Preparation method of ultrahigh-strength C250 super-large-specification vacuum consumable steel ingot

Abstract

The invention relates to the technical field of metal material manufacturing, and particularly discloses a preparation method of an ultrahigh-strength C250 super-large-specification vacuum consumable steel ingot. The preparation method comprises the steps of vacuum induction smelting and vacuum consumable remelting. And in the vacuum induction furnace alloying process, chemical components are accurately controlled, specifically, the chemical components comprise 0.006 + / -0.001 wt% of C, 18.0 + / -0.20 wt% of Ni, 8.0 + / -0.05 wt% of Co, 5.0 + / -0.10 wt% of Mo, 0.40 + / -0.01 wt% of Ti and 0.10 + / -0.02 wt% of Al. The problems of chemical component point control, chemical component uniformity control and the like of a C250 ultra-large-specification vacuum induction phi710mm electrode and a phi810mm vacuum consumable steel ingot are solved, and the metallurgical quality of the ultra-large-specification vacuum consumable steel ingot completely reaches the physical level of a small-specification steel bar.

Description

Technical Field

[0001] The present application relates to the technical field of metal material manufacturing, and more specifically, to a method for preparing ultra-high strength C250 ultra-large size vacuum consumable steel ingots. Background Art

[0002] An aircraft engine is a highly complex and sophisticated thermal machine that provides aircraft with the power they need to fly. As the heart of an aircraft, it is known as the "flower of industry" and directly affects the performance, reliability and economy of an aircraft. It is an important manifestation of a country's scientific, industrial and national defense strength.

[0003] With the rapid development of my country's national defense construction, the updating and iteration of weapons and equipment has accelerated, and aircraft have developed towards large-scale and long-range, and the raw materials for engine shafts have developed towards large specifications and large sizes. At present, the C250 steel used for the shafts of civil aviation engines in my country adopts vacuum induction and vacuum consumable production processes. The production specifications of steel bars are mainly Φ≤304mm, and the size of the vacuum consumable steel ingots used is Φ660mm. In order to meet the needs of large-scale, the specifications of raw materials are required to be greatly increased, from the original Φ≤304mm to Φ≤375mm; at the same time, in order to increase the utilization rate of forgings in each batch of furnaces, it is necessary to increase the weight of the finished steel bars delivered by expanding the size and weight of the steel ingots, from the original Φ660mm steel ingots to Φ810mm steel ingots.

[0004] There is no mature technology for vacuum induction smelting and consumable remelting of ultra-large vacuum consumable ingots of C250 steel. It is necessary to conduct process exploration, testing and trial production of vacuum smelting of 12-ton vacuum induction Φ710mm electrode rods and consumable remelting of Φ810mm ingots, so that the comprehensive metallurgical quality of ultra-large C250 steel bars can fully meet the technical specifications of small-sized Φ300mm round bars, which makes production difficult. Summary of the invention

[0005] In view of the above relevant analysis, the present application aims to provide a method for preparing ultra-high strength C250 ultra-large size vacuum consumable steel ingots, which can prominently solve the following technical problems: (1) precise point control of the chemical composition of Φ710mm electrode rods produced by a 12-ton vacuum induction furnace; (2) low segregation control of the composition structure of Φ810mm steel ingots produced by a 12-ton vacuum consumable furnace, ensuring the uniformity of the chemical composition of the head and tail of the ultra-large size steel ingots.

[0006] The present application provides a method for preparing ultra-high strength C250 ultra-large size vacuum consumable steel ingot, which adopts a smelting method of a vacuum induction furnace + a vacuum consumable furnace to produce a chemical composition of C0.006±0.001wt%, Ni18.0±0.20wt%, Co8.0±0.05wt%, Mo5.0±0.10wt%, Ti0.40±0.01wt%, and Al0.10±0.02wt%.

[0007] The preparation method includes vacuum induction smelting and vacuum consumable remelting; In the vacuum induction smelting, the chemical composition batching requirements are as follows: C 0.006±0.001wt%; Mn≤0.05wt%; Si≤0.05wt%; S≤0.001wt%; P≤0.005wt%; Ni 18.0±0.20wt%; Co 8.0±0.05wt%; Ti 0.40±0.01wt%; Mo 5.0±0.10wt%; AI 0.10±0.02wt%; O≤0.0010wt%; N≤0.0010wt%; Vacuum induction melting process: full melting temperature T is 1490-1540℃; Vacuum induction refining process: refining temperature T is 1540-1610℃, vacuum degree ≤5Pa; Alloying process in vacuum induction furnace: precise control of chemical composition, specifically C0.006±0.001wt%, Ni18.0±0.20wt%, Co8.0±0.05wt%, Mo5.0±0.10wt%, Ti0.40±0.01wt%, Al0.10±0.02wt%; Vacuum induction pouring process: pouring temperature T is 1550-1580℃, vacuum degree ≤300Pa; Cooling process of vacuum induction electrode rod: The cooling time t of electrode rod in mold is 1-3h, and air cooling is carried out after demoulding; Vacuum induction electrode rod surface polishing; In the vacuum consumable remelting, the vacuum consumable melting stage: melting rate R = 5.5-6.5Kg / min; The vacuum consumable steel ingot is air-cooled and the surface is polished.

[0008] Optionally, the raw materials for the vacuum induction smelting are composed of refined steel, alloy materials, and metal materials, and the raw material composition is required to be accurate and the surface is free of rust, oil, and dirt.

[0009] Optionally, the chemical composition of the vacuum consumable steel ingot is ensured to be precisely controlled to ensure uniform chemical composition.

[0010] In summary, this application has the following beneficial effects: (1) This application adopts a 12-ton vacuum induction furnace, and realizes the control of chemical element points in steel through precise batching and accurate calculation. By controlling the content of Mn, Si, S, and P in steel, the generation and aggregation of inclusions in steel are reduced, the purity of steel is improved, and a high degree of matching of strength and toughness of steel is achieved.

[0011] (2) In the vacuum induction furnace refining process, the present application adopts a low vacuum stirring method to continuously remove O and N in the steel, thereby improving the purity of the molten steel and the uniformity of the chemical composition of the electrode rod.

[0012] (3) In the vacuum induction furnace pouring process, the present application adopts low-temperature pouring to reduce the shrinkage holes of the oversized electrode rods, so that the chemical composition segregation area moves upward, and the chemical composition of the oversized electrode rods is uniform and consistent.

[0013] (4) In the vacuum consumable remelting process, the present application strictly controls the electrode melting rate (R=5.5-6.5Kg / min) to improve the uniformity of macrostructure of ultra-large steel bars and solve the problems of radial segregation of macrostructure and excessive annular patterns. DETAILED DESCRIPTION

[0014] Before describing the embodiments of the present application in detail, it should be understood that the terms used herein are only used for the purpose of describing specific embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by ordinary technicians in the field to which the terms belong.

[0015] At present, the C250 steel for civil aviation engine shafts in my country is manufactured by vacuum induction + vacuum consumable smelting method. In order to meet the needs of large-scale and long-distance development, the Φ≤304mm steel bars produced by the current mature Φ660mm steel ingots can no longer meet the requirements. It is necessary to increase the size and weight of the steel ingots, increase the size of the finished steel bars, increase the delivery weight of the steel bars, and improve the utilization rate of each batch of forgings to further meet the needs of large-scale tasks.

[0016] As the size of steel ingots continues to expand, the inclusions and chemical composition of steel ingots are seriously segregated, which greatly affects the performance indicators of super-large steel ingots. In order to meet the performance specifications of small specifications, the production of ultra-high strength C250 super-large steel ingots is an urgent problem that needs to be solved in my country.

[0017] This application achieves precise point control of the composition of large-size Φ710mm electrode rods and low segregation control of Φ810mm vacuum consumable steel ingots by accurately controlling the steps of the vacuum induction smelting production process. The comprehensive mechanical properties of the ultra-large-size steel ingots can meet the technical specifications and are stable.

[0018] The present application provides a method for preparing ultra-high strength C250 ultra-large vacuum consumable steel ingots, using a 12-ton vacuum induction furnace. The preparation method comprises: (1) Vacuum induction smelting The raw materials for vacuum induction furnace smelting are C250 steel special ultra-pure refined steel; Ni plate, M-Co, M-Mo, M-Ti, M-Al and other metal materials; the raw materials are required to have accurate chemical composition and no rust, oil or dirt on the surface. The specific control requirements for the chemical composition (wt%) of the electrode rod are as follows: C 0.006±0.001wt%; Mn≤0.05wt%; Si≤0.05wt%; S≤0.001wt%; P≤0.005wt%; Ni 18.0±0.20wt%; Co 8.0±0.05wt%; Ti 0.40±0.01wt%; Mo 5.0±0.10wt%; AI0.10±0.02wt%; O≤0.0010wt%; N≤0.0010wt%.

[0019] Vacuum induction melting process: the total melting temperature T is 1490-1540℃.

[0020] Vacuum induction refining process: refining temperature T is 1540-1610℃, vacuum degree ≤5Pa.

[0021] Vacuum induction furnace alloying process: the chemical composition (wt%) is precisely controlled, specifically C0.006±0.001wt%, Ni18.0±0.20wt%, Co8.0±0.05wt%, Mo5.0±0.10wt%, Ti0.40±0.01wt%, Al0.10±0.02wt%.

[0022] Vacuum induction pouring process: pouring temperature T is 1550-1580℃, vacuum degree ≤300Pa.

[0023] Vacuum induction electrode rod cooling process: The electrode rod mold cooling time t is 1-3h, and air cooling is performed after demoulding.

[0024] The surface of the vacuum induction electrode rod is polished.

[0025] (2) Vacuum consumable remelting The beginning stage of vacuum self-consumption: voltage 21.0-24.0V; current 6-16KA.

[0026] Vacuum consumable melting stage: melting rate R = 5.5-6.5Kg / min; vacuum degree 0.35-045Pa.

[0027] The vacuum consumable steel ingot is air-cooled and the surface is polished.

[0028] Compared with the current C250 double vacuum technology, this application provides the vacuum induction smelting technology for ultra-large Φ810mm steel ingots for the first time, which is an unprecedented breakthrough in metallurgical technology.

[0029] The strict control of the vacuum consumable remelting process of the present application solves the problem of low-magnification uniformity of structure, chemical composition and inclusion segregation of super-large-sized steel ingots. The preparation method of the present application can obtain super-pure, super-high-strength C250 super-large-sized steel ingots, which are qualified by magnetic particle inspection.

[0030] By adopting the preparation method of the present application, the heat treatment mechanical properties of super-large-sized steel ingots are excellent, which can fully meet the technical index requirements of small-sized bars, and at the same time, the yield rate of steel ingots is greatly improved.

[0031] To make the purpose, technical solutions and advantages of this application clearer, the technical solutions in the embodiments of this application are described clearly and completely below. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of this application.

[0032] The present application is further described in detail below in conjunction with the embodiments and performance test results. Example Example 1

[0033] This embodiment provides a method for preparing ultra-high strength C250 ultra-large vacuum consumable steel ingot. This embodiment uses a 12-ton vacuum induction furnace.

[0034] The preparation method specifically comprises the following steps: (I) Vacuum induction furnace smelting 1. The raw materials for vacuum induction furnace smelting are C250 steel special ultra-pure refined steel; Ni plate, M-Co, M-Mo, M-Ti, M-Al and other metal materials; the raw materials are required to have accurate chemical composition and no rust, oil or dirt on the surface. The specific control requirements for the chemical composition points of the electrode rod are shown in Table 1.

[0035] 2. Vacuum induction melting process: Add the raw materials into the crucible in batches and melt them with electricity. The total melting temperature T is 1530℃.

[0036] 3. Vacuum induction refining process: After the charge is fully melted, evacuate the furnace for refining. The refining temperature T is 1575℃, stirring is performed, and the vacuum degree is 3.5Pa.

[0037] 4. Vacuum induction alloying process: After melting and refining the charge, samples were taken for analysis, including 0.005% C, 17.89% Ni, 5.05% Mo, 0.35% Ti, and 0.12% Al. According to the chemical composition requirements, the control points were accurately calculated and adjusted to complete the alloying process so that the chemical composition met the technical standard requirements.

[0038] 5. Vacuum induction pouring process: pouring is carried out after the chemical composition meets the technical standard requirements, the pouring temperature is 1555℃ and the vacuum degree is 230Pa.

[0039] 6. Cooling process of vacuum induction electrode rod: The electrode rod is mold-cooled for 2 hours and then air-cooled.

[0040] 7. Polishing the surface of vacuum induction electrode rod.

[0041] The chemical composition of the finished vacuum induction electrode rod is shown in Table 1.

[0042] Table 1 Chemical composition of finished electrode rod (wt%)

[0043] (II) Vacuum consumable remelting 1. The beginning stage of vacuum self-consumption: voltage 21.0-24.0V; current 6-16KA.

[0044] 2. Vacuum consumable melting stage: melting rate R = 6.5Kg / min; vacuum degree 0.41Pa.

[0045] 3. Vacuum self-consumable hot capping stage: the starting weight of the hot capping of the steel ingot is 500Kg; the ending weight of the hot capping of the steel ingot is 120Kg.

[0046] 4. Heat treatment process of vacuum consumable steel ingot: vacuum consumable steel ingot is air-cooled and surface polished. Example 2

[0047] This embodiment provides a method for preparing an ultra-high strength C250 ultra-large size vacuum consumable steel ingot.

[0048] The differences between this embodiment and embodiment 1 are as follows: (I) The chemical composition of the finished vacuum induction electrode rod is shown in Table 1. The differences in vacuum induction furnace smelting are as follows: The total melting temperature T of the vacuum induction melting process is 1525°C.

[0049] The refining temperature T of the vacuum induction refining process is 1580°C and the vacuum degree is 3.6Pa.

[0050] Vacuum induction alloying process: After melting and refining the charge, sampling and analysis were performed, including C 0.006%, Ni 17.83%, Mo4.97%, Ti 0.37%, and Al 0.07%. According to the control requirements of the electrode rod chemical composition requirements, precise calculations and adjustments were made to complete the alloying process so that the chemical composition meets the technical standard requirements.

[0051] The pouring temperature of the vacuum induction pouring process is 1560°C and the vacuum degree is 220Pa.

[0052] (II) The differences between vacuum consumable remelting are as follows: Vacuum consumable melting stage: melting rate R = 6.4Kg / min; vacuum degree 0.40Pa. Example 3

[0053] This embodiment provides a method for preparing an ultra-high strength C250 ultra-large size vacuum consumable steel ingot.

[0054] The differences between this embodiment and embodiment 1 are as follows: (I) The chemical composition of the finished vacuum induction electrode rod is shown in Table 1. The differences in vacuum induction furnace smelting are as follows: The total melting temperature T of the vacuum induction melting process is 1528°C.

[0055] The refining temperature T of the vacuum induction refining process is 1578°C and the vacuum degree is 3.5Pa.

[0056] Vacuum induction alloying process: After melting and refining the charge, sampling and analysis were performed, including C 0.006%, Ni 17.99%, Mo5.09%, Ti 0.37%, and Al 0.11%. According to the control requirements of the electrode rod chemical composition requirements, precise calculations and adjustments were made to complete the alloying process so that the chemical composition meets the technical standard requirements.

[0057] The pouring temperature of the vacuum induction pouring process is 1560°C and the vacuum degree is 225Pa.

[0058] (II) The differences between vacuum consumable remelting are as follows: Vacuum consumable melting stage: melting rate R = 6.3Kg / min; vacuum degree 0.45Pa. Performance testing

[0059] The following performance tests were performed on the ultra-high strength C250 ultra-large size vacuum consumable steel ingots prepared in the above examples.

[0060] 1. Chemical composition analysis and testing The detection method refers to "3 Sampling and sample preparation methods for finished product analysis" and "5 Allowable deviations of chemical composition of finished products" in GB / T222-2006 "Allowable tolerances for chemical composition of finished steel products" and GB / T223 "Chemical analysis methods for steel and alloys".

[0061] The test results are shown in Table 2.

[0062] Table 2 Chemical composition of steel ingot (wt%)

[0063] 2. Low-magnification tissue detection The test method refers to ASTM A604-2007 "Standard Practice for Macroetching of Consumable Electrode Remelted Steel Bars and Billets".

[0064] The test results are shown in Table 3.

[0065] Table 3 Low-magnification tissue detection results

[0066] (III) Mechanical properties testing The test methods refer to GB / T 228 "Room Temperature Tensile Test Method for Metallic Materials", GB / T 229 "Charpy Notch Impact Test Method for Metallic Materials", GB / T 230 "Rockwell Hardness Test Method for Metallic Materials", and GB / T4161 "Plane Strain Fracture Toughness KIC Test Method for Metallic Materials".

[0067] The test results are shown in Table 4.

[0068] Table 4 Mechanical properties test results

[0069] (IV) Non-metallic impurities and grain size detection The detection method refers to GB / T 10561 "Standard rating chart microscopic examination method for determination of non-metallic inclusion content in steel".

[0070] The test results are shown in Table 5.

[0071] Table 5 Non-metallic impurities and grain size

[0072] According to the test results of Tables 2 to 5, the chemical composition, macrostructure, mechanical properties, non-metallic impurities and grain size of the ultra-high strength C250 ultra-large size vacuum consumable steel ingot prepared by the preparation method of the present application can meet the requirements of the technical standards. Comparative Example

[0073] This comparative example provides a method for preparing an ultra-high strength C250 ultra-large vacuum consumable steel ingot. The difference between this comparative example and Example 1 is that: (ii) the melting rate R in the vacuum consumable melting stage in the vacuum consumable remelting step is 7.0 Kg / min. The remaining operation steps are consistent with Example 1.

[0074] The ultra-high strength C250 ultra-large vacuum consumable steel ingot prepared in the above preparation example was subjected to low-power microstructure testing. The testing method was based on ASTM A604-2007 "Standard Practice for Macroscopic Etching Tests of Consumable Electrode Remelted Steel Bars and Billets".

[0075] The test results are shown in Table 6.

[0076] Table 6 Macroscopic tissue test results of Example 1 and Comparative Example

[0077] It can be seen from Table 6 that by comparing the macrostructure detection results of Example 1 and the comparative example, when the melting rate R=7.0Kg / min in the vacuum consumable smelting stage in the vacuum consumable remelting step, it will obviously affect the radial segregation and annular pattern results of the ultra-high strength C250 ultra-large specification vacuum consumable steel ingot, thereby failing to meet the requirements of the corresponding technical standards.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing ultra-high strength C250 ultra-large size vacuum consumable steel ingot, characterized in that: The preparation method includes vacuum induction smelting and vacuum consumable remelting; In the vacuum induction smelting, the chemical composition batching requirements are as follows: C 0.006±0.001wt%; Mn≤0.05wt%; Si≤0.05wt%; S≤0.001wt%; P≤0.005wt%; Ni 18.0±0.20wt%; Co 8.0±0.05wt%; Ti 0.40±0.01wt%; Mo 5.0±0.10wt%; AI 0.10±0.02wt%; O≤0.0010wt%; N≤0.0010wt%; Vacuum induction melting process: full melting temperature T is 1490-1540℃; Vacuum induction refining process: refining temperature T is 1540-1610℃, vacuum degree ≤5Pa; Alloying process in vacuum induction furnace: precise control of chemical composition, specifically C0.006±0.001wt%, Ni18.0±0.20wt%, Co8.0±0.05wt%, Mo5.0±0.10wt%, Ti0.40±0.01wt%, Al0.10±0.02wt%; Vacuum induction pouring process: pouring temperature T is 1550-1580℃, vacuum degree ≤300Pa; Cooling process of vacuum induction electrode rod: The cooling time t of electrode rod in mold is 1-3h, and air cooling is carried out after demoulding; Vacuum induction electrode rod surface polishing; In the vacuum consumable remelting, the vacuum consumable melting stage: melting rate R = 5.5-6.5Kg / min; The vacuum consumable steel ingot is air-cooled and the surface is polished.

2. The method for preparing the ultra-high strength C250 ultra-large size vacuum consumable steel ingot according to claim 1, characterized in that: The raw materials for vacuum induction smelting are composed of refined steel, alloy materials and metal materials, and the raw materials are required to have accurate composition and be free of rust, oil and dirt on the surface.

3. The method for preparing the ultra-high strength C250 ultra-large size vacuum consumable steel ingot according to claim 1, characterized in that: The chemical composition of the vacuum consumable steel ingot is ensured to be precisely controlled to ensure uniform chemical composition.

4. The method for preparing the ultra-high strength C250 ultra-large size vacuum consumable steel ingot according to claim 1, characterized in that: The vacuum induction smelting adopts a 12-ton vacuum induction furnace.

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