JP2009287070A - Method for preparatorily baking holder and apparatus for determining completion of preparatory baking - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preparatorily baking a holder, which can give a stable nitriding potential and a nitriding quality to a workpiece in the first heat treatment of the workpiece without performing a complicated preparation work, when heat-treating the workpiece in a heat treatment furnace into which ammonia gas is supplied, and to provide an apparatus for determining the completion of preparatory baking. <P>SOLUTION: The method for preparatorily baking the holder 22 which is used when the workpiece 21 to be heat-treated in the heat treatment furnace 2 into which the ammonia gas is supplied is placed in the heat treatment furnace 2 includes: preparatorily baking the holder 22 which is mounted in the heat treatment furnace 2 before heat-treating the workpiece 21; measuring a concentration of remaining ammonia in an atmospheric gas in the heat treatment furnace 2 which is preparatorily baking the holder; and determining the completion of the preparatory baking of the holder 22 based on a value of the measured concentration of the remaining ammonia. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an empty baking method and an empty baking completion determination device for a jig used when a workpiece to be heat-treated in a heat treatment furnace to which ammonia gas is supplied is placed in the heat treatment furnace.

Conventionally, treatment for intruding nitrogen into the surface of a steel material, such as nitriding quenching and carburizing and nitriding quenching, has been performed.
For example, as described in Patent Document 1, by nitriding austenitic stainless steel at a high temperature, nitrogen is penetrated into the surface of the austenitic stainless steel to harden the surface.

When such a treatment for intruding nitrogen into the steel surface is performed by atmospheric heat treatment using a heat treatment furnace, the workpiece to be treated is placed in the heat treatment furnace via a jig.
In addition, when performing a treatment to infiltrate nitrogen into the steel surface, heat treatment is performed while supplying ammonia at a predetermined flow rate into the heat treatment furnace, but before actually performing heat treatment on the workpiece, heat treatment in an atmosphere in which ammonia is supplied. Only the jig is baked in the furnace to remove the gas adsorbed on the jig, or the atmosphere in the heat treatment furnace is adsorbed on the jig surface in advance.

This is done to stabilize the nitriding potential in the atmosphere in the heat treatment furnace when heat-treating the workpiece, but the conditions for performing the baking such as time and number of times are not clearly defined, Depending on the intuition and knack on site, the baking is performed once or twice as appropriate in the processing time.
The nitriding potential is generally expressed by the following equation using the ammonia gas concentration P (NH ₃ ) and the hydrogen gas concentration P (H ₂ ). The ammonia gas concentration P (NH ₃ ) Depends on the height.
(Nitriding potential) = K · P (NH ₃ ) / {P (H ₂ ) ^3/2 }
K in the above formula is a constant.

  However, when nitriding is performed at a high temperature such as nitriding and quenching, even if the jig is baked about once or twice, when the workpiece is actually heat-treated, the processing during the first few batches is performed. However, the target nitriding potential and nitriding quality cannot be obtained, and the target nitriding potential and nitriding quality are approached with the number of treatments.

For example, after the jig A having the first shape and the jig B having the second shape (the jig B is smaller than the jig A) are baked once in a predetermined time, the workpiece When the nitriding and quenching treatment is performed, the nitriding potential in the heat treatment furnace as shown in FIG. 7 is a value deviating from the target value in the first treatment in both the jig A and the jig B. As the number of processing is repeated, the target value is approached.
Further, as shown in FIG. 8, the depth of the hardened layer of the workpiece subjected to the nitriding and quenching treatment is also a value deviated from the target value in the first treatment in both the jig A and the jig B, and the number of treatments The target value will be approached as the values are repeated.

Therefore, if the nitridation quality of the workpiece is checked after each process and the nitridation quality such as nitriding potential and hardened layer depth has not converged to the target value and is stable, the production of the product As a result, the preparatory work before the heat treatment of the work was started was very complicated.
Japanese Patent Laid-Open No. 5-222512

  Therefore, in the present invention, a jig capable of obtaining a stable nitriding potential and nitriding quality from the time of the first heat treatment of the workpiece without performing complicated preparatory work on the heat treatment of the workpiece performed after the jig is baked. An empty baking method and an empty baking completion determination device are provided.

The jig baking method and the baking completion determination device for solving the above-described problems have the following characteristics.
That is, according to the first aspect of the present invention, there is provided a jig baking method used when a workpiece to be heat-treated in a heat treatment furnace to which ammonia gas is supplied is placed in the heat treatment furnace, and the workpiece is heat-treated. Before, the jig placed in the heat treatment furnace is baked, the residual ammonia concentration in the atmosphere in the heat treatment furnace being baked is measured, and based on the value of the measured residual ammonia concentration, the treatment is performed. Judge the completion of baking of the ingredients.

  In addition, as described in claim 2, the determination of the completion of the baking of the jig is performed when the amount of change over time in the residual ammonia concentration measured during the baking is within a predetermined range. Do.

  The apparatus according to claim 3, wherein the apparatus is used for determining completion of empty firing of a jig used when a workpiece to be heat-treated in a heat-treatment furnace supplied with ammonia gas is placed in the heat-treatment furnace. Measuring means for measuring the residual ammonia concentration in the furnace, and determination means for determining completion of empty baking of the jig based on the value of the residual ammonia concentration measured by the measuring instrument.

  According to a fourth aspect of the present invention, the determination means includes a calculation unit that calculates a temporal change amount of the residual ammonia concentration measured by the measuring instrument, and a temporal change of the residual ammonia concentration calculated by the calculation unit. A determination unit configured to determine whether the jig has been baked or not when the amount falls within a predetermined range.

  According to the present invention, a jig of various sizes and shapes is baked by the same process (by baking the jig until the residual ammonia concentration becomes constant), Since it is possible to obtain a constant nitriding potential and hardened layer depth from the first heat treatment, it is possible to improve the quality of the heat-treated workpiece while simplifying the preparation work for a wide range of workpieces. it can.

  Next, modes for carrying out the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a heat treatment furnace 2 for performing a treatment for intruding nitrogen into the surface of a steel material such as nitriding and carburizing and nitriding, and a jig 22 used for installing a workpiece 21 in the heat treating furnace 2. The baking completion determination apparatus 1 is shown.

The treatment for intruding nitrogen into the steel material surface is performed by atmospheric heat treatment using the heat treatment furnace 2, and the workpiece 21 to be treated is placed in the heat treatment furnace 2 via the jig 22.
The heat treatment furnace 2 is connected to an ammonia gas supply pipe 25 for supplying ammonia gas into the heat treatment furnace 2. When performing heat treatment of the workpiece 21 and empty firing of the jig 22, the ammonia gas supply pipe 25 is connected to the heat treatment furnace 2. A predetermined amount of ammonia gas is supplied into the heat treatment furnace 2 through the gas supply pipe 25.

  That is, in the process of injecting nitrogen into the work 21, the work 21 is installed in the heat treatment furnace 2 via the jig 22, and a predetermined flow rate of ammonia gas is supplied into the heat treatment furnace 2 in which the work 21 is installed. This is performed by heating the atmosphere in the heat treatment furnace 2 to a predetermined temperature.

  When performing a treatment for intruding nitrogen into the surface of the work 21, only the jig 22 is baked in the heat treatment furnace 2 in an atmosphere to which ammonia gas is supplied before the heat treatment is actually performed on the work 21. The gas adsorbed on the jig 22 and the oxide film formed on the surface of the jig 22 are removed, or the atmosphere in the heat treatment furnace 2 is adsorbed on the surface of the jig 22.

  The jig 22 is baked in order to stabilize the nitriding potential in the atmosphere in the heat treatment furnace 2 when the work 21 is heat-treated. There are cases where the atmosphere in the heat treatment furnace 2 is not stable when the heat treatment for the workpiece 21 is started only by performing empty baking once or twice in time.

This is due to the following reason.
That is, ammonia gas (NH ₃ ) is decomposed by the catalytic action of the member when it comes into contact with the high-temperature member, but ammonia supplied into the heat treatment furnace 2 when the jig 22 is baked. The gas is decomposed by the catalytic action on the surface of the jig 22 that has become high temperature.
Therefore, if the composition (area covered by the oxide film) on the surface of the jig 22 that performs the catalytic action changes, the decomposition rate of ammonia gas changes, and the nitriding potential in the heat treatment furnace 2 and the nitriding quality of the work 21 are changed. Will fluctuate.

In addition, an oxide film is formed on the surface of the jig 22 during the manufacturing process, and the formed oxide film is reduced according to the equation shown in FIG. Decrease.
That is, the ammonia gas supplied into the heat treatment furnace 2 is decomposed at a high temperature to generate nitrogen gas (N ₂ ) and hydrogen gas (H ₂ ). The oxide film such as iron (Fe), chromium (Cr), and molybdenum (Mo), which are components, is reduced, and the oxide film formed on the surface of the jig 22 is reduced.

Further, when the ammonia gas in the heat treatment furnace 2 comes into contact with the surface of the jig 22, the decomposition proceeds due to the catalytic action of the metal member constituting the jig 22, but the surface of the jig 22 is covered with the oxide film. If so, contact with the metal member having a catalytic action is hindered and decomposition is suppressed.
Therefore, the residual ammonia concentration in the heat treatment furnace 2 changes depending on the amount of the oxide film formed on the surface of the jig 22, and the nitriding potential in the heat treatment furnace 2 and the nitriding quality of the work 21 change.

Thus, heating the jig 22 to a high temperature reduces the amount of oxide film on the surface of the jig 22, and the residual ammonia concentration in the heat treatment furnace 2 changes depending on the amount of oxide film on the surface of the jig 22. When the heat treatment of the workpiece 21 is started with the oxide film remaining on the jig 22 even after baking, the oxide film of the jig 22 is reduced during the heat treatment of the workpiece 21 and gradually decreases. Since the residual ammonia concentration in the heat treatment furnace 2 changes, it becomes difficult to obtain the nitriding potential in the heat treatment furnace 2 and the nitriding quality of the work 21 as intended.
Therefore, when the jig 22 is baked, all the oxide film on the surface of the jig 22 is removed, and the decomposition behavior of the ammonia gas in the heat treatment furnace 2 is stabilized and the residual ammonia concentration becomes constant. is important.

  However, since the shape (including size) of the jig 22 used at the time of heat treatment of the workpiece 21 and the amount of the oxide film formed at the time of manufacturing the jig 22 differ depending on the workpiece 21 and the jig 22, the oxide film is completely The baking conditions, such as the baking time required for removal, cannot be generally determined.

  Therefore, in this example, when performing the blank firing of the jig 22, the blank firing completion determination device 1 determines that the blank firing of the jig 22 has been completed, and from the first processing of the workpiece 21. The nitriding potential in the heat treatment furnace 2 and the nitriding quality of the work 21 can be obtained.

  The empty baking completion determination device 1 is supplied with an atmosphere in the heat treatment furnace 2 and measures the residual ammonia concentration in the supplied atmosphere in the heat treatment furnace 2, and the residual ammonia concentration measurement instrument. And a determination device 12 that determines completion of empty baking of the jig 22 based on the value of the residual ammonia concentration measured by 11.

  The determination device 12 includes a calculation unit 12a that calculates a temporal change amount of the residual ammonia concentration measured by the residual ammonia concentration measuring instrument 11, and a temporal change of the residual ammonia concentration calculated by the calculation unit 12a. The determination part 12b which determines completion of the baking of the jig | tool 22 based on quantity is provided, and the memory | storage part 12c in which the determination criteria of the determination by the said determination part 12b, etc. were memorize | stored.

  When determining the completion of the baking of the jig 22 using the empty baking completion determination device 1 configured as described above, first, the atmosphere in the heat treatment furnace 2 in which the jig 22 is burned is taken out as a derived gas, The residual ammonia concentration measuring device 11 measures the residual ammonia concentration of the extracted gas.

The measurement of the residual ammonia concentration by the residual ammonia concentration measuring instrument 11 is repeated continuously or intermittently during the baking of the jig 22, and the measurement value by the residual ammonia concentration measuring instrument 11 is determined by the determination device. 12 is input.
In the determination device 12, the amount of change over time in the residual ammonia concentration is calculated by the calculation unit 12a using the input measurement value.

Here, when the jig 22 is baked in the heat treatment furnace 2, as described above, the oxide film of the jig 22 is reduced and gradually reduced in the heat treatment furnace 2. The residual ammonia concentration changes.
Specifically, as shown in FIG. 3, the residual ammonia concentration decreases with time, and reaches a constant residual ammonia concentration C when a predetermined time T elapses.
Further, as shown in FIG. 4, the amount of change in the residual ammonia concentration with time decreases with time, and becomes 0 when the residual ammonia concentration reaches a constant value C.

In the heat treatment furnace 2, the decomposition of ammonia gas is suppressed as described above while there are many oxide films with low ammonia gas decomposition action on the surface of the jig 22 as in the early stage of baking. Residual ammonia concentration increases and nitriding potential increases.
Thereafter, as time passes, the oxide film on the surface of the jig 22 decreases, the area of the surface of the jig 22 in contact with the ammonia gas increases, the decomposition of the ammonia gas proceeds, and the residual ammonia concentration gradually increases. The nitriding potential also decreases.
When the oxide film on the surface of the jig 22 is completely removed by the reduction reaction, the area of the surface of the jig 22 in contact with the ammonia gas becomes constant. Therefore, the degree of decomposition of the ammonia gas is stabilized, and the oxide film The residual ammonia concentration, which has decreased with the decrease, becomes constant. At this time, the amount of change over time in the residual ammonia concentration becomes zero.

  That is, when the oxide film on the surface of the jig 22 is completely removed by the reduction reaction, the residual ammonia concentration in the atmosphere in the heat treatment furnace 2 becomes constant and stable, so the residual ammonia concentration in the heat treatment furnace 2 The determination device 12 is configured to determine whether the jig 22 has been baked, assuming that the baking of the jig 22 has been completed at a point in time when the jig 22 has become constant.

  Specifically, when the change over time of the residual ammonia concentration calculated by the arithmetic unit 12a decreases with time and becomes zero, the determination unit 12b determines that the baking of the jig 22 has been completed. can do.

However, considering that the measurement value of the residual ammonia concentration measured by the residual ammonia concentration measuring device 11 is noisy or the measurement value fluctuates slightly due to a disturbance, the change amount of the residual ammonia concentration with time is zero. It can also be configured to determine that the baking of the jig 22 has been completed when a value in the range r to -r is reached.
The value r serving as a determination criterion for determining whether or not the jig 22 has been baked is set in accordance with the magnitude of noise, the amount of fluctuation of the measurement value, and the like, and is determined in advance. Is stored in the storage unit 12c.

  In this way, while the jig 22 is being baked, the residual ammonia concentration measuring instrument 11 sequentially monitors the residual ammonia concentration in the heat treatment furnace 2, and when the residual ammonia concentration becomes constant and stable, The determination device 12 determines that the jig 22 has been baked.

  Thereby, it becomes possible to start the heat treatment for the workpiece 21 by the heat treatment furnace 2 in a state where the residual ammonia concentration is constant, and a stable nitriding potential and nitriding quality can be obtained from the time of the first heat treatment of the workpiece 21. The quality of the workpiece 21 that has been heat-treated can be improved.

  For example, for the jig A having the first shape and the jig B having the second shape (the jig B is smaller than the jig A), the baking is completed by the baking completion determination device 1. When the workpiece 22 is subjected to nitriding and quenching after the jig 22 is baked until it is determined that the nitriding potential in the heat treatment furnace 2 is as shown in FIG. In both cases B, the substantially target value is shown from the first processing, and the target value is stably shown even if the processing is repeated thereafter.

  Further, as shown in FIG. 6, the depth of the hardened layer of the workpiece 21 subjected to the nitriding and quenching treatment also shows a substantially target value from the first treatment in both the jig A and the jig B, and the treatment is repeated thereafter. Even if it goes, it will show a stable target value.

  In other words, in this example, the residual ammonia concentration in the heat treatment furnace 2 during the baking of the jig 22 is continuously measured and monitored by the residual ammonia concentration measuring device 11, and the residual ammonia concentration is constant. Since the jig 22 is baked until it becomes stable, the nitridation is performed as intended from the time of the first heat treatment on the workpiece 21 regardless of the amount of the oxide film formed on the surface of the jig 22. It is possible to obtain potential and hardened layer depth (since the jig 22 is baked until the residual ammonia concentration becomes constant, the baked time becomes longer in the jig 22 having a large amount of oxide film. In the jig 22 having a small amount of oxide film, the baking time is shortened).

  As a result, the jig 22 having various sizes and shapes is also baked by the same process (by baking the jig 22 until the residual ammonia concentration becomes constant). Since it is possible to obtain a constant nitriding potential and hardened layer depth from the time of the first heat treatment for the workpiece 21, it is possible to improve the quality of the heat-treated workpiece 21 while simplifying the preparation work of the heat treatment for a wide variety of workpieces 21. Can be planned.

It is the schematic which shows a heat processing furnace and an empty baking completion determination apparatus. It is a figure which shows the decomposition reaction of ammonia gas in the heat treatment furnace at the time of empty baking. It is a figure which shows the relationship between the residual ammonia density | concentration in the heat processing furnace at the time of empty baking, and time. It is a figure which shows the relationship between the variation | change_quantity of the residual ammonia concentration in the heat processing furnace at the time of empty baking, and time. It is a figure which shows the nitriding potential at the time of performing the heat processing of a workpiece | work after it determines with the blanking completion determination apparatus having determined that the blanking of the jig was completed. It is a figure which shows the hardened layer depth of the workpiece | work at the time of heat-processing a workpiece | work after determining with the blank baking completion determination apparatus having completed the baking of the jig | tool. It is a figure which shows the nitriding potential at the time of heat-processing a workpiece | work after performing the blank baking of the jig | tool by the conventional method. It is a figure which shows the hardening layer depth of the workpiece | work at the time of heat-processing a workpiece | work after performing the blank baking of the jig | tool by the conventional method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Empty burning completion determination apparatus 2 Heat processing furnace 11 Residual ammonia concentration measuring device 12 Judgment apparatus 12a Operation part 12b Judgment part 12c Memory | storage part 21 Work 22 Jig 25 Ammonia gas supply pipe

Claims (4)

An empty baking method of a jig used when a workpiece to be heat-treated in a heat treatment furnace to which ammonia gas is supplied is installed in the heat treatment furnace,
Before performing heat treatment on the workpiece, perform a blank firing of the jig placed in the heat treatment furnace,
Measure the residual ammonia concentration in the atmosphere in the heat treatment furnace during baking,
Based on the value of the measured residual ammonia concentration, determine the completion of baking of the jig,
A jig baking method characterized by the above. Judgment of the completion of baking of the jig is as follows:
When the amount of change over time in the residual ammonia concentration measured during baking is within a predetermined range set in advance,
The method for baking an empty jig according to claim 1. An apparatus for determining completion of empty firing of a jig used when a workpiece to be heat-treated in a heat treatment furnace to which ammonia gas is supplied is installed in the heat treatment furnace,
A measuring means for measuring the residual ammonia concentration in the heat treatment furnace;
Based on the value of the residual ammonia concentration measured by the measuring instrument, a determination means for determining completion of empty baking of the jig,
An apparatus for determining whether a jig has been completely baked. The determination means includes
A calculation unit for calculating a temporal change in residual ammonia concentration measured by the measuring device;
A determination unit configured to determine whether the jig has been baked or not when a temporal change amount of the residual ammonia concentration calculated by the arithmetic unit is within a predetermined range set in advance.
The apparatus for determining whether or not the jig has been baked according to claim 3.

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