CN116445828A - Ultra-pure austenitic stainless steel and preparation method thereof - Google Patents

Abstract

The invention relates to the technical field of metallurgy, and particularly discloses ultra-pure austenitic stainless steel and a preparation method thereof. The ultra-pure austenitic stainless steel comprises the following components in percentage by weight: less than or equal to 0.007 percent of C, less than or equal to 0.05 percent of Mn, less than or equal to 0.30 percent of Si, less than or equal to 0.002 percent of S, less than or equal to 0.01 percent of P, 14.5 to 15.0 percent of Ni, 16.5 to 17.0 percent of Cr, 2.20 to 2.50 percent of Mo, less than or equal to 0.01 percent of Al, less than or equal to 0.0002 percent of H, less than or equal to 0.0015 percent of O, less than or equal to 0.015 percent of N, less than or equal to 0.10 percent of Cu, and the balance of Fe and unavoidable impurities. According to the invention, through designing alloy components, the proportion of each component is reasonable, and Mo, ni and Cr elements are synergistic, so that the corrosion resistance of austenitic stainless steel can be obviously improved, and the proper Cr/Ni/Mo proportion is beneficial to fundamentally reducing the formation of ferrite and controlling the content of ferrite; meanwhile, by strictly controlling harmful elements and residual elements, the ultra-pure austenitic stainless steel has the advantages of low inclusion content and high purity, and has good ductility, plasticity and impact toughness.

Description

A kind of ultrapure austenitic stainless steel and preparation method thereof

technical field

The invention relates to the technical field of metallurgy, in particular to an ultra-pure austenitic stainless steel and a preparation method thereof.

Background technique

Austenitic stainless steel has been widely used in various industries because of its comprehensive properties such as good high-temperature strength, plastic toughness, corrosion resistance and weldability. With the rapid development of nuclear industry, ocean engineering and other industries, the service environment of steel materials is becoming more and more complex. Some precision parts or special equipment may require materials to have good corrosion resistance, oxidation resistance and mechanical properties at the same time, especially nuclear grade Austenitic stainless steel requires extremely low non-metallic inclusions, which requires the design and development of special austenitic stainless steel to meet more stringent requirements.

316 series austenitic stainless steel is a kind of CrNiMo stainless steel, which can be used in semiconductor equipment, nuclear power project pipelines and reactor shielding rods. In order to improve its resistance to high temperature stress corrosion resistance between crystals, a certain amount of Mo element needs to be added to the steel Compared with other austenitic stainless steels, it is easier to form high-temperature δ-ferrite, which reduces the hot workability and hot formability of the steel, and makes the steel from tough to brittle, which affects its high-temperature durability and reduces its service life. At the same time, the internal inclusions of 316 series austenitic stainless steel prepared by the existing smelting process are ≤ 1.0, and the purity is low, while the purity required for semiconductor and nuclear power steel is relatively high, otherwise it will be in the two phases during high temperature use. Crack sources are formed at the interface of the steel, causing nuclear leakage and seriously endangering human life and property safety. It is particularly important to control the content of ferrite and inclusions in steel. Therefore, it is of great significance to develop an ultra-pure austenitic stainless steel with compact structure, good plasticity and high purity.

Contents of the invention

In view of this, the present invention provides an ultra-pure austenitic stainless steel and its preparation method. By designing the alloy components, the ratio of each component is reasonable, and the ferrite content is less than 1%. The content of inclusions is small and the purity is high. At the same time, it still has good ductility, plasticity and impact toughness.

In order to achieve the above-mentioned purpose of the invention, the embodiment of the present invention adopts the following technical solutions:

In the first aspect, the present invention provides an ultra-pure austenitic stainless steel, which comprises the following components by weight percentage: C≤0.007%, Mn≤0.05%, Si≤0.30%, S≤0.002%, P≤0.01%, Ni : 14.5%～15.0%, Cr: 16.5%～17.0%, Mo: 2.20%～2.50%, Al≤0.01%, H≤0.0002%, O≤0.0015%, N≤0.015%, Cu≤0.10%, balance For Fe and unavoidable impurities.

Compared with the prior art, the ultra-pure austenitic stainless steel provided by the present invention has the following advantages:

The present invention controls the content of the Cr element at 16.5% to 17.0%, controls the content of the Mo element at 2.20% to 2.50%, controls the content of the Ni element at 14.5% to 15.0%, and controls the content of the Ni element at 14.5% to 15.0%. The synergy of , Ni and Cr elements can significantly improve the corrosion resistance of austenitic stainless steel, and the appropriate Cr/Ni/Mo ratio is conducive to fundamentally reducing the formation of ferrite and controlling its content; at the same time, through strict control Harmful elements and residual elements have achieved the ferrite content of ultra-pure austenitic stainless steel <1%, with less inclusion content and high purity, while still having good ductility, plasticity and impact toughness.

The composition of the ultra-pure austenitic stainless steel provided by the present invention is designed based on the following ideas:

C: Carbon is an austenite element, which can inhibit the formation of ferrite and increase the strength of the material. At the same time, it is easy to combine with chromium to form carbides, reduce the content of solid-solution chromium in steel, and form primary batteries around carbides, thereby reducing Corrosion resistance of austenitic stainless steels. Therefore, the present invention sets the upper limit of C element content in steel as 0.007%.

Mn: Manganese is an austenite element, which can stabilize the austenite phase and expand the austenite phase zone; however, during welding, harmful gases with low vapor pressure will be generated on the surface of the molten metal, and the harmful gases will adhere to the inner wall of the pipe after solidification, and Mn is enriched in the heat-affected zone of welding to form oxides and cause localized corrosion. Therefore, the present invention sets the upper limit of the content of Mn element in steel as 0.05%.

Ni: Nickel is the main alloying element in austenitic stainless steel, which can form and stabilize the austenite phase, and improve the machinability, rust resistance and corrosion resistance of the alloy. At the same time, Ni and Cr are combined in severe corrosion environments There is a synergistic effect for austenitic stainless steels; however, increased nickel content leads to increased susceptibility to intergranular corrosion in austenitic stainless steels. Therefore, the present invention controls the Ni element content in the steel to be 14.5%-15.0%.

Si element and Al element are deoxidizing elements of austenitic stainless steel. Silicon and aluminum can synergistically improve the shape of inclusions and reduce the content of gas elements in molten steel, refine grains, and ensure the deoxidation effect of steel. Therefore, the present invention sets the upper limit of the content of Al in the steel as 0.01%, and the upper limit of the content of Si as 0.30%.

S: Sulfur is one of the harmful element impurities in steel. It is easy to combine with manganese in steel to form A-type inclusions (sulfides) with low hardness, which increases the cracking risk of steel. Therefore, the present invention sets the upper limit of S element content in steel as 0.002%.

P: Phosphorus is one of the harmful element impurities in steel, which will increase the cold brittleness of steel, deteriorate the welding performance, reduce plasticity, and phosphorus is also particularly sensitive to radiation embrittlement. Therefore, the present invention sets the upper limit of P element content in steel as 0.01%.

Cr: Chromium can improve the corrosion resistance and strength of stainless steel. However, chromium is a strong ferrite-forming element. A large amount of austenite-forming elements such as nickel, manganese, and nitrogen need to be added to high-chromium austenitic stainless steel. Therefore, the present invention controls the Cr element content in the steel to be 16.5%-17.0%.

Mo: Molybdenum can improve the pitting corrosion resistance and crevice corrosion resistance of steel in chloride environment, and can also improve the corrosion resistance of steel in reducing environment such as hydrochloric acid and dilute sulfuric acid, and under the action of chromium, molybdenum in steel However, the molybdenum element participates in the formation of harmful secondary phases and promotes the formation of high-temperature δ-ferrite in austenitic stainless steel, resulting in a decrease in the hot workability and hot formability of the steel, and the formation of unstable High-temperature oxides have adverse effects on high-temperature oxidation resistance. Therefore, the present invention controls the Mo element content in the steel to be 2.2%-2.5%.

In a second aspect, the present invention also provides a method for preparing the above-mentioned ultra-pure austenitic stainless steel, comprising the following steps:

Step 1. Mix the raw materials according to the preset ratio, smelt in a vacuum induction furnace, cast, electroslag remelting and vacuum self-consumption remelting, control the content of each element to meet the requirements of the ultra-pure austenitic stainless steel, and obtain a steel ingot ;

Step 2: heating, forging and heat treating the steel ingot to obtain the ultra-pure austenitic stainless steel.

Compared with the prior art, the preparation method of the ultra-pure austenitic stainless steel provided by the present invention has the following advantages:

By adopting vacuum induction + electroslag remelting + vacuum self-consumption triple smelting process, the present invention can effectively control the shape and distribution of crystal grains in steel, greatly improve the purity inside the alloy, and realize the control of ultra-purification inside the alloy. The prepared ultra-pure austenitic stainless steel has the advantages of dense structure, good plasticity, high purity and excellent performance. The non-metallic inclusions B and D fine series inclusions are below 0.5, and the other types of inclusions are none. The grain size level Grade 6.5 or above, tensile strength R _m ≥ 490MPa, yield strength Rp _0.2 ≥ 220MPa, reduction of area Ψ ≥ 80%, which can meet the needs of high-end semiconductors and key nuclear power equipment, and has broad market application prospects.

Optionally, in step 1, the vacuum induction furnace smelting process specifically includes: after mixing the raw materials, performing melting treatment, refining treatment and fine-tuning treatment in the vacuum induction furnace, and then tapping to obtain molten alloy steel; wherein, In the melting treatment, the temperature of complete melting is 1530°C-1550°C; in the refining treatment, the vacuum degree is ≤3Pa, the refining temperature is 1540°C-1570°C, and the refining time is 30min-70min. The optimal vacuum induction furnace smelting process is conducive to controlling the impurity elements in molten steel at a low level, reducing the number of inclusions in molten steel, improving the purity of molten steel, and thus improving the mechanical properties of stainless steel.

Optionally, in step 1, the casting temperature is 1540°C-1560°C.

Optionally, in step 1, during the electroslag remelting process, the melting rate is 5.0kg/min-6.0kg/min, and the slag used for smelting is DRZ-1910 slag series.

Optionally, the DRZ-1910 slag system includes the following components by weight percentage: CaF ₂ : 50%-70%, CaO: 5%-15%, Al ₂ O ₃ : 15%-20%, MgO: 5% % ~ 15%. The preferred slag system has a good adsorption effect on inclusions, can reduce the oxygenation of molten steel and the content of inclusions, and improve the purity of molten steel for electrode ingots.

Optionally, in step 1, in the vacuum self-consumption remelting process, the vacuum degree is ≤0.5Pa, the current in the arcing stage is 4.0kA-10.5kA, and the melting rate in the smelting stable stage is 2.5kg/min-6.5kg/min , The feeding phase current is 2.5kA ~ 6.0kA.

Optionally, in step 2, the heating process specifically includes: heating the steel ingot to 600°C-650°C, keeping it warm for 1h-2h, and then raising the temperature to 800°C at a heating rate of 80°C/h-100°C/h ~810°C, hold for 1.5h~2h, then raise the temperature to 1160°C~1180°C at a heating rate of 80°C/h~100°C/h, hold for 3h~4h and then forge for production. The invention adopts three-stage heating, which is beneficial to keep the steel ingot in the best thermoplastic zone, ensures the uniformity of temperature and structure, effectively controls the grain size and avoids the occurrence of forging cracking problems.

Optionally, in step 2, during the forging process, the starting forging temperature is ≥ 1000°C, the final forging temperature is ≥ 850°C, the heating temperature of the billet returning to the furnace is 1140°C-1160°C, and the returning time is 60min-90min.

Optionally, in step 2, the heat treatment specifically includes: sending the forged billet to a heating furnace for high-temperature solution heat treatment, the heat treatment temperature is 1000°C-1020°C, and the holding time is 20min-30min. The optimal heat treatment temperature and time can fully dissolve the ferrite while effectively avoiding elongated grains at the edge and ensuring that the grain size of the finished steel is within a reasonable range.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the embodiments. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For Those of ordinary skill in the art can also obtain other drawings based on these drawings without making creative efforts.

Fig. 1 is the distribution diagram of head and tail inclusions in ultra-pure austenitic stainless steel provided by Example 1 of the present invention;

Fig. 2 is a distribution diagram of ferrite at the head and tail of the ultra-pure austenitic stainless steel provided by Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

In order to better illustrate the present invention, the following examples are used for further illustration.

Example 1

An embodiment of the present invention provides an ultra-pure austenitic stainless steel, the chemical composition of which is as follows:

C: 0.007%, Mn: 0.04%, Si: 0.12%, S: 0.0008%, P: 0.005%, Ni: 14.8%, Cr: 16.76%, Mo: 2.35%, Al: 0.004%, H: 0.0001%, O: 0.001%, N: 0.0034%, Cu: 0.02%, and the balance is Fe and unavoidable impurities.

The preparation steps of the above-mentioned ultra-pure austenitic stainless steel are as follows:

S1. Vacuum induction furnace smelting: configure the raw materials according to the above ratio of main chemical components, mix the raw materials, and carry out melting treatment, refining treatment and fine-tuning treatment in the vacuum induction furnace in sequence, control the temperature of full melting to 1540 ℃, and control the refining period The degree of vacuum is 3 Pa, the refining temperature is 1555°C, and the refining time is 50 minutes, and the molten alloy steel is obtained by tapping.

S2. Casting: Cast the above alloy molten steel, and obtain a Φ480mm steel ingot after cooling. The whole process of casting is protected by argon gas, and the casting temperature is controlled at 1550°C.

S3. Electroslag remelting: After cleaning and finishing the surface of the steel ingot above, electroslag remelting is carried out. The whole process is smelted with argon protection, and the melting speed is controlled at 5.5kg/min. In terms of percentage, its chemical composition is: CaF ₂ : 60%, CaO: 10%, Al ₂ O ₃ : 20%, MgO: 10%.

S4. Vacuum consumable remelting: Carry out vacuum consumable remelting of the steel ingot after electroslag remelting, control the vacuum degree of the vacuum consumable furnace to 0.5Pa, the current at the arc starting stage is 8.0kA, and the melting speed at the smelting stable stage is 4.5kg/min, the feeding phase current is 4.0kA.

S5. Forging: Grind the steel ingot after vacuum self-consumption remelting, heat it to 620°C, keep it warm for 1.5h, then raise the temperature to 805°C at a heating rate of 90°C/h, keep it warm for 1.7h, and then heat it at 90°C/h The heating rate is raised to 1170 ° C, and the forging is produced after holding for 3.5 hours. During the forging process, the starting forging temperature is controlled to be 1000°C, the final forging temperature is 850°C, the heating temperature of the billet returning to the furnace is 1150°C, and the returning time is 80 minutes. After the final fire forging, the forged billet is sent to the heating furnace for high-temperature solution heat treatment to obtain ultra-pure austenitic stainless steel. The controlled heat treatment temperature is 1010°C and the holding time is 25 minutes.

Example 2

An embodiment of the present invention provides an ultra-pure austenitic stainless steel, the chemical composition of which is as follows:

C: 0.006%, Mn: 0.03%, Si: 0.14%, S: 0.001%, P: 0.006%, Ni: 14.75%, Cr: 16.78%, Mo: 2.32%, Al: 0.008%, H: 0.00009%, O: 0.001%, N: 0.004%, Cu: 0.02%, and the balance is Fe and unavoidable impurities.

The preparation steps of the above-mentioned ultra-pure austenitic stainless steel are as follows:

S1. Vacuum induction furnace smelting: configure the raw materials according to the above ratio of main chemical components, mix the raw materials, and carry out melting treatment, refining treatment and fine-tuning treatment in the vacuum induction furnace in sequence, control the temperature of full melting to 1530 ℃, and control the refining period The degree of vacuum is 3 Pa, the refining temperature is 1540°C, and the refining time is 30 minutes, and the molten alloy steel is obtained by tapping.

S2. Casting: Cast the above molten alloy steel, and obtain a Φ480mm steel ingot after cooling. The whole process of casting is protected by argon gas, and the casting temperature is controlled at 1540°C.

S3. Electroslag remelting: After cleaning and finishing the surface of the above-mentioned steel ingots, carry out electroslag remelting. The whole process is smelted with argon protection, and the melting rate is controlled at 5.0kg/min. The slag used for smelting is DRZ-1910 slag series. In terms of percentage, its chemical composition is: CaF ₂ : 50%, CaO: 15%, Al ₂ O ₃ : 20%, MgO: 15%.

S4. Vacuum consumable remelting: Carry out vacuum consumable remelting of the steel ingot after electroslag remelting, control the vacuum degree of the vacuum consumable furnace to 0.5Pa, the current at the arc starting stage is 4.0kA, and the melting speed at the smelting stable stage is 2.5kg/min, the feeding phase current is 2.5kA.

S5. Forging: Grind the steel ingot after vacuum self-consumption remelting, heat it to 600°C, keep it warm for 1h, then raise the temperature to 800°C at a heating rate of 80°C/h, keep it warm for 1.5h, and then heat it at a temperature of 80°C/h. The heating rate is raised to 1160°C, and the forging is produced after holding the heat for 3 hours. During the forging process, the starting forging temperature is controlled to be 1020°C, the final forging temperature is 860°C, the heating temperature of the billet returning to the furnace is 1140°C, and the returning time is 60 minutes. After the final fire forging, the forged steel billet is sent to the heating furnace for high-temperature solution heat treatment to obtain ultra-pure austenitic stainless steel. The controlled heat treatment temperature is 1000°C and the holding time is 20 minutes.

Example 3

An embodiment of the present invention provides an ultra-pure austenitic stainless steel, the chemical composition of which is as follows:

C: 0.006%, Mn: 0.03%, Si: 0.13%, S: 0.0009%, P: 0.005%, Ni: 14.78%, Cr: 16.71%, Mo: 2.30%, Al: 0.006%, H: 0.0001%, O: 0.0009%, N: 0.0038%, Cu: 0.025%, and the balance is Fe and unavoidable impurities.

The preparation steps of the above-mentioned ultra-pure austenitic stainless steel are as follows:

S1. Vacuum induction furnace smelting: configure the raw materials according to the above ratio of main chemical components, mix the raw materials, and sequentially perform melting treatment, refining treatment and fine-tuning treatment in the vacuum induction furnace, control the temperature of full melting to 1550°C, and control the refining period The vacuum degree is 3 Pa, the refining temperature is 1570°C, and the refining time is 70 minutes, and the alloy steel liquid is obtained by tapping.

S2. Casting: Cast the above molten alloy steel, and obtain a Φ480mm steel ingot after cooling. The whole process of casting is protected by argon gas, and the casting temperature is controlled at 1560°C.

S3. Electroslag remelting: After cleaning and finishing the surface of the above-mentioned steel ingots, electroslag remelting is carried out. The whole process is smelted with argon protection, and the melting rate is controlled at 6.0kg/min. The slag used for melting is DRZ-1910 slag series. In terms of percentage, its chemical composition is: CaF ₂ : 70%, CaO: 5%, Al ₂ O ₃ : 15%, MgO: 10%.

S4. Vacuum consumable remelting: Carry out vacuum consumable remelting of the steel ingot after electroslag remelting, control the vacuum degree of the vacuum consumable furnace to 0.5Pa, the current at the arc starting stage is 10.5kA, and the melting speed at the smelting stable stage is 6.5kg/min, the feeding phase current is 6.0kA.

S5. Forging: Grind the steel ingot after vacuum self-consumption remelting, heat it to 650°C, keep it warm for 2h, then raise the temperature to 810°C at a heating rate of 100°C/h, keep it warm for 2h, and then heat it up at a rate of 100°C/h Raise the temperature to 1180°C, hold for 4 hours and then forge for production. During the forging process, the starting forging temperature is controlled to be 1050°C, the final forging temperature is 880°C, the heating temperature of the billet returning to the furnace is 1160°C, and the returning time is 90 minutes. After the final fire forging, the forged billet is sent to the heating furnace for high-temperature solution heat treatment to obtain ultra-pure austenitic stainless steel. The controlled heat treatment temperature is 1020°C and the holding time is 30 minutes.

Example 4

An embodiment of the present invention provides an ultra-pure austenitic stainless steel, the chemical composition of which is as follows:

C: 0.005%, Mn: 0.05%, Si: 0.13%, S: 0.001%, P: 0.004%, Ni: 14.74%, Cr: 16.73%, Mo: 2.33%, Al: 0.005%, H: 0.00008%, O: 0.001%, N: 0.0041%, Cu: 0.01%, and the balance is Fe and unavoidable impurities.

The preparation steps of the above ultra-pure austenitic stainless steel are the same as those in Example 1.

Example 5

An embodiment of the present invention provides an ultra-pure austenitic stainless steel, the chemical composition of which is as follows:

C: 0.006%, Mn: 0.04%, Si: 0.13%, S: 0.001%, P: 0.005%, Ni: 14.76%, Cr: 16.75%, Mo: 2.30%, Al: 0.004%, H: 0.0001%, O: 0.0008%, N: 0.0038%, Cu: 0.015%, and the balance is Fe and unavoidable impurities.

The preparation steps of the above ultra-pure austenitic stainless steel are the same as those in Example 1.

Samples were randomly cut from the ultra-pure austenitic stainless steel prepared in Examples 1 to 5, and the content of non-metallic inclusions, ferrite content and grain size were detected, and the high-magnification results of the full cross-section were shown in Table 1; The test results are shown in Table 2.

Fig. 1 is the full-section metallographic diagram of the inclusions of the ultra-pure austenitic stainless steel prepared in Example 1 under the scale of 100 μm. It can be seen from the figure that there are only a small amount of B and D types; Schematic diagram of the full-section metallographic diagram of the ferrite of the prepared super austenitic stainless steel under the 50 μm scale, and there is no ferrite in each sample. Table 1 Test results of non-metallic inclusions

Table 2 performance test results

It can be seen from Table 1-2 that the ultra-pure austenitic stainless steel provided by the present invention has extremely low non-metallic inclusions and ferrite content, and the austenite structure is stable. At the same time, the tensile strength and yield strength are under the composition design , elongation and reduction of area and other performance indicators meet the requirements of ASTM A182/A182M-2020, GB/T1220-2007 standards.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (10)

1. An ultrapure austenitic stainless steel, characterized in that it comprises the following components in weight percent: less than or equal to 0.007 percent of C, less than or equal to 0.05 percent of Mn, less than or equal to 0.30 percent of Si, less than or equal to 0.002 percent of S, less than or equal to 0.01 percent of P, 14.5 to 15.0 percent of Ni, 16.5 to 17.0 percent of Cr, 2.20 to 2.50 percent of Mo, less than or equal to 0.01 percent of Al, less than or equal to 0.0002 percent of H, less than or equal to 0.0015 percent of O, less than or equal to 0.015 percent of N, less than or equal to 0.10 percent of Cu, and the balance of Fe and unavoidable impurities.

2. A method of producing the ultrapure austenitic stainless steel of claim 1, comprising the steps of:

firstly, mixing the raw materials according to a preset proportion, smelting by a vacuum induction furnace, casting, electroslag remelting and vacuum consumable remelting, and controlling the content of each element to meet the requirement of the ultra-pure austenitic stainless steel to obtain a steel ingot;

and step two, heating, forging and heat treatment are carried out on the steel ingot, so that the ultra-pure austenitic stainless steel is obtained.

3. The method for producing ultra-pure austenitic stainless steel according to claim 2, wherein in the first step, the vacuum induction furnace smelting process is specifically: after mixing the raw materials, sequentially carrying out melting treatment, refining treatment and fine adjustment component treatment in a vacuum induction furnace, and tapping to obtain molten alloy steel;

wherein, in the melting treatment, the temperature of the full melting is 1530-1550 ℃;

in the refining treatment, the vacuum degree is less than or equal to 3Pa, the refining temperature is 1540-1570 ℃, and the refining time is 30-70 min.

4. The method of producing ultra-pure austenitic stainless steel according to claim 2, wherein in step one, the casting temperature is 1540 ℃ to 1560 ℃.

5. The method for producing an ultrapure austenitic stainless steel according to claim 2, wherein in the step one, in the electroslag remelting process, a melting speed is 5.0kg/min to 6.0kg/min, and a slag system of DRZ-1910 is used as the slag for melting.

6. The method for producing ultra-pure austenitic stainless steel according to claim 5, wherein the DRZ-1910 slag system comprises the following components in weight percentage: caF (CaF) ₂ :50％～70％，CaO:5％～15％，Al ₂ O ₃ :15％～20％，MgO：5％～15％。

7. The method for producing an ultrapure austenitic stainless steel according to claim 2, wherein in the step one, in the vacuum consumable remelting process, the vacuum degree is not more than 0.5Pa, the current in the arcing stage is 4.0kA to 10.5kA, the melting speed in the melting stabilization stage is 2.5kg/min to 6.5kg/min, and the current in the feeding stage is 2.5kA to 6.0kA.

8. The method for producing an ultrapure austenitic stainless steel according to claim 2, wherein in the second step, the heating process is specifically: heating the steel ingot to 600-650 ℃, preserving heat for 1-2 h, then heating to 800-810 ℃ at the heating rate of 80-100 ℃/h, preserving heat for 1.5-2 h, heating to 1160-1180 ℃ at the heating rate of 80-100 ℃/h, preserving heat for 3-4 h, and forging.

9. The method for producing ultra-pure austenitic stainless steel according to claim 2, wherein in the second step, the forging temperature is not less than 1000 ℃, the final forging temperature is not less than 850 ℃, the heating temperature of the blank returning to the furnace is 1140-1160 ℃, and the time for returning to the furnace is 60-90 min.

10. The method for producing an ultrapure austenitic stainless steel according to claim 2, wherein in the second step, the heat treatment is specifically: and (3) hot-conveying the forged steel billet to a heating furnace for high-temperature solution heat treatment, wherein the heat treatment temperature is 1000-1020 ℃, and the heat preservation time is 20-30 min.