Novel vacuum induction melting graphite electrode denitrification process

Abstract

The invention discloses a novel vacuum induction melting graphite electrode denitrification process which comprises the following steps: firstly, adding a to-be-melted alloy material into a crucible, dissolving the material until the material is clear, controlling the temperature of molten steel to be 50-100 DEG C above the melting point of the alloy, then penetrating a prefabricated graphite electrode into the molten steel by adopting a feeding device of a feeding chamber on an induction furnace, keeping for a certain time, and cooling to the room temperature; the nitrogen element in the molten steel is completely removed by utilizing bubbles generated by violent reaction of graphite carbon and oxygen in the molten steel. According to the method, the nitrogen partial pressure in the bubbles generated by the violent reaction of the carbon element and the oxygen in the molten steel is almost zero, and the bubbles can effectively adsorb the nitrogen element in the surrounding molten steel, so that the purpose of rapidly removing the nitrogen element in the molten steel is achieved. The method is simple to operate and can be applied to industrial large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of denitrification, in particular to a new vacuum induction melting graphite electrode denitrification process. Background Art

[0002] The N element is generally an impurity element in the alloy. It is very easy to react with the alloying elements in the molten steel during the smelting process to form nitride inclusions, such as chromium nitride, titanium nitride, niobium nitride and other inclusions. It is extremely difficult to completely remove them during the smelting process. The inclusions that remain in the ingot will eventually seriously affect the mechanical properties of the alloy. In the vacuum induction smelting process, by controlling the feeding method, the raw materials with higher nitrogen content and the raw materials with weaker nitrogen affinity are added first, and the Joule heat generated by the induced current is first melted into molten steel, and the high vacuum conditions of the vacuum induction furnace are used to effectively remove the nitrogen in the molten steel; however, this method often takes a long time to make the nitrogen content in the molten steel reach the target removal amount. Summary of the invention

[0003] The object of the present invention is to provide a new vacuum induction melting graphite electrode denitrification process to solve the problems raised in the above background technology.

[0004] To achieve the above objectives, the present application discloses 1. a new vacuum induction melting graphite electrode denitrification process, comprising the following steps:

[0005] S1. First, add the alloy to be melted and the material into the crucible, dissolve the material, and control the temperature of the molten steel above the melting point of the alloy;

[0006] S2, then use the charging device in the charging chamber of the induction furnace to deeply put the prefabricated graphite electrode into the molten steel and keep it for a certain period of time;

[0007] S3. The nitrogen in the molten steel is removed by using bubbles generated by the violent reaction between graphite carbon and oxygen in the molten steel.

[0008] Preferably, the melting point of the S1 alloy ranges from 50 to 100°C.

[0009] Preferably, the material in S1 is a material with weak oxygen-nitrogen affinity or a material with strong oxygen-nitrogen affinity.

[0010] Preferably, the nitrogen content in the molten steel is measured by sampling in S3. If the nitrogen content does not reach the target removal amount, the operation of S3 is repeated until the nitrogen content in the molten steel reaches the target removal amount.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] The bubbles produced by the violent reaction between carbon and oxygen in the molten steel have a nitrogen partial pressure of almost zero. The bubbles can effectively absorb nitrogen in the surrounding molten steel, thereby achieving the purpose of quickly removing nitrogen from the molten steel. The method is simple to operate and can be applied to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Please refer to the figure, the present invention provides a technical solution: Case 1: Graphite electrode denitrification process in vacuum induction melting of GH4169 alloy.

[0016] According to the characteristics of GH4169 alloy elements, iron, nickel, and molybdenum have weaker affinity with nitrogen, followed by chromium and niobium, and titanium and aluminum have the strongest affinity with nitrogen. Therefore, this smelting adopts the two-stage graphite electrode denitrification process. After each stage of denitrification, the target removal amount of nitrogen is ≤15ppm.

[0017] First add iron, nickel and molybdenum into the crucible, wait for the materials to dissolve, and raise the temperature of the molten steel to (1530~1550)℃.

[0018] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 20 to 25 minutes.

[0019] A sample was taken before the furnace and the nitrogen content was measured to be 10ppm, achieving the expected removal purpose.

[0020] Add molybdenum, chromium and niobium materials into the crucible, dissolve the molten steel, and raise the temperature of the molten steel to between 1480 and 1500°C.

[0021] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 20 to 25 minutes.

[0022] The sample was taken before the furnace and the nitrogen content was measured to be 12ppm, achieving the expected removal purpose.

[0023] Add aluminum and titanium materials into the crucible, dissolve the molten steel, and raise the temperature of the molten steel to between 1420 and 1430°C.

[0024] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 20 to 25 minutes.

[0025] A sample was taken before the furnace and the nitrogen content was measured to be 10ppm, achieving the expected removal purpose.

[0026] The temperature of the molten steel is raised to the pouring temperature of 1430-1440°C and the steel is tapped.

[0027] Case 2: Graphite electrode denitrification process during vacuum induction melting of A-100 alloy.

[0028] According to the characteristics of A-100 alloy elements, iron, molybdenum, and nickel have weaker affinity with nitrogen, and chromium has the second strongest affinity with nitrogen. Therefore, this smelting adopts a two-stage graphite electrode denitrification process. After each stage of denitrification, the target nitrogen removal amount is ≤10ppm.

[0029] First add iron, nickel and molybdenum into the crucible, wait for the materials to dissolve, and raise the temperature of the molten steel to (1550~1570)℃.

[0030] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 30 to 35 minutes.

[0031] The sample was taken before the furnace and the nitrogen content was measured to be 8ppm, achieving the expected removal purpose.

[0032] Add chromium material into the crucible, dissolve the molten steel, and raise the temperature of the molten steel to between 1540 and 1560°C.

[0033] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 20 to 25 minutes.

[0034] A sample was taken before the furnace and the nitrogen content was measured to be 6ppm, achieving the expected removal purpose.

[0035] The temperature of the molten steel is raised to the pouring temperature of 1570-1580°C and the steel is tapped.

[0036] Case 3: Graphite electrode denitrification process in vacuum induction melting of GH738 alloy.

[0037] According to the characteristics of GH738 alloy elements, molybdenum, nickel, and cobalt have weaker affinity with nitrogen, followed by chromium, and titanium, aluminum, zirconium, nickel and boron have the strongest affinity with nitrogen. Therefore, this smelting adopts a two-stage graphite electrode denitrification process. After each stage of denitrification, the target removal amount of nitrogen is ≤15ppm.

[0038] First add molybdenum, nickel and cobalt into the crucible, wait for the materials to dissolve, and raise the temperature of the molten steel to (1530~1550)℃.

[0039] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 15 to 20 minutes.

[0040] The sample was taken before the furnace and the nitrogen content was measured to be 12ppm, achieving the expected removal purpose.

[0041] Add chromium material into the crucible, dissolve the molten steel, and raise the temperature of the molten steel to between 1540 and 1560°C.

[0042] Then, the prefabricated graphite electrode is immersed into the molten steel through the charging chamber of the induction furnace, and the graphite electrode is taken out after maintaining for 20 to 25 minutes.

[0043] A sample was taken before the furnace and the nitrogen content was measured to be 10ppm, achieving the expected removal purpose.

[0044] Titanium, aluminum, zirconium, nickel and boron are added to the crucible material to dissolve. The nitrogen content is measured by sampling and is 10ppm, achieving the expected removal purpose. The temperature of the molten steel is raised to the pouring temperature of 1570-1580℃ and the steel is tapped.

[0045] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new vacuum induction melting graphite electrode denitrification process, characterized in that: The steps include: S1. First, add the alloy to be melted and the material into the crucible, dissolve the material, and control the temperature of the molten steel above the melting point of the alloy; S2, then use the charging device in the charging chamber of the induction furnace to deeply insert the prefabricated graphite electrode into the molten steel and keep it for a certain period of time; S3. The nitrogen in the molten steel is removed by using bubbles generated by the violent reaction between graphite carbon and oxygen in the molten steel.

2. A new vacuum induction melting graphite electrode denitrification process according to claim 1, characterized in that: The melting point of the S1 alloy ranges from 50 to 100°C.

3. A new vacuum induction melting graphite electrode denitrification process according to claim 1, characterized in that: The material in S1 is a material with weak oxygen-nitrogen affinity or a material with strong oxygen-nitrogen affinity.

4. A new vacuum induction melting graphite electrode denitrification process according to claim 1, characterized in that: In the step S3, the nitrogen content in the molten steel is measured by sampling. If the nitrogen content does not reach the target removal amount, the operation of S3 is repeated until the nitrogen content in the molten steel reaches the target removal amount.

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