Free forging process for ultra-large-diameter TP347H seamless steel pipe

Abstract

The invention relates to a free forging process for an ultra-large-diameter TP347H seamless steel pipe, which comprises the following steps of: firstly, finishing the surface of an electroslag ingot, sawing the tail end of the electroslag ingot, and chamfering the tail end and a riser end of the electroslag ingot; secondly, the punched blank is returned to a heating furnace to be heated, the blank is drawn out through a core shaft of the upper-flat and lower-V-shaped anvil, the blank is returned to the furnace to be heated, the blank is drawn out through a swaging core shaft until the two ends of the blank protrude, and the blank is subjected to heat treatment; the method comprises the following steps of: returning to a furnace for heating, drawing to the size of a finished forging stock by adopting a swaging core shaft, quickly hoisting the forged blank to a water tank for water cooling, and freely forging the TP347H stainless steel seamless steel pipe with the outer diameter of more than 800mm, the wall thickness of 80-100mm and the length of not less than 6000mm, thereby solving the manufacturing problem that the existing hot rolling mill cannot produce the ultra-large-diameter seamless steel pipe. The surface quality of the TP347H seamless steel pipe with the ultra-large diameter can be effectively controlled, and the grain size level and uniformity of the forging stock can be improved.

Description

Technical Field

[0001] This invention belongs to the field of ultra-large diameter austenitic stainless steel forging technology, specifically involving a free forging process for ultra-large diameter TP347H seamless steel pipes. It is mainly used for the free forging of TP347H stainless steel seamless steel pipes with an outer diameter of over 800mm, a wall thickness of 80-100mm, and a length of not less than 6000mm. Background Technology

[0002] As a crucial pillar of my country's energy system, the coal chemical industry plays an irreplaceable strategic role in promoting the clean and efficient conversion of coal resources and safeguarding national energy security. Currently, my country's coal chemical industry is accelerating its transformation towards high-quality development, exhibiting trends towards larger-scale equipment, integrated processes, and industrial clusters. Against this backdrop, performance optimization of the tertiary hydrogenation reaction pipeline—a key piece of equipment in coal chemical plants—has become a key focus of technological research in the industry.

[0003] TP347H austenitic stainless steel, with its unique niobium stabilization design, exhibits excellent high-temperature mechanical properties, superior creep resistance, and outstanding corrosion resistance, perfectly matching the stringent high-temperature, high-pressure, and highly corrosive working conditions required in coal-to-oil and coal chemical production processes.

[0004] Driven by both the continued rise in global energy demand and the clean energy transition, coal-to-oil and coal chemical industries, as important technological pathways for the clean utilization of coal, are ushering in a new round of development opportunities. This directly promotes...

[0005] The market for high-end pipe materials such as TP347H stainless steel pipes is growing rapidly. According to authoritative market research data, in recent years, the global annual demand for TP347H stainless steel pipes in the coal chemical industry has maintained a stable growth of 8%-12%. TP347H material pipes are already maturely used in the coal chemical industry abroad, while the adoption of TP347H material in China started relatively late.

[0006] Currently, the largest TP347H pipe produced by special steel manufacturers in my country has a diameter of 711mm, a wall thickness of 88mm, and a length of 6000mm, formed by pipe rolling. With the upgrading of coal chemical technology, the demand for larger pipe sizes in coal chemical applications is increasing. Due to the high deformation resistance of TP347H material, existing pipe rolling mills are no longer capable of manufacturing larger pipes (diameters exceeding 711mm). The market demand for TP347H pipes with diameters of 800mm and above requires hydraulic high-speed forging machines. However, this material has strict technical requirements, surface quality is difficult to control, and hollow free forging is challenging, especially the grain size requirement of 4-7, which is extremely stringent. There is no domestic experience in producing ultra-large diameter TP347H seamless steel pipes using hydraulic high-speed forging machines. To address this market demand challenge, there is an urgent need for a forging process that utilizes hydraulic high-speed forging machines to manufacture ultra-large diameter TP347H seamless steel pipes. Summary of the Invention

[0007] In view of the above, the purpose of this invention is to overcome the shortcomings of the prior art and provide a free forging process for ultra-large diameter TP347H seamless steel pipes, so as to solve the urgent manufacturing problem of ultra-large diameter TP347H seamless steel pipes in the coal chemical industry.

[0008] The objective of this invention is achieved as follows: a free forging process for ultra-large diameter TP347H seamless steel pipes, wherein the forging process is carried out according to the following procedure:

[0009] Step 1) Perform finishing treatment on the surface of the electroslag ingot to remove surface creases, cracks, and toad skin defects. The purpose of surface finishing treatment is to provide preliminary conditions for controlling surface quality during the forging process.

[0010] Step 2) Sawing the tail end of the electroslag ingot and chamfering the tail and riser ends of the electroslag ingot; Sawing requirements: Sawing off the slag-covered part at the tail end of the ingot, cutting off 50mm; Chamfering requirements: Determined according to the diameter of the electroslag ingot, it is 5% of the diameter of the electroslag ingot; The purpose of sawing the end and chamfering is to prevent the end corner cracks;

[0011] Step 3) Heat treatment: The furnace temperature for this steel grade is 1230-1250℃. Too high a temperature will cause high-temperature ferrite phase precipitation, while too low a temperature is not conducive to plastic deformation.

[0012] Step 4) Lightly press the entire electroslag ingot once, using an upper flat and lower V-shaped anvil to lightly press the entire ingot once, with a pressing amount of 30mm. After lightly pressing the entire ingot, maintain the billet's slope, which is 10mm / meter.

[0013] Step 5) Use a 7000-ton or larger hydraulic forging press to roughen the electroslag ingot. After standing the electroslag ingot vertically with the larger end facing down, first lightly press the electroslag ingot to fix its position, pressing down by 20-30mm. Then use the lower platform of the upper spherical roughing plate to roughen the electroslag ingot. The roughing process is carried out slowly, roughening the electroslag ingot to 50%-60% of its original height.

[0014] Step 6) Punching: Use a punch with the same diameter as the inner hole of the forging billet to punch holes in the roughened billet, and flatten the end face after punching.

[0015] Step 7) Return to furnace for reheating: Return the punched billet to the heating furnace for reheating at a temperature of 1230-1250℃.

[0016] Step 8) Use a 900mm upper flat lower V anvil mandrel to lengthen the billet once. After the billet reaches the temperature, insert the mandrel into the 900mm upper flat lower V anvil to lengthen the billet. Press the two ends first, and then press the middle.

[0017] Step 9) Return to the furnace for reheating, with the furnace temperature set at 1230-1250℃;

[0018] Step 10) The billet is drawn to a shape with protruding ends using a mandrel. After the billet has been drawn once, it is inserted into the mandrel and drawn again using a mandrel. This step is carried out in multiple passes, with the number of passes controlled at 2-3. During the drawing process, the two ends are pressed first, and then the middle is pressed, and the material is pressed evenly to prevent the mandrel from getting stuck. Before returning the billet to the furnace in the last pass, the billet is drawn to a shape with protruding ends. That is, the diameter of the 500mm long billet at both ends is 1.2 times the diameter of the finished forging billet, and the diameter of the remaining middle part is 1.1 times the diameter of the finished forging billet.

[0019] Step 11) Reheat in the furnace to a temperature of 1150-1200℃ and hold for 2-3 hours;

[0020] Step 12) Use a mandrel to lengthen to the finished forging size, press both ends first, then press the middle. After pressing the outer diameter to the finished size, pull out the mandrel, finish it, and close the holes at both ends for about 100mm.

[0021] Step 13) Water cooling after forging: Quickly hoist the forged billet to the water tank for water cooling. Water is passed through the upper and lower parts of the billet during the water cooling process to ensure the water cooling effect. The billet is cooled to room temperature.

[0022] The positive effects of this invention are as follows:

[0023] 1. The forging process of this invention can open up the hollow free forging manufacturing process of ultra-large diameter TP347H seamless steel pipes, and solve the manufacturing problem faced by existing hot rolling mills that cannot produce ultra-large diameter seamless steel pipes.

[0024] 2. The forging process of this invention can not only effectively control the surface quality of ultra-large diameter TP347H seamless steel pipes, but more importantly, it can improve the grain size level and uniformity of the forging billet, solving the technical problem of grain size that has troubled engineers. Detailed Implementation

[0025] To fully understand the inventiveness of this invention, the free forging process of ultra-large diameter TP347H seamless steel pipe will be described in detail in the embodiments to fully illustrate the content of this invention.

[0026] Example 1: A free forging process for ultra-large diameter TP347H seamless steel pipes. The finished TP347H seamless steel pipe has specifications of Φ813mm*Φ653mm*6000mm, and the forging billet has specifications of Φ860mm*Φ580mm*6600mm. The electroslag ingot weighs 22 tons, with a diameter of Ф1180mm / Ф1220mm and a length of approximately 2500mm. A 7000t hydraulic forging press is used. This forging process is carried out according to the following procedure:

[0027] Step 1) Perform finishing treatment on the surface of the electroslag ingot to remove defects such as surface creases, cracks, and toad skin.

[0028] Step 2) Cut off the 40mm long end of the electroslag ingot and chamfer the end of the electroslag ingot and the riser end by 60mm.

[0029] Step 3) Heat treatment: The heating curve is 350-400℃ for 6 hours, 1200℃ for 25 hours, and 1250℃ for 20 hours.

[0030] Step 4) Lightly press the entire electroslag ingot once: When the electroslag ingot reaches the temperature and is taken out of the furnace for forging, use an upper flat and lower V anvil to lightly press the entire ingot once, with a pressing amount of 30mm. After the entire ingot is lightly pressed, maintain the billet slope, which is 10mm / meter.

[0031] Step 5) Use a 7000-ton hydraulic forging press to roughen the electroslag ingot: After standing the electroslag ingot upright with the larger end (the end with the larger diameter) facing down, first gently press the electroslag ingot to fix its position, pressing down by 30mm, and then use the lower platform of the upper spherical roughing plate to roughen the electroslag ingot. The roughing process is carried out slowly. After roughening to half, pause for 3 seconds, and then roughen the electroslag ingot to 1500mm.

[0032] Step 6) Punching: Use a Ф580 punch to punch holes in the roughened blank, and flatten the end face after punching.

[0033] Step 7) Return to furnace for heating: Return the punched billet to the heating furnace for heating at 1240℃ for 4 hours;

[0034] Step 8) Use a 900mm upper flat lower V-shaped anvil mandrel to lengthen the billet once: After the billet reaches the desired temperature, insert a Ф580 mandrel on a 900mm upper flat lower V-shaped anvil to lengthen the billet to Ф1200mm, with a length of about 3000mm. During the lengthening process, press the two ends first, then press the middle, press down with rapid large deformation, and press down with overlapping and staggered anvils. This process does not require uniform compaction, just ensure that the whole body is spun and pressed 2-3 times.

[0035] Step 9) Reheating: Heat the furnace to 1250℃ and hold for 4 hours;

[0036] Step 10) Using a wrench mandrel, the billet is drawn to a length of 500mm at both ends with a diameter of 1050mm, and the remaining middle part has a diameter of 960mm. This step is completed in 2 heats. During the drawing process, the two ends are pressed first, and then the middle part is pressed, and the compaction is even. The pressing of the two ends requires half anvil feed and large pressing amount forging. The remaining middle part is fed with full anvil feed and forging with overlapping anvils.

[0037] Step 11) Reheating: Heat the furnace to 1180℃ and hold for 2.5 hours;

[0038] Step 12) Use a mandrel to lengthen to the finished forging size: first press the two ends, then press the middle. During the pressing of the two ends, half anvil feed is required, and a large amount of forging is applied. The remaining middle part is fed with full anvil feed, and the anvils are overlapped and staggered forging is used. After the outer diameter is pressed to the finished size, the mandrel is pulled out. The two ends are first holed about 100mm in length, and then finished.

[0039] Step 13) Water cooling after forging: Quickly hoist the forged billet to the water tank for water cooling. Water is passed through the upper and lower parts of the billet during the water cooling process. The billet is cooled to room temperature. The water temperature is controlled below 35℃ before the billet is put into the water.

[0040] The TP347H seamless steel pipe with forging dimensions of Φ860mm*Φ580mm*6600mm produced according to the above steps was then rough-processed and heat-treated. Samples were cut from both ends and the grain size was tested according to ASTM E112 standard. The results are shown in Table 1.

[0041] Table 1. Grain size detection results

[0042]

[0043] Example 2: Free forging process for ultra-large diameter TP347H seamless steel pipe. The finished TP347H seamless steel pipe has specifications of Φ914mm*Φ714mm*6000mm, and the forging billet has specifications of Φ960mm*Φ650mm*6600mm. The electroslag ingot weighs 27 tons, with a diameter of Ф1300mm / Ф1350mm and a length of approximately 2500mm. The equipment used is an 11000t hydraulic forging press. This forging process is carried out according to the following procedure:

[0044] Step 1) Perform finishing treatment on the surface of the electroslag ingot to remove defects such as surface creases, cracks, and toad skin.

[0045] Step 2) Cut off 50mm of the tail end of the electroslag ingot with a saw, and chamfer the tail end and riser end of the electroslag ingot by 65mm;

[0046] Step 3) Heat treatment: The heating curve is 350-400℃ for 6 hours, 1200℃ for 25 hours, and 1250℃ for 20 hours.

[0047] Step 4) Lightly press the entire electroslag ingot once: When the electroslag ingot reaches the temperature and is taken out of the furnace for forging, use an upper flat and lower V anvil to lightly press the entire ingot once, with a pressing amount of 30mm. After the entire ingot is lightly pressed, maintain the billet slope, which is 10mm / meter.

[0048] Step 5) Use an 11,000-ton hydraulic forging press to roughen the electroslag ingot: After standing the electroslag ingot upright with the larger end (the end with the larger diameter) facing down, first gently press the electroslag ingot to fix its position, pressing down by 30mm, and then use the lower platform of the upper spherical roughing plate to roughen the electroslag ingot. The roughing process is carried out slowly. After roughening to half, pause for 3 seconds, and then roughen the electroslag ingot to 1500mm.

[0049] Step 6) Punching: Use a Ф650 punch to punch holes in the roughened blank; flatten the end face after punching;

[0050] Step 7) Return to furnace for heating: Return the punched billet to the heating furnace for heating at 1240℃ for 4 hours;

[0051] Step 8) Use a 900mm upper flat lower V anvil mandrel to lengthen the billet once: After the billet reaches the temperature, insert a Ф650 mandrel on a 900mm upper flat lower V anvil to lengthen the billet to Ф1350mm, with a length of about 3000mm. During the lengthening process, press the two ends first, then press the middle, press down with rapid large deformation, and press down with overlapping and staggered anvils. This process does not require uniform compaction, just ensure that the whole body is spun and pressed 2-3 times.

[0052] Step 9) Reheating: Heat the furnace to 1250℃ and hold for 4 hours;

[0053] Step 10) Using a wrench mandrel, the billet is drawn to a length of 500mm at both ends with a diameter of 1170mm, and the remaining middle part has a diameter of 1070mm. This step is completed in 2 heats. During the drawing process, the two ends are pressed first, and then the middle part is pressed, and the compaction is even. The pressing of the two ends requires half anvil feed and large pressing amount forging. The remaining middle part is fed with full anvil feed and forging with overlapping anvils.

[0054] Step 11) Reheating: Heat the furnace to 1200℃ and hold for 2.5 hours.

[0055] Step 12) Use a mandrel to lengthen to the finished forging size: first press the two ends, then press the middle. During the pressing of the two ends, half anvil feed is required, and a large amount of forging is applied. The remaining middle part is fed with full anvil feed, and the anvils are overlapped and staggered forging is used. After the outer diameter is pressed to the finished size, the mandrel is pulled out. The two ends are first holed about 100mm in length, and then finished.

[0056] Step 13) Water cooling after forging: Quickly hoist the forged billet to the water tank for water cooling. Water is passed through the upper and lower parts of the billet during the water cooling process. The billet is cooled to room temperature. The water temperature is controlled below 35℃ before the billet is put into the water.

[0057] The TP347H seamless steel pipe with forging dimensions of Φ960mm*Φ650mm*6600mm produced according to the above steps was then rough-processed and heat-treated. Samples were cut from both ends and the grain size was tested according to ASTM E112 standard. The results are shown in Table 2.

[0058] Table 2 Grain size detection results

[0059]

Claims

1. A free forging process for ultra-large diameter TP347H seamless steel pipe, characterized in that: This forging process is carried out according to the following procedure: Step 1) Perform finishing treatment on the surface of the electroslag ingot to remove surface creases, cracks, and toad skin defects. The purpose of surface finishing treatment is to provide preliminary conditions for controlling surface quality during the forging process. Step 2) Sawing the tail end of the electroslag ingot and chamfering the tail and riser ends of the electroslag ingot; Sawing requirements: Sawing off the slag-covered part at the tail end of the ingot, cutting off 50mm; Chamfering requirements: Determined according to the diameter of the electroslag ingot, which is 5% of the diameter of the electroslag ingot; The purpose of sawing the end and chamfering is to prevent end corner cracking; Step 3) Heat treatment: The furnace temperature for this steel grade is 1230-1250℃. Too high a temperature will cause high-temperature ferrite phase precipitation, while too low a temperature is not conducive to plastic deformation. Step 4) Lightly press the entire electroslag ingot once, using an upper flat and lower V anvil to lightly press the entire ingot once, with a pressing amount of 30mm. After lightly pressing the entire ingot, maintain the billet's slope, which is 10mm / meter. Step 5) Use a 7000-ton or larger hydraulic forging press to roughen the electroslag ingot. After standing the electroslag ingot vertically with the larger diameter end facing down, first lightly press the electroslag ingot to fix its position, pressing down by 20-30mm. Then use the lower platform of the upper spherical roughing plate to roughen the electroslag ingot. The roughing process is carried out slowly, roughening the electroslag ingot to 50%-60% of its original height. Step 6) Punching: Use a punch with the same diameter as the inner hole of the forging billet to punch holes in the roughened billet, and flatten the end face after punching. Step 7) Return to furnace for reheating: Return the punched billet to the heating furnace for reheating at a temperature of 1230-1250℃. Step 8) Use a 900mm upper flat lower V anvil mandrel to lengthen the billet once. After the billet reaches the temperature, insert the mandrel into the 900mm upper flat lower V anvil to lengthen the billet. Press the two ends first, and then press the middle. Step 9) Return to the furnace for reheating, with the furnace temperature set at 1230-1250℃; Step 10) The billet, after one drawing pass, is lengthened to a shape with protruding ends using a mandrel. This step is performed in multiple passes, controlled to 2-3 passes. During the lengthening process, the ends are pressed first, then the middle, ensuring even compaction to prevent the mandrel from jamming. Before the final drawing pass, the billet is lengthened to a shape with protruding ends, meaning the diameter of the 500mm long billet at both ends is 1.2 times the diameter of the finished forging billet, and the remaining middle portion is 1.1 times the diameter of the finished forging billet. Step 11) Reheat in the furnace to a temperature of 1150-1200℃ and hold for 2-3 hours; Step 12) Use a mandrel to lengthen to the finished forging size, press both ends first, then press the middle. After pressing the outer diameter to the finished size, pull out the mandrel, finish it, and close the holes at both ends for about 100mm. Step 13) Water cooling after forging: Quickly hoist the forged billet to the water tank for water cooling. Water is passed through the upper and lower parts of the billet during the water cooling process to ensure the water cooling effect. The billet is cooled to room temperature.

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