CN113981322A - Low-carbon CrNiMo gear steel and preparation method thereof - Google Patents
Low-carbon CrNiMo gear steel and preparation method thereof Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 101
- 239000010959 steel Substances 0.000 title claims abstract description 101
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 32
- 229910019932 CrNiMo Inorganic materials 0.000 title claims abstract description 29
- 238000002360 preparation method Methods 0.000 title claims abstract description 17
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- 238000000034 method Methods 0.000 claims abstract description 34
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- 238000007664 blowing Methods 0.000 claims abstract description 33
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 26
- 238000010079 rubber tapping Methods 0.000 claims abstract description 26
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 24
- 230000008569 process Effects 0.000 claims abstract description 24
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- 238000003723 Smelting Methods 0.000 claims abstract description 21
- 239000002893 slag Substances 0.000 claims abstract description 21
- 238000009749 continuous casting Methods 0.000 claims abstract description 19
- 239000000126 substance Substances 0.000 claims abstract description 16
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- 229910052742 iron Inorganic materials 0.000 claims abstract description 15
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- 238000009489 vacuum treatment Methods 0.000 claims abstract description 15
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 14
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 14
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- 229910052802 copper Inorganic materials 0.000 claims abstract description 10
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 10
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 10
- 229910052717 sulfur Inorganic materials 0.000 claims abstract description 10
- 239000000956 alloy Substances 0.000 claims abstract description 9
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 8
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims abstract description 6
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 6
- 229910052791 calcium Inorganic materials 0.000 claims abstract description 6
- 239000011575 calcium Substances 0.000 claims abstract description 6
- 238000005266 casting Methods 0.000 claims description 19
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- 238000009792 diffusion process Methods 0.000 claims description 12
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- 238000003756 stirring Methods 0.000 claims description 9
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- 229910052786 argon Inorganic materials 0.000 claims description 5
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- 235000008733 Citrus aurantifolia Nutrition 0.000 claims description 4
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 4
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- 238000007872 degassing Methods 0.000 claims description 3
- 238000004886 process control Methods 0.000 claims description 3
- 230000001681 protective effect Effects 0.000 claims description 3
- OSMSIOKMMFKNIL-UHFFFAOYSA-N calcium;silicon Chemical compound [Ca]=[Si] OSMSIOKMMFKNIL-UHFFFAOYSA-N 0.000 claims description 2
- 239000011261 inert gas Substances 0.000 claims description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 6
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- 239000001301 oxygen Substances 0.000 abstract description 6
- 230000003749 cleanliness Effects 0.000 abstract description 4
- 238000005086 pumping Methods 0.000 abstract description 2
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- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 14
- 230000001276 controlling effect Effects 0.000 description 10
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- 239000000378 calcium silicate Substances 0.000 description 2
- OYACROKNLOSFPA-UHFFFAOYSA-N calcium;dioxido(oxo)silane Chemical compound [Ca+2].[O-][Si]([O-])=O OYACROKNLOSFPA-UHFFFAOYSA-N 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
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- 238000010248 power generation Methods 0.000 description 2
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 2
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- 229910000604 Ferrochrome Inorganic materials 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
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- 229910052729 chemical element Inorganic materials 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- 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
- C21C7/0056—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00 using cored wires
-
- 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
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- 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
- C21C7/10—Handling in a vacuum
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- 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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
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Abstract
The invention provides low-carbon CrNiMo gear steel and a preparation method thereof, wherein the low-carbon CrNiMo gear steel comprises the following chemical components in percentage by weight: c: 0.15 to 0.21%, Si: 0.15-0.30%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50 to 1.70%, Mo: 0.25 to 0.35%, Al: 0.025-0.038%, Cu is less than or equal to 0.20%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and N: 0.0075-0.0130% and the balance of iron and other inevitable impurities. The preparation method comprises the steps of electric furnace smelting, LF refining, VD vacuum treatment and continuous casting. The total oxygen content in the molten steel is controlled by controlling tapping carbon; controlling alloy components to basically reach the right position in the process of electric furnace tapping, and performing LF fine adjustment; adding a proper amount of slag during tapping, feeding an Al wire in the early stage of LF in place, and only soft blowing in the middle and later stages without adjusting components; the inclusions are denatured by weak calcium treatment before VD vacuum pumping, nitrogen is increased by bottom blowing nitrogen in a vacuum state, and the soft blowing time after VD vacuum breaking is reasonably controlled to ensure that the inclusions fully float upwards and are adsorbed by slag, so that the cleanliness of molten steel is improved, and the quality of inclusions of products is improved.
Description
Technical Field
The invention belongs to the field of steel for gears, and particularly relates to low-carbon CrNiMo gear steel and a preparation method thereof.
Background
With the increasing use requirements of wind power gear mechanical parts, particularly in offshore and high-altitude desert regions, the maintenance cost is high, sometimes the cost of replacing parts is even equivalent to the material cost, and in order to ensure that a wind power generation gear box is stably used for twenty years and not changed, the standards of gear steel inclusion for wind power by downstream users are increasingly strict.
At present, the cleanliness of common low-carbon CrNiMo gear steel is difficult to adapt to the use requirements of wind power industry under large load and complex environment. With the decline of the subsidy dividend of the country to the wind power industry, the enthusiasm of downstream users for beach installation is reduced, but the requirement of green clean power generation is continuously increased, and especially the increasingly tense energy requirement of the east region of China is met. Although the wind power industry in China develops rapidly in recent years, the yield, quality and production level of some high-requirement wind power steel products have a large gap with foreign advanced steel production countries (such as America, Japan and the like). In the aspects of molten steel cleanliness and inclusions, once improper control is achieved, the steel is extremely easy to become a fatigue crack source in the using process, and the service life of the steel is shortened.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
Aiming at the defects, the invention provides the low-carbon CrNiMo gear steel and the preparation method thereof, and the steel tapping carbon is controlled to control the total oxygen content in molten steel; controlling alloy components to basically reach the right position in the process of electric furnace tapping, and performing LF fine adjustment; adding a proper amount of slag during tapping, feeding an Al wire in the early stage of LF in place, and only soft blowing in the middle and later stages without adjusting components; the inclusions are denatured by weak calcium treatment before VD vacuum pumping, nitrogen is increased by bottom blowing nitrogen in a vacuum state, and the soft blowing time after VD vacuum breaking is reasonably controlled to ensure that the inclusions fully float upwards and are adsorbed by slag, so that the cleanliness of molten steel is improved, and the quality of inclusions of products is improved.
The invention is realized by the following technical scheme: the low-carbon CrNiMo gear steel comprises the following chemical components in percentage by weight:
c: 0.15 to 0.21%, Si: 0.15-0.30%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50 to 1.70%, Mo: 0.25 to 0.35%, Al: 0.025-0.038%, Cu is less than or equal to 0.20%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and N: 0.0075-0.0130% and the balance of iron and other inevitable impurities.
In the above scheme, in order to ensure stable and controllable mechanical properties, the following chemical components are preferably selected in percentage by weight:
c: 0.16 to 0.19%, Si: 0.20 to 0.28%, Mn: 0.64-0.70%, Cr: 1.60-1.70%, Ni: 1.52-1.60%, Mo: 0.28 to 0.32%, Al: 0.025-0.036%, Cu is less than or equal to 0.10%, P is less than or equal to 0.010%, S is less than or equal to 0.010%, and N: 0.0075-0.0120% of iron and the balance of other inevitable impurities. The production process controls each chemical element according to the following target values:
c: 0.18%, Si: 0.26%, Mn: 0.68%, P: 0.006%, S: 0.003%, Cr: 1.65%, Ni: 1.58%, Mo: 0.30%, Al: 0.030%, [ N ]: 0.0095%, Cu: 0.01%, and the balance Fe and inevitable impurities.
The preparation method of the low-carbon CrNiMo gear steel comprises the steps of electric furnace smelting, LF refining, VD vacuum treatment and continuous casting;
the molten iron ratio smelted by the electric furnace is more than or equal to 70 percent, the [ C ] at the tapping end point is 0.06-0.12 percent, the [ P ] is less than or equal to 0.008 percent, and the tapping temperature is more than or equal to 1650 ℃;
the process from smelting and tapping of the electric furnace to LF refining comprises the following components and temperature control target requirements: c: 0.08-0.15%, Si: 0.10 to 0.20%, Mn: 0.50-0.65%, Cr: 1.58-1.65% at a temperature not lower than 1550 ℃;
the LF refining adopts precipitation deoxidation combined with diffusion deoxidation, molten steel is put into a station to produce white slag, the white slag holding time is more than or equal to 20min, the smelting time is more than or equal to 40min, and a diffusion deoxidizer is added in multiple times at the middle and later stages of smelting;
in the VD vacuum treatment step, after molten steel reaches a VD station, feeding a calcium silicate wire for weak calcium treatment, then vacuumizing, degassing and refining, keeping the vacuum degree below 67Pa for more than or equal to 15min, feeding a small amount of aluminum wire after breaking the vacuum to adjust the aluminum content in the molten steel, increasing nitrogen by bottom blowing nitrogen, and carrying out soft blowing for 10-40 min;
and in the continuous casting step, the casting is protected in the whole process, the low superheat degree is adopted for casting, the superheat degree of molten steel is controlled to be 18-30 ℃, three-section type electromagnetic stirring is adopted, and the blank is drawn at a constant drawing speed in the whole process.
In the scheme, 1.3kg/t of large aluminum blocks are added for deoxidation when molten steel is tapped to 1/3 in the electric furnace smelting step, alloy primary adjustment chemical components are added to a process control target, and finally 3kg/t of cleaning promoter and 8kg/t of lime are added for slagging.
In the scheme, in the LF refining step, after the molten steel reaches the LF station, a diffusion deoxidizer and a precipitation deoxidizer are added for composite deoxidation, the aluminum wire is adjusted in place in the early stage of refining and is controlled to be 0.030-0.045%, the temperature of the molten steel is not less than 1650 ℃, the aluminum wire is not fed in the later stage of the LF process, the composition is finely adjusted and controlled to be in the early-middle stage, and the time for blowing inert gas in the LF soft blowing process is not less than 25 min.
In the scheme, in the VD vacuum treatment step, the flow rate of bottom-blown nitrogen is controlled to be 60-120 NL/min, and the soft blowing time is controlled to be 15-30 min after the VD breaks the air.
In the scheme, in the continuous casting step, the whole-process protective casting adopts long-nozzle argon protection, an integral submerged nozzle and a tundish covering agent.
In the scheme, in the continuous casting step, the three-section type electromagnetic stirring is M-EMS + S-EMS + F-EMS, the molten steel liquid level is ensured to be stable at a constant drawing speed in the whole process, and slag inclusion is avoided from being rolled into a casting blank.
In the scheme, the casting section in the continuous casting step is phi 600mm, and the whole process constant drawing speed blank drawing speed is 0.27 m/min.
In the scheme, the continuous casting step is followed by slow cooling treatment, the pit entry temperature of slow cooling is more than or equal to 600 ℃, the slow cooling time is more than or equal to 40 hours, and the pit exit temperature is less than or equal to 150 ℃.
Compared with the prior art, the invention has the beneficial effects that:
according to the invention, the total oxygen content in the molten steel is controlled by controlling tapping carbon, so that the molten steel is prevented from being oxidized excessively; controlling alloy components to basically reach the right position in the process of electric furnace tapping, and performing LF fine adjustment; adding a proper amount of slag charge during tapping, feeding the aluminum wire in place in the early stage of LF, and only soft blowing in the middle and later stages without adjusting components; carrying out weak calcium treatment before VD (vacuum distillation) vacuumizing, producing a large amount of fine and dispersed high-melting-point inclusions during the vacuum treatment, taking the fine and dispersed high-melting-point inclusions as cores, and wrapping CaS on the peripheries of the fine and dispersed high-melting-point inclusions so as to reduce MnS generation, wherein the shape of the inclusions is changed from strip-shaped or chain-shaped inclusions into single-point-shaped inclusions; in addition, after VD vacuum treatment, the inclusion is polymerized after the steel slag is mixed and stirred, and large-size inclusion is formed to be convenient for floating; and (3) bottom blowing nitrogen in a vacuum state for nitrogen increase, and controlling the soft blowing time after reasonable VD (vacuum degassing) is broken to ensure that impurities are fully floated and adsorbed by the molten slag.
The low-carbon CrNiMo gear steel prepared by the chemical components and the preparation method meets the following performance requirements:
non-metallic inclusions: the A fineness is less than or equal to 2.0 grade, the A thickness is less than or equal to 1.5 grade, the B fineness is less than or equal to 2.0 grade, the B fineness is less than or equal to 1.0 grade, the C fineness is less than or equal to 0.5 grade, the C thickness is less than or equal to 0.5 grade, the D fineness is less than or equal to 1.0 grade, the D thickness is less than or equal to 1.0 grade, and the Ds is less than or equal to 1.5 grade; according to ASTM E2283 standard, when the standard field area A0Is 150mm2The characteristic size of the maximum inclusion of the low-carbon CrNiMo gear steel is not more than 25.58 mu m, and the characteristic size of the traditional gear steel is more than 170 mu mThe above.
Mechanical properties: the tensile strength is more than or equal to 1320MPa, the yield strength is more than or equal to 1180MPa, the elongation after fracture is more than or equal to 12 percent, and the reduction of area is more than or equal to 40 percent; the impact KV2 (room temperature) is not less than 60J, and the product strength of the invention is higher than that of steel manufactured by the traditional method, and the impact toughness is better.
The preparation method can effectively improve the purity of the molten steel and improve the inclusion quality.
Drawings
Fig. 1 is an analysis diagram of extreme value data of inclusion length according to an embodiment of the present invention.
FIG. 2 is a graph showing the analysis of extreme value data of the length of inclusions in comparative examples.
Detailed Description
Preferred embodiments of the present invention will be described in more detail with reference to specific examples. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The low-carbon CrNiMo gear steel comprises the following chemical components in percentage by weight:
c: 0.15 to 0.21%, Si: 0.15-0.30%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50 to 1.70%, Mo: 0.25 to 0.35%, Al: 0.025-0.038%, Cu is less than or equal to 0.20%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and N: 0.0075-0.0130% and the balance of iron and other inevitable impurities.
Preferably, the low-carbon CrNiMo gear steel comprises the following chemical components in percentage by weight: c: 0.16 to 0.19%, Si: 0.20 to 0.28%, Mn: 0.64-0.70%, Cr: 1.60-1.70%, Ni: 1.52-1.60%, Mo: 0.28 to 0.32%, Al: 0.025-0.036%, Cu is less than or equal to 0.10%, P is less than or equal to 0.010%, S is less than or equal to 0.010%, and N: 0.0075-0.0120% of iron and the balance of other inevitable impurities.
The preparation method of the low-carbon CrNiMo gear steel comprises the steps of electric furnace smelting, LF refining, VD vacuum treatment, continuous casting and the like, and the specific requirements of the steps are as follows:
(1) electric furnace smelting
In order to control harmful residual elements in steel, reasonable matching of high-quality molten iron and pure steel scrap is realized, the manufacturing cost of steel making is greatly reduced, an electric furnace adopts a molten iron hot charging technology, and the molten iron ratio needs to be controlled to be more than or equal to 70%.
Preferably, the furnace wall of the electric furnace adopts multifunctional module oxygen blowing and carbon powder blowing technologies.
Preferably, the [ C ] of the tapping terminal point is 0.06-0.12%, and the preferable target is 0.08-0.12%; [ P ] 0.008% or less, preferably with a target of [ P ] 0.005% or less, a tapping temperature of 1650 ℃ or more, preferably with a target tapping temperature of 1680 ℃ or more.
Preferably, the process from electric furnace smelting tapping to LF refining comprises the following components and temperature control target requirements: c: 0.08-0.15%, Si: 0.10 to 0.20%, Mn: 0.50-0.65%, Cr: 1.58-1.65%; the temperature is more than or equal to 1550 ℃.
Preferably, in the tapping process, 1.3kg/t of large aluminum blocks are preferentially added for precipitation deoxidation when molten steel is tapped to 1/3 steel, the chemical components are primarily adjusted to a process control target by adding metal manganese and ferrochrome alloy through a high-position bunker, and finally 3kg/t of cleaning promoter and 8kg/t of lime are added for slagging so as to prepare for slagging in the next refining step.
(2) LF refining
The step adopts precipitation deoxidation and diffusion deoxidation. Molten steel enters a station to rapidly produce white slag, the white slag retention time is more than or equal to 20min, and the smelting time is more than or equal to 40 min; in order to effectively reduce the oxygen content in steel, feeding an Al wire for deoxidation in place 1-2 times in the early stage of smelting, controlling the Al content to be 0.030-0.045%, and not feeding the Al wire in the middle and later stages; the nickel beans or nickel plates are added at one time through a high-level bunker in the early-middle period, the Ni content is controlled to be 1.52-1.60%, the temperature of molten steel is guaranteed to be not less than 1650 ℃, and a small amount of diffusion deoxidizers are added in multiple batches in the middle-later period of smelting to keep the reducing atmosphere in the furnace; in the refining process, the foamed white slag is produced, so that impurities in the steel are effectively adsorbed, the time for blowing Ar gas in LF soft blowing is not less than 25min, and the purity of the molten steel is ensured.
Preferably, the diffusion deoxidizer takes the composite silicon carbide as a main material and the ferrosilicon powder as an auxiliary material, and the mass ratio of the diffusion deoxidizer to the ferrosilicon powder is 9: 1.
(3) VD vacuum treatment
In the VD vacuum treatment step, molten steel is fed into a VD station and then is fed into a 50-100 m/furnace silicon-calcium line for weak calcium treatment, each furnace is 100t molten steel, a large amount of fine and dispersed high-melting-point inclusions are produced during vacuum treatment, the inclusions serve as cores, and the periphery of the inclusions is wrapped with CaS, so that the generation of MnS is reduced, and the shapes of the inclusions are changed from strip-shaped or chain-shaped inclusions into single-point-shaped inclusions; and vacuumizing, degassing and refining, wherein N is increased in a bottom blowing nitrogen mode in the vacuum process, secondary oxidation caused by violent turnover of molten steel due to feeding of a nitrogen line after VD is broken is avoided, when the high vacuum is below 67Pa, the flow of the bottom blowing nitrogen is controlled to be 60-120 NL/min, steel ladles are prevented from being eroded by violent turnover of the molten steel, an Al line is fed in place once after VD is broken, the Al content in the molten steel is controlled to be 0.28-0.35%, the soft blowing time is controlled to be 15-30 min, so that impurities float upwards for a sufficient time and are adsorbed by the molten slag, nitrogen is increased by bottom blowing nitrogen, the soft blowing time is 10-40 min and is not more than 40min, and the original adsorbed impurities in the molten slag can return to the molten steel again to cause the deterioration of purity. The Al content of the vacuum-treated vacuum chamber is between 0.013 and 0.015 percent after the vacuum chamber is broken by VD, and is improved by 30 to 50 percent compared with the Al content of the vacuum chamber which is less than 0.010 percent after the vacuum chamber is broken by VD in the traditional method.
Preferably, during soft blowing, argon switching can be performed according to the nitrogen content of the molten steel, and pipeline blockage caused by molten steel backflow in the gas switching process is avoided, so that the soft blowing effect is influenced.
(4) Continuous casting
The radius of the continuous casting arc is 17m, the static pressure is large, and the solidification feeding is facilitated. The casting is protected in the whole process in the step, and the secondary oxidation of the molten steel is prevented. And (3) casting with low superheat degree, wherein the superheat degree of molten steel is controlled at 18-30 ℃. Three-stage electromagnetic stirring is adopted, the casting section phi is 600mm, the whole process of constant drawing speed blank drawing is adopted, the drawing speed is 0.27m/min, the liquid level fluctuation is reduced, and the surface slag entrapment is prevented.
Preferably, the continuous casting configuration combined type electromagnetic stirring system is an M-EMS + S-EMS + F-EMS three-section electromagnetic stirring system, the solidification structure can be regulated and controlled according to the requirement, the crystal structure of the casting blank is effectively controlled, the segregation of the casting blank is reduced, and the internal defects of the casting blank are reduced.
Preferably, the whole protection in the step adopts measures such as long-nozzle argon protection, integral submerged nozzle, tundish special covering agent and the like, so that the casting is protected and the secondary oxidation is prevented.
After the steps are finished, slow cooling treatment is carried out, preferably, the pit entry temperature of slow cooling is more than or equal to 600 ℃, the slow cooling time is more than or equal to 40 hours, and the pit exit temperature is less than or equal to 150 ℃. And after slow cooling, finishing, weighing, marking and warehousing.
Examples
The low-carbon CrNiMo gear steel comprises the following chemical components in percentage by mass: c: 0.18%, Si: 0.26%, Mn: 0.68%, P: 0.006%, S: 0.003%, Cr: 1.65%, Ni: 1.58%, Mo: 0.30%, Al: 0.030%, [ N ]: 0.0095%, Cu: 0.01%, and the balance Fe and inevitable impurities.
The preparation method of the low-carbon CrNiMo gear steel comprises the following steps: molten iron → electric furnace smelting → LF refining → VD vacuum treatment → continuous casting → slow cooling → finishing → weighing → marking → warehousing.
Electric furnace smelting:
the hot charging technology of molten iron is adopted, and the molten iron ratio is 82.3%.
1. Tapping indexes are as follows: tapping [ C ] 0.08%; tapping [ P ] 0.0035%; the tapping temperature is 1688 ℃.
2. And (5) tapping auxiliary material requirements: 1.3kg/t of aluminum, 8kg/t of lime and 3kg/t of cleaning promoter are added.
LF arrival index: c: 0.14%, Si: 0.18%, Mn: 0.60%, Cr: 1.62 percent; the temperature is 1580 ℃. Adding metal elements or alloys according to the lower limit of the alloy requirement to prevent the alloy from exceeding the target requirement.
LF refining:
1.80kg/t of diffusion deoxidizer composite silicon carbide and 0.20kg/t of ferrosilicon powder are added in small batches in multiple batches. Molten steel is put into a station to rapidly produce white slag, the white slag time is 40 minutes, and the smelting time is 80 minutes. In order to effectively reduce the oxygen content in steel, feeding an Al wire 2 times in the early stage of smelting to deoxidize to a proper position, controlling the Al content to be 0.040%, and not feeding the Al wire in the middle and later stages; the nickel beans are added into the furnace through a high-level bunker at one time in the early-middle period, the Ni content is controlled to be 1.58 percent, the temperature of the molten steel is ensured to be not less than 1650 ℃, and a small amount of diffusion deoxidizers are added into the furnace in multiple batches in the middle-later period to keep the reducing atmosphere in the furnace; in the refining process, the foamed white slag is produced, so that impurities in the steel are effectively adsorbed, the time for blowing Ar gas in LF soft blowing is not less than 25min, and the purity of the molten steel is ensured.
VD vacuum treatment:
feeding a 60 m/furnace calcium silicate wire after arrival, keeping the vacuum degree at 57Pa for 20 minutes, increasing N by bottom blowing nitrogen, and controlling the flow at 80 NL/min; feeding an aluminum wire after the air is broken to adjust the content of Al in the molten steel to be about 0.033 percent; the soft blowing time is 25min to ensure that the non-metallic inclusions in the molten steel float up sufficiently.
Continuous casting:
the continuous casting configuration combined type electromagnetic stirring system (M-EMS + S-EMS + F-EMS) adopts measures such as long-nozzle argon protection, integral submerged nozzle, tundish special covering agent and the like, realizes whole-course protective casting and prevents secondary oxidation.
Casting with low superheat degree, controlling the superheat degree of molten steel at 25 ℃, performing M-EMS + S-EMS + F-EMS three-stage electromagnetic stirring, controlling the casting section diameter to be 600mm, and controlling the pulling speed to be 0.27M/min under the action of weak cooling water by adopting constant pulling speed.
Slow cooling: the pit entry temperature is 680 ℃, the slow cooling time is 68h, and the pit exit temperature is 120 ℃.
The low-carbon CrNiMo gear steel hot-rolled round steel prepared in the embodiment is compared with the detection result of the traditional gear steel (comparative example), and the chemical components are shown in Table 1.
TABLE 1 chemical composition wt%
The examples and comparative examples were tested according to GB/T10561 Standard A method, and the inclusion rating results are shown in Table 2. Example analysis chart of extreme value data of inclusions in FIG. 1, where the reduction variable (Red. Var) is-LN (Pi)), where Pi is number/25, number is 1 to 24, and area A of the inclusions0＝150mm2Length of inclusion 2.648 ═ red. var) +7.293, it can be seen that the maximum inclusion feature size is not greater than 25.58 μm; comparative example length extreme value data analysis chart of inclusions shown in FIG. 2, area A of inclusions0＝150mm2Length of inclusionsThe Length is 18.324 (red. var) +47.430, and the maximum inclusion feature size is no greater than 174.0 μm.
TABLE 2 non-metallic inclusions
The largest size of the inclusions in the steel is estimated according to American standard ASTM E2283, the size (25.58um) of the inclusions estimated in the examples is far smaller than that of the inclusions (174um), the purity of molten steel in the examples is higher, and the size of the inclusions in the steel is smaller, so that the fracture of the inclusions on a steel matrix is reduced, the mechanical property of the steel is improved, and the service life of a product can be obviously prolonged.
Examples the mechanical properties (tensile, impact) are excellent, see table 3.
TABLE 3 mechanical Properties
As can be seen from Table 3, the strength and ductility indexes of the embodiment are obviously superior to those of the comparative example, and the product can bear larger load in the running and use process, can stably run in severer and complex desert, plateau and ocean environments, improves the fatigue life of the product and prolongs the service cycle of the wind power system.
The low-carbon CrNiMo gear steel prepared by the chemical components and the preparation method meets the following performance requirements:
non-metallic inclusions: the A fineness is less than or equal to 2.0 grade, the A thickness is less than or equal to 1.5 grade, the B fineness is less than or equal to 2.0 grade, the B fineness is less than or equal to 1.0 grade, the C fineness is less than or equal to 0.5 grade, the C thickness is less than or equal to 0.5 grade, the D fineness is less than or equal to 1.0 grade, the D thickness is less than or equal to 1.0 grade, and the Ds is less than or equal to 1.5 grade; according to ASTM E2283 standard, when the standard field area A0Is 150mm2The characteristic size of the maximum inclusion of the low-carbon CrNiMo gear steel is not more than 25.58 mu m, and the characteristic size of the maximum inclusion of the traditional gear steel is more than 170 mu m.
Mechanical properties: the tensile strength is more than or equal to 1320MPa, the yield strength is more than or equal to 1180MPa, the elongation after fracture is more than or equal to 12 percent, and the reduction of area is more than or equal to 40 percent; the impact KV2 (room temperature) is not less than 60J, and the product strength of the invention is higher than that of steel manufactured by the traditional method, and the impact toughness is better.
The preparation method can effectively improve the purity of the molten steel and improve the inclusion quality.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and technical principles of the described embodiments, and such modifications and variations should also be considered as within the scope of the present invention.
Claims (10)
1. The low-carbon CrNiMo gear steel is characterized by comprising the following chemical components in percentage by weight:
c: 0.15 to 0.21%, Si: 0.15-0.30%, Mn: 0.60-0.90%, Cr: 1.55-1.80%, Ni: 1.50 to 1.70%, Mo: 0.25 to 0.35%, Al: 0.025-0.038%, Cu is less than or equal to 0.20%, P is less than or equal to 0.020%, S is less than or equal to 0.010%, and N: 0.0075-0.0130% and the balance of iron and other inevitable impurities.
2. The low carbon CrNiMo gear steel according to claim 1, comprising the following chemical composition in weight percent:
c: 0.16 to 0.19%, Si: 0.20 to 0.28%, Mn: 0.64-0.70%, Cr: 1.60-1.70%, Ni: 1.52-1.60%, Mo: 0.28 to 0.32%, Al: 0.025-0.036%, Cu is less than or equal to 0.10%, P is less than or equal to 0.010%, S is less than or equal to 0.010%, and N: 0.0075-0.0120% of iron and the balance of other inevitable impurities.
3. The low carbon CrNiMo gear steel according to claim 1, comprising the following chemical composition in weight percent:
c: 0.18%, Si: 0.26%, Mn: 0.68%, P: 0.006%, S: 0.003%, Cr: 1.65%, Ni: 1.58%, Mo: 0.30%, Al: 0.030%, [ N ]: 0.0095%, Cu: 0.01%, and the balance Fe and inevitable impurities.
4. A preparation method of the low-carbon CrNiMo gear steel according to any one of claims 1 to 3, characterized by comprising the steps of electric furnace smelting, LF refining, VD vacuum treatment and continuous casting;
the molten iron ratio smelted by the electric furnace is more than or equal to 70 percent, the [ C ] at the tapping end point is 0.06-0.12 percent, the [ P ] is less than or equal to 0.008 percent, and the tapping temperature is more than or equal to 1650 ℃;
the process from smelting and tapping of the electric furnace to LF refining comprises the following components and temperature control target requirements: c: 0.08-0.15%, Si: 0.10 to 0.20%, Mn: 0.50-0.65%, Cr: 1.58-1.65% at a temperature not lower than 1550 ℃;
the LF refining adopts precipitation deoxidation combined with diffusion deoxidation, molten steel is put into a station to produce white slag, the white slag holding time is more than or equal to 20min, the smelting time is more than or equal to 40min, and a diffusion deoxidizer is added in multiple times at the middle and later stages of smelting;
in the VD vacuum treatment step, after molten steel reaches a VD station, feeding a calcium-silicon wire for weak calcium treatment, then vacuumizing, degassing and refining, keeping the vacuum degree below 67Pa for more than or equal to 15min, feeding an aluminum wire after breaking the vacuum to adjust the aluminum content in the molten steel, increasing nitrogen by bottom blowing nitrogen, and carrying out soft blowing for 10-40 min;
and in the continuous casting step, the casting is protected in the whole process, the low superheat degree is adopted for casting, the superheat degree of molten steel is controlled to be 18-30 ℃, three-section type electromagnetic stirring is adopted, and the blank is drawn at a constant drawing speed in the whole process.
5. The method for preparing low-carbon CrNiMo gear steel according to claim 4, wherein 1.3kg/t of large aluminum blocks are added for deoxidation when tapping to 1/3 molten steel in the step of electric furnace smelting, the alloy is added to primarily adjust chemical components to a process control target, and finally 3kg/t of cleaning promoter and 8kg/t of lime slagging are added.
6. The preparation method of the low-carbon CrNiMo gear steel according to claim 4, wherein in the LF refining step, a diffusion deoxidizer and a precipitation deoxidizer are added into molten steel after the molten steel reaches an LF station for composite deoxidation, the aluminum wire is adjusted to be in place in the early stage of refining and is controlled to be 0.030-0.045%, the temperature of the molten steel is not less than 1650 ℃, the aluminum wire is not fed into the late stage of the LF process, the composition fine adjustment is controlled to be in the early middle stage, and the time for LF soft blowing of inert gas is not less than 25 min.
7. The preparation method of the low-carbon CrNiMo gear steel as claimed in claim 4, wherein in the VD vacuum treatment step, the flow rate of bottom-blown nitrogen is controlled to be 60-120 NL/min, and after the VD is broken, the soft-blowing time is controlled to be 15-30 min.
8. The method for preparing the low-carbon CrNiMo gear steel as claimed in claim 4, wherein in the continuous casting step, the whole-process protective casting adopts long nozzle argon protection, an integral submerged nozzle and a tundish covering agent; the three-stage electromagnetic stirring is M-EMS + S-EMS + F-EMS.
9. The method for preparing low-carbon CrNiMo gear steel according to claim 4, wherein the casting section in the continuous casting step is phi 600mm, and the whole-process constant-drawing-speed blank drawing speed is 0.27 m/min.
10. The preparation method of the low-carbon CrNiMo gear steel as claimed in claim 4, wherein the continuous casting step is followed by slow cooling treatment, the pit entry temperature of the slow cooling treatment is more than or equal to 600 ℃, the slow cooling time is more than or equal to 40h, and the pit exit temperature is less than or equal to 150 ℃.
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| CN115233090A (en) * | 2022-06-17 | 2022-10-25 | 山东钢铁股份有限公司 | Low-carbon steel for track pin sleeve and preparation method thereof |
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