Ultrahigh-strength HIC-corrosion-resistant X100 pipeline steel coil plate and manufacturing method thereof

Abstract

The ultrahigh-strength hydrogen sulfide corrosion resistant X100 pipeline steel coil plate comprises the following chemical components in percentage by weight: 0.03 to 0.07 percent of C, 0.1 to 0.3 percent of Si, 1.4 to 1.75 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.001 percent of S, 0.01 to 0.03 percent of Ti, 0.08 to 0.11 percent of Nb, 0.2 to 0.4 percent of Cr, 0.2 to 0.5 percent of Mo, 0.5 to 0.9 percent of Ni, 0.25 to 0.50 percent of W, more than or equal to 1.15 percent of Ni + Cr + W, more than or equal to 1.00 percent of Ni / W, more than or equal to 1.65 percent of Ni / Cr, 0.02 to 0.05 percent of Als, 0.002 to 0.006 percent of Ca, less than or equal to 0.008 percent of N and the balance of Fe and inevitable elements. And a low-carbon high-niobium microalloy design is adopted, so that the HIC resistance is good.

Description

Technical Field

[0001] The present invention relates to the manufacture of hot-rolled coil plates of pipeline steel for oil and gas transportation, and particularly to an ultra-high strength X100 pipeline steel and its manufacturing method, the HIC index of which for resisting hydrogen sulfide corrosion satisfies CTR < 5%, CLR < 15%, and CSR < 1.5%. Background Art

[0002] At present, pipeline transportation has become the most economical and safest way for transporting oil and natural gas recognized in the world today. To improve transportation efficiency and reduce project investment, the development of pipeline steel for long-distance oil and gas transportation towards high steel grades has become a trend.

[0003] With the rapid development of China's social economy, the demand for energy is increasing continuously, the contradiction between energy supply and demand is becoming increasingly prominent, and the development of high-sulfur oil and natural gas containing acidic media has been included in China's energy development agenda. Therefore, the demand for corrosion-resistant pipeline steel used in acidic environments is showing a rapid growth trend.

[0004] When X100 pipeline steel is used to transport acidic oil and gas, H2S is in contact with the inside of the pipeline. Hydrogen sulfide (H2S) is one of the most corrosive harmful media in oil and natural gas, and its main corrosion and damage forms are hydrogen-induced cracking (HIC) and sulfide stress corrosion (SSCC). Hydrogen-induced cracking can cause the pipeline to crack suddenly without any obvious signs, and its destructiveness and harmfulness are extremely great. Therefore, to ensure the safety and normal operation of oil and gas transportation, the pipeline must have good corrosion resistance.

[0005] At present, there is no report on ultra-high strength HIC-resistant X100 pipeline steel coil plates. The following briefly introduces the patent documents relatively close to the present invention:

[0006] 1) Chinese Patent CN102162072A, an ultra-high strength X100 pipeline steel and its production method. The composition contains C: 0.02% - 0.08%, Si ≤ 0.6%, Mn: 1.50% - 2.50%, P ≤ 0.015%, S ≤ 0.0030%, Nb: 0.04% - 0.10%, V ≤ 0.10%, Ti: 0.005% - 0.03%, Alt ≤ 0.06%, N ≤ 0.01%, Mo: 0.2% - 0.6%, Cu ≤ 0.5%, Ni: 0.1% - 1.0%, Cr: 0.1% - 1.0%. This invention is a production method of ultra-high strength X100 disclosed by Shagang. The product is rolled in the austenite recrystallization zone and the non-recrystallization zone, and the finish rolling temperature and finish cooling temperature are controlled to produce X100 grade hot-rolled plates. This invention is only ordinary X100 pipeline steel and does not have HIC resistance.

[0007] 2) Chinese Patent CN102304667A, an X100 pipeline steel plate with excellent low-temperature toughness and its preparation method. The composition contains C: 0.03% - 0.07%, Si: 0.10% - 0.45%, Mn: 1.50% - 1.79%, P ≤ 0.012%, S ≤ 0.0030%, Alt: 0.02% - 0.06%, Nb: 0.05% - 0.10%, V: 0.02% - 0.08%, Ti: 0.005% - 0.040%, Ni: 0.2% - 0.5%, Mo: 0.2% - 0.5%, N ≤ 0.008%. This invention is a production method of an X100 steel plate with excellent low-temperature toughness disclosed by Shougang, including processes of hot metal desulfurization, converter smelting, secondary refining, continuous casting, heating, rolling, cooling, and straightening. This invention is only an ordinary X100 pipeline steel and does not have HIC resistance performance. Summary of the Invention

[0008] Aiming at the technical problems that the currently produced X100 pipeline steel coils do not have the performance of resisting hydrogen sulfide corrosion, cannot adapt to acidic service environments, and have poor safety, the purpose of this invention is to provide an ultra-high-strength X100 grade pipeline steel coil and its manufacturing method, with a yield strength above 700 MPa, a tensile strength above 760 MPa, and HIC resistance indexes meeting CTR < 5%, CLR < 15%, CSR < 1.5%, as a pipeline steel coil for oil and gas transportation. This invention adopts a low-carbon and high-niobium microalloy design, can be hot-rolled at high temperatures, and has a simple manufacturing process; Cr, Ni, and W jointly improve the strength and HIC resistance performance; Mo improves the performance of the coil, making it more uniform throughout the coil, and has higher safety in pipeline engineering.

[0009] One of the technical solutions of this invention is to propose an ultra-high-strength hydrogen sulfide corrosion-resistant X100 pipeline steel coil. Its chemical composition by weight percentage is: C: 0.03% - 0.07%, Si: 0.1% - 0.3%, Mn: 1.4% - 1.75%, P: ≤ 0.01%, S: ≤ 0.001%, Ti: 0.01% - 0.03%, Nb: 0.08% - 0.11%, Cr: 0.2% - 0.4%, Mo: 0.2% - 0.5%, Ni: 0.5% - 0.9%, W: 0.25% - 0.50%, Ni + Cr + W: ≥ 1.15%, Ni / W: ≥ 1.00, Ni / Cr: ≥ 1.65, Als: 0.02% - 0.05%, Ca: 0.002% - 0.006%, N: ≤ 0.008%, and the rest are Fe and inevitable elements.

[0010] Compared with the prior art, the present invention adopts a low-carbon high-niobium microalloy design, with good HIC resistance; it can be hot-rolled at high temperature, and the manufacturing process is simple; Cr, Ni, and W jointly improve strength and HIC resistance; Mo improves the properties of the plate coil, making it more uniform throughout the coil, and has higher safety in pipeline engineering.

[0011] C: It is a carbide-forming element, the most effective element to ensure strength, which can improve hardenability and ensure the strength and hardness of the material. Carbon significantly improves strength through solid-solution strengthening and phase transformation strengthening. Only by ensuring sufficient carbon can sufficient acicular ferrite and martensite-austenite (M-A) structures be formed. If the carbon content is too low, the strength and hardness of the material cannot be guaranteed; if the content is too high, it will affect the weldability, plasticity, and impact toughness of the product. The optimal range is 0.03% - 0.07%.

[0012] Si: It can dissolve into ferrite and austenite, playing a certain role in solid-solution strengthening, significantly improving the hardness and strength of the steel. At the same time, it promotes the coarsening of ferrite grains, reduces the effect of crystal anisotropy, and improves HIC resistance. However, if the content is too high, it will significantly reduce the plasticity and toughness of the steel. The optimal range is 0.1% - 0.3%.

[0013] Mn: Manganese has a solid-solution strengthening effect, can also increase the stability of austenite, is beneficial to improving hardenability, and effectively guarantees the strength of the steel. Manganese can compensate for the strength decline caused by the decrease in carbon content, and is the most important and economical strengthening element. Manganese can shift the C curve to the right, promote the transformation of bainite, is conducive to the formation of acicular ferrite, significantly improving strength and HIC resistance, and the toughness does not decrease significantly. However, if the manganese content is too large, it can increase the tendency of center segregation in continuous casting billets, increase the banded structure in the steel plate, increase the brittleness of the steel plate, and reduce plasticity. The optimal range is 1.4% - 1.75%.

[0014] P, S, N: They are inevitable impurity elements in steel, and the lower the better, but too low requirements will increase production costs. In the present invention, P ≤ 0.01%, S ≤ 0.001%, and N ≤ 0.008%.

[0015] Ti: Titanium is a strong nitrogen-fixing element. When about 0.015% of Ti is added, fine and high-temperature stable TiN precipitation phases can be formed during slab continuous casting. These fine TiN precipitation phases can effectively prevent the growth of austenite grains during the heating process of continuous casting billets. At the same time, it has an obvious effect on improving the toughness of the heat-affected zone during steel welding. A small amount of precipitated TiC produces a strong precipitation strengthening effect, which can ensure that the grains do not grow significantly during the subsequent normalizing heat treatment of pipe making, thus ensuring the uniformity of the steel pipe properties and the HIC resistance of the whole pipe. However, if the content is too high, the effect is not obvious, and large particle inclusions are easily formed. The optimal range is 0.01% - 0.03%.

[0016] Nb: Niobium is one of the important elements in low-carbon microalloyed steel. Niobium can significantly increase the austenite recrystallization temperature of steel, expand the range of the non-recrystallized zone, and also inhibit the growth of austenite grains, showing significant effects of fine grain strengthening and precipitation strengthening. By adopting a low carbon content and increasing the niobium content simultaneously, during the TMCP rolling process of steel, the austenite recrystallization temperature can be increased by using dissolved niobium, enabling controlled rolling to be carried out at a higher temperature, thereby reducing the mill load, especially reducing the rolling difficulty of ultra-high strength steel such as X100. Utilizing the influence of dissolved niobium on phase transformation to promote the formation of acicular ferrite or low-carbon bainite, achieving excellent high strength and HIC resistance performance. If the niobium content is low, the high-temperature rolling process cannot be realized, and the grain refinement effect is limited. Its optimal range is 0.08% - 0.11%.

[0017] Cr: Chromium can increase strength through solid solution strengthening. Cr can dissolve into the solid solution like Mn, improving the hardenability of steel and playing a role in increasing strength. After the Cr element dissolves into austenite, it increases the stability of supercooled austenite, shifts the C curve to the right, promotes the formation of supercooled structures such as low-carbon bainite and martensite-austenite (M-A), and improves the strength and hardness of the steel. When Cr is combined with Ni and W, the corrosion resistance can also be improved. However, too high a chromium content will significantly increase the brittle transition temperature of the steel, reduce the elongation rate, and easily form coarse carbides, leading to deterioration of toughness. The appropriate range is 0.2% - 0.4%.

[0018] Mo: Molybdenum improves the strength of the base metal by increasing the hardenability of steel. Since in order to smoothly coil the head of the steel strip for pipeline steel, generally less water is sprayed at the head during the cooling stage, and its coiling temperature is generally higher than that of the middle and tail parts, the strength and toughness of the head are prone to be lower than those of the middle and tail parts. The Mo element effectively improves the hardenability of the steel strip, enabling the head high-temperature zone to also obtain the same mixed structure of acicular ferrite (AF) and martensite-austenite (M-A) as the middle and tail parts, ensuring the stability of the through-strip performance of the steel strip. Mo is an element that expands the γ phase region, can reduce the γ→α phase transformation temperature of steel, and with the increase of Mo content, the phase transformation temperature gradually decreases, which can effectively promote bainite transformation and play a role in phase transformation strengthening, obtaining finer lath bainite, granular bainite and martensite-austenite (M-A) phase transformation structures. Mo also has a certain effect on resisting acid corrosion. Too high a content of Mo increases the alloy cost and is detrimental to plasticity and toughness. Its optimal range is 0.2% - 0.5%.

[0019] Ni: Nickel can strongly increase the strength of steel and always maintain extremely high low-temperature toughness. Nickel can form a solid solution, which is beneficial to improving the hardenability of steel, can reduce the critical point and increase the stability of austenite. When it is combined with Cr, W or C, Mo, the hardenability is improved more significantly. Nickel can also significantly improve the HIC resistance of steel. However, if the content is too high, the alloy cost is high. Its optimal range is 0.5% - 0.9%.

[0020] W: Tungsten can form carbides in steel, and partially dissolve into iron to form solid solution. The effect of tungsten on the hardenability of steel is not as strong as that of molybdenum and chromium, but its combination with Ni can significantly improve the hardenability, thereby increasing the strength. With appropriate addition amount, tungsten can improve the corrosion resistance and toughness of steel, increase its fracture toughness, and improve the service safety of steel. However, too much tungsten content will cause a significant decrease in the toughness of steel, and the appropriate range is 0.25% - 0.50%.

[0021] Als: Aluminum is a commonly used deoxidizer. Adding a small amount of aluminum to steel can refine the grain, improve the strength and impact toughness, and also improve the corrosion resistance of steel, especially when used in combination with elements such as Mo, Si, and Cr, the effect is better. The Als content of the present invention is 0.02% - 0.05%.

[0022] Ca: Added during the secondary refining process, mainly to modify the inclusions to achieve the purpose of spheroidizing the inclusions and ensuring the toughness of steel. Adding calcium to steel can improve the HIC resistance and lamellar tearing resistance. Excessive content will form large particle inclusions, and its optimal range is 0.002% - 0.006%.

[0023] The thickness of the coil plate of the present invention is 14 - 20 mm.

[0024] The final mechanical properties of the coil plate of the present invention: the yield strength is above 700 MPa, preferably 700 - 730 MPa; the tensile strength is above 760 MPa, preferably 780 - 820 MPa; the yield ratio ≤ 0.91, preferably 0.89 - 0.91; the elongation ≥ 20%, preferably 20% - 24%; the impact energy at -20 °C ≥ 240 J, preferably 240 - 280 J; the DWTT drop weight at -10 °C ≥ 95%, preferably 95% - 100%; the HIC resistance index meets CTR < 5%, CLR < 15%, CSR < 1.5%, CTR < 5%, preferably 0 - 4%, CLR < 15%, preferably 1% - 8%, CSR < 1.5%, preferably 0.3% - 1.2%, belonging to the X100 steel grade specified in API Spec 5L. API Spec 5L stipulates that for the X100 grade, the yield strength is 690 - 840 MPa, the tensile strength is 760 - 990 MPa, the elongation ≥ 14%, the yield ratio ≤ 0.97, the average impact energy Akv at 0 °C ≥ 54 J, and the average drop weight (DWTT) at 0 °C ≥ 85%.

[0025] The final microstructure of the coil plate of the present invention is a mixed microstructure of acicular ferrite (AF) and martensite - retained austenite (M - A). By volume percentage, the proportion of acicular ferrite is 97% - 99%, and the proportion of martensite - retained austenite (M - A) is 1% - 3%.

[0026] The ultra-high-strength hydrogen sulfide corrosion-resistant X100 pipeline steel coil plate of the present invention is a hot-rolled coil plate of ultra-high-strength hydrogen sulfide corrosion-resistant X100 pipeline steel. The yield strength can reach above 700 MPa, the tensile strength is above 760 MPa, and the anti-HIC indexes meet CTR < 5%, CLR < 15%, and CSR < 1.5%.

[0027] The second technical solution of the present invention is to propose a manufacturing method for an ultra-high-strength hydrogen sulfide corrosion-resistant X100 pipeline steel coil plate, which includes the following steps:

[0028] 1) Smelting and continuous casting process: Molten iron pretreatment, converter smelting, secondary refining (including LF furnace refining and RH furnace refining), light desulfurization treatment in the LF furnace to control S: ≤ 0.003% and calcium treatment to control the inclusion morphology and improve the ductility, toughness, and cold bending performance of the steel; the molten steel is continuously cast into a slab, and electromagnetic stirring or dynamic soft reduction of 6 - 10 mm is adopted, and the thickness of the continuously cast slab is 170 - 230 mm.

[0029] 2) Rolling, cooling, and coiling process: The continuously cast slab is heated in a heating furnace to 1150 - 1260 °C, and then thermo-mechanical rolling is adopted. This temperature range enables the full solution of alloys such as Nb, Mo, Cr, and Ni, and at the same time is conducive to the large precipitation of Ti, refining the austenite grain size, which is beneficial to improving the yield and tensile strength. The finishing rolling temperature of the rough rolling is 1030 - 1080 °C, and the reduction rate per pass is greater than 20%. This temperature is conducive to the precipitation of TiC, hindering the growth of austenite grains, refining the grains, and increasing the strength; the starting rolling temperature of the finish rolling is 930 - 1000 °C, and the finishing rolling temperature is 830 - 880 °C, and the cumulative reduction rate is 60% - 65%. The temperature range of the finishing rolling is conducive to the precipitation of Nb, refining the grain size, and improving the strength, toughness, and anti-HIC performance; adopting a large reduction rate can generate a large number of dislocations and twins, playing a role in dislocation strengthening, and significantly improving the yield strength and tensile strength. After rolling, laminar water cooling is adopted, the final cooling temperature is 400 - 500 °C, the cooling rate is 20 - 45 °C / s, and coiling is carried out after cooling. This final cooling temperature and cooling rate are conducive to obtaining a mixed structure of uniformly sized acicular ferrite and martensite-austenite (M-A), which has good low-temperature toughness and anti-HIC performance.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1) Adopting a low-carbon high-niobium microalloy design, with a low C content and slight segregation, which is beneficial to improving the corrosion resistance performance. At the same time, it is conducive to the full precipitation of the Nb element. The fine grain strengthening effect of Nb is significant and more uniform, and the anti-HIC performance is good;

[0032] 2) It can realize the high-temperature HTP rolling process, with a small load on the rolling mill equipment and a simple manufacturing process;

[0033] 3) Add Cr, Ni, and W jointly, and control Ni + Cr + W ≥ 1.15%, Ni / W ≥ 1.00, Ni / Cr ≥ 1.65 to improve strength and HIC resistance performance;

[0034] 4) Mo improves the performance of the coil plate, and the through-thickness performance is more uniform. The yield strength fluctuation range is less than 30 MPa, which has higher safety in pipeline engineering. Description of the Drawings

[0035] Figure 1 It is the microstructural diagram of the ultra-high strength HIC-resistant corrosion X100 pipeline steel coil plate prepared in Example 7 of the present invention. The volume percentages of AF and M-A are 98% and 2% respectively. Detailed Implementation Modes

[0036] The following non-limiting examples can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0037] Examples 1 - 8

[0038] In Examples 1 - 8, the chemical compositions of the steel are shown in Table 1, the heating, rolling, and cooling process parameters in the manufacturing method are shown in Table 2, and the mechanical properties and microstructure test results of the prepared steel are shown in Table 3.

[0039] Table 1 Chemical Compositions of Examples wt%

[0040]

[0041] Table 2 Heating, Rolling, and Cooling Processes

[0042]

[0043]

[0044] Table 3 Mechanical Properties and Microstructure Proportions

[0045]

[0046] In the table, the yield strength fluctuation value is the difference between the maximum and minimum values of the yield strength among the head, middle, and tail of the coil plate.

[0047] As can be seen from Tables 1 - 3, by using the composition design and rolling and coiling processes of the present invention, the produced ultra-high strength HIC-resistant corrosion pipeline steel coil plates meet the mechanical property requirements of API SPEC 5L standard X100 and have good HIC resistance performance.

Claims

1. An ultra-high strength hydrogen sulfide corrosion resistant X100 pipeline steel coil, characterized in that: Its chemical composition by weight percentage is: C: 0.03%-0.07%, Si: 0.1%-0.3%, Mn: 1.4%-1.75%, P: ≤0.01%, S: ≤0.001%, Ti: 0.01%-0.03%, Nb: 0.08%-0.11%, Cr: 0.2%-0.4%, Mo: 0.2%-0.5%, Ni: 0.5%-0.9%, W: 0.25%-0.50%, Ni+Cr+W: ≥1.15%, Ni / W: ≥1.00, Ni / Cr: ≥1.65, Als: 0.02%-0.05%, Ca: 0.002%-0.006%, N: ≤0.008%, and the rest are Fe and unavoidable elements.

2. The ultra-high strength X100 pipeline steel coil according to claim 1 is characterized in that: The thickness of the rolled plate is 14-20mm.

3. The ultra-high strength hydrogen sulfide corrosion resistant X100 pipeline steel coil according to claim 1 is characterized in that: The yield strength of the coil is above 700MPa, the tensile strength is above 760MPa, the yield strength ratio is ≤0.91, the elongation is ≥20%, the impact energy at -20℃ is ≥240J, and the DWTT drop hammer at -10℃ is ≥95%; the anti-HIC index meets CTR<5%, CLR<15%, and CSR<1.5%.

4. The ultra-high strength hydrogen sulfide corrosion resistant X100 pipeline steel coil according to claim 1 is characterized in that: The microstructure of the rolled plate is a mixed microstructure of acicular ferrite and martensite-parallel. Calculated by volume percentage, the acicular ferrite is 97%-99%, and the martensite-parallel is 1%-3%.

5. The method for manufacturing the ultra-high strength hydrogen sulfide corrosion resistant X100 pipeline steel coil according to any one of claims 1 to 4, characterized in that: The steps include: 1) Smelting and continuous casting process: the molten iron is pre-treated, smelted in a converter, refined outside the furnace, and continuously cast into slabs; 2) Rolling, cooling and coiling process: The continuous casting slab is heated to 1150-1260°C in a heating furnace, and then thermomechanical rolling is adopted, the rough rolling and final rolling temperature is 1030-1080°C, the finishing rolling start temperature is 930-1000°C, the final rolling temperature is 830-880°C, and the cumulative reduction rate is 60%-65%; after rolling, laminar water cooling is adopted, the final cooling temperature is 400-500°C, the cooling rate is 20-45°C / s, and the coiling is carried out after cooling.

6. The manufacturing method according to claim 5, characterized in that: In step 1), the refining outside the furnace includes LF refining and RH refining. The LF refining adopts light desulfurization treatment to control S: ≤ 0.003% and performs calcium treatment.

7. The manufacturing method according to claim 5, characterized in that: In step 1), the continuous casting adopts electromagnetic stirring or dynamic soft pressure to reduce 6-10 mm, and the thickness of the continuous casting slab is 170-230 mm.

8. The manufacturing method according to claim 5, characterized in that: In step 2), the reduction ratio of the rough rolling pass is greater than 20%.

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