A pipeline steel with a yield strength of 290 MPa and resistance to microbial corrosion and carbon dioxide corrosion and a production method thereof

Abstract

The invention discloses a pipeline steel with a yield strength of 290MPa and resistance to microbial corrosion and carbon dioxide corrosion and a production method thereof. The chemical composition and weight percentage of the pipeline steel are as follows: C: 0.031-0.059%, Si≤0.29%, Mn: 0.51-0.59%, P≤0.010%, S≤0.0015%, Cr: 3.1-3.5%, Cu: 0.31-0.35%, Nb≤0.020%, Ti: 0.010-0.020%, Ca: 0.0010-0.0020%, V, Mo and Ni are not contained, and the rest is Fe and inevitable inclusions; the pipeline steel has excellent low-temperature toughness, excellent resistance to microbial corrosion and resistance to carbon dioxide corrosion, and can adapt to a complex service environment where a variety of corrosive media coexist.

Description

Technical Field

[0001] The invention belongs to the technical field of pipeline steels, and in particular relates to a 290MPa-grade microbial corrosion-resistant and carbon dioxide corrosion-resistant pipeline steel and a production method thereof. Background Art

[0002] Microorganisms attach to the surface of materials and form biofilms. The bacteria in the biofilms can obtain electrons from metals through direct or indirect electron transfer, thus leading to the occurrence of microbial corrosion. Biofilms are the main factor leading to microbial corrosion. The most prominent hazard of microbial corrosion is the local corrosion of materials, which accelerates the progression of corrosion and expands the severity of the hazard.

[0003] In the service environment of pipelines, there is not only microbial corrosion, but also CO2 corrosion, which accelerates the corrosion failure process of gathering and transportation pipelines. Traditional pipeline steel materials based on carbon, manganese and micro-alloy elements cannot resist the overall corrosion and local pitting corrosion of carbon dioxide. Although stainless steel has good resistance to carbon dioxide corrosion, it is expensive.

[0004] In the prior art, for high-strength pipeline steel, the corrosion resistance of the pipeline steel is often improved by adding a high content of alloy elements with corrosion-resistant properties thereto.

[0005] For example, Chinese patent CN109234616A discloses "a kind of microbial corrosion resistant pipeline steel and its preparation method", whose chemical composition and weight percentage are: C: 0.02-0.08%, Si: 0.10-0.50%, Mn: 0.50-1.20%, P≤0.030%, S≤0.020%, Cu: 0.10-1.00%, Ga: 0.10-0.80%, Ce: 0.01-0.20%. This patent realizes the microbial corrosion resistance of the material by adding Cu, Ga and Ce elements in combination, but its yield strength is above 400MPa.

[0006] Chinese patent CN110205541A discloses "a X65 grade high-toughness microbial corrosion resistant pipeline steel and its preparation method", with chemical composition: C: 0.02-0.035%; Si≤0.2%; Mn≤0.10%; Cu: 1.0-2.0%; Mo: 0.10-0.20%; Nb: 0.04-0.045%; Ti: 0.01-0.02%; S≤0.0015%; P≤0.0050%; the balance is Fe. The pipeline steel is prepared by a method of slow cooling after hot rolling, so that the Cu dissolved in the steel undergoes natural aging precipitation, achieving the purpose of better toughness and microbial corrosion resistance, but the Cu content in the patent is relatively high, and the yield strength is above 500MPa.

[0007] Chinese patent CN 102409253 A discloses a weathering steel for high corrosion resistance and high strength railway vehicles and its manufacturing method, the chemical composition mass percentage content (wt%) is: C: 0.015% to 0.065%, Si: 0.10% to 0.50%, Mn: 0.20% to 0.60%, P: 0.015% or less, S: 0.008% or less, Ti: 0.01% to 0.08%, Nb: 0.005% to 0.05%, Cr: 2.15% to 4.0%, Ni: 0.12% to 1.0%, Cu: 0.20% to 0.60%, Al: 0.01% to 0.05%, the balance is Fe and unavoidable impurities. The yield strength of the steel designed by the patent is ≥550MPa, the tensile strength is ≥650MPa, and the yield strength ratio is >0.80.

[0008] Chinese patent CN105296885A discloses a titanium-containing high-chromium weathering steel and its preparation method, the chemical composition mass percentage content (wt%) is C≤0.07%, Si≤0.50%, Mn≤1.5%, P≤0.02%, S≤0.010%, Cu: 0.20-0.55%, Cr: 3.0-5.5%, Ni: 0.10-0.65%, Ti: 0.04-0.10%, the rest is Fe and unavoidable impurities. The steel designed in this patent has a yield strength of 480-530MPa, a tensile strength of 580-650MPa, and a yield strength ratio>0.79.

[0009] Chinese patent CN105274446 A discloses a high chromium weathering steel and its preparation method, the chemical composition mass percentage content (wt%) is: C ≤ 0.07%, Si ≤ 0.50%, Mn ≤ 1.5%, P ≤ 0.02%, S ≤ 0.010%, Cu: 0.20-0.55%, Cr: 4.5-5.5%, Ni: 0.10-0.65%, Ti: 0.01-0.03%, the rest is Fe and unavoidable impurities. The steel designed in this patent has a yield strength of 450-510MPa, a tensile strength of 550-630MPa, and a yield strength ratio> 0.80.

[0010] Chinese patent CN104862607A discloses a carbon dioxide corrosion resistant pipeline steel plate and its preparation method, wherein the composition is as follows: C≤0.05%, Si0.2~0.3%, Mn0.50~0.80%, P≤0.020%, S≤0.010%, Cr4.0~7.0%, Nb≤0.080%, Ti≤0.050%, V≤0.080%, Mo0.2~0.50%, Ni≤0.30%, Cu≤0.5%, N≤0.010%, B≤0.0010%, the remainder is Fe and unavoidable impurities. Although the corrosion rate of the steel can be as low as 0.0581mm / a, the yield strength is greater than 500MPa, the tensile strength is greater than 550MPa, the elongation is greater than 25%, the impact energy at -20℃ is greater than 150J, and the average value of -20℃ DWTT is 100%.

[0011] The above patents all improve the corrosion resistance of steel by adding high content of corrosion-resistant alloying elements thereto. However, for low-strength pipeline steel, if too high content of corrosion-resistant alloying elements is added, the strength level of the steel will often increase, while reducing the content of corrosion-resistant alloying elements will lead to a decrease in corrosion resistance. How to produce low-strength pipeline steel such as hot-rolled coils with a yield strength of 290MPa that are resistant to sulfide stress corrosion, microbial corrosion and carbon dioxide corrosion is a technical difficulty in this field. Summary of the invention

[0012] The object of the present invention is to provide a pipeline steel with a yield strength of 290 MPa and resistance to microbial corrosion and carbon dioxide corrosion, and a production method thereof. The pipeline steel has excellent low-temperature toughness, excellent resistance to microbial corrosion and resistance to carbon dioxide corrosion, and can adapt to a complex service environment where a variety of corrosive media coexist.

[0013] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0014] A pipeline steel with a yield strength of 290 MPa and resistance to microbial corrosion and carbon dioxide corrosion. The chemical composition and weight percentage of the pipeline steel are as follows: C: 0.031-0.059%, Si≤0.29%, Mn: 0.51-0.59%, P≤0.010%, S≤0.0015%, Cr: 3.1-3.5%, Cu: 0.31-0.35%, Nb≤0.020%, Ti: 0.010-0.020%, Ca: 0.0010-0.0020%, V, Mo, Ni are not contained, and the rest is Fe and unavoidable inclusions.

[0015] The metallographic structure of the pipeline steel is quasi-polygonal ferrite, and the grain size is 10-11.

[0016] The yield strength Rt of the pipeline steel 0.5 : 290~390MPa, tensile strength Rm: 415~535MPa, yield strength ratio ≤0.75, elongation A 50 ≥35%, -20℃ impact energy ≥250J, 180° cold bending test D=2a qualified. The lower the yield strength ratio, the greater the deformation capacity of the steel pipe from the initial plastic deformation to the final fracture. Too high a yield strength ratio will damage the uniform deformation capacity and ultimate plastic deformation capacity of the material, reducing the material's ability to ease stress concentration, relax local stress at the crack tip and limit crack expansion, which will have an adverse effect on the safe service of the pipeline structure.

[0017] The pipeline steel was tested for 168 hours in an environment with an SRB concentration of 25,000 / mL and a CO2 partial pressure of 0.3 MPa, and its uniform corrosion rate was ≤0.22 mm / a and the maximum pitting depth was ≤2.2 μm.

[0018] The present invention provides a production method for the 290MPa yield strength microbial corrosion-resistant and carbon dioxide corrosion-resistant pipeline steel, which comprises the following steps: molten iron pretreatment → converter smelting → LF refining → RH vacuum degassing → continuous casting → slab heating → controlled rolling → controlled cooling → coiling.

[0019] In the RH vacuum degassing step, calcium treatment is carried out to reduce the total content of sulfur-containing inclusions and spheroidize their shapes to reduce the harmful effects of sulfur-containing inclusions; at the same time, in order to avoid the disadvantages of calcium treatment, the upper limit of calcium content in steel is controlled to 0.0020%.

[0020] In the continuous casting step, low superheat casting and protective slag are used for protective casting, the superheat of molten steel in the tundish is controlled at 10-25°C; the protective slag basicity is 0.90-1.40, the viscosity at 1300°C is 0.030-0.150 Pa·s, and the melting point is 1030-1150°C; the continuous casting billet drawing speed is controlled at ≤1.5m / min.

[0021] In the slab heating step, the outlet temperature of the first heating section of the heating furnace is controlled at 1050-1070°C, the second heating section is rapidly heated to 1150-1200°C at a rate of 150-170°C / h, the slab outlet temperature is ≤1200°C, and the time in the furnace is 120-180min; the heating furnace adopts a reducing atmosphere, and the excess air coefficient is less than 1.0.

[0022] In the controlled rolling step, the starting temperature of rough rolling is 1080-1100°C, the starting temperature of finishing rolling is controlled at 960-980°C, and the final temperature of finishing rolling is controlled at 870-900°C.

[0023] The reduction rate in the rough rolling stage is 0.75-0.85%; the reduction rate in the finish rolling stage is 0.70-0.85%.

[0024] The thickness of the intermediate billet after rough rolling is 35 to 45 mm.

[0025] In the coiling step, the coiling temperature is 550-600°C.

[0026] The main alloy elements and mass percentage design principles of the microbial corrosion-resistant and carbon dioxide corrosion-resistant pipeline steel with a yield strength of 290 MPa provided by the present invention are as follows:

[0027] Cr (chromium): Cr is an important alloying element that improves the atmospheric corrosion resistance of steel. It can be enriched on the surface of steel to promote the formation of a dense protective rust layer with good adhesion to the matrix, preventing corrosive media such as oxygen and water from diffusing into the steel. Cr can also improve the hardenability of the material and promote the formation of bainite structure. Too high Cr content will deteriorate the welding performance of steel, increase strength and manufacturing cost, so the Cr content is designed to be 3.1-3.5%.

[0028] Cu (copper): Cu can significantly improve the atmospheric corrosion resistance of the material, and improve the atmospheric corrosion resistance when combined with Cr. However, the melting point of Cu is relatively low, only 1083°C. Too high a content can easily lead to steel leakage during continuous casting and edge cracks during hot rolling. Therefore, the Cu content is designed to be 0.31-0.35%.

[0029] In order to achieve nickel-free design and obtain the benefits of reducing precious resource consumption and manufacturing costs, the present invention needs to control surface quality defects such as continuous casting breakout, hot rolling curling cracks and surface warping that may be caused by the presence of Cu during production. These measures include but are not limited to: (1) using low superheat casting and special protective slag for protective casting to avoid breakout. The superheat of molten steel in the tundish is controlled at 10-25°C; the basicity of the protective slag is 0.90-1.40, the viscosity at 1300°C is 0.030-0.150 Pa·s, and the melting point is 1030-1150°C; (2) the continuous casting billet drawing speed is controlled at ≤1.5m / min; (3) in order to avoid the "copper brittleness" defect, the residence time of the billet in the high temperature stage is reduced to reduce the enrichment of liquid copper at the austenite grain boundary, the outlet temperature of the first heating section of the heating furnace is controlled at 1050-1070°C, and the second heating section is rapidly heated to 1150-1200°C at a rate of 150-170°C / h, the billet out of the furnace temperature is ≤1200°C, and the time in the furnace is 120-180min. (4) The heating furnace adopts a reducing atmosphere, and the excess air coefficient is less than 1.0.

[0030] In order to improve the toughness and corrosion resistance of the material, the present invention reduces the level of S and P, adopts a low-phosphorus and low-sulfur design, and the P content is less than 0.0100% and the S content is less than 0.0015%. In order to achieve the control of low S and P content, the present invention selects low-phosphorus molten iron in specific implementation measures, and implements calcium treatment in the vacuum degassing process to reduce the total content of sulfur-containing inclusions and sphericalize the shape to reduce the harmful effects of sulfur-containing inclusions; at the same time, in order to avoid the shortcomings of calcium treatment, the upper limit of calcium content in steel is set to 0.0020%. The ultimate goal is to improve the cleanliness of steel, reduce the segregation of P and S elements at grain boundaries, avoid reducing the bonding force of grain boundaries, and thus improve toughness and corrosion resistance. The purpose of the present invention is to produce low-strength pipeline steel that is resistant to microbial corrosion and carbon dioxide corrosion. For low-strength corrosion-resistant pipeline steel, the Cr and Cu contents in the steel must be reduced, otherwise the yield strength of the pipeline steel will remain above 400MPa and low-strength corrosion-resistant pipeline steel cannot be obtained. Reducing the content of elements such as Cr and Cu that can improve corrosion resistance will inevitably lead to reduced corrosion resistance of pipeline steel. The present invention compensates for the reduced corrosion resistance caused by low Cr and Cu contents by improving the cleanliness of the steel. In addition, in the production process, RH vacuum degassing is performed after LF refining to reduce the content of harmful gases such as O and N to a lower level to improve the cleanliness of molten steel.

[0031] The present invention improves the cleanliness and uniformity of steel and reduces the crack tendency of ingot by reducing the contents of Cu, Cr, harmful gases, P and S. Thus, there is no need to perform the ingot stacking and slow cooling process after continuous casting, which will reduce storage capacity and capital occupation and save process costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the microstructure diagram of the pipeline steel in Example 1 at 3 meters away from the tail of the outer ring. It can be seen that the microstructure is quasi-polygonal ferrite with a grain size range of 10 to 11; DETAILED DESCRIPTION

[0033] The invention provides a microbial corrosion-resistant and carbon dioxide corrosion-resistant pipeline steel with a yield strength of 290 MPa. The chemical composition and weight percentage of the steel are as follows: C: 0.031-0.059%, Si≤0.29%, Mn: 0.51-0.59%, P≤0.010%, S≤0.0015%, Cr: 3.1-3.5%, Cu: 0.31-0.35%, Nb≤0.020%, Ti: 0.010-0.020%, Ca: 0.0010-0.0020%, V, Mo and Ni are not contained, and the rest is Fe and inevitable inclusions.

[0034] The production method of the 290MPa yield strength microbial corrosion and carbon dioxide corrosion resistant pipeline steel comprises the following steps: molten iron pretreatment → converter smelting → LF refining → RH vacuum degassing → continuous casting → slab heating → controlled rolling → controlled cooling → coiling.

[0035] In the RH vacuum degassing step, calcium treatment is carried out to reduce the total content of sulfur-containing inclusions and spheroidize their shapes to reduce the harmful effects of sulfur-containing inclusions; at the same time, in order to avoid the disadvantages of calcium treatment, the upper limit of calcium content in steel is controlled to 0.0020%.

[0036] In the continuous casting step, low superheat casting and protective slag are used for protective casting, the superheat of molten steel in the tundish is controlled at 10-25°C; the protective slag basicity is 0.90-1.40, the viscosity at 1300°C is 0.030-0.150 Pa·s, and the melting point is 1030-1150°C; the continuous casting billet drawing speed is controlled at ≤1.5m / min.

[0037] In the slab heating step, the outlet temperature of the first heating section of the heating furnace is controlled at 1050-1070°C, the second heating section is rapidly heated to 1150-1200°C at a rate of 150-170°C / h, the slab outlet temperature is ≤1200°C, and the time in the furnace is 120-180min; the heating furnace adopts a reducing atmosphere, and the excess air coefficient is less than 1.0.

[0038] In the controlled rolling step, the starting temperature of rough rolling is 1080-1100°C, the starting temperature of finishing rolling is controlled at 960-980°C, and the final temperature of finishing rolling is controlled at 870-900°C.

[0039] The reduction rate in the rough rolling stage is 0.75-0.85%; the reduction rate in the finish rolling stage is 0.70-0.85%.

[0040] In the coiling step, the coiling temperature is 550-600°C.

[0041] The present invention is described in detail below with reference to the embodiments.

[0042] The chemical composition and weight percentage of the pipeline steel in each embodiment and comparative example are shown in Table 1.

[0043] Table 1

[0044]

[0045] The production process parameters of the pipeline steel in each embodiment and comparative example are shown in Table 2.

[0046] Table 2

[0047]

[0048] The mechanical properties of the pipeline steel in each embodiment and comparative example are shown in Table 3. Two tensile specimens were tested in each case.

[0049] Table 3

[0050]

[0051] The Charpy impact energy of the pipeline steel in each embodiment and comparative example is shown in Table 4, wherein the impact energy size of Example 1 is 5 mm×10 mm×55 mm.

[0052] Table 4

[0053]

[0054] With reference to GB / T 14643.5 Determination of sulfate-reducing bacteria in industrial circulating cooling water and NACE SP0775-2013 Standard operating procedure for preparation, installation, analysis and interpretation of corrosion specimens in oilfield operations, the test examples and comparative examples of pipeline steel were tested in an environment containing sulfate reducing bacteria (SRB) and CO2 to test the microbial and CO2 corrosion behavior, observe the corrosion pit shape and uniform corrosion rate, and evaluate the degree of SRB corrosion.

[0055] The antibacterial performance test results of the embodiments of the present invention and the comparative examples are shown in Table 5. Although the uniform corrosion rate and the maximum pitting depth of the comparative example are better than those of the embodiments, the cost of the comparative example is higher and the strength level cannot meet the requirements of the present application, while the embodiments achieve the target performance at a relatively low cost.

[0056] Table 5

[0057]

[0058] The pipeline steel in the embodiment was subjected to HIC test according to NACE TM0284-2016 standard. After immersion in solution A for 96 hours, the sample was taken out. There was no hydrogen bubbling on the surface of the sample, and no cracks were found in the cross-section metallographic observation.

[0059] The pipeline steel in the embodiment was subjected to an SSC test according to the NACE TM0177-2016 test standard, a four-point bending test in solution A, the test time was 720 hours, the sample loading stress was 290 MPa, and no cracks were found on the surface of the tensile test piece after the test.

[0060] The above-mentioned reference embodiments provide a detailed description of a microbial corrosion-resistant and carbon dioxide corrosion-resistant pipeline steel with a yield strength of 290 MPa and a production method thereof. This is illustrative rather than restrictive, and several embodiments may be listed within the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A pipeline steel with a yield strength of 290 MPa and resistance to microbial corrosion and carbon dioxide corrosion, the chemical composition and weight percentage of the pipeline steel are: C: 0.031-0.059%, Si≤0.29%, Mn: 0.51-0.59%, P≤0.010%, S≤0.0015%, Cr: 3.1-3.5%, Cu: 0.31-0.35%, Nb≤0.020%, Ti: 0.010-0.020%, Ca: 0.0010-0.0020%, does not contain V, Mo, Ni, and the rest is Fe and unavoidable inclusions; The metallographic structure of the pipeline steel is quasi-polygonal ferrite, and the grain size is 10-11; The yield strength Rt of the pipeline steel 0.5 : 290~390MPa, tensile strength Rm: 415~535MPa, yield strength ratio ≤0.75, elongation A 50 ≥35%, -20℃ impact energy ≥250J, 180° cold bending test D=2a qualified; The pipeline steel was tested for 168 hours in an environment with an SRB concentration of 25,000 / ml and a CO2 partial pressure of 0.3 MPa, and its uniform corrosion rate was ≤0.22 mm / a and the maximum pitting depth was ≤2.2 μm.

2. The method for producing pipeline steel with a yield strength of 290 MPa and resistance to microbial corrosion and carbon dioxide corrosion according to claim 1, characterized in that: The production method comprises the following steps: molten iron pretreatment→converter smelting→LF refining→RH vacuum degassing→continuous casting→slab heating→controlled rolling→controlled cooling→coiling.

3. The production method according to claim 2, characterized in that: In the continuous casting step, low superheat casting and protective slag are used for protective casting, the superheat of molten steel in the tundish is controlled at 10-25°C; the protective slag basicity is 0.90-1.40, the viscosity at 1300°C is 0.030-0.150 Pa·s, and the melting point is 1030-1150°C; the continuous casting billet drawing speed is controlled at ≤1.5m / min.

4. The production method according to claim 2, characterized in that: In the slab heating step, the outlet temperature of the first heating section of the heating furnace is controlled to be 1050-1070°C, the second heating section is rapidly heated to 1150-1200°C at a rate of 150-170°C / h, the slab outlet temperature is ≤1200°C, and the time in the furnace is 120-180min; the heating furnace adopts a reducing atmosphere, and the excess air coefficient is less than 1.

0.

5. The production method according to claim 2, characterized in that: In the controlled rolling step, the starting temperature of the rough rolling is 1080-1100°C, the starting temperature of the finishing rolling is controlled at 960-980°C, and the final rolling temperature of the finishing rolling is controlled at 870-900°C.

6. The production method according to claim 5, characterized in that The reduction rate in the rough rolling stage is 0.75-0.85%; the reduction rate in the finishing rolling stage is 0.70-0.85%.

7. The production method according to claim 2, characterized in that: In the coiling step, the coiling temperature is 550-600°C.

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