Purification smelting process for high-temperature heat-resistant steel

Abstract

The invention belongs to the technical field of alloy casting, and particularly relates to a high-temperature heat-resistant steel purification smelting process. According to the process, an additive is prepared according to the content condition of impurity elements in selected raw materials, a prefabricated crucible is adopted to smelt the alloy, through two purification processes, oxygen, sulfur, phosphorus and other impurity elements in the alloy are fully removed, the content of inclusions in the alloy is reduced, the temperature bearing capacity and high-temperature oxidation resistance of the heat-resistant steel are improved, and the service life of the heat-resistant steel is prolonged. And meanwhile, the mechanical property of the alloy is not damaged due to the fact that excessive additive residues are introduced. According to the process, the impurity removal effect of the additive can be fully exerted, the adverse effect of additive residues on the alloy performance can be effectively eliminated, large-scale industrial application can be conveniently achieved, and an effective way is provided for pure smelting of the high-temperature heat-resistant steel.

Description

Technical Field:

[0001] The present invention belongs to the technical field of alloy casting, and particularly relates to a process for the purification smelting of high-temperature heat-resistant steel. Background Art:

[0002] High-temperature heat-resistant steel is a type of heat-resistant alloy used at temperatures above 900 °C. It is commonly used to manufacture rotors and blades of steam turbines and gas turbines, boiler heaters, bolts and springs operating at high temperatures, intake and exhaust valves of internal combustion engines, petroleum and hydrogen reactors, etc. These service environments require the alloy to have good temperature-bearing capacity and high-temperature oxidation resistance at high temperatures, and at the same time be able to withstand considerable additional stresses and have certain mechanical properties. Therefore, strict control requirements are imposed on the content of impurity elements in high-temperature heat-resistant steel. Excessive impurity elements will lower the melting point of the alloy and form inclusions in the alloy, damaging the high-temperature service performance of the alloy. Currently, for high-temperature heat-resistant steel, methods such as electric furnaces or intermediate-frequency induction furnaces are often used for smelting and preparation. However, with the continuous improvement of the performance requirements for high-temperature heat-resistant steel, more and more active metal elements need to be added to the alloy to play a strengthening role. This results in the inability to effectively remove impurity elements and inclusions when smelting the alloy by traditional preparation methods, and a vacuum induction melting furnace needs to be used to smelt the alloy. For existing vacuum induction purification smelting methods, either process parameters are adjusted (Chinese Patent Publication No.: CN106319255A), or elements such as calcium are added (Chinese Patent Publication No.: CN107686901A) and special crucibles are used (Chinese Patent Publication No.: CN103526037A), etc. to reduce the impurity elements in the alloy. However, the method of adjusting process parameters is often only applicable to alloys with a specific composition, and special crucibles such as yttrium oxide are expensive and have poor stability, making it difficult to be applied on a large scale industrially. When improving the smelting quality of the alloy by adding elements such as calcium, there is also a problem that it is difficult to control the addition amount of the additive. If the addition amount is too small, it is difficult to fully remove impurities, and if the addition amount is too high, it will cause too much residue, affecting the mechanical properties of the alloy. Summary of the Invention:

[0003] The object of the present invention is to overcome the deficiencies of the above-mentioned existing technologies, and provide a process for the purification smelting of high-temperature heat-resistant steel, which can not only give full play to the impurity removal effect of the additive, but also effectively eliminate the adverse effects of additive residues on the alloy properties, and is convenient for large-scale industrial application, providing an effective way for the purification smelting of high-temperature heat-resistant steel.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A process for the purification smelting of high-temperature heat-resistant steel, and the specific process steps are as follows:

[0006] (1) Weigh raw materials according to the designed composition of high-temperature heat-resistant steel;

[0007] (2) Prepare additives according to the content of impurity elements in the selected raw materials;

[0008] (3) Use a pre-formed crucible to make the furnace lining, load the raw materials into the crucible, and reduce the impurity elements in the alloy by adding additives. The additive is added last by hanging the material;

[0009] (4) The first pure purification process: melt the alloy under the condition of a vacuum degree of 30 - 10 Pa. After the smelting process ends, cut off the power supply and let it cool naturally until the alloy liquid begins to form a film; then fill argon gas to 0.05 - 0.09 MPa, and add additives in sequence; after each additive is added, give power of 80 - 120 kW for stirring, and the stirring time for each time is 30 - 90 s. After the stirring ends, cut off the power supply; cool naturally until the alloy liquid forms a film again, stir with the same power again, stir 2 - 3 times and then cut off the power supply and let it stand for more than 3 min. Adjust the temperature until the alloy liquid begins to form a film and add the next additive; finally, cast under argon protection to obtain the master alloy rod;

[0010] (5) The second pure purification process: when the vacuum degree is 0.9 - 0.09 Pa, give power of 60 - 90 kW to make the master alloy turn red, and then reduce the power to 20 - 50 kW to remelt the master alloy; after melting and clearing, carry out long-term refining, and the refining time ≥ 15 min; after the refining is completed, cut off the power supply and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain the heat-resistant steel casting.

[0011] For the above-mentioned pure purification smelting process of high-temperature heat-resistant steel, the additives are metallic magnesium and rare earth element cerium, and the addition amounts and meet: 1 ≤ t ≤ 10; where, m Ce is the mass fraction of rare earth element cerium, m Mg is the mass fraction of metallic magnesium, m S is the mass fraction of sulfur content in the used raw materials, m P is the mass fraction of phosphorus content in the used raw materials, m O is the mass fraction of oxygen content in the used raw materials; the addition sequence of the additives is: add metallic magnesium first, and then add rare earth element cerium.

[0012] For the above-mentioned pure purification smelting process of high-temperature heat-resistant steel, in the master alloy rod prepared by the first pure purification process in step (4), in terms of mass fraction, the residual content of each additive is ≥ 0.0080%.

[0013] For the above-mentioned pure purification smelting process of high-temperature heat-resistant steel, in the heat-resistant steel casting obtained by casting in step (5), in terms of mass fraction, the residual content of each additive is ≤ 0.0010%.

[0014] The described high-temperature heat-resistant steel purification smelting process fully removes oxygen, sulfur, and phosphorus impurity elements in the alloy through two purification processes, reducing the inclusion content in the alloy.

[0015] The technical principle of the present invention is as follows:

[0016] The present invention formulates additives according to the content of impurity elements in the selected raw materials, smelts the alloy using a preformed crucible, and through two purification processes, fully removes impurity elements such as oxygen, sulfur, and phosphorus in the alloy, reduces the inclusion content in the alloy, improves the temperature-bearing capacity and high-temperature oxidation resistance of the heat-resistant steel, and at the same time does not introduce excessive additive residues to damage the mechanical properties of the alloy, making it easy to achieve large-scale industrial applications.

[0017] The process of the present invention reduces the impurity elements in the alloy by adding additives and can be applied to more grades of high-temperature heat-resistant steel. However, the addition amount and addition method of the additives must satisfy both the full play of the impurity removal effect of the additives and the effective elimination of the adverse effects of additive residues on the alloy properties. In the first purification smelting process of the present invention, the burning loss of the additives is reduced by filling argon, making the content of the additives in this process in a supersaturated state, and through 2 to 3 times of high-power stirring, the additives fully react with impurity elements such as oxygen, sulfur, and phosphorus in the alloy. After the stirring ends, through long-term static freezing, the formed inclusions fully float up, and finally, the master alloy rod is cast under argon protection, making the inclusions concentrated at the primary shrinkage cavity of the alloy rod and removed during the subsequent processing.

[0018] In the present invention, the master alloy rod of high-temperature heat-resistant steel prepared after the first purification process still contains a certain amount of additives, and secondary purification can be carried out during the remelting of the master alloy. In the secondary purification process, by increasing the vacuum degree and extending the refining time, the remaining additives can undergo more sufficient secondary reactions, further deeply removing impurity elements while increasing the consumption of the additives, reducing the residue of the additives in the finished heat-resistant steel castings, so that the final residue amount does not affect the properties of the alloy.

[0019] The present invention selects metallic magnesium and rare earth element cerium as additives. Metallic magnesium has a strong binding force with impurity elements such as oxygen, sulfur, and phosphorus. However, the burning loss rate of magnesium element is high, and it is difficult to add. Moreover, adding excessive magnesium will seriously damage the high-temperature mechanical properties of the alloy and reduce the plasticity of the alloy, etc. Rare earth element cerium has a stronger ability to combine with oxygen and sulfur. Adding it after magnesium can further remove inclusions, and it can also form large-sized and low-density magnesium-cerium composite inclusions together with magnesium, which are convenient to float to the slag for removal. However, similarly, the melting point of cerium is relatively low, and it is also difficult to add. And excessive cerium will lead to the formation of inclusion segregation clusters, which is not conducive to the mechanical properties of the alloy. Therefore, on the one hand, through the appropriate ratio of the addition amount to the impurity elements in the alloy raw materials, the products after impurity removal can finally float at the primary shrinkage cavity of the alloy rod, so that impurities can be fully removed while not introducing new solid inclusion cores into the alloy. On the other hand, through reasonable process control, when smelting the master alloy, the burning loss rate of magnesium and cerium is reduced by filling argon, so that they can fully react with impurity elements; subsequently, casting is carried out under argon protection, so that the remaining magnesium and cerium continue to remain in the master alloy rod; finally, the master alloy rod is remelted under high vacuum. Utilizing the characteristics that the saturated vapor pressures of magnesium and cerium are relatively large and they are easy to volatilize under vacuum, the additives remaining in the master alloy are fully removed during the secondary vacuum remelting process, and at the same time, they can react with impurity elements such as oxygen and sulfur again. Through the control of the two melting processes, the impurity removal effect of the magnesium-cerium composite additive can be fully exerted, and the residual amount of the additive can be controlled at an extremely low level so as not to affect the normal performance of the alloy.

[0020] The smelting process of the present invention is applicable to various high-temperature heat-resistant steels with different grades, and the process cost is relatively low, having good universality and excellent comprehensive economic benefits.

[0021] The advantages and beneficial effects of the present invention are as follows:

[0022] 1. In the present invention, by reasonably selecting the addition amounts of magnesium and cerium additives, sufficient additive content can be formed during the primary purification smelting process of the high-temperature heat-resistant steel master alloy, playing a role in fully removing impurity elements.

[0023] 2. The present invention utilizes the characteristics that the saturated vapor pressures of magnesium and cerium are relatively large and they are easy to volatilize under vacuum to carry out secondary purification treatment during the remelting process of the master alloy, removing impurities again while fully reducing the residual amount of the additive and eliminating the adverse effects of additive residues on the alloy properties.

[0024] 3. The implementation method of the present invention is simple and effective, the process cost is relatively low, it is applicable to various high-temperature heat-resistant steels with different grades, and it has good engineering application value and excellent comprehensive economic benefits. Specific implementation manners:

[0025] The specific embodiments of the present invention will be further described in detail below in combination with examples and comparative examples. It should be noted here that the descriptions of these embodiments are used to help understand the present invention, but do not constitute a limitation on the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] Example 1

[0027] In this example, a high-strength high-temperature heat-resistant steel is smelted. First, additives are prepared according to the content of impurity elements in the selected raw materials. The chemical composition of the alloy ingredients used in Example 1 and the oxygen, sulfur, and phosphorus contents in the raw materials are shown in Table 1. The mass fraction of additive magnesium is determined to be 0.03% according to the content of impurity elements in the raw materials, the mass fraction of cerium is 0.1%, and t = 1.05.

[0028] Table 1 Chemical composition of the ingredients in Example 1 and oxygen and sulfur contents in the raw materials (wt.%)

[0029] Element C Cr W Nb Ti Al Ni O S P Content 0.4 28 4 0.8 3 2 The balance 0.038 0.012 0.006

[0030] Use an alumina preformed crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium by hanging the materials last; melt the alloy under a vacuum of 30 Pa, and after the smelting process is completed, cut off the power and let it cool naturally until the alloy liquid begins to form a film; then fill argon to 0.09 MPa, add metallic magnesium, give power of 80 kW and stir for 30 s, then cut off the power and let it cool naturally until the alloy liquid forms a film again, and stir at the same power again; after stirring twice, cut off the power and let it stand for 5 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing processes. Finally, cast under argon protection to obtain a master alloy rod.

[0031] When the vacuum is 0.8 Pa, give power of 65 kW to make the master alloy turn red, and then reduce the power to 25 kW to slowly remelt the master alloy; after melting clear, carry out refining for 15 min; after the refining is completed, cut off the power and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain a heat-resistant steel casting.

[0032] Comparative Example 1-1

[0033] In this comparative example, a high-strength high-temperature heat-resistant steel is smelted. The chemical composition of the alloy ingredients used in Comparative Example 1-1 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 1.

[0034] Use an alumina preformed crucible to make the furnace lining, load the raw materials into the crucible; melt the alloy under a vacuum of 30 Pa, and cast to obtain a master alloy rod.

[0035] When the vacuum degree is 0.8 Pa, power of 65 kW is supplied to the master alloy until it turns red, and then the power is reduced to 25 kW to slowly remelt the master alloy; after melting, refining is carried out for 15 min; after the refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

[0036] Comparative Example 1-2

[0037] In this comparative example, a high-strength high-temperature heat-resistant steel is smelted. The chemical components of the alloy ingredients and the oxygen, sulfur, and phosphorus contents in the raw materials used in Comparative Example 1-2 are exactly the same as those in Example 1. The mass fraction of the selected additive magnesium is: 0.03%, the mass fraction of cerium is: 0.1%, and t = 1.05.

[0038] Use an alumina preformed crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium by hanging the materials last; melt the alloy under a vacuum degree of 30 Pa, and after the smelting process is completed, power is cut off and it is naturally cooled until the alloy liquid begins to form a film; add metallic magnesium, supply power of 80 kW for stirring for 30 s and then cut off the power, and it is naturally cooled until the alloy liquid forms a film again, and stir with the same power again; after stirring 2 times, cut off the power and let it stand for 5 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing processes. Finally, cast to obtain a master alloy rod.

[0039] When the vacuum degree is 0.8 Pa, power of 65 kW is supplied to the master alloy until it turns red, and then the power is reduced to 25 kW to slowly remelt the master alloy; after melting, refining is carried out for 15 min; after the refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

[0040] Comparative Example 1-3

[0041] In this comparative example, a high-strength high-temperature heat-resistant steel is smelted. The chemical components of the alloy ingredients and the oxygen, sulfur, and phosphorus contents in the raw materials used in Comparative Example 1-3 are exactly the same as those in Example 1. The mass fraction of the selected additive magnesium is: 0.05%, the mass fraction of cerium is: 0.06%, and t = 0.53.

[0042] Use an alumina preformed crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium by hanging the materials last; melt the alloy under a vacuum degree of 30 Pa, and after the smelting process is completed, power is cut off and it is naturally cooled until the alloy liquid begins to form a film; add metallic magnesium, supply power of 80 kW for stirring for 30 s and then cut off the power, and it is naturally cooled until the alloy liquid forms a film again, and stir with the same power again; after stirring 2 times, cut off the power and let it stand for 5 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing processes. Finally, cast to obtain a master alloy rod.

[0043] When the vacuum degree is 0.8 Pa, power of 65 kW is supplied to the master alloy until it turns red, and then the power is reduced to 25 kW to slowly remelt the master alloy; after melting is complete, refining is carried out for 15 minutes; after refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain heat-resistant steel castings.

[0044] Comparative Examples 1-4

[0045] In this comparative example, a high-strength high-temperature heat-resistant steel is smelted. The chemical compositions of the alloy ingredients used in Comparative Examples 1-4 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 1. The mass fraction of the selected additive magnesium is: 0.2%, the mass fraction of cerium is: 0.3%, and t = 10.79.

[0046] Use a preformed alumina crucible to make the furnace lining, load the raw materials into the crucible, and finally add magnesium and cerium by hanging; melt the alloy under a vacuum degree of 30 Pa, and after the smelting process is completed, power is cut off and it is naturally cooled until the alloy liquid begins to form a film; add metallic magnesium, supply power of 80 kW for stirring for 30 s and then cut off the power, and naturally cool until the alloy liquid forms a film again, and stir at the same power again; after stirring 2 times, cut off the power and let it stand for 5 minutes, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing processes. Finally, cast to obtain a master alloy rod.

[0047] When the vacuum degree is 0.8 Pa, power of 65 kW is supplied to the master alloy until it turns red, and then the power is reduced to 25 kW to slowly remelt the master alloy; after melting is complete, refining is carried out for 15 minutes; after refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain heat-resistant steel castings.

[0048] The contents of additives and impurity elements in the alloys of Example 1 of the present invention and Comparative Examples 1-1 to 1-4 are shown in Table 2. It can be seen that the final impurity element content of the alloy in Example 1 of the present invention is lower, and the residual amount of additives is less.

[0049] Table 2 Contents of additives and impurity elements in the alloys of Example 1 and Comparative Examples 1-1 to 1-4 (wt.%)

[0050]

[0051] The initial melting temperatures and high-temperature creep rupture properties of the alloys of Example 1 of the present invention and Comparative Examples 1-1 to 1-4 are shown in Table 3. It can be seen that the alloy in Example 1 of the present invention has the highest initial melting temperature and the best high-temperature creep rupture property, and the high-temperature service performance is the most excellent.

[0052] Table 3 Initial melting temperatures and high-temperature creep rupture properties of the alloys of Example 1 and Comparative Examples 1-1 to 1-4

[0053]

[0054] The implementation results show that although the same additives as those in Example 1 were used in Comparative Examples 1-2, during the primary purification process, magnesium and cerium were directly added without argon filling, and argon protection was not used when casting the master alloy rod, resulting in poor implementation effects of the additives and certain influence on the high-temperature creep properties. At the same time, magnesium and cerium were not used as additives in Comparative Example 1-1, and the addition amounts of magnesium and cerium used as additives in Comparative Example 1-3 were relatively low, resulting in poor high-temperature creep properties. Comparative Example 1-3 with a small amount of added magnesium and cerium was superior to Comparative Example 1-1 without added magnesium and cerium. In Comparative Example 1-4, the addition amounts of magnesium and cerium used as additives were relatively high, resulting in more residue of the additives and the worst high-temperature creep properties.

[0055] Example 2

[0056] In this example, a high-temperature heat-resistant steel was smelted. First, additives were prepared according to the content of impurity elements in the selected raw materials. The chemical compositions of the alloy ingredients used in Example 2 and the contents of oxygen, sulfur, and phosphorus in the raw materials are shown in Table 4. According to the content of impurity elements in the raw materials, the mass fraction of additive magnesium was determined to be: 0.1%, the mass fraction of cerium was: 0.24%, and t = 9.55.

[0057] Table 4 Chemical Compositions of the Ingredients in Example 2 and the Contents of Oxygen and Sulfur in the Raw Materials (wt.%)

[0058] Element Cr Al B Ni Fe O S P Content 20 4 0.008 40 The balance 0.022 0.018 0.008

[0059] A furnace lining was made by using a preformed magnesia crucible, and the raw materials were loaded into the crucible. Magnesium and cerium were added last by hoisting; the alloy was melted under a vacuum of 10 Pa. After the smelting process was completed, the power was cut off and the alloy was naturally cooled until the alloy liquid began to form a film. Subsequently, argon was filled to 0.05 MPa, metallic magnesium was added, and after stirring at a high power of 110 kW for 90 s, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film again, and stirring was carried out at the same power again. After stirring 3 times, the power was cut off and the alloy was left standing for 6 min. The temperature was adjusted and the rare earth element cerium was added, and the above stirring and standing processes were repeated. Finally, the master alloy rod was obtained by casting under argon protection.

[0060] When the vacuum was 0.09 Pa, power was supplied at a high power of 80 kW until the master alloy glowed red, and then the power was reduced to 45 kW to slowly remelt the master alloy; after melting was complete, refining was carried out for 20 min; after the refining was completed, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film, and the temperature was adjusted for casting to obtain a heat-resistant steel casting.

[0061] Comparative Example 2-1

[0062] In this comparative example, a high-temperature heat-resistant steel was smelted. The chemical compositions of the alloy ingredients used in Comparative Example 2-1 and the contents of oxygen, sulfur, and phosphorus in the raw materials were exactly the same as those in Example 2.

[0063] Use a prefabricated magnesia crucible to make the furnace lining, and load the raw materials into the crucible; melt the alloy under a vacuum of 10 Pa, and cast to obtain a master alloy rod.

[0064] When the vacuum is 0.09 Pa, supply power of 80 kW at high power until the master alloy turns red, and then reduce the power to 45 kW to slowly remelt the master alloy; after melting is complete, conduct refining for 20 min; after refining is completed, cut off the power and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain a heat-resistant steel casting.

[0065] Comparative Example 2-2

[0066] In this comparative example, a high-temperature heat-resistant steel was smelted. The chemical composition of the alloy ingredients used in Comparative Example 2-2 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 2. The mass fraction of the selected additive magnesium is: 0.1%, the mass fraction of cerium is: 0.24%, and t = 9.55.

[0067] Use a prefabricated magnesia crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium as hanging materials last; melt the alloy under a vacuum of 10 Pa, and after the smelting process is completed, cut off the power and let it cool naturally until the alloy liquid begins to form a film; add metallic magnesium, supply power at high power of 110 kW and stir for 90 s, then cut off the power, and let it cool naturally until the alloy liquid forms a film again, and stir at the same power again; after stirring 3 times, cut off the power and let it stand for 6 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing process. Finally, cast to obtain a master alloy rod.

[0068] When the vacuum is 0.09 Pa, supply power of 80 kW at high power until the master alloy turns red, and then reduce the power to 45 kW to slowly remelt the master alloy; after melting is complete, conduct refining for 20 min; after refining is completed, cut off the power and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain a heat-resistant steel casting.

[0069] Comparative Example 2-3

[0070] In this comparative example, a high-temperature heat-resistant steel was smelted. The chemical composition of the alloy ingredients used in Comparative Example 2-3 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 2. The mass fraction of the selected additive magnesium is: 0.06%, the mass fraction of cerium is: 0.08%, and t = 0.45.

[0071] Use a preformed magnesia crucible to make the furnace lining, load the raw materials into the crucible, and finally add the magnesium and cerium by hanging; melt the alloy under a vacuum of 10 Pa. After the smelting process is completed, cut off the power supply and let it cool naturally until the alloy liquid begins to form a film; then fill with argon to 0.05 MPa, add metallic magnesium, give power at a high power of 110 kW and stir for 90 s, then cut off the power supply and let it cool naturally until the alloy liquid forms a film again, and stir at the same power again; after stirring 3 times, cut off the power supply and let it stand for 6 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing process. Finally, cast the master alloy rod under argon protection.

[0072] When the vacuum is 0.09 Pa, give power at a high power of 80 kW until the master alloy turns red, and then reduce the power to 45 kW to slowly remelt the master alloy; after melting clear, carry out refining for 20 min; after the refining is completed, cut off the power supply and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain a heat-resistant steel casting.

[0073] Comparative Examples 2-4

[0074] In this comparative example, a high-temperature heat-resistant steel is smelted. The chemical composition of the alloy ingredients used in Comparative Examples 2-4 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 2. The mass fraction of the selected additive magnesium is: 0.2%, the mass fraction of cerium is: 0.2%, and t = 12.27.

[0075] Use a preformed magnesia crucible to make the furnace lining, load the raw materials into the crucible, and finally add the magnesium and cerium by hanging; melt the alloy under a vacuum of 10 Pa. After the smelting process is completed, cut off the power supply and let it cool naturally until the alloy liquid begins to form a film; add metallic magnesium, give power at a high power of 110 kW and stir for 90 s, then cut off the power supply and let it cool naturally until the alloy liquid forms a film again, and stir at the same power again; after stirring 3 times, cut off the power supply and let it stand for 6 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing process. Finally, cast to obtain the master alloy rod.

[0076] When the vacuum is 0.09 Pa, give power at a high power of 80 kW until the master alloy turns red, and then reduce the power to 45 kW to slowly remelt the master alloy; after melting clear, carry out refining for 20 min; after the refining is completed, cut off the power supply and let it cool naturally until the alloy liquid forms a film, adjust the temperature and cast to obtain a heat-resistant steel casting.

[0077] The contents of additives and impurity elements in the alloys of Example 2 of the present invention and Comparative Examples 2-1 to 2-4 are shown in Table 5. It can be seen that the final impurity element content of the alloy in Example 2 of the present invention is relatively low, and the residual amount of additives is relatively small.

[0078] Table 5 Contents of additives and impurity elements in the alloys of Example 2 and Comparative Examples 2-1 to 2-4 (wt.%)

[0079]

[0080]

[0081] In Example 2 of the present invention and Comparative Examples 2-1 to 2-4, the initial melting temperatures and high-temperature tensile properties at 900 °C of each alloy are shown in Table 6. It can be seen that the alloy of Example 2 of the present invention has the highest initial melting temperature and the best high-temperature tensile properties, and excellent service performance.

[0082] Table 6 Initial melting temperatures and high-temperature tensile properties at 900 °C of each alloy in Example 2 and Comparative Examples 2-1 to 2-4

[0083]

[0084] The implementation results show that although Comparative Example 2-2 uses the same additives as Example 2, in the primary purification process, magnesium and cerium are directly added without argon filling, and argon protection is not used when casting the master alloy rod, resulting in a certain impact on its high-temperature tensile properties at 900 °C. At the same time, magnesium and cerium are not used as additives in Comparative Example 2-1, and the addition amounts of magnesium and cerium used as additives in Comparative Example 2-3 are relatively low, resulting in poor high-temperature tensile properties at 900 °C. Comparative Example 2-3 with a small amount of added magnesium and cerium is better than Comparative Example 2-1 without added magnesium and cerium. And in Comparative Example 2-4, the addition amount of magnesium and cerium used as additives is relatively high, resulting in the worst high-temperature tensile properties at 900 °C.

[0085] Example 3

[0086] In this example, a high-temperature heat-resistant steel is smelted. First, additives are prepared according to the content of impurity elements in the selected raw materials. The chemical composition of the alloy ingredients used in Example 3 and the contents of oxygen, sulfur, and phosphorus in the raw materials are shown in Table 7. According to the content of impurity elements in the raw materials, the mass fraction of additive magnesium is determined to be: 0.05%, the mass fraction of cerium is: 0.08%, and t = 4.67.

[0087] Table 7 Chemical composition of the ingredients in Example 3 and the contents of oxygen and sulfur in the raw materials (wt.%)

[0088] Element C Cr Co W Mo Al Ti Nb Ta Ni O S P Content 0.15 16 8.5 2.6 1.7 4 3.8 0.7 1.7 The balance 0.015 0.008 0.004

[0089] Use an alumina preformed crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium by hanging the materials at the end; melt the alloy under a vacuum of 21 Pa. After the smelting process is completed, cut off the power and let it cool naturally until the alloy liquid begins to form a film; then fill it with argon to 0.07 MPa, add metallic magnesium, stir at a high power of 95 kW for 65 s and then cut off the power, and let it cool naturally until the alloy liquid forms a film again, and stir at the same power again; after stirring 3 times, cut off the power and let it stand for 7 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing processes. Finally, cast the master alloy rod under argon protection.

[0090] When the vacuum degree is 0.4 Pa, power of 75 kW is supplied to the master alloy until it turns red, and then the power is reduced to 35 kW to slowly remelt the master alloy; after melting is complete, refining is carried out for 18 min; after refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

[0091] Comparative Example 3-1

[0092] In this comparative example, a high-temperature heat-resistant steel is smelted. The chemical composition of the alloy ingredients used in Comparative Example 3-1 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 3.

[0093] Use a preformed alumina crucible to make the furnace lining, and load the raw materials into the crucible; melt the alloy under a vacuum degree of 21 Pa, and cast to obtain a master alloy rod.

[0094] When the vacuum degree is 0.4 Pa, power of 75 kW is supplied to the master alloy until it turns red, and then the power is reduced to 35 kW to slowly remelt the master alloy; after melting is complete, refining is carried out for 18 min; after refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

[0095] Comparative Example 3-2

[0096] In this comparative example, a high-temperature heat-resistant steel is smelted. The chemical composition of the alloy ingredients used in Comparative Example 3-2 and the oxygen, sulfur, and phosphorus contents in the raw materials are exactly the same as those in Example 3. The mass fraction of the selected additive magnesium is: 0.05%, the mass fraction of cerium is: 0.08%, and t = 4.67.

[0097] Use a preformed alumina crucible to make the furnace lining, load the raw materials into the crucible, and add magnesium and cerium by hanging the materials at the end; melt the alloy under a vacuum degree of 21 Pa, and after the smelting process is completed, power is cut off and it is naturally cooled until the alloy liquid begins to form a film; add metallic magnesium, supply power of 95 kW for stirring for 65 s and then cut off the power, and naturally cool until the alloy liquid forms a film again, and stir at the same power again; after stirring 3 times, cut off the power and let it stand for 7 min, adjust the temperature and add the rare earth element cerium, and repeat the above stirring and standing process. Finally, cast to obtain a master alloy rod.

[0098] When the vacuum degree is 0.4 Pa, power of 75 kW is supplied to the master alloy until it turns red, and then the power is reduced to 35 kW to slowly remelt the master alloy; after melting is complete, refining is carried out for 18 min; after refining is completed, power is cut off and it is naturally cooled until the alloy liquid forms a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

[0099] Comparative Example 3-3

[0100] In this comparative example, a high-temperature heat-resistant steel was smelted. The chemical composition of the alloy ingredients used in Comparative Example 3-3 and the oxygen, sulfur, and phosphorus contents in the raw materials were exactly the same as those in Example 3. The mass fraction of the selected additive magnesium was: 0.03%, the mass fraction of cerium was: 0.042%, and t = 0.8.

[0101] An alumina preformed crucible was used to make the furnace lining, and the raw materials were loaded into the crucible. Magnesium and cerium were added last by hanging; the alloy was melted under a vacuum of 21 Pa. After the smelting process ended, the power was cut off and the alloy was naturally cooled until the alloy liquid began to form a film; metallic magnesium was added, and after stirring at a high power of 95 kW for 65 s, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film again, and then stirred at the same power again; after stirring 3 times, the power was cut off and the alloy was left standing for 7 min. The temperature was adjusted and the rare earth element cerium was added, and the above stirring and standing processes were repeated. Finally, a master alloy rod was obtained by casting.

[0102] When the vacuum was 0.4 Pa, the power was supplied at a high power of 75 kW until the master alloy glowed red, and then the power was reduced to 35 kW to slowly remelt the master alloy; after melting was complete, refining was carried out for 18 min; after refining was completed, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film, and the temperature was adjusted and casting was carried out to obtain a heat-resistant steel casting.

[0103] Comparative Example 3-4

[0104] In this comparative example, a high-temperature heat-resistant steel was smelted. The chemical composition of the alloy ingredients used in Comparative Example 3-4 and the oxygen, sulfur, and phosphorus contents in the raw materials were exactly the same as those in Example 3. The mass fraction of the selected additive magnesium was: 0.15%, the mass fraction of cerium was: 0.15%, and t = 16.

[0105] An alumina preformed crucible was used to make the furnace lining, and the raw materials were loaded into the crucible. Magnesium and cerium were added last by hanging; the alloy was melted under a vacuum of 21 Pa. After the smelting process ended, the power was cut off and the alloy was naturally cooled until the alloy liquid began to form a film; then argon was filled to 0.07 MPa, metallic magnesium was added, and after stirring at a high power of 95 kW for 65 s, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film again, and then stirred at the same power again; after stirring 3 times, the power was cut off and the alloy was left standing for 7 min. The temperature was adjusted and the rare earth element cerium was added, and the above stirring and standing processes were repeated. Finally, a master alloy rod was obtained by casting under argon protection.

[0106] When the vacuum was 0.4 Pa, the power was supplied at a high power of 75 kW until the master alloy glowed red, and then the power was reduced to 35 kW to slowly remelt the master alloy; after melting was complete, refining was carried out for 18 min; after refining was completed, the power was cut off and the alloy was naturally cooled until the alloy liquid formed a film, and the temperature was adjusted and casting was carried out to obtain a heat-resistant steel casting.

[0107] The contents of the additives and impurity elements in the alloys of Example 3 of the present invention and Comparative Examples 3-1 to 3-4 are shown in Table 8. It can be seen that the final impurity element content of the alloy in Example 3 of the present invention is relatively low, and the residual amount of the additive is relatively small.

[0108] Table 8 Contents of Additives and Impurity Elements in Alloys of Example 3 and Comparative Examples 3-1 to 3-4 (wt.%)

[0109]

[0110] The high-temperature tensile properties at 800 °C of the alloys of Example 3 and Comparative Examples 3-1 to 3-4 of the present invention are shown in Table 9. It can be seen that the alloy of Example 3 of the present invention has the highest high-temperature tensile strength and plasticity, and the mechanical properties are the most excellent.

[0111] Table 9 High-Temperature Tensile Properties at 800 °C of Alloys of Example 3 and Comparative Examples 3-1 to 3-4

[0112]

[0113] The implementation results show that although Comparative Example 3-2 uses the same additives as Example 3, in the primary purification process, magnesium and cerium are directly added without argon filling, and argon protection is not used when casting the master alloy rod, resulting in a certain impact on its high-temperature tensile properties at 800 °C. At the same time, Comparative Example 3-1 does not use magnesium and cerium as additives, and the addition amount of magnesium and cerium used in Comparative Example 3-3 is relatively low, resulting in poor high-temperature tensile properties at 800 °C. Instead, Comparative Example 3-1 without the addition of magnesium and cerium is superior to Comparative Example 3-3 with a small amount of addition of magnesium and cerium. In Comparative Example 3-4, the addition amount of magnesium and cerium used is too high, resulting in the worst high-temperature tensile properties at 800 °C.

[0114] The above are only the embodiments of the present invention, and do not limit the protection scope of the present invention accordingly. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. Any equivalent changes or modifications made according to the spirit and essence of the present invention are equally covered within the protection scope of the present invention.

Claims

1. A high temperature heat-resistant steel purification smelting process, characterized in that: The specific process steps are as follows: (1) Take the raw materials according to the designed high temperature heat-resistant steel composition; (2) Preparing additives based on the content of impurity elements in the selected raw materials; (3) Using a prefabricated crucible to make a furnace lining, loading the raw materials into the crucible, and reducing the impurity elements in the alloy by adding additives, and the additives are added last; (4) Primary purification process: melt the alloy under vacuum conditions of 30-10Pa, turn off the power after the smelting process is completed, and cool naturally until the alloy liquid begins to form a film; then fill with argon gas to 0.05-0.09MPa, and add additives in sequence; after each additive is added, it is necessary to stir with a high power of 80-120kW, and each stirring time is 30-90s. After the stirring is completed, turn off the power; cool naturally until the alloy liquid forms a film again, stir again with the same power, stir 2-3 times, turn off the power and let it stand for more than 3 minutes, adjust the temperature until the alloy liquid begins to form a film, and add the next additive; finally, cast under argon protection to obtain the master alloy rod; (5) Secondary purification process: At a vacuum degree of 0.9-0.09 Pa, a high power of 60-90 kW is applied until the master alloy turns red, and then the power is reduced to 20-50 kW to remelt the master alloy; after purification, a long refining period is carried out, with the refining time being ≥15 min; after refining, the power is turned off and the alloy is naturally cooled to form a film, and the temperature is adjusted for casting to obtain a heat-resistant steel casting.

2. A high temperature heat-resistant steel purification smelting process according to claim 1, characterized in that: The additives are metal magnesium and rare earth element cerium, and the addition amount And it meets the following conditions: 1≤t≤10; where m Ce is the mass fraction of rare earth element cerium, m Mg is the mass fraction of metallic magnesium, m S is the mass fraction of sulfur in the raw materials used, m P is the mass fraction of phosphorus in the raw materials used, m O is the mass fraction of oxygen content in the raw materials used; the order of adding additives is: first add metallic magnesium, then add rare earth element cerium.

3. A high temperature heat-resistant steel purification smelting process according to claim 2, characterized in that: In the master alloy rod prepared through a purification process in step (4), the residual content of each additive is ≥0.0080% by mass.

4. A high temperature heat-resistant steel purification smelting process according to claim 3, characterized in that: In the heat-resistant steel casting obtained by casting in step (5), the residual content of each additive is ≤0.0010% by mass.

5. A high temperature heat-resistant steel purification smelting process according to any one of claims 1 to 4, characterized in that: Through two purification processes, the oxygen, sulfur and phosphorus impurity elements in the alloy are fully removed and the inclusion content in the alloy is reduced.

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