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Method for smelting COST-FB2 steel through gas-phase nitriding under negative pressure condition

A COST-FB2, gas-phase nitriding technology, applied in the direction of coating, metal material coating process, solid-state diffusion coating, etc.

Active Publication Date: 2019-08-06
NORTHEASTERN UNIV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

But at present, there is no effective gas-phase nitriding smelting process, which can accurately control the nitrogen content during smelting under COST-FB2 negative pressure conditions

Method used

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  • Method for smelting COST-FB2 steel through gas-phase nitriding under negative pressure condition
  • Method for smelting COST-FB2 steel through gas-phase nitriding under negative pressure condition
  • Method for smelting COST-FB2 steel through gas-phase nitriding under negative pressure condition

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Experimental program
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Effect test

Embodiment 1

[0074] Present embodiment adopts 30kg vacuum induction furnace to smelt target steel type COST-FB2, and its target composition is as table 4. The quality of this smelting is 22kg, and the nitrogen content is controlled at 0.02%. The ultimate vacuum of the furnace is 0.01Pa, and the maximum power is 100kW. The smelting process uses a magnesium-aluminum crucible with an inner diameter of 140mm and an inner depth of 300mm.

[0075] Table 4: Composition requirements of FB2 steel (wt / %)

[0076]

[0077] The smelting steps are as follows:

[0078] 1, determine the quality of every kind of alloy material according to table 4 and table 3, and carry out weighing batching, the required graphite carbon is equally divided into two parts.

[0079] 2. Distributing the alloy materials weighed above, including chromium, nickel, molybdenum, cobalt, industrial pure iron and half of carbon, which are added with the furnace, while the other half of carbon, silicon, vanadium, niobium, ferro...

Embodiment 2

[0088] In this embodiment, a 30kg vacuum induction furnace is used to smelt the target steel grade with a quality of 22kg, and the nitrogen content is controlled at 0.03%. The rest of the ingredients are shown in Table 4. Determine according to table 4 and table 3 the quality that needs every kind of alloy material, and carry out weighing batching, the required graphite carbon is equally divided into two parts.

[0089] The smelting steps are as follows:

[0090] 1. Distribute the alloy material weighed above, among which chromium, nickel, molybdenum, cobalt, industrial pure iron and half of carbon are added with the furnace, while the other half of carbon, silicon, vanadium, niobium, ferroboron and manganese are put in order In the silo.

[0091] 2. Slowly increase the power to about 52kW during the melting process and turn on the three-stage vacuum pump step by step until the vacuum degree is about 0.1Pa to ensure dehydrogenation, denitrification and deoxidation during the ...

Embodiment 3

[0099] Present embodiment adopts 100kg vacuum induction furnace smelting quality to be the target steel grade of 76kg, and nitrogen content is controlled at 0.02%, and all the other compositions are shown in Table 3. The magnesium-aluminum crucible used has an inner diameter of 210mm, an inner depth of 560mm, a nominal smelting mass of 85kg, a furnace limit vacuum of 1.2Pa, and a maximum power of 200kW. According to formula (8), the nitriding pressure is 2200Pa, and the nitriding time is 24min.

[0100] The smelting steps are as follows:

[0101] 1. According to Table 4 and Table 3, determine the quality of each alloy material required, and weigh the ingredients, and divide the required carbon equally into two parts.

[0102] 2. Distributing the alloy materials weighed above, including chromium, nickel, molybdenum, cobalt, industrial pure iron and half of carbon, which are added with the furnace, while the other half of carbon, silicon, vanadium, niobium, ferroboron and manga...

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Abstract

The invention relates to a method for smelting COST-FB2 steel through gas-phase nitriding under a negative pressure condition. The method comprises the following steps that firstly carbon deep deoxidation is performed under the condition of high vacuum degree, deoxidation is completed after the surface of molten steel is stable and bubbles do not rush out any longer; then an alloy element for promoting nitrogen dissolution is added and completely molten, and then gas-phase nitriding is started; during gas-phase nitriding, nitriding pressure during gas-phase nitriding is calculated by using thermodynamic calculation software Factsage, the molten steel temperature is accurately controlled, and the nitriding time is calculated and determined through the surface area of the molten steel, the volume of the molten steel and the nitrogen balance content; when gas-phase nitriding is about to be completed, the alloy element boron and the volatile manganese are added, then through argon filling,pressurization is performed until the high pressure is reached, pressurization casting is performed under the condition that the nitrogen partial pressure is kept unchanged, the under-pressure stateis kept in the solidification process, vacuum breaking is performed after complete solidification, and a COST-FB2 steel cast ingot which has the content of N being 0.015%-0.03% and the content of O being less than or equal to 0.0035%, is uniform in component and compact in structure is prepared.

Description

technical field [0001] The invention relates to the field of metal smelting, in particular to a method for smelting COST-FB2 steel by gas-phase nitriding under negative pressure conditions. Background technique [0002] COST-FB2 steel is developed by the European COST (CO-operation in Science and Technology) project team and can be used for steam turbine rotor steel under the ultra-supercritical condition of 625℃ / 32MPa. This steel mainly improves its high temperature strength through precipitation strengthening, solid solution strengthening and grain boundary strengthening, among which the addition of about 0.01% B in the steel significantly improves its high temperature creep performance, prolongs its high temperature service life, and significantly improves its The power generation efficiency of thermal power generating units can increase the current average power generation efficiency in my country from 45% to 49.7%, and reduce the emission of greenhouse gases such as carb...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C23C8/26C21C7/06C21C7/10C22C33/04C22C38/02C22C38/04C22C38/44C22C38/46C22C38/48C22C38/52C22C38/54
CPCC21C7/06C21C7/10C22C33/04C22C38/02C22C38/04C22C38/44C22C38/46C22C38/48C22C38/52C22C38/54C23C8/26
Inventor 姜周华彭雷朕耿鑫刘福斌李花兵李晓凯侯昱李星李博洋
Owner NORTHEASTERN UNIV
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