CN113981186A - Atmosphere protection heat treatment process for preventing decarbonization and recarburization - Google Patents

Atmosphere protection heat treatment process for preventing decarbonization and recarburization Download PDF

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CN113981186A
CN113981186A CN202111115107.7A CN202111115107A CN113981186A CN 113981186 A CN113981186 A CN 113981186A CN 202111115107 A CN202111115107 A CN 202111115107A CN 113981186 A CN113981186 A CN 113981186A
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heat treatment
treatment furnace
protective atmosphere
introducing
oxygen potential
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CN113981186B (en
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王奇飞
闫海生
陆红波
吴波
傅岳超
孔祥升
卿建华
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Zheshang Zhongtuo Group Zhejiang New Material Technology Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/76—Adjusting the composition of the atmosphere
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

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Abstract

The invention discloses an atmosphere protection heat treatment process for preventing decarbonization and recarburization, which mainly comprises the following steps: introducing N with the volume 3-4 times that of the heat treatment furnace2Discharging air in the heat treatment furnace; introducing a protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace, wherein the protective atmosphere comprises CO in percentage by volume20.7％、CO 19.27％、CH42.47% and H277.56 percent; when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing the protective atmosphere, and simultaneously introducing N2Maintaining the pressure, controlling the temperature of the heat treatment furnace at 750-; after the heat preservation time is over, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2The protective atmosphere in the heat treatment furnace is discharged until the furnace is finishedCooling the heat treatment furnace to 540-560 ℃ or below, and taking out the steel to complete the heat treatment process. The invention avoids the unstable condition of the components of the protective atmosphere, avoids the decarburization and the recarburization and ensures the heat treatment quality of the steel.

Description

Atmosphere protection heat treatment process for preventing decarbonization and recarburization
Technical Field
The invention relates to the technical field of heat treatment, in particular to an atmosphere protection heat treatment process for preventing decarbonization and recarburization.
Background
The cold heading wire rod, namely the wire rod material leaving the factory from a steel mill, needs to be subjected to the working procedures of spheroidizing annealing, acid washing, phosphorization and saponification, wire drawing and the like, so that the plasticity and toughness of the material are improved, the individualized requirements of customers on specifications are met, and the cold heading performance of the material is improved. In the key procedure spheroidizing annealing process, the steel is easy to decarbonize under the high-temperature condition. Decarburization of steel has two processes: firstly, C atoms on the surface are oxidized; secondly, the loss of C atoms on the surface causes the reduction of the concentration of C on the surface, wherein O2, H2O and the like belong to oxidizing gases and can perform oxidation and decarburization reaction with the C atoms in the steel to cause the decarburization of the steel surface; CO, H2, etc. are reducing gases that reduce the oxide and decarburized layers on the steel surface to restore the original composition of the steel surface. According to the equilibrium principle of chemical reaction, the oxidation reaction and the reduction reaction on the surface of steel are carried out simultaneously, and if the speed of the oxidation reaction is higher than that of the reduction reaction, the surface of the material is decarburized; otherwise, the carburization phenomenon, that is, the phenomenon of carbon content enrichment on the surface of the material, occurs.
After the oxidation and decarburization phenomena appear on the surface of steel, the surface state is very rough and loses luster, and a rough surface is easily formed, so that the surface quality of a product is influenced. During cold heading production, the decarburized surface can be adhered to a die to cause product galling, subsequent heat treatment can cause conditions such as quenching cracks, soft spots and insufficient hardness, carburization can cause the product to crack during cold heading, and if the product is a high-strength bolt, the hydrogen embrittlement sensitivity of the product can be increased.
At present, the commonly used anti-decarbonization atmosphere process is methanol instillation cracking as a protective atmosphere, the cracking principle is that CH3OH is directly dripped into a hearth heated at high temperature, and through high-temperature cracking and cracking of organic matters, reductive mixed gas containing CO, H2 and the like is generated, so that the aim of preventing decarbonization is achieved, but the method of using methanol instillation cracking as the protective atmosphere generally needs other organic liquids such as ethanol and isopropanol because the carbon potential of a cracked product is low when cracked gas is generated. The dripping amount and the dripping agent are easily influenced by factors such as material, charging amount, furnace volume, temperature and the like. In addition, the instillation cracking of the methanol can cause carbon deposition on the furnace wall, which hinders the heat radiation conduction, the cracking of the methanol is insufficient, which causes the unstable components of the cracking gas, the phenomena of the surface decarburization and the uncontrolled recarburization of the material, and further the product scrapping.
Disclosure of Invention
The invention provides a heat treatment process for preventing decarburization and recarburization under the protection of protective atmosphere in order to avoid the defects of the prior art.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides an atmosphere protection heat treatment process for decarbonization prevention and recarburization, which comprises the following steps:
s100, placing the steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3-4 times of the volume of the heat treatment furnace into the heat treatment furnace2Discharging air in the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace; s200, when the oxygen potential value in the heat treatment furnace reaches the value of 900-910, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace, wherein the protective atmosphere comprises CO in percentage by volume2 0.7％、CO 19.27％、CH42.47% and H277.56 percent; s300, when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing protective atmosphere and simultaneously introducing N2Maintaining the pressure, controlling the temperature of the heat treatment furnace at 750-; s400, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2Will beAnd discharging the protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 540-.
In several embodiments, the steel is specifically SCM435 alloy steel.
In several embodiments, in S300, the N2At a feed rate of 4 to 10m3/h。
In several embodiments, in S300, the oxygen potential value is controlled to stabilize at 1050 during the soak time.
In several embodiments, in S100 to S400, the oxygen potential value in the heat treatment furnace is monitored by a detection probe.
The invention has the following beneficial effects:
the invention is realized by feeding N2Discharging oxidizing gas existing in the furnace, and preventing the material from decarbonizing due to the reaction of the material and oxygen at high temperature; second pass CO2 0.7％、CO 19.27％、CH42.47% and H277.56% of specific protective atmosphere proportion, combined with the oxygen potential value condition in the furnace, can protect the steel, make the oxidation reaction and the reduction reaction on the steel surface go on simultaneously, avoid the condition of decarbonization, recarburization, and because the proportion of protective atmosphere is fixed, avoid the unstable condition of protective atmosphere composition, guarantee steel heat treatment quality.
Drawings
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not to be considered limiting of the scope of the present disclosure.
FIG. 1 is a line graph schematically showing the relationship between nitrogen gas feeding amount and oxygen potential value;
FIG. 2 schematically shows the decarburisation and recarburisation of a steel at an oxygen potential value of 900;
FIG. 3 schematically shows the decarburization and the recarburization of a steel at an oxygen potential value of 980;
FIG. 4 schematically illustrates decarburization and recarburization of a steel at a value of 1050 oxygen potential;
FIG. 5 schematically shows decarburization and recarburization of a steel at an oxygen potential value of 1100.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below, and the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention, and all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without inventive efforts shall fall within the scope of the present invention.
The terminology used herein is for the purpose of describing embodiments only and is not intended to be limiting and/or limiting of the invention.
In the invention, the adopted steel is SCM435 alloy steel, and the SCM435 alloy structural steel has chemical compositions (%): 0.33-0.38 percent of carbon C, 0.15-0.35 percent of silicon Si, 0.60-0.90 percent of manganese Mn, 0.030 percent of allowable residual content of sulfur S, 0.030 percent of allowable residual content of phosphorus P, 0.90-1.20 percent of chromium Cr, 0.15-0.30 percent of nickel Ni, and 0.25 percent of allowable residual content of molybdenum Mo, wherein the production process of the SCM435 alloy steel is 'two-ball two-drawing', namely spheroidizing annealing, acid pickling phosphorus saponification, semi-finished product drawing, spheroidizing annealing, acid pickling phosphorus saponification and finished product drawing, wherein the spheroidizing annealing process aims to spheroidize carbides in steel to obtain granular pearlite.
Specifically, the heat treatment process comprises the following steps:
firstly, putting steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3-4 times of the volume of the heat treatment furnace into the heat treatment furnace2Discharging the air containing oxidizing gas in the heat treatment furnace by the nitrogen gas charged, and monitoring the oxygen potential in the heat treatment furnace by a detection probeAnd (4) judging whether the air in the furnace is completely discharged or not according to the oxygen potential value.
Secondly, when the oxygen potential value in the heat treatment furnace reaches the value of 900-910, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace through a detection probe, wherein the protective atmosphere comprises CO in percentage by volume20.7％、CO 19.27％、CH42.47% and H2 77.56％。
When the oxygen potential value in the heat treatment furnace reaches the value of 900-:
TABLE 1 relationship table of nitrogen gas feeding amount and oxygen potential value
Amount of nitrogen introduced 1 time nitrogen gas 2 times of nitrogen 3 times of nitrogen 3.5 times of nitrogen 4 times of nitrogen
Oxygen potential value 780 850 900 910 910
Wherein, 1-4 times of nitrogen gas means 1-4 times of the volume of the heat treatment furnace, and according to table 1 and fig. 1, when 3 times or more of nitrogen gas is introduced, the oxygen potential value tends to be stabilized at about 900, and thus the nitrogen gas introduction amount of 3-4 times is selected.
Then, the oxygen potential value is continuously monitored, when the oxygen potential value in the heat treatment furnace reaches 1050, the protective atmosphere is continuously introduced, and N is introduced at the same time2Pressure maintaining, N2At a feed rate of 4 to 10m3And/h, controlling the temperature of the heat treatment furnace to be 750-770 ℃, and the heat preservation time to be 10-12h, wherein the oxygen potential value in the heat treatment furnace needs to be stably controlled to be 1050 within the heat preservation time.
After the protective atmosphere is introduced into the furnace, the oxygen-containing gas in the furnace can be continuously reduced, the oxygen potential value is increased again, and the decarburization and recarburization conditions of the material under different oxygen potential values are shown in the table 2:
TABLE 2SCM435 decarbonization and recarburization in different oxygen potential values
Figure BDA0003275303650000031
And fig. 1-3 show decarburization and recarburization at oxygen potential values of 900, 980, 1050, and 1100, respectively.
In combination with Table 2 and FIGS. 2-5, when the oxygen potential value in the furnace is 1050, in combination with the protective atmosphere, no decarburization and no recarburization of the steel occur.
Finally, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2And discharging the residual protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 540-560 ℃ or below, taking out the steel, and preventing decarburization caused by reaction between the high-temperature surface of the material and air during discharging, thereby completing the heat treatment process, wherein the residual unreacted protective atmosphere is subjected to combustion treatment.
Example 1
An atmosphere protection heat treatment process for preventing decarbonization and recarburization comprises the following steps:
s100, placing the steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3 times of the volume of the heat treatment furnace into the heat treatment furnace2Monitoring the oxygen potential value in the heat treatment furnace through a detection probe;
s200, when the oxygen potential value in the heat treatment furnace reaches 900, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace through a detection probe, wherein the protective atmosphere comprises CO in percentage by volume2 0.7％、CO 19.27％、CH42.47% and H2 77.56％。
S300, when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing protective atmosphere and simultaneously introducing N2Pressure maintaining, N2At a feed rate of 6m3And/h, controlling the temperature of the heat treatment furnace at 750-.
S400, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2And discharging the residual protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 550 ℃ or below, taking out the steel, and finishing the heat treatment.
Example 2
An atmosphere protection heat treatment process for preventing decarbonization and recarburization comprises the following steps:
s100, placing the steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3 times of the volume of the heat treatment furnace into the heat treatment furnace2Monitoring the oxygen potential value in the heat treatment furnace through a detection probe;
s200, when the oxygen potential value in the heat treatment furnace reaches 900, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace through a detection probe, wherein the protective atmosphere comprises CO in percentage by volume2 0.7％、CO 19.27％、CH42.47% and H2 77.56％。
S300, when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing protective atmosphere and simultaneously introducing N2Pressure maintaining, N2At a feed rate of 4m3H, controlling heat treatmentThe temperature of the treatment furnace is kept at 750-770 ℃, and the holding time is 10 h.
S400, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2And discharging the residual protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 540 ℃ or below, taking out the steel, and finishing the heat treatment.
Example 3
An atmosphere protection heat treatment process for preventing decarbonization and recarburization comprises the following steps:
s100, placing the steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3 times of the volume of the heat treatment furnace into the heat treatment furnace2Monitoring the oxygen potential value in the heat treatment furnace through a detection probe;
s200, when the oxygen potential value in the heat treatment furnace reaches a value of 910, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace through a detection probe, wherein the protective atmosphere comprises CO in percentage by volume2 0.7％、CO 19.27％、CH42.47% and H2 77.56％。
S300, when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing protective atmosphere and simultaneously introducing N2Pressure maintaining, N2At an inlet velocity of 10m3And/h, controlling the temperature of the heat treatment furnace at 750-.
S400, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2And discharging the residual protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 560 ℃ or below, taking out the steel, and completing the heat treatment.
The present invention describes preferred embodiments, including the best mode known to the inventors for carrying out the invention. Of course, variations of these preferred embodiments will be apparent to those skilled in the art. The inventors envision that the variations may be used as appropriate by those skilled in the art and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the claims. Moreover, any and all possible variations of the above-described elements are encompassed by the present invention unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims (5)

1. An atmosphere protection heat treatment process for preventing decarbonization and recarburization is characterized by comprising the following steps:
s100, placing the steel into a heat treatment furnace, controlling the heat treatment furnace to heat up, and simultaneously introducing N3-4 times of the volume of the heat treatment furnace into the heat treatment furnace2Discharging air in the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace;
s200, when the oxygen potential value in the heat treatment furnace reaches the value of 900-910, introducing protective atmosphere into the heat treatment furnace, and monitoring the oxygen potential value in the heat treatment furnace, wherein the protective atmosphere comprises CO in percentage by volume2 0.7％、CO 19.27％、CH42.47% and H2 77.56％；
S300, when the oxygen potential value in the heat treatment furnace reaches 1050, continuously introducing protective atmosphere and simultaneously introducing N2Maintaining the pressure, controlling the temperature of the heat treatment furnace at 750-;
s400, after the heat preservation time is finished, controlling the heat treatment furnace to cool, stopping introducing the protective atmosphere and continuously introducing N2And discharging the protective atmosphere in the heat treatment furnace until the temperature of the heat treatment furnace is reduced to 540-.
2. The decarbonization-preventing recarburization-enhancing atmosphere-protecting heat treatment process of claim 1, wherein the steel is SCM435 alloy steel.
3. The decarbonization-preventing recarburizing-enhancing atmosphere-protecting heat treatment process of claim 2, wherein in S300, N is2At a feed rate of 4 to 10m3/h。
4. The process of claim 3, wherein the oxygen potential value is controlled to be 1050 during the holding time in S300.
5. The process of claim 4, wherein the oxygen potential in the furnace is monitored by a probe at S100 to S400.
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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003201512A (en) * 2002-01-04 2003-07-18 Chugai Ro Co Ltd Method for stabilization of furnace atmosphere in batch- type annealing furnace
CN104988288A (en) * 2015-07-29 2015-10-21 西安市北恒实业有限公司 No-hydrogen atmosphere protection heat treatment process completely without decarburization for steel
EP3168314A1 (en) * 2015-11-13 2017-05-17 Air Liquide Deutschland GmbH Method for heat treating metallic work pieces

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2003201512A (en) * 2002-01-04 2003-07-18 Chugai Ro Co Ltd Method for stabilization of furnace atmosphere in batch- type annealing furnace
CN104988288A (en) * 2015-07-29 2015-10-21 西安市北恒实业有限公司 No-hydrogen atmosphere protection heat treatment process completely without decarburization for steel
EP3168314A1 (en) * 2015-11-13 2017-05-17 Air Liquide Deutschland GmbH Method for heat treating metallic work pieces

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