Method for manufacturing 30crmnisia high-toughness ultrahigh-strength steel pipe

Abstract

This invention provides a method for manufacturing high-toughness and ultra-high-strength steel pipes, comprising the following steps: 1) electric arc furnace smelting; 2) ladle refining; 3) VD vacuum degassing; 4) continuous casting; 5) low-temperature annealing; 6) through-hole drilling; 7) heating; 8) skew rolling piercing; 9) periodic pipe rolling; 10) mist cooling; 11) normalizing + tempering; 12) internal and external grinding. This invention, through electric arc furnace smelting + ladle refining + VD vacuum degassing + continuous casting, not only meets the requirements for high-purity steel with low phosphorus and low sulfur content, but also has lower smelting costs than other processes. By using a round billet center mill to add through-holes, the amount of piercing deformation is reduced, metal flow conditions are optimized, and internal and external surface defects under complex stress conditions during piercing are improved. Based on the integrated deformation of forging, rolling, and extrusion, four processes—forging and rolling, precision rolling, sizing, and pipe removal—are realized, which not only refines the product grains and makes the longitudinal and transverse properties uniform, but also improves the geometric dimensional accuracy and internal and external surface quality of the steel pipe.

Description

Technical Field

[0001] This invention belongs to the field of pipe manufacturing and processing technology, specifically a method for manufacturing 30CrMnSiA high-toughness ultra-high-strength steel pipes that can not only further improve the strength of steel without reducing toughness, but also improve the weldability of steel. Background Technology

[0002] With the development of equipment technology, higher requirements have been placed on the comprehensive performance of pipe materials. The market needs a high-toughness, ultra-high-strength steel pipe. Compared with ordinary pipe products, this product requires higher flexibility, impact resistance, high uniformity, ultra-high strength, and good processing performance, facilitating mass production and offering high added value. It can be widely used in gas, power, mining, high-pressure vessels, military, and other fields. Traditional pipe manufacturing methods can no longer meet the technical requirements of customers. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for manufacturing high-toughness and ultra-high-strength steel pipes by means of electric arc furnace smelting + ladle refining + VD vacuum degassing + continuous casting, which not only meets the requirements for high-purity steel with low P and low S, but also has a lower smelting cost compared to other process routes.

[0004] The technical solution of this invention is achieved as follows: A method for manufacturing 30CrMnSiA high-toughness ultra-high-strength steel pipe includes the following steps:

[0005] Step 1) The furnace charge consists of 40-70% high-quality steel scrap, 20-40% pig iron, and 10-30% returned steel scrap, according to the total charge. 1-2 tons of lime and 0.5-1.5 tons of carbon raiser are added to the furnace or charge basket according to the charge conditions. Sampling and analysis of the molten steel are performed to control As, Sn, Pb, Sb, and Bi to be ≤0.015%. Electric arc furnace tapping conditions: [C]: 0.05-0.25%, [P] ≤0.003%, temperature ≥1640℃. 1.0-3.0 kg / t of aluminum blocks and 4-6 kg / t of lime are added to the ladle. During tapping, 10-13 kg / t of ferrosilicon alloy, 10-13 kg / t of ferromanganese alloy, and 12-13 kg / t of ferrochrome alloy are added.

[0006] Step 2) Ladle refining: During the slag formation process in the ladle, deoxidize in batches using 1-2 kg / t of calcium carbide, 2-4 kg / t of carbon powder and ferrosilicon powder. Then, after temperature measurement and sampling, argon is blown and aluminum wire is fed according to the residual aluminum content. The slag amount is controlled at 1.0-1.2 t and the basicity is 2-4. Strengthen the deoxidation operation. After the slag turns white, maintain the reducing atmosphere with 0.5-1.0 kg / t of carbon powder, 1.0-2.0 kg / t of aluminum powder, and 1.0-2.0 kg / t of calcium silicate powder. The white slag should be maintained for ≥20 min. The composition adjustment is completed before ladle hoisting. The carbon content of the intermediate ladle sample is controlled at 0.26-0.28%.

[0007] Step 3) VD Vacuum Degassing: The ladle is fed into the vacuum tank at a temperature of 1660–1680℃ from the LF furnace. After the ladle is in place, the temperature is measured and maintained at ≤0.7 mbar for ≥20 min. The temperature is controlled to meet the requirements of the continuous casting platform after weak stirring in the VD system. After breaking the vacuum, hydrogen and oxygen are determined online, controlling [H] ≤0.8 ppm and [O] ≤4.0 ppm. A gas sample is taken from a glass tube to analyze the nitrogen content, controlling [N] ≤40 ppm and [Al] 0.015–0.03%. If insufficient, aluminum wire is fed in for adjustment. Calcium wire is fed at 0.1–0.3 m / t for calcium treatment (feeding speed 120 m / min). After feeding, argon is blown and weakly stirred for ≥12 min. The initial furnace ladle temperature is 1565–1575℃, and the continuous casting ladle temperature is 1560–1570℃.

[0008] Step 4) Continuous casting: The tundish is baked for 4.5-6 hours. After the tundish baking is stopped, the argon blowing replacement pipe is immediately inserted. The long nozzle argon blowing pipe is checked to ensure that the argon blowing is unobstructed and well sealed. The ladle is drained outside the tundish. The long nozzle is opened for argon blowing before the continuous casting begins. The crystallizer protective slag is WBP-7. The tundish is protected with 300-400 kg of carbon-free covering agent and carbonized rice husk double layer. Casting speed: 0.22 m / min for superheat ≤ 20℃, 0.2 m / min for superheat 20-40℃, and 0.18 m / min for superheat > 40℃.

[0009] Step 5) Low-temperature annealing: Heat at 500-650℃ for 3 hours, raise the temperature to 700℃ at a rate of ≤100℃ / h, hold for 9 hours, and cool down to ≤200℃ at a rate of ≤30℃ / h before removing from the furnace;

[0010] Step 6) Drilling through holes: Use a milling machine to drill a Φ110 through hole in the billet. After drilling the through hole, use an endoscope to check the quality of the inner hole.

[0011] Step 7) Heating: Use a multi-stage heating method. Preheat at 650℃ for 3 hours, rapidly increase to 850℃ and hold for 4 hours, then increase to 1000℃ and hold for 3 hours, then increase to 1100℃ and hold for 1.5 hours, then increase to 1260℃ and hold for 2.25 hours, and finally slowly decrease to 1250℃ and hold for 2 hours to obtain good plastic deformation ability.

[0012] Step 8) Skew rolling piercing: The billet with the through hole is pierced using a two-roll skew rolling piercing mill. The process adopts diameter expansion deformation. The roll gap of the two rolls of skew rolling piercing, the guide distance of the upper and lower guide plates and the diameter of the mandrel are accurately calculated.

[0013] Step 9) Cyclic rolling: Rolling is performed using a Pilger rolling mill. Cooling water is reduced during forging and rolling. The roll pass curve adopts a hyperbolic non-circular pass curve. A special pass is designed and manufactured according to the finished product specifications. A special tapered mandrel with a ratio of 2000:1 is used. The rotation speed is 35-40 rpm and the feed rate is 35-40 mm. The rolling temperature is controlled above 850℃ during the rolling process.

[0014] Step 10) Fogging: After forging and rolling, the product is transferred to a fogging area for fogging and cooled to room temperature;

[0015] Step 11) Normalizing + Tempering: Normalizing temperature 890±10℃, holding time 2.5h, heating rate not greater than 100℃ / h, Tempering: 650±10℃, holding time not less than 5h.

[0016] Step 12) Internal and external grinding: The inside and outside of the pipe are rough ground to a smooth finish, so that there are no visible folds or cracks on the surface of the steel pipe, ensuring that the outer diameter deviation is ≤ ±4mm, the wall thickness deviation is -2.0~+3.5mm, and the out-of-roundness is ≤ 5mm.

[0017] The steel is 30CrMnSiA, wherein P≤0.008%, S≤0.002%, Al:0.015%~0.035%, Ni:0.5%~0.8%, and the gaseous components H≤1.2ppm, O≤15ppm, and N≤50ppm.

[0018] The continuously cast billet is a Φ600mm continuous casting billet.

[0019] The finished pipe specifications are Φ377×30 (wall thickness) mm and Φ473×30 (wall thickness) mm;

[0020] Before the forging and rolling slant rolling piercing, a through hole needs to be drilled. The through hole specification is Φ110mm, and the process adopts diameter expansion deformation. During the periodic rolling of the tube, a Pilger tube rolling mill is used, and the rolling temperature is controlled above 850℃ during the rolling process.

[0021] The steel pipe is rolled by a combination of skew rolling and longitudinal rolling. The finishing strip adopts a hyperbolic non-circular die and uses special die types Dk387 and Dk482. In addition, the mandrel taper is 2000:1, the surface roughness is ≤Ra1.6, and the ellipticity is ≤0.2mm.

[0022] After the tubing is formed, it is fog-cooled, and then normalized and tempered.

[0023] The pipe has a tensile strength Rm of ≥1650MPa, a specified non-proportional elongation strength Rp0.2 of ≥1300MPa, and an impact absorption energy KU2 of ≥50J.

[0024] The positive effects of this invention are as follows: The process flow is not complex. Through electric arc furnace smelting + ladle refining + VD vacuum degassing + continuous casting, it meets the requirements for high-purity steel with low phosphorus and low sulfur content, and the smelting cost is lower compared to other process routes. By adding through holes to the round billet center, the amount of piercing deformation is reasonably reduced, the metal flow conditions are optimized, and the internal and external surface defects caused by complex stress conditions during piercing are improved. Based on the integrated deformation of forging, rolling, and extrusion, four processes—forging and rolling, precision rolling, sizing, and tube removal—are realized, which not only refines the product grain and makes the longitudinal and transverse properties uniform, but also improves the geometric dimensional accuracy and internal and external surface quality of the steel pipe. By controlling rolling and cooling, the strength of the steel can be further improved without reducing toughness, and the weldability of the steel can also be improved. Detailed Implementation

[0025] The technical solution of the present invention will be illustrated below with specific embodiments:

[0026] Example 1:

[0027] The pipe specifications in this embodiment are: Φ473*30mm, the weight of the continuously cast billet used is 4.13t, the specifications are Φ600*1860(0,+30)mm, the material is 30CrMnSiA, and the manufacturing method of the high-toughness ultra-high-strength steel pipe is as follows:

[0028] Step 1) Electric Arc Furnace Smelting: The furnace charge consists of 40-70% high-quality steel scrap, 20-40% pig iron, and 10-30% returned steel scrap, depending on the charge composition. 1-2 tons of lime and 0.5-1.5 tons of carbon raiser are added to the furnace or charge basket according to the charge composition. Sampling and analysis of the molten steel are performed to control the content of As, Sn, Pb, Sb, and Bi to be ≤0.015%. Electric arc furnace tapping conditions: [C]: 0.05-0.25%, [P] ≤0.003%, temperature ≥1640℃. 1.0-3.0 kg / t of aluminum blocks and 4-6 kg / t of lime are added to the ladle. During the tapping process, 10-13 kg / t of ferrosilicon alloy, 10-13 kg / t of ferromanganese alloy, and 12-13 kg / t of ferrochrome alloy are added.

[0029] Step 2) Ladle refining: During the ladle slag formation process, deoxidize the ladle in batches using 1-2 kg / t of calcium carbide, 2-4 kg / t of carbon powder and ferrosilicon powder. Then, after temperature measurement and sampling, argon is blown and aluminum wire is fed according to the residual aluminum content. The slag quantity is controlled at 1.0-1.2 t and the basicity is 2-4. Strengthen the deoxidation operation. After the slag turns white, maintain the reducing atmosphere with 0.5-1.0 kg / t of carbon powder, 1.0-2.0 kg / t of aluminum powder, and 1.0-2.0 kg / t of calcium silicate powder. The white slag should be maintained for ≥20 min. The composition adjustment is completed before ladle hoisting. The carbon content of the intermediate ladle sample is controlled at 0.26-0.28%.

[0030] Step 3) VD Vacuum Degassing: The ladle is fed into the vacuum tank at a temperature of 1660–1680℃ from the LF furnace. After the ladle is in place, the temperature is measured and maintained at ≤0.7 mbar for ≥20 min. The temperature is controlled to meet the requirements of the continuous casting platform after weak stirring in the VD system. After breaking the vacuum, hydrogen and oxygen are determined online, controlling [H] ≤0.8 ppm and [O] ≤4.0 ppm. A gas sample is taken from a glass tube to analyze the nitrogen content, controlling [N] ≤40 ppm and [Al] 0.015–0.03%. If insufficient, aluminum wire is fed in for adjustment. Calcium wire is fed at 0.1–0.3 m / t for calcium treatment (feeding speed 120 m / min). After feeding, argon is blown and weakly stirred for ≥12 min. The initial furnace ladle temperature is 1565–1575℃, and the continuous casting ladle temperature is 1560–1570℃.

[0031] Step 4) Continuous casting: The tundish is baked for 4.5-6 hours. After the tundish baking is stopped, the argon blowing replacement pipe is immediately inserted. The long nozzle argon blowing pipe is checked to ensure that the argon blowing is unobstructed and well sealed. The ladle is drained outside the tundish. The long nozzle is opened for argon blowing before the continuous casting begins. The crystallizer protective slag is WBP-7. The tundish is protected with 300-400 kg of carbon-free covering agent and carbonized rice husk double layer. Casting speed: 0.22 m / min for superheat ≤ 20℃, 0.2 m / min for superheat 20-40℃, and 0.18 m / min for superheat > 40℃.

[0032] Step 5) Low-temperature annealing: Heat at 500-650℃ for 3 hours, raise the temperature to 700℃ at a rate of ≤100℃ / h, hold for 9 hours, and cool down to ≤200℃ at a rate of ≤30℃ / h before removing from the furnace;

[0033] Step 6) Drilling through holes: Use a milling machine to drill a Φ110 through hole in the billet. After drilling the through hole, use an endoscope to check the quality of the inner hole.

[0034] Step 7) Heating: Use a multi-stage heating method. Preheat at 650℃ for 3 hours, rapidly increase to 850℃ and hold for 4 hours, then increase to 1000℃ and hold for 3 hours, then increase to 1100℃ and hold for 1.5 hours, then increase to 1260℃ and hold for 2.25 hours, and finally slowly decrease to 1250℃ and hold for 2 hours to obtain good plastic deformation ability.

[0035] Step 8) Skew rolling piercing: The billet with the through hole is pierced using a two-roll skew rolling piercing mill. The process adopts diameter expansion deformation. The roll gap of the two rolls of skew rolling piercing, the guide distance of the upper and lower guide plates and the diameter of the mandrel are accurately calculated.

[0036] Step 9) Cyclic rolling: Rolling is performed using a Pilger rolling mill. Cooling water is reduced during forging and rolling. The roll pass curve adopts a hyperbolic non-circular pass curve. A special pass is designed and manufactured according to the finished product specifications. A special tapered mandrel with a ratio of 2000:1 is used. The rotation speed is 35-40 rpm and the feed rate is 35-40 mm. The rolling temperature is controlled above 850℃ during the rolling process.

[0037] Step 10) Fogging: After forging and rolling, the product is transferred to a fogging area for fogging and cooled to room temperature;

[0038] Step 11) Normalizing + Tempering: Normalizing temperature 890±10℃, holding time 2.5h, heating rate not greater than 100℃ / h, Tempering: 650±10℃, holding time not less than 5h.

[0039] Step 12) Internal and external grinding: The inside and outside of the pipe are rough ground to a smooth finish, so that there are no visible folds or cracks on the surface of the steel pipe, ensuring that the outer diameter deviation is ≤ ±4mm, the wall thickness deviation is -2.0~+3.5mm, and the out-of-roundness is ≤ 5mm.

[0040] After forging and annealing, tensile and impact specimens were cut, and the results of their longitudinal mechanical properties are shown in Table 1.

[0041]

[0042]

[0043] Mechanical property testing results show that the process of electric arc furnace smelting + ladle refining + VD vacuum degassing + continuous casting meets the requirements for low-P, low-S, and high-purity steel. The use of a round billet center mill to add through-holes reasonably reduces piercing deformation, optimizes metal flow conditions, and improves internal and external surface defects caused by complex stress conditions during piercing. Periodic forging and rolling mill deformation not only refines the product grains and improves the uniformity of longitudinal and transverse properties, but also enhances the geometric accuracy and internal and external surface quality of the steel pipe. Controlled rolling and cooling not only further improve the steel's strength without reducing toughness, but also improves its weldability, achieving longitudinal performance indicators of Rm≥1650MPa, Rp0.2≥1300MPa, A≥9%, Z≥40%, and KU2≥50J at room temperature, meeting customer requirements for high-toughness, ultra-high-strength steel pipes.

Claims

1. A method for manufacturing 30CrMnSiA high-toughness ultra-high-strength steel pipe, characterized in that, Includes the following steps: Step 1) Electric Arc Furnace Smelting: The furnace charge consists of 40-70% high-quality steel scrap, 20-40% pig iron, and 10-30% returned steel scrap, depending on the charge composition. 1-2 tons of lime and 0.5-1.5 tons of carbon raiser are added to the furnace or charge basket according to the charge composition. Sampling and analysis of the molten steel are performed to control the content of As, Sn, Pb, Sb, and Bi to be ≤0.015%. Electric arc furnace tapping conditions: [C]: 0.05-0.25%, [P] ≤0.003%, temperature ≥1640℃. 1.0-3.0 kg / t of aluminum blocks and 4-6 kg / t of lime are added to the ladle. During tapping, 10-13 kg / t of ferrosilicon alloy, 10-13 kg / t of ferromanganese alloy, and 12-13 kg / t of ferrochrome alloy are added. Step 2) Ladle refining: During the slag formation process in the ladle, deoxidize in batches using 1-2 kg / t of calcium carbide, 2-4 kg / t of carbon powder and ferrosilicon powder. Then, after temperature measurement and sampling, argon is blown and aluminum wire is fed according to the residual aluminum content. The slag volume is controlled at 1.0-1.2 t and the basicity is 2-4. Strengthen the deoxidation operation. After the slag turns white, maintain the reducing atmosphere with 0.5-1.0 kg / t of carbon powder, 1.0-2.0 kg / t of aluminum powder, and 1.0-2.0 kg / t of calcium silicate powder. The white slag should be maintained for ≥20 min. The composition adjustment is completed before ladle hoisting. The carbon content of the intermediate ladle sample is controlled at 0.26-0.28%. Step 3) VD Vacuum Degassing: The ladle is fed into the vacuum tank at a temperature of 1660-1680℃ from the LF furnace. After the ladle is in place, the temperature is measured and maintained at ≤0.7mbar for ≥20min. After weak stirring in VD, the temperature meets the requirements of the continuous casting platform. After breaking the vacuum, hydrogen and oxygen are determined online, and [H] is controlled to ≤0.8ppm and [O] to ≤4.0ppm. A gas sample is taken from the glass tube to analyze the nitrogen content, and [N] is controlled to ≤40ppm and [Al] to 0.015-0.03%. If insufficient, aluminum wire is fed in for adjustment. Calcium wire is fed in at a rate of 0.1-0.3m / t for calcium treatment at a feeding speed of 120m / min. After feeding, argon is blown and weakly stirred for ≥12min. The temperature of the first furnace ladle is 1565-1575℃, and the temperature of the continuous casting ladle is 1560-1570℃. Step 4) Continuous casting: The tundish is baked for 4.5-6 hours. After the tundish baking is stopped, the argon blowing replacement pipe is immediately inserted. The long nozzle argon blowing pipe is checked to ensure that the argon blowing is unobstructed and well sealed. The ladle is drained outside the tundish. The long nozzle is opened for argon blowing before the continuous casting begins. The crystallizer protective slag is WBP-7. The tundish is protected with 300-400 kg of carbon-free covering agent and carbonized rice husk double layer. Casting speed: 0.22 m / min for superheat < 20℃, 0.2 m / min for superheat 20-40℃, and 0.18 m / min for superheat > 40℃. Step 5) Low-temperature annealing: Heat at 500-650℃ for 3 hours, raise the temperature to 700℃ at a rate of ≤100℃ / h, hold for 9 hours, and cool down to ≤200℃ at a rate of ≤30℃ / h before removing from the furnace; Step 6) Drilling a through hole: Use a milling machine to drill a Φ110mm through hole in the billet. After drilling the through hole, use an endoscope to check the quality of the inner hole. Step 7) Heating: Use a multi-stage heating method. Preheat at 650℃ for 3 hours, rapidly increase to 850℃ and hold for 4 hours, then increase to 1000℃ and hold for 3 hours, then increase to 1100℃ and hold for 1.5 hours, then increase to 1260℃ and hold for 2.25 hours, and finally slowly decrease to 1250℃ and hold for 2 hours to obtain good plastic deformation ability. Step 8) Skew rolling piercing: The billet with the through hole is pierced using a two-roll skew rolling piercing mill. The process adopts diameter expansion deformation. The roll gap of the two rolls of skew rolling piercing, the guide distance of the upper and lower guide plates and the diameter of the mandrel are accurately calculated. Step 9) Cyclic tube rolling: Use a Pilger tube rolling mill for tube rolling. Reduce the cooling water during forging and rolling. Use a hyperbolic non-circular roll pass curve. Design and manufacture special passes according to the finished product specifications. Use a special tapered mandrel with a ratio of 2000:

1. Rotation speed is 35-40 rpm. Feed rate is 35-40 mm. Control the rolling temperature above 850℃ during the rolling process. Step 10) Fogging: After forging and rolling, the product is transferred to a fog cooling area for fog cooling until it reaches room temperature; Step 11) Normalizing + Tempering: Normalizing temperature 890±10℃, holding time 2.5 h, heating rate not greater than 100 ℃ / h; Tempering: 650±10℃, holding time not less than 5 h. Step 12) Internal and external grinding: The inside and outside of the pipe are rough ground to a smooth finish, so that there are no visible folds or cracks on the surface of the steel pipe, ensuring that the absolute value of the outer diameter deviation is ≤4mm, the wall thickness deviation is -2.0~+3.5mm, and the out-of-roundness is ≤5mm.

2. The method for manufacturing a 30CrMnSiA high-toughness ultra-high-strength steel pipe according to claim 1, characterized in that, The pipe is made of 30CrMnSiA material, wherein P≤0.008%, S≤0.002%, Al:0.015%~0.035%, Ni:0.5%~0.8%, and the gaseous components H≤1.2ppm, O≤15ppm, and N≤50ppm.

3. The method for manufacturing a 30CrMnSiA high-toughness ultra-high-strength steel pipe according to claim 1, characterized in that, The billet is a Φ600mm continuous casting billet.

4. The method for manufacturing a 30CrMnSiA high-toughness ultra-high-strength steel pipe according to claim 1, characterized in that, The finished pipes are Φ377×30 mm (wall thickness) and Φ473×30 mm (wall thickness).

5. The method for manufacturing a 30CrMnSiA high-toughness ultra-high-strength steel pipe according to claim 1, characterized in that, The rolling process is a combination of skew rolling and longitudinal rolling. The finishing strip uses a hyperbolic non-circular die and special die types Dk387 and Dk482. In addition, the mandrel taper is 2000:1, the surface roughness is ≤Ra1.6, and the ellipticity is ≤0.2mm.

6. The method for manufacturing a 30CrMnSiA high-toughness ultra-high-strength steel pipe according to claim 1, characterized in that, The pipe has a tensile strength Rm of ≥1650MPa, a specified non-proportional elongation strength Rp0.2 of ≥1300MPa, and an impact absorption energy KU2 of ≥50J.

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