Ultralow-carbon high-oxygen industrial pure iron and preparation method thereof

Abstract

The invention relates to the technical field of high-cleanliness special steel production, and particularly discloses ultra-low-carbon high-oxygen industrial pure iron and a preparation method thereof, and the pure iron comprises the following components: C, O and Fe; c is 0.012 wt% to 0.068 wt%, and C / O is in a range of 0.75 to 0.85. The preparation method comprises the following steps: selecting a pure iron raw material, pure iron oxide scales and high-purity graphite carbon blocks according to component requirements; smelting in a vacuum induction furnace until the content of N is not greater than 0.001%, and ending the carbon-oxygen reaction; then refining treatment is carried out, after the carbon and oxygen components are adjusted to be 0.006%-0.068% of C, 0.008%-0.080% of O and 0.75%-0.85% of C / O, tapping and pouring are carried out, and a cast ingot is obtained; and annealing the cast ingot, and heating and rolling to obtain a pure iron raw material bar. According to the method, the pure iron is added with carbon and oxygen in a specific proportion for deoxidation, decarbonization and denitrification, the requirements for ultralow carbon, ultralow nitrogen and high purity are met, the smelting time of the induction furnace is shortened, the efficiency is improved, and finally the low-carbon, ultralow-nitrogen and high-oxygen industrial pure iron with C / O meeting a certain proportion is prepared and has extremely high application and popularization 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 purpose of strengthening. 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 maraging steel of the ultimate ultra-high strength level, to obtain better toughness and plasticity, a higher cleanliness level is required, and in particular, the carbon and nitrogen contents need to be controlled to extremely low levels.

[0003] Currently, for high-purity maraging steel, the ultra-low carbon C≤0.005%, the gas requirement for 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, the carbon-oxygen reaction is restricted when producing high-purity maraging steel by a vacuum induction furnace, 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% - 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 method for preparing the ultra-low carbon and high-oxygen industrial pure iron described above, including: Step 1: Select pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks according to the component requirements. 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 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 and 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 and casting to obtain an ingot. Step 4: After annealing the ingot, heat and roll it into a pure iron raw material bar.

[0009] 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%.

[0010] In some embodiments, in the pure iron raw materials of Step 1, S ≤ 0.001 wt%, P ≤ 0.0015%.

[0011] In some embodiments, the pure iron raw materials are charged into the furnace, and the pure iron oxide scale and high-purity graphite carbon blocks are added respectively when charging into the furnace and adjusting the carbon and oxygen components.

[0012] In some embodiments, in Step 2, melting the selected pure iron raw materials, pure iron oxide scale, and high-purity graphite carbon blocks in a vacuum induction furnace includes: Load pure iron raw materials with the furnace. By mass percentage, in all the raw materials charged with the furnace, O: 0.09 - 0.011%, C: 0.060 - 0.080%. When starting melting, the required vacuum degree ≤ 1 Pa; after melting is complete, heat up to 1610 - 1630 °C and enter the high-temperature boiling carbon-oxygen reaction, maintaining for 35 - 45 min.

[0013] 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, then sample and detect the N content again until N ≤ 0.001%, and after stirring for a predetermined time, the carbon-oxygen reaction ends.

[0014] In some embodiments, in step two, when melting the selected pure iron raw materials, pure iron scale, and high-purity graphite carbon blocks 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.

[0015] In some embodiments, in step two, the tapping and casting are electro-tapping 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 casting and furnace cooling for 15 - 20 minutes, break the vacuum, and use a long spoon to add a heating agent and a covering agent to the surface of the ingot.

[0016] In some embodiments, in step four, after annealing the ingot, hot rolling it into a pure iron raw material rod includes: By mass percentage, roll pure iron raw material rods 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 rod gradually increases; 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 rods, second-specification rods, and third-specification rods respectively, and the diameter of the second-specification rods is greater than that of the first-specification rods and less than that of the third-specification rods.

[0017] Adopting the above technical solution, the present invention has at least the following beneficial effects: A kind of ultra-low-carbon high-oxygen industrial pure iron and its preparation method provided by the present invention, when melting maraging steel, superalloy, and ultra-low-carbon stainless steel in a vacuum induction furnace, use specific proportions of carbon and oxygen in pure iron for deoxidation, decarburization, and denitrification, meet the requirements of ultra-low carbon, ultra-low nitrogen, and high purity, shorten the melting time of the induction furnace, improve the efficiency, and finally prepare industrial pure iron with a certain ratio of C / O, low carbon, ultra-low nitrogen, and high oxygen, which has extremely high popularization and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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 use in the description of the embodiments or the prior art. Obviously, the drawings in the following description 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.

[0019] Figure 1 It is the carbon and oxygen content values under different vacuum pressures in a 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

[0020] The following will further describe in detail the embodiments of the present disclosure in conjunction with the drawings and embodiments. The detailed description of the following embodiments and the drawings 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 in the text, but including all technical solutions falling within the scope of the claims.

[0021] 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 values described in these embodiments should be interpreted as merely exemplary, rather than as limitations.

[0022] It should be noted that in the description of the present disclosure, unless otherwise stated, the meaning of "a plurality" is greater than or equal to two; the orientation or positional relationships indicated by terms such as "upper", "lower", "left", "right", "inner", "outer", etc. are 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 understood as a limitation of the present disclosure. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

[0023] In addition, the "first", "second" and similar terms used in the present disclosure do not represent any order, quantity or importance, but are only used to distinguish different parts. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range. Terms such as "including" or "comprising" 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.

[0024] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" 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 a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present 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.

[0025] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as those, should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0026] 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.

[0027] Some embodiments of the present invention disclose a low-carbon, ultra-low-nitrogen, high-oxygen industrial pure iron and a preparation method thereof. The 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.

[0028] 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: 1) Select pure iron raw materials with strict component requirements of 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 oxide scale; high-purity graphite carbon blocks.

[0029] 2) Melting in a vacuum induction furnace. Charge pure iron, partial pure iron mill scale, and ultra-pure graphite carbon blocks with the furnace. In terms of mass percentage, in the charge, O: 0.09 - 0.011%, C: 0.060 - 0.080%. The other pure iron mill scale and high-purity graphite carbon blocks are added separately during subsequent adjustment of carbon and oxygen components. When starting melting, the required vacuum degree is ≤1 Pa, and melting is carried out at high power (200 KW - 300 KW). After melting is complete, heat up to 1620 °C and enter the high-temperature boiling carbon-oxygen reaction, which is maintained 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.

[0030] 3) Tapping with electricity at a temperature of 1580 ± 10 °C. Argon is filled throughout the pouring process, and pouring is carried out while maintaining 1 atmospheric pressure of argon.

[0031] 4) Annealing the ingot. Heat and roll into pure iron raw material bars with different specifications of Ф60 - 100 mm according to different O contents: 0.008% - 0.080%.

[0032] In the above step 1), as a preferred implementation manner, it is optional that in the pure iron raw material, S ≤ 0.001 wt%, P ≤ 0.0015%.

[0033] In the above step 2), as a preferred implementation manner, the ultra-pure graphite carbon blocks can also be added to the furnace when charging with the furnace and adjusting the carbon and oxygen components.

[0034] In the above step 2), after the furnace charge is melted, during the denitrification by 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.

[0035] In the above step 2), during the later stage of the carbon-oxygen reaction, sample and analyze the mass content of N. If N ≤ 0.001%, stir for 5 minutes and then go to the next step. If N > 0.001%, continue the high-temperature boiling carbon-oxygen reaction for denitrification for 20 min and then sample again. The key points for controlling time and enhancing stirring are to ensure that N ≤ 0.001% when the denitrification by high-temperature boiling carbon-oxygen reaction ends.

[0036] In the above step 3), tapping with electricity for pouring to ensure a pouring temperature of 1580 ± 10 °C. Argon is filled throughout the pouring process, and pouring is carried out while maintaining 90000 - 100000 Pa.

[0037] In the above step 3), after the mold casting is cooled in the furnace for 15 minutes, breaking the vacuum is allowed. Heat - generating agents and covering agents can be added to the surface of the ingot using a long spoon, and the mold - cast ingot can be air - cooled after demolding.

[0038] In the above step 4), according to three intervals of O content: 0.008% - 0.020%, 0.02% - 0.04%, 0.04% - 0.08%, bars with corresponding three specifications of Ф60mm, Ф80mm, and Ф100mm are rolled.

[0039] In the above step 4), the contents of C, O, and N in the bars are accurately detected, clearly marked, and stored by furnace and by specification for subsequent use as raw materials.

[0040] The following examples 1 - 5 are listed to describe in detail the preparation method of the low - carbon high - oxygen industrial pure iron of the present invention.

[0041] 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.

[0042] 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.

[0043] Based on this, the steps of the above - mentioned preparation method of low - carbon high - oxygen industrial pure iron are specifically as follows: Select high - quality industrial pure iron raw materials → Vacuum induction furnace melting (denitrifying, controlling O, controlling C) → Mold casting, rolling, and marking.

[0044] In each example, the selected industrial pure iron components are shown in Table 1. The components of low - carbon, ultra - low - nitrogen, high - oxygen industrial pure iron after melting, denitrifying, controlling oxygen, and controlling carbon in a 150 kg vacuum induction furnace are shown in Table 2.

[0045] When the vacuum induction furnace starts to melt, the vacuum degree ≤1 Pa, and the melting period is 3 h.

[0046] After melting to clear, heat up to 1620°C and enter the high-temperature boiling vacuum carbon-oxygen reaction for deep denitrification. The vacuum degree of the induction furnace should be ≤1 Pa, and the holding time should be no less than 40 min. At the end of refining, N≤0.001%.

[0047] After the carbon-oxygen reaction ends and enter the refining temperature of 1550 - 1560°C, charge argon at 5000 - 7000 Pa to adjust the carbon and oxygen components. Before tapping, ensure that in the steel, C: 0.006% - 0.068%, O: 0.008% - 0.080%, and C / O meets 0.75 - 0.85.

[0048] Charge argon at 1 atmospheric pressure and tap the molten steel with electricity. Tapping temperature: 1580 ± 10°C.

[0049] After the ingot casting is completed and cooled in the furnace for 15 minutes, break the vacuum and use a long spoon to add heating agent and covering agent to the surface of the ingot. After the ingot casting is demolded, air-cool it.

[0050] For Examples 1 - 5, select the round billet of Ф200mm ingot type and anneal the ingot. According to the O content level, for Example 1, roll Ф60mm bars, for Examples 2 and 3, roll Ф80mm bars, and for Examples 4 and 5, roll Ф100mm bars.

[0051] Mark clearly according to the C and O contents and store them by furnace and specification.

[0052]

[0053]

[0054] 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%, and the Si and Al contents are slightly reduced, further purifying the industrial pure iron. In Examples 1 - 5, the contents of residual elements 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%. At the same time, 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.

[0055] The low-carbon, ultra-low-nitrogen, and high-oxygen industrial pure iron prepared by the technical scheme described in the present invention is particularly suitable for use as the raw material for denitrification in the production of maraging steel, superalloys, ultra-low-carbon stainless steel, etc. by vacuum induction furnace melting, meeting the requirements of ultra-low-carbon, ultra-low-nitrogen, and high purity, shortening the melting time of the induction furnace, improving the denitrification efficiency, and having extremely high popularization and application value. It can also be applied to the production of other ultra-low-carbon, ultra-low-nitrogen, and high-purity special alloy steels, etc.

[0056] In addition to the above embodiments, the present invention may also have other embodiments, such as alloying methods for other steel grades by using the vacuum induction furnace process to purify industrial pure iron alloys. All technical solutions formed by equivalent substitution or equivalent transformation shall fall within the protection scope required by the present invention.

[0057] Thus far, the various embodiments of the present disclosure have been described in detail. 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.

[0058] 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 for illustrative purposes only 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 various technical features mentioned in each embodiment can be combined in any way.

Claims

1. An ultra-low carbon high oxygen industrial pure iron, characterized in that: The components include: C, O, Fe; in terms of mass percentage, C: 0.012% to 0.068%, and C / O meets 0.75-0.

85.

2. The ultra-low carbon high oxygen industrial pure iron according to claim 1, characterized in that: Calculated by weight percentage: 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%, the balance is Fe and unavoidable impurities.

3. The method for preparing ultra-low carbon high oxygen industrial pure iron according to claim 1 or 2, characterized in that: include: Step 1: Selecting pure iron raw materials, pure iron oxide scale and high-purity graphite carbon blocks according to component requirements; Step 2: Smelting the selected pure iron raw material, pure iron oxide scale and high-purity graphite carbon block in a vacuum induction furnace until the N content is no more than 0.001% and the carbon-oxygen reaction is completed; Step 3: After the carbon-oxygen reaction is completed, refining begins at a temperature of 1550-1560°C, argon is filled at 5000-7000Pa, and the carbon-oxygen composition is adjusted. By weight percentage, before tapping, the system is guaranteed to have C: 0.006%-0.068%, O: 0.008%-0.080%, and C / O meets 0.75-0.85, then tapping and pouring is performed to obtain an ingot; Step 4: After annealing, the ingot is heated and rolled into a pure iron raw material bar.

4. The preparation method according to claim 3, characterized in that: In the pure iron raw material 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%, and Bi≤0.0005%.

5. The preparation method according to claim 4, characterized in that: In the pure iron raw material of step 1, S≤0.001wt%, P≤0.0015%.

6. The preparation method according to claim 3, characterized in that: The selected pure iron raw material is loaded into the furnace, and the pure iron oxide scale and high-purity graphite carbon block are added into the furnace and when adjusting the carbon and oxygen components, respectively.

7. The preparation method according to claim 3, characterized in that: In step 2, the selected pure iron raw material, pure iron oxide scale and high-purity graphite carbon block are subjected to vacuum induction furnace smelting, which includes: Pure iron raw materials, pure iron oxide scale and ultrapure graphite carbon blocks are loaded into the furnace. In terms of mass percentage, O: 0.09-0.011%, C: 0.060-0.080%; When melting, the vacuum degree should be ≤1Pa; after melting, the temperature should be raised to 1610-1630℃ to enter the high-temperature boiling carbon-oxygen reaction, and maintained for 35-45 minutes; Take samples to detect the N content, calculated as a percentage by mass. If N ≤ 0.001%, the carbon-oxygen reaction ends after stirring for a predetermined time. If N > 0.001%, continue to perform high-temperature boiling carbon-oxygen reaction for denitrification for 15-25 minutes, then take samples to detect the N content again until N ≤ 0.001%. After stirring for a predetermined time, the carbon-oxygen reaction ends.

8. The preparation method according to claim 3, characterized in that: In step 2, when the selected pure iron raw material, pure iron oxide scale and high-purity graphite carbon block are smelted in a vacuum induction furnace, after the charge is melted, the vacuum degree of the induction furnace is not higher than 1Pa during high-temperature boiling carbon-oxygen reaction denitrification, and the holding time is not less than 40 minutes.

9. The preparation method according to claim 3, characterized in that: In step three, the steel tapping and casting are live steel tapping and casting, ensuring that the casting temperature is 1580±10°C, and the entire pouring process is filled with argon to maintain 90000-100000Pa for pouring; after the pouring is completed, the furnace is cooled for 15-20 minutes and then the air is broken, and a heating agent and a covering agent are added to the surface of the ingot using a long spoon.

10. The preparation method according to claim 3, characterized in that: In step 4, after annealing the ingot, the ingot is heated and rolled into a pure iron raw material bar, which includes: Rolling pure iron raw material bars of different specifications according to the oxygen content in terms of mass percentage, and with the increase of oxygen content, the diameter of the pure iron raw material bars gradually increases; Alternatively, in terms of mass percentage, corresponding first specification bars, second specification bars and third specification bars are rolled according to three oxygen content ranges of 0.008% to 0.020%, 0.02% to 0.04% and 0.04% to 0.08%, respectively, and the diameter of the second specification bar is larger than that of the first specification bar and smaller than that of the third specification bar.

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