Strengthening treatment method for titanium-free maraging steel with 2.2GPa tensile strength

Abstract

The invention discloses a strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa. The method comprises the following steps: selecting a plate-shaped maraging steel composed of nickel, cobalt, molybdenum, carbon, silicon, sulfur, phosphorus and iron, wherein the mass percentages of the components in the maraging steel are as follows: nickel: 16%-20%, cobalt: 12%-16%, molybdenum: 5%-8%, carbon: less than 0.03%, silicon: less than 0.01%, sulfur: less than 0.001%, phosphorus: less than 0.001%, and the balance being iron; and sequentially performing cold rolling deformation treatment, solid solution treatment, temperature reduction cycle heat treatment and short-time nitriding aging treatment on the maraging steel to obtain a workpiece of titanium-free maraging steel with a tensile strength of 2.2 GPa. The maraging steel workpiece of the invention has the characteristics of ultrahigh tensile strength, certain ductility and no oxide layer on the surface.

Description

Technical Field

[0001] The invention belongs to the technical field of maraging steel production process, and in particular relates to a strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa. Background Art

[0002] The tensile strength of maraging steel is achieved by precipitating nano-scale intermetallic compounds during the aging treatment, that is, ultra-low carbon steel that achieves dispersion strengthening effect; the carbon content of ultra-low carbon steel usually does not exceed 0.03%, and its main alloying elements are nickel, cobalt, molybdenum and titanium. The smelting of maraging steel usually adopts a double vacuum smelting process of vacuum induction furnace melting + vacuum consumable furnace remelting. The above process can effectively control the content of impurity elements in the steel, reduce the element segregation ratio and improve the uniformity of the material, thereby ensuring that the strength of the material is not affected.

[0003] Maraging steel has a very broad development prospect in the field of structural materials and ultra-high strength steel due to its outstanding advantages such as ultra-high strength, good processing performance and excellent welding performance. However, the improvement of material strength is often accompanied by a decrease in plasticity and toughness. After traditional solution treatment and aging treatment, maraging steel, taking 18Ni (350) maraging steel as an example, has a maximum tensile strength of more than 2300MPa, but the elongation after fracture is less than 10%, and the cross-sectional shrinkage rate drops to less than 55%. Therefore, how to improve the plasticity and toughness of maraging steel while ensuring that the strength level is not affected is an urgent problem to be solved.

[0004] In addition, the wear resistance of maraging steel is average and cannot directly withstand long-term high-frequency friction. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing process and provide a strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is:

[0007] A strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa, comprising the following steps:

[0008] Selecting a plate-shaped maraging steel composed of nickel, cobalt, molybdenum, carbon, silicon, sulfur, phosphorus and iron, wherein the mass percentages of the components in the maraging steel are as follows: nickel: 16%-20%, cobalt: 12%-16%, molybdenum: 5%-8%, carbon: less than 0.03%, silicon: less than 0.01%, sulfur: less than 0.001%, phosphorus: less than 0.001%, and the balance is iron;

[0009] The maraging steel is subjected to cold rolling deformation treatment, solid solution treatment, cooling cycle heat treatment and short-time nitriding aging treatment in sequence to obtain a workpiece of titanium-free maraging steel with a tensile strength of 2.2 GPa; wherein the solid solution treatment and the cooling cycle heat treatment are both carried out in a vacuum recovery purified gas quenching furnace;

[0010] The vacuum recovery and purification gas quenching furnace comprises a furnace body, a heating chamber and a cooling chamber arranged in the left part of the furnace body; a furnace door is arranged at the left end of the furnace body, the heating chamber is located on the left side of the cooling chamber, a plurality of heaters are arranged on the heating chamber, a feed port is arranged at the left end of the heating chamber, and a flip cover is arranged on the feed port; a high-temperature gas recovery and purification mechanism and a cooling circulation mechanism are arranged in the right part of the furnace body; an opening is arranged on the upper side wall of the furnace body, a sealing cover is arranged on the opening, a temperature insulation plate that can pass through the opening is arranged between the heating chamber and the cooling chamber, and a feeding device is arranged on the bottom plate of the heating chamber; a first temperature and pressure sensor is arranged at the top of the heating chamber, and a second temperature and pressure sensor is arranged on the wall of the cooling chamber; and a vacuum pump for evacuating the cooling chamber and a vacuum pump for filling the cooling chamber with helium are also included. an external gas cylinder for gas; a first solenoid valve is arranged on the external gas cylinder; the cooling circulation mechanism comprises a U-shaped gas pipeline opening to the left, a plurality of gas nozzles arranged at the top and the bottom of the cooling chamber, and a high-temperature gas recovery and purification mechanism is located between the right side wall of the cooling chamber and the left side wall of the right end of the gas pipeline; the gas pipeline is respectively connected to each gas nozzle, an air-cooling motor is arranged on the right side wall of the right end of the gas pipeline, an air-cooling fan is arranged on the air-cooling motor, and a plurality of air-cooling nozzles for spraying air into the gas pipeline are arranged on the air-cooling fan; and a controller is also included, which is respectively electrically connected to the first solenoid valve, the air-cooling motor, the high-temperature gas recovery and purification mechanism, the vacuum pump, the first temperature and pressure sensor, the second temperature and pressure sensor and each heater.

[0011] The plasticity, toughness and brittleness are characterized by the elongation after fracture, the reduction of area and the impact work, and the wear resistance is characterized by the surface Vickers hardness.

[0012] Compared with the common 18Ni maraging steel, the maraging steel of the present invention removes the titanium element and increases the cobalt and molybdenum contents.

[0013] Titanium can easily combine with carbon and nitrogen to form Ti (C, N) inclusions, especially for parts that need to be nitrided. During the nitriding process, a large number of active nitrogen atoms are more likely to form brittle inclusions with the titanium in maraging steel, which greatly reduces the plasticity and toughness of the parts.

[0014] In the titanium-free maraging steel of the present invention, the increase in the cobalt and molybdenum content can increase the precipitation of the molybdenum-containing aging phase, ensuring that the material strength will not decrease significantly, and the molybdenum element can hinder the precipitation of the aging phase at the grain boundary in the early stage of aging, reducing the risk of fracture along the grain boundary. At the same time, the cobalt element can maintain the stability of the matrix and effectively hinder the coarsening of the aging phase. Therefore, compared with the traditional maraging steel, the plastic toughness of the titanium-free maraging steel of the present invention is improved.

[0015] The wall of the heating chamber is provided with a heat-insulating layer, and the heating elements are evenly distributed on the front wall and the bottom of the heating chamber.

[0016] The cooling gas used in the gas quenching of the present invention is helium. The heat transfer rates of several common cooling gases in gas quenching are compared with those of air under the same conditions: taking air as 1, argon as 0.70, nitrogen as 0.99, helium as 6, and hydrogen as 7.

[0017] Hydrogen has the best cooling effect, but as the strength increases, the hydrogen embrittlement sensitivity of high-strength steel will further increase, and the danger is relatively large, so it is not suitable as a cooling gas for gas quenching of maraging steel;

[0018] Nitrogen is the most common air cooling medium with low price, but its heat transfer rate is average, equivalent to that of air. In addition, brittle nitrides may form on the metal surface in a high-temperature nitrogen environment, which has a great impact on the subsequent aging nitriding treatment.

[0019] The heat transfer rate of argon is lower than that of air, and it is more expensive, so it is only used in special environments;

[0020] Helium has an outstanding cooling effect, takes less time to cool, is stable, has low activity, and is not easy to react with metals in a high temperature environment. Although the price is high, the vacuum recovery and purification gas quenching furnace described in the present invention can be used to recycle and purify the gas, significantly reducing costs and ensuring quenching quality. In addition, helium has a low density, and the power consumption of the motor when driving the gas circulation is low, which can further save costs.

[0021] Therefore, the obtained maraging steel of the present invention has ultra-high tensile strength and certain ductility. The comprehensive performance of the titanium-free maraging steel with 2.2 GPa tensile strength is improved through a strengthening treatment method combining mechanical deformation with heat treatment technology, and the production cost is effectively reduced.

[0022] Preferably, the high-temperature gas recovery and purification mechanism includes an absorber, a first heat exchanger, an exhaust pump, an adsorption filter, a compressor, a second heat exchanger, a gas separator and a recovery gas cylinder which are connected in sequence. The gas separator and the recovery gas cylinder are connected by a connecting pipe, and an air guide pipe is provided on the connecting pipe. A second solenoid valve is provided at a portion of the connecting pipe close to the recovery gas cylinder. The air guide pipe is connected to the left side wall of the right end of the gas pipeline, and a third solenoid valve is provided on the air guide pipe; the recovery gas cylinder is connected to the cooling chamber, and a fourth solenoid valve is provided between the recovery gas cylinder and the cooling chamber; the controller is electrically connected to the absorber, the first heat exchanger, the exhaust pump, the compressor, the second heat exchanger, the gas separator, the second solenoid valve, the third solenoid valve and the fourth solenoid valve, respectively.

[0023] Preferably, the feeding device includes a retractable electromagnetic push rod and a feeding table made of iron material, the feeding table is provided with evenly distributed air holes, and a plurality of rollers are provided at the bottom of the feeding table; a round rod is provided at the right end of the retractable electromagnetic push rod, and a vertical groove matching the round rod is provided on the left side surface of the feeding table; two gas guide plates are provided on the left side wall at the right end of the gas pipeline; the absorber includes a heating element and a copper wire mesh, and the mesh size of the copper wire mesh is 20 mesh-100 mesh; the adsorption filter includes activated carbon and a molecular filter.

[0024] Preferably, the inner wall of the furnace body is made of refractory bricks, insulation bricks and quartz sand, and the outer shell of the furnace body is made of carbon steel; the insulation plate is made of two layers of molybdenum plates and three layers of stainless steel plates; the gas separation membrane in the gas separator is made of polycarbonate or polyimide; the feeding table, each gas nozzle, gas channel, connecting pipe, air guide pipe, the gas guide plate, the air-cooling nozzle and the air-cooling fan are all made of silicon carbide ceramic material.

[0025] Preferably, the cold rolling deformation process comprises the following steps:

[0026] The staff used longitudinal rolling to roll the plate-shaped maraging steel at room temperature, with a cold rolling reduction rate of 60%-80%.

[0027] Cold deformation texture will be produced in maraging steel after cold rolling, and the texture remains stable after solution treatment. These textures enable the martensitic matrix to form fine substructures, promote lattice distortion, and further increase the matrix dislocation density, preparing for subsequent heat treatment strengthening processes.

[0028] Preferably, the solution treatment comprises the following steps:

[0029] Step 6-1: The staff puts the maraging steel plate after cold rolling and deformation on the feeding table of the heating chamber, pulls the insulation plate out of the furnace body, and covers it with a sealing cover; the staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observes the air pressure data detected by the first temperature and pressure sensor to make the air pressure reach 5×10-1 After Pa, the vacuum pump stops working;

[0030] Step 6-2, insert the insulation board downward into the furnace body, control each heater to heat at a heating rate of 6°C / min-10°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 800°C-850°C, keep the temperature for 45 minutes-65 minutes, and then stop working each heater;

[0031] Step 6-3, let the plate cool with the furnace, observe the temperature data detected by the first temperature pressure sensor, when the temperature in the heating chamber is 600℃-700℃, the staff will pull the insulation board upward out of the furnace body and cover it with a sealing cover; turn on the power of the electromagnetic push rod, make the round rod of the electromagnetic push rod magnetic, connect the round rod with the vertical groove, extend the electromagnetic push rod, use the electromagnetic push rod to push the feeding table into the cooling chamber, turn off the power of the electromagnetic push rod, separate the electromagnetic push rod from the feeding table, and insert the insulation board downward into the furnace body;

[0032] The controller controls the first solenoid valve to open, and helium is filled into the cooling chamber from an external gas cylinder. The air pressure data detected by the second temperature and pressure sensor is observed to maintain the air pressure in the cooling chamber within the range of 0.5MPa-1.5MPa. The controller controls the vacuum pump to work, so that the helium enters the gas pipeline after being purified by the recovery and purification mechanism.

[0033] The air-cooling motor is controlled by the controller to drive the air-cooling fan, so that the cooled helium is quickly sprayed toward the plate through each gas nozzle to cool the plate until the temperature data detected by the second temperature and pressure sensor drops to room temperature. The air-cooling motor is turned off, the vacuum pump is controlled to work for 30 minutes to 60 minutes, the second solenoid valve is opened, and the cooled helium is pumped into the recovery gas cylinder, and then the second solenoid valve is controlled to close.

[0034] Solution treatment can promote the full dissolution of alloy elements in the material, and obtain lath martensite with high dislocation density after quenching, preparing for subsequent aging treatment; this process can greatly reduce the internal stress generated by the previous cold rolling deformation treatment, restore the mechanical properties of the plate, and improve the processing performance of the plate.

[0035] Preferably, the cooling cycle heat treatment comprises the following steps:

[0036] Step 7-1-1, process the plate after solution treatment into a workpiece and place it on the feeding table of the heating chamber, pull the insulation plate upward out of the furnace body, and cover it with a sealing cover; the staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observe the air pressure data detected by the first temperature and pressure sensor. When the air pressure reaches 5×10 -1 After Pa, stop the vacuum pump and insert the insulation board into the furnace body;

[0037] Step 7-1-2, control each heater to heat at a heating rate of 8°C / min-12°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 900°C±10°C, keep warm for 10-15 minutes, and then stop working each heater;

[0038] Step 7-1-3, the staff pulls the insulation board upward out of the furnace body and covers it with a sealing cover; turns on the power of the electromagnetic push rod, so that the round rod of the electromagnetic push rod has magnetism, and the round rod is connected with the vertical slot to extend the electromagnetic push rod, and uses the electromagnetic push rod to push the feeding table into the cooling chamber, turns off the power of the electromagnetic push rod, separates the electromagnetic push rod from the feeding table, and inserts the insulation board into the furnace body;

[0039] Step 7-1-4, control the fourth solenoid valve to open through the controller, so that the helium in the recovery gas cylinder is filled into the cooling chamber, and observe the air pressure data detected by the second temperature and pressure sensor to maintain the air pressure in the cooling chamber within the range of 0.5MPa-1MPa; start the vacuum pump to allow the helium to enter the gas pipeline after being purified by the recovery and purification mechanism;

[0040] Step 7-1-5, the controller controls the air cooling motor to work, drives the air cooling fan, and allows the cooled helium to be quickly sprayed toward the plate through each gas nozzle to perform gas cooling on the workpiece until the temperature data detected by the second temperature and pressure sensor drops to room temperature;

[0041] Turn off the air-cooling motor, open the second solenoid valve, control the vacuum pump to work for 30 minutes to 60 minutes, and after the cooled helium is pumped into the recovery gas cylinder, the first cycle heat treatment is completed; control the vacuum pump to stop working and close the second solenoid valve;

[0042] Step 7-2, repeating steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 860±10°C, and the air pressure in the cooling chamber in step 7-1-4 is maintained in the range of 0.5MPa-1MPa, and the second cycle heat treatment is completed;

[0043] Step 7-3, repeat steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 820±10°C, and the air pressure in the cooling chamber in step 7-1-4 is maintained in the range of 0.3MPa-0.6Mpa, and the cooling cycle heat treatment is completed.

[0044] Cooling cycle heat treatment can be combined with cold rolling deformation treatment to further refine the grains on the basis of high-density dislocation martensite. As the total length of the grain boundary increases after grain refinement, the dislocation movement is hindered by the grain boundary, and the dislocation entanglement caused by the high dislocation density significantly improves the strength of the material. At the same time, the expansion of the crack needs to continuously break through the obstruction of the grain boundary, which hinders the rapid extension of the crack. The overall force of the material is more coordinated and uniform, and its plastic toughness is optimized. Through vacuum gas quenching treatment with helium as the medium, the cooling rate is greatly improved, and the workpiece surface is clean, without oxidation and decarburization.

[0045] Preferably, the helium is purified by a recovery and purification mechanism and then enters the gas pipeline, comprising the following steps:

[0046] The staff controls the third solenoid valve to open through the controller, and the vacuum pump drives the helium in the cooling chamber into the absorber. The copper wire mesh of the absorber causes the oxygen in the helium to undergo oxidation reaction to turn into copper oxide, thereby removing the oxygen. The first heat exchanger cools the helium, and the adsorption filter removes impurities and dust present when filtering helium for recovery. The compressor increases the pressure of the helium, allowing the helium to pass smoothly through the gas separation membrane of the gas separator. The gas separation membrane filters the nitrogen impurities contained in the helium, and the stored helium enters the right part of the gas pipeline.

[0047] The vacuum pump of the present invention does not always draw a vacuum. Due to the sealing of the furnace body, a very small amount of air will enter the cooling chamber through gaps such as the sealing ring, resulting in a small amount of air in the cooling chamber. The above steps can be used to remove oxygen, nitrogen and impurity dust.

[0048] The short-time nitriding aging treatment in the present invention comprises the following steps:

[0049] Put the workpiece after the cooling cycle heat treatment into a closed box-type nitriding furnace, close the furnace cover, and pass nitrogen for exhaust. After exhausting for 15 minutes, raise the furnace temperature to 300℃ at a heating rate of 6-10℃ / min. After keeping warm for 15 minutes, continue heating to 480℃-520℃, stop exhausting, pass ammonia, adjust the ammonia flow rate, and adjust the ammonia decomposition rate to 40-60%. After keeping warm for 3-6 hours, turn off the power to cool down, stop the ammonia passing, pass nitrogen to remove ammonia and continue to supply gas to maintain positive pressure in the furnace. After the workpiece cools to 300℃ with the furnace, it is taken out of the furnace and oil-cooled.

[0050] The compound layer after short-time nitriding and aging treatment is thinner and less brittle. The wear resistance of the workpiece surface is greatly improved, the surface friction coefficient is reduced, and the corrosion resistance of the workpiece is improved. Short-time nitriding and aging treatment not only strengthens the surface, but also strengthens the core of the workpiece. Due to the deformation texture produced by cold rolling deformation treatment, the grain size is refined by cooling cycle heat treatment, and the strengthening phase after aging treatment is evenly distributed and dispersed. The precipitated strengthening phase and high-density dislocation interact with each other to produce a stress field. In addition, the synergistic strengthening effect of the two and the grain boundary significantly improves the strengthening and toughening level of the material. The aging temperature of the martensitic aging steel is similar to the nitriding temperature. Performing nitriding and aging treatment at the same time can reduce the processing procedures and save time and cost. In addition, the nitriding aging time is short, the temperature is low, the cooling rate is slow, the workpiece deformation is small, the dimensional accuracy is high, and it is not easy to produce over-aging phenomenon, which further ensures the strengthening and toughening level of the workpiece.

[0051] Therefore, the present invention has the following beneficial effects:

[0052] The maraging steel workpiece obtained by the invention has ultra-high tensile strength, certain ductility, no oxide layer on the surface, improved wear resistance of the workpiece, and a thin compound layer on the surface of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a cross-sectional view of the present invention;

[0054] Figure 2 is a top view of the feeding device of the present invention;

[0055] Figure 3 This is a process diagram for explaining the short-time nitriding aging treatment of the present invention;

[0056] Figure 4 This is a microstructure picture of the core of a maraging steel after solution treatment and aging treatment using the prior art;

[0057] Figure 5 It is a microstructure picture of the core of the workpiece obtained by the present invention. DETAILED DESCRIPTION

[0058] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0059] Example 1

[0060] A strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa, comprising the following steps:

[0061] A plate-shaped maraging steel composed of nickel, cobalt, molybdenum, carbon, silicon, sulfur, phosphorus and iron is selected, and the mass percentages of the components in the maraging steel are: 18.2% nickel, 13.6% cobalt, 5.4% molybdenum, 0.01% carbon, 0.003% silicon, less than 0.001% sulfur, less than 0.001% phosphorus, and the balance is iron.

[0062] In this embodiment, taking a 9mm thick martensitic aging steel plate as an example, the 2.2GPa tensile strength titanium-free martensitic aging steel strengthening treatment method includes cold rolling deformation treatment, solid solution treatment, cooling cycle heat treatment and short-time nitriding aging treatment arranged in sequence, and each treatment process is closely connected and mutually inherited. Among them, the solid solution treatment and the cooling cycle heat treatment are both carried out in a special vacuum recyclable gas quenching furnace by gas quenching, and the cooling gas is helium.

[0063] like Figure 1-Figure 2 As shown, the vacuum recovery and purification gas quenching furnace includes a furnace body 1, a heating chamber 2 and a cooling chamber 3 arranged in the left part of the furnace body; a furnace door 11 is arranged at the left end of the furnace body, the heating chamber is located on the left side of the cooling chamber, a plurality of heaters 20 are arranged on the heating chamber, a feed port 200 is arranged at the left end of the heating chamber, and a flip cover 201 is arranged on the feed port; a high-temperature gas recovery and purification mechanism and a cooling circulation mechanism are arranged in the right part of the furnace body; an opening is arranged on the upper side wall of the furnace body, a sealing cover is arranged on the opening, a temperature insulation plate 21 that can pass through the opening is arranged between the heating chamber and the cooling chamber, and a feeding device 22 is arranged on the bottom plate of the heating chamber; a first temperature and pressure sensor 23 is arranged at the top of the heating chamber, and a second temperature and pressure sensor 31 is arranged on the wall of the cooling chamber; it also includes a vacuum pump 6 for evacuating the cooling chamber and a vacuum pump 6 for evacuating the cooling chamber. The chamber is filled with an external gas cylinder 7 of helium; the external gas cylinder is provided with a first electromagnetic valve 71; the cooling circulation mechanism includes a U-shaped gas pipeline 51 opening to the left, a plurality of gas nozzles 52 arranged at the top and bottom of the cooling chamber, and a high-temperature gas recovery and purification mechanism is located between the right side wall of the cooling chamber and the left side wall of the right end of the gas pipeline; the gas pipeline is connected to each gas nozzle, and an air-cooling motor 54 is provided on the right side wall of the right end of the gas pipeline, and an air-cooling fan 55 is provided on the air-cooling motor, and two air-cooling nozzles 56 for spraying air into the gas pipeline are provided on the air-cooling fan; and a controller is also included, and the controller is electrically connected to the first electromagnetic valve, the air-cooling motor, the high-temperature gas recovery and purification mechanism, the vacuum pump, the first temperature and pressure sensor, the second temperature and pressure sensor and each heater. The exhaust pipe connected to the exhaust of the vacuum pump extends out of the furnace body.

[0064] The high-temperature gas recovery and purification mechanism includes an absorber 41, a first heat exchanger 42, an exhaust pump 43, an adsorption filter 44, a compressor 45, a second heat exchanger 46, a gas separator 47 and a recovery gas bottle 48 which are connected in sequence. The gas outlet of the vacuum pump is also connected to the gas inlet of the gas separator through a ventilation pipe 60. A fifth solenoid valve 61 is provided on the ventilation pipe. The gas separator and the recovery gas bottle are connected through a connecting pipe 49. An air guide pipe 492 is provided on the connecting pipe. A second solenoid valve 491 is provided at a portion of the connecting pipe close to the recovery gas bottle. The air guide pipe is connected to the left side wall of the right end of the gas pipeline. A third solenoid valve 493 is provided on the air guide pipe. The recovery gas bottle is connected to the cooling chamber. A fourth solenoid valve 494 is provided between the recovery gas bottle and the cooling chamber. The controller is electrically connected to the absorber, the first heat exchanger, the exhaust pump, the compressor, the second heat exchanger, the gas separator, the second solenoid valve, the third solenoid valve, the fourth solenoid valve and the fifth solenoid valve, respectively.

[0065] The feeding device includes a retractable electromagnetic push rod 221 and a feeding table 222 made of iron material, the feeding table is provided with evenly distributed air holes 223, and the lower part of the feeding table is provided with 4 rollers; a round rod 225 is provided at the right end of the retractable electromagnetic push rod, and a vertical groove matching the round rod is provided on the left side surface of the feeding table; two gas guide plates 40 are provided on the left side wall of the right end of the gas pipeline; the absorber includes a heating element and a copper wire mesh, and the mesh size of the copper wire mesh is 20 mesh-100 mesh; the adsorption filter includes activated carbon and a molecular filter.

[0066] The inner wall of the furnace body is made of refractory bricks, insulation bricks and quartz sand, and the outer shell of the furnace body is made of carbon steel; the insulation plate is made of two layers of molybdenum plates and three layers of stainless steel plates; the gas separation membrane in the gas separator is made of polycarbonate or polyimide; the feeding table, each gas nozzle, gas channel, connecting pipe, air guide pipe, the gas guide plate, the air-cooling nozzle and the air-cooling fan are all made of silicon carbide ceramic material.

[0067] The steps include:

[0068] (1) Cold rolling deformation treatment. Before rolling, the hydraulic system and lubrication system of the rolling mill must be ensured to work normally. Process cooling lubricant (blending oil) must be added between the contact surface of the rollers and the material. At room temperature, the dust-free plate is aligned with the center line of the six-roller rolling mill rolls. The feeding speed does not exceed 0.3m / s. The longitudinal rolling method is used to perform multiple cold rolling passes with the same reduction. During the rolling process, the single reduction is 0.6mm, and the plate thickness is reduced to 3mm. The deformed plate is degreased and cleaned.

[0069] (2) Solution treatment: Solution treatment includes the following steps:

[0070] Step 6-1: The staff puts the maraging steel plate after cold rolling and deformation on the feeding table of the heating chamber, pulls the insulation plate out of the furnace body, and covers it with a sealing cover; the staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observes the air pressure data detected by the first temperature and pressure sensor to make the air pressure reach 5×10 -1 After Pa, the vacuum pump stops working;

[0071] Step 6-2, insert the insulation board downward into the furnace body, control each heater to heat at a heating rate of 6°C / min-10°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 830°C, keep warm for 55 minutes, and then stop each heater;

[0072] Step 6-3, let the plate cool with the furnace, observe the temperature data detected by the first temperature pressure sensor, when the temperature in the heating chamber reaches 650°C, the staff pulls the insulation board upward out of the furnace body and covers it with a sealing cover; turn on the power of the electromagnetic push rod, make the round rod of the electromagnetic push rod magnetic, connect the round rod with the vertical groove, extend the electromagnetic push rod, use the electromagnetic push rod to push the feeding table into the cooling chamber, turn off the power of the electromagnetic push rod, separate the electromagnetic push rod from the feeding table, and insert the insulation board downward into the furnace body;

[0073] The controller controls the first solenoid valve to open, fills the cooling chamber with helium from an external gas cylinder, and observes the air pressure data detected by the second temperature and pressure sensor to maintain the air pressure in the cooling chamber within the range of 1.2 MPa;

[0074] The vacuum pump is controlled by the controller. The staff controls the third solenoid valve to open through the controller. The vacuum pump drives the helium in the cooling chamber into the absorber. The copper wire mesh of the absorber causes the oxygen in the helium to undergo oxidation reaction to become copper oxide, thereby removing the oxygen. The first heat exchanger cools the helium. The adsorption filter removes impurities and dust present when filtering helium for recovery. The compressor increases the pressure of the helium, allowing the helium to pass smoothly through the gas separation membrane of the gas separator. The gas separation membrane filters the nitrogen impurities contained in the helium. The helium that has been extracted enters the right part of the gas pipeline.

[0075] The air-cooling motor is controlled by the controller to drive the air-cooling fan, so that the cooled helium is quickly sprayed toward the plate through each gas nozzle to cool the plate until the temperature data detected by the second temperature pressure sensor drops to room temperature. The air-cooling motor is turned off, the vacuum pump is controlled to work for 30 minutes, the second solenoid valve is opened, and the third solenoid valve is closed. After the cooled helium is pumped into the recovery gas cylinder, the second solenoid valve is controlled to be closed; the electromagnetic push rod is used to pull the feeding table to take out the plate.

[0076] Among them, when placing the plate on the feeding table of the heating chamber and pushing and pulling the feeding table by the electromagnetic push rod, it is necessary to open the furnace door and the flip cover, and close the flip cover and the furnace door.

[0077] (3) Cooling cycle heat treatment; the cooling cycle heat treatment comprises the following steps:

[0078] Step 7-1-1, process the plate after solution treatment into a workpiece and place it on the feeding table of the heating chamber. Take the size of the workpiece as an example, the thin plate with the specification of 80mm×20mm×3mm. Pull the insulation plate upward out of the furnace body and cover it with a sealing cover. The staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observe the air pressure data detected by the first temperature and pressure sensor. When the air pressure reaches 5×10 -1 After Pa, stop the vacuum pump and insert the insulation board into the furnace body;

[0079] Step 7-1-2, control each heater to heat at a heating rate of 8°C / min-12°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 900°C, keep warm for 15 minutes, and then stop each heater;

[0080] Step 7-1-3, the staff pulls the insulation board upward out of the furnace body and covers it with a sealing cover; turns on the power of the electromagnetic push rod, so that the round rod of the electromagnetic push rod has magnetism, and the round rod is connected with the vertical slot to extend the electromagnetic push rod, and uses the electromagnetic push rod to push the feeding table into the cooling chamber, turns off the power of the electromagnetic push rod, separates the electromagnetic push rod from the feeding table, and inserts the insulation board into the furnace body;

[0081] Step 7-1-4, control the fourth solenoid valve to open through the controller, so that the helium in the recovery gas cylinder is filled into the cooling chamber, and observe the air pressure data detected by the second temperature and pressure sensor to maintain the air pressure in the cooling chamber at 1MPa;

[0082] The vacuum pump is controlled by the controller. The staff controls the third solenoid valve to open through the controller. The vacuum pump drives the helium in the cooling chamber into the absorber. The copper wire mesh of the absorber causes the oxygen in the helium to undergo oxidation reaction to become copper oxide, thereby removing the oxygen. The first heat exchanger cools the helium. The adsorption filter removes impurities and dust present when filtering helium for recovery. The compressor increases the pressure of the helium, allowing the helium to pass smoothly through the gas separation membrane of the gas separator. The gas separation membrane filters the nitrogen impurities contained in the helium. The helium that has been extracted enters the right part of the gas pipeline.

[0083] Step 7-1-5, the controller controls the air cooling motor to work, drives the air cooling fan, and allows the cooled helium to be quickly sprayed toward the plate through each gas nozzle to perform gas cooling on the workpiece until the temperature data detected by the second temperature and pressure sensor drops to room temperature;

[0084] Turn off the air-cooling motor, open the second solenoid valve, close the third solenoid valve, control the vacuum pump to work for 30 minutes to 60 minutes, and after the cooled helium is pumped into the recovery gas cylinder, the first cycle heat treatment is completed; control the vacuum pump to stop working and close the second solenoid valve;

[0085] Step 7-2, repeating steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 860°C, and the air pressure in the cooling chamber in step 7-1-4 is maintained at 0.8MPa, and the second cycle heat treatment is completed;

[0086] Step 7-3, repeat steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 820°C, the air pressure in the cooling chamber in step 7-1-4 is maintained at 0.6Mpa, and the cooling cycle heat treatment is completed; use the electromagnetic push rod to pull the feed table to take out the workpiece.

[0087] Among them, when placing the workpiece on the feeding table of the heating chamber and pushing and pulling the feeding table by the electromagnetic push rod, it is necessary to open the furnace door and the flip cover first, and close the flip cover and the furnace door after the operation.

[0088] Finally, the staff controlled the vacuum pump through the controller, blocked the exhaust pipe, opened the third solenoid valve and the fifth solenoid valve, and the vacuum pump evacuated the nitrogen impurities adsorbed on the gas separation membrane of the gas separator.

[0089] (4) Short-time nitriding aging treatment:

[0090] Before nitriding aging, the gas cylinder, temperature control instrument, ammonia decomposition tester and various pipeline systems need to be checked to ensure the normal operation of the equipment. The temperature difference in the furnace should be less than 5°C. The workpiece after cooling cycle heat treatment is surface polished, sharp corners and sharp edges are polished, and the non-nitriding part of the workpiece is treated with a coating method for anti-seepage. After degreasing and cleaning the workpiece, put it into a closed box-type nitriding furnace, close the furnace cover, and the heat treatment method process is as follows Figure 3 As shown, nitrogen is introduced for exhaust before heating. After exhausting for 15 minutes, the furnace temperature is raised to 300°C at a heating rate of 8°C / min. After keeping warm for 15 minutes, it is continued to be heated to 480°C at a heating rate of 6°C / min. The exhaust is stopped, ammonia is introduced, the gas pressure in the furnace is controlled to be 0.1-0.2MPa, the ammonia flow rate is adjusted, and the ammonia decomposition rate is adjusted to 55%. After keeping warm for 4 hours, the power is turned off to cool down, the ammonia introduction is stopped, nitrogen is introduced to remove ammonia and the positive pressure in the furnace is maintained by continuous gas supply. After cooling to 300°C with the furnace, the workpiece is taken out of the furnace and oil-cooled, and the short-term nitriding aging treatment is completed.

[0091] Example 2

[0092] In Example 2, the mass percentages of the components in the maraging steel are: nickel: 16%, cobalt: 16%, molybdenum: 5%, carbon: less than 0.03%, silicon: less than 0.01%, sulfur: less than 0.001%, phosphorus: less than 0.001%, and the balance is iron; the other structures and methods in Example 2 are the same as those in Example 1.

[0093] Example 3

[0094] In Example 3, the mass percentages of the components in the maraging steel are: nickel: 20%, cobalt: 12%, molybdenum: 8%, carbon: less than 0.03%, silicon: less than 0.01%, sulfur: less than 0.001%, phosphorus: less than 0.001%, and the balance is iron; the other structures and methods in Example 3 are the same as those in Example 1.

[0095] Performance Analysis:

[0096] The mechanical property data of the workpiece (serial number 1) after conventional solution treatment and aging treatment and the mechanical property data of the workpiece (serial number 2) according to the strengthening treatment method of this embodiment 1 are shown in Table 1. The conventional solution treatment (820°C, 1h) and aging treatment (510°C, 3h) are both carried out in a muffle furnace, and after the heat preservation, the steel is taken out of the furnace and air-cooled. The tensile strength of the titanium-free martensitic aging steel in this embodiment is 2.2GPa.

[0097] Table 1 Mechanical properties of workpieces

[0098]

[0099] Note: The V-notch specimen used in the impact test is a 2.5mm small-size specimen, and the impact energy value is converted according to the standard size.

[0100] like Figure 4 and Figure 5 As shown, the 2.2GPa tensile strength titanium-free martensitic aging steel strengthening treatment method of the present invention has a significant effect on the grain refinement of the core of the workpiece compared with the traditional solution treatment and aging treatment methods. The refined grain size is between 7-10μm, and the organization is evenly distributed and dense, which provides important conditions for improving the strength and toughness level of the material. The plastic toughness and brittleness are characterized by the elongation after fracture, the cross-sectional shrinkage rate and the impact work, and the wear resistance is characterized by the surface Vickers hardness.

[0101] The strengthening treatment method for the comprehensive performance of 2.2GPa-level tensile strength titanium-free maraging steel described in the present invention includes a cold rolling deformation treatment, a solid solution treatment, a cooling cycle heat treatment and a short-time nitriding aging treatment arranged in sequence, and each treatment process is closely connected and mutually inherited. After the strengthening treatment, the comprehensive performance of the maraging steel is further optimized on the original basis. While maintaining ultra-high strength, the plastic toughness of the treated workpiece is significantly improved. The surface hardness of the workpiece after nitriding is high, and the wear resistance and corrosion resistance are improved. The solid solution treatment and the cooling cycle heat treatment in the process are both carried out in a special vacuum recovery and purification gas quenching furnace. Helium is used as the cooling gas, the quenching intensity is high, the heat treatment process is relatively stable, the environmental pollution is small, the material surface is clean, and the helium can be repeatedly recovered and purified in the furnace for recycling, saving costs and ensuring the quenching quality; the short-time nitriding aging treatment temperature is low, the time is short, the workpiece distortion is small, the dimensional accuracy is high, and the surface brittleness is small.

[0102] The above embodiments are only used to supplement the present invention. In addition, there are many different embodiments. The above embodiments are only preferred embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa, characterized in that: The steps include: Selecting a plate-shaped maraging steel composed of nickel, cobalt, molybdenum, carbon, silicon, sulfur, phosphorus and iron, wherein the mass percentages of the components in the maraging steel are as follows: nickel: 16%-20%, cobalt: 12%-16%, molybdenum: 5%-8%, carbon: less than 0.03%, silicon: less than 0.01%, sulfur: less than 0.001%, phosphorus: less than 0.001%, and the balance is iron; The maraging steel is subjected to cold rolling deformation treatment, solid solution treatment, cooling cycle heat treatment and short-time nitriding aging treatment in sequence to obtain a workpiece of titanium-free maraging steel with a tensile strength of 2.2 GPa; wherein the solid solution treatment and the cooling cycle heat treatment are both carried out in a vacuum recovery purified gas quenching furnace; The vacuum recovery and purification gas quenching furnace comprises a furnace body (1), a heating chamber (2) and a cooling chamber (3) arranged in the left part of the furnace body; a furnace door (11) is arranged at the left end of the furnace body, the heating chamber is located on the left side of the cooling chamber, a plurality of heaters (20) are arranged on the heating chamber, a feed port (200) is arranged at the left end of the heating chamber, and a flip cover plate (201) is arranged on the feed port; a high-temperature gas recovery and purification mechanism and a cooling circulation mechanism are arranged in the right part of the furnace body; an opening is arranged on the upper side wall of the furnace body, a sealing cover plate is arranged on the opening, a temperature insulation plate (21) that can pass through the opening is arranged between the heating chamber and the cooling chamber, and a feeding device (22) is arranged on the bottom plate of the heating chamber; a first temperature and pressure sensor (23) is arranged at the top of the heating chamber, and a second temperature and pressure sensor (31) is arranged on the wall of the cooling chamber; and the furnace also comprises a vacuum pump (6) for evacuating the cooling chamber and a vacuum pump (6) for evacuating the cooling chamber. An external gas cylinder (7) for filling helium into the cooling chamber; a first solenoid valve (71) is provided on the external gas cylinder; the cooling circulation mechanism includes a U-shaped gas pipeline (51) opening to the left, and a plurality of gas nozzles (52) provided at the top and bottom of the cooling chamber; the high-temperature gas recovery and purification mechanism is located between the right side wall of the cooling chamber and the left side wall of the right end of the gas pipeline; the gas pipeline is connected to each gas nozzle, an air-cooling motor (54) is provided on the right side wall of the right end of the gas pipeline, an air-cooling fan (55) is provided on the air-cooling motor, and a plurality of air-cooling nozzles (56) for spraying air into the gas pipeline are provided on the air-cooling fan; and a controller is also included, the controller is electrically connected to the first solenoid valve, the air-cooling motor, the high-temperature gas recovery and purification mechanism, the vacuum pump, the first temperature and pressure sensor, the second temperature and pressure sensor and each heater; The cooling cycle heat treatment includes the following steps: Step 7-1-1, process the plate after solution treatment into a workpiece and place it on the feeding table of the heating chamber, pull the insulation plate upward out of the furnace body, and cover it with a sealing cover; the staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observe the air pressure data detected by the first temperature and pressure sensor. When the air pressure reaches 5×10 -1 After Pa, stop the vacuum pump and insert the insulation board into the furnace body; Step 7-1-2, control each heater to heat at a heating rate of 8°C / min-12°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 900°C±10°C, keep warm for 10-15 minutes, and then stop each heater; Step 7-1-3, the staff pulls the insulation board upward out of the furnace body and covers it with a sealing cover; turns on the power of the electromagnetic push rod, so that the round rod of the electromagnetic push rod has magnetism, and the round rod is connected with the vertical slot to extend the electromagnetic push rod, and uses the electromagnetic push rod to push the feeding table into the cooling chamber, turns off the power of the electromagnetic push rod, separates the electromagnetic push rod from the feeding table, and inserts the insulation board into the furnace body; Step 7-1-4, control the fourth solenoid valve to open through the controller, so that the helium in the recovery gas cylinder is filled into the cooling chamber, and observe the air pressure data detected by the second temperature and pressure sensor to maintain the air pressure in the cooling chamber within the range of 0.5 MPa-1 MPa; start the vacuum pump to allow the helium to enter the gas pipeline after being purified by the recovery and purification mechanism; Step 7-1-5, the controller controls the air cooling motor to work, drives the air cooling fan, and allows the cooled helium to be quickly sprayed toward the plate through each gas nozzle to perform gas cooling on the workpiece until the temperature data detected by the second temperature and pressure sensor drops to room temperature; Turn off the air-cooling motor, open the second solenoid valve, control the vacuum pump to work for 30 minutes to 60 minutes, and after the cooled helium is pumped into the recovery gas cylinder, the first cycle heat treatment is completed; control the vacuum pump to stop working and close the second solenoid valve; Step 7-2, repeating steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 860±10°C, and the air pressure in the cooling chamber in step 7-1-4 is maintained in the range of 0.5 MPa-1MPa, and the second cycle heat treatment is completed; Step 7-3, repeat steps 7-1-2 to 7-1-5, wherein the temperature in the heating chamber in step 7-1-2 is 820±10°C, and the air pressure in the cooling chamber in step 7-1-4 is maintained in the range of 0.3 MPa -0.6Mpa, and the cooling cycle heat treatment is completed.

2. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 1, characterized in that: The high-temperature gas recovery and purification mechanism comprises an absorber (41), a first heat exchanger (42), an air extraction pump (43), an adsorption filter (44), a compressor (45), a second heat exchanger (46), a gas separator (47) and a recovery gas cylinder (48) which are connected in sequence. The gas separator and the recovery gas cylinder are connected via a connecting pipe (49). An air guide pipe (492) is provided on the connecting pipe. A second solenoid valve (491) is provided at a portion of the connecting pipe close to the recovery gas cylinder. The air guide pipe is connected to the left side wall of the right end of the gas pipeline. A third solenoid valve (493) is provided on the air guide pipe. The recovery gas cylinder is connected to a cooling chamber. A fourth solenoid valve (494) is provided between the recovery gas cylinder and the cooling chamber. The controller is electrically connected to the absorber, the first heat exchanger, the air extraction pump, the compressor, the second heat exchanger, the gas separator, the second solenoid valve, the third solenoid valve and the fourth solenoid valve, respectively.

3. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 2, characterized in that: The feeding device comprises a retractable electromagnetic push rod (221) and a feeding table (222) made of iron material, the feeding table is provided with evenly distributed air holes (223), and the lower part of the feeding table is provided with a plurality of rollers; a round rod (225) is provided at the right end of the retractable electromagnetic push rod, and a vertical groove matching the round rod is provided on the left side surface of the feeding table; two gas guide plates (40) are provided on the left side wall at the right end of the gas pipeline; the absorber comprises a heating element and a copper wire mesh, and the mesh size of the copper wire mesh is 20 meshes to 100 meshes; the adsorption filter comprises activated carbon and a molecular filter.

4. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 3, characterized in that: The inner wall of the furnace body is made of refractory bricks, insulation bricks and quartz sand, and the outer shell of the furnace body is made of carbon steel; the insulation plate is made of two layers of molybdenum plates and three layers of stainless steel plates; the gas separation membrane in the gas separator is made of polycarbonate or polyimide; the feeding table, each gas nozzle, gas channel, connecting pipe, air guide pipe, the gas guide plate, the air-cooling nozzle and the air-cooling fan are all made of silicon carbide ceramic material.

5. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 3, characterized in that: The cold rolling deformation process includes the following steps: The staff used longitudinal rolling to roll plate-shaped maraging steel at room temperature, with a cold rolling reduction rate of 60%-80%. After cold rolling, maraging steel will produce cold deformation texture, and the texture remains stable after solution treatment. These textures enable the martensitic matrix to form fine substructures, promote lattice distortion, and further increase the matrix dislocation density, preparing for subsequent heat treatment strengthening processes.

6. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 5, characterized in that: Solution treatment includes the following steps: Step 6-1: The staff puts the maraging steel plate after cold rolling and deformation on the feeding table of the heating chamber, pulls the insulation plate out of the furnace body, and covers it with a sealing cover; the staff controls the vacuum pump through the controller to evacuate the heating chamber and the cooling chamber at the same time, and observes the air pressure data detected by the first temperature and pressure sensor to make the air pressure reach 5×10 -1 After Pa, the vacuum pump stops working; Step 6-2, insert the insulation board downward into the furnace body, control each heater to heat at a heating rate of 6°C / min-10°C / min through the controller, observe the temperature data detected by the first temperature and pressure sensor, make the temperature in the heating chamber reach 800°C-850°C, keep the temperature for 45 minutes-65 minutes, and then stop each heater; Step 6-3, let the plate cool with the furnace, observe the temperature data detected by the first temperature pressure sensor, when the temperature in the heating chamber is 600℃-700℃, the staff will pull the insulation board upward out of the furnace body and cover it with a sealing cover; turn on the power of the electromagnetic push rod, make the round rod of the electromagnetic push rod magnetic, connect the round rod with the vertical groove, extend the electromagnetic push rod, use the electromagnetic push rod to push the feeding table into the cooling chamber, turn off the power of the electromagnetic push rod, separate the electromagnetic push rod from the feeding table, and insert the insulation board downward into the furnace body; The controller controls the first solenoid valve to open, fills the cooling chamber with helium from an external gas cylinder, and observes the air pressure data detected by the second temperature and pressure sensor to maintain the air pressure in the cooling chamber within the range of 0.5 MPa-1.5 MPa; the controller controls the vacuum pump to work, so that the helium enters the gas pipeline after being purified by the recovery and purification mechanism; The air-cooling motor is controlled by the controller to drive the air-cooling fan, so that the cooled helium is quickly sprayed toward the plate through each gas nozzle to cool the plate until the temperature data detected by the second temperature and pressure sensor drops to room temperature. The air-cooling motor is turned off, the vacuum pump is controlled to work for 30 minutes to 60 minutes, the second solenoid valve is opened, and the cooled helium is pumped into the recovery gas cylinder, and then the second solenoid valve is controlled to close.

7. The strengthening treatment method for titanium-free maraging steel with a tensile strength of 2.2 GPa according to claim 1 or 6, characterized in that: The steps of making helium enter the gas pipeline after being purified by the recovery and purification mechanism include: The staff controls the third solenoid valve to open through the controller, and the vacuum pump drives the helium in the cooling chamber into the absorber. The copper wire mesh of the absorber causes the oxygen in the helium to undergo oxidation reaction to turn into copper oxide, thereby removing the oxygen. The first heat exchanger cools the helium, and the adsorption filter removes impurities and dust present when filtering helium for recovery. The compressor increases the pressure of the helium, allowing the helium to pass smoothly through the gas separation membrane of the gas separator. The gas separation membrane filters the nitrogen impurities contained in the helium, and the stored helium enters the right part of the gas pipeline.

Images