CN108676961B

CN108676961B - Vacuum induction furnace smelting rapid denitrification method

Info

Publication number: CN108676961B
Application number: CN201810594632.3A
Authority: CN
Inventors: 沈海军; 张丕军; 程兴德
Original assignee: Jiangsu Jicui Advanced Metal Material Institute Co ltd
Current assignee: Jiangsu Jicui Advanced Metal Material Institute Co ltd
Priority date: 2018-06-11
Filing date: 2018-06-11
Publication date: 2020-07-21
Anticipated expiration: 2038-06-11
Also published as: CN108676961A

Abstract

The invention discloses a method for rapid denitrification by vacuum induction furnace smelting, which has the following beneficial technical effects: the N content removal rate in the high-performance alloy can be up to more than 70 percent and the lowest N content removal rate can be up to less than 10ppm, the increased smelting time is not more than 60min, and the influence on the erosion of a furnace lining is small.

Description

Vacuum induction furnace smelting rapid denitrification method

Technical Field

The invention belongs to the field of special metallurgy, and particularly relates to a denitrification process for special steel and high-performance alloy (corrosion-resistant alloy and high-temperature alloy).

Background

The high-performance alloy mainly refers to high-strength steel, high-temperature corrosion-resistant alloy and the like which are used for aerospace, nuclear power, energy chemical engineering and other purposes, and Ti, Al, Nb and the like are usually used as precipitation strengthening elements to improve service performance. However, since N has a high affinity for Ti, Al, and Nb, and is liable to form inclusions of TiN, AlN, and NbN, which have high hardness, high melting point, and irregular shape, and are difficult to remove even in a subsequent remelting step, the control of the N content of the high-performance alloy in vacuum induction melting is very strict.

At present, two methods for controlling the content of N in industrial production are mainly adopted, and an ultralow-N raw material is selected and/or the raw material is kept still for a long time of more than 6 hours under vacuum. The two methods have the defects that the raw material and the manufacturing cost of the material are obviously improved, the long-time standing causes the corrosion of a refractory lining to be aggravated, the quantity of oxide inclusions and slag inclusion is increased, the purity level of the material is reduced, the reduction range of the N content is limited, and the N content is hardly lower than the 15ppm level.

CN107190158A mentions that N can be efficiently removed by C-O reaction in combination with vacuum standing. However, since the C content of the high performance alloy is generally required to be less than 0.1%, the C, O has a large difficulty in precise matching, and therefore the number of bubbles is limited. CN106868345A mentions that ultra-high temperature refining is adopted for N removal, but ultra-high temperature operation can cause the corrosion of the furnace lining to be intensified and the quantity of inclusions and slag inclusions to be increased. CN105238934A and CN106222460B mention that elements such as Nb, Al, Ti and the like which have strong affinity with N are added at the later stage of smelting, which is a common practice in industrial production, but the problem of removing N from main raw materials at the earlier stage is not effectively solved. CN102703794B, CN102719686B and CN103114172A all refer to a method for denitrifying by assembling a gas permeable brick in the middle of the bottom of a vacuum induction furnace and generating bubbles through bottom blowing argon, the method is a denitrification method with controllable cost and basically without generating side effects (lining erosion), but has two defects, firstly, because the vacuum induction melting pool flows downwards from the middle and upwards from two sides of the bottom, the gas permeable brick is placed in the middle to inhibit the effective floating of the argon bubbles and influence the N-removing effect; secondly, according to the western Walter law, the solubility of N is related to the vacuum degree, and the working vacuum degree is obviously reduced due to the release of O in the vacuum degrees in the smelting period and the refining period, so that an effective means is adopted to reduce the O content of a molten pool.

Disclosure of Invention

The invention aims to solve the problems in the prior art and provide a cost-controllable and effective high-performance alloy vacuum induction melting rapid N-removing method.

The technical scheme of the invention is as follows: a method for rapid denitrification in vacuum induction furnace smelting comprises the following steps:

the method comprises the following steps: according to the characteristics that a vacuum induction melting pool flows downwards from the middle and upwards from two sides of the bottom, a gas permeable brick is respectively arranged at the 1/2 radius positions of two sides of the bottom of the crucible, and argon is introduced before feeding to check whether the gas permeable brick is normal;

step two: before smelting, according to the oxygen content in the electrolytic nickel plate of the main raw material and the carbon-chromium iron in the industrial pure iron, adding corresponding carbon powder according to the C/O mass ratio of 0.5:1-2:1 and placing the carbon powder at the bottom in a crucible;

step three: closing the furnace cover, and vacuumizing the furnace to a set value;

step four: electrifying and melting;

step five: after the raw materials are completely melted down, opening bottom blowing argon until bubbles on the surface of a molten pool escape, and continuously blowing argon for 30-60 min;

step six: and (3) entering a refining period after argon blowing is finished, judging the refining period according to the dynamic gas leakage rate, finishing refining when the difference between the dynamic gas leakage rates of two continuous times is not more than 5%, adding ferroniobium and a return material, adding Ai and Ti in the third stage, and finishing the denitrification process.

The beneficial technical effects of the invention are as follows: the N content removal rate in the high-performance alloy can be up to more than 70 percent and the lowest N content removal rate can be up to less than 10ppm, the increased smelting time is not more than 60min, and the influence on the erosion of a furnace lining is small.

Drawings

FIG. 1 is a schematic view of a melting crucible of a vacuum induction furnace with double air bricks at two sides at the bottom, wherein 1 is a refractory lining, 2 is a melting pool, 3 is a bottom air brick, and 4 is a bubble.

Detailed Description

Example 1

Opening an argon switch, checking whether two air bricks at the bottom of the crucible are normal, if not, replacing a smelting preparation stage, estimating according to oxygen contents of main raw materials such as an electrolytic nickel plate, industrial pure iron, medium carbon ferrochrome and the like, adding carbon powder according to the mass fraction of 50%, and placing the carbon powder at the bottom of the crucible. Closing the furnace cover, and starting to vacuumize until the absolute vacuum degree reaches about 10^-2Pa, and the static gas leakage rate does not exceed 300Pa, L/s, if abnormal leakage detection and treatment are needed, electrifying and melting are carried out, full carbon-oxygen reaction is helpful to remove a part of N, after the furnace burden is completely melted down, a bottom blowing argon switch is opened, the flow or pressure is adjusted, the condition that bubbles on the surface of a molten pool are obviously escaped is observed, the time is 30min, dynamic gas leakage rate detection is carried out every 5min after the bottom blowing is finished, when the difference between two adjacent dynamic gas leakage rates does not exceed 5%, a refining period is finished, ferroniobium, return materials and the like are added through a material supplementing chamber, Al, Ti and the like enter a third stage, the operations of desulfurization, deslagging and the like are continuously carried out, pouring is carried out, and the N content of GH4169 is reduced to 12ppm of a finished ingot from the initial 60 ppm.

Example 2

And opening an argon switch, checking whether the two air bricks at the bottom of the crucible are normal or not, and replacing if the two air bricks are not normal.

In the smelting preparation stage, according to the estimation of oxygen content of industrial pure iron, electrolytic nickel plates, ferrosilicon and the like as main raw materials, corresponding carbon powder is added according to the mass fraction of 150% and is placed at the bottom of the crucible. Closing the furnace cover, and starting to vacuumize until the absolute vacuum degree reaches about 10^-2Pa, and static gas leakage rate not more than 300Pa, L/s, detecting leakage and treating if abnormal, electrifying for melting, removing part of N due to sufficient carbon-oxygen reaction, opening bottom-blowing argon switch, regulating flow or pressure, and observing gas on the surface of molten poolThe time is 60min, subject to the obvious bubble escape. And (4) entering a refining period after bottom blowing is finished, checking the dynamic air leakage rate every 5min, and finishing the refining period when the difference between the dynamic air leakage rates of two adjacent times is not more than 5%. Cr, V, return materials and the like are added through the feeding chamber. And carrying out operations such as desulfurization, deslagging and the like continuously. And (6) casting. By the above operation, the N content of 300M was reduced from the initial 40ppm to 5ppm of the finished ingot.

Claims

1. A method for rapid denitrification in vacuum induction furnace smelting comprises the following steps:

the method comprises the following steps: two air bricks are arranged at the radius of 1/2 at the outer bottom of the crucible of the vacuum induction furnace;

step two: before smelting, estimating according to the oxygen content in the main raw materials of an electrolytic nickel plate, industrial pure iron and medium carbon ferrochrome, adding corresponding carbon powder according to a certain proportion, and placing the carbon powder at the bottom in a crucible;

step four: electrifying and melting;

step five: judging the smelting process according to the vacuum degree and the dynamic gas leakage rate, and after the raw materials are melted down, opening bottom blowing argon until bubbles escape from the surface of a molten pool;

step six: and judging the refining period according to the dynamic gas leakage rate, finishing the refining period when the difference between the dynamic gas leakage rates of two continuous times is not more than 5%, then adding ferrocolumbium and return material, adding Al and Ti in the third stage, and finishing the denitrification process.

2. The method for rapid nitrogen removal by melting in a vacuum induction furnace as claimed in claim 1, wherein in the step two, corresponding carbon powder is added according to the C/O mass fraction of 0.5:1-2:1 according to the oxygen content in the furnace burden, and the carbon powder is spread on the bottom of the crucible.

3. The method for rapid denitrification by vacuum induction furnace melting according to claim 1, wherein the alloy raw materials are an initial raw material Ni plate, industrial pure Fe and MoFe which are not deoxidized and have small affinity with N, and after the refining period, the metals Nb and NbFe are added, and then Al and Ti are added.