CN112733465A - Method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and preparation method - Google Patents

Method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and preparation method Download PDF

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CN112733465A
CN112733465A CN202011502368.XA CN202011502368A CN112733465A CN 112733465 A CN112733465 A CN 112733465A CN 202011502368 A CN202011502368 A CN 202011502368A CN 112733465 A CN112733465 A CN 112733465A
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李花兵
朱红春
何志禹
冯浩
姜周华
王剑飞
张树才
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Northeastern University China
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Abstract

The invention provides a method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and a preparation method thereof, belonging to the technical field of high-nitrogen stainless steel smelting. The acquisition method accurately acquires the solidification pressure of the pressurized electroslag remelting high-nitrogen austenitic stainless steel based on the cooling speed, component segregation, superheat degree and electrode embedding depth in the pressurized electroslag remelting process, and the solidification pressure acquired by the method can inhibit the formation of nitrogen pores and improve the performance of the high-nitrogen austenitic stainless steel.

Description

Method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and preparation method
Technical Field
The invention relates to the technical field of high-nitrogen stainless steel smelting, in particular to a method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and a preparation method thereof.
Background
Because the solubility of nitrogen in molten steel is low, the distribution coefficient in austenite is small, and the like, nitrogen escapes in the solidification process, nitrogen bubbles are formed, and the like; how to prevent nitrogen from escaping and forming nitrogen bubbles is one of the key preparation technical problems which need to be solved urgently for high-nitrogen austenitic stainless steel.
At present, nitrogen pressurized smelting can effectively solve the technical problem and is considered to be one of the most promising preparation methods of the high-nitrogen austenitic stainless steel. As an important component of nitrogen pressurized smelting, the preparation of high-nitrogen austenitic stainless steel by pressurized electroslag remelting is widely applied. However, how to accurately determine the technological parameters such as solidification pressure and the like of the high-nitrogen austenitic stainless steel prepared by pressurized electroslag remelting and reasonably match the technology becomes a great technical problem of nitrogen pressurized smelting.
The solidification pressure is one of important process parameters of pressurized electroslag remelting closely related to nitrogen escape and nitrogen bubble formation, the accuracy of the solidification pressure is critical, the solidification pressure is directly related to the quality of the structure and the performance of high-nitrogen austenitic stainless steel, and serious problems of direct material scrapping, shortened equipment service life, even safety accidents and the like can be caused by over-high and over-low conditions.
Recently, industrial-grade pressurized electroslag furnaces are successively built in domestic Tianma bearing groups and Fushun special steels, but industrial production is still in a starting stage, the preparation technology is not mature, key process parameters such as solidification pressure and the like are mostly determined by repeated tests and experiences, and the obtained solidification pressure is inaccurate, high in randomness and poor in reliability, so that the high-nitrogen austenitic stainless steel is poor in performance.
Disclosure of Invention
In view of the above, the present invention aims to provide a method for obtaining a solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel and a preparation method thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the invention provides a method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel, which comprises the following steps of:
obtaining the slag depth coefficient f of a slag system for pressurized electroslag remeltingsObtaining the depth H of the slag bath through a formula (1)s：
Hs＝1.03fsDi±0.02 (1)；
In the formula (1), DiThe diameter of the electroslag ingot is m;
according to the formula (2), obtaining the depth H of the molten poolm：
Hm＝0.004ALm-0.001B (2)；
In the formula (2), LmThe perimeter m of a crystallizer of a pressurized electroslag furnace for pressurized electroslag remelting; a and B are characteristic constants of a slag system for pressurized electroslag remelting;
obtaining the nitrogen diffusion coefficient DsNitrogen solute distribution coefficient k, solidus temperature TSLiquidus temperature TLDensity of molten steel rhomSlag system density rhoSMaximum macrosegregation ratio of nitrogen and Srmax(ii) a Obtaining a nitrogen macrosegregation parameter M through a formula (3)N：
Figure BDA0002843983630000021
In the formula (3) [% N]Is the mass percentage content of nitrogen element in the high-nitrogen austenitic stainless steel, vcThe cooling rate is 1-5K/s;
according to equations (4) and (5), the nitrogen activity is obtained:
Figure BDA0002843983630000022
Figure BDA0002843983630000023
in equations (4) and (5):
Figure BDA0002843983630000024
the action coefficient of nitrogen element to nitrogen element;
Figure BDA0002843983630000025
is the first order interaction coefficient of element j to nitrogen element;
Figure BDA0002843983630000026
is a secondary interaction parameter of element j to nitrogen; delta T is the superheat degree of the molten steel, and delta T is 300-400K;
according to the formulas (6) to (8), the solidification pressure P of the pressurized electroslag remelting high-nitrogen austenitic stainless steel is obtainedS：
Figure BDA0002843983630000027
Figure BDA0002843983630000028
PS≥max(PS0；PS1) (8)；
In equations (6) to (8): pS0And PS1Are respectively a middle changeQuantity, pmThe density of the molten steel is; [% N]The mass percentage of N element in the high-nitrogen austenitic stainless steel is shown; heThe electrode is buried to a depth;
the high-nitrogen austenitic stainless steel comprises the following elements in percentage by mass: c: less than or equal to 0.2 percent, Mn: 13-20%, Cr: 15-22%, Si: less than or equal to 1 percent, Mo: 0-4.5%, N: 0.7-2%, Ni: 0-4% and the balance Fe.
Preferably, the maximum macrosegregation ratio Sr of the obtained nitrogenmaxThe method comprises the following steps:
preparing a high-nitrogen austenitic stainless steel ingot by adopting pressurized electroslag remelting, and comprises the following steps of preparing a consumable electrode, paving an arc striking agent, baking slag, arcing slagging, pressurizing electroslag remelting and tapping:
the preparing the consumable electrode comprises: smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
the laying of the arc striking agent comprises the following steps: placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
the slag baking and arc striking slagging comprises the following steps: baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
the pressurized electroslag remelting comprises: after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 1-3 MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40-45V, starting pressurizing electroslag remelting when the current reaches 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurizing voltage remelting;
the tapping comprises the following steps: lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to 0.6-1.0 MPa by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
obtaining the maximum macrosegregation ratio of nitrogen: longitudinally splitting the high-nitrogen austenitic stainless steel ingot, and measuring the content Cs of nitrogen elements at the positions 0, 30, 60, 90 and 120mm away from the center by using a nitrogen-oxygen analyzer at the height of 3/4 of the high-nitrogen austenitic stainless steel ingot, so that the macrosegregation ratio Sr of the nitrogen elements is CS/C0Wherein, C0The average concentration of the nitrogen element of the ingot; selecting the maximum Sr value as the maximum macrosegregation ratio Sr of nitrogenmax。
Preferably, in the pressurized electroslag remelting, the melting rate of the pressurized electroslag remelting is obtained by:
V＝(0.30～0.40)×D (9)；
wherein V is the melting speed and the unit is kg/h; d is the size of the crystallizer of the pressurized electroslag furnace for pressurized electroslag remelting and the unit is mm.
Preferably, in the pressurized electroslag remelting, the current fluctuation is less than +/-3%, the voltage fluctuation is less than +/-0.5%, and the melting speed fluctuation is less than +/-0.5 kg/h.
Preferably, the nitrogen diffusion coefficient DsCalculated by a DICTRA module in Thermo-Cal software.
Preferably, the nitrogen solute distribution coefficient k is calculated by an equilibrium solidification model in Thermo-Cal software.
Preferably, the solidus temperature TSLiquidus temperature TLDensity of molten steel rhomAnd slag system density ρSThrough Thermo-Cal softwareAnd calculating an equilibrium solidification model.
The invention also provides a preparation method of the pressurized electroslag remelting high-nitrogen austenitic stainless steel ingot, which comprises the following steps:
smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 1-3 MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40-45V, starting pressurized electroslag remelting when the current is 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurized electroslag remelting;
lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to a target solidification pressure by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
the target solidification pressure is the solidification pressure obtained by the acquisition method of the technology.
The invention provides a method for acquiring the solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel, which is based on the cooling speed, component segregation, superheat degree and electrode embedding depth in the pressurized electroslag remelting process, and has the advantages of high reliability, capability of inhibiting nitrogen pore formation and improvement on the performance of the high-nitrogen austenitic stainless steel.
Drawings
FIG. 1 is an internal sectional view of a high nitrogen austenitic stainless steel ingot obtained in example 1;
fig. 2 is an internal sectional view of the ingot of high nitrogen austenitic stainless steel obtained in example 2.
Detailed Description
The invention provides a method for acquiring solidification pressure required by pressurized electroslag remelting high-nitrogen austenitic stainless steel, which comprises the following steps of:
obtaining the slag depth coefficient f of a slag system for pressurized electroslag remeltingsObtaining the depth H of the slag bath through a formula (1)s：
Hs＝1.03fsDi±0.02 (1)；
In the formula (1), DiThe diameter of the electroslag ingot is m;
according to the formula (2), obtaining the depth H of the molten poolm：
Hm＝0.004ALm-0.001B (2)；
In the formula (2), LmThe perimeter m of a crystallizer of a pressurized electroslag furnace for pressurized electroslag remelting; a and B are characteristic constants of a slag system for pressurized electroslag remelting;
obtaining the nitrogen diffusion coefficient DsNitrogen solute distribution coefficient k, solidus temperature TSLiquidus temperature TLDensity of molten steel rhomSlag system density rhoSMaximum macrosegregation ratio of nitrogen and Srmax(ii) a Obtaining a high nitrogen segregation parameter M through a formula (3)N：
Figure BDA0002843983630000051
In the formula (3) [% N]Is the mass percentage content of nitrogen element, vcThe cooling rate is 1-5K/s;
according to equations (4) and (5), the nitrogen activity is obtained:
Figure BDA0002843983630000061
Figure BDA0002843983630000062
in equations (4) and (5):
Figure BDA0002843983630000063
the action coefficient of nitrogen element to nitrogen element;
Figure BDA0002843983630000064
is the first order interaction coefficient of element j to nitrogen element;
Figure BDA0002843983630000065
is a secondary interaction parameter of element j to nitrogen; delta T is the superheat degree of the molten steel, and delta T is 300-400K;
according to the formulas (6) to (8), the solidification pressure P of the pressurized electroslag remelting high-nitrogen austenitic stainless steel is obtainedS：
Figure BDA0002843983630000066
Figure BDA0002843983630000067
PS≥max(PS0；PS1) (8)；
In equations (6) to (8): pS0And PS1Respectively an intermediate variable, pmThe density of the molten steel is; [% N]The mass percentage of N element in the high-nitrogen austenitic stainless steel is shown; heThe electrode is buried to a depth;
the high-nitrogen austenitic stainless steel comprises the following elements in percentage by mass: c: less than or equal to 0.2 percent, Mn: 13-20%, Cr: 15-22%, Si: less than or equal to 1 percent, Mo: 0-4.5%, N: 0.7-2%, Ni: 0-4% and the balance Fe.
The invention obtains the slag depth coefficient f of the slag system for the pressurized electroslag remeltingsObtaining the depth H of the slag bath through a formula (1)s：
Hs＝1.03fsDi±0.02 (1)；
In the formula (1), DiThe diameter of the electroslag ingot is m.
In the present invention, the high nitrogen austenitic stainless steel preferably includes the following elements by mass percent: c: less than or equal to 0.2 percent, Mn: 13-20%, Cr: 15-22%, Si: less than or equal to 1 percent, Mo: 0-4.5%, N: 0.7-2%, Ni: 0-4% and the balance Fe.
In the invention, the slag depth coefficient f of the slag system for the pressurized electroslag remelting is obtainedsThe method (2) is preferably: when the components of the high-nitrogen austenitic stainless steel are confirmed, a slag system of the high-nitrogen austenitic stainless steel is also confirmed; then according to the selected slag system, the slag depth coefficient f can be obtained by looking up the tool books(ii) a In the embodiment of the invention, when the slag is ANF-6 slag, the slag depth coefficient fsIs 0.54.
The invention obtains the depth H of the molten pool according to the formula (2)m：
Hm＝0.004ALm-0.001B (2)；
In the formula (2), LmThe perimeter m of a crystallizer of a pressurized electroslag furnace for pressurized electroslag remelting; a and B are characteristic constants of the slag system for pressurized electroslag remelting.
In the invention, after the components of the high-nitrogen austenitic stainless steel are confirmed, a slag system of the high-nitrogen austenitic stainless steel is also confirmed; and then according to the selected slag system, the characteristic constants A and B of the slag system for the pressurized electroslag remelting can be obtained by looking up the tool book.
The invention obtains the nitrogen diffusion coefficient DsNitrogen solute distribution coefficient k, solidus temperature TSLiquidus temperature TLDensity of molten steel rhomSlag system density rhoSMaximum macrosegregation ratio of nitrogen and Srmax(ii) a Obtaining a nitrogen macrosegregation parameter M through a formula (3)N：
Figure BDA0002843983630000071
In the formula (3) [% N]Is the mass percentage content of nitrogen element, vcThe cooling rate is preferably 1 to 5K/s.
In the present invention, the nitrogen diffusion coefficient DsPreferably, the method is obtained by calculation through a DICTRA module in Thermo-Cal software; the nitrogen solute distribution coefficient k is preferably calculated through a balanced solidification model in Thermo-Cal software; the solidus temperature TSLiquidus temperature TLDensity of molten steel rhomAnd slag system density ρSPreferably, the calculation is carried out through a balanced solidification model in Thermo-Cal software; specifically, it is preferable that: the above parameters can be obtained by inputting the element composition and content of the high-nitrogen austenitic stainless steel into relevant software.
In the present invention, the maximum macrosegregation ratio Sr of the obtained nitrogenmaxThe method comprises the following steps:
preparing a high-nitrogen austenitic stainless steel ingot by adopting pressurized electroslag remelting, and comprises the following steps of preparing a consumable electrode, paving an arc striking agent, baking slag, arcing slagging, pressurizing electroslag remelting and tapping:
the preparing the consumable electrode comprises: smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
the laying of the arc striking agent comprises the following steps: placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
the slag baking and arc striking slagging comprises the following steps: baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
the pressurized electroslag remelting comprises: after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 1-3 MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40-45V, starting pressurizing electroslag remelting when the current reaches 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurizing voltage remelting;
the tapping comprises the following steps: lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to 0.6-1.0 MPa by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
obtaining the maximum macrosegregation ratio of nitrogen: longitudinally splitting the high-nitrogen austenitic stainless steel ingot, and measuring the content Cs of nitrogen elements at the positions 0, 30, 60, 90 and 120mm away from the center by using a nitrogen-oxygen analyzer at the height of 3/4 of the high-nitrogen austenitic stainless steel ingot, so that the macrosegregation ratio Sr of the nitrogen elements is CS/C0Wherein, C0The average concentration of the nitrogen element of the ingot; selectingMaximum Sr value as maximum macrosegregation ratio Sr of nitrogenmax。
In the present invention, in the pressurized electroslag remelting, the melting rate of the pressurized electroslag remelting is obtained in a manner of V ═ 0.30 to 0.40 × D; v is the melting speed in kg/h, and D is the inner diameter of the crystallizer of the pressurized electroslag furnace for pressurized electroslag remelting in mm. In the invention, in the pressurized electroslag remelting, the current fluctuation is less than +/-3 percent, the voltage fluctuation is less than +/-0.5 percent, and the melting speed fluctuation is less than +/-0.5 kg/h.
According to the invention, the nitrogen element activity is obtained according to the formulas (4) and (5):
Figure BDA0002843983630000081
Figure BDA0002843983630000082
in equations (4) and (5):
Figure BDA0002843983630000083
the action coefficient of nitrogen element to nitrogen element;
Figure BDA0002843983630000084
is the first order interaction coefficient of element j to nitrogen element;
Figure BDA0002843983630000085
is a secondary interaction parameter of element j to nitrogen; and delta T is the superheat degree of the molten steel, and is 300-400K.
In the present invention, in the case of the present invention,
Figure BDA0002843983630000091
and
Figure BDA0002843983630000092
preferably by consulting a tool book for the composition of the high nitrogen austenitic stainless steel alloy.
The invention obtains addition according to formulas (6) to (8)Solidification pressure P of piezoelectric slag remelting high-nitrogen austenitic stainless steelS：
Figure BDA0002843983630000093
Figure BDA0002843983630000094
PS≥max(PS0；PS1) (8)；
In equations (6) to (8): pS0And PS1Respectively an intermediate variable, pmThe density of the molten steel is; [% N]The mass percentage of N element in the high-nitrogen austenitic stainless steel is shown; heThe electrode embedding depth is shown, and g is the acceleration of gravity.
The invention also provides a preparation method of the pressurized electroslag remelting high-nitrogen austenitic stainless steel ingot, which comprises the following steps:
smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
after slagging is finished, filling nitrogen into the smelting chamber, pressurizing to 1-3 MPa, synchronously increasing the pressure of cooling water in a crystallizer of a pressurized electroslag furnace, keeping the pressures on two sides of the copper wall of the crystallizer basically consistent, adjusting the voltage to 38-43V, starting pressurized electroslag remelting when the current is 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurized electroslag remelting is carried out;
lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to a target solidification pressure by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
the target solidification pressure is the solidification pressure obtained by the acquisition method in the technical scheme.
The method for obtaining the solidification pressure required for the pressurized electroslag remelting high nitrogen austenitic stainless steel and the preparation method thereof provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of the present invention.
In examples 1 and 2 of the present invention, the main components of the raw materials for smelting used are shown in Table 1.
TABLE 1 Main Components (wt%) of smelting raw materials
Figure BDA0002843983630000101
Example 1
The target high-nitrogen austenitic stainless steel is 19Cr14Mn4Mo0.9N, and the component control range and smelting control target are shown in Table 2.
Table 219 Cr14Mn4Mo0.9N component control Range and control target (wt%)
Figure BDA0002843983630000102
The method for acquiring the solidification pressure comprises the following steps:
in the example, 19Cr14Mn4Mo0.9N steel is prepared by pressurized electroslag remelting, and the slag system is 70% CaF2-30％Al2O3Namely ANF-6 slag, according to the characteristics of slag system, the slag depth coefficient fsIs 0.54, by the formula (1), in combination with the diameter D of the electroslag ingotiThe depth H of the slag pool is calculated to be 0.15msIs 0.083 m.
Calculating the depth H of the molten pool through a formula (2)m0.02m, wherein the mold circumference Lm0.471m, 15.5 and 8.82 for A and B, respectively.
According to the target components of the high-nitrogen austenitic stainless steel, the nitrogen diffusion coefficient D in the solid phase of the high-nitrogen austenitic stainless steel is calculated by a Thermo-calc software DICTRA modulesIs 2.4X 10-9Calculating to obtain a solute distribution coefficient k of 0.18 according to the balanced solidification model, and calculating to obtain a solidus temperature T through the balanced solidification modelS1594.18K, liquidus temperature TL1649.27K, molten steel density rhom6500kg/m3And slag system density ρS2600kg/m3；vcIs 5K/s;
the acquisition of the maximum macrosegregation ratio of nitrogen comprises the following steps:
the preparation of the high-nitrogen austenitic stainless steel ingot by adopting the pressurized electroslag remelting comprises the steps of preparing a consumable electrode, paving an arc striking agent, baking slag, arcing slagging, pressurizing electroslag remelting and tapping:
preparing a consumable electrode: smelting a consumable parent metal of the high-purity high-nitrogen austenitic stainless steel according to the components of the high-nitrogen austenitic stainless steel, forging the consumable parent metal into a consumable electrode with a size suitable for electroslag remelting in a pressurized electroslag furnace, and then cooling in air; removing surface oxide skin, welding the electrode to a false electrode, and connecting the electrode with an electrode holder;
laying an arc striking agent: an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel are placed on a pressurized electroslag furnace bottom water tank below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode, the arc striking scraps and the bottom water tank are electrified;
baking slag and arc starting slagging: baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 650 ℃ for 7 hours; and (3) starting a water supply system to introduce normal-pressure cooling water into the pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, and sealing the smelting chamber. Introducing nitrogen into the smelting chamber at a speed of 15L/min for 5min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 36V, the current is 2300A, and the slagging time is 23 min;
pressurizing electroslag remelting: after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 2.8MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40V and the current to 3500A, namely starting pressurizing electroslag remelting, wherein the melting speed is obtained in a mode of V being (0.30-0.40) multiplied by D; v is the melting speed in kg/h, and D is the inner diameter of a crystallizer of the pressurized electroslag furnace for pressurized electroslag remelting in mm; controlling the current fluctuation less than +/-3%, the voltage fluctuation less than +/-0.5% and the melting speed fluctuation less than +/-0.5 kg/h; simultaneously, uniformly adding 120g of silicon-calcium alloy by using a stepping type feeder to deoxidize;
tapping: lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to 0.6-1.0 MPa by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
obtaining the maximum macrosegregation ratio of nitrogen: at the height of 3/4, the content Cs of nitrogen element at 0, 30, 60, 90 and 120mm from the center is measured by nitrogen-oxygen analyzer, and then the macrosegregation ratio Sr of nitrogen element is CS/C0Wherein, C0The average concentration of the nitrogen element of the ingot; selecting the maximum Sr value as the maximum macrosegregation ratio Sr of nitrogen to be 1.25; calculating nitrogen macrosegregation parameter M by formula (3)N1.88, wherein the maximum macrosegregation ratio of nitrogen SrmaxIs 1.25.
By equations (4) and (5), the nitrogen activity is obtained:
Figure BDA0002843983630000121
Figure BDA0002843983630000122
wherein the superheat degree Delta T of the molten steel is 380K.
Determination of the solidification pressure: determining the solidification pressure P of the pressurized electroslag remelting high-nitrogen austenitic stainless steel through formulas (6) to (8)S：
Figure BDA0002843983630000123
Figure BDA0002843983630000124
Therefore P isSNot less than 0.80MPa, namely the minimum solidification pressure is 0.80MPa when 19Cr14Mn4Mo0.9N is prepared by pressurizing electroslag remelting.
Preparing high-nitrogen austenitic stainless steel according to the acquisition mode and parameters of the maximum macrosegregation ratio of nitrogen, and setting the solidification pressure to be 0.9 MPa;
fig. 1 is an internal sectional view of a high nitrogen austenitic stainless steel ingot obtained in example 1, as can be seen from fig. 1: the cast ingot prepared by the solidification pressure has compact structure and no nitrogen pore defect.
The chemical composition is shown in table 3.
TABLE 3 chemical composition of the finished Steel (wt%)
Figure BDA0002843983630000125
Example 2
The target high-nitrogen austenitic stainless steel is 18Cr18Mn2Mo0.9N, and the component control range and smelting control target are shown in Table 4.
Table 418 Cr18Mn2Mo0.9N component control range and control target (wt%)
Figure BDA0002843983630000131
The method for acquiring the solidification pressure comprises the following steps:
in the embodiment, 18Cr18Mn2Mo0.9N steel is prepared by pressurized electroslag remelting, and the slag system is 70 percent CaF2-30％Al2O3Namely ANF-6 slag, according to the characteristics of slag system, the slag depth coefficient fs0.54 by equation (1) in combination with the average size D of the electroslag ingotiThe depth H of the slag pool is calculated to be 0.15msIs 0.083 m.
Calculating the depth H of the molten pool through a formula (2)m0.02m, wherein the mold circumference Lm0.471m, 15.5 and 8.82 for A and B, respectively.
According to the target components of the high-nitrogen austenitic stainless steel, the nitrogen diffusion coefficient D in the solid phase of the high-nitrogen austenitic stainless steel is calculated by a Thermo-calc software DICTRA modulesIs 1.6X 10-9Calculating to obtain a solute distribution coefficient k of 0.18 according to the balanced solidification model, and calculating to obtain a solidus temperature T through the balanced solidification modelS1594.18K, liquidus temperature TL1649.27K, molten steel density rhom6500kg/m3And slag system density ρS2600kg/m3，vcIs 5K/s;
the acquisition of the maximum macrosegregation ratio of nitrogen comprises the following steps:
the preparation of the high-nitrogen austenitic stainless steel ingot by adopting the pressurized electroslag remelting comprises the steps of preparing a consumable electrode, paving an arc striking agent, baking slag, arcing slagging, pressurizing electroslag remelting and tapping:
preparing a consumable electrode: smelting a consumable parent metal of the high-purity high-nitrogen austenitic stainless steel according to the components of the high-nitrogen austenitic stainless steel, forging the consumable parent metal into a consumable electrode with a size suitable for electroslag remelting in a pressurized electroslag furnace, and then cooling in air; removing surface oxide skin, welding the electrode to a false electrode, and connecting the electrode with an electrode holder;
laying an arc striking agent: an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel are placed on a pressurized electroslag furnace bottom water tank below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode, the arc striking scraps and the bottom water tank are electrified;
baking slag and arc starting slagging: baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 700 ℃ for 6 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 15L/min for 5min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc starting and slagging by adopting a solid-state arc starting method, wherein: the voltage is 37V, the current is 2400A, and the slagging time is 21 min;
pressurizing electroslag remelting: after slagging is finished, filling nitrogen into the smelting chamber, pressurizing to 3.0MPa, synchronously increasing the pressure of cooling water in a crystallizer of the pressurized electroslag furnace to 3.0MPa, adjusting the voltage to 41V and the current to 3700A, namely starting pressurized electroslag remelting, wherein the smelting speed is obtained in a mode of V ═ 0.30-0.40 multiplied by D; v is the melting speed in kg/h, and D is the inner diameter of a crystallizer of the pressurized electroslag furnace for pressurized electroslag remelting in mm; controlling the current fluctuation less than +/-3%, the voltage fluctuation less than +/-0.5% and the melting speed fluctuation less than +/-0.5 kg/h; simultaneously, uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder;
tapping: lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to 0.6-1.0 MPa by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
obtaining the maximum macrosegregation ratio of nitrogen: at the height of 3/4, the content Cs of nitrogen element at 0, 30, 60, 90 and 120mm from the center is measured by nitrogen-oxygen analyzer, and then the macrosegregation ratio Sr of nitrogen element is CS/C0Wherein, C0The average concentration of the nitrogen element of the ingot; selecting the maximum Sr value as the maximum macrosegregation ratio Sr of nitrogen to be 1.21; calculating nitrogen macrosegregation parameter M by formula (3)N1.86, maximum macroscopic view of nitrogen thereinSegregation ratio SrmaxIs 1.21.
The nitrogen activity was obtained by the formulas (4) and (5)
Figure BDA0002843983630000141
Figure BDA0002843983630000142
Wherein, the superheat degree Delta T of the molten steel is 400K.
Determination of the solidification pressure: determining the solidification pressure P of the pressurized electroslag remelting high-nitrogen austenitic stainless steel through formulas (6) to (8)S：
Figure BDA0002843983630000143
Figure BDA0002843983630000144
Therefore P isSNot less than 0.60MPa, namely the minimum solidification pressure is 0.60MPa when 18Cr18Mn2Mo0.9N is prepared by pressurizing electroslag remelting.
Preparing the high-nitrogen austenitic stainless steel according to the acquisition mode and parameters of the maximum macrosegregation ratio of nitrogen, and setting the solidification pressure to be 0.7 MPa.
Fig. 2 is an internal sectional view of the ingot of high nitrogen austenitic stainless steel obtained in example 2, as can be seen from fig. 2: the cast ingot prepared by the solidification pressure has compact structure and no nitrogen pore defect.
The chemical composition is shown in table 5.
TABLE 5 chemical composition of the finished Steel (wt%)
Figure BDA0002843983630000151
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (8)

1. The method for acquiring the solidification pressure required by the pressurized electroslag remelting high-nitrogen austenitic stainless steel is characterized by comprising the following steps of:
obtaining the slag depth coefficient f of a slag system for pressurized electroslag remeltingsObtaining the depth H of the slag bath through a formula (1)s：
Hs＝1.03fsDi±0.02 (1)；
In the formula (1), DiThe diameter of the electroslag ingot is m;
according to the formula (2), obtaining the depth H of the molten poolm：
Hm＝0.004ALm-0.001B (2)；
In the formula (2), LmThe perimeter m of a crystallizer of a pressurized electroslag furnace for pressurized electroslag remelting; a and B are characteristic constants of a slag system for pressurized electroslag remelting;
obtaining the nitrogen diffusion coefficient DsNitrogen solute distribution coefficient k, solidus temperature TSLiquidus temperature TLDensity of molten steel rhomSlag system density rhoSMaximum macrosegregation ratio of nitrogen and Srmax(ii) a Obtaining a nitrogen macrosegregation parameter M through a formula (3)N：
Figure FDA0002843983620000011
In the formula (3) [% N]Is the mass percentage content of nitrogen element in the high-nitrogen austenitic stainless steel, vcThe cooling rate is 1-5K/s;
according to equations (4) and (5), the nitrogen activity is obtained:
Figure FDA0002843983620000012
Figure FDA0002843983620000013
in equations (4) and (5):
Figure FDA0002843983620000014
the action coefficient of nitrogen element to nitrogen element;
Figure FDA0002843983620000015
is the first order interaction coefficient of element j to nitrogen element;
Figure FDA0002843983620000016
is a secondary interaction parameter of element j to nitrogen; delta T is the superheat degree of the molten steel, and delta T is 300-400K;
according to the formulas (6) to (8), the solidification pressure P of the pressurized electroslag remelting high-nitrogen austenitic stainless steel is obtainedS：
Figure FDA0002843983620000017
Figure FDA0002843983620000018
PS≥max(PS0；PS1) (8)；
In equations (6) to (8): pS0And PS1Respectively an intermediate variable, pmThe density of the molten steel is; [% N]The mass percentage of N element in the high-nitrogen austenitic stainless steel is shown; heThe electrode is buried to a depth;
the high-nitrogen austenitic stainless steel comprises the following elements in percentage by mass: c: less than or equal to 0.2 percent, Mn: 13-20%, Cr: 15-22%, Si: less than or equal to 1 percent, Mo: 0-4.5%, N: 0.7-2%, Ni: 0-4% and the balance Fe.
2. The method of claim 1, wherein the maximum macrosegregation ratio Sr of the captured nitrogenmaxThe method comprises the following steps:
preparing a high-nitrogen austenitic stainless steel ingot by adopting pressurized electroslag remelting, and comprises the following steps of preparing a consumable electrode, paving an arc striking agent, baking slag, arcing slagging, pressurizing electroslag remelting and tapping:
the preparing the consumable electrode comprises: smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
the laying of the arc striking agent comprises the following steps: placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
the slag baking and arc striking slagging comprises the following steps: baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
the pressurized electroslag remelting comprises: after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 1-3 MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40-45V, starting pressurizing electroslag remelting when the current reaches 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurizing voltage remelting;
the tapping comprises the following steps: lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to 0.6-1.0 MPa by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
obtaining the maximum macrosegregation ratio of nitrogen: longitudinally splitting the high-nitrogen austenitic stainless steel ingot, and measuring the content Cs of nitrogen elements at the positions 0, 30, 60, 90 and 120mm away from the center by using a nitrogen-oxygen analyzer at the height of 3/4 of the high-nitrogen austenitic stainless steel ingot, so that the macrosegregation ratio Sr of the nitrogen elements is CS/C0Wherein, C0The average concentration of the nitrogen element of the ingot; selecting the maximum Sr value as the maximum macrosegregation ratio Sr of nitrogenmax。
3. The method according to claim 2, wherein the melting rate of the pressurized electroslag remelting in the pressurized electroslag remelting is obtained by:
V＝(0.30～0.40)×D (9)；
wherein V is the melting speed and the unit is kg/h; d is the size of the crystallizer of the pressurized electroslag furnace for pressurized electroslag remelting and the unit is mm.
4. The method according to claim 3, characterized in that in the pressurized electroslag remelting, the current fluctuation is < ± 3%, the voltage fluctuation is < ± 0.5%, and the melting rate fluctuation is < ± 0.5 kg/h.
5. The acquisition method according to claim 1, characterised in that said nitrogen diffusion coefficient DsCalculated by a DICTRA module in Thermo-Cal software.
6. The acquisition method according to claim 1, wherein the nitrogen solute distribution coefficient k is calculated by an equilibrium solidification model in Thermo-Cal software.
7. Root of herbaceous plantThe acquisition method according to claim 1, characterized in that said solidus temperature T isSLiquidus temperature TLDensity of molten steel rhomAnd slag system density ρSCalculated by an equilibrium solidification model in Thermo-Cal software.
8. A preparation method of a pressurized electroslag remelting high-nitrogen austenitic stainless steel ingot is characterized by comprising the following steps:
smelting raw materials according to the components of the high-nitrogen austenitic stainless steel, forging, and air cooling to obtain a consumable electrode; the consumable electrode is suitable for the electroslag remelting size of the pressurized electroslag furnace; removing the oxide skin on the surface of the consumable electrode, welding the consumable electrode to a false electrode, and connecting the false electrode with an electrode holder;
placing an arc striking ring and 0.45 +/-0.05 kg of arc striking scraps which are made of the same material as the smelted high-nitrogen austenitic stainless steel on a bottom water tank of the pressurized electroslag furnace below the consumable electrode, so that the consumable electrode, the arc striking scraps and the bottom water tank are in close contact, and current is ensured to pass after the consumable electrode is electrified;
baking pre-melted slag suitable for the high-nitrogen austenitic stainless steel at 600-800 ℃ for 5-7 hours; opening a water supply system to introduce normal-pressure cooling water into a pressurized electroslag furnace crystallizer, adding the baked premelting slag into the crystallizer at one time, sealing a smelting chamber, introducing nitrogen into the smelting chamber at the speed of 10-15L/min for 5-L0 min to discharge air in the smelting chamber, closing an alternating current power supply, and carrying out arc striking and slagging by adopting a solid-state arc striking method, wherein: the voltage is 35-40V, the current is 2000-2500A, and the slag melting time is 20-25 min;
after slagging is finished, nitrogen is filled into the smelting chamber to be pressurized to 1-3 MPa, and the pressure of cooling water in a crystallizer of the pressurized electroslag furnace is synchronously increased, so that the pressures on two sides of the copper wall of the crystallizer are basically kept consistent; adjusting the voltage to 40-45V, starting pressurized electroslag remelting when the current is 3000-4200A, and uniformly adding 0.4-0.7 kg/ton steel of calcium-silicon alloy for deoxidation by using a stepping type feeder while the pressurized electroslag remelting;
lifting the consumable electrode after the pressurized electroslag remelting feeding to finish the pressurized electroslag remelting, and releasing the pressure to a target solidification pressure by using an air release valve; closing the alternating current power supply for 5min, then releasing pressure to normal pressure, synchronously reducing the cooling water pressure in the crystallizer of the pressurized electroslag furnace to normal pressure, and removing the steel ingot after the temperature of the steel ingot is reduced to room temperature to obtain a high-nitrogen austenitic stainless steel ingot;
the target solidification pressure is the solidification pressure obtained by the obtaining method of any one of claims 1 to 7.
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ZHU, HC 等: "Effect of solidification pressure on thermodynamic and kinetic parameters of 19Cr14Mn4Mo0.9N high nitrogen steel" *
李可斌: "压力对高氮奥氏体不锈钢凝固组织和偏析的影响规律研究" *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN116024398A (en) * 2023-02-24 2023-04-28 东北大学 Determination method for minimum value of solidification pressure for inhibiting nitrogen pores, application of determination method and preparation method of high-nitrogen stainless steel cast ingot

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