An extra-low-carbon and high-oxygen industrial pure iron and its preparation method

Abstract

The present invention relates to the technical field of high-purity special steel production, and specifically discloses an ultra-low-carbon and high-oxygen industrial pure iron and a preparation method thereof. The components of the pure iron include: C, O, and Fe; C: 0.012% to 0.068 wt%, and C / O satisfies 0.75 - 0.85. The preparation method includes: carefully selecting pure iron raw materials, pure iron scale, and high-purity graphite carbon blocks according to the component requirements; carrying out vacuum induction furnace melting until the content of N is not greater than 0.001% and the carbon-oxygen reaction ends; then carrying out refining treatment, adjusting the carbon and oxygen components to C: 0.006% to 0.068%, O: 0.008% to 0.080%, and after C / O satisfies 0.75 - 0.85, tapping and casting to obtain an ingot; after annealing treatment of the ingot, heating and rolling it into a pure iron raw material rod. The present invention uses pure iron plus carbon and oxygen in a specific ratio for deoxidation, decarburization, and denitrification to meet the requirements of ultra-low carbon, ultra-low nitrogen, and high purity, shortens the induction furnace melting time, improves efficiency, and finally prepares low-carbon, ultra-low nitrogen, and high-oxygen industrial pure iron with a certain ratio of C / O, which has extremely high popularization and application value.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity special steel production, and particularly to an ultra-low carbon and high-oxygen industrial pure iron and a preparation method thereof. Background Art

[0002] During the aging process of maraging steel, strengthening alloying elements such as Co, Mo, Ti, etc. precipitate intermetallic compounds in the Fe-Ni-based supersaturated martensite to achieve the strengthening purpose. The Ti content in the steel ranges from 0.2% to 1.4%. To obtain excellent mechanical properties such as high strength, good toughness and ductility, maraging steel requires a very high cleanliness level. Especially for ultra-high strength grade maraging steel, to obtain better ductility and plasticity, a higher cleanliness level is required, and in particular, the carbon and nitrogen contents need to be controlled to an extremely low level.

[0003] Currently, for high-purity maraging steel, the ultra-low carbon C≤0.005%, the gas requirements are low O≤0.0015%, and N≤0.0015%. When using a vacuum induction furnace to produce maraging steel, only by selecting high-quality raw materials, the oxygen content, carbon content, and nitrogen content in the actual batching are low. The carbon-oxygen reaction in the steel is weak, and the ability to deoxidize, decarburize, and denitrify during the process is weak. Only by strengthening stirring and increasing the melting time can the denitrification purpose be achieved. In this way, when using a vacuum induction furnace to produce high-purity maraging steel, the carbon-oxygen reaction is restricted, and it is difficult to control ultra-low nitrogen, resulting in a long smelting time, low efficiency, and increased production costs.

[0004] Based on this, the existing technology still needs to be improved. Summary of the Invention

[0005] To solve the above technical problems, an embodiment of the present invention provides an ultra-low carbon and high-oxygen industrial pure iron and a preparation method thereof, so as to solve the technical problem that the production of aging steel in the existing technology cannot meet the production requirements.

[0006] To solve the above technical problems, on the one hand, some embodiments of the present invention disclose an ultra-low carbon and high-oxygen industrial pure iron, the components of which include: C, O, Fe; in terms of mass percentage, C: 0.012% - 0.068%, and C / O satisfies 0.75 - 0.85.

[0007] In some embodiments, by weight percentage, it includes: O: 0.016% to 0.080%, N ≤ 0.001%, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%, and the balance is Fe and inevitable impurities.

[0008] On the other hand, the embodiments of the present invention also disclose a preparation method of the aforementioned extra-low carbon and high-oxygen industrial pure iron, including:

[0009] Step 1: Select pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks according to the component requirements;

[0010] Step 2: Melt the selected pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks in a vacuum induction furnace until the content of N is not more than 0.001% and the carbon-oxygen reaction ends;

[0011] Step 3: After the carbon-oxygen reaction ends and enters refining, the temperature is 1550 - 1560 °C, argon is filled at 5000 - 7000 Pa, the carbon and oxygen components are adjusted. By mass percentage, before tapping, ensure that in the system, C: 0.006% to 0.068%, O: 0.008% to 0.080%, and after C / O meets 0.75 - 0.85, tap and pour to obtain an ingot;

[0012] Step 4: After annealing the ingot, heat and roll it into a pure iron raw material bar.

[0013] In some embodiments, in the pure iron raw materials of Step 1, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%.

[0014] In some embodiments, in the pure iron raw materials of Step 1, S ≤ 0.001 wt%, P ≤ 0.0015%.

[0015] In some embodiments, the pure iron raw materials are charged with the furnace, and the pure iron oxide scale and high-purity graphite carbon blocks are added respectively when charging with the furnace and adjusting the carbon and oxygen components.

[0016] In some embodiments, in step two, the vacuum induction furnace melting of the selected pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks includes:

[0017] Load the pure iron raw materials into the furnace. By mass percentage, in all the raw materials charged with the furnace, O: 0.09 - 0.011%, C: 0.060 - 0.080%;

[0018] When starting to melt, the required vacuum degree is ≤ 1 Pa; after melting clear, heat up to 1610 - 1630 °C and enter the high-temperature boiling carbon-oxygen reaction, and maintain it for 35 - 45 min.

[0019] Sample and detect the N content. By mass percentage, if N ≤ 0.001%, after stirring for a predetermined time, the carbon-oxygen reaction ends; if N > 0.001%, then continue the high-temperature boiling carbon-oxygen reaction for denitrification for 15 - 25 min, and then sample and detect the N content until N ≤ 0.001%, and after stirring for a predetermined time, the carbon-oxygen reaction ends.

[0020] In some embodiments, in step two, when the selected pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks are melted in a vacuum induction furnace, after the furnace charge is melted clear, during the high-temperature boiling carbon-oxygen reaction for denitrification, the vacuum degree of the induction furnace is not higher than 1 Pa, and the holding time is not less than 40 min.

[0021] In some embodiments, in step two, the tapping and casting are electro-tapping casting, ensuring that the casting temperature is 1580 ± 10 °C, the whole casting process is filled with argon, and the casting is carried out at 90000 - 100000 Pa; after the furnace is cooled for 15 - 20 minutes after casting, break the vacuum, and use a long spoon to add heat-generating agents and covering agents to the ingot surface.

[0022] In some embodiments, in step four, after annealing the ingot, the hot rolling into pure iron raw material bars includes:

[0023] By mass percentage, roll pure iron raw material bars of different specifications according to the size of the O content, and as the O content increases, the diameter of the pure iron raw material bars gradually increases;

[0024] Or, by mass percentage, according to three intervals of O content of 0.008% - 0.020%, 0.02% - 0.04%, and 0.04% - 0.08%, roll the corresponding first-specification bars, second-specification bars, and third-specification bars respectively, and the diameter of the second-specification bars is greater than that of the first-specification bars and less than that of the third-specification bars.

[0025] Adopting the above technical solution, the present invention has at least the following beneficial effects:

[0026] An ultra-low-carbon and high-oxygen industrial pure iron and its preparation method provided by the present invention utilize specific proportions of carbon and oxygen in the pure iron for deoxidation, decarburization, and denitrification during the melting of maraging steel, superalloys, and ultra-low-carbon stainless steel in a vacuum induction furnace, meeting the requirements of ultra-low carbon, ultra-low nitrogen, and high purity, shortening the melting time of the induction furnace, improving efficiency, and finally preparing an industrial pure iron with low carbon, ultra-low nitrogen, and high oxygen where C / O meets a certain ratio, which has extremely high popularization and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is the carbon and oxygen content values under different vacuum pressures in the preparation method of an ultra-low-carbon and high-oxygen industrial pure iron disclosed in some embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The following will further describe in detail the embodiments of the present disclosure in conjunction with the drawings. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms, not limited to the specific embodiments disclosed herein, but including all technical solutions falling within the scope of the claims.

[0030] The present disclosure provides these embodiments to make the present disclosure thorough and complete, and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions, and numerical values described in these embodiments should be construed as merely exemplary, rather than as limitations.

[0031] It should be noted that in the description of the present disclosure, unless otherwise stated, "a plurality of" means greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicate the orientation or positional relationship only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present disclosure. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

[0032] In addition, the "first", "second" and similar terms used in this disclosure do not denote any order, quantity, or importance, but are merely used to distinguish different parts. "Vertical" does not mean strictly vertical, but within the allowable error range. "Parallel" does not mean strictly parallel, but within the allowable error range. Words such as "comprising" or "including" mean that the elements before this word cover the elements listed after this word, and do not exclude the possibility of also covering other elements.

[0033] It should also be noted that in the description of this disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "joined" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this disclosure can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0034] All terms used in this disclosure have the same meanings as those understood by those of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, for example, should be interpreted as having meanings consistent with their meanings in the context of the related art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0035] Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the specification.

[0036] Some embodiments of the present invention disclose a low-carbon, ultra-low-nitrogen, high-oxygen industrial pure iron and its preparation method. Its chemical composition (wt%) is as follows: C: 0.012% - 0.068%, O: 0.016% - 0.080%, C / O satisfies 0.75 - 0.85, N ≤ 0.001%, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%, and the balance is Fe and unavoidable impurities.

[0037] Embodiments of the present invention also disclose a preparation method of the low-carbon, ultra-low-nitrogen, high-oxygen industrial pure iron of the foregoing embodiments, including:

[0038] 1) Select pure iron raw materials with strict component requirements: Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%; clean and dry pure iron scale; high-purity graphite carbon blocks.

[0039] 2) Melting in a vacuum induction furnace. Charge the furnace with pure iron, part of the pure iron scale and ultra-high-purity graphite carbon blocks. By mass percentage, in the charge, O: 0.09 - 0.011%, C: 0.060 - 0.080%. The other pure iron scale and high-purity graphite carbon blocks are added respectively during subsequent adjustment of carbon and oxygen components. When starting to melt, the required vacuum degree is ≤ 1 Pa, and melt with high power (200KW - 300KW). After melting to completion, raise the temperature to 1620 °C to enter the high-temperature boiling carbon-oxygen reaction and maintain it for 40 min. When the sampled N ≤ 0.001%, the carbon-oxygen reaction ends. If N does not meet the standard, continue the high-temperature boiling carbon-oxygen reaction for denitrification for 20 min and then sample again. After the carbon-oxygen reaction ends, enter the refining process. The temperature is 1550 - 1560 °C, and argon is filled at 5000 - 7000 Pa to adjust the carbon and oxygen components. Before tapping, ensure that in the system, C: 0.006% - 0.068%, O: 0.008% - 0.080%, and C / O meets 0.75 - 0.85.

[0040] 3) Tapping with electricity at a temperature of 1580 ± 10 °C, and argon is filled throughout the pouring process, and pour while maintaining 1 atmospheric pressure of argon filling.

[0041] 4) Annealing of the ingot, and hot-roll into pure iron raw material bars with different specifications of Ф60 - 100 mm according to different O contents: 0.008% - 0.080%.

[0042] In the above step 1), as a preferred implementation, it is optional that in the pure iron raw materials, S ≤ 0.001 wt%, P ≤ 0.0015%.

[0043] In the above step 2), as a preferred implementation, the ultra-high-purity graphite carbon blocks can also be added to the furnace when charging the furnace and adjusting the carbon and oxygen components.

[0044] In the above step 2), after the furnace charge is melted to completion, when denitrifying by the high-temperature boiling carbon-oxygen reaction, the vacuum degree of the induction furnace is not higher than 1 Pa, and the holding time is not less than 40 min.

[0045] In step 2) above, sample and analyze the mass content of N in the later stage of the carbon-oxygen reaction. If N ≤ 0.001%, stir for 5 minutes and then proceed to the next step. If N > 0.001%, continue the high-temperature boiling carbon-oxygen reaction to remove nitrogen for 20 min, and then sample again. The key points for controlling time and enhanced stirring are to ensure that N ≤ 0.001% at the end of the high-temperature boiling carbon-oxygen reaction for nitrogen removal.

[0046] In step 3) above, tap the molten steel and pour it while being charged with electricity to ensure a pouring temperature of 1580 ± 10 °C. Argon is filled throughout the pouring process, and the pouring is carried out under a pressure of 90000 - 100000 Pa.

[0047] In step 3) above, after the mold casting is cooled in the furnace for 15 minutes, it is allowed to break the vacuum. A long spoon can be used to add heat-generating agents and covering agents to the surface of the ingot. The mold-cast ingot can be air-cooled after demolding.

[0048] In step 4) above, roll bars with three corresponding specifications of Ф60mm, Ф80mm, and Ф100mm according to three intervals of O content: 0.008% - 0.020%, 0.02% - 0.04%, and 0.04% - 0.08%.

[0049] In step 4) above, accurately detect the C, O, and N contents of the bars, mark them clearly, and store them by furnace and specification for subsequent use as raw materials.

[0050] The following lists Examples 1 - 5 to describe in detail the preparation method of the low-carbon high-oxygen industrial pure iron of the present invention.

[0051] A preparation method of low-carbon high-oxygen industrial pure iron, the chemical composition (wt%) of the low-carbon high-oxygen industrial pure iron is as follows: C: 0.012% - 0.068%, O: 0.016% - 0.080%, C / O satisfies 0.75 - 0.85, N ≤ 0.001%, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%, and the balance is Fe and unavoidable impurities.

[0052] Under vacuum, the carbon-oxygen reaction: [C] + [O] → CO↑, the values of [C%] × [O%] under different vacuum pressures are as Figure 1 shown. It can be seen that the lower the vacuum degree, the lower the equilibrium carbon and oxygen contents.

[0053] Based on this, the steps of the above-mentioned preparation method of low-carbon high-oxygen industrial pure iron are specifically as follows:

[0054] Selected industrial pure iron raw materials → melted in a vacuum induction furnace (denitrification, oxygen control, carbon control) → marked by die casting and rolling.

[0055] In each example, the selected industrial pure iron composition is shown in Table 1. The composition of low-carbon, ultra-low-nitrogen, and high-oxygen industrial pure iron after melting and denitrification, oxygen control, and carbon control in a 150 kg vacuum induction furnace is shown in Table 2.

[0056] When the vacuum induction furnace starts to melt, the vacuum degree ≤ 1 Pa, and the melting period is 3 h.

[0057] After melting is complete, the temperature is raised to 1620 °C and enter the high-temperature boiling vacuum carbon-oxygen reaction for deep denitrification. The vacuum degree of the induction furnace ≤ 1 Pa, and the holding time is not less than 40 min. At the end of refining, N ≤ 0.001%.

[0058] After the carbon-oxygen reaction ends, enter the refining temperature of 1550 - 1560 °C, and argon is charged at 5000 - 7000 Pa to adjust the carbon and oxygen components. Before tapping, ensure that C in the steel is 0.006% - 0.068%, O is 0.008% - 0.080%, and C / O meets 0.75 - 0.85.

[0059] Tapping is carried out with 1 atmospheric pressure of argon charged, and the tapping temperature is: 1580 ± 10 °C.

[0060] After the die casting is completed and the furnace is cooled for 15 minutes, the vacuum is broken, and a heating agent and a covering agent are added to the surface of the ingot using a long spoon. After the die-cast ingot is demoulded, it is air-cooled.

[0061] For Examples 1 - 5, a round billet of Ф200 mm ingot type is selected, and the ingot is annealed. According to the O content level, in Example 1, Ф60 mm bars are rolled, in Examples 2 and 3, Ф80 mm bars are rolled, and in Examples 4 and 5, Ф100 mm bars are rolled.

[0062] Mark clearly according to the C and O contents, and store separately by furnace and specification.

[0063]

[0064]

[0065] As can be seen from Table 1 and Table 2, after melting in a vacuum induction furnace, the N content is reduced to less than 0.001%, the Si and Al contents are reduced, and the industrial pure iron is further purified. In Examples 1 - 5, the contents of each residual element in the low-carbon, ultra-low-nitrogen, and high-oxygen industrial pure iron all meet the technical requirements. In particular, the N content can be controlled below 0.001%, while C in the pure iron is controlled at 0.006% - 0.068%, O is controlled at 0.008% - 0.080%, and C / O meets 0.75 - 0.85.

[0066] The medium and low carbon, ultra-low nitrogen, high oxygen industrial pure iron prepared by the technical solution of the present invention is particularly suitable for being used as a raw material for denitrification in the smelting of maraging steel, superalloys, ultra-low carbon stainless steel, etc. by a vacuum induction furnace, meeting the requirements of ultra-low carbon, ultra-low nitrogen and high purity, shortening the melting time of the induction furnace and improving the denitrification efficiency, and having extremely high popularization and application value. It can also be applied to the production of other special alloy steels with ultra-low carbon, ultra-low nitrogen and high purity, etc.

[0067] In addition to the above embodiments, the present invention can also have other implementation manners, such as an alloying method for applying the industrial pure iron alloy purified by the vacuum induction furnace process to other steel grades. Any technical solution formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

[0068] So far, the embodiments of the present disclosure have been described in detail. In order to avoid obscuring the concept of the present disclosure, some details well known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0069] Although some specific embodiments of the present disclosure have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present disclosure. Those skilled in the art should understand that the above embodiments can be modified or partial technical features can be equivalently replaced without departing from the scope and spirit of the present disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way.

Claims

1. A kind of extra-low carbon and high oxygen industrial pure iron, characterized in that, The components include: C, O, Fe; by mass percentage, C: 0.012% - 0.068%, and C / O satisfies 0.75 - 0.85; By weight percentage, it includes: O: 0.016% - 0.080%, N ≤ 0.001%, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%, and the balance is Fe and inevitable impurities.

2. The preparation method of the extra-low-carbon and high-oxygen industrial pure iron according to claim 1, characterized in that, It includes: Step 1: Select pure iron raw materials, pure iron scale, and high-purity graphite carbon blocks according to the component requirements; Step 2: Melt the selected pure iron raw materials, pure iron scale, and high-purity graphite carbon blocks in a vacuum induction furnace until the content of N is not greater than 0.001% and the carbon-oxygen reaction ends; Step 3: After the carbon-oxygen reaction ends, enter the refining process. The temperature is 1550 - 1560°C, and argon is filled at 5000 - 7000 Pa. Adjust the carbon-oxygen components. By mass percentage, ensure that in the system, C: 0.006% - 0.068%, O: 0.008% - 0.080%, and C / O satisfies 0.75 - 0.85 before tapping. Then tap and pour to obtain an ingot; Step 4: After annealing the ingot, heat and roll it into pure iron raw material bars.

3. The preparation method according to claim 2, wherein In the pure iron raw materials in Step 1, Mn ≤ 0.02%, Cr ≤ 0.01%, Ni ≤ 0.01%, Mo ≤ 0.005%, Ti ≤ 0.001%, Cu ≤ 0.01%, S ≤ 0.002%, P ≤ 0.002%, Al ≤ 0.005%, Si ≤ 0.005%, As ≤ 0.003%, Sn ≤ 0.0005%, Pb ≤ 0.0005%, Sb ≤ 0.0005%, Bi ≤ 0.0005%.

4. The preparation method according to claim 3, characterized in that, In the pure iron raw materials in Step 1, S ≤ 0.001 wt%, P ≤ 0.0015%.

5. The preparation method according to claim 2, characterized in that, The selected pure iron raw materials are charged into the furnace, and the pure iron scale and high-purity graphite carbon blocks are added respectively when charging into the furnace and adjusting the carbon-oxygen components.

6. The preparation method according to claim 2, characterized in that, In Step 2, melting the selected pure iron raw materials, pure iron scale, and high-purity graphite carbon blocks in a vacuum induction furnace includes: Charge the pure iron raw materials, pure iron scale, and ultra-pure graphite carbon blocks into the furnace. By mass percentage, in the raw materials charged into the furnace, O: 0.09 - 0.011%, C: 0.060 - 0.080%; When starting to melt, the required vacuum degree is ≤ 1 Pa; after melting clear, heat up to 1610 - 1630°C and enter the high-temperature boiling carbon-oxygen reaction, and maintain it for 35 - 45 min; The nitrogen content is sampled and detected. In terms of mass percentage, if N ≤ 0.001%, after stirring for a predetermined time, the carbon-oxygen reaction ends; if N > 0.001%, then the high-temperature boiling carbon-oxygen reaction for denitrification is continued for 15 - 25 min, and then the nitrogen content is sampled and detected until N ≤ 0.001%, and after stirring for a predetermined time, the carbon-oxygen reaction ends.

7. The preparation method according to claim 2, characterized in that, In step two, when melting the selected pure iron raw material, pure iron scale and high-purity graphite carbon block in a vacuum induction furnace, after the furnace charge is melted, during the high-temperature boiling carbon-oxygen reaction for denitrification, the vacuum degree of the induction furnace is not higher than 1 Pa, and the holding time is not less than 40 min.

8. The preparation method according to claim 2, wherein In step three, the tapping and casting are carried out by electrically tapping and casting, ensuring that the casting temperature is 1580 ± 10 °C, argon is filled throughout the casting process, and casting is carried out at 90000 - 100000 Pa; after the casting is completed and furnace-cooled for 15 - 20 minutes, the air is released, and a heating agent and a covering agent are added to the surface of the ingot with a long spoon.

9. The preparation method according to claim 2, wherein In step four, after annealing the ingot, the heating and rolling into pure iron raw material bars includes: In terms of mass percentage, pure iron raw material bars of different specifications are rolled according to the oxygen content, and as the oxygen content increases, the diameter of the pure iron raw material bars gradually increases; Or, in terms of mass percentage, according to three intervals of oxygen content of 0.008% - 0.020%, 0.02% - 0.04%, and 0.04% - 0.08%, the corresponding first-specification bars, second-specification bars, and third-specification bars are respectively rolled, and the diameter of the second-specification bars is larger than that of the first-specification bars and smaller than that of the third-specification bars.

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