Ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry and manufacturing method thereof

Abstract

The invention relates to an ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry and a manufacturing method. The manufacturing method of the steel pipe comprises the following steps that 1, smelting is conducted, specifically, an IF + AOD + LF + VD + IC + ESR six-link smelting process is adopted, and ultralow gas content ([H] is smaller than or equal to 2 ppm, and [O] is smaller than or equal to 25 ppm) and high-purity molten steel control are achieved through AOD whole-process argon blowing and VD deep vacuum degassing; electroslag remelting is carried out, a 65: 25: 10 pre-melted slag system is adopted, and the melting rate is controlled to be 910-1040 kg / h so as to avoid Nb segregation; 2, forging is conducted, the electroslag ingot is subjected to multi-fire precision forging, the heating process includes annealing furnace preheating and high-temperature furnace heating at 40 DEG C / h, the temperature is increased to 1230 DEG C, heat preservation is conducted for 10 h, then the temperature is increased to 1240 DEG C, heat preservation is conducted for 4 h, the forging ratio is 4.5, and the grain size of an obtained pipe blank is 3-5 levels; and 3, pipe manufacturing is conducted, specifically, three-section temperature control heating is conducted at the temperature of 500 DEG C, 750 DEG C and 1220 DEG C, the processes of perforation, Pilger forging rolling, sizing and water discharging are conducted, solution treatment at the temperature of 1080 DEG C and stabilizing treatment at the temperature of 900 DEG C are matched, and the grain size reaches 5.0-6.0 grades. The product provided by the invention has excellent mechanical properties, intergranular corrosion resistance and high-temperature stability, and is suitable for high-temperature and high-pressure environments in the coal chemical industry.

Description

Technical Field

[0001] This invention belongs to the field of seamless steel pipe manufacturing technology, specifically relating to an ultra-large diameter thick-walled TP347H stainless steel seamless steel pipe for coal chemical industry and its manufacturing method. Background Technology

[0002] With the increasing scale of the coal chemical industry, the requirements for key materials in oil refining plants with capacities of tens of millions of tons and ethylene plants with capacities of millions of tons are becoming increasingly stringent. TP347H austenitic stainless steel pipes, due to their high high-temperature strength and good oxidation resistance, have become the preferred material for core components in hydrocracking and residue hydrotreating processes. However, existing technologies for large-diameter, thick-walled TP347H steel pipes often suffer from problems such as uneven grain size (requiring grade 4-7), Nb segregation, and high gas content, leading to unstable product performance. Traditional processes, such as single smelting or simple heat treatment, are insufficient to meet the requirements for ultra-low gas content and fine grain size. For example, conventional forging heating processes easily result in coarse grains, while improper control of electroslag remelting parameters can induce Nb segregation. Therefore, it is necessary to develop a fully optimized process to achieve the manufacture of steel pipes with high purity, fine grain size, and excellent corrosion resistance. Summary of the Invention

[0003] To address the aforementioned shortcomings, this invention aims to provide an ultra-large diameter, thick-walled TP347H stainless steel seamless pipe for coal chemical industry and its manufacturing method, solving problems such as difficulty in controlling grain size, high gas content, and Nb segregation in the existing technology.

[0004] Therefore, the technical solution adopted by the present invention is as follows: a super large diameter thick-walled TP347H stainless steel seamless steel pipe for coal chemical industry, the chemical composition of which, by mass percentage, includes C 0.04-0.10%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.010%, Cr 17.00-19.00%, Ni 9.00-13.00%, Nb 8×C%-1.0%, with the balance being Fe and unavoidable impurities.

[0005] Furthermore, its chemical composition, by mass percentage, includes C 0.06%, Si 0.41%, Mn 0.95%, P 0.021%, S 0.002%, Cr 17.49%, Ni 9.27%, Nb 0.61%, with the balance being Fe and unavoidable impurities.

[0006] A method for manufacturing ultra-large diameter, thick-walled TP347H stainless steel seamless pipes for coal chemical industry includes the following steps: 1) Smelting: Control the [H] in the molten steel to ≤2ppm and [O] to ≤25ppm, and control the melting rate to 910-1040kg / h; 2) Forging: Forging yields tube blanks with a grain size of 3-5; 3) Tube making: The tube blank is heated under controlled temperature, pierced by a piercing mill, then subjected to Pilger forging and sizing, and immediately cooled in water. Subsequently, it undergoes solution treatment and stabilization treatment, and finally the grain size reaches grade 5.0-6.0.

[0007] Furthermore, in step 1), the [O] content in the molten steel is controlled to be ≤15ppm.

[0008] Furthermore, in step 1), the ppm concentrations of [H] and [O] are controlled by a six-stage smelting process of IF+AOD+LF+VD+IC+ESR, through full-process argon blowing in AOD and deep vacuum degassing in VD.

[0009] Furthermore, in step 1), the melting rate control adopts electroslag remelting, using a pre-melted slag system of CaF2:Al2O3:CaO=65:25:10.

[0010] Furthermore, in step 2), after the electroslag ingot is preheated in an annealing furnace, it is heated to 1230°C in a high-temperature furnace at a rate of 40°C / h and held for 10h, then heated to 1240°C and held for 4h. After upsetting and drawing forging, with a forging ratio of 4.5, a tube blank with a grain size of 3-5 is obtained.

[0011] Furthermore, in step 3), the tube blank is heated in three temperature-controlled stages at 500℃, 750℃, and 1220℃, pierced by a piercing mill, then subjected to Pilger forging and sizing, and immediately cooled in water. Subsequently, it undergoes solution treatment at 1080℃±10℃ for 160-200 min and stabilization treatment at 900℃±10℃ for 300-350 min, ultimately achieving a grain size of 5.0-6.0.

[0012] Furthermore, in step 1), the ppm concentration of [O] is controlled by preparing a high-content MgO+Al2O3 slag system through LF refining and using strong aluminum deoxidation.

[0013] Furthermore, in step 3), the piercing is performed using a conical roller piercing mill with a piercing deformation temperature of 1180-1220℃; the Pilger forging temperature range is 1150-1200℃; and the sizing is performed using a rotary sizing mill.

[0014] The advantages of this invention are: the steel pipe manufactured by this invention has a uniform chemical composition, low content of harmful elements, and excellent mechanical properties: room temperature tensile strength ≥515MPa, yield strength ≥205MPa, elongation ≥25%; high temperature (500℃) yield strength ≥139MPa; no cracks in 180° bending during intergranular corrosion testing (ASTM A262); no defects in low magnification structure and low content of non-metallic inclusions; the product of this invention has excellent mechanical properties, resistance to intergranular corrosion and high temperature stability, and is suitable for high temperature and high pressure environments in coal chemical industry. Attached Figure Description

[0015] Figure 1 This is a temperature curve of the solution treatment in this invention.

[0016] Figure 2 This is a temperature curve for the stabilization treatment of the present invention.

[0017] Figure 3 This is a metallographic diagram of the φ813mm×80mm structure of the present invention.

[0018] Figure 4 This is a diagram of intergranular corrosion of φ813mm×80mm in this invention. Detailed Implementation

[0019] Example 1: Manufacturing of φ813mm×80mm TP347H steel pipe Step 1: Smelting The process employs a six-step process: IF (Induction Remelting), AOD (Alternating Current Desulfurization), LF (Fuel Desulfurization), VD (Vacuum Desulfurization), IC (Induction Remelting), and ESR (Electroslag Remelting). After IF pretreatment of molten iron, AOD (Alternating Current Desulfurization) involves argon blowing for decarburization, LF (Alremainder Refining) for refining and alloying (target composition: C 0.050%, Al 0.015%), and VD (Vacuum Desulfurization) to control [H] ≤ 2ppm and [O] ≤ 25ppm. ESR (Electroslag Remelting) uses a 65:25:10 pre-melted slag with a melting rate of 950 kg / h.

[0020] Step 2: Forging The electroslag ingot (φ850mm) was preheated in an annealing furnace, then transferred to a high-temperature furnace and heated to 1230℃ at a rate of 40℃ / h, held for 10h, and then heated to 1240℃ and held for 4h. After upsetting and drawing forging, with a forging ratio of 4.5, the tube blank had a grain size of 4.0 grade.

[0021] Step 3: Tube making The tube blank is heated in three stages at 500℃, 750℃, and 1220℃, then pierced (mandrel diameter 660mm, incoming material temperature 1213℃), and then forged and rolled by Pilger (roll pass 813mm, mandrel diameter 665mm). After sizing, it is immediately placed in water. It undergoes solution treatment at 1080℃±10℃ for 160min, and stabilization treatment at 900℃±10℃ for 300min.

[0022] Performance testing The chemical composition conforms to ASTM A312 standard (see Table 1); room temperature mechanical properties: tensile strength 604-618MPa, yield strength 228-249MPa, elongation 46-49%; grain size 5.0-6.0 grade; no cracks when bending due to intergranular corrosion.

[0023] Table 1 Chemical composition (mass percentage) of φ813mm×80mm TP347H steel pipe

[0024] Table 2. Room temperature performance of φ813mm×80mm

[0025] Table 3 High Temperature Performance of φ813mm×80mm

[0026] Table 4 Hardness of φ813mm×80mm

[0027] Table 5 Grain size of φ813mm×80mm

[0028] Example 2: Manufacturing of φ914mm×100mm TP347H steel pipe The process is the same as in Example 1, with the following parameters adjusted: ESR melting rate 1000 kg / h; grain size of the forged billet 4.0-4.5; solution treatment holding for 200 min, stabilization holding for 350 min. The finished product has a grain size of 5.0-6.0 and a high-temperature (500℃) yield strength of 186-194 MPa, all of which meet the performance standards.

Claims

1. A coal chemical industry use super-large-diameter thick-wall TP347H stainless steel seamless pipe, characterized in that, The chemical composition includes C 0.04-0.10%, Si≤1.00%, Mn≤2.00%, P≤0.030%, S≤0.010%, Cr 17.00-19.00%, Ni 9.00-13.00%, Nb 8xC%-1.0% by mass percent, and the balance is Fe and inevitable impurities.

2. The coal chemical industry with super large diameter thick wall TP347H stainless steel seamless pipe according to claim 1, characterized in that, The chemical composition includes C 0.06%, Si 0.41%, Mn 0.95%, P 0.021%, S 0.002%, Cr 17.49%, Ni 9.27%, Nb 0.61% by mass percent, and the balance is Fe and inevitable impurities.

3. A manufacturing method of a coal chemical super-large-diameter thick-wall TP347H stainless steel seamless pipe, characterized by, The method comprises the following steps: 1) smelting: controlling [H]≤2ppm and [O]≤25ppm in the molten steel, and controlling the melting rate to be 910-1040 kg / h; 2) forging: obtaining a pipe blank with a grain size of 3-5 levels by forging; 3) pipe making: after the pipe blank is heated at a controlled temperature and perforated by a perforator set, pilger forging and sizing treatment are performed, and then the pipe blank is immediately cooled, followed by solid solution treatment and stabilization treatment, and finally the grain size reaches 5.0-6.0 levels.

4. The manufacturing method of the ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 1), the [O] in the molten steel is controlled to be ≤15ppm.

5. The manufacturing method of the ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 1), the ppm concentrations of [H] and [O] are controlled by using an IF+AOD+LF+VD+IC+ESR six-furnace smelting process, and by using AOD full-range argon blowing and VD deep vacuum degassing.

6. The manufacturing method of the ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 1), the melting rate is controlled by using electroslag remelting, and a pre-melted slag system of CaF2:Al2O3:CaO=65:25:10 is used.

7. The manufacturing method of the ultra-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 2), after the electroslag ingot is preheated in an annealing furnace, it is heated to 1230℃ at a rate of 40℃ / h in a high-temperature furnace and kept for 10h, and then heated to 1240℃ and kept for 4h, and then upset and drawn to obtain a pipe blank with a grain size of 3-5 levels.

8. The manufacturing method of a super-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 3), after the pipe blank is heated at a controlled temperature of 500℃, 750℃ and 1220℃, and perforated by a perforator set, pilger forging and sizing treatment are performed, and then the pipe blank is immediately cooled, followed by 1080℃±10℃ solid solution treatment, keeping for 160-200min, and 900℃±10℃ stabilization treatment, keeping for 300-350min, and finally the grain size reaches 5.0-6.0 levels.

9. The manufacturing method of a super-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 4, characterized in that, In the step 1), the ppm concentration of [O] is controlled by using LF refining to prepare a high-content MgO+Al2O3 slag system and using strong aluminum deoxidation.

10. The manufacturing method of a super-large-diameter thick-wall TP347H stainless steel seamless pipe for coal chemical industry according to claim 3, characterized in that, In the step 3), a conical roller perforator set is used for perforation, the perforation deformation temperature is 1180-1220℃, the pilger forging temperature is 1150-1200℃, and a rotary sizing machine is used for sizing.

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