Rare earth element control method for high-temperature alloy purification smelting
Technical Field
The invention relates to the technical field of high-temperature alloy master alloy purification smelting, in particular to a rare earth element control method for high-temperature alloy purification smelting.
Background
The high-temperature alloy has excellent high-temperature oxidation resistance and mechanical property, and is often used for manufacturing key structural parts of engines such as turbines, gas turbines and the like which work in an ultrahigh-temperature environment. Research shows that in an alloy smelting room, when the content of gas elements such as O, N, S in molten steel is high, fine nonmetallic inclusions are easily precipitated from the alloy during solidification, the alloy has certain tissue inheritance, and can be left in an alloy casting to seriously influence the service performance of the alloy casting. Therefore, the control of the content of gas elements in the advanced high-temperature alloy is often extremely strict, and the purification smelting technology of the alloy is increasingly emphasized by the worldwide material research workers. At present, a vacuum induction furnace is mainly used for producing the high-temperature alloy, although reaction between molten steel and air can be avoided during alloy smelting, the purity of a raw material simple substance is low, and the reaction between the molten steel and a refractory material during smelting is still the main reason that the gas content in the nickel-based high-temperature alloy is difficult to further reduce. Although the gas content in the alloy product is reduced by using high-purity raw materials and refractory materials with higher stability, the two modes inevitably increase the production cost of the alloy greatly and are not beneficial to large-scale production.
Research shows that the addition of a small amount of rare earth elements into the alloy has the effects of purifying the alloy grain boundary and improving the purity of the alloy, and can greatly improve the mechanical property of the alloy, so that the rare earth elements are often used as deep deoxidizers during the alloy smelting at present. However, the adding time of the rare earth elements during smelting is difficult to master, and the deep purification effect of the rare earth elements cannot be fully exerted by adding the rare earth elements too early or too late. Due to the active chemical property of the rare earth elements, when the content of the rare earth elements in the alloy exceeds 0.2 percent or the rare earth elements do not exist in the master alloy completely in the form of solid solution atoms, the secondary oxidation of the alloy during remelting is easily caused, a large amount of scum is generated, and the sand sticking phenomenon is also easily caused during casting. Therefore, when a small amount of rare earth elements exist in the designed components of the alloy, how to accurately control the content of the rare earth elements in the alloy and reduce the dross content during remelting of the mother alloy containing the rare earth elements is a key problem to be solved.
China is a big country for producing rare earth elements, the reserve amount and export amount of rare earth are the first world, but the production technology of the high-temperature alloy in China has a larger gap compared with developed countries, so that the utilization rate of the rare earth elements is improved by designing a rare earth element control method for purifying and smelting the high-temperature alloy, the purification degree of the high-temperature alloy is improved, the development of the rare earth-containing alloy in China is promoted, and the method has important social significance and economic significance for the development of alloy smelting technology.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a rare earth element control method for high-temperature alloy purification smelting. The method can achieve the effect of accurately controlling the content of the rare earth element, obviously reduce the content of scum during remelting and improve the purity of the master alloy.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a rare earth element control method for purifying and smelting high-temperature alloy is characterized in that a rare earth intermediate alloy is added in the process of smelting the high-temperature alloy so as to avoid oxidation generated during the storage of raw materials and reduce the burning loss rate of the rare earth element during smelting; the rare earth intermediate alloy is one or more of Ni-Ce intermediate alloy, Al-Y intermediate alloy and Al-La intermediate alloy.
In the process of smelting the high-temperature alloy, calculating the oxygen supply and sulfur supply amount of the alloy raw materials according to the formulas (1) to (2);
in the formulas (1) to (2), i represents the ith raw material (i is 1, 2, … …, n is the number of the raw materials) for smelting the high-temperature alloy; c
OIs the total weight content of O element in all raw materials, C
SIs the total weight content of the S element in all raw materials,
is the weight content of the O element in the ith raw material,
is the weight content of S element in the ith raw material, C
iThe weight percentage concentration is added for the design of the ith raw material in the alloy.
The process for smelting the high-temperature alloy comprises the following steps:
(1) preparing alloy raw materials according to the chemical components of the high-temperature alloy, wherein the rare earth elements are prepared in a rare earth intermediate alloy mode;
(2) adding an alloy raw material without Al and rare earth intermediate alloy into a vacuum induction smelting furnace for melting, and carrying out high-temperature refining;
(3) cooling after high-temperature refining, and adding rare earth intermediate alloy, Al metal and residual alloy raw materials in the cooling process; cooling to low-temperature refining temperature and then carrying out low-temperature refining;
(4) and casting the alloy melt into a master alloy ingot.
In the process of smelting the high-temperature alloy, the adding time of the rare earth elements depends on the purpose of adding the rare earth.
If the main purpose of adding the rare earth is purification, the rare earth element needs to be added after high-temperature refining and when the temperature is reduced to 10-20 ℃ higher than the low-temperature refining temperature, and the rare earth element is added according to the weight content calculated by the formula (3), so that the deep purification effect can be achieved, the O content in the obtained product alloy is lower than 6ppm, the N content is lower than 5ppm, the S content is lower than 1ppm, and the rare earth element content is lower than 10ppm, the purity of the alloy is ensured, the rare earth residual quantity in the alloy is extremely low, and secondary oxidation during remelting is avoided.
In the formula (3), CRAREDenotes the amount of addition of the rare earth element, max (C)O,CS) The term "addition of rare earth" means deoxidation or desulfurization, and is used to indicate that the main purpose of deoxidation is calculated based on the content of the O element in the alloy material, and that the main purpose of desulfurization is calculated based on the content of the S element in the alloy material.
If the rare earth element is required by the components in the target alloy, the rare earth element needs to be added after high-temperature refining, and the temperature of the molten steel is 40-70 ℃ higher than the low-temperature refining point, or the rare earth element is added after Al simple substance is added, and the adding content is determined according to the type of the rare earth element. When the rare earth element is the component requirement in the target alloy, the addition amount of the rare earth element is calculated according to the following formulas (4) to (6);
in formulae (4) to (6), c0According to this method, the error range between the actual measurement value and the design value of the rare earth element in the master alloy can be controlled within 20ppm for the design component content of the rare earth element, and the equations (4) to (6) are applied to the case where two or more rare earth elements are added simultaneously. The rare earth element is added at a higher temperature, so that the rare earth element can be fully alloyed with the molten steel, the scum content during remelting of the mother alloy containing the rare earth is obviously reduced, the purity of the mother alloy is ensured, and the effect of accurately controlling the content of the rare earth element can be achieved.
The invention has the advantages and positive effects that:
compared with the prior art, the method not only improves the purity of the mother alloy, reduces the content of O, N, S and other gas elements to an extremely low level, but also can achieve the effect of accurately controlling the content of rare earth elements, obviously reduces the content of scum during remelting and improves the purity of the mother alloy. The method is suitable for controlling the addition of various rare earth elements during the smelting of most high-temperature alloys, can select the types of the added rare earth elements according to actual needs, and is flexible and changeable and high in practicability.
Detailed Description
The rare earth element adding and controlling method provided by the invention comprises the following steps:
(1) designing the types and the contents of the rare earth to be added according to the formula (1) or the formulas (2) to (4) according to the requirements, and wrapping the rare earth by using an aluminum foil or a nickel foil for later use;
(2) if the main purpose of adding the rare earth element is deep deoxidation, adding the rare earth element raw material when the melt is refined at high temperature and cooled to 10-20 ℃ higher than the low-temperature refining point, and then refining at low temperature and casting to obtain a product master alloy;
(3) if the rare earth element is required by the target alloy component, the melt can be refined at high temperature and cooled to 40-70 ℃ higher than the low-temperature refining point, or Al simple substance is added, the temperature is kept for 1-10 min, the temperature keeping time is changed along with the mass of the charging materials, and according to experience, the relationship between the temperature keeping time and the charging materials is shown in table 1:
TABLE 1 Heat preservation time corresponding to different charging material quality
And after the surface of the melt is stable, cooling to a low-temperature refining point for low-temperature refining and casting to obtain the product master alloy.
Example 1:
smelting master alloy K417G, smelting quality 10kg, adding rare earth element Y, in order to reduce O content in the alloy.
The elemental raw material in the master alloy was calculated to have an O content of about 146ppm and an S content of about 39ppm, and the Al — Y master alloy to be added (Y content 28.8 wt.% in the master alloy) was calculated to have a content of about 51ppm, i.e., 0.005 wt.%, according to equation (3), and was wrapped with nickel foil for future use.
Alloy preparation process (vacuum induction furnace, vacuum degree higher than 10)-1Pa):
(1) High-temperature refining: multiplying at 1500 ℃ for 10 min;
(2) when the temperature of the melt is reduced to about 1390 ℃, adding elements such as Al, Ti, B, Zr and the like, increasing the temperature of the melt to 1450 ℃, standing for 1min after the liquid level is stable, and then reducing the temperature;
(3) adding Al-Y intermediate alloy when the temperature of the melt is reduced to 1420 ℃, and preserving heat for 1 min;
(4) low-temperature refining: multiplying at 1400 ℃ for 5 min;
(5) pouring temperature: 1430 ℃.
The product master alloy obtained by the method has O, N, S scum content during remelting compared with the traditional process, such as shown in the following table 2:
TABLE 2
Example 2
Smelting alloy K465 with smelting mass of 500kg, and adding rare earth elements Y and Ce to obtain a master alloy with the contents of 0.002 wt.% of Y and 0.005 wt.% of Ce.
The content of O in the raw material simple substance in the master alloy was calculated to be about 101ppm, the content of S was calculated to be about 32ppm, the added Al-Y master alloy (Y content 28.8 wt.%), and the Ni-Ce master alloy (Ce content 20.0 wt.%) were calculated to be 0.016 wt.% and 0.042 wt.%, respectively, according to formulas (4) - (5), and they were wrapped with nickel foil for use.
Alloy preparation process (vacuum induction furnace, vacuum degree higher than 10)-1Pa)
(1) High-temperature refining: 1530 ℃ for 40 min;
(2) when the temperature of the melt is reduced to about 1400 ℃, adding Al element, and heating to 1460 ℃;
(3) after the liquid level of the melt is stable, adding Al-Y, Ni-Ce, and keeping the temperature for 5 min;
(4) adding Zr and B;
(5) low-temperature refining: multiplying at 1410 deg.C for 30 min;
(6) casting temperature: 1430 ℃.
The product master alloy obtained by the method has O, N, S, Y, Ce scum content during remelting compared with other processes as shown in table 3:
TABLE 3