Process for the production of low cost x65ms sour service line single sheet rolled steel plate

Abstract

The application provides a production method of a low-cost X65MS acid-resistant pipeline single-plate rolled steel plate, and chemical components and mass percentages thereof are as follows: C: 0.035wt%-0.050wt%, Si: 0.15wt%-0.25wt%, Mn: 1.20wt%-1.30wt%, P: <=0.012wt%, S: <=0.0015wt%, Al: 0.025wt%-0.050wt%, Cr: 0.26wt%-0.35wt%, Nb: 0.055wt%-0.065wt%, Ti: 0.010wt%-0.020wt%, N: <=0.0050wt%, O: <=0.0020wt%, H: <=0.00020wt%, Ca: 0.0010wt%-0.0020wt%, and the acid-resistant pipeline steel plate X65MS prepared by the application has good mechanical properties, HIC resistance and good plate shape.

Description

Technical Field

[0001] This invention relates to the field of metal material forming technology, specifically to a low-cost method for producing single-sheet rolled steel plates for X65MS acid-resistant pipelines. Background Technology

[0002] With the continuous development of sulfur-containing gas fields, the demand for pipelines transporting sulfur-containing moist gas is constantly increasing, and the required steel grades are also gradually improving, from the initial low-strength X52MS to the higher-grade X65MS. H2S in sulfur-containing moist gas easily induces sulfide stress corrosion cracking (SSC) and hydrogen-induced cracking (HIC). To address this issue, it is necessary to improve the purity of molten steel by adding alloying elements such as Mo, Ni, and Cu to reduce C and Mn segregation and microstructure inhomogeneity. However, this will increase the cost of high-grade acid-resistant pipeline steel X65MS. Furthermore, during the cooling process of single-sheet rolled steel plates on a cooling bed, secondary phase transformations can cause deformation and warping of the steel plates, significantly impacting the yield rate of the steel plate shape.

[0003] Chinese patent CN202210699006.7 discloses "a production method of acid-resistant pipeline steel X65MS", the chemical composition of which is C: 0.03~0.04, Si: 0.10~0.20, Mn: 1.20~1.25, P≤0.012, S≤0.0010, Nb: 0.038~0.044, Ti: 0.012~0.018, Al≤0.015, Ni: 0.10~0.13, Cr: 0.15~0.18, Mo: 0.08~0.10, Cu: 0.15~0.18, V: 0.03~0.04. The C control range is narrow, the smelting is difficult and the cost is high, and the addition of precious alloys such as Ni, Mo, Cu and V leads to high cost.

[0004] Chinese patent documents, represented by application numbers CN202310634479.3, CN202111396784.0, CN202110727061.8, CN202010243677.3, CN202010096717.6, CN202010096718.0, and CN201810237038.9, disclose production methods for hot-rolled coils of X65MS grade acid-resistant pipeline steel. Their chemical compositions often employ low-C, low-Mn, and Nb components, or omit Cu, Cr, Ni, Mo, and V, or add precious alloys such as Ni, Mo, Cu, and V, and utilize continuous hot rolling. However, due to the significant differences between continuous hot rolling and single-sheet rolling, and the thinness and narrowness of the produced dimensions, the existing composition and continuous rolling process are not suitable for single-sheet rolling production methods.

[0005] In summary, the existing technology has the following problems: based on single-sheet rolling process, there is a lack of a process production method for X65MS acid-resistant pipeline with moderate production difficulty and low overall cost. Summary of the Invention

[0006] This invention provides a low-cost method for producing single-sheet rolled steel plates for X65MS acid-resistant pipelines, thereby solving the problems of high cost and difficult production of single-sheet rolled X65MS acid-resistant pipelines.

[0007] Therefore, this invention proposes a low-cost method for producing single-sheet rolled steel plates for X65MS acid-resistant pipelines.

[0008] The chemical composition and mass percentage of the steel are as follows: C: 0.035wt%-0.050wt%, Si: 0.15wt%-0.25wt%, Mn: 1.20wt%-1.30wt%, P: ≤0.012wt%, S: ≤0.0015wt%, Al: 0.025wt%-0.050wt%, Cr: 0.26wt%-0.35wt%, Nb: 0.055wt%-0.065wt%, Ti: 0.010wt%-0.020wt%, N: ≤0.0050wt%, O: ≤0.0020wt%, H: ≤0.00020wt%, Ca: 0.0010wt%~0.0020wt%, with the remainder being Fe and unavoidable impurities.

[0009] Furthermore, the production method of the low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate also includes some process steps:

[0010] S1, Smelting;

[0011] S2, continuous casting;

[0012] S3, Heating;

[0013] S4, rough rolling;

[0014] S5. Finishing rolling: The starting temperature for finishing rolling is ≤980℃;

[0015] S6. Cooling: Direct quenching + accelerated cooling, initial cooling temperature is 740℃~780℃, final cooling temperature is 150℃~230℃, cooling rate is ≥25℃ / s.

[0016] Furthermore, the finished thickness of the acid-resistant pipeline steel plate X65MS is 15.0mm-26.0mm.

[0017] Furthermore, in step S2 continuous casting: the ladle casting adopts long nozzle argon sealing protection casting, electric stirring, and heavy pressure to continuously cast the molten steel obtained in step S1 into a slab with a thickness of 300mm. The slab is stacked and slowly cooled for more than 24 hours, and then warmly or coldly charged into the heating furnace of the medium and heavy plate rolling mill, with a furnace charging temperature ≤500℃.

[0018] Furthermore, in step S3, the heating temperature is 1160℃~1200℃, and the holding time after reaching the temperature is ≥70min.

[0019] Furthermore, in step S4 rough rolling: the rough rolling end temperature is 1040℃~1080℃, and the thickness of the intermediate billet at the rough rolling exit is 3.5H~4.5H, where H is the finished product thickness in mm.

[0020] Furthermore, roughing: adopts horizontal rolling to widen and finally roll to the bottom, with a single-pass reduction rate of ≥20% in the last two passes of roughing.

[0021] Furthermore, a two-stand rolling mill is used for single-sheet rolling.

[0022] Furthermore, the final cooling temperature is 190℃~210℃.

[0023] Furthermore, the finishing rolling temperature is 940℃~960℃.

[0024] Furthermore, the cooling rate is 28℃ / s to 32℃ / s.

[0025] This invention also provides a low-cost X65MS acid-resistant pipeline steel plate produced based on a single-sheet rolling process. The chemical composition and mass percentage of the steel are as follows: C: 0.035wt%-0.050wt%, Si: 0.15wt%-0.25wt%, Mn: 1.20wt%-1.30wt%, P: ≤0.012wt%, S: ≤0.0015wt%, Al: 0.025wt%-0.050wt%, Cr: 0.26wt%-0.35wt%, Nb: 0.055wt%-0.065wt%, Ti: 0.010wt%-0.020wt%, N: ≤0.0050wt%, O: ≤0.0020wt%, H: ≤0.00020wt%, Ca: 0.0010wt%~0.0020wt%, with the remainder being Fe and unavoidable impurities.

[0026] Furthermore, the finished thickness of the acid-resistant pipeline steel plate X65MS is 15.0mm-26.0mm.

[0027] This invention uses 0.035-0.050%C, 0.25-0.30%Cr, and 0.055-0.065%Nb as the basic chemical composition, without adding expensive alloys such as Ni, Mo, Cu, and V. By controlling rolling, high cooling rate, and low final cooling temperature, a single-sheet rolling process is used to manufacture X65MS acid-resistant pipeline steel plates with a thickness of 15.0mm-26.0mm, a width ≤3600mm (width is 1500~3600mm), and excellent comprehensive performance. The X65MS acid-resistant pipeline steel plate obtained by this invention has good mechanical properties, HIC resistance, and good plate shape. Its microstructure and properties have the following characteristics:

[0028] 1) Microstructure: Ferrite + Bainite;

[0029] 2) Mechanical properties: Yield strength 450-550MPa, tensile strength 550-650MPa, elongation ≥30%, Charpy impact performance at -40℃ ≥200J, DWTT SA at -20℃ ≥90%, hardness HV10≤210;

[0030] 3) HIC performance: Tested according to NACE TM0284 standard, using NACE TM0284-A solution, stress-free, for 96 hours. For a single specimen and a single cross section: CLR≤15%, CSR≤2%, CTR≤5%.

[0031] 4) SSC performance: According to ASTM G39 standard, a 4-point bending test was conducted in solution A of NACE TM0177 for 720 hours. The stress on the specimen was 72% of the minimum yield strength of the steel plate. After the test, the tensile surface of the specimen was examined with a 10X magnifying glass and no SSC cracks were found.

[0032] 5) Plate type: Unevenness ≤ 5mm / m. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the core structure of the finished steel plate according to Embodiment 2 of the present invention, magnified 50 times;

[0034] Figure 2 This is a schematic diagram of the core microstructure of the finished steel plate of Comparative Example 2 of the present invention, magnified 50 times.

[0035] Figure 3 This is a schematic diagram of the structure of the fine spherical inclusions dispersed inside the finished steel plate of Embodiment 5 of the present invention, magnified 100 times;

[0036] Figure 4 This is a schematic diagram of the Al2O3 inclusions inside the finished steel plate of Comparative Example 1 of the present invention, magnified 100 times. Detailed Implementation

[0037] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention is now described.

[0038] This invention uses 0.035-0.050%C, 0.25-0.30%Cr, and 0.055-0.065%Nb as the basic chemical composition, without adding expensive alloys such as Ni, Mo, Cu, and V. By controlling rolling, high cooling rate, and low final cooling temperature, a single-sheet rolling process is used to manufacture X65MS acid-resistant pipeline steel plates with a thickness of 15.0mm-26.0mm, a width ≤3600mm, and excellent comprehensive performance. Specific compositional considerations include:

[0039] Carbon (C): When increasing the strength of steel, an increase in C content can easily lead to segregation problems, resulting in a decrease in resistance to HIC (high carbon dioxide) formation. Furthermore, converter smelting requires controlling C content below 0.03%, which transforms converter production from a delicate operation to an extreme operation, significantly increasing the difficulty. Therefore, this invention limits the carbon content to the range of 0.035wt%-0.050wt%.

[0040] Silicon (Si): A solid solution strengthening element; excessive content may reduce weldability. Therefore, this invention limits the Si content to 0.15wt%-0.25wt%.

[0041] Manganese (Mn): A solid solution strengthening element that is prone to segregation, it can exacerbate the heterogeneity of tissue properties, resulting in a significant reduction in resistance to HIC. Therefore, the Mn content in this invention is limited to the range of 1.20 wt% to 1.30 wt%.

[0042] Aluminum (Al): A strong deoxidizer, adding an appropriate amount of aluminum can reduce the oxygen content in steel to a minimum. The remaining aluminum after deoxidation can react with nitrogen in the steel to form AlN precipitates, which is beneficial for refining grains and improving the strength and toughness of the steel. Therefore, this invention controls the Al content to 0.025wt%-0.050wt%.

[0043] Chromium (Cr): Forms a dense oxide film or protective rust layer on the surface of steel, enhancing its passivation ability and significantly improving its corrosion resistance; it also improves hardenability and solid solution strengthening effect. However, when the Cr content is too high, it will adversely affect the weldability, and its segregation degree is similar to that of Mn, which is detrimental to the control of material microstructure uniformity. Therefore, this invention controls the Cr content at 0.25wt%-0.30wt%.

[0044] Niobium (Nb): By significantly increasing the recrystallization temperature, steel can achieve non-recrystallization controlled rolling at higher temperatures; during controlled rolling and cooling, fine Nb (C, N) precipitates, thereby achieving grain refinement and precipitation strengthening; it lowers the phase transformation temperature to promote lath bainite formation while inhibiting the formation of granular bainite. Therefore, this invention controls the Nb content within the range of 0.055wt%-0.065wt%.

[0045] Titanium (Ti): During controlled rolling and cooling, TiC and Ti(NC) precipitate, achieving grain refinement and precipitation strengthening effects; during welding, TiC and Ti(NC) contribute to the formation of acicular ferrite. Therefore, the Ti content in this invention is controlled at 0.010wt%~0.02wt%.

[0046] Phosphorus, sulfur, nitrogen, oxygen, and hydrogen elements (P, S, N, O, H): In the steel of this invention, P, S, N, O, and H are all harmful elements. In particular, the MnS formed by S and Mn, as well as H, can directly and significantly reduce the resistance to HIC. Therefore, P ≤ 0.012 wt%, S ≤ 0.0015 wt%, N ≤ 0.0050 wt%, O ≤ 0.0020 wt%, and H ≤ 0.00020 wt%.

[0047] Calcium (Ca) improves the morphology of inclusions in steel and enhances its impact toughness and corrosion resistance. However, excessive addition can reduce the cleanliness of the steel and adversely affect its low-temperature toughness and corrosion resistance. This invention controls the Ca content to be between 0.0010 wt% and 0.0020 wt%.

[0048] Therefore, the chemical composition and mass percentage of the steel are determined as follows: C: 0.035wt%-0.050wt%, Si: 0.15wt%-0.25wt%, Mn: 1.20wt%-1.30wt%, P: ≤0.012wt%, S: ≤0.0015wt%, Al: 0.025wt%-0.050wt%, Cr: 0.26wt%-0.35wt%, Nb: 0.055wt%-0.065wt%, Ti: 0.010wt%-0.020wt%, N: ≤0.0050wt%, O: ≤0.0020wt%, H: ≤0.00020wt%, Ca: 0.0010wt%~0.0020wt%, with the remainder being Fe and unavoidable impurities.

[0049] Implementation plan:

[0050] Based on the applicant's existing process flow for producing X65MS steel plates—KR hot metal pre-desulfurization—250-ton combined blowing converter smelting—LF refining—RH vacuum treatment—CC (slab continuous casting)—slab heating—3800mm double-stand rolling mill (first stand: reversible roughing mill—only roughing reciprocating, widening (fixed width), large reduction for billet opening; second stand: reversible finishing mill—intermediate billet is transported, separately reciprocating finishing, fixed size (thickness), plate shape,)—ACC cooling, the implementation plan is as follows:

[0051] 1. The target composition of the steel grade is shown in Table 0.

[0052] Table 0 Chemical Composition of X65MS Steel Plate

[0053] CE pcm ≤020.

[0054]

[0055] 2. Implementation process

[0056] 1) Smelting: The steel is smelted by desulfurization of hot iron, converter smelting, argon blowing at the argon station, LF ladle furnace, RH vacuum treatment refining and calcium treatment processes in sequence. The chemical composition and mass percentage of the molten steel meet the requirements of the aforementioned acid-resistant pipeline steel X65MS.

[0057] 2) Continuous casting: The steel ladle is cast using argon sealing protection with a long nozzle, electric stirring, and heavy pressure to continuously cast the molten steel obtained in step S1 into slabs with a thickness of up to 300mm. Then, the slabs are flame-cut according to the required length of the finished steel plate. The slabs are stacked and slowly cooled for more than 24 hours, and then warmly or coldly charged into the heating furnace of the medium and heavy plate rolling mill. The furnace charging temperature is ≤500℃.

[0058] 3) Heating: The heating temperature is 1160℃~1200℃, and the holding time after reaching the temperature is ≥70min;

[0059] 4) Rough rolling: The horizontal rolling is used to widen the rolling process and roll to the bottom. The single-pass reduction rate of the last two passes of rough rolling is ≥20%, for example, 20%~32%, in order to achieve appropriate reduction in the rough rolling stage. The rough rolling end temperature is 1040℃~1080℃, and the thickness of the intermediate billet at the rough rolling exit is 3.5Hmm~4.5Hmm (H is the finished product thickness).

[0060] 5) Finish rolling: The initial rolling temperature for finish rolling is ≤980℃;

[0061] 6) Cooling: After pre-straightening the steel plate prepared in step S5, it is cooled using the DQ+ACC (direct quenching + accelerated cooling) process. The initial cooling temperature is 740℃~780℃, the final cooling temperature is 150℃~230℃, and the cooling rate is ≥25℃ / s. After hot straightening, it is then sent to a finishing cooling bed for further cooling and sheared into finished steel plates. When the steel plate cools to below 200℃, the bainitic phase transformation is completely completed, and the temperature of the entire plate surface and cross-section becomes extremely uniform. The internal stress caused by the phase transformation and temperature difference is significantly released and relaxed, thus essentially eliminating the deformation and warping of the steel plate on the cooling bed.

[0062] Furthermore, an acid-resistant pipeline steel plate X65MS with a thickness of 15.0mm-26.0mm, a width of ≤3600mm, a Charpy impact resistance of ≥200J at -40℃, and an unevenness of ≤8mm / m was obtained. 3. Specific Implementation Examples

[0064] 1) Chemical composition, see Table 1

[0065] Table 1 Chemical composition (wt, %) of comparative examples and embodiments

[0066] The Ni in Examples 1-6 and Comparative Example 2 is naturally present in the molten iron and is not added specifically.

[0067] The carbon equivalent of Comparative Examples 1 and 2 is significantly higher than that of Examples 1-6. Comparative Example 1 contains precious alloying elements such as Mo, V, and Ni, and its cost is significantly higher.

[0068] 2) Hot metal pretreatment process

[0069] The molten iron in Examples 1-6 and Comparative Example 1 were all subjected to KR deep desulfurization treatment, and the sulfur content of the molten iron after treatment was 0.001%.

[0070] Comparative Example 2: The molten iron was treated with powder injection desulfurization, and the sulfur content of the molten iron after desulfurization was 0.0018%.

[0071] 1) Converter smelting process, see Table 2

[0072] Table 2. Parameters related to the converter smelting process

[0073] In Examples 1-6, the converter smelting endpoint temperature is low, which helps to reduce the P content at the smelting endpoint. In contrast, the endpoint temperatures of Comparative Examples 1 and 2 are high, and the P content is also relatively high.

[0074] 2) LF refining process, see Table 3

[0075] Table 3. Parameters related to the LF refining process

[0076] 3) The RH vacuum degassing process is shown in Table 4.

[0077] Table 4 RH Vacuum Degassing Parameter Table

[0078] The CaSi wire has a Ca content of 25% and a core mass of 260 kg / m.

[0079] 4) Continuous casting process

[0080] During continuous casting, differences in the effectiveness of protective casting will result in varying degrees of increase in nitrogen (N) and hydrogen (H), as shown in Table 5.

[0081] Table 5 Continuous Casting Parameters

[0082] 5) Heating and rolling processes, see Table 6

[0083] Table 6 Heating and Rolling Process

[0084] 6) Finished product performance, see Table 7

[0085] Table 7 Finished Product Performance Table

[0086] Metallographic structure:

[0087] Example 2: Microstructure of the core of the finished steel plate (uniform structure, microstructure: ferrite + bainite, no obvious segregation bands, segregation grade 0.5), as shown. Figure 1 ;

[0088] Comparative Example 2: Microstructure of the core of the finished steel plate (with obvious segregation bands, segregation grade 2), such as... Figure 2 ;

[0089] Example 5: Dispersed fine spherical inclusions inside the finished steel plate, such as... Figure 3 ;

[0090] Comparative Example 1: Al2O3 inclusions inside the finished steel plate (due to the lack of silicon-calcium wire feeding for inclusion modification treatment), such as Figure 4 .

[0091] Compared to hot continuous rolling, which requires multiple stands and has a very high rolling speed (8-16 m / s for thicknesses > 6 mm, and even faster for thinner plates), this invention enables reversible rolling of medium-thick plates at speeds of 1.36-2.09 m / s. However, hot continuous rolling also involves coiling. Rolling X65MS steel to a maximum thickness of 20 mm is already quite difficult; beyond 20 mm, coiling becomes much more difficult, and at a certain thickness, coiling becomes impossible. In other words, it is impossible to roll larger thicknesses of X65MS using hot continuous rolling.

[0092] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. The various components of the present invention can be combined with each other without conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for producing a low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate, characterized in that, The production method of the low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate includes: The chemical composition and mass percentage of the steel are as follows: C: 0.035wt%-0.050wt%, Si: 0.15wt%-0.25wt%, Mn: 1.20wt%-1.30wt%, P: ≤0.012wt%, S: ≤0.0015wt%, Al: 0.025wt%-0.050wt%, Cr: 0.26wt%-0.35wt%, Nb: 0.055wt%-0.065wt%, Ti: 0.010wt%-0.020wt%, N: ≤0.0050wt%, O: ≤0.0020wt%, H: ≤0.00020wt%, Ca: 0.0010wt%~0.0020wt%, with the remainder being Fe and unavoidable impurities.

2. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plates as described in claim 1, characterized in that, The production method of the low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate also includes the following process steps: S1, Smelting; S2, continuous casting; S3, Heating; S4, rough rolling; S5. Finishing rolling: The starting temperature for finishing rolling is ≤980℃; S6. Cooling: Direct quenching + accelerated cooling, initial cooling temperature is 740℃~780℃, final cooling temperature is 150℃~230℃, cooling rate is ≥25℃ / s.

3. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, The thickness of the finished acid-resistant pipeline steel plate X65MS is 15.0mm-26.0mm.

4. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, In step S2 continuous casting: the ladle casting adopts long nozzle argon sealing protection casting, electric stirring, and heavy pressure to continuously cast the molten steel obtained in step S1 into a 300mm thick slab. The slab is stacked and slowly cooled for more than 24 hours, and then warmly or coldly charged into the heating furnace of the medium and heavy plate rolling mill. The furnace charging temperature is ≤500℃.

5. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, In step S3, during heating: the heating temperature is 1160℃~1200℃, and the holding time after reaching the temperature is ≥70min.

6. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, In step S4 rough rolling: the rough rolling end temperature is 1040℃~1080℃, and the thickness of the intermediate billet at the rough rolling exit is 3.5H~4.5H, where H is the finished product thickness in mm.

7. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, Rough rolling: The horizontal rolling is used to widen the rolling process and roll to the bottom. The single-pass reduction rate of the last two passes of rough rolling is ≥20%.

8. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, Single-sheet rolling is performed using a two-stand rolling mill.

9. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, The final cooling temperature is 190℃~210℃.

10. The method for producing low-cost X65MS acid-resistant pipeline single-sheet rolled steel plate as described in claim 1, characterized in that, The finishing rolling temperature is 940℃~960℃.

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