Production method of SA537CL1 acid-resistant steel plate

Abstract

The invention discloses a production method of an SA537CL1 acid-resistant steel plate, and belongs to the technical field of steel and iron material manufacturing. The method aims at the problem that an existing SA537CL1 steel plate is unstable in acid resistance, and the SA537CL1 acid-resistant steel plate with excellent hydrogen induced cracking resistance and sulfide stress corrosion resistance is produced through systematic combination of component optimization design, a pure steel smelting process and a controlled rolling and controlled cooling technology. The key technology comprises the steps that a low-carbon component design is adopted, and the carbon equivalent Ceq is controlled to be smaller than or equal to 0.45%; the ultra-low sulfur control S is less than or equal to 0.001% through the processes of molten iron pretreatment, converter smelting and refining; a soft reduction technology is adopted in the continuous casting process to reduce center segregation; and rolling adopts a two-stage controlled rolling and controlled cooling process. The SA537CL1 acid-resistant steel plate produced by the method provided by the invention has the banded structure level of less than or equal to 1.5 level, has the HIC resistance qualification rate of 100%, and completely meets the use requirements of pressure vessels in an acidic environment.

Description

Technical Field

[0001] This invention belongs to the field of steel material manufacturing technology, and relates to a method for producing SA537CL1 acid-resistant steel plates. Background Technology

[0002] SA537CL1 steel plate is a heat-treated carbon-manganese-silicon steel plate for pressure vessels according to the American Society of Mechanical Engineers (ASME) standard. It belongs to the lowest strength grade of the SA537 series and is typically delivered in the normalized condition. This steel plate has good strength, toughness, and weldability, and is widely used in the manufacture of pressure vessels in the petrochemical and power industries, such as reactors, separators, and storage tank shells. However, in acidic environments in the petroleum and chemical industries, especially in media containing hydrogen sulfide (H2S), ordinary SA537CL1 steel plate is prone to hydrogen-induced cracking (HIC) and sulfide stress corrosion (SSC). HIC occurs when hydrogen atoms produced by the corrosion reaction penetrate into the steel, accumulate and combine into hydrogen molecules at defects such as non-metallic inclusions and segregation zones, creating enormous internal pressure that leads to step-like cracks in the steel. SSC, on the other hand, is a brittle cracking phenomenon caused by the combined effects of tensile stress and hydrogen sulfide corrosion.

[0003] Currently, while the production process of ordinary SA537CL1 steel plates can meet the requirements of conventional pressure vessels, it has the following shortcomings in terms of acid resistance: First, the sulfur and phosphorus content is not strictly controlled. The sulfur content of ordinary SA537CL1 steel plates is required to be ≤0.035%, and the phosphorus content is ≤0.035%. This level of content is insufficient to resist corrosion in acidic environments. Second, the control of non-metallic inclusions is insufficient. MnS inclusions are the main origin of HIC cracks, and ordinary production processes lack effective control over the morphology of inclusions. Third, the composition design is not optimized for acid resistance. Conventional composition design mainly considers mechanical properties and does not optimize for acid resistance. Fourth, the microstructure is not uniform, with a severe banded structure, which provides an expansion channel for HIC.

[0004] In existing technologies, some improved production methods for SA537CL1 steel plates still have limitations. For example, Chinese patent CN117418159A discloses a 60-100mm thick SA537CL1 steel plate with excellent die-welding performance, which uses a lower carbon content (0.06-0.09%) and carbon equivalent (Ceq≤0.36%) to improve weldability. However, this technology mainly focuses on the performance after die welding, with limited improvement in acid resistance, and the thickness range is limited to 60-100mm.

[0005] Therefore, there is an urgent need to develop a method to comprehensively optimize the production of SA537CL1 acid-resistant steel plates, controlling the process from composition design, smelting process, rolling process and heat treatment process in all aspects, so as to produce SA537CL1 acid-resistant steel plates with excellent resistance to HIC and SSC. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for comprehensively optimizing the production of SA537CL1 acid-resistant steel plates. By optimizing the composition design and controlling the entire process, the HIC and SSC resistance of SA537CL1 steel plates is significantly improved, while maintaining good mechanical and weldability properties, meeting the stringent requirements of pressure vessels in acidic environments.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for producing SA537CL1 acid-resistant steel plate, wherein the chemical composition of the steel is as follows (weight percentage): C = 0.12%–0.20%, Si = 0.20%–0.50%, Mn = 1.20%–1.60%, P ≤ 0.008%, S ≤ 0.001%, Alt = 0.020%–0.050%, Ca = 0.0010%–0.0030%, with the remainder being Fe and unavoidable residual elements, and a carbon equivalent (CE) ≤ 0.45%; the method includes the following process steps: 1) Steel smelting: The steel composition is controlled by using hot metal pretreatment, converter smelting, LF refining and VD vacuum treatment processes.

[0008] 2) Continuous casting process: control the superheat at 6-13℃, adopt light reduction technology, and expand the proportion of equiaxed crystal regions.

[0009] 3) Slab heating: The heating temperature is controlled at 1180~1250℃, and the holding time is 2~5h.

[0010] 4) Controlled rolling: A two-stage rolling process is adopted, with roughing temperature of 1100~1150℃ and finishing temperature of 820~880℃.

[0011] 5) Controlled cooling: An accelerated cooling process is adopted, with a cooling rate of 5-20℃ / s. After cooling to 500-550℃, air cooling is performed.

[0012] 6) Heat treatment: Normalizing treatment is adopted, with a normalizing temperature of 880~910℃ and a holding time of 1.5~2.5 times the plate thickness (mm×min).

[0013] Further, in step 1) steelmaking: the molten iron pretreatment includes desulfurization treatment to make the sulfur content of the molten iron ≤0.002%; the LF refining includes a calcium treatment process, with the calcium-sulfur ratio controlled at 0.8 to 1.5.

[0014] Furthermore, in step 2) continuous casting process: the total reduction is 4-10 mm.

[0015] Further, in step 4), controlled rolling: in the controlled rolling, the roughing stage adopts a large reduction process, with a single-pass reduction rate of not less than 15% and a total reduction rate of not less than 65%; in the finishing stage, rolling is carried out in the non-recrystallization zone, with a cumulative deformation of not less than 60%.

[0016] Further, step 5) controlled cooling: after controlled cooling, the steel plates are stacked for slow cooling, the stacking temperature is not lower than 300℃, and the slow cooling time is not less than 48h.

[0017] Furthermore, the obtained acid-resistant steel plate has a banded structure grade ≤1.5, a Charpy impact energy ≥100J at -46℃, HIC resistance that meets the NACE TM0284 standard requirements, a crack length ratio (CLR) ≤5%, a crack thickness ratio (CTR) ≤1.5%, and a crack sensitivity ratio (CSR) ≤0.5%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) Innovative composition design: The low-carbon composition design significantly improves toughness and weldability while ensuring strength; the calcium treatment controls the morphology of sulfides, fundamentally improving the resistance to HIC.

[0019] (2) Full-process pure steel technology: The sulfur content is controlled from the pretreatment of molten iron, and the content of sulfur, phosphorus, gas and inclusions is further reduced through LF refining and VD vacuum treatment, ensuring the purity of steel.

[0020] (3) Advanced continuous casting technology: By controlling the superheat and light reduction, columnar crystal development is effectively suppressed, the proportion of equiaxed crystal zone is expanded, the secondary dendrite spacing is reduced, and element segregation and central porosity are significantly reduced.

[0021] (4) Optimized controlled rolling and cooling process: Through two-stage rolling and accelerated cooling process, a refined ferrite + pearlite structure is obtained, reducing hydrogen trap sites and improving acid resistance.

[0022] (5) Excellent product quality: Through ultra-low sulfur and phosphorus control, inclusion morphology control, and microstructure homogenization, the steel plate's resistance to HIC and SSC is significantly improved. The product can pass the NACE TM0284 standard HIC test, with a crack length ratio (CLR) ≤ 5%, a crack thickness ratio (CTR) ≤ 1.5%, and a crack sensitivity rate (CSR) ≤ 0.5%. The produced SA537CL1 acid-resistant steel plate has a banded microstructure level ≤ 1.5, a Charpy impact energy at -46℃ ≥ 100J, and can reach more than 200J, far exceeding the standard requirement of 27J. The steel plate has excellent surface quality with a 100% pass rate, a Class I flaw detection pass rate of over 99%, a performance pass rate of 100%, and a HIC resistance test pass rate of 100%. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the microstructure of the SA537CL1 steel plate produced in Example 1. Detailed Implementation

[0024] The present invention will be further described below through specific embodiments. Example 1

[0025] The specific steps for producing 40mm thick SA537CL1 acid-resistant steel plates are as follows: 1) Steelmaking: The process involves hot metal pretreatment (S ≤ 0.002% after desulfurization), converter smelting, LF refining, and VD vacuum treatment to control the steel composition to: C = 0.16%, Si = 0.30%, Mn = 1.50%, P = 0.007%, S = 0.001%, Alt = 0.035%, Ca = 0.0020%, with the remainder being Fe and unavoidable residual elements. Carbon equivalent (CE) = 0.42%.

[0026] 2) Continuous casting process: control the superheat of the tundish to 11°C, implement light reduction, and the total reduction is 6mm; the secondary cooling zone adopts a weak cooling system.

[0027] 3) Slab heating: heating temperature 1180℃, holding time 2.5h.

[0028] 4) Controlled rolling: A two-stage rolling process is adopted, with a roughing temperature of 1080℃ and a finishing temperature of 820℃. The roughing stage adopts a large reduction process, with a single-pass reduction rate of 18% and a total reduction rate of 70%.

[0029] 5) Controlled cooling: An accelerated cooling process is adopted, with a cooling rate of 15℃ / s. After cooling to 500℃, air cooling is performed. After cooling, the steel plates are stacked for slow cooling at a stacking temperature of 350℃ for 48 hours.

[0030] 6) Heat treatment: normalizing treatment is adopted, with a normalizing temperature of 890℃ and a holding time of 60 minutes (calculated at 1.5 minutes / mm thickness). Example 2

[0031] The specific steps for producing 100mm thick SA537CL1 acid-resistant steel plates are as follows: 1) Steelmaking: Hot metal pretreatment (S ≤ 0.002% after desulfurization), converter smelting, LF refining, and RH vacuum treatment are employed to control the steel composition to achieve: C = 0.18%, Si = 0.40%, Mn = 0.002%. ： 1.55%, P ： 0.006%, S=0.0008%, Alt=0.040%, Ca=0.0020%, with the remainder being Fe and unavoidable residual elements. Carbon equivalent Ceq=0.45%.

[0032] 2) Continuous casting process: control the superheat of the tundish to 10°C, implement light reduction, and the total reduction is 8mm; the secondary cooling zone adopts a weak cooling system.

[0033] 3) Slab heating: heating temperature 1220℃, holding time 5h.

[0034] 4) Controlled rolling: A two-stage rolling process is adopted, with a roughing temperature of 1150℃ and a finishing temperature of 840℃. The roughing stage adopts a large reduction process, with a single-pass reduction rate of 20% and a total reduction rate of 75%.

[0035] 5) Controlled cooling: An accelerated cooling process is adopted, with a cooling rate of 12℃ / s, and the steel plates are air-cooled after reaching 520℃. After cooling, the steel plates are stacked for slow cooling at a stacking temperature of 380℃ for 60 hours.

[0036] 6) Heat treatment: normalizing treatment is adopted, with a normalizing temperature of 910℃ and a holding time of 200 minutes (calculated based on 2.0 minutes / mm thickness).

[0037] Comparative example: 40mm thick SA537CL1 steel plate was produced using traditional processes: the composition was controlled according to ordinary standards (S≤0.025%, P≤0.025%), no calcium treatment was performed, the continuous casting superheat was 30℃, no light reduction technology was used, the slab heating temperature was 1150℃, the holding time was 1.5h, the rolling process was hot rolling, and no controlled cooling was used.

[0038] Performance testing: Performance tests were conducted on the steel plates produced in Examples 1, 2 and the comparative example, and the results are shown in Table 1.

[0039] Test results show that the SA537CL1 acid-resistant steel plate produced using the method of this invention has a significantly reduced banded structure level, its mechanical properties fully meet and far exceed the standard requirements, its HIC resistance is excellent, and its flaw detection pass rate reaches 100%. In contrast, the steel plate produced in the comparative example has a high banded structure level, average impact performance, and unqualified HIC resistance, thus failing to meet the requirements for use in acidic environments.

[0040] Table 1 Comparison of performance test results between the examples and comparative examples .

Claims

1. A method for producing SA537CL1 acid-resistant steel plate, characterized in that: The chemical composition of the steel by weight percentage is: C = 0.12%–0.20%, Si = 0.20%–0.50%, Mn = 1.20%–1.60%, P ≤ 0.008%, S ≤ 0.001%, Alt = 0.020%–0.050%, Ca = 0.0010%–0.0030%, with the remainder being Fe and unavoidable residual elements; the carbon equivalent CE ≤ 0.45%. The process includes the following steps: 1) Steelmaking: The steel composition is controlled by employing hot metal pretreatment, converter smelting, LF refining and VD vacuum treatment processes. 2) Continuous casting process: control the superheat at 6-13℃, adopt light reduction technology, and expand the proportion of equiaxed crystal regions; 3) Slab heating: The heating temperature is controlled at 1180~1250℃, and the holding time is 2~5h; 4) Controlled rolling: A two-stage rolling process is adopted, with roughing temperature of 1100~1150℃ and finishing temperature of 820~880℃; 5) Controlled cooling: An accelerated cooling process is adopted, with a cooling rate of 5-20℃ / s, and air cooling is performed after cooling to 500-550℃; 6) Heat treatment: Normalizing treatment is adopted, with a normalizing temperature of 880~910℃ and a holding time of 1.5~2.5 times the plate thickness (mm×min).

2. The method for producing SA537CL1 acid-resistant steel plate according to claim 1, characterized in that: Step 1) Steelmaking: The pretreatment of molten iron includes desulfurization treatment to make the sulfur content of molten iron ≤0.002%; the LF refining includes calcium treatment process, with the calcium-sulfur ratio controlled at 0.8-1.

5.

3. The method for producing SA537CL1 acid-resistant steel plate according to claim 1, characterized in that: Step 2) Continuous casting process: The total reduction is 4-10 mm.

4. The method for producing an SA537CL1 acid-resistant steel plate according to claim 1, characterized in that: Step 4) Controlled rolling: In the controlled rolling, the roughing stage adopts a large reduction process, with a single-pass reduction rate of not less than 15% and a total reduction rate of not less than 65%; the finishing stage is rolled in the non-recrystallization zone, with a cumulative deformation of not less than 60%.

5. The method for producing SA537CL1 acid-resistant steel plate according to claim 1, characterized in that: Step 5) Controlled cooling: After controlled cooling, the steel plates are stacked for slow cooling. The stacking temperature is not lower than 300℃ and the slow cooling time is not less than 48 hours.

6. The method for producing SA537CL1 acid-resistant steel plate according to claim 1, characterized in that: The obtained acid-resistant steel plate has a banded structure grade ≤1.5, a Charpy impact energy ≥100J at -46℃, HIC resistance that meets the requirements of NACE TM0284 standard, crack length ratio (CLR) ≤5%, crack thickness ratio (CTR) ≤1.5%, and crack sensitivity ratio (CSR) ≤0.5%.

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