Super soft austenitic stainless steel and method of making

Abstract

The application discloses a super-soft austenitic stainless steel and a preparation method thereof. The super-soft austenitic stainless steel is composed of carbon C, nitrogen N, silicon Si, manganese Mn, chromium Cr, nickel Ni, copper Cu and iron Fe. The mass percentage of each component in the super-soft austenitic stainless steel is as follows: C: 0.005%-0.02%, N: 0.05%-0.2%, Si: 0.01%-0.1%, Mn: 1.5%-6.5%, Cr: 15.5%-19.6%, Ni: 7.5%-13.5%, Cu: 1.8%-5.3%, and the balance is iron. The super-soft austenitic stainless steel has the characteristics of low tensile strength and hardness, low strain-induced martensite in the bending process, low crack initiation rate and low failure fracture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of super-soft austenitic stainless steel, in particular to a super-soft austenitic stainless steel and a preparation method thereof. BACKGROUND

[0002] The evaporator and the condenser are important components of refrigeration equipment such as air conditioners and refrigerators, and the weight accounts for about 30-40% of the total weight of the machine, and the power consumption accounts for 20-30% of the total power consumption, and the performance directly affects the refrigeration (heating) capacity of the entire refrigeration system.

[0003] Due to good thermal conductivity and easy processing and convenient pipeline connection, copper materials are widely used in heat exchangers as refrigerant transmission pipelines of heat exchangers.

[0004] China is poor in copper resources and has a large demand, and copper materials are the third largest resource import product, among which, copper for air conditioners and refrigerators accounts for 75% of the total demand. In recent years, with the gradual reduction of copper resource reserves, the price of copper materials has shown an upward trend, which has increased the production cost of the refrigeration industry such as air conditioners and refrigerators, and the copper pipe is prone to corrosion, which can cause copper pipe leakage.

[0005] Stainless steel materials are cheap, and if used to make refrigerant transmission pipelines of heat exchangers, the production cost of the refrigeration industry such as air conditioners and refrigerators will be greatly reduced; however, common austenitic stainless steel has high hardness and is not easy to deform and process, and is prone to cracks in the large deformation area, which eventually leads to material fracture and affects the service life. SUMMARY

[0006] The present application aims to overcome the problems of high hardness of austenitic stainless steel, difficulty in deformation processing, and cracks in the large deformation area, and to provide a super-soft austenitic stainless steel and a preparation method thereof.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A super-soft austenitic stainless steel, the super-soft austenitic stainless steel is composed of carbon C, nitrogen N, silicon Si, manganese Mn, chromium Cr, nickel Ni, copper Cu and iron Fe; the mass percentage of each component in the super-soft austenitic stainless steel is as follows: C: 0.005%-0.02%, N: 0.05%-0.2%, Si: 0.01%-0.1%, Mn: 1.5%-6.5%, Cr: 15.5%-19.6%, Ni: 7.5%-13.5%, Cu: 1.8%-5.3% ， The balance is iron; wherein, the Ni equivalent Ni in the super-soft austenitic stainless steel eq ≥ 26.5;

[0009] Nieq = Ni + 12.93C + 1.11Mn + 0.72Cr - 0.27Si + 0.53Cu + 7.55N

[0010] Stacking fault forming index SFI in the super soft austenitic stainless steel is greater than or equal to 30;

[0011] SFI = 2.2Ni + 6Cu - 1.1Cr - 13Si - 1.2Mn + 32.

[0012] The present application increases the carbon content to improve the hardness and tensile strength of the austenitic stainless steel.

[0013] The nitrogen atom in the present application is dissolved in the phase matrix to refine the austenite grains, thereby improving the yield strength and tensile strength of the material. The nitrogen element can inhibit the formation of ferrite in the matrix, avoiding the martensitic transformation of the matrix during cold deformation processing. Nitrogen plays an important role in the corrosion resistance of stainless steel, especially in localized corrosion such as pitting and crevice corrosion, thereby improving the intergranular corrosion resistance of austenitic stainless steel.

[0014] Silicon in the present application acts as a deoxidizer when melting the austenitic stainless steel, playing a role in controlling the oxygen content.

[0015] Manganese in the present application is an austenite forming element, which can reduce the cost of the material, and almost no strain-induced martensite is produced during forming, and the yield strength, work hardening degree and compression deformation resistance are reduced.

[0016] Chromium in the present application can be passivated on the surface of the stainless steel into a dense oxide film, which can improve the potential barrier of the austenitic matrix to further corrosion, and also can absorb electrons of iron to make iron passivated, thereby ensuring the austenitic stainless steel has good corrosion resistance.

[0017] Nickel in the present application is the most important matrix stabilizing phase in austenitic steel. Nickel element is beneficial to expand the austenite phase region, making the matrix completely austenitized. Nickel element improves the thermal stability of the austenitic steel, making the steel have good corrosion resistance in non-oxidizing media. Nickel also improves the machinability and weldability of the steel, because of its optimization effect on toughness and ductility. In addition, nickel also makes the austenitic stainless steel non-magnetic, expanding its application range.

[0018] Copper in the present application can increase the Ni equivalent, inhibit the work hardening caused by the generation of strain-induced martensite. During the forming process, copper can interact with dislocations to form a strengthening phase that hinders the sliding of dislocations. It can increase the resistance to stacking fault movement and improve the stacking fault energy, thereby softening the austenitic stainless steel.

[0019] Room temperature Ni equivalent Ni eq(Ni equivalent is to indicate the tendency to form martensite during cooling or deformation) is controlled at not less than 26.5 according to the austenite elements (such as nickel, carbon, manganese, etc.) contained in the structure, according to the intensity of its austenitization, which is equivalent to the total of several nickel. The stacking fault formation index SFI≥30 (optimum 35 or more), SFI refers to the tendency of dislocation formation between adjacent layers in the crystal structure.

[0020] The present application controls the Ni equivalent by using the above-mentioned Ni equivalent formula, controls the Ni equivalent at 26.5 or more at room temperature, ensures the content of strain-induced martensite when the super-soft austenitic stainless steel is deformed, reduces the crack initiation at large deformation, and improves the service life of the austenitic stainless steel.

[0021] At the same time, the present application uses the stacking fault formation index SFI to predict the possibility of generating stacking faults. When the stacking fault formation index SFI is less than 30, a large number of stacking faults are generated in the matrix, the diffusion of dislocations is inhibited, and the hardness of the austenitic stainless steel is improved.

[0022] As preferred, the super-soft austenitic stainless steel further contains one or more of the following components, and the mass percentage of each component is: titanium Ti: 0.01%-0.1%, niobium Nb: 0.01%-0.3%, vanadium V: 0.03%-0.2%, molybdenum Mo: 0.5%-3.0%;

[0023] Among them, the Ni equivalent Ni eq of the super-soft austenitic stainless steel eq1

[0024] Ni eq1 = Ni + 12.93C + 1.11Mn + 0.72Cr - 0.27Si + 0.53Cu +

[0025] 7.55N - 0.24Ti + 0.19Nb + 0.9V + 0.88Mo.

[0026] If the super-soft austenitic stainless steel contains titanium Ti and niobium Nb, and does not contain vanadium V and molybdenum Mo, then V=0 and Mo=0 in the formula; that is, the components not contained in the super-soft austenitic stainless steel have a value of 0 in the formula.

[0027] Molybdenum is an element that stabilizes the passivation film in austenitic stainless steel, promotes the uniform distribution of Cr elements and steadily improves the stability of the passivation film on the surface of the stainless steel, so that the steel exhibits more excellent performance in terms of pitting corrosion resistance, crevice corrosion, etc.

[0028] Ti and Nb can easily combine with carbon to form carbide, both of which have higher binding capacity with C than Cr. Ti / Nb is usually added in austenitic stainless steel to fix C in the steel, thereby improving the intergranular corrosion resistance of the steel.

[0029] Vanadium can improve the corrosion resistance of austenitic stainless steel and improve the thermal stability.

[0030] As preferred, the ultra-soft austenitic stainless steel further contains the following components, each in a mass percentage of: boron B: 0.05%-0.3%, aluminum Al: 0.001%-0.005%;

[0031] Among them, the Ni equivalent Ni eq = Ni eq2

[0032] Ni eq2 = Ni+12.93C+1.11Mn+0.72Cr-0.27Si+0.53Cu+

[0033] 7.55N-0.24Ti+0.19Nb+0.9V+0.88Mo-0.69Al.

[0034] B is an element that can enhance the corrosion resistance of austenitic stainless steel, and the passivation film of austenitic stainless steel containing B element is more dense and stable.

[0035] Al can reduce the austenite phase region in the steel, refine the grains of the austenitic stainless steel, and increase the grain coarsening temperature of the austenitic stainless steel.

[0036] A preparation method of an ultra-soft austenitic stainless steel, comprising the following steps:

[0037] Step 1, smelting:

[0038] After weighing each component of the ultra-soft austenitic stainless steel according to the mass percentage, put it into the smelting furnace for smelting, heat the smelting furnace at a speed of 400℃ / h, keep the temperature at 1600℃-1650℃ for 20-30min, and pour the molten steel into a flat billet after smelting;

[0039] Step 2, heating:

[0040] Coat a protective layer on the flat billet, and put the flat billet into a vacuum induction furnace and heat it to 1150℃-1230℃, then take it out of the vacuum induction furnace;

[0041] Step 3, forging:

[0042] Forge the flat billet, with an initial forging temperature of 1100℃-1150℃ and a final forging temperature of 950℃-1000℃.

[0043] Step 4, repeating step 2-step 3, finally forging the slab steel with a size of 20cm-30cm;

[0044] Forging can change the coarse dendrite and columnar crystal into equiaxed crystal with fine and uniform size, and can compact and weld the original segregation, porosity, pores, inclusions and other defects in the slab steel, and improve the performance of the ultra-soft austenitic stainless steel.

[0045] Step 5, heating:

[0046] A protective layer is coated on the slab steel, and the slab steel is placed in a vacuum induction furnace, so that the temperature in the vacuum induction furnace reaches 1100℃-1150℃, and the temperature is maintained for 5-10min;

[0047] Heating can prevent the growth of the grain of the slab steel.

[0048] Step 6, hot rolling:

[0049] The slab steel is taken out of the vacuum induction furnace for hot rolling, and the opening rolling temperature is 1100℃-1120℃, and the final rolling temperature is 850℃-900℃;

[0050] Step 7, repeating step 5-step 6, finally, the slab steel is rolled into a steel plate material with a thickness of 4mm-5mm;

[0051] Step 8, pickling:

[0052] The steel plate material is placed in a pickling solution for pickling for 25s-30s;

[0053] The pickling solution is: nitric acid+hydrofluoric acid, the concentration of nitrate ions in the pickling solution is 300g / L-350g / L, the concentration of fluoride ions is 10g / L-50g / L, and the temperature of the pickling solution is 75℃-85℃;

[0054] Step 9, cold rolling:

[0055] The pickled steel plate material is cold-rolled, wherein the rolling reduction is 25%-30% each time, and finally the steel plate material is cold-rolled into a steel plate material with a thickness of 0.3mm-0.7mm;

[0056] Step 10, annealing:

[0057] The steel plate material is placed in a vacuum furnace for annealing, and the annealing temperature is 1100℃-1150℃, and the temperature is maintained for 20min-30min, and then the steel plate material is water-cooled.

[0058] As preferred, including smelting furnace and vacuum mechanism, smelting furnace includes furnace body, the feeding port being arranged on the furnace body, the sealing cover being arranged on the feeding port, the crucible fixing seat being arranged in the furnace body, a plurality of heaters being arranged on the inner side wall of the crucible fixing seat, the temperature pressure sensor being arranged on the furnace body, the smelting crucible being arranged on the crucible fixing seat;The lower end of the furnace body is provided with the gas outlet pipe and the gas inlet pipe;The vacuum mechanism includes the first electromagnetic valve being arranged on the gas outlet pipe, the vacuum pump being connected with the free end of the gas outlet pipe;The second electromagnetic valve is arranged on the gas inlet pipe, the gas cylinder and the air pump are connected with the free end of the gas inlet pipe;It also includes the controller, the controller is electrically connected with each heater, temperature pressure sensor, first electromagnetic valve, vacuum pump, second electromagnetic valve and air pump respectively;Step 1 is replaced by the following steps:

[0059] After the components of super-soft austenitic stainless steel are weighed according to mass percentage, they are placed in the smelting crucible, the sealing cover is removed from the feeding port, the smelting crucible is placed on the crucible fixing seat, and the sealing cover is covered on the feeding port.

[0060] The controller controls the first electromagnetic valve to open, so that the vacuum pump works to vacuumize the furnace body, until the temperature pressure sensor reaches 1x10 -3 MPa, the vacuum pump stops working, and the first electromagnetic valve is closed.

[0061] The controller controls the second electromagnetic valve to open, and the air pump works to suck the argon gas beside the gas cylinder into the furnace body, when the air pressure detected by the temperature pressure sensor reaches 3MPa, the controller controls the second electromagnetic valve to close, and the air pump stops working.

[0062] The controller starts the heater, so that the temperature in the furnace body reaches 1600-1650 DEG C, and the temperature is kept for 25-30 minutes, the components in the smelting crucible are melted into molten steel, the controller controls each heater to stop heating, the sealing cover is removed from the feeding port, the smelting crucible is taken out from the furnace body, and the molten steel in the smelting crucible is poured into a flat steel billet.

[0063] The super-soft austenitic stainless steel of the application is smelted in inert gas protection atmosphere, which can reduce the non-metallic inclusions generated in the smelting process and improve the purity of the super-soft austenitic stainless steel.

[0064] The super-soft austenitic stainless steel of the application has low hardness, and the large deformation during rolling does not affect the mechanical properties of the material, so that the rolling frequency is reduced, and the forming cost of the super-soft austenitic stainless steel is reduced.

[0065] As preferred, the waste gas treatment mechanism is further included, the waste gas treatment mechanism comprises a waste gas pipe connected with the furnace body, a first electronic valve arranged on the waste gas pipe, a compressor, a waste gas heat exchanger and an absorption reaction chamber connected in sequence, a desulfurizing agent supply pump connected with the lower part of the absorption reaction chamber through a material guide pipe, a mixing tank connected with the desulfurizing agent supply pump, a CaO bin and a MgO bin connected with the mixing tank; a barrier membrane is arranged in the lower part of the absorption reaction chamber, the waste gas heat exchanger and the material guide pipe are connected with the absorption reaction chamber below the barrier membrane, the free end of the waste gas pipe is connected with the compressor, a second electronic valve is arranged on the material guide pipe, a third electronic valve is arranged on the connecting pipe between the CaO bin and the mixing tank, and a fourth electronic valve is arranged on the connecting pipe between the MgO bin and the mixing tank; the controller is electrically connected with the first electronic valve, the compressor, the waste gas heat exchanger, the desulfurizing agent supply pump, the second electronic valve, the third electronic valve and the fourth electronic valve respectively; after the smelting is completed, the waste gas treatment process is further included:

[0066] The controller controls the first electronic valve to be opened, controls the compressor to work, the flue gas generated in the smelting process enters the waste gas pipe, the compressor increases the pressure of the flue gas, the temperature of the flue gas is reduced after the flue gas passes through the waste gas heat exchanger, and the flue gas enters the absorption reaction chamber below the barrier membrane; the controller controls the third electronic valve and the fourth electronic valve to be opened, CaO particles in the CaO bin and MgO particles in the MgO bin flow into the mixing tank, the desulfurizing agent supply pump is controlled to work, the second electronic valve is opened, the CaO particles and the MgO particles are sent into the absorption reaction chamber, the flue gas, the CaO particles and the MgO particles react, and the gas generated after the reaction passes through the barrier membrane into the upper part of the absorption reaction chamber, and the solid particles generated after the reaction remain in the absorption reaction chamber below the barrier membrane.

[0067] The absorber comprises a heating element and copper mesh wires, and the mesh size of the copper mesh wires is 20-80 meshes. The waste gas treatment mechanism can perform desulfurization treatment on the waste gas, thereby reducing the pollution of the waste gas to the environment.

[0068] As preferred, the water recovery treatment mechanism is further included, the water recovery treatment mechanism comprises a water tank, a water inlet pump and a water inlet pipe connected in sequence, a water outlet pipe, an absorber and a water heat exchanger connected in sequence; the water inlet pipe is connected with the upper part of the absorption reaction chamber, the water outlet pipe is connected with the middle part of the absorption reaction chamber, a water outlet pump is arranged on the water outlet pipe, the water heat exchanger is connected with the water tank, a first water electronic valve is arranged on the water inlet pipe, and a second water electronic valve is arranged on the water outlet pipe; the controller is electrically connected with the water inlet pump, the absorber, the water outlet pump, the water heat exchanger, the first water electronic valve and the second water electronic valve respectively; the water treatment process of the waste gas is further included:

[0069] The controller opens the first water electronic valve, controls the water inlet pump to work, and sucks the water in the water tank into the absorption reaction chamber, the water-soluble gas in the gas generated by the desulfurization reaction is dissolved in the water, and the gas difficult to dissolve in the water is discharged through the opening at the upper end of the absorption reaction chamber; the controller controls the water outlet pump to work to pump the water out of the absorption reaction chamber, the impurities generated by the reaction are removed when the water passes through the absorber, and the temperature of the water is reduced when the water passes through the water heat exchanger, and finally the water flows back to the water tank.

[0070] The water recovery treatment can further dissolve the water-soluble CO2 and the like in the water.

[0071] As preferred, the ultrasonic stirring mechanism further comprises a fixed plate arranged on the sealing cover, an air spring rod connected with the fixed plate, a push plate connected with the air spring rod, a support shaft in sliding connection with the push plate, a plurality of groups of vibration structures penetrating through the support shaft, a signal processor and an ultrasonic transmitter; the vibration structure comprises a copper electrode plate, a piezoelectric ceramic and a vibrating diaphragm arranged between the copper electrode plate and the piezoelectric ceramic; the copper electrode plate of the uppermost vibration structure is in contact with the lower surface of the push plate, the copper electrode plate of the lowermost vibration structure is connected with the upper surface of the signal processor, the lower end of the support shaft is fixedly connected with the upper surface of the signal processor, and the signal processor is electrically connected with the ultrasonic transmitter; the controller is electrically connected with the air spring rod, the signal processor and the ultrasonic transmitter respectively.

[0072] During smelting, the controller controls the air spring rod to work, so that the hydraulic column inside the air spring rod is stretched up and down, the push plate is driven to reciprocate up and down, the vibrating diaphragm is squeezed, the deformation between the copper electrode plate and the piezoelectric ceramic occurs, the deformation amount is transmitted to the signal processor, the signal processor transmits the signal to the ultrasonic transmitter, the ultrasonic transmitter emits ultrasonic waves, the ultrasonic waves are transmitted into the crucible to stir the molten steel inside the crucible, until the smelting is completed, the controller controls the air spring rod, the signal processor and the ultrasonic transmitter to stop working, and the stirring is completed.

[0073] The inner layer of the ultrasonic transmitter is made of quartz material, and the shell of the ultrasonic stirring mechanism is made of refractory material.

[0074] As preferred, the push plate comprises a circular plate and a downwardly open U-shaped plate connected with the upper surface of the circular plate, the upper part of the support shaft penetrates through the circular plate, and the upper end of the support shaft is located at the lower side of the middle part of the U-shaped plate.

[0075] Therefore, the present application has the following beneficial effects: the tensile strength and hardness of the ultra-soft austenitic stainless steel are relatively low, strain-induced martensite is hardly generated in the bending process, the crack initiation rate is low, failure fracture is not easy to occur, and the corrosion resistance is obviously superior to that of copper. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 is a structural schematic view of the present application;

[0077] Figure 2 This is a schematic diagram of the ultrasonic stirring mechanism of the present invention;

[0078] Figure 3 It is a curve showing the change of strain-induced martensite content with the amount of deformation. Detailed Implementation

[0079] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0080] Example 1

[0081] like Figures 1-2 The illustrated embodiment is an ultra-soft austenitic stainless steel, which is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), titanium (Ti), niobium (Nb), boron (B), aluminum (Al), iron, and fe. The mass percentages of each component in the ultra-soft austenitic stainless steel are as follows: C: 0.005%, N: 0.05%, Si: 0.01%, Mn: 1.6%, Cr: 15.9%, Ni: 11.7%, Cu: 3.2%, titanium (Ti): 0.01%, niobium (Nb): 0.01%, boron (B): 0.05%, aluminum (Al): 0.001%, with the balance being iron.

[0082] Among them, the Ni equivalent Ni in ultra-soft austenitic stainless steel eq ≥26.5;

[0083] Ni eq =Ni+12.93C+1.11Mn+0.72Cr-0.27Si+0.53Cu+

[0084] 7.55N-0.24Ti+0.19Nb+0.9V+0.88Mo-0.69Al.

[0085] Stacking fault formability index (SFI) in ultra-soft austenitic stainless steel is ≥30;

[0086] SFI=2.2Ni+6Cu-1.1Cr-13Si-1.2Mn+32.

[0087] A method for preparing ultra-soft austenitic stainless steel includes the following steps:

[0088] Step 1, Smelting:

[0089] The application relates to a smelting furnace and a vacuum mechanism, wherein the smelting furnace comprises a furnace body 10, a feeding port 11 arranged on the furnace body, a sealing cover 110 arranged on the feeding port, a crucible fixing seat 12 arranged in the furnace body, a plurality of heaters 13 arranged on the inner side wall of the crucible fixing seat, a temperature and pressure sensor 14 arranged on the furnace body, and a smelting crucible 15 arranged on the crucible fixing seat; an air outlet pipe 16 and an air inlet pipe 17 are arranged at the lower end of the furnace body; a sealing ring is arranged between the sealing cover and the feeding port; the vacuum mechanism comprises a first electromagnetic valve 20 arranged on the air outlet pipe and a vacuum pump 21 connected with the free end of the air outlet pipe; a second electromagnetic valve 24 is arranged on the air inlet pipe, an air cylinder 22 and an air suction pump 23 are connected with the free end of the air inlet pipe; a controller is further arranged and electrically connected with each of the heaters, the temperature and pressure sensor, the first electromagnetic valve, the vacuum pump, the second electromagnetic valve and the air suction pump; and the application comprises the following steps:

[0090] After each component of the super-soft austenitic stainless steel is weighed according to the mass percentage, the component is placed into the smelting crucible, the sealing cover is taken off from the feeding port, the smelting crucible is placed on the crucible fixing seat, and the sealing cover is covered on the feeding port;

[0091] The controller controls the first electromagnetic valve to be opened, so that the vacuum pump works to suck the air in the furnace body, until the display value of the temperature and pressure sensor reaches 1x10 -3 MPa, the vacuum pump is controlled to stop working, and the first electromagnetic valve is closed;

[0092] The controller controls the second electromagnetic valve to be opened, so that the air suction pump works to suck the argon in the air cylinder into the furnace body; when the air pressure detected by the temperature and pressure sensor reaches 3 MPa, the controller controls the second electromagnetic valve to be closed, and the air suction pump stops working;

[0093] The controller starts the heaters, so that the temperature in the furnace body reaches 1630 DEG C, and the temperature is kept for 28 min; each component in the smelting crucible is melted into molten steel; the controller controls each heater to stop heating, the sealing cover is taken off from the feeding port, the smelting crucible is taken out from the furnace body, and the molten steel in the smelting crucible is poured into a flat steel billet.

[0094] Step 2, heating:

[0095] A protective layer is coated on the flat steel billet, the flat steel billet is placed into a vacuum induction furnace, and the flat steel billet is taken out from the vacuum induction furnace after being heated to 1180 DEG C;

[0096] Step 3, forging:

[0097] The flat steel billet is forged, the initial forging temperature is 1130 DEG C, and the final forging temperature is 980 DEG C;

[0098] Step 4, repeating steps 2-3, and finally forging the flat steel billet into a block steel with a size of 25 cm;

[0099] Step 5, heating:

[0100] The bulk steel is coated with a protective layer, and the bulk steel is placed in a vacuum induction furnace, and the temperature in the vacuum induction furnace is raised to 1130℃, and the temperature is kept for 8min;

[0101] Step 6, hot rolling:

[0102] The bulk steel is taken out of the vacuum induction furnace for hot rolling, and the opening rolling temperature is 1120℃, and the final rolling temperature is 880℃;

[0103] Step 7, repeat step 5-Step 6, finally, the bulk steel is rolled into a steel plate material with a thickness of 4.5mm;

[0104] Step 8, pickling:

[0105] The steel plate material is placed in the pickling solution for 28s;

[0106] The pickling solution is: nitric acid + hydrofluoric acid, the concentration of nitrate ions in the pickling solution is 330g / L, the concentration of fluoride ions is 40g / L, and the temperature of the pickling solution is 80℃;

[0107] Step 9, cold rolling:

[0108] The pickled steel plate material is cold-rolled, wherein the rolling reduction is 25%-30% each time, and the steel plate material is finally cold-rolled into a steel plate material with a thickness of 0.6mm;

[0109] Step 10, annealing:

[0110] The steel plate material is placed in a vacuum furnace for annealing, and the annealing temperature is 1130℃, and the temperature is kept for 28min, and then the steel plate material is water-cooled.

[0111] In addition, it also includes a waste gas treatment mechanism, the waste gas treatment mechanism includes a waste gas pipe 31 connected with the furnace body, a first electronic valve 32 arranged on the waste gas pipe, a compressor 33, a waste gas heat exchanger 34 and an absorption reaction chamber 35 connected in sequence, a desulfurizing agent supply pump 36 connected with the lower part of the absorption reaction chamber through the material guide pipe 30, a mixing tank 37 connected with the desulfurizing agent supply pump, a CaO bin 38 and a MgO bin 39 connected with the mixing tank; The lower part of the absorption reaction chamber is provided with a barrier film 301, and the waste gas heat exchanger and the material guide pipe are connected with the absorption reaction chamber below the barrier film, and the free end of the waste gas pipe is connected with the compressor; A second electronic valve 302 is arranged on the material guide pipe, a third electronic valve 303 is arranged on the connecting pipe between the CaO bin and the mixing tank, and a fourth electronic valve 304 is arranged on the connecting pipe between the MgO bin and the mixing tank; The controller is electrically connected with the first electronic valve, the compressor, the waste gas heat exchanger, the desulfurizing agent supply pump, the second electronic valve, the third electronic valve and the fourth electronic valve; After the smelting is finished, the waste gas treatment process is also included:

[0112] The controller opens the first electronic valve, controls the compressor to work, and the flue gas generated during the smelting process enters the exhaust gas pipe. The compressor increases the pressure of the flue gas, and the temperature of the flue gas decreases after passing through the exhaust gas heat exchanger. The flue gas then enters the absorption reaction chamber below the barrier membrane. The controller opens the third and fourth electronic valves, and the CaO particles in the CaO silo and the MgO particles in the MgO silo flow into the mixing tank. The controller also controls the desulfurizer supply pump to work and opens the second electronic valve, sending the CaO and MgO particles into the absorption reaction chamber. This causes the flue gas to react with the CaO and MgO particles. The gas produced after the reaction passes through the barrier membrane and enters the upper part of the absorption reaction chamber, while the solid particles produced after the reaction remain in the absorption reaction chamber below the barrier membrane.

[0113] It also includes a water recycling and treatment mechanism, which comprises a water tank 41, an inlet pump 42, and an inlet pipe 43 connected in sequence, and an outlet pipe 44, an absorber 45, and a water heat exchanger 46 connected in sequence. The inlet pipe is connected to the upper part of the absorption reaction chamber, and the outlet pipe is connected to the middle part of the absorption reaction chamber. An outlet pump 47 is installed on the outlet pipe, and the water heat exchanger is connected to the water tank. A first water electronic valve 48 is installed on the inlet pipe, and a second water electronic valve 49 is installed on the outlet pipe. The controller is electrically connected to the inlet pump, absorber, outlet pump, water heat exchanger, first water electronic valve, and second water electronic valve, respectively. It also includes a water treatment process for waste gas.

[0114] The controller opens the first water electronic valve, controlling the water inlet pump to draw water from the tank into the absorption reaction chamber. Water-soluble gases from the desulfurization reaction dissolve in the water, while gases that are difficult to dissolve in water are discharged through the opening at the top of the absorption reaction chamber. The controller then controls the outlet pump to draw water out of the absorption reaction chamber. As the water passes through the absorber, impurities from the reaction are removed. As the water passes through the water heat exchanger, its temperature is lowered. Finally, the water flows back into the tank.

[0115] It also includes an ultrasonic stirring mechanism 5, which includes a fixed plate 51 on the sealing cover, a gas spring rod 52 connected to the fixed plate, a push plate 53 connected to the gas spring rod, a support shaft 54 ​​slidably connected to the push plate, several sets of vibration structures passing through the support shaft, a signal processor 55, and an ultrasonic transmitter 56; the vibration structure includes a copper electrode plate 501, a piezoelectric ceramic 502, and a vibrating diaphragm 503 located between the copper electrode plate and the piezoelectric ceramic; the copper electrode plate of the uppermost vibration structure is in contact with the lower surface of the push plate, the copper electrode plate of the lowermost vibration structure is connected to the upper surface of the signal processor, the lower end of the support shaft is fixedly connected to the upper surface of the signal processor, and the signal processor is electrically connected to the ultrasonic transmitter; the controller is electrically connected to the gas spring rod, the signal processor, and the ultrasonic transmitter respectively.

[0116] The push plate includes a circular plate 531 and a downward-opening U-shaped plate 532 connected to the upper surface of the circular plate. The upper part of the support shaft passes through the circular plate, and the upper end of the support shaft is located on the lower side of the middle of the U-shaped plate.

[0117] During smelting, the controller controls the gas spring rod to operate, causing the hydraulic column inside the gas spring rod to extend and retract up and down, driving the push plate to reciprocate up and down. This squeezes the vibrating diaphragm, causing deformation between the copper electrode plate and the piezoelectric ceramic. The amount of deformation is transmitted to the signal processor, which then transmits the signal to the ultrasonic transmitter. The ultrasonic transmitter emits ultrasonic waves, which are transmitted into the crucible to stir the molten steel inside until the smelting is completed. At this point, the controller stops the gas spring rod, signal processor, and ultrasonic transmitter, and the stirring ends.

[0118] Example 2

[0119] The ultra-soft austenitic stainless steel of Example 2 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), titanium (Ti), niobium (Nb), boron (B), aluminum (Al), iron, and Fe.

[0120] The mass percentages of the components in the ultra-soft austenitic stainless steel are as follows: C: 0.02%, N: 0.2%, Si: 0.1%, Mn: 6.5%, Cr: 19.5%, Ni: 7.8%, Cu: 5.1%, Titanium (Ti): 0.1%, Molybdenum (Mo): 2.9%, Niobium (Nb): 0.3%, Boron (B): 0.3%, Aluminum (Al): 0.005%, Vanadium (V): 0.2%, with the balance being iron;

[0121] The other structural and methodological aspects of Example 2 are the same as those in Example 1.

[0122] Example 3

[0123] The ultra-soft austenitic stainless steel of Example 3 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), titanium (Ti), niobium (Nb), boron (B), aluminum (Al), iron, and fe. The mass percentages of each component in the ultra-soft austenitic stainless steel are as follows: C: 0.01%, N: 0.18%, Si: 0.1%, Mn: 5.8%, Cr: 16.5%, Ni: 10.2%, Cu: 2.5%, titanium (Ti): 0.08%, molybdenum (Mo): 1.7%, niobium (Nb): 0.05%, boron (B): 0.2%, aluminum (Al): 0.003%, vanadium (V): 0.1%, with the balance being iron.

[0124] The other structural and methodological aspects of Example 3 are the same as those in Example 1.

[0125] Example 4

[0126] The ultra-soft austenitic stainless steel of Example 4 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), vanadium (V), molybdenum (Mo), boron (B), aluminum (Al), iron, and Fe.

[0127] Ultra-soft austenitic stainless steel is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), and iron (Fe). The mass percentages of each component in ultra-soft austenitic stainless steel are as follows: C: 0.01%, N: 0.13%, Si: 0.05%, Mn: 3.3%, Cr: 17.2%, Ni: 9.3%, Cu: 4.1%, molybdenum (Mo): 0.6%, boron (B): 0.24%, aluminum (Al): 0.0028%, vanadium (V): 0.03%, with the balance being iron.

[0128] The other structural and methodological aspects of Example 4 are the same as those in Example 1.

[0129] Example 5

[0130] The ultra-soft austenitic stainless steel of Example 5 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), vanadium (V), molybdenum (Mo), boron (B), aluminum (Al), iron, and Fe.

[0131] The mass percentages of the components in the ultra-soft austenitic stainless steel are as follows: C: 0.012%, N: 0.08%, Si: 0.03%, Mn: 4.7%, Cr: 18.3%, Ni: 11.7%, Cu: 4.6%, Mo: 1.2%, B: 0.1%, Al: 0.0027%, V: 0.18%, with the balance being iron;

[0132] The other structural and methodological aspects of Example 5 are the same as those in Example 1.

[0133] Example 6

[0134] The ultra-soft austenitic stainless steel of Example 6 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), vanadium (V), molybdenum (Mo), boron (B), aluminum (Al), iron, and Fe.

[0135] The mass percentages of the components in the ultra-soft austenitic stainless steel are as follows: C: 0.02%, N: 0.06%, Si: 0.12%, Mn: 5.2%, Cr: 18.8%, Ni: 9.5%, Cu: 2.1%, Boron (B): 0.1%, Aluminum (Al): 0.0023%, Vanadium (V): 0.12%, Molybdenum (Mo): 0.8%, with the balance being iron;

[0136] The other structural and methodological aspects of Example 6 are the same as those in Example 1.

[0137] Example 7

[0138] The ultra-soft austenitic stainless steel of Example 7 is composed of carbon (C), nitrogen (N), silicon (Si), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), molybdenum (Mo), boron (B), aluminum (Al), iron, and Fe.

[0139] The mass percentages of the components in the ultra-soft austenitic stainless steel are as follows: C: 0.006%, N: 0.05%, Si: 0.03%, Mn: 5.5%, Cr: 16.2%, Ni: 8.1%, Cu: 3.7%, Molybdenum (Mo): 2.1%, Boron (B): 0.12%, Aluminum (Al): 0.00315%, Vanadium (V): 0.08%, with the balance being iron;

[0140] The other structural and methodological aspects of Example 7 are the same as those in Example 1.

[0141] The mechanical properties of the ultra-soft austenitic stainless steels prepared in Examples 1-7 were tested, and the results are shown in Table 1 below:

[0142] Steel grade Tensile strength Yield strength Vickers hardness Elongation Reduction of area ′ maraging steel ​ 1 483 MPa 172.6 MPa 139.3 HV 45.6％ 38.6％ 2.14％ 2 464.3 MPa 162.9 MPa 126.4 HV 52.2％ 50.1％ 4.06％ 3 457.6 MPa 159.7 MPa 114.7 HV 66.5％ 62.3％ 4.17％ 4 459 MPa 163.2 MPa 118.4 HV 63.3％ 59.7％ 3.85％ 5 475.3 168.4 MPa 133.2 HV 46.5％ 43.3％ 3.35％ 6 467.7 MPa 165.36 MPa 128 HV 57.5％ 54.1％ 4.37％ 7 451 MPa 158.7 MPa 108.3 HV 70.1％ 65.2％ 5.41％

[0143] Table 1

[0144] As can be seen from Table 1, the tensile strength of the obtained ultra-soft austenitic stainless steel is all below 500 MPa, the yield strength is below 180 MPa, and the Vickers hardness is below 150 MPa. Compared with ordinary austenitic stainless steels such as forged 304 (tensile strength: 736 MPa, yield strength: 254 MPa) and forged 316 (tensile strength: 592 MPa, yield strength: 245 MPa), the strength of the ultra-soft austenitic stainless steel of the present invention is significantly reduced, and the strain-induced martensite content generated during the deformation of the transmission pipeline is less, which can effectively alleviate the generation and fracture problems of microcracks in the transmission pipeline. After using the present invention to make air conditioning refrigerant transmission pipelines, the stable use of condensers and heat exchangers can be guaranteed, and the production cost of condensers and heat exchangers can be reduced, saving copper resources.

[0145] Figure 3 The diagram shows a tensile test conducted on forged 304 austenitic stainless steel, with the strain-induced martensite content at the fracture surface measured as a function of elongation. When the strain-induced martensite α′ content generated by deformation exceeds its maximum value, cracks and stress concentration will occur. This schematic diagram represents the critical value for fracture failure under different deformation amounts. Table 1 shows that the strain-induced martensite content of the ultra-soft austenitic stainless steel of this invention is lower than [value missing] at different elongations. Figure 3 The strain-induced martensite content shown does not lead to strain strengthening during deformation, thus altering the properties of ultra-soft austenitic stainless steel.

[0146] When the strain-induced martensite α′ content generated by deformation exceeds the maximum value, cracks and stress concentration are likely to occur. This schematic diagram is used to represent the critical value of fracture failure under different deformation amounts.

[0147] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-soft austenitic stainless steel, characterized in that, The mass percentages of the components in ultra-soft austenitic stainless steel are as follows: C: 0.005%-0.02%, N: 0.05%-0.2%, Si: 0.01%-0.1%, Mn: 1.5%-6.5%, Cr: 15.5%-19.6%, Ni: 7.5%-13.5%, Cu: 1.8%-5.3%, Boron B: 0.05%-0.3%, Aluminum Al: 0.001%-0.005%; ultra-soft austenitic stainless steel also contains one or more of the following components, with the mass percentages of each component being: Titanium Ti: 0.01%-0.1%, Niobium Nb: 0.01%-0.3%, Vanadium V: 0.03%-0.2%, Molybdenum Mo: 0.5%-3.0%, with the balance being iron; Among them, the Ni equivalent in ultra-soft austenitic stainless steel ≥26.5; Stacking fault formability index (SFI) in ultra-soft austenitic stainless steel is ≥30; SFI=2.2Ni+6Cu-1.1Cr-13Si-1.2Mn+32; The preparation method includes the following steps: Step 1, heating: A protective layer is applied to a block of steel made of various components of ultra-soft austenitic stainless steel. The block of steel is then placed in a vacuum induction furnace, and the temperature in the vacuum induction furnace is raised to 1100℃-1150℃ and held for 5-10 minutes. Step 2, hot rolling: The block steel is taken out of the vacuum induction furnace and hot rolled at an initial rolling temperature of 1100℃-1120℃ and a final rolling temperature of 850℃-900℃. Step 3: Repeat steps 1 to 2 until the block steel is rolled into a steel plate with a thickness of 4mm-5mm. Step 4, pickling: Immerse the steel plate in the pickling solution for 25-30 seconds; The pickling solution is composed of nitric acid and hydrofluoric acid. The concentration of nitrate ions in the pickling solution is 300g / L-350g / L, the concentration of fluoride ions is 10g / L-50g / L, and the temperature of the pickling solution is 75℃~85℃. Step 5, cold rolling: The pickled steel sheet is cold rolled, with a rolling reduction rate of 25%-30% each time, and finally the steel sheet is cold rolled into a steel sheet with a thickness of 0.3mm-0.7mm; Step 6, Annealing: The steel plate is placed in a vacuum furnace for annealing at a temperature of 1100℃-1150℃ for 20-30 minutes, and then the steel plate is water-cooled.

2. The method for preparing ultra-soft austenitic stainless steel according to claim 1, characterized in that, The following steps precede step 1: Step 1-1, Smelting: After weighing the components of the ultra-soft stainless steel according to their mass percentages, the steel is placed in a melting furnace for melting. The furnace is heated at a rate of 400℃ / h until it reaches 1600℃-1650℃. The temperature is then maintained for 20-30 minutes. The molten steel is then poured into flat steel billets. Steps 1-2, heating: Apply a protective layer to the flat steel billet, place the flat steel billet in a vacuum induction furnace, heat it to 1150℃-1230℃, and then remove the flat steel billet from the vacuum induction furnace. Steps 1-3, forging: The flat steel billet is forged at an initial forging temperature of 1100℃-1150℃ and a final forging temperature of 950℃-1000℃. Steps 1-4, repeat steps 1-2 to 1-3, and finally forge the flat steel billet into block steel with a size of 20cm-30cm.

3. The method for preparing ultra-soft austenitic stainless steel according to claim 2, characterized in that, The system includes a smelting furnace and a vacuum mechanism. The smelting furnace includes a furnace body (10), a feeding port (11) on the furnace body, a sealing cover (110) on the feeding port, a crucible fixing seat (12) in the furnace body, several heaters (13) on the inner wall of the crucible fixing seat, a temperature and pressure sensor (14) on the furnace body, and a smelting crucible (15) on the crucible fixing seat. The lower end of the furnace body is provided with an outlet pipe (16) and an inlet pipe (17). The vacuum mechanism includes a first solenoid valve (20) on the outlet pipe and a vacuum pump (21) connected to the free end of the outlet pipe. The inlet pipe is provided with a second solenoid valve (24), a gas cylinder (22) and a vacuum pump (23) connected to the free end of the inlet pipe. The system also includes a controller, which is electrically connected to each heater, temperature and pressure sensor, first solenoid valve, vacuum pump, second solenoid valve and vacuum pump respectively. Step 1-1 is replaced by the following steps: Weigh each component of the ultra-soft austenitic stainless steel according to the mass percentage, put them into the melting crucible, remove the sealing cap from the feed port, place the melting crucible on the crucible fixing seat, and put the sealing cap on the feed port. The controller opens the first solenoid valve, activating the vacuum pump to evacuate the furnace until the temperature and pressure sensors read 1×10⁻⁶. -3 After reaching MPa, the vacuum pump stops working and the first solenoid valve closes. The controller controls the second solenoid valve to open, and the vacuum pump to work, drawing argon gas from the side of the gas cylinder into the furnace. When the gas pressure detected by the temperature and pressure sensor reaches 3MPa, the controller controls the second solenoid valve to close, and the vacuum pump to stop working. The controller starts the heaters, raising the temperature inside the furnace to 1600℃-1650℃. The temperature is maintained for 25-30 minutes, during which the components in the melting crucible melt into molten steel. The controller then stops heating each heater, removes the sealing cover from the feed port, removes the melting crucible from the furnace, and pours the molten steel from the melting crucible into flat steel billets.

4. The method for preparing ultra-soft austenitic stainless steel according to claim 3, characterized in that, It also includes a waste gas treatment mechanism, which includes a waste gas pipe (31) connected to the furnace body, a first electronic valve (32) installed on the waste gas pipe, a compressor (33), a waste gas heat exchanger (34) and an absorption reaction chamber (35) connected in sequence, a desulfurizing agent supply pump (36) connected to the lower part of the absorption reaction chamber through a feed pipe (30), a mixing tank (37) connected to the desulfurizing agent supply pump, and a CaO silo (38) and an MgO silo (39) connected to the mixing tank; a barrier membrane (301) is provided at the lower part of the absorption reaction chamber for waste gas heat exchange. Both the feed pipe and the guide pipe are connected to the absorption reaction chamber below the barrier membrane. The free end of the exhaust pipe is connected to the compressor. A second electronic valve (302) is installed on the feed pipe. A third electronic valve (303) is installed on the connecting pipe between the CaO silo and the mixing tank. A fourth electronic valve (304) is installed on the connecting pipe between the MgO silo and the mixing tank. The controller is electrically connected to the first electronic valve, the compressor, the exhaust heat exchanger, the desulfurizing agent supply pump, the second electronic valve, the third electronic valve, and the fourth electronic valve, respectively. After the smelting is completed, the exhaust gas treatment process is also included. The controller opens the first electronic valve, controls the compressor to work, and the flue gas generated during the smelting process enters the exhaust gas pipe. The compressor increases the pressure of the flue gas, and the temperature of the flue gas decreases after passing through the exhaust gas heat exchanger. The flue gas then enters the absorption reaction chamber below the barrier membrane. The controller opens the third and fourth electronic valves, and the CaO particles in the CaO silo and the MgO particles in the MgO silo flow into the mixing tank. The controller also controls the desulfurizer supply pump to work and opens the second electronic valve, sending the CaO and MgO particles into the absorption reaction chamber. This causes the flue gas to react with the CaO and MgO particles. The gas produced after the reaction passes through the barrier membrane and enters the upper part of the absorption reaction chamber, while the solid particles produced after the reaction remain in the absorption reaction chamber below the barrier membrane.

5. The method for preparing ultra-soft austenitic stainless steel according to claim 4, characterized in that, It also includes a water recycling and treatment mechanism, which comprises a water tank (41), an inlet pump (42), and an inlet pipe (43) connected in sequence, and an outlet pipe (44), an absorber (45), and a water heat exchanger (46) connected in sequence; the inlet pipe is connected to the upper part of the absorption reaction chamber, the outlet pipe is connected to the middle part of the absorption reaction chamber, an outlet pump (47) is installed on the outlet pipe, the water heat exchanger is connected to the water tank, a first water electronic valve (48) is installed on the inlet pipe, and a second water electronic valve (49) is installed on the outlet pipe; the controller is electrically connected to the inlet pump, absorber, outlet pump, water heat exchanger, first water electronic valve, and second water electronic valve respectively; it also includes a water treatment process for waste gas: The controller opens the first water electronic valve, controlling the water inlet pump to draw water from the tank into the absorption reaction chamber. Water-soluble gases from the desulfurization reaction dissolve in the water, while gases that are difficult to dissolve in water are discharged through the opening at the top of the absorption reaction chamber. The controller then controls the outlet pump to draw water out of the absorption reaction chamber. As the water passes through the absorber, impurities from the reaction are removed. As the water passes through the water heat exchanger, its temperature is lowered. Finally, the water flows back into the tank.

6. The method for preparing ultra-soft austenitic stainless steel according to claim 2, characterized in that, It also includes an ultrasonic stirring mechanism (5), which includes a fixed plate (51) on the sealing cover, a gas spring rod (52) connected to the fixed plate, a push plate (53) connected to the gas spring rod, a support shaft (54) slidably connected to the push plate, several sets of vibration structures passing through the support shaft, a signal processor (55) and an ultrasonic transmitter (56); the vibration structure includes a copper electrode plate (501), a piezoelectric ceramic (502), and a vibrating diaphragm (503) located between the copper electrode plate and the piezoelectric ceramic; the copper electrode plate of the uppermost vibration structure is in contact with the lower surface of the push plate, the copper electrode plate of the lowermost vibration structure is connected to the upper surface of the signal processor, the lower end of the support shaft is fixedly connected to the upper surface of the signal processor, and the signal processor is electrically connected to the ultrasonic transmitter; the controller is electrically connected to the gas spring rod, the signal processor and the ultrasonic transmitter respectively.

7. The method for preparing ultra-soft austenitic stainless steel according to claim 6, characterized in that, The push plate includes a circular plate (531) and a U-shaped plate (532) with a downward opening connected to the upper surface of the circular plate. The upper part of the support shaft passes through the circular plate, and the upper end of the support shaft is located on the lower side of the middle of the U-shaped plate.

Images