Manufacturing method of 14CrMnSi thick pipe plate for pressure vessel

Abstract

The invention provides a manufacturing method of a 14CrMnSi thick pipe plate for a pressure vessel. The manufacturing method comprises the following steps: (1) preparing materials; (2) blanking; (3) heating before forging: heating the raw materials to 1250 DEG C, and keeping the temperature for more than or equal to 24 hours; (4) forging is conducted, specifically, upsetting is conducted firstly, drawing-out, upsetting and spinning upsetting are conducted through an FM method, and then upsetting, rounding, flattening and forming are conducted in a double-face center indenting mode; (5) composite pre-heat treatment: after forging, slowly cooling to 280-350 DEG C, and carrying out hydrogen diffusion treatment; then carrying out heat preservation at 920-940 DEG C, then carrying out furnace cooling to 660-700 DEG C, and carrying out isothermal annealing; and (6) performance heat treatment is conducted, specifically, the workpiece is heated to 940-970 DEG C for quenching, and tempering is conducted at 650-670 DEG C after water cooling. The problems that the low-temperature impact performance of the thick-wall forge piece is insufficient, internal structure defects are difficult to eliminate, and performance attenuation is serious after simulation welding are solved.

Description

Technical Field

[0001] This invention relates to the field of pressure vessel manufacturing technology, and specifically to a method for manufacturing 14CrMnSi thick tube plates for pressure vessels. Background Technology

[0002] Currently, the requirements for low-temperature impact toughness, strength, and microstructure uniformity of materials for thick-walled tubes used in pressure vessels are extremely high in low-temperature environments. Commonly used materials such as 20MnMoNb and 14Cr1Mo suffer from insufficient low-temperature impact performance under large thickness conditions, significant performance degradation after simulated welding, and difficulty in eliminating internal microstructure defects.

[0003] In particular, for 14CrMnSi (Russian standard 14XГС) material, the control of microstructure genetic defects and low-temperature toughness in thick-walled forgings has become a technical challenge.

[0004] 1. The material has limited applications in related industries and is suitable for low-temperature environments. Its low-temperature impact performance cannot meet stringent requirements, and its performance degrades significantly when simulated with weld thickness.

[0005] 2. Internal structural defects in thick-walled forgings (>500mm) made of 14CrMnSi material are difficult to eliminate, and the hereditary structural defects are prominent. Summary of the Invention

[0006] The present invention aims to provide a manufacturing method for 14CrMnSi thick tube plates, which solves the problems of insufficient low-temperature impact performance, difficulty in eliminating internal structural defects, and severe performance degradation after simulated welding in the prior art.

[0007] The present invention adopts the following technical solution: A method for manufacturing 14CrMnSi thick tube plates for pressure vessels includes the following steps: (1) Material preparation: 14CrMnSi steel ingots were smelted using the EAF+LF+VD process. The composition was controlled by weight percentage as follows: C: 0.11~0.16%, Si: 0.40~0.70%, Mn: 0.90~1.30%, P≤0.030%, S≤0.030%, Cr: 0.50~0.80%, Ni: 0.20~0.30%, Cu≤0.30%, V: 0.030~0.050%, Nb: 0.02~0.03%, As≤0.08%, Al: 0.020~0.045%, with the balance being Fe; Si: Deoxidizes and purifies molten steel, strengthens it through solid solution treatment to improve its strength, and enhances its forging and heat treatment processability; Mn: Solid solution strengthening, improves the toughness and hardenability of steel, and assists in deoxidation and desulfurization; Cr: Improves the corrosion resistance, strength, and hardenability of steel, and enhances its low-temperature impact performance; Ni: Improves low-temperature impact toughness and enhances the plasticity and toughness reserves of steel; V: Refines grains, precipitation strengthens, and improves the strength and toughness of steel; Nb: refines grains, inhibits austenite growth, and enhances strength, toughness, and weldability; Al: A strong deoxidizer that refines grains and improves the low-temperature impact toughness of steel.

[0008] (2) Feeding (3) Pre-forging heating: Heat the raw material to 1250℃ and hold for ≥24 hours; return it to the furnace during the process, with a heating temperature of 1230~1250℃ and a holding time of 0.2~0.6min / mm to ensure that the core position reaches the required temperature and meets the forging requirements; (4) Forging: Using a press of 15000T or above, first upsetting, then drawing using the FM method, upsetting, spinning upsetting, then upsetting using the double-sided center dent method, rolling, flattening, and forming; (5) Composite preheating treatment: After forging, the temperature is slowly cooled to 280-350℃ and hydrogen diffusion treatment is carried out; then, after holding at 920-940℃, the temperature is furnace cooled to 660-700℃ for isothermal annealing. (6) Performance heat treatment: Heat the workpiece to 940-970℃ for quenching, water cool it and then temper it at 650-670℃.

[0009] Preferably, the double-sided center indentation in step (2) is performed in two steps, with the first indentation depth being 100-150 mm and the second indentation depth being 60-100 mm.

[0010] Preferably, the isothermal annealing holding time in step (5) above is 30 to 50 hours.

[0011] Preferably, in step (6) above, the quenching holding time is 1000mm × 1.5 minutes / mm = 1500 minutes, water cooling after removal from the furnace, and the tempering holding time is 1000mm × 3 minutes / mm = 3000 minutes, air cooling after removal from the furnace.

[0012] The core protection of this invention lies in its integrated solution for the low-temperature operating requirements of 14CrMnSi (14XГС) thick-walled tube sheet forgings, which combines precise composition analysis, composite forging processes, and a customized heat treatment system. This solution addresses the pain points of insufficient low-temperature impact toughness and difficulty in eliminating microstructural defects in 14CrMnSi thick-walled forgings that cannot be solved by existing technologies, demonstrating significant inventiveness, as detailed below: (1) Composition ratio of 14CrMnSi (14XГС) material suitable for thick-walled low-temperature working conditions; The weight percentage range of the 14CrMnSi material composition is limited, with particular emphasis on controlling the proportions of Nb (0.02–0.03%), Al (0.020–0.045%), Ni (0.20–0.30%), and Cr (0.50–0.80%).

[0013] (2) Composite forging process of FM drawing + double-sided center dent Existing technologies conventionally employ a process of upsetting + simple drawing + upsetting, which easily leads to insufficient core compaction and microstructural defects in thick-walled forgings. The FM (Medium-Flattening) method, through drawing, creates triaxial compressive stress, welding together the internal porosity and shrinkage cavities of the ingot. Simultaneously, double-sided indentation addresses the problem of uneven surface-core deformation in thick-walled forgings.

[0014] (3) Composite pre-heat treatment process of hydrogen diffusion + isothermal annealing Existing technology: The conventional process involves a combination of normalizing and tempering, which fails to address the issue of uneven microstructure in thick-walled forgings. After hydrogen diffusion, a second heating to 920–940℃ followed by furnace cooling to the isothermal phase transformation range ensures a uniform transformation of austenite into ferrite and pearlite, laying the foundation for subsequent performance heat treatment.

[0015] (4) Heat treatment parameters adapted to simulated weld performance High-temperature quenching ensures more complete austenitization. Then, the corresponding tempering temperature ensures that the tempered solid meets the strength requirements while avoiding carbide coarsening caused by high-temperature tempering, which would affect low-temperature impact toughness.

[0016] (5) Integrated manufacturing involving composition, forging, and heat treatment A closed-loop system is formed, consisting of precise composition, composite forging, composite pre-heat treatment, and performance heat treatment, specifically designed to meet the requirements of simulated welding performance at low temperatures for thick-walled forgings made of 14CrMnSi material.

[0017] The beneficial effects of this invention are: 1. Appropriate ingredient ratio – synergistic effect of multiple elements Technical effect: Constructing a composite strengthening system of grain refinement + solid solution strengthening + dispersion strengthening reduces the difference between internal and external structures on the original basis, and achieves a balanced performance of high strength and high and low temperature toughness.

[0018] Mechanism of action: On the one hand, Si's deoxidizing and purifying effect reduces the content of non-metallic inclusions, preventing them from becoming fracture sources. On the other hand, Cr and Al improve hardenability, ensuring a uniform microstructure and refined grains in the core of thick forgings. Simultaneously, in combination with Ni, V, and Nb, it inhibits austenite grain growth during subsequent forging, pre-heat treatment, and performance heat treatment, refining grain size during forging and heat treatment, while promoting dispersion strengthening. In particular, VC and NbC maintain a fine and dispersed state at high temperatures, more effectively inhibiting grain growth.

[0019] 2. Composite forging process for thick tube plates – effective compaction process scheme Technical effects: The FM forging method and the central dent composite forging process enhance the core compaction effect, eliminate structural defects, and refine the grains.

[0020] Mechanism of action: Addressing the propagation of internal defects caused by tensile stress in the core, the FM method induces plastic flow in the core metal, compacting and welding away defects such as porosity and shrinkage cavities. Simultaneously, it breaks down the original coarse columnar grains, forming fine austenite grains and disrupting the original microstructure. During the upsetting stage, a double-sided center indentation method is used, employing specialized tooling to apply concentrated pressure to the central area of ​​the upper and lower surfaces of the forging. This results in greater deformation in the core metal compared to the surface layer, promoting subsequent recrystallization and further refining the core grains.

[0021] 3. Composite pre-heat treatment process – eliminating white spots and optimizing microstructure Technical effect: It completely eliminates hydrogen-induced white spot defects in thick forgings, transforming the forging microstructure into a uniform ferrite + pearlite, providing a uniform and stable original microstructure for subsequent performance heat treatment.

[0022] Mechanism of action: During the isothermal annealing process, the austenite is transformed into ferrite + pearlite at a uniform rate. Compared with the ordinary normalizing + tempering process, the ferrite grains formed by isothermal annealing are finer, the pearlite lamellae are more uniform, and there are no unstable phases such as residual austenite and martensite in the microstructure.

[0023] 4. Targeted performance heat treatment process – high-temperature quenching + precision tempering Technical benefits: High-temperature heating of 940-970℃, which is higher than the conventional quenching temperature, ensures complete austenitization of the core of the thick-walled forging. During the quenching process, finer martensite laths are formed, ensuring the dispersion and precipitation of more carbides during the subsequent tempering process. Detailed Implementation

[0024] The present invention will be further described below with reference to embodiments. These embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention. Example 1

[0025] The steps for preparing a Φ3320×955mm pressure vessel base forging are as follows: 1. Raw material preparation Ingot specifications: 14CrMnSi alloy ingots were prepared using the EAF+LF+VD process, weighing 103 tons. The chemical composition is as follows (wt%).

[0026]

[0027] 2. Composite forging process (1) Pre-forging heating Heating equipment: Gas-fired furnace, temperature control accuracy ±15℃ Heating parameters: Heat to 850℃ and hold for >6 hours; then heat to 1250℃ at a rate of <150℃ / h and hold for ≥24 hours. The equipment is then returned to the furnace during the process, with a heating temperature of 1230~1250℃ and a holding time calculation coefficient of 0.2~0.6min / mm.

[0028] (2) Upsetting and forging Equipment: 15000T hydraulic press 1) Pre-upsetting: Upset to approximately H≈2000mm; 2) FM method drawing: 35%–45% reduction per pass. Drawing to Φ1700×4300mm; 3) Upsetting by vertical forming to Φ2200×2830mm; upsetting by spinning to Φ3150×1250mm 4) Use tooling to perform double-sided denting. The first indentation was made to a depth of 120mm. The second indentation was performed, with an indentation depth of 80mm; 5) Flatten the top and bottom surfaces, roll them round, and correct the dimensions to Φ3400×1020mm. The forming is now complete.

[0029] 3. Post-forging composite pre-heat treatment process After forging, transfer the tube sheet to a sand pit to avoid rapid cooling. Slowly cool it to 280–350°C, then heat it in the furnace and hold it for 2–3 hours until it reaches the desired temperature. Increase the temperature to 650°C ± 20°C according to the power rating and hold for 2–4 hours. Continue heating to 920–940°C and hold for approximately 1020 × 1.5 minutes / mm = 1530 minutes. Air cool it to 320 ± 20°C and hold for approximately 1020 × 1.8 minutes / mm = 1836 minutes, meaning the holding time is greater than 30 hours.

[0030] After hydrogen expansion, the workpiece is heated to 650℃ at a rate of 50-80℃ / h, held for 3-4 hours, then heated to 920-940℃ and held for 18 hours. It is then furnace cooled to 660-700℃ and held for 40 hours before being removed from the furnace and air-cooled.

[0031] 4. Performance heat treatment 1) Austenitizing treatment Process parameters: Heat to 960℃, hold for 1000mm × 1.5 minutes / mm = 1500 minutes, then water cool after removal from the furnace. Water cooling time is greater than 2 hours.

[0032] 2) Tempering treatment Process parameters: Heat to 660℃, hold for 1000mm × 3 minutes / mm = 3000 minutes, then air cool after removal from the furnace.

[0033] 5. Performance Testing

[0034] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for manufacturing a 14CrMnSi thick tube plate for pressure vessels, characterized in that, Includes the following steps: (1) Material preparation: Prepare 14CrMnSi steel by weight percentage, with the following chemical composition: C: 0.11~0.16%, Si: 0.40~0.70%, Mn: 0.90~1.30%, P≤0.030%, S≤0.030%, Cr: 0.50~0.80%, Ni: 0.20~0.30%, Cu≤0.30%, V: 0.030~0.050%, Nb: 0.02~0.03%, As≤0.08%, Al: 0.020~0.045%, with the balance being Fe; (2) Feeding (3) Pre-forging heating: Heat the raw material to 1250℃ and hold for ≥24 hours; return it to the furnace during the process, with a heating temperature of 1230~1250℃ and a holding time of 0.2~0.6min / mm, to ensure that the core position reaches the required temperature and meets the forging requirements; (4) Forging: Using a press of 15000T or above, first upsetting, then drawing using the FM method, upsetting, spinning upsetting, then upsetting using the double-sided center dent method, rolling, flattening, and forming; (5) Composite preheating treatment: After forging, the temperature is slowly cooled to 280-350℃ and hydrogen diffusion treatment is carried out; then, after holding at 920-940℃, the temperature is furnace cooled to 660-700℃ for isothermal annealing. (6) Performance heat treatment: Heat the workpiece to 940-970℃ for quenching, water cool it and then temper it at 650-670℃.

2. The manufacturing method of a 14CrMnSi thick tube plate for pressure vessels according to claim 1, characterized in that, In step (2), the double-sided center indentation is performed twice. The depth of the first indentation is 100-150 mm, and the depth of the second indentation is 60-100 mm.

3. The manufacturing method of a 14CrMnSi thick tube plate for pressure vessels according to claim 1, characterized in that, The isothermal annealing and heat preservation time in step (5) is 30 to 50 hours.

4. The manufacturing method of a 14CrMnSi thick tube plate for pressure vessels according to claim 1, characterized in that, In step (6), the quenching holding time is 1000mm × 1.5 minutes / mm = 1500 minutes, and the furnace is cooled by water. The tempering holding time is 1000mm × 3 minutes / mm = 3000 minutes, and the furnace is cooled by air.

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