JP5024647B2 - Vacuum carburizing quality control method and vacuum carburizing furnace - Google Patents

Description

    The present invention relates to a vacuum carburizing quality control method for determining the degree of variation in carburizing quality within the same operation batch or between operation batches in a vacuum carburizing process, and a vacuum carburizing furnace that reduces variations in carburizing quality.

  Carburizing is a process of diffusing and penetrating carbon into the surface of a steel material. Usually, after carburizing, quenching is performed to harden the surface to produce a part composed of a highly wear-resistant surface and a tough core.

  Examples of carburizing treatment include gas carburizing, plasma carburizing, and vacuum carburizing. Among these, the gas carburizing method is a method in which natural gas, propane, butane and the like are modified to produce a carburizing gas mainly composed of CO, and thereby carburizing a steel material. Since the gas carburizing method performs carburizing while controlling the atmosphere based on the carbon potential, the surface carbon concentration of the article to be treated can be stably controlled. For this reason, the gas carburizing method has the advantage that the reproducibility of the carburizing quality for the article to be processed is good. However, the gas carburizing method has problems such as a large amount of carburizing gas used, danger of burning exhaust gas, and grain boundary oxidation on the surface of the product to be processed.

  On the other hand, the vacuum carburizing method is a kind of gas carburizing method, and is a gas carburizing method in which carburizing treatment is performed under reduced pressure (see, for example, Patent Documents 1 to 3 below). Hereinafter, in this specification, “gas carburizing” means a gas carburizing method performed under atmospheric pressure, and “vacuum carburizing” means a gas carburizing method performed under reduced pressure.

  In vacuum carburizing, after the surface carbon concentration reaches the carbon solid solubility limit (Acm) immediately after the start of carburizing, the desired surface carbon concentration and carbon concentration distribution can be obtained by managing the carburizing gas input time (carburizing time) and diffusion time. It has gained. The carbon inflow depth (diffusion depth) in the product to be treated is controlled by the diffusion time for both gas carburizing and vacuum carburizing.

JP 2001-81543 A JP 2001-240954 A JP 2002-212702 A

  In gas carburization, the atmosphere was controlled based on the carbon potential as described above. However, since the reaction forms differ between gas carburizing and vacuum carburizing, control of the atmosphere based on the carbon potential in gas carburizing is changed to vacuum carburizing. It is impossible to apply. For this reason, in the case of vacuum carburizing, the uniformity of carburizing quality (surface carburizing concentration and carburizing concentration distribution) for the products to be processed has been ensured by controlling conditions such as carburizing / diffusion temperature, carburizing time, and gas input amount.

However, in the conventional carburization, it is inevitable that the carburizing quality varies between the operation batches even under the above-described condition management, and further, the carburizing quality within the same operation batch also varies. It was. For this reason, in vacuum carburizing, it is necessary to manage the degree of variation in the carburizing quality of the workpiece. However, in the condition management items as described above, there is no method for managing the carburizing quality during the processing, and conventionally, it has been necessary to verify the carburizing quality by performing a sampling test of the article to be processed after the carburizing process.
Thus, in the prior art, there is a problem that the determination of the degree of variation in carburization quality is complicated. In addition, since the carburizing atmosphere was not controlled, there was a problem that the reproducibility of carburizing quality was poor.

  An object of the present invention is to provide a vacuum carburizing quality control method and a vacuum carburizing furnace that can easily determine the degree of variation in carburizing quality and easily manage carburizing quality in view of the above-described problems. To do. Another object of the present invention is to provide a vacuum carburizing furnace that can improve the reproducibility of carburizing quality, reduce the variation in carburizing quality, and ensure its uniformity.

  A first invention created to achieve the above object is a quality control method for vacuum carburizing, in which carburizing treatment is performed on a product under reduced pressure and heating with a carburizing gas composed of hydrocarbons. Depending on the required effective hardened layer depth (carburization depth) and surface carbon concentration, the theoretical flow rate of carburizing gas based on the amount of carbon required for carburizing treatment based on the diffusion of carbon inside the treated product. The time change is obtained, and based on the time change of the theoretical flow rate, the partial pressure ratio of hydrogen generated by the carburization reaction at the theoretical flow rate to the total pressure in the processing chamber is defined as the theoretical hydrogen partial pressure ratio, and the time change of the theoretical hydrogen partial pressure ratio is obtained. The time variation of the theoretical hydrogen partial pressure ratio is compared with the time variation of the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during actual carburizing treatment, and the variation in carburizing quality within the same operation batch is based on the degree of approximation. Every time Determining, that a quality control method for vacuum carburizing characterized by.

According to a first reference example created to achieve the above object, there is provided a quality control method for vacuum carburizing, in which carburizing treatment is performed on a product under reduced pressure and heating with a carburizing gas composed of hydrocarbon, Compare the time variation of the hydrogen partial pressure ratio with respect to the total pressure in the treatment chamber during processing and the time variation of the hydrogen partial pressure ratio with respect to the total pressure in the treatment chamber during the previous carburizing treatment, and determine each operation based on the degree of approximation. A quality control method for vacuum carburizing, characterized in that the degree of variation in carburizing quality between batches is determined.

A second invention created to achieve the above object is to provide a furnace body having a processing chamber for containing a product to be processed and carburizing the product to be processed in a reduced pressure and a heated state, and from the hydrocarbon to the processing chamber. In a vacuum carburizing furnace comprising a carburizing gas introducing means for introducing a carburizing gas and a gas exhausting means for exhausting the gas in the processing chamber and maintaining the pressure in a predetermined reduced pressure state, the total pressure in the processing chamber during the carburizing process The hydrogen partial pressure ratio detection means for detecting the hydrogen partial pressure ratio, and the time of the theoretical flow rate of carburizing gas required for carburizing treatment based on the internal diffusion of the material according to the carburizing depth and surface carbon concentration required for the workpiece Based on the process for obtaining the change and the temporal change in the theoretical flow rate, the partial pressure ratio of the hydrogen generated by the carburization reaction at the theoretical flow rate to the total pressure in the processing chamber is defined as the theoretical hydrogen partial pressure ratio. An arithmetic processing means for performing a process for obtaining a change in time, an output means for displaying a temporal change in the theoretical hydrogen partial pressure ratio, and a temporal change in the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detecting means. Is a vacuum carburizing furnace.

According to a third invention, in the second invention, a gas introduction amount adjusting means for adjusting an introduction amount of the carburizing gas by the carburizing gas introduction means, a temporal change in the theoretical hydrogen partial pressure ratio obtained by the arithmetic processing means, A control means for comparing the time variation of the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detecting means and controlling the gas introduction amount adjusting means based on the degree of approximation. is there.

In addition, the second reference example includes a furnace body having a processing chamber that accommodates an article to be processed and carburizes the article to be processed in a decompressed and heated state, and carburizing that introduces a carburizing gas made of hydrocarbons into the processing chamber. Hydrogen for detecting a hydrogen partial pressure ratio with respect to the total pressure in the processing chamber in a carburizing process in a vacuum carburizing furnace provided with a gas introduction unit and a gas exhaust unit that exhausts the gas in the processing chamber and maintains the pressure in a predetermined reduced pressure state A vacuum carburizing furnace comprising: a partial pressure ratio detecting means; and an output means for displaying a temporal change in the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detecting means.

A third reference example is the same as the second reference example , except that the gas introduction amount adjusting means for adjusting the introduction amount of the carburizing gas by the carburizing gas introduction means and the time of the hydrogen partial pressure ratio detected by the hydrogen partial pressure detecting means. A control means for comparing the change with the temporal change in the hydrogen partial pressure ratio during the previous carburizing process and controlling the gas introduction amount adjusting means based on the degree of approximation. It is.

  In the present invention, “carburization quality” is a concept that indicates the state of the ratio, range, depth, etc. of carbon in the article to be treated, such as the surface carbon concentration and carbon concentration distribution of the article to be treated subjected to carburizing treatment. It is.

  “Display” means to express the target information to the outside, including the concept of displaying by electromagnetic or magnetic method like a monitor, or displaying by tangible method by printing like a printer. It is.

  “Hydrogen partial pressure ratio detection means” means a device having a function for detecting the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during carburizing, and a device that achieves such a function by combining a plurality of devices. It is a concept that includes. In the embodiment, a combination of some of the functions of the hydrogen sensor, the vacuum gauge, and the arithmetic processing device corresponds to this.

  “Arithmetic processing means” means a function having a function of performing a process for obtaining a temporal change in the theoretical flow rate and a process for obtaining a temporal change in the theoretical hydrogen partial pressure ratio, and by using a part of the functions of an electronic computer. It is a concept including what achieves such a function. In the embodiment, the arithmetic processing device corresponds to this.

  The meaning of other terms will become apparent from the following description of this specification.

  According to the first invention, the theoretical change in the theoretical flow rate of the carburizing gas required for the carburizing process is obtained, and the theoretical hydrogen partial pressure ratio corresponding to the theoretical flow rate of the carburized gas is obtained based on the change in time. Compare the time variation of the partial pressure ratio with the time variation of the hydrogen partial pressure ratio in the processing chamber during actual carburizing treatment, and based on the approximate degree, determine the degree of variation in carburizing quality within the same operation batch. Unlike the technology, it is not necessary to carry out a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed. As will be described in detail later, the inventor of the present application stated that the temporal change in the hydrogen partial pressure ratio in the processing chamber during actual carburizing treatment corresponds to the theoretical hydrogen partial pressure ratio (the amount of carburizing gas A new finding was obtained that the degree of variation in the carburizing quality was smaller as the time variation of the theoretical hydrogen partial pressure ratio to the total pressure in the treatment chamber generated by the carburizing reaction at the theoretical flow rate was approximated. The present invention utilizes such novel knowledge. That is, the time variation of the theoretical hydrogen partial pressure ratio is compared with the time variation of the actual hydrogen partial pressure ratio, and the degree of variation in carburizing quality within the same operation batch can be determined based on the degree of approximation.

According to the first reference example, the time variation of the hydrogen partial pressure ratio during the carburizing process in each operation batch is compared, and the degree of variation in carburizing quality between each operation batch is determined based on the degree of approximation. Thus, unlike the prior art, it is not necessary to carry out a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed. As described in detail later, the inventor of the present application has obtained a novel finding that there is a correlation between the time change of the hydrogen partial pressure ratio in the processing chamber during the carburizing process and the carburizing quality. The present invention utilizes such novel knowledge. That is, the time variation of the hydrogen partial pressure ratio during the carburizing process in each operation batch can be compared, and the degree of variation in carburizing quality between the operation batches can be determined based on the degree of approximation. Therefore, for example, the time change of the hydrogen partial pressure ratio in the processing chamber during the carburizing process is equal to or not equivalent to the time change of the hydrogen partial pressure ratio in the processing chamber during the carburizing process performed before that time. When the difference is within the allowable range, it can be determined that the reproducibility of the carburizing quality is good.

According to the second invention, the theoretical hydrogen partial pressure ratio described above is obtained by the arithmetic processing means, and the time change of the theoretical hydrogen partial pressure ratio and the time change of the hydrogen partial pressure ratio during actual carburizing treatment are displayed by the output means. Therefore, the theoretical hydrogen partial pressure ratio can be compared with the hydrogen partial pressure ratio in the processing chamber during the actual carburizing process. For this reason, as described above, the degree of variation in carburizing quality within the same operation batch can be determined based on the degree of approximation. Therefore, unlike the prior art, it is not necessary to perform a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed.

According to the third aspect of the invention, since the gas introduction amount adjusting means and the control means for controlling the gas introduction means based on the approximation degree are provided, the hydrogen partial pressure ratio in the processing chamber is controlled during the operation of the vacuum carburizing furnace. The gas introduction amount adjusting means can be controlled to adjust the introduction amount of the carburizing gas into the processing chamber so that the time change approaches the time change of the theoretical hydrogen partial pressure ratio. As described above, since the time variation of the hydrogen partial pressure ratio in the treatment chamber during actual carburizing treatment approximates the time variation of the theoretical hydrogen partial pressure ratio, the degree of variation in carburization quality is small. By bringing the time change closer to the time change of the theoretical hydrogen partial pressure ratio, the degree of variation in carburizing quality within the same operation batch can be reduced, and uniformity can be ensured.

According to the second reference example, the vacuum carburizing furnace includes the hydrogen partial pressure ratio detecting means for detecting the hydrogen partial pressure ratio at the time of the carburizing process, and the output means for displaying or recording the time change of the hydrogen partial pressure ratio. The time change of the hydrogen partial pressure ratio during the carburizing process in each operation batch can be compared. For this reason, as described above, the degree of variation in carburizing quality between the operation batches can be determined based on the degree of approximation. Therefore, unlike the prior art, it is not necessary to perform a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed.

According to the third reference example, since the gas introduction amount adjusting means and the control means for controlling the gas introduction means based on the approximate degree are provided, the hydrogen partial pressure ratio in the processing chamber during the operation of the vacuum carburizing furnace is provided. Thus, the gas introduction amount adjusting means can be controlled to adjust the introduction amount of the carburizing gas into the processing chamber so that the time change of the time is the same as or within the allowable range of the previous operation batch. As described above, since there is a correlation between the time variation of the hydrogen partial pressure ratio in the processing chamber during carburizing treatment and the carburizing quality, the time variation of the hydrogen partial pressure ratio in the processing chamber during carburizing treatment is By making it the same as the time change of the hydrogen partial pressure ratio, the degree of variation in carburization quality between operation batches can be reduced, and uniformity can be ensured.

  As described above, according to the present invention, it is possible to easily determine the degree of variation in carburizing quality and easily manage the carburizing quality, improve the reproducibility of carburizing quality, and reduce the variation in carburizing quality. Thus, the excellent effect of ensuring the uniformity can be obtained.

  Before describing specific embodiments of the present invention, various matters for understanding the problem-solving principles of the present invention will be described first in order to facilitate understanding of the present invention.

First, the “theoretical flow rate of carburizing gas necessary for carburizing treatment” will be described. In the vacuum carburizing process, a carburizing gas (for example, acetylene) is introduced into a processing chamber in a predetermined vacuum state, and a carburizing reaction occurs between the introduced carburizing gas and the surface of the workpiece in the processing chamber. In this case, when the carburizing gas is acetylene, the reaction of H ₂ C ₂ → 2C + H ₂ is performed.

  That is, in the carburization reaction on the surface of the article to be treated, carbon is input to the surface of the article to be treated and hydrogen is released. Normally, the carburizing gas introduced into the processing chamber includes a portion that does not contribute to the carburizing reaction. On the other hand, when the carburizing gas introduced into the processing chamber contributes to the 100% carburizing reaction, the flow rate of the carburizing gas theoretically necessary to obtain the required surface carburizing concentration and carbon concentration distribution is expressed as “carburizing gas. Defined as “theoretical flow rate”.

The relationship between the theoretical flow rate V of the carburizing gas necessary for the carburizing process and the carburizing time t, that is, V = f (t), that is, how to obtain the temporal change in the theoretical flow rate of the carburizing gas is as follows. The diffusion rate into the material to be treated in the carburizing process is expressed by Formula (1) of Formula 1 from Fick's second law, and the diffusion coefficient of carbon is expressed by Formula (2). Here, C is the concentration, x is the distance from the surface, D is the diffusion coefficient [m ² / s], D0 is the frequency factor [m ² / s], Q is the activation energy [kJ / mol], and R is the gas Constant [kJ / K · mol] , T is temperature [K].

The initial condition is C = C ₀ (C ₀ is the base material carbon concentration), and C = C _S (C _S is the surface carbon concentration) on the surface during carburizing. The relationship between the distance x at T, the time t, and the carbon concentration C can be obtained. From this, the relationship V = f (t) between the theoretical flow rate V of the carburizing gas and the carburizing time t can be calculated from the required carburizing depth, carbon concentration, and surface carbon concentration. Based on the relational expression thus obtained, the time change of the theoretical flow rate V of the carburizing gas can be expressed as illustrated in FIG.

Next, the “theoretical hydrogen partial pressure ratio” will be described. In conventional vacuum carburization, the flow rate of the carburizing gas to be actually introduced into the treatment chamber, does not coincide with the theoretical flow rate V as described above, the ratio is, the actual carburizing gas flow is introduced into the processing chamber actual flow rate V _R Is expressed by the following formula (3).
Theoretical flow rate V / actual flow rate V _R (3)

In this case, assuming that an ideal carburizing process has been performed, the amount of hydrogen generated when the carburizing reaction is performed with a carburizing gas in an amount corresponding to the theoretical flow rate is equal to the amount of carburizing that has performed the carburizing reaction. It becomes the same number of moles as the gas. This can be understood from the fact that when the carburizing gas is acetylene, a reaction of H ₂ C ₂ → 2C + H ₂ is performed. Then, it can be said that the theoretical hydrogen amount V _TH generated by the (ideal) carburizing reaction by introducing the theoretical flow rate is theoretically the same as the theoretical flow rate V of the carburizing gas. That is, the following relationship (4) is established.
Theoretical flow rate V = theoretical hydrogen amount V _TH (4)

When the theoretical flow rate V is replaced with the theoretical hydrogen amount V _TH from the above equations (3) and (4), the following equation (5) is derived.
Theoretical hydrogen amount V _TH / actual flow rate V _R (5)

And what was represented by the said (5) Formula is the theoretical value of the hydrogen partial pressure ratio with respect to the total pressure in a process chamber at the time of a carburizing process. That is, the theoretical value of the hydrogen partial pressure ratio, (3) can be obtained (4) from the equation, the theoretical flow rate V, the actual flow rate V _R. In the present invention, the theoretical value of the hydrogen partial pressure ratio represented by the above formula (5) is defined as “theoretical hydrogen partial pressure ratio”.

  Next, the relationship between the temporal change in the theoretical hydrogen partial pressure ratio and the temporal change in the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during the actual carburizing process will be described with reference to FIG. In FIG. 2, the horizontal axis represents carburizing elapsed time (sec), and the vertical axis represents hydrogen partial pressure ratio (%). In the figure, A, B, and C indicate the time variation of the theoretical hydrogen partial pressure ratio, and the actual input amount (actual flow rate) of the carburizing gas at that time is 10 L / m, 20 L / m, and 30 L / m, respectively. is there. Further, in the figure, a, b, and c indicate temporal changes in the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during the actual carburizing process, and correspond to A, B, and C, respectively. Further, ΔC% added to a, b, and c indicates the degree of variation in carburizing quality after the end of each carburizing step and diffusion step.

  From FIG. 2, it can be seen that the earlier the actual hydrogen partial pressure ratio decreases, the less the variation in carburizing quality. It can also be seen that the closer the actual hydrogen partial pressure ratio is to the corresponding theoretical hydrogen partial pressure ratio, the less the variation in carburizing quality. This will be described with reference to FIG.

When considering the inflow of carbon to the article to be treated during carburizing treatment on the condition of the presence or absence of variation, it can be explained as follows.
(1) When the product to be treated is uniformly carburized (in the case of FIG. 3A)
There is no difference depending on the position of the carbon concentration near the surface layer, and there is no difference in carbon inflow.
(2) When non-uniform carburization occurs in the product to be processed (in the case of FIG. 3B)
A difference in position occurs in the carbon concentration of the surface layer, and the carbon inflow amount decreases at a location where the carbon concentration is high, but the carbon inflow amount increases at a location where the concentration is low compared to a location where the carbon concentration is high.
(3) In the above two states, the time change (decrease rate) of the hydrogen partial pressure ratio approaches the ideal state in uniform carburization (b and c in FIG. 2), but is non-uniform (there is variation). In the case), since the carbon inflow continues, it is delayed from the ideal state (a in FIG. 2).

Based on the above facts, the present inventor has obtained the following novel findings.
(1) The degree of variation in carburization quality decreases as the time change in the hydrogen partial pressure ratio in the processing chamber during actual carburizing treatment approximates the time change in the theoretical hydrogen partial pressure ratio. Using this, the time variation of the theoretical hydrogen partial pressure ratio is compared with the time variation of the hydrogen partial pressure ratio in the treatment chamber during actual carburizing treatment, and the carburizing quality varies within the same operation batch based on the degree of approximation. Determine the degree.
(2) From the knowledge of the above (1) that there is a correlation between the time variation of the hydrogen partial pressure ratio in the processing chamber during carburizing treatment and the carburizing quality, if the time variation of the hydrogen partial pressure ratio is the same, the carburizing quality is also It can be estimated that they are the same. Using this, the time variation of the hydrogen partial pressure ratio during the carburizing process in each operation batch is compared, and the degree of variation in carburizing quality between each operation batch is determined based on the degree of approximation.

  The present invention is based on the above-described novel findings. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

  FIG. 4 is a diagram showing a schematic configuration of the vacuum carburizing furnace 10 according to the first embodiment of the present invention. As shown in FIG. 4, the vacuum carburizing furnace 10 includes a furnace body 12 having a processing chamber 17 therein, a gas introduction line 20, and a gas exhaust line 22. A heat insulating wall 14 is provided inside the furnace wall 16 of the furnace body 12. The processing chamber in which the product 1 is accommodated in the heat insulating wall 14 and carburized for the product 1 under reduced pressure and heating. 17 is formed. A heater 19 is installed in the processing chamber 17 so as to heat the heating chamber 17 and the workpiece 1 to a predetermined temperature.

  The gas introduction line 20 is connected to the heat insulating wall 14 and functions as “carburization gas introduction means” for introducing a carburizing gas made of hydrocarbon (for example, acetylene) into the processing chamber 17. The gas exhaust line 22 is connected to the heat insulating wall 14 and exhausts the gas in the processing chamber 17. Further, the gas exhaust line 22 is connected to a vacuum pump 24, and the gas exhaust line 22 and the vacuum pump 24 function as “gas exhaust means” for exhausting the gas in the processing chamber 17 and holding it in a predetermined reduced pressure state. To do.

  Further, the vacuum carburizing furnace 10 includes a hydrogen sensor 30 that detects the hydrogen pressure in the processing chamber 17 during the carburizing process, a vacuum gauge 32 that detects the total pressure in the processing chamber 17 during the carburizing process, and various calculations and controls. An arithmetic processing unit 34 to perform, a display 36 for displaying an output from the arithmetic processing unit 34, and a printer 38 for printing the output from the arithmetic processing unit 34 are provided. The arithmetic processing unit 34 is connected with a keyboard 40 and a mouse 42 as input means.

  The hydrogen sensor 30 can be composed of, for example, a quadrupole mass spectrometer, and the vacuum gauge 32 can be composed of, for example, a Baratron vacuum gauge. The hydrogen sensor 30 and the vacuum gauge 32 are connected to the arithmetic processing unit 34 and output the detected hydrogen partial pressure and total pressure in the processing chamber 17, and the output signals are input to the arithmetic processing unit 34. .

  The arithmetic processing unit 34 includes at least a CPU and a storage unit and can execute various types of information processing / calculation / control, and can be configured by a personal computer or a dedicated electronic computer. The arithmetic processing unit 34 in the present embodiment calculates and obtains the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber 17 during the carburizing process based on the hydrogen partial pressure from the hydrogen sensor 30 and the total pressure from the vacuum gauge 32. Process. As described above, in this embodiment, the hydrogen sensor 30, the vacuum gauge 32, and the arithmetic processing unit 34 serve as “hydrogen partial pressure ratio detecting means” that detects the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber 17 during the carburizing process. Has achieved the function.

  Moreover, the arithmetic processing unit 34 performs a process for obtaining a temporal change in the theoretical flow rate of the carburizing gas necessary for the carburizing process and a process for obtaining a temporal change in the theoretical hydrogen partial pressure ratio. The meanings of “theoretical flow rate of carburizing gas” and “theoretical hydrogen partial pressure ratio” are as described above. Specifically, the theoretical flow rate of the carburizing gas necessary for the carburizing treatment can be obtained based on the internal diffusion of the material according to the carburizing depth and surface carbon concentration required for the article 1 to be processed. Further, the temporal change of the theoretical hydrogen partial pressure ratio can be obtained from the partial pressure ratio of the hydrogen generated by the carburizing reaction at the theoretical flow rate to the total pressure in the processing chamber based on the temporal change of the theoretical flow rate of the carburizing gas.

  Thus, in this embodiment, the theory of the carburizing gas necessary for the carburizing process based on the internal diffusion of the material according to the carburizing depth and the surface carbon concentration required for the workpiece 1 by the arithmetic processing unit 34. Based on the process for obtaining the time change of the flow rate and the time change of the theoretical flow rate, the partial pressure ratio of the hydrogen generated by the carburizing reaction at the theoretical flow rate to the total pressure in the processing chamber 17 is defined as the theoretical hydrogen partial pressure ratio. The function as the “arithmetic processing means” for performing the process for obtaining the time change is achieved.

  The display 36 outputs the time change of the theoretical hydrogen partial pressure ratio obtained by the arithmetic processing unit 34 and the time change of the actual hydrogen partial pressure ratio by image display. Further, the printer 38 outputs the time change of the theoretical hydrogen partial pressure ratio obtained by the arithmetic processing unit 34 and the time change of the actual hydrogen partial pressure ratio by printing. Thus, in the present embodiment, the display 36 or the printer 38 functions as an “output unit” that displays the temporal change in the theoretical hydrogen partial pressure ratio and the temporal change in the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detecting unit.

  According to the vacuum carburizing furnace 10 configured as described above, hydrogen with respect to the total pressure in the processing chamber 17 during the actual carburizing process by the hydrogen sensor 30, the vacuum gauge 32, and the arithmetic processing unit 34 functioning as a hydrogen partial pressure detecting means. The partial pressure ratio is detected, the theoretical hydrogen partial pressure ratio is obtained by the arithmetic processing unit 34 functioning as the arithmetic processing means, and the time change of the theoretical hydrogen partial pressure ratio and the actual carburizing process are performed by the display 36 or the printer 38 functioning as the output means. Since the time change of the hydrogen partial pressure ratio at the time is displayed, it is possible to compare this theoretical hydrogen partial pressure ratio with the hydrogen partial pressure ratio in the processing chamber during the actual carburizing process. As described above, the degree of variation in carburization quality decreases as the time change in the hydrogen partial pressure ratio in the processing chamber during actual carburizing treatment approximates the time change in the theoretical hydrogen partial pressure ratio. For this reason, the degree of variation in carburizing quality within the same operation batch can be determined based on the degree of approximation. Therefore, unlike the prior art, it is not necessary to perform a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed.

  Next, a second embodiment of the present invention will be described. FIG. 5 is a diagram showing a schematic configuration of the vacuum carburizing furnace 10 according to the second embodiment of the present invention. The vacuum carburizing furnace 10 according to the present embodiment is obtained by adding a gas flow rate adjusting valve 26 to the vacuum carburizing furnace 10 according to the first embodiment described above. The gas flow rate adjusting valve 26 functions as a “gas introduction amount adjusting means” for adjusting the amount of carburizing gas introduced by the carburizing gas introducing means (gas introduction line 20). Other device configurations are the same as those in the first embodiment described above.

  Further, the arithmetic processing unit 34 in the second embodiment compares the obtained temporal change in the theoretical hydrogen partial pressure ratio with the temporal change in the actual hydrogen partial pressure ratio, and sets the gas flow rate control valve 26 based on the degree of approximation. It comes to control. Specifically, during operation of the vacuum carburizing furnace 10, the gas flow rate control valve 26 is controlled so that the temporal change in the hydrogen partial pressure ratio in the processing chamber 17 approaches the temporal change in the theoretical hydrogen partial pressure ratio, and the processing chamber The amount of carburizing gas introduced to 17 is adjusted.

  Thus, in the second embodiment, the arithmetic processing unit 34 compares the temporal change in the theoretical hydrogen partial pressure ratio obtained by the arithmetic processing means with the temporal change in the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detecting means, A function as a “control unit” for controlling the gas introduction unit based on the degree of approximation is achieved.

  As described above, the degree of variation in carburizing quality decreases as the time change in the hydrogen partial pressure ratio in the processing chamber 17 during actual carburizing treatment approximates the time change in the theoretical hydrogen partial pressure ratio. For this reason, according to the vacuum carburizing furnace according to the second embodiment, the time variation of the hydrogen partial pressure ratio in the processing chamber 17 is brought close to the time variation of the theoretical hydrogen partial pressure ratio, so that the degree of variation in carburizing quality in the same operation batch. The uniformity can be ensured.

  Next, a third embodiment of the present invention will be described. Since the vacuum carburizing furnace according to the third embodiment is basically the same as the equipment configuration of the vacuum carburizing furnace 10 according to the first embodiment shown in FIG. 4, the third embodiment will also be described with reference to FIG. To do.

  The arithmetic processing unit 34 according to the third embodiment can store the time change of the hydrogen partial pressure ratio during the carburizing process in the storage unit, and the display 36 or the printer 38 can perform the carburizing process in different operation batches. The time change of the hydrogen partial pressure ratio can be output simultaneously or sequentially by image display or printing.

  Therefore, according to the vacuum carburizing furnace 10 by 3rd Embodiment, the time change of the hydrogen partial pressure ratio at the time of the carburizing process in each operation batch can be compared. As described above, from the knowledge that there is a correlation between the time change of the hydrogen partial pressure ratio in the processing chamber during carburizing treatment and the carburizing quality, if the time change of the hydrogen partial pressure ratio is the same, the carburizing quality is also the same. Can be estimated. For this reason, the variation degree of the carburizing quality between each operation batch can be determined based on the degree of approximation. Therefore, unlike the prior art, it is not necessary to perform a sampling test after carburizing treatment, and the reproducibility of carburizing quality can be easily confirmed.

  Next, a fourth embodiment of the present invention will be described. Since the vacuum carburizing furnace according to the fourth embodiment is basically the same as the equipment configuration of the vacuum carburizing furnace 10 according to the second embodiment shown in FIG. 5, the fourth embodiment will also be described with reference to FIG. To do.

  The fourth embodiment is different from the third embodiment in that a gas flow rate adjusting valve 26 is further added to the vacuum carburizing furnace 10 according to the above-described third embodiment and the operation content of the arithmetic processing unit 34. That is, the arithmetic processing unit 34 in the fourth embodiment compares the time change of the hydrogen partial pressure ratio with the time change of the hydrogen partial pressure ratio during the carburizing process of the operation batch performed before that, and based on the degree of approximation. Thus, the gas flow rate adjusting valve 26 is controlled. Specifically, during the operation of the vacuum carburizing furnace 10, the gas flow rate control valve 26 is set so that the temporal change in the hydrogen partial pressure ratio in the processing chamber 17 is the same as or within the allowable range of the previous operation batch. The amount of carburizing gas introduced into the processing chamber 17 is controlled.

  Thus, in the fourth embodiment, the arithmetic processing unit 34 compares the time change of the hydrogen partial pressure ratio detected by the hydrogen partial pressure detection means with the time change of the hydrogen partial pressure ratio during the previous carburizing process, A function as a “control unit” for controlling the gas introduction amount adjusting unit based on the degree of approximation is achieved.

  As described above, there is a correlation between the time variation of the hydrogen partial pressure ratio in the processing chamber 17 during the carburizing process and the carburizing quality. For this reason, according to the vacuum carburizing furnace 10 according to the fourth embodiment, the time change of the hydrogen partial pressure ratio in the processing chamber 17 during the carburizing process is equivalent to the time change of the hydrogen partial pressure ratio in the previous operation batch. By doing so, the degree of variation in carburization quality between operation batches can be reduced, and uniformity can be ensured.

  As is clear from the above description, according to the present invention, it is possible to easily determine the degree of variation in carburizing quality and easily manage the carburizing quality, improve the reproducibility of the carburizing quality, and improve the carburizing quality. It is possible to obtain an excellent effect that the uniformity can be ensured by reducing the variation of.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a figure which shows the relationship between the theoretical flow volume of carburizing gas, and carburizing time. It is a figure which shows the relationship between a theoretical hydrogen partial pressure ratio and an actual hydrogen partial pressure ratio. It is a figure which shows the relationship between the carburization variation generation | occurrence | production situation and carbon inflow. It is a figure which shows schematic structure of the vacuum carburizing furnace by 1st Embodiment (or 3rd Embodiment) of this invention. It is a figure which shows schematic structure of the vacuum carburizing furnace by 2nd Embodiment (or 4th Embodiment) of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Product 10 Vacuum carburizing furnace 12 Furnace body 14 Heat insulation wall 16 Furnace wall 17 Processed chamber 20 Gas introduction line 22 Gas exhaust line 24 Vacuum pump 26 Gas flow control valve 30 Hydrogen sensor 32 Vacuum gauge 34 Processing unit 36 Display 38 Printer 40 Keyboard 42 Mouse

Claims (3)

A quality control method for vacuum carburizing, in which carburizing treatment is performed on a product to be processed in a reduced pressure and heated state with a carburizing gas composed of hydrocarbon,
The carburizing temperature T is calculated from the equations (1) and (2) based on the diffusion of carbon into the processed product according to the effective hardened layer depth (carburized depth) and surface carbon concentration required for the processed product. The relationship between the distance x from the surface, time t and the carbon concentration C is calculated, and the relationship between the carburizing gas theoretical flow rate V and the carburizing time t is calculated from the required carburizing depth, carbon concentration and surface carbon concentration. , Find the time change of the theoretical flow rate of carburizing gas required for carburizing treatment,
Next, based on the time change of the theoretical flow rate, the partial pressure ratio of the hydrogen generated by the carburization reaction at the theoretical flow rate to the total pressure in the processing chamber is defined as the theoretical hydrogen partial pressure ratio, and the time change of this theoretical hydrogen partial pressure ratio is expressed by Equation (3). Seeking
Comparing the time variation of the theoretical hydrogen partial pressure ratio with the time variation of the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during actual carburizing treatment, and based on the approximation, the degree of variation in carburizing quality within the same operation batch A quality control method for vacuum carburizing, characterized by: determining.
Theoretical flow rate V / actual flow rate V _R (3)
C: Carbon concentration (initial condition is C = C ₀ (C ₀ is base material carbon concentration), and C = C _S (C _S is surface carbon concentration) on the surface during carburization)
x: distance from the surface D: diffusion coefficient [m ² / s]
D0: Frequency factor [m ² / s]
Q: Activation energy [kJ / mol]
R: Gas constant [kJ / K · mol]
T: Temperature [K]
V _R : Actual carburizing gas flow rate introduced into the processing chamber A quality control device for vacuum carburizing that performs a carburizing process on a product to be processed in a reduced pressure and heated state with a carburizing gas made of hydrocarbon,
The carburizing temperature T is calculated from the equations (1) and (2) based on the diffusion of carbon into the processed product according to the effective hardened layer depth (carburized depth) and surface carbon concentration required for the processed product. The relationship between the distance x from the surface, time t and the carbon concentration C is calculated, and the relationship between the carburizing gas theoretical flow rate V and the carburizing time t is calculated from the required carburizing depth, carbon concentration and surface carbon concentration. Then, based on the time change of the theoretical flow rate of the carburizing gas required for the carburizing treatment , and then the time change of the theoretical flow rate, the partial pressure ratio of hydrogen generated by the carburizing reaction at the theoretical flow rate to the total pressure in the processing chamber is theoretically calculated. A hydrogen partial pressure ratio, and a process for obtaining a temporal change in the theoretical hydrogen partial pressure ratio by the equation (3) , and an arithmetic processing means comprising:
The time variation of the theoretical hydrogen partial pressure ratio is compared with the time variation of the hydrogen partial pressure ratio with respect to the total pressure in the processing chamber during actual carburizing treatment. Based on the approximation, the carburizing gas composed of hydrocarbons in the processing chamber is compared . A quality control device for vacuum carburizing , comprising: a control means for controlling introduction .
Theoretical flow rate V / actual flow rate V _R (3)
C: Carbon concentration (initial condition is C = C ₀ (C ₀ is base material carbon concentration), and C = C _S (C _S is surface carbon concentration) on the surface during carburization)
x: distance from the surface D: diffusion coefficient [m ² / s]
D0: Frequency factor [m ² / s]
Q: Activation energy [kJ / mol]
R: Gas constant [kJ / K · mol]
T: Temperature [K]
V _R : Actual carburizing gas flow rate introduced into the processing chamber A furnace body having a processing chamber for containing the product to be processed and carburizing the product to be processed under reduced pressure and heating, carburizing gas introduction means for introducing a carburizing gas composed of hydrocarbons into the processing chamber, In a vacuum carburizing furnace provided with a gas exhaust means for exhausting gas and maintaining a predetermined reduced pressure state,
A hydrogen partial pressure ratio detecting means for detecting a hydrogen partial pressure ratio with respect to the total pressure in the processing chamber at the time of carburizing;
The distance x from the surface at the carburizing temperature T, time t, and carbon concentration C based on the internal diffusion of the material, depending on the carburization depth and surface carbon concentration required for the workpiece. The relationship between the theoretical flow rate V of the carburizing gas and the carburizing time t is calculated from the required carburizing depth, carbon concentration and surface carbon concentration, and the time of the theoretical flow rate of the carburizing gas necessary for the carburizing process is calculated. The process of seeking change,
Next, based on the time change of the theoretical flow rate, the partial pressure ratio of the hydrogen generated by the carburization reaction at the theoretical flow rate to the total pressure in the processing chamber is defined as the theoretical hydrogen partial pressure ratio. An arithmetic processing means for performing processing to obtain,
An output means for displaying the time change of the theoretical hydrogen partial pressure ratio and the time change of the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detection means;
Gas introduction amount adjusting means for adjusting the amount of carburizing gas introduced by the carburizing gas introduction means;
The time change of the theoretical hydrogen partial pressure ratio obtained by the arithmetic processing means is compared with the time change of the hydrogen partial pressure ratio detected by the hydrogen partial pressure ratio detection means, and the gas introduction amount adjusting means is controlled based on the degree of approximation. A vacuum carburizing furnace, comprising:
Theoretical flow rate V / actual flow rate V _R (3)
C: Carbon concentration (initial condition is C = C ₀ (C ₀ is base material carbon concentration), and C = C _S (C _S is surface carbon concentration) on the surface during carburization)
x: distance from the surface D: diffusion coefficient [m ² / s]
D0: Frequency factor [m ² / s]
Q: Activation energy [kJ / mol]
R: Gas constant [kJ / K · mol]
T: Temperature [K]
V _R : Actual carburizing gas flow rate introduced into the processing chamber