A smelting method of 316L stainless steel with low carbon and oxygen content and 316L stainless steel

Abstract

The application discloses a smelting method of 316L stainless steel with low carbon and oxygen content and the 316L stainless steel, and relates to the technical field of stainless steel smelting. The application optimizes a smelting process, reduces the [C][O] concentration product by using high vacuum, and enhances the deoxidization and desulfurization effects by using the Ca element with strong chemical activity. In order to improve the volatilization loss of high-steam-pressure Ca, the application uses the high-melting-point Ni-Ca intermediate alloy to slow down the release of Ca. The production mode is simple, can meet the demand of small batch and multiple specifications, and the quality of the prepared stainless steel ingot is more superior.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel smelting, in particular to a 316L stainless steel smelting method with low carbon and oxygen content and 316L stainless steel. BACKGROUND

[0002] Conventional stainless steel is smelted by an electric furnace, and the chemical composition of the alloy is usually adjusted by refining methods such as AOD (argon oxygen decarburization) argon oxygen refining or VOD (vacuum oxygen decarburization) vacuum oxygen decarburization to reduce the content of harmful impurities such as C, Mn, Si, P and S. In order to ensure ultra-high purity and ultra-low non-metallic inclusions, high-purity (HP) and ultra-high-purity (UHP) 316L stainless steel used for semiconductor equipment needs to control lower impurity content, such as C≤0.03% and S≤0.005%. Therefore, a double vacuum smelting method is needed, that is, vacuum induction smelting (VIM) is first used, and then vacuum arc remelting (VAR) treatment is performed to ensure that the alloy has lower impurity content and more excellent performance. The material obtained by this smelting method is called 316LVV, that is, VIM+VAR double vacuum smelting.

[0003] For example, the Chinese patent application with the publication number CN117845145A discloses a super-purity 316LVV stainless steel ingot and its triple smelting process and application. The triple smelting process of vacuum induction smelting, electroslag remelting and vacuum consumable remelting is adopted. In order to control the content of large non-metallic inclusions and sulfur in the rod, and to improve the number of electrode rod shrinkage and dark shrinkage holes, the existing double process is changed to a triple smelting process. The content of C in the alloy is controlled to be ≤0.01%, the actual smelted alloy has O of 8 ppm, N of 5 ppm and H of 0.5 ppm.

[0004] The Chinese patent application with the publication number CN118028714A discloses a super-pure 316L(N) austenitic stainless steel and a preparation method thereof. Through the VIM+IESR double smelting process, the 316L(N) austenitic stainless steel is subjected to deep O and S removal and effective modification treatment of inclusions through vacuum carbon deoxidization pretreatment and finally Mg+Ca composite deoxidization and desulfurization.

[0005] The above technical solutions mostly use double or triple processes, and AOD and / or VOD traditional smelting methods to prepare 316L stainless steel. The process is complicated, and the method for controlling the content of C, O and N impurities is complex. SUMMARY

[0006] The application aims to provide a 316L stainless steel smelting method with low carbon and oxygen content and a 316L stainless steel, and solve the problems of complicated preparation process and complicated method for controlling C, O and N impurity content caused by the double or triple process (including AOD and / or VOD) in the existing 316L stainless steel preparation method.

[0007] To achieve the above-mentioned purpose, the embodiments of the application adopt the following technical solutions: a 316L stainless steel smelting method with low carbon and oxygen content, comprising the following steps:

[0008] The required raw materials are proportioned, and the raw materials include iron bar, metal molybdenum, chromium and nickel; half of the chromium and other raw materials are loaded into a crucible, and the remaining half of the chromium is loaded into a secondary charging bin;

[0009] The vacuum induction smelting furnace is vacuumized, and the vacuumization is stopped after the vacuum degree is lower than 1 Pa; argon is introduced, and the vacuum degree is re-vacuumized to 0.03-0.07 MPa; the heating power source is started after the vacuum degree is lower than 1 Pa; and the raw materials in the crucible are melted;

[0010] After the raw materials in the crucible are completely melted, the remaining chromium in the secondary charging bin is slowly added into the melt;

[0011] The heating power is increased, the temperature of the melt is increased to 1500-1550 DEG C for refining, the vacuum degree is controlled to be less than or equal to 1 Pa, and the refining time is greater than or equal to 30 min;

[0012] After the melt is deoxidized and precipitated, the melt is poured into a heated and baked cast iron mold.

[0013] In the above technical solution, the embodiments of the application optimize the process of the 316L stainless steel smelting process to one-time vacuum induction smelting, reduce the [C][O] concentration product by using high vacuum, and are different from the existing double or triple process; the smelting process is simple, can meet the needs of small batch and multiple specifications, and the quality of the prepared stainless steel is more superior.

[0014] Further, according to the embodiments of the application, the crucible is a MgO crucible, an Al2O3 crucible, a magnesium-aluminum spinel crucible or a CaO crucible.

[0015] Further, according to the embodiments of the application, the deoxidization and precipitation of the melt comprises the following steps:

[0016] The Ni-Ca intermediate alloy is added into the secondary charging bin;

[0017] The heating power is reduced, 0.02-0.05 MPa of helium gas is filled, the temperature of the melt is adjusted to 1450-1480 DEG C, and the Ni-Ca intermediate alloy in the secondary charging bin is added;

[0018] After adding the Ni-Ca intermediate alloy for 2-5 minutes, the temperature of the melt is raised to 1500-1550 DEG C again for refining, and the refining time is greater than or equal to 15 minutes.

[0019] Further, according to the embodiment of the present application, the melting point of the Ni-Ca intermediate alloy is 1200-1450 DEG C.

[0020] Further, according to the embodiment of the present application, the amount of the Ni-Ca intermediate alloy added is 0.018-0.02% of the total amount of the raw materials.

[0021] Further, according to the embodiment of the present application, the temperature of the melt is adjusted to 1460-1500 DEG C when the melt is poured into the heated and baked cast iron mold.

[0022] Further, according to the embodiment of the present application, the raw materials include iron bars with a purity greater than or equal to 99.5%, metal molybdenum with a purity greater than or equal to 99.99%, chromium with a purity greater than or equal to 99.99%, and nickel with a purity greater than or equal to 99.98%.

[0023] In order to achieve the above-mentioned purpose, the embodiment of the present application also discloses a 316L stainless steel ingot prepared by the melting method of the 316L stainless steel ingot.

[0024] Further, according to the embodiment of the present application, the content of trace elements and impurities in the 316L stainless steel ingot is as follows: C is less than or equal to 0.0050%, O is less than or equal to 0.0020%, S is less than or equal to 0.0010%, N is less than or equal to 0.0010%, and H is less than or equal to 0.0002% according to the mass percentage.

[0025] Compared with the prior art, the present application has the following beneficial effects: in order to overcome the problems that the melting process of the existing 316L stainless steel is complicated, and the method for controlling the content of C, O and N impurities is complex, and in order to avoid the fact that low carbon and low oxygen in the melt is not conducive to the reaction of [C]+[O]=CO (g), and affects the deoxidation and desulfurization effect, the present application optimizes the melting process, reduces the concentration product of [C][O] by using high vacuum, and enhances the deoxidation and desulfurization effect by using the Ca element with strong chemical activity. In order to improve the volatilization loss of high steam pressure Ca, the present application uses high melting point Ni-Ca intermediate alloy to delay the release of Ca. The production method is simple, can meet the demand of small batch and multiple specifications, and the quality of the prepared stainless steel ingot is more superior. BRIEF DESCRIPTION OF DRAWINGS

[0026] The present application will be further described below in combination with the drawings and examples.

[0027] Figure 1 is a non-metallic inclusion diagram of the 316L stainless steel prepared by the present application.

[0028] Figure 2 is a schematic diagram of the metallographic structure of 316L stainless steel prepared by the present application. DETAILED DESCRIPTION

[0029] In order to make the objects, technical solutions of the present application clear, complete and the advantages more clear and apparent, the embodiments of the present application are further described in detail below with reference to the drawings. It should be understood that the specific embodiments described herein are part of the embodiments of the present application, rather than all the embodiments, and are only used to explain the embodiments of the present application, and do not limit the embodiments of the present application, and all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0030] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms "center", "middle", "upper", "lower", "left", "right", "inner", "outer", "top", "bottom", "side", "vertical", "horizontal" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "one", "first", "second", "third", "fourth", "fifth", "sixth" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0031] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication inside two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0032] For the purpose of simplicity and illustration, the principles of the embodiments are mainly described by reference to examples. In the following description, many specific details are presented in order to provide a thorough understanding of the embodiments. However, it is obvious to those of ordinary skill in the art that the embodiments can not be limited to these specific details in practice. In some examples, well-known methods and structures are not described in detail to avoid unnecessarily complicating the embodiments. In addition, all embodiments can be used in combination with each other.

[0033] In order to overcome the problems of complicated smelting process and complex method for controlling C, O and N impurity contents of the existing 316L stainless steel, the application provides a method for short-process vacuum induction smelting of ultra-low-carbon and ultra-low-oxygen stainless steel, and in order to avoid the reaction of [C]+[O]=CO(g) in the melt, which is not conducive to deoxidation and desulfurization effect, the application optimizes the smelting process, reduces the concentration product of [C][O] by using high vacuum, and enhances the deoxidation and desulfurization effect by using Ca element with strong chemical activity. In order to improve the volatilization loss of high steam pressure Ca, the application uses high melting point Ni-Ca intermediate alloy to delay the release of Ca. The production method is simple, can meet the demand of small batch and multiple specifications, and the quality of the prepared stainless steel ingot is more superior.

[0034] In order to achieve the above-mentioned purpose, the application provides a 316L stainless steel with double low carbon and oxygen content, and the trace element and impurity content is as follows: C≤0.0050%, O≤0.0020%, S≤0.0010%, N≤0.0010%, H≤0.0002%, and the rest of the alloy elements Cr, Ni, Mo and trace elements Mn, Si, Al, P and the like meet the requirements of GB / T 20878-2007 standard.

[0035] For this purpose, the smelting method of the above-mentioned 316L stainless steel with double low carbon and oxygen content is as follows:

[0036] Firstly, the purity of the melt is ensured from the purity of the raw materials. Specifically, DT4 grade iron bar with purity≥99.5%, TMo-1 grade metal molybdenum with purity≥99.99%, Cr99.99 grade high-purity chromium with purity≥99.99%, and nickel with purity≥99.98%, and high melting point Ni-Ca intermediate alloy are used, and the raw materials are ensured to be dry, without stains and without oxide skin.

[0037] Secondly, the concentration product of [C][O] is reduced by high vacuum. Specifically, after the vacuum of the vacuum induction smelting furnace is lower than 1Pa, stop vacuumizing, introduce high-purity argon to 0.03-0.07MPa, re-vacuumize to less than 1Pa, after the materials in the crucible and the secondary charging bin are completely melted, the melt temperature is increased to 1500-1550℃ for refining, the vacuum degree is controlled to be less than or equal to 1Pa, and the refining time is greater than or equal to 30min.

[0038] Finally, the Ca element with strong chemical activity is used to enhance the deoxidation and desulfurization effect. Specifically, high-purity argon gas is filled at 0.02-0.05 MPa, the melt temperature is adjusted to 1450-1480℃, a certain amount of Ni-Ca intermediate alloy is added for deoxidation, and after maintaining for 2-5 min, the melt is refined at 1500-1550℃ for more than 15 min, the melt temperature is adjusted to about 1460-1500℃, and the melt is poured into a heated and baked cast iron mold, so that good deoxidation and decarburization effects are finally achieved.

[0039] Further, the melting method of the 316L stainless steel specifically includes the following steps:

[0040] S1 preparation: according to the nominal composition of the alloy, the required raw materials are proportioned, DT4 grade iron rods with a purity of ≥99.5%, TMo-1 grade metal molybdenum with a purity of ≥99.99%, Cr99.99 grade high-purity chromium with a purity of ≥99.99%, and nickel with a purity of ≥99.98%, and high-melting point Ni-Ca intermediate alloy are used, and it is ensured that the raw materials are dry, free of stains, and free of oxide skins. The melting point of the Ni-Ca intermediate alloy is 1200-1450℃.

[0041] Half of the high-purity chromium and other raw materials are loaded into a thermally stable oxide crucible, and the Ni-Ca intermediate alloy and the remaining half of the high-purity chromium are loaded into a secondary charging bin. The thermally stable oxide crucible includes MgO, Al2O3, magnesia-alumina spinel, and CaO crucibles.

[0042] S11: Check the water, electricity and gas of the vacuum induction melting furnace, especially ensure that the pressure rise rate of the melting furnace is ≤3 Pa / h.

[0043] S12: Load the cast iron mold that has been heated and baked at 500℃ for 1h.

[0044] S2 melting: start the vacuum system to evacuate the vacuum induction melting furnace, stop evacuating when the vacuum is lower than 1 Pa, introduce high-purity argon gas to 0.03-0.07 MPa, close the valve, restart the vacuum system to evacuate, start the heating power when the vacuum is lower than 1 Pa, and quickly melt the raw materials in the crucible.

[0045] S3 alloying: after the raw materials in the crucible are completely melted, the remaining high-purity chromium in the secondary charging bin is slowly added to the melt. The application alloys by adding chromium twice, which controls the dissolution and distribution of chromium, thereby reducing the burning loss and volatilization of chromium at high temperature, and preventing the formation of carbides due to excessive local chromium concentration

[0046] S4 refining: increase the heating power to raise the melt temperature to 1500-1550℃ for refining, control the vacuum degree to be ≤1 Pa, and the refining time to be ≥30 min.

[0047] S5: Precipitation deoxidation: reduce the power of the heating power, fill in 0.02-0.05 MPa high-purity argon, adjust the melt temperature to 1450-1480℃, and add the Ni-Ca intermediate alloy in the second charging bin. After adding the Ni-Ca intermediate alloy for 2-5 min, the melt temperature is increased to 1500-1550℃ for refining, and the refining time is ≥15 min. Specifically, the addition amount of the Ni-Ca intermediate alloy is 0.018-0.02wt% of the total addition amount of the raw materials.

[0048] S6: Pouring: adjust the melt temperature to 1460-1500℃, and pour the melt into a heated cast iron mold.

[0049] In the above technical solution, the process of the 316L stainless steel smelting process is optimized to one-time vacuum induction smelting, the high vacuum is used to reduce the [C][O] concentration product, and the Ca element with strong chemical activity is used to enhance the deoxidation and desulfurization effect. Different from the existing double or triple process, the smelting process described in the application is simple, can meet the needs of small batch and multiple specifications, and the quality of the prepared stainless steel ingot is more superior.

[0050] The technical effects of the application will be further described below by listing examples 1-2, but the application is not limited to these examples. Example 1

[0051] Check the water, electricity and gas system of the vacuum induction smelting furnace, test the pressure rise rate of the smelting furnace 1.2 Pa / h, and the cast iron ingot mold is baked at 500℃*1h before being loaded into the furnace.

[0052] According to the nominal composition of the alloy, the required raw materials are allocated, that is, 1329g of 99.5% pure DT4 grade iron bar, 45g of 99.99% pure TMo-1 grade metal molybdenum, 340g of 99.99% pure Cr99.99 grade high-purity chromium, and 248g of 99.98% high-purity nickel, and 40g of high-melting-point Ni-Ca intermediate alloy, the raw materials are dry, no stains, and no oxide scale.

[0053] Half of the high-purity chromium and other raw materials are loaded into the alumina crucible, and the Ni-Ca intermediate alloy and the remaining half of the high-purity chromium are loaded into the second charging bin.

[0054] Start the vacuum system to evacuate, stop evacuating when the vacuum is lower than 1 Pa, introduce high-purity argon to 0.04 MPa, close the valve, restart the vacuum system to evacuate, start the heating power when the vacuum is lower than 1 Pa, and quickly heat and melt the raw materials in the crucible.

[0055] After all the material in the crucible has melted, slowly add the remaining high-purity chromium from the secondary feeding bin into the melt. Increase the heating power to raise the melt temperature to 1520℃ for refining, controlling the vacuum degree to ≤1Pa, and refine for 30 minutes.

[0056] After the refining period, reduce the heating power, introduce 0.04 MPa of high-purity argon gas, adjust the melt temperature to 1450℃, and add 40g of Ni-Ca master alloy for deoxidation. Maintain this temperature for 3 minutes after adding the deoxidizer, then raise the melt temperature back to 1520℃ for refining for 15 minutes. Adjust the melt temperature to approximately 1480℃, and pour the melt into a preheated cast iron ingot mold.

[0057] Figure 1 This is a diagram of non-metallic inclusions in 316L stainless steel obtained in Example 1. Figure 1 As shown, the 316L stainless steel has few non-metallic inclusions, small size, and sparse distribution, which is a direct reflection of the "efficient deoxidation + impurity removal" of the vacuum melting process. The negative impact on the material properties is negligible, and the overall quality is at an excellent level.

[0058] Figure 2 This is a schematic diagram of the metallographic structure of the 316L stainless steel obtained in Example 1. Figure 2 As shown, the metallographic structure of this 316L stainless steel is mainly dendritic austenite.

[0059] The impurities and trace components of the 316L stainless steel obtained in Example 1 are shown in Table 1 below.

[0060] Table 1. Impurities and trace components (wt%) of the 316L stainless steel prepared in Example 1

[0061] Element C Mn Si O S N H Content 0.003 0.10 0.30 0.0018 0.0010 0.0009 0.0002 Example 2

[0062] Inspect the water, electricity, and gas systems of the vacuum induction melting furnace, test the furnace pressure rise rate to 1.2 Pa / h, and load the cast iron ingot mold into the furnace after baking at 500℃ for 1 hour.

[0063] The required raw materials according to the nominal composition of the alloy are 1329g of DT4 grade iron rod with 99.5% purity, 45g of TMo-1 grade metallic molybdenum with 99.99% purity, 340g of Cr99.99 grade high-purity chromium with 99.99% purity, 248g of 99.98% high-purity nickel, and 40g of high-melting-point Ni-Ca master alloy. The raw materials are dry, free of stains and oxide scale.

[0064] Half of the high-purity chromium and other raw materials are loaded into the alumina crucible, and the Ni-Ca master alloy and the remaining half of the high-purity chromium are loaded into the secondary feeding hopper.

[0065] Start the vacuum system to evacuate, stop the evacuation when the vacuum is lower than 1 Pa, introduce high purity argon to 0.04 MPa, close the valve, restart the vacuum system to evacuate, start the heating power when the vacuum is lower than 1 Pa, and rapidly heat to melt the raw materials in the crucible.

[0066] After the materials in the crucible are completely melted, slowly add the remaining high purity chromium in the second feeding bin to the melt. Increase the heating power to raise the melt temperature to 1500°C for refining, control the vacuum to be less than or equal to 1 Pa, and refine for 30 min.

[0067] After the refining period is over, reduce the melting power, fill in 0.04 MPa of high purity argon, adjust the melt temperature to 1480°C, and add 40 g of Ni-Ca intermediate alloy deoxidizer. Keep for 3 min after adding the deoxidizer, then raise the melt temperature to 1550°C for refining, and refine for 15 min. Adjust the melt temperature to about 1480°C, and pour the melt into the baked cast iron ingot mold.

[0068] The impurities and trace elements of the 316L stainless steel prepared in Example 2 are shown in Table 1 below.

[0069] Table 2 Impurities and trace elements of the 316L stainless steel prepared in Example 2 (wt%)

[0070] Element C Mn Si O S N H Content 0.006 0.10 0.24 0.0028 0.0015 0.0009 0.00012

[0071] Although the above describes the illustrative specific embodiments of the present application in order to enable a person skilled in the art to understand the present application, the present application is not limited to the scope of the specific embodiments, and for those of ordinary skill in the art, all the inventions utilizing the concept of the present application within the spirit and scope of the present application defined and determined by the appended claims are included in the protection of the present application.

Claims

1. A method of smelting a carbon, oxygen content bi-low 316L stainless steel, characterized by, It comprises the following steps: Preparation: proportioning the required raw materials, which include iron bar, metal molybdenum, chromium and nickel; loading half of the chromium and all of the iron bar, metal molybdenum and nickel into a crucible, and loading the remaining half of the chromium into a secondary charging bin; Melting: vacuumizing the vacuum induction melting furnace, stopping vacuumizing when the vacuum degree is lower than 1 Pa, introducing argon, re-vacuumizing when the vacuum degree is 0.03-0.07 MPa, starting the heating power after the vacuum degree is lower than 1 Pa, and melting the raw materials in the crucible; Alloying: slowly adding the remaining chromium in the secondary charging bin into the melt after the raw materials in the crucible are completely melted; Refining: increasing the power of the heating power, increasing the temperature of the melt to 1500-1550 ℃ for refining, controlling the vacuum degree to be ≤1 Pa, and controlling the refining time to be ≥30 min; Pouring: after deoxidizing and precipitating the melt, pouring the melt into a heated and baked cast iron mold; The deoxidizing and precipitating of the melt comprises the following steps: adding Ni-Ca intermediate alloy into the secondary charging bin; decreasing the power of the heating power, filling 0.02-0.05 MPa helium, adjusting the temperature of the melt to be 1450-1480 ℃, and adding the Ni-Ca intermediate alloy in the secondary charging bin; after adding the Ni-Ca intermediate alloy for 2-5 min, increasing the temperature of the melt to 1500-1550 ℃ for refining again, and controlling the refining time to be ≥15 min; The carbon content of the 316L stainless steel is less than or equal to 0.0050%, and the oxygen content is less than or equal to 0.0020%.

2. The carbon and oxygen content both low 316L stainless steel smelting method according to claim 1, characterized in that, The crucible is an MgO crucible, an Al2O3 crucible, a magnesium-aluminum spinel crucible or a CaO crucible.

3. The carbon and oxygen content both low 316L stainless steel smelting method according to claim 1, characterized in that, The melting point of the Ni-Ca intermediate alloy is 1200-1450 ℃.

4. The carbon and oxygen content both low 316L stainless steel smelting method according to claim 1, characterized in that, The adding amount of the Ni-Ca intermediate alloy is 0.018-0.02 wt% of the total adding amount of the raw materials.

5. The carbon and oxygen content both low 316L stainless steel smelting method according to claim 1, characterized in that, The temperature of the melt is adjusted to be 1460-1500 ℃ when the melt is poured into the heated and baked cast iron mold.

6. The carbon and oxygen content both low 316L stainless steel melting method according to claim 1, characterized in that, The raw materials include iron bar with a purity of ≥99.5%, metal molybdenum with a purity of ≥99.99%, chromium with a purity of ≥99.99%, and nickel with a purity of ≥99.98%.

7. A 316L stainless steel prepared by the carbon and oxygen content double-low 316L stainless steel melting method in claim 1.

8. A 316L stainless steel according to claim 7, characterized in that, According to the mass percentage, the trace element and impurity content is: C≤0.0050%, O≤0.0020%, S≤0.0010%, N≤0.0010%, H≤0.0002%.

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