CN114457281B - Method for effectively reducing iron and hydrogen contents of hypereutectic 20-cast ferrite containing niobium and chromium - Google Patents

Method for effectively reducing iron and hydrogen contents of hypereutectic 20-cast ferrite containing niobium and chromium Download PDF

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CN114457281B
CN114457281B CN202111606068.0A CN202111606068A CN114457281B CN 114457281 B CN114457281 B CN 114457281B CN 202111606068 A CN202111606068 A CN 202111606068A CN 114457281 B CN114457281 B CN 114457281B
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cast iron
chromium
powder
hypereutectic
nitrogen
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CN114457281A (en
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周正
赵四勇
田辉
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Guangxi Changcheng Mechanical Ltd By Share Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/06—Cast-iron alloys containing chromium
    • C22C37/08—Cast-iron alloys containing chromium with nickel
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/04—Removing impurities other than carbon, phosphorus or sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C1/00—Refining of pig-iron; Cast iron
    • C21C1/08—Manufacture of cast-iron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/072—Treatment with gases
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C22C33/06—Making ferrous alloys by melting using master alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/08—Making cast-iron alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C37/00—Cast-iron alloys
    • C22C37/10—Cast-iron alloys containing aluminium or silicon

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Abstract

The invention discloses a method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium, which comprises the following steps: smelting and nitrogen blowing treatment; (2) inoculation treatment; (3) covering a slagging material and blowing nitrogen; (4) adjusting chemical components; (5) sedation within the device; and (6) controlling temperature and tapping. The hypereutectic 20-niobium-chromium-containing cast iron obtained by covering a slagging material and nitrogen blowing treatment has the oxygen content of 8.1ppm, the hydrogen content of 1.9ppm and the Rockwell hardness value of 62.8, and can meet the application requirements of producing small (6-inch) pump overflowing parts, pump bodies, impellers, various powder conveying pipelines and linings.

Description

Method for effectively reducing iron and hydrogen contents of hypereutectic 20-cast ferrite containing niobium and chromium
Technical Field
The invention belongs to the technical field of refined chromium cast iron, and particularly relates to a method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-chromium cast iron.
Background
The chromium cast iron is formed according to different chromium contents, comprises 20 chromium cast iron, and is one of wear-resistant materials which are widely applied at home and abroad at present. In the smelting process of the chromium 20 cast iron liquid, a certain amount of harmful gases such as oxygen and hydrogen exist in the chromium 20 cast iron liquid due to reasons such as air suction and the like, and in order to ensure that the chromium 20 cast iron liquid forms a casting in a pure state, the molten chromium 20 cast iron liquid needs to be refined and purified to achieve a purification effect, so that the product performance of the chromium 20 cast iron is improved to meet application requirements for producing small (6-inch) pump overflowing part pump bodies, impellers, various powder conveying pipelines, linings and the like.
Disclosure of Invention
In order to solve the problems of the background art, the invention provides a method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium comprises the following steps:
(1) Gradually putting the prepared raw materials into a device for smelting, starting to open a flow regulator to blow and inject nitrogen when a chromium cast iron material is molten to form a molten pool, leading the nitrogen to pass through a gas permeable block to participate in the molten iron smelting process until completely molten cast iron is obtained, and increasing the flow of the blown nitrogen along with the increase of the molten iron as smelting continues;
(2) Inoculation treatment: inoculating the completely molten cast iron liquid obtained in the step (1) by adopting a ladle bottom flushing method;
(3) Covering a slagging material on the surface of the liquid iron which is inoculated in the step (2), blowing nitrogen gas for treatment at the same time until furnace burden is completely melted, and sampling and analyzing the components in the furnace;
(4) Adjusting chemical components: calculating and adding the adjusting material according to the sampling analysis result until the adjusting material is completely melted;
(5) Sedation in the device: after the chromium cast iron liquid in the device reaches the required temperature, stopping power supply, continuously blowing nitrogen gas to ensure that the chromium cast iron liquid is homogenized at the uniform temperature, and impurities and gas fully float upwards to be combined with a liquid surface slagging material;
(6) Controlling temperature and tapping: controlling the temperature, pouring, annealing and quenching after tapping to prepare the hypereutectic 20-containing niobium-chromium cast iron with low oxygen and hydrogen content.
Further, in the step (1), when the chromium cast iron material is melted to form a molten pool, namely the cast iron liquid covers over 29cm of the furnace bottom, the flow regulator is opened to blow and inject nitrogen.
Further, in the step (1), as the smelting is continued, the flow rate of the nitrogen-blowing gas is increased along with the increase of the molten iron, and the specific control process is as follows: controlling the flow of the nitrogen blowing gas at 15.8-16.3L/min for the first 9-13 min; controlling the flow of the nitrogen blowing gas at 17-17.2L/min at 14-20 min; controlling the flow of the nitrogen blowing gas at 17.6-17.8L/min in 21-30 min.
Further, the inoculation treatment in the step (2) adopts an inoculant which accounts for 3 percent of the weight of the cast iron liquid and has the granularity of less than 14mm, and the inoculant comprises a master alloy and a rare earth alloy in a weight ratio of 4; the master alloy comprises the following chemical components in percentage by mass: c:2.7%, cr:1.3%, si:0.7%, ni:0.5%, ti:0.4%, mo:0.5 percent, and the balance of Fe; the rare earth alloy comprises manganese, silicon, praseodymium, cerium and samarium according to a mass ratio of 10.
Further, the addition amount of the slagging material in the step (3) is 0.71 kg/ton of chromium cast iron.
Further, the nitrogen flow rate of the nitrogen blowing treatment in the step (3) is controlled to be 16.5-16.8L/min.
Further, the hypo-oxygen and hydrogen-content hypereutectic 20-chromium-niobium-containing cast iron in the step (6) comprises the following components in percentage by mass: 3.89% carbon, 0.72% manganese, 20.34% chromium, 0.22% silicon, 0.03% phosphorus, 0.04% sulfur, 0.74% nickel, 0.65% molybdenum, 0.31% vanadium, 0.51% titanium, 0.86% copper, 0.72% niobium, 0.25% misch metal, 0.00081% oxygen, 0.00019% hydrogen, and the balance Fe.
Further, the mixed rare earth consists of praseodymium, cerium and samarium according to a mass ratio of 3.
The invention has the following beneficial effects:
the invention can effectively reduce the oxygen and hydrogen contents by covering slag-making materials and nitrogen blowing treatment, the oxygen content of the obtained hypereutectic 20 cast iron containing niobium and chromium is only 8.1ppm, the hydrogen content is only 1.9ppm, and under the condition of unchanged components, a higher Rockwell hardness value is obtained, which reaches 62.8, and the invention can meet the application requirements of producing small (6 inch) pump overflowing parts, pump bodies, impellers, various powder conveying pipelines and linings.
Detailed Description
In order to facilitate a better understanding of the invention, the following examples are given to illustrate, but not to limit the scope of the invention.
In an embodiment of the present invention, the method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-containing niobium-chromium casting includes the following steps:
(1) Gradually putting the prepared raw materials into a device for smelting, starting to open a flow regulator to blow and inject nitrogen when a chromium cast iron material is molten to form a molten pool, leading the nitrogen to pass through a gas permeable block to participate in the molten iron smelting process until completely molten cast iron is obtained, and increasing the flow of the blown nitrogen along with the increase of the molten iron as smelting continues;
(2) Inoculation treatment: inoculating the completely molten cast iron liquid obtained in the step (1) by adopting a ladle bottom flushing method;
(3) Covering a slagging material on the surface of the liquid iron which is inoculated in the step (2), blowing nitrogen gas for treatment at the same time until furnace burden is melted down, and sampling and analyzing the components in the furnace;
(4) Adjusting chemical components: calculating and adding the adjusting material according to the sampling analysis result until the adjusting material is completely melted;
(5) Sedation in the device: after the chromium cast iron liquid in the device reaches the required temperature, stopping power supply, continuously blowing nitrogen to ensure that the chromium cast iron liquid is uniform in temperature and homogeneous, and impurities and gas are fully floated and combined with a liquid surface slagging material;
(6) Controlling temperature and tapping: controlling the temperature, pouring, annealing and quenching after tapping to prepare hypereutectic 20-chromium-niobium-containing cast iron with low oxygen and hydrogen content.
The following is a more specific example.
Example 1
A method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium comprises the following steps:
(1) The method comprises the following steps of gradually putting prepared raw materials into a device for smelting, starting to open a flow regulator to blow and inject nitrogen when chromium cast iron materials are molten to form a molten pool, namely when cast iron liquid covers the furnace bottom by 29.4cm, leading the nitrogen to participate in the molten iron smelting process through a gas permeable block until completely molten cast iron liquid is obtained, and increasing the flow of the nitrogen-blowing gas along with the increase of the cast iron liquid along with the continuation of smelting, wherein the specific control process is as follows: controlling the flow of the nitrogen blowing gas at 15.8-16.3L/min for the first 9-13 min; controlling the flow of the nitrogen blowing gas at 17-17.2L/min in 14-20 min; controlling the flow of the nitrogen blowing gas at 17.6-17.8L/min within 21-30 min;
(2) Inoculation treatment: inoculating the completely molten cast iron liquid obtained in the step (1) by adopting a ladle bottom flushing method, wherein the inoculation is carried out by adopting an inoculant which accounts for 3% of the weight of the cast iron liquid and has a granularity of less than 14mm, and the inoculant comprises a master alloy and a rare earth alloy in a weight ratio of 4.7; the master alloy comprises the following chemical components in percentage by mass: c:2.7%, cr:1.3%, si:0.7%, ni:0.5%, ti:0.4%, mo:0.5 percent, and the balance of Fe; the rare earth alloy comprises manganese, silicon, praseodymium, cerium and samarium according to a mass ratio of 10;
(3) Covering a slagging material on the surface of the liquid iron which is inoculated in the step (2), wherein the addition amount of the slagging material is 0.71 kg/ton of chromium cast iron; simultaneously blowing nitrogen gas, controlling the flow of the nitrogen gas at 16.5-16.8L/min until furnace burden is melted down, sampling and analyzing the components in the furnace;
(4) Adjusting chemical components: calculating and adding the adjusting material according to the sampling analysis result until the adjusting material is completely melted;
(5) Sedation in the device: after the chromium cast iron liquid in the device reaches the required temperature, stopping power supply, continuously blowing nitrogen to ensure that the chromium cast iron liquid is uniform in temperature and homogeneous, and impurities and gas are fully floated and combined with a liquid surface slagging material;
(6) Controlling temperature and tapping: controlling the temperature, pouring, annealing and quenching after tapping to prepare hypereutectic niobium-chromium-containing 20 cast iron with low oxygen and hydrogen content, and adopting spectral analysis to obtain the hypereutectic niobium-chromium-containing 20 cast iron with low oxygen and hydrogen content, wherein the hypereutectic niobium-chromium-containing 20 cast iron comprises the following components in percentage by mass: 3.89% carbon, 0.72% manganese, 20.34% chromium, 0.22% silicon, 0.03% phosphorus, 0.04% sulfur, 0.74% nickel, 0.65% molybdenum, 0.31% vanadium, 0.51% titanium, 0.86% copper, 0.72% niobium, 0.25% misch metal, 0.00081% oxygen, 0.00019% hydrogen, the balance being Fe;
the mixed rare earth consists of praseodymium, cerium and samarium according to a mass ratio of 3.
The slagging material in the step (3) comprises the following raw materials in parts by weight: 12 parts of perlite powder, 5 parts of aluminum powder, 17 parts of montmorillonite powder, 6 parts of fluorspar powder, 15 parts of talcum powder, 8 parts of passivated lime powder, 10 parts of magnesium carbonate powder, 7 parts of medical stone powder, 5 parts of quartz powder, 4.6 parts of sesbania gum and 24 parts of water;
the granularity of the perlite powder is 900 meshes;
the granularity of the aluminum powder is 1000 meshes;
the montmorillonite powder has the following quality indexes: siO 2 2 :73.87 percent and the granularity of 1000 meshes;
the quality indexes of the fluorite powder are as follows: caF 2 :77.48 percent and the granularity is 900 meshes;
the quality indexes of the talcum powder are as follows: siO 2 2 :64.06 percent and the granularity of 900 meshes;
the quality indexes of the passivated lime raw material are as follows: caO:93.64 percent; s: less than or equal to 0.04 percent;
the granularity of the magnesium carbonate powder is 900 meshes;
the granularity of the medical stone powder is 900 meshes;
the granularity of the quartz powder is 800 meshes;
the preparation method of the slagging material comprises the following steps:
1) Adding perlite powder, aluminum powder, montmorillonite powder, fluorspar powder, talcum powder, passivated lime powder, magnesium carbonate powder, medical stone powder and quartz powder into a stirrer in parts by weight, and stirring for 0.8h at the temperature of 50 ℃ and the rotating speed of 300r/min to prepare slurry a;
2) Adding sesbania gum and water into the slurry a prepared in the step 1), and stirring for 0.4h at the temperature of 46 ℃ and the rotating speed of 300r/min to prepare slurry b;
3) Adding the slurry b prepared in the step 2) into a mould, and preparing into particles with the particle size of 1.5cm after vacuum suction filtration molding;
4) And (3) feeding the granules prepared in the step 3) into an oven, and drying at 93 ℃ for 7.5h to prepare the slagging material.
Comparative example 1
The method for reducing the iron and hydrogen contents of hypereutectic 20-Nb-Cr cast iron was substantially the same as that of example 1, except that the covering slag-forming material was not subjected to the impurity removal in the step (3).
Comparative example 2
The method for reducing the iron and hydrogen contents of hypereutectic 20-niobium-chromium cast iron is basically the same as that of the example 1, except that nitrogen gas blowing for impurity removal is not carried out in the step (1) and the step (3).
The hypereutectic niobium chromium 20 cast irons prepared in example 1 and comparative examples 1 and 2 were tested for oxygen and hydrogen content and Rockwell hardness number (HRC) and the average value was determined by repeating the test 3 times for each index as follows:
test group Oxygen content/ppm Hydrogen content/ppm HRC
Example 1 8.1 1.9 62.8
Comparative example 1 110.7 28.9 56.2
Comparative example 2 146.3 39.7 52.5
Note: each index in the table is an average value of repeated 3 times, and the oxygen and hydrogen contents are detected by adopting spectral analysis; the Rockwell hardness test was carried out according to the GB/T230.1 specification.
From the above table, it can be seen that: the hypereutectic niobium chromium 20-containing cast iron obtained by the method of example 1 has extremely low oxygen and hydrogen contents, the oxygen content is only 8.1ppm, the hydrogen content is only 1.9ppm, and under the condition of unchanged components, a higher Rockwell hardness value is obtained and reaches 62.8. As can be seen from a comparison of the data obtained in example 1, comparative example 1 and comparative example 2, the Rockwell hardness value obtained by covering the slag-forming material with oxygen and hydrogen was increased by 11.7% in example 1 as compared to comparative example 1. Example 1 compared with comparative example 2, the Rockwell hardness value obtained by removing oxygen and hydrogen by blowing nitrogen is improved by 19.6%. It is explained above that covering the slag-forming material and nitrogen-blowing treatment can both effectively reduce the oxygen and hydrogen content and further increase the rockwell hardness value, probably because: montmorillonite powder, fluorspar powder, magnesium carbonate powder, medical stone powder and quartz powder are added into the slagging material and are matched with one another, so that the oxygen and hydrogen contents in the hypereutectic 20 cast iron containing niobium and chromium are effectively reduced, and the Rockwell hardness value of the hypereutectic 20 cast iron containing niobium and chromium is synergistically improved. The nitrogen is an inert gas, which is not dissolved in the cast iron liquid, does not react with elements in the cast iron to form inclusions, does not pollute the cast iron liquid, is blown into the cast iron liquid, and has fine and fully and uniformly dispersed nitrogen bubbles, when the nitrogen passes through the cast iron liquid, oxygen and hydrogen dissolved in the cast iron liquid automatically diffuse and enter the nitrogen bubbles to be discharged from the cast iron liquid along with the rising of the bubbles, thereby purifying the cast iron liquid, reducing the content of oxygen and hydrogen, and improving the Rockwell hardness value of hypereutectic 20 cast iron containing niobium and chromium.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium is characterized by comprising the following steps:
(1) Gradually putting the prepared raw materials into a device for smelting, starting to open a flow regulator to blow and inject nitrogen when a chromium cast iron material is molten to form a molten pool, leading the nitrogen to pass through a gas permeable block to participate in the molten iron smelting process until completely molten cast iron is obtained, and increasing the flow of the blown nitrogen along with the increase of the molten iron as smelting continues;
(2) Inoculation treatment: inoculating the completely molten cast iron liquid obtained in the step (1) by adopting a ladle bottom flushing method;
(3) Covering a slagging material on the surface of the liquid iron which is inoculated in the step (2), blowing nitrogen gas for treatment at the same time until furnace burden is completely melted, and sampling and analyzing the components in the furnace;
the slagging material comprises the following raw materials in parts by weight: 12 parts of perlite powder, 5 parts of aluminum powder, 17 parts of montmorillonite powder, 6 parts of fluorite powder, 15 parts of talcum powder, 8 parts of passivated lime powder, 10 parts of magnesium carbonate powder, 7 parts of medical stone powder, 5 parts of quartz powder, 4.6 parts of sesbania gum and 24 parts of water;
the granularity of the perlite powder is 900 meshes;
the granularity of the aluminum powder is 1000 meshes;
the montmorillonite powder has the following quality indexes: siO 2 2 :73.87 percent and the granularity of 1000 meshes;
the quality indexes of the fluorite powder are as follows: caF 2 :77.48 percent and the granularity is 900 meshes;
the quality indexes of the talcum powder are as follows: siO 2 2 :64.06 percent and the granularity of 900 meshes;
the quality indexes of the passivated lime raw material are as follows: caO:93.64 percent; s: less than or equal to 0.04 percent;
the granularity of the magnesium carbonate powder is 900 meshes;
the granularity of the medical stone powder is 900 meshes;
the granularity of the quartz powder is 800 meshes;
(4) Adjusting chemical components: calculating and adding the adjusting material according to the sampling analysis result until the adjusting material is completely melted;
(5) Sedation in the device: after the chromium cast iron liquid in the device reaches the required temperature, stopping power supply, continuously blowing nitrogen to ensure that the chromium cast iron liquid is uniform in temperature and homogeneous, and impurities and gas are fully floated and combined with a liquid surface slagging material;
(6) Controlling temperature and tapping: controlling the temperature, pouring, annealing and quenching after tapping to prepare hypereutectic 20-chromium-niobium-containing cast iron with low oxygen and hydrogen content.
2. The method for effectively reducing the iron and hydrogen contents of hypereutectic 20-th cast iron containing niobium and chromium according to claim 1, wherein in the step (1), when the chromium cast iron material is melted to form a molten pool, i.e. the molten cast iron is coated over 29cm of the bottom of the furnace, the flow regulator is opened to blow nitrogen.
3. The method for effectively reducing the contents of ferrite and hydrogen in hypereutectic 20-cast iron containing niobium and chromium according to claim 1, wherein in the step (1), as the smelting is continued, the flow rate of nitrogen-blowing gas is increased along with the increase of the cast iron liquid, and the specific control process is as follows: controlling the flow of the nitrogen blowing gas at 15.8-16.3L/min for the first 9-13 min; controlling the flow of the nitrogen blowing gas at 17-17.2L/min in 14-20 min; controlling the flow of the nitrogen blowing gas at 17.6-17.8L/min in 21-30 min.
4. The method for effectively reducing the iron and hydrogen contents of hypereutectic 20-cast iron containing niobium and chromium as claimed in claim 1, wherein the inoculation treatment in step (2) is carried out by using an inoculant which is 3% by weight of the cast iron liquid and has a particle size of less than 14mm, and the inoculant comprises a mixture of a master alloy and a rare earth alloy in a weight ratio of 4; the master alloy comprises the following chemical components in percentage by mass: c:2.7%, cr:1.3%, si:0.7%, ni:0.5%, ti:0.4%, mo:0.5 percent, and the balance of Fe; the rare earth alloy comprises manganese, silicon, praseodymium, cerium and samarium according to a mass ratio of 10.
5. The method for effectively reducing the ferrite and hydrogen contents of hypereutectic 20-chromium-niobium cast iron according to claim 1, wherein the addition amount of the slag forming material in the step (3) is 0.71 kg/ton of chromium cast iron.
6. The method for effectively reducing the iron and hydrogen contents of hypereutectic 20-th cast iron containing niobium and chromium according to claim 1, wherein the nitrogen flow rate in the nitrogen blowing treatment in the step (3) is controlled to be 16.5-16.8L/min.
7. The method for effectively reducing the iron and hydrogen contents of hypereutectic niobium-chromium-containing 20 cast iron according to claim 1, wherein the hypereutectic niobium-chromium-containing 20 cast iron with low oxygen and hydrogen contents in the step (6) comprises the following components in percentage by mass: 3.89% carbon, 0.72% manganese, 20.34% chromium, 0.22% silicon, 0.03% phosphorus, 0.04% sulfur, 0.74% nickel, 0.65% molybdenum, 0.31% vanadium, 0.51% titanium, 0.86% copper, 0.72% niobium, 0.25% misch metal, 0.00081% oxygen, 0.00019% hydrogen, and the balance Fe.
8. The method for effectively reducing the contents of ferrite and hydrogen in the hypereutectic 20-cast iron containing niobium-chromium according to claim 7, wherein the misch metal consists of praseodymium, cerium and samarium in a mass ratio of 3.
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