Ultra-low-sulfur ultra-pure ferrochrome for high-cobalt-nickel secondary hardening steel and preparation method of ultra-low-sulfur ultra-pure ferrochrome

Abstract

The invention relates to the technical field of metallurgical production, in particular to ultra-low-sulfur ultra-pure ferrochrome for high-cobalt-nickel secondary hardening steel and a preparation method of the ultra-low-sulfur ultra-pure ferrochrome. The chromium iron comprises, by mass, 1%-25% of Cr, smaller than or equal to 0.3% of C, smaller than or equal to 0.01% of Si, smaller than or equal to 0.002% of P, smaller than or equal to 0.0007% of S, smaller than or equal to 0.0020% of O, smaller than or equal to 0.01% of Al, smaller than or equal to 0.001 wt% of Ti, smaller than or equal to 0.01% of Mn and the balance Fe and inevitable impurities. The concentration range of part of residual elements in the purified ferrochrome alloy is lower than that of metal chromium JCr99-A, the purity range of the residual elements is smaller than that of ultrapure electrolytic metal chromium JCr99.95-A, the ferrochrome alloy can replace the ultrapure electrolytic metal chromium and industrial ultrapure iron to serve as raw materials for alloying chromium and iron when special alloy is prepared, and cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical production technology, and in particular to an ultra-low sulfur ultra-pure ferrochrome for high-cobalt-nickel secondary hardening steel and a preparation method thereof. Background Art

[0002] High cobalt-nickel secondary hardening steels for special equipment mainly include AF1410, AerMet 100, Ferrium M54, FerriumS53, Ferrium C64, CSS-42L, etc. High cobalt-nickel secondary hardening steels for special equipment are a type of steel with excellent performance. Therefore, their cleanliness requirements are extremely high. Ultra-pure raw materials are selected during the smelting process, and VIM+VAR processes are adopted.

[0003] Ferrochrome alloy and metallic chromium are important intermediate alloys for preparing high cobalt-nickel secondary hardening steel for special equipment. Generally speaking, the product standards of ferrochrome intermediate alloys are not very strict on sulfur content. For example, high carbon ferrochrome requires S content ≤0.04%, medium carbon ferrochrome, low carbon ferrochrome and micro carbon ferrochrome require S content ≤0.025%, and metallic chromium JCr99-A requires residual element S ≤0.01%, which cannot meet the requirements for ultra-low S content as alloying raw materials in the preparation of special alloys. When the 99.96% ultra-pure electrolytic metallic chromium JCr99.95-A with a higher purity is used as an alloying raw material for high cobalt-nickel secondary hardening steel, although it can meet the requirements for ultra-low S, P, Si, Mn, Al and Ti content, its selling price is more than ten times that of ferrochrome or metallic chromium, and the cost is too high. Summary of the invention

[0004] The purpose of the present invention is to provide an ultra-low sulfur ultra-pure ferrochrome for high-cobalt-nickel secondary hardening steel and a preparation method thereof, and further purify the specific residual elements of the ferrochrome alloy. After purification, the concentration range of some residual elements in the ferrochrome alloy is lower than that of metallic chromium JCr99-A, and is comparable to or even exceeds the purity range of ultra-pure electrolytic metallic chromium JCr99.95-A. The ferrochrome alloy can be used as a raw material for chromium and iron instead of ultra-pure electrolytic metallic chromium and ultra-pure electrolytic metallic iron in the production of high-cobalt-nickel secondary hardening steel for ultra-pure special equipment.

[0005] The present invention selects pure iron with low sulfur, low phosphorus and low titanium and metallic chromium raw materials with low sulfur, low phosphorus, low silicon and low aluminum, and then uses carbon blocks for deoxidation and denitrification in a vacuum induction furnace, avoiding the addition of additional deoxidizers such as aluminum, silicon and manganese for deoxidation, so as to avoid increasing the content of aluminum, silicon and manganese in the ferrochrome alloy; adding a trace amount of mixed rare earth at the end of deoxidation can effectively further remove O, S and modify inclusions in the ferrochrome alloy. In the process of electroslag remelting, the S content in the chromium-vanadium ferroalloy is further reduced, and the content of O, Si, Mn and Al is further reduced, and large particle inclusions are removed.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides an ultra-low sulfur ultra-pure ferrochrome for high-cobalt-nickel secondary hardening steel. The ferrochrome has the following composition, measured by mass percentage: Cr: 1%-25%, C≤0.3%, Si≤0.01%, P≤0.002%, S≤0.0007%, O≤0.0020%, Al≤0.01%, Ti≤0.001wt%, Mn≤0.01%, and the balance is Fe and unavoidable impurities.

[0008] Another aspect of the present invention provides a method for preparing the ultra-low sulfur ultra-pure ferrochrome for high cobalt-nickel secondary hardening steel, the method comprising the following steps:

[0009] 1) Select pure iron raw material, requiring P≤0.002wt%, S≤0.002wt%, Si≤0.01wt%, Mn≤0.01wt%, Al≤0.01wt%, Ti≤0.001wt%, C≤0.2wt%; select metal chromium JCr99-A raw material, requiring P≤0.002wt%, S≤0.005wt%, Si≤0.1wt%, Al≤0.2wt%;

[0010] 2) According to the composition of ferrochrome, pure iron, metallic chromium JCr99-A raw materials and ultra-pure graphite carbon blocks are loaded into the furnace for vacuum induction furnace smelting;

[0011] 3) The refined molten steel is subjected to low temperature mold casting, with the tapping temperature being 1580-1590°C to obtain an ingot;

[0012] 4) Under atmospheric conditions, the ingot obtained in step 3) is subjected to electroslag remelting and purification, the purified slag is composed of CaF2, Al2O3, and CaO, and the mass ratio thereof is CaF2:Al2O3:CaO=4:3:3, and the purified slag is required to have SiO2+MnO+FeO≤1wt% after the ingredients are prepared.

[0013] In the above technical solution, further, in step 2), the carbon content of the ultrapure graphite carbon block is controlled to be 0.2%-0.3%, the vacuum degree is required to be below 1Pa when melting begins, high power melting is required, the refining temperature is 1600±10°C, and the refining time is greater than 30 minutes.

[0014] In the above technical scheme, further, in step 2), after the charge is melted, the vacuum degree of the induction furnace is not higher than 1Pa during vacuum deep deoxidation in the refining period, and the holding time is not less than 50min. Samples are taken for analysis of [N] in the later stage of refining. If [N]≤0.01wt%, stir for 5 minutes and proceed to the next step. If [N]>0.01wt%, continue to add ultra-pure graphite carbon blocks to continue deoxidation and denitrification to ensure that [N]≤0.01wt% at the end of refining.

[0015] In the above technical solution, further, in step 2), at the end of vacuum deep deoxidation in the refining period, 0.15-0.20 kg / t of cerium, lanthanum or a mixture of lanthanum, cerium, praseodymium and neodymium is added through a vacuum silo.

[0016] In the above technical solution, further, in step 3), after mold casting, the ingot is allowed to be broken into air after furnace cooling for 15 minutes, and a heating agent and a covering agent are added to the surface of the ingot. The ingot is demolded and air-cooled, and the specification limit of the ingot is based on whether it can be directly used as an electroslag remelting consumable electrode after peeling.

[0017] In the above technical solution, further, in step 4), the ingot shape is Ф250mm and the slag amount is 17±2kg / t.

[0018] The present invention also provides an application of the ultra-low sulfur ultra-pure ferrochrome in the preparation of high cobalt-nickel secondary hardening steel.

[0019] The chromium content of the ferrochrome used to prepare AF1410 is 2.5-2.9%; the chromium content of the ferrochrome used to prepare AerMet 100 is 4.0-4.4%; the chromium content of the ferrochrome used to prepare Ferrium M54 is 1.1-1.5%; the chromium content of the ferrochrome used to prepare Ferrium C64 is 4.5-4.9%; the chromium content of the ferrochrome used to prepare Ferrium S53 is 12.7-13.3%; the chromium content of the ferrochrome used to prepare CSS-42L is 17.6-18.2%.

[0020] The beneficial effects of the present invention are:

[0021] 1. The concentration range of some residual elements in the ferrochrome alloy after purification is lower than that of metallic chromium JCr99-A, and is comparable to the purity range of ultrapure electrolytic metallic chromium JCr99.95-A. It can replace ultrapure electrolytic metallic chromium and industrial ultrapure iron as raw materials for alloying chromium and iron in the preparation of special alloys, thereby reducing costs.

[0022] 2. The present invention expands the composition design of ultra-low sulfur ultra-pure ferrochrome alloy, and at the same time expands the application of ultra-low sulfur ultra-pure ferrochrome in new fields, so that ultra-low sulfur ultra-pure ferrochrome alloy can be used as a raw material for chromium and iron in the production of high-cobalt-nickel secondary hardening steel for ultra-pure special equipment instead of ultra-pure electrolytic metallic chromium and ultra-pure electrolytic metallic iron (or industrial ultra-pure iron). DETAILED DESCRIPTION

[0023] The present invention is described in detail below in conjunction with specific implementation modes, but the present invention is not limited thereto.

[0024] An ultra-low sulfur ultra-pure ferrochrome, whose components are as follows: Cr: 1%-25%, C≤0.3%, Si≤0.01%, P≤0.002%, S≤0.0007%, O≤0.0020%, Al≤0.01%, Ti≤0.001wt%, Mn≤0.01%, and the balance is Fe and unavoidable impurities.

[0025] The method for preparing the ultra-low sulfur ultra-pure ferrochrome comprises the following steps:

[0026] 1) Select pure iron raw material, requiring P≤0.002wt%, S≤0.002wt%, Si≤0.01wt%, Mn≤0.01wt%, Al≤0.01wt%, Ti≤0.001wt%, C≤0.2wt%; select metal chromium JCr99-A raw material, requiring P≤0.002wt%, S≤0.005wt%, Si≤0.1wt%, Al≤0.2wt%;

[0027] 2) According to the composition of ferrochrome, pure iron, metallic chromium JCr99-A raw materials and ultra-pure graphite carbon blocks are loaded into the furnace for vacuum induction furnace smelting;

[0028] The carbon content of ultra-pure graphite carbon blocks is controlled to be 0.2%-0.3%. When melting, the vacuum degree is required to be below 1Pa, high power melting, refining temperature is 1600±10℃, and refining time is greater than 30 minutes;

[0029] If the chromium content of the mixture is high, chromium can be added to the furnace in batches during the furnace, smelting and refining intervals;

[0030] After the charge is melted, the vacuum degree of the induction furnace is not higher than 1Pa during vacuum deep deoxidation in the refining period, and the holding time is not less than 50 minutes. Sample and analyze [N] in the later stage of refining. If [N] ≤ 0.01%, stir for 5 minutes and then go to the next step. If [N] > 0.01%, continue to add ultra-pure graphite carbon blocks to continue deoxidation and denitrification to ensure that [N] ≤ 0.01% at the end of refining.

[0031] At the end of vacuum deep deoxidation during the refining period, 0.15-0.2kg / t cerium, lanthanum or a mixture of lanthanum, cerium, praseodymium and neodymium is added through a vacuum silo for deep desulfurization, deep deoxidation and denaturation of inclusions in ferrochrome alloys;

[0032] 3) The refined molten steel is subjected to low temperature mold casting, with the tapping temperature being 1580-1590°C to obtain an ingot;

[0033] After mold casting, the furnace is cooled for 15 minutes before being allowed to be broken into air. Exothermic agent and covering agent are added to the surface of the ingot. The ingot is demoulded and air-cooled. The ingot specification limit is based on whether it can be directly used as a consumable electrode for electroslag remelting after peeling.

[0034] 4) Under atmospheric conditions, the ingot obtained in step 3) is subjected to electroslag remelting, the slag is composed of CaF2, Al2O3, and CaO, and the mass ratio thereof is CaF2:Al2O3:CaO=4:3:3, and after the slag is purified, the SiO2+MnO+FeO in the slag is required to be no more than 1%, the ingot shape is Ф250mm, and the slag amount is 17±2kg.

[0035] Select a non-protective atmosphere electroslag remelting furnace. Under non-protective atmosphere conditions, the slag contacts the atmosphere during the electroslag remelting process. The sulfur in the slag can be removed through gasification reaction, and the S, Si, and Al contents in the ferrochrome alloy can also be significantly reduced.

[0036] During the electroslag remelting process, no deoxidizers such as aluminum, silicon, and calcium are added. Only carbon powder is added to deoxidize the slag system to ensure the stability of the slag system, thereby ensuring the consistency of the purity of the components at the arc starting end and the feeding end of the electroslag ingot.

[0037] Examples 1-3

[0038] The composition contents of the ultra-low sulfur ultra-pure ferrochrome of Examples 1-3 are shown in Table 1.

[0039] Table 1 Ultra-low sulfur ultra-pure ferrochrome content in Examples 1-3 (wt%)

[0040] Group C Cr Si Mn S P Al Ti O N Fe Example 1 0.17 4.22 0.005 0.005 0.0005 0.0019 0.005 0.0009 0.0017 0.0065 Bal. Example 2 0.18 4.23 0.005 0.005 0.0005 0.0019 0.005 0.0009 0.0018 0.0060 Bal. Example 3 0.17 4.22 0.005 0.005 0.0006 0.0019 0.005 0.0010 0.0019 0.0061 Bal.

[0041] The method for preparing the ultra-low sulfur ultra-pure ferrochrome comprises the following steps:

[0042] 1) Selecting pure iron raw material and metallic chromium JCr99-A raw material. The components and proportions of pure iron and metallic chromium JCr99-A in Examples 1-3 are shown in Table 2;

[0043] Table 2 Composition of metallic chromium JCr99-A raw material and pure iron raw material in Examples 1-3 (wt%)

[0044]

[0045] 2) According to the content of ultra-low sulfur ultra-pure ferrochrome, pure iron, metallic chromium JCr99-A raw materials, and ultra-pure graphite carbon blocks are charged into the furnace, with a carbon content of 0.2%, and smelted in a 150kg vacuum induction furnace. The vacuum degree of the vacuum induction furnace is ≤1Pa when the vacuum induction furnace starts to melt, and the melting period is 3h. The vacuum degree of the induction furnace is ≤1Pa during vacuum deep deoxidation during the refining period, and the high power melting is carried out. The refining temperature is 1600°C, and the holding time is not less than 50min. At the end of refining, N is ≤0.01%, and stirring is performed for 5min;

[0046] At the end of vacuum deep deoxidation during the refining period, 0.15kg / t of rare earth lanthanum is added through the vacuum silo for deep desulfurization, deep deoxidation and denaturation of inclusions in ferrochrome alloy;

[0047] 3) The refined molten steel is low-temperature mold-casted, and the tapping temperature is 1585°C. After the mold is cast, it is allowed to be broken into air after cooling in the furnace for 15 minutes. A long spoon is used to add a heating agent and a covering agent to the surface of the ingot. The ingot can be demoulded and air-cooled. The ingot is a 200mm ingot;

[0048] 4) Under atmospheric conditions, the ingot obtained in step 3) is subjected to 150kg electroslag remelting for purification, the purified slag is composed of CaF2, Al2O3, and CaO, wherein CaF2:Al2O3:CaO=40:30:30 (wt%), and the purified slag is required to have SiO2+MnO+FeO≤1% in the slag after batching, the ingot shape is Ф250mm, and the corresponding slag amount is 17±2kg / t.

[0049] As can be seen from Tables 1 and 2, after the electroslag remelting process, the contents of S, Si, Mn, Al, P, and O are all reduced, and the ferrochrome alloy is further purified. As can be seen from Table 1, the contents of each residual element in the ultra-low sulfur ultra-pure ferrochrome alloy in Examples 1-3 meet the technical requirements, especially the sulfur content can be controlled at 0.0006% or less, the Si, Mn, and Al contents are controlled at 0.005% or less, and the titanium content is controlled at 0.001% or less.

[0050] Embodiment 4-6

[0051] The ultrapure ferrochromium alloys of Examples 1-3 were used as raw materials to prepare AerMet 100 steels, which were prepared by smelting using the VIM+VAR process flow.

[0052] When using the ultrapure chromium-iron master alloys in Examples 1-3 to prepare AerMet 100 steel, almost no additional chromium and iron need to be added during batching.

[0053] Comparative Example 1

[0054] AerMet 100 steel is prepared by using 99.96% ultra-pure electrolytic metallic chromium JCr99.95-A as the raw material of chromium and industrial ultra-pure iron as the raw material of iron, and is prepared by smelting using the VIM+VAR process flow.

[0055] Table 3 is a comparison of the cleanliness of AerMet 100 steels prepared in Examples 4-6 and Comparative Example 1.

[0056] Table 3 Comparison of cleanliness of AerMet 100 steel obtained in Examples 4-6 and Comparative Example 1

[0057]

[0058] Comparing the cleanliness control levels of Examples 4-6 and Comparative Example 1 from Table 3, the O, N, and P contents of the two are at the same level, but the residual element contents of S, Si, Mn, Al, and Ti of Examples 4-6 are slightly lower.

[0059] The corresponding comprehensive mechanical properties of AerMet 100 steel in Examples 4-6 and Comparative Example 1 are shown in Table 4. It can be seen from Table 4 that the comprehensive mechanical properties of AerMet 100 steel in Examples 4-6 and Comparative Example 1 can meet the standard requirements of AerMet 100 steel. IC Range: 132-145MPa·m 1 / 2 , the impact toughness AKU value range is 70-78J. The fracture toughness K IC Range: 122-125MPa·m 1 / 2 , and the impact toughness AKU value ranges from 67 to 68 J. The tensile properties of Examples 4-6 are comparable to those of Comparative Example 1, but their area shrinkage, fracture toughness and impact toughness indicators are relatively better, which may be because the residual element contents of S, Si, Mn, Al, and Ti in Examples 4-6 are lower than those in Comparative Example 1, especially the difference in S content has a greater impact on fracture toughness and impact toughness.

[0060] Table 4 Comprehensive mechanical properties of AerMet 100 steel in Examples 4-6 and Comparative Example 1

[0061]

[0062] In addition to the above embodiments, the present invention may also have other implementations, such as designing a specific ultra-low sulfur ultra-pure ferrochrome alloy composition for other ultra-pure steels containing carbon and chromium, and using an induction furnace + electroslag remelting process to purify the ferrochrome alloy and apply it to an alloying method for other ultra-pure steels containing carbon and chromium. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. An ultra-low sulfur ultra-pure ferrochrome for high cobalt-nickel secondary hardening steel, characterized in that: The ferrochromium composition is as follows, in percentage by mass: Cr: 1%-25%, C≤0.3%, Si≤0.01%, P≤0.002%, S≤0.0007%, O≤0.0020%, Al≤0.01%, Ti≤0.001wt%, Mn≤0.01%, and the remainder is Fe and unavoidable impurities.

2. A method for preparing ultra-low sulfur ultra-pure ferrochrome for high cobalt-nickel secondary hardening steel according to claim 1, characterized in that: The method comprises the following steps: 1) Select pure iron raw material, requiring P≤0.002wt%, S≤0.002wt%, Si≤0.01wt%, Mn≤0.01wt%, Al≤0.01wt%, Ti≤0.001wt%, C≤0.2wt%; select metal chromium JCr99-A raw material, requiring P≤0.002wt%, S≤0.005wt%, Si≤0.1wt%, Al≤0.2wt%; 2) According to the composition of ferrochrome, pure iron, metallic chromium JCr99-A raw materials and ultra-pure graphite carbon blocks are loaded into the furnace for vacuum induction furnace smelting; 3) The refined molten steel is subjected to low temperature mold casting, with the tapping temperature being 1580-1590°C to obtain an ingot; 4) Under atmospheric conditions, the ingot obtained in step 3) is subjected to electroslag remelting and purification, the purified slag is composed of CaF2, Al2O3, and CaO, and the mass ratio thereof is CaF2:Al2O3:CaO=4:3:3, and the purified slag is required to have SiO2+MnO+FeO≤1wt% after the ingredients are prepared.

3. The preparation method according to claim 2, characterized in that: In step 2), the carbon content of the ultrapure graphite carbon block is controlled to be 0.2%-0.3%, the vacuum degree is required to be below 1Pa when melting begins, high power melting is required, the refining temperature is 1600±10°C, and the refining time is greater than 30 minutes.

4. The preparation method according to claim 2, characterized in that: In step 2), after the charge is melted, the vacuum degree of the induction furnace is not higher than 1Pa during vacuum deep deoxidation in the refining period, and the holding time is not less than 50min. Samples are taken for analysis of [N] in the later stage of refining. If [N] ≤ 0.01wt%, stir for 5 minutes and proceed to the next step. If [N] > 0.01wt%, continue to add ultrapure graphite carbon blocks to continue deoxidation and denitrification to ensure that [N] ≤ 0.01wt% at the end of refining.

5. The preparation method according to claim 2, characterized in that: In step 2), at the end of vacuum deep deoxidation in the refining stage, 0.15-0.20 kg / t of cerium, lanthanum or a mixture of lanthanum, cerium, praseodymium and neodymium is added through a vacuum silo.

6. The preparation method according to claim 2, characterized in that: In step 3), after mold casting, the mold is allowed to be broken after furnace cooling for 15 minutes, and a heating agent and a covering agent are added to the surface of the ingot. The ingot is demolded and air-cooled. The specification limit of the ingot is based on whether it can be directly used as an electroslag remelting consumable electrode after peeling.

7. The preparation method according to claim 2, characterized in that: In step 4), the ingot shape is Φ250 mm and the slag amount is 17±2 kg / t.

8. Use of the ultra-low sulfur ultra-pure ferrochrome according to claim 1 in the preparation of high cobalt-nickel secondary hardening steel.

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