in step S5 is controlled to include, in terms of percentage by weight, C: 0.04-0.06%, Si: 0.10-0.30%, Mn: 1.0-1.1%, Nb: 0.07-0.08%, V: 0.10-0.12%, Ni: 0.20-0.30%, Mo: 0.05-0.08%, Al: 0.03-0.06%, Ca: 0.0005-0.0030%, P≤0.008%, S≤0.002%, [N]: 0.004-0.006%, [O]≤0.002%, [H]≤0.0015%, B≤0.0008%, and the rest is Fe and inevitable impurities.

6. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, In step S6, the center segregation of the continuous casting billet is not higher than C0.5 level, the center porosity is not higher than 0.5 level, and the A, B, C and D type inclusions in the continuous casting billet are all not higher than 1 level.

7. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, In step S8, the non-recrystallization temperature Tnr is calculated by using an empirical formula, specifically: Tnr(℃)=887+464*[C]+(6445*[Nb]-644*sqrt[Nb])+(1732*[V]-230*sqrt[V])+890*[Ti])+363*[Al]-357*[Si], [C], [Nb], [V], [Ti], [Al] and [Si] are the percentages by weight of the elements in the anti-acid pipeline steel, and sqrt is the arithmetic square root function; The flattened grain height in the steel plate after rolling in step S8 is not more than 5μm.

8. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, After the rapid water cooling in step S9, the microstructure of the steel plate is the initial structure of ferrite, bainite and martensite-austenite islands, and the proportions of the initial structures are 75%-85%, 10%-25% and 5%-8% respectively.

9. The method of manufacturing an anti-acid line pipe steel according to claim 1, characterized by, The strength difference of the head, middle and tail of the anti-acid pipeline steel prepared in step S10 is not more than 30MPa.

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