CN109022925B - Method for reducing Laves phase in nickel-based superalloy steel ingot - Google Patents
Method for reducing Laves phase in nickel-based superalloy steel ingot Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C19/00—Alloys based on nickel or cobalt
- C22C19/03—Alloys based on nickel or cobalt based on nickel
- C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
- C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
- C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C1/00—Making non-ferrous alloys
- C22C1/02—Making non-ferrous alloys by melting
- C22C1/023—Alloys based on nickel
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- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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- C22C1/03—Making non-ferrous alloys by melting using master alloys
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- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
- C22F1/10—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of nickel or cobalt or alloys based thereon
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Abstract
The invention relates to a nickel-base high-temperature alloy steelThe method for preparing the Laves phase in the ingot comprises the following steps: 1) taking a nickel-based superalloy as a master alloy; 2) taking a master alloy, and carrying out vacuum induction melting: refining after full melting, wherein the vacuum degree at the final stage of refining is more than or equal to 3Pa, closing a valve, charging Ar to 7-9kPa, adding ferrovanadium intermediate alloy, fully stirring and oscillating, adjusting the temperature to 1470 and 1500 ℃ after 5min, continuously casting at a slow speed, and discharging to obtain steel ingots; 3) electroslag smelting: using CaF as mass percentage2：CaO：Al2O3MgO = 60: 15: 20: 5 electroslag slag, 4) homogenizing annealing at 1140 ℃ for × 24h, the precipitation amount of Laves phase in the solidification process of the steel ingot obtained by the method is obviously reduced, the uniformity of the steel ingot structure is improved, the difficulty of subsequent homogenizing treatment of the steel ingot is reduced, and the mechanical property of the nickel-based superalloy can be ensured.
Description
Technical Field
The invention relates to a metallurgical process, in particular to a method for reducing Laves phase in a nickel-based superalloy steel ingot.
Background
The molten steel is poured into a casting mould through a ladle and is solidified to form a steel ingot. After the molten steel is smelted, the molten steel is processed only by casting into ingots or billets with certain shapes. The quality of the steel ingot has very important influence on the subsequent production processes of forging, hot rolling, machining and the like. The steel ingot with excellent quality is an important foundation for producing alloy part products.
The nickel-based high-temperature alloy takes nickel element (Ni) as a matrix, the Ni content is usually more than 50 percent, and the nickel-based high-temperature alloy has higher strength and good oxidation resistance and fuel gas corrosion resistance in the temperature range of 650-1000 ℃. GH4169 is a typical representative of the alloy, and is made by imitating Inconel 718 alloy in the sixties of the last century, and in the next decades, a great deal of research work is carried out domestically, so that the quality of the domestic GH4169 alloy is continuously improved, and the GH4169 alloy is widely applied to manufacturing of key parts in the fields of aviation, nuclear energy, petroleum industry and the like.
In GH4169, Nb and Mo are considered as very important alloying elements, and they often play an important role in changing the microstructure and mechanical properties of the alloy. In GB/T30566-2014 GH4169 alloy bar, forging and ring, the content ranges of Nb and Mo in the alloy are respectively 4.75-5.50% and 2.8-3.3%, and the Nb and the Mo form a gamma' strengthening phase to play a key role in strengthening and become the most main segregation elements in the alloy during the solidification process of the alloy steel ingot. Particularly, in the solidification stage of steel ingots, a large amount of harmful Laves phases rich in Nb and Mo are precipitated, so that the phenomena of local enrichment of Nb and Mo in solidification structures and depletion of Nb and Mo in matrixes are caused. The Laves phase is generally considered to be an important reason for influencing the high-temperature performance of the alloy and causing the crack initiation of parts in the service process.
Currently, a lot of researchers have made a lot of studies on how to improve and eliminate Laves in alloys. The following methods are mainly used: 1. the Laves phase is controlled in the process of laser additive manufacturing of the nickel-based high-temperature alloy, and the method can effectively control the precipitation behavior of the Laves phase in the process of laser additive manufacturing of the nickel-based high-temperature alloy, reduce the cracking sensitivity of parts manufactured by laser additive manufacturing and improve the microstructure through a laser modulation method; 2. eliminating Laves phase in the alloy by a homogenization heat treatment method. The method is a classical method for eliminating the Laves phase in the manufacturing process of the nickel-based high-temperature alloy, and Nb and Mo elements in an alloy steel ingot can be diffused at a high enough temperature in the homogenization heat treatment process, so that the purpose of reducing and eliminating the Laves phase is achieved.
However, the above method, especially the homogenization heat treatment, eliminates the Laves phase in the alloy, the required temperature is high, the time is long, and in addition, the diffusion rate of the Nb and Mo elements in the GH4169 alloy is small, the micro segregation is serious, and the homogenization treatment is difficult.
If the precipitation quantity of the Laves phase in the steel ingot solidification process can be reduced, the difficulty of the later homogenization treatment is greatly reduced.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a method for reducing Laves phase in a nickel-based superalloy steel ingot.
The technical scheme of the invention is as follows:
a method for reducing Laves phase in nickel-based superalloy steel ingot comprises the following steps:
1) taking a nickel-based superalloy as a master alloy;
2) taking a master alloy, and carrying out vacuum induction melting: melting for at least 30 minutes, refining after full melting, wherein the refining power is 30-35kW, the time is 15 minutes, the vacuum degree at the final stage of refining is better than 3Pa, closing a valve, filling Ar to 7-9kPa, adding ferrovanadium intermediate alloy, fully electromagnetically and mechanically stirring and oscillating, adjusting the temperature to 1470 ℃ and 1500 ℃ after 5 minutes, continuously casting at a slow speed, breaking vacuum and discharging to obtain a steel ingot;
3) electroslag smelting: using CaF as mass percentage2：CaO：Al2O3: MgO is 60: 15: 20: 5, the smelting current of the electroslag slag is 3 +/-1 kA, the voltage is 45 +/-5V, and the feeding current is 1-2 kA/s;
4) homogenizing and annealing at 1140 ℃ for × 24 h;
the nickel-based high-temperature alloy in the step 1) comprises the following components in percentage by weight: less than or equal to 0.08 percent of C, less than or equal to 0.35 percent of Si, less than or equal to 0.35 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, 17.0 to 21.0 percent of Cr, 50.0 to 55.0 percent of Ni, 2.8 to 3.3 percent of Mo, less than or equal to 1.0 percent of Co, less than or equal to 0.30 percent of Cu, 0.20 to 0.80 percent of Al, less than or equal to 0.006 percent of B, 4.75 to 5.5 percent of Nb, 0.65 to 1..
And 2) obtaining the ferrovanadium intermediate alloy, wherein the vanadium element accounts for 50% by mass.
The final addition amount of the vanadium element is 0.2-1.0% of the weight of the master alloy.
Vanadium belongs to rare metal materials, has high melting point and is not easy to melt into an alloy matrix. Compared with a simple substance of vanadium, the ferrovanadium intermediate alloy has the advantages of lower melting point, higher dissolving speed and more stable actual yield, and is widely applied to accurate addition and component adjustment of elements in the alloy production process. Compared with the method for adding the simple substance of vanadium, the method adopts the ferrovanadium intermediate alloy with 50 percent of vanadium by mass, so that the melting temperature of the alloy is reduced when the nickel-based high-temperature alloy is prepared, the melting time of the metal material is shortened, and the melting temperature is reduced. Meanwhile, the ferrovanadium intermediate alloy is added before steel ingot casting, so that the burning loss of rare metal vanadium can be reduced, and the formation of oxides of the rare metal vanadium can be reduced, thereby obtaining a metal material with accurate chemical components and uniform distribution and higher element yield.
The applicant verifies through experiments that when no ferrovanadium intermediate alloy is added, a large white and bright Laves phase is obviously separated out from the GH4169 steel ingot structure, and Nb and Mo elements are seriously segregated; after the ferrovanadium intermediate alloy is added, the Laves phase precipitation is obviously reduced, and the integral structure uniformity of the steel ingot is improved; after homogenization for 24 hours, the ingots without vanadium addition (example 1) still have Laves phase, while the ingots with vanadium addition in examples 2-4 have no Laves phase. The method greatly reduces the homogenization treatment time and obviously improves the solidification structure of the steel ingot.
The steel ingot obtained by the method has the advantages that the precipitation amount of the Laves phase is obviously reduced, the subsequent homogenization treatment difficulty is greatly reduced, the homogenization treatment time is shortened, the crack initiation in the subsequent processing and service processes is reduced, and the mechanical property is not obviously changed.
Drawings
FIG. 1 is a scanning electron micrograph (a) and an energy spectrum analysis (b) of a Laves phase of a microstructure of a steel ingot in example 1;
FIG. 2 is a metallographic structure of a steel ingot according to examples 1 to 4, wherein a to d respectively show a metallographic structure of example 1, a metallographic structure of example 2, a metallographic structure of example 3, and a metallographic structure of example 4 in this order;
FIG. 3 is a graph showing the change of the volume fraction of the precipitated Laves phase in the steel ingot in examples 1 to 4;
FIG. 4 is a metallographic structure of a steel ingot solidified after homogenization treatment in examples 1 to 4, wherein a to d respectively show the metallographic structure of example 1, the metallographic structure of example 2, the metallographic structure of example 3, and the metallographic structure of example 4 in this order.
Detailed Description
The invention is further illustrated by the following examples:
the GH4169 nickel-based high-temperature alloy (master alloy) comprises the following components in percentage by mass: less than or equal to 0.08 percent of C, less than or equal to 0.35 percent of Si, less than or equal to 0.35 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, 17.0 to 21.0 percent of Cr, 50.0 to 55.0 percent of Ni, 2.8 to 3.3 percent of Mo, less than or equal to 1.0 percent of Co, less than or equal to 0.30 percent of Cu, 0.20 to 0.80 percent of Al, less than or equal to 0.006 percent of B, 4.75 to 5.5 percent of Nb, 0.65 to 1. The components are all in percentage by mass. 300Kg of alloy is smelted as mother alloy for standby.
Example 1
Taking 50Kg of master alloy, carrying out vacuum induction melting and casting to obtain a steel ingot. Taking a metallographic sample for microscopic structure observation and analysis, then carrying out electroslag smelting on the master alloy, wherein the weight of the master alloy is about 5-7kg and the mass percent of the master alloy is CaF2：CaO：Al2O3: MgO is 60: 15: 20: 5 of electroslag slag with a crystallizer diameter of
Smelting at 3 +/-1 kA and 45 +/-5V, feeding at 1-2kA/s, homogenizing and annealing at 1140 deg.c for × 24 hr, maintaining at 1080 +/-15 deg.c for 120min, forging at the initial forging temperature of 1080 deg.c, the final forging temperature of 980 deg.c, and the total forging ratio of 4 to 4, and measuring the mechanical performance.
Referring to fig. 1, (a) and (b) in fig. 1 represent the composition of the Laves phase and the scanning electron microscope image of the Laves phase in the steel ingot structure of example 1, respectively. It can be seen that a large amount of Nb and Mo elements are enriched in the Laves phase, which inevitably causes the depletion of the two elements in the matrix and the enrichment of other elements, so that the alloy elements are unevenly distributed in the steel ingot structure, and considerable difficulty is brought to the subsequent homogenization annealing. If the Laves phase precipitation can be reduced or reduced, the uniform distribution of elements and tissues is promoted, the difficulty of the subsequent process is inevitably reduced, and the time and the energy cost are saved.
Example 2
Taking 50Kg of master alloy, adding ferrovanadium intermediate alloy to ensure that the weight percentage of vanadium element is 0.2 percent of the weight of the master alloy, carrying out vacuum induction melting and casting, taking a metallographic phase sample for observing and analyzing a microstructure, and measuring the mechanical property of the metallographic phase sample by the same steps as in example 1.
Example 3
Taking 50Kg of master alloy, adding ferrovanadium intermediate alloy to ensure that the weight percentage of vanadium element is 0.5 percent of the weight of the master alloy, carrying out vacuum induction melting and casting, taking a metallographic phase sample for observing and analyzing a microstructure, and measuring the mechanical property of the metallographic phase sample by the same steps as in example 1.
Example 4
Taking 50Kg of master alloy, adding ferrovanadium intermediate alloy to ensure that the weight percentage of vanadium element is 1.0 percent of the weight of the master alloy, carrying out vacuum induction melting and casting, taking a metallographic phase sample, carrying out microscopic structure observation and analyzing the rest steps, and determining the mechanical property of the metallographic phase sample in the same way as in example 1.
Metallographic observation, scanning electron microscope observation and energy spectrum analysis were performed on the steel ingot solidification structure of the above example.
Referring to FIG. 2, (a-d) in FIG. 2 represent metallographic micrographs of the steel ingots of examples 1-4, respectively. As can be seen from the figure, the addition of vanadium element reduces the precipitation of Laves phase, and the distribution is more dispersed.
Referring to fig. 3, fig. 3 shows that the Laves phase volume fraction in the ingot gradually decreases and stabilizes as the vanadium content increases.
In order to further illustrate the influence of the method of the invention on the GH4169 steel ingot structure, metallographic microstructure observation was performed on the steel ingot solidified structure after the homogenization annealing in the above examples. The microstructure images are shown in FIG. 4, in which (a-d) represent metallographic micrographs of the steel ingots of examples 1-4 after the same heat treatment of the homogenization annealing, respectively.
The mechanical properties of examples 1-4 were measured and the values are shown in the following table:
and (4) conclusion: after the same homogenization heat treatment process, the master alloy of example 1 still had significant bulk Laves phase not redissolved into the base alloy, and the Laves phases of examples 2-4 had substantially all redissolved, leaving only long chain and dotted carbonitrides. Therefore, the method provided by the invention obviously reduces the difficulty of subsequent homogenization heat treatment of the steel ingot structure. The method does not obviously affect the final mechanical property of the GH4169 nickel-based high-temperature alloy on the basis of improving the steel ingot structure and the element distribution uniformity.
Claims (5)
1. A method for reducing Laves phase in a nickel-based superalloy steel ingot is characterized by comprising the following steps:
1) taking a nickel-based high-temperature alloy as a master alloy, wherein the nickel-based high-temperature alloy is GH4169 nickel-based high-temperature alloy;
2) taking a master alloy, and carrying out vacuum induction melting: refining after full melting, wherein the vacuum degree at the final stage of refining is more than or equal to 3Pa, closing a valve, charging Ar to 7-9kPa, adding ferrovanadium intermediate alloy, fully stirring and oscillating, adjusting the temperature to 1470 and 1500 ℃ after 5min, continuously casting at a slow speed, and discharging to obtain steel ingots;
3) electroslag smelting: using CaF as mass percentage2：CaO：Al2O3: MgO is 60: 15: 20: 5, the smelting current of the electroslag slag is 3 +/-1 kA, the voltage is 45 +/-5V, and the feeding current is 1-2 kA/s;
4) homogenizing annealing at 1140 deg.c for × 24 hr.
2. The method of claim 1, wherein: the nickel-based high-temperature alloy in the step 1) comprises the following components in percentage by mass: less than or equal to 0.08 percent of C, less than or equal to 0.35 percent of Si, less than or equal to 0.35 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, 17.0 to 21.0 percent of Cr, 50.0 to 55.0 percent of Ni, 2.8 to 3.3 percent of Mo, less than or equal to 1.0 percent of Co, less than or equal to 0.30 percent of Cu, 0.20 to 0.80 percent of Al, less than or equal to 0.006 percent of B, 4.75 to 5.5 percent of Nb, 0.65 to 1..
3. The method of claim 1, wherein: and 2) obtaining the ferrovanadium intermediate alloy, wherein the vanadium element accounts for 50% by mass.
4. The method of claim 3, wherein: the final addition amount of the vanadium element is 0.2-1.0% of the weight of the master alloy.
5. The method of claim 1, wherein: the refining power is 30-35kW, and the refining time is 15 minutes.
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| CN110499483B (en) * | 2019-09-24 | 2020-06-05 | 西北有色金属研究院 | High-alloying GH4720Li alloy single-stage homogenization annealing process |
| CN110846515A (en) * | 2019-11-21 | 2020-02-28 | 重庆材料研究院有限公司 | Preparation method of nickel-based alloy 690 with ultralow gas content |
| CN111809128B (en) * | 2020-06-06 | 2022-04-08 | 北京钢研高纳科技股份有限公司 | Method for rapidly dissolving and deforming Laves phase in high-temperature alloy ingot by pulse current |
| CN113046566B (en) * | 2021-03-09 | 2022-10-14 | 陕西科技大学 | Laves phase and niobium-silicon compound synergistically enhanced in-situ self-generated composite material and preparation process thereof |
| CN113444889A (en) * | 2021-05-19 | 2021-09-28 | 重庆材料研究院有限公司 | Method for uniformly distributing aluminum and titanium of nickel-based alloy electroslag ingot |
| CN114855047B (en) * | 2022-04-08 | 2022-11-18 | 大连理工大学 | Controllable Cr of Laves phase x MoNbWTi refractory high-entropy alloy and preparation method thereof |
| CN114921674B (en) * | 2022-05-11 | 2023-03-14 | 重庆材料研究院有限公司 | Vacuum induction melting method of 625 alloy |
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