JP3318316B2 - Control method of carburizing condition in carburizing process - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a carburizing state in a carburizing treatment of a metal surface.

[0002]

2. Description of the Related Art Generally, carburizing treatment methods for metal surfaces include solid carburizing methods using coke, graphite, and charcoal, methane, ethane, propane, carbon monoxide, oil vapor, and the like.
A gas carburizing method performed in alcohol and a plasma carburizing method performed in plasma generated by applying a DC high voltage or high frequency to a mixed gas of methane, ethane, propane, and the like and a hydrogen gas are known. In these carburizing methods, a method of introducing a material to be treated into a carburizing furnace and controlling the heating with a heat pattern to perform carburizing is generally adopted.

However, this method is an empirical rule based on the past carburizing results, and cannot perform universal surface control. In addition, this is an empirical rule specific to the carburizing furnace used, and must be established by performing carburizing treatment for each carburizing furnace.

[0004] As a technique for giving universality to a carburizing treatment control method depending on a heat pattern based on guesses and empirical rules, there are the following techniques.
A method of controlling the atmosphere by obtaining a carbon potential from a change in electric resistance of a carburized material (Japanese Patent Application Laid-Open No. 63-17186)
No. 4), a carburizing control material that allows a certain amount of activated carbon to pass through in a carburizing atmosphere is attached to the carburizing control surface of the material to be carburized and carburized for a predetermined time to reduce the carburizing layer thickness of the carburizing control surface. Control method (Japanese Patent Application Laid-Open No. Hei 3-20452), after applying a paste-like reduced plating composition to the surface of a material to be carburized to form a plating film, and then carburizing to form a carburized layer having a desired thickness. Forming method (JP-A-6-2102)
No.) is disclosed.

[0005]

However, the methods disclosed in the above publications do not directly measure the surface carbon concentration of the material to be carburized, and cannot measure the carbon concentration accurately. Further, it is impossible to measure the change with time of the surface carbon concentration being formed during the carburizing treatment, and it is not possible to control the carburizing treatment using the measurement results.

[0006] The production of high quality carburized materials requires the production of extremely high precision carburized layers. In addition, in order to reflect the measurement result in carburizing control, it is necessary to measure safely, simply, quickly, and without affecting the quality of the material to be treated. Under these conditions, the methods disclosed in the above publications cannot be said to be sufficient measurement methods.

In order to solve these problems, the present inventors have conducted intensive studies and found that the refractive index n of the surface of the material to be carburized shows a monotonically increasing relationship with the carbon concentration of the carburized layer (hereinafter, carburized concentration). , the refractive index time variation of the carburized workpiece surface is found to exhibit the relationship monotonically increases with respect to carburizing rate. Thus, during the carburizing process, the surface of the material to be treated is irradiated with polarized light in the visible region, the reflected light is measured, and the carburizing control factor is fed back based on the result of calculating the refractive index and carbon concentration of the surface of the material to be treated. br /> by controlling click, it is to propose that performing an immediate control of the measurement and carburizing condition of the carbon concentration during carburization.

[0008]

According to the method of the present invention for solving the above-mentioned problems, the method is applied during carburizing.
By irradiating the surface of the treated material with polarized light and measuring the reflected light
Ri, measured over time the refractive index of the treated material surface, Ri by time change of <br/> refractive index to calculate the concentration of carbon <br/> absolute value than the treated material surface of the refractive index carburizing Calculate the speed and the above carbon concentration
Carburizing control factor based on the calculation result of the carburizing rate and fee <br/> Dobakku control and, the treated material surface is to correspond to the target carbon concentration
It is characterized in that carburizing is performed until a state of exhibiting a high refractive index is obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below. In the present invention, the surface of the material to be treated is irradiated with polarized light in the visible region during the carburizing process, the reflected light is measured, and the surface of the material to be treated is refracted. calculating the rate and surface carbon concentration, due to <br/> feedback control of the carburizing control factor and proposes an immediate control method of the measurement and carburizing condition of surface carbon concentration in carburizing.

In this method, polarized light is made incident on a material to be processed, and reflected light emitted from the surface of the material to be processed is measured.
The polarized light having a wavelength in the range of 200 nm to 800 nm is effective. The temporal changes in the refractive index and carburizing concentration of the carburized surface layer can be calculated from the intensity and phase difference between the incident light and the reflected light, and the optical constants of the material to be treated and the carburized surface layer of the material to be treated. Preferably, a spectroscopic ellipsometer is used. As a result, spectral characteristics of optical constants can be obtained, so that more accurate information can be obtained.

In the method of the present invention, the surface carbon concentration and the carburizing speed are calculated from the time change of the refractive index of the carburized surface layer. The monotonically increasing relationship between the refractive index of the carburized surface and the surface carbon concentration, the change in the refractive index over time, and the carburizing rate are the first behaviors confirmed by this study. Each of the carbon concentration and the carburizing rate is uniquely determined. Further, the thickness of the carburized layer formed on the material to be treated can be easily calculated from the diffusion constant, the carburizing pressure and the temperature of the material to be treated.

FIG. 1 shows the change in the refractive index of the surface of the material to be processed with respect to the processing time. A mild steel plate was placed on the cathode as a material to be treated, CH ₄ gas was introduced into the carburizing furnace at a flow rate of 400 ccm, and carburizing treatment was performed with DC methane plasma at a furnace temperature of 930 ° C. and an applied voltage of 550 V. Carburizing treatment was performed at a furnace pressure of 2.2 Torr for 12 minutes, after which the plasma was stopped for 7 minutes to diffuse carbon into the material to be treated, and carburizing treatment was performed again at a furnace pressure of 3.4 Torr for 5 minutes. The refractive index of the surface of the material to be treated increased monotonically with the increase of the surface carbon concentration accompanying the progress of the carburizing treatment. According to this method, the surface carbon concentration of the material to be treated accompanying the carburizing treatment can be immediately measured by measuring the refractive index.

The gradient of the refractive index with respect to time changes with the change of the CH ₄ gas flow rate, and the gradient of the refractive index increases as the gas flow rate increases. Since the gas flow rate and the surface carbon concentration of the material to be treated have a monotonically increasing relationship, the carburization rate on the surface of the material to be treated can be measured immediately by associating the gradient of the refractive index with the gas flow rate.

FIG. 2 shows the change in carburizing concentration with respect to the surface refractive index of the material to be treated during carburization, obtained by polarization measurement. The carburized concentration of the material to be treated is the relative refractive index change during carburization Δ <n> / <n
> Tended to increase monotonically. The relationship between the refractive index and the carburizing concentration is unique and universal for each type of material to be treated, and by obtaining the relationship between the refractive index and the carburizing concentration for each material as a regression line or regression curve, the relationship between the measured refractive index and It is possible to immediately obtain the carburized concentration of the treated material and to immediately control the carburizing process.

[0015] performing refractive index measurement in the method, carburizing concentration obtained by a change measuring refractive index time, the feedback control to the carburizing apparatus <br/> charcoal regulators immersion by carburization rate. Gas carburizing equipment and plasma carburizing equipment are effective as carburizing equipment, and the carburizing layer of target quality is applied to the material to be treated by associating the control conditions of each equipment with the carburizing concentration and carburizing speed measurement results. It becomes possible to perform such control.

Acquisition of refractive index and refractive index time change measurement results;
Conversion of refractive index, refractive index time change measurement results to surface carbon concentration, carburizing speed, carburizing equipment control conditions and surface carbon concentration,
It is very effective to use an electronic computer and an attached communication device for associating with a carburizing speed measurement result and designating control conditions to a carburizing apparatus. This makes it possible to monitor the surface properties of the material to be carburized during the carburizing process at equal time intervals and to immediately control the carburizing conditions.

[0017]

[Example] CH ₄ gas was introduced into a carburizing furnace at a flow rate of 400 ccm, a mild steel plate (50 mm × 50 mm × 5 mm) was used as a cathode, a furnace temperature of 930 ° C., an applied voltage of 550 V, and a furnace after the start of processing. Carburizing treatment with DC methane plasma was performed at a pressure of 2.2 Torr. Immediate measurement of the refractive index n was performed during the carburizing treatment, and the carburizing treatment was performed until the surface of the material to be treated showed a refractive index corresponding to the target surface carbon concentration (0.55 mass%). After carburizing,
Chemical analysis was performed with an electron probe microscope to measure the carbon concentration on the surface of the material to be treated. The results are shown in the upper column of Table 1.

[0018]

[Comparative Example] Injection of CH ₄ gas into a carburizing furnace at a flow rate of 400 ccm, carburizing with DC methane plasma at a furnace temperature of 930 ° C and an applied voltage of 550 V using a mild steel plate (50 mm x 50 mm x 5 mm) as a cathode. Processing was performed. At furnace pressure 2.2 Torr for 9 minutes, 12
For 15 minutes, carburized samples were prepared, and the surface carbon concentration of each sample was measured using an electron probe microscope.
Based on the relationship between the carburizing time and the surface carbon concentration, the carburizing time corresponding to the target surface carbon concentration (0.55 mass%) was calculated recursively, and the mild steel sheet was carburized again with methane plasma to produce a sample surface. The carbon concentration was measured with an electron probe microscope. The results are shown in the lower column of Table 1.

As is clear from the results shown in Table 1, in the example and the comparative example (conventional method), the error with respect to the target value is 1%.
There is a one-fold difference and it is clear that the method according to the invention is much more accurate.

[0020]

[Table 1]

[0021]

According to the method of the present invention configured as described above, since the surface carbon concentration is directly measured by optical measurement, compared with the method proposed in the above conventional method,
Extremely accurate carbon concentration can be measured in a short time. In addition, since the measurement method uses polarized light in the visible region, safe, simple, and highly accurate measurement is possible, and measurement can be performed without affecting the progress of carburization and the quality of the material to be treated. It is.

[0022] In yet a method of the present invention, it is possible to feedback control the carburization regulators against carburizing furnace by carburization concentration measurement results to be performed in a short time. Therefore, it is possible to immediately control the thickness of the carburized layer by directly measuring the carburized concentration.

[Brief description of the drawings]

FIG. 1 shows the change over time in the refractive index n of the surface of a mild steel sheet that has been carburized by the method described in the example. The horizontal axis shows the time since the sample was introduced into the carburizing furnace. Shows the carburization start time (applied voltage 550 V, furnace pressure 2.2 Torr). Indicates the carburization end time. The recarburization start time (applied voltage 550 V, furnace pressure 3.4 Torr) is shown. Indicates the end time of recarburization. This shows the carbon diffusion end time in the surface area of the material to be treated.

FIG. 2 shows a change in surface carbon concentration with respect to a refractive index relative change Δ <n> / <n> of a surface of a mild steel sheet subjected to a carburizing treatment according to an example. The broken line indicates the measured value, and the solid line indicates the regression line obtained from the measured value.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Moriya 1060 Nishikawazu-cho, Matsue-shi, Shimane Pref. Shimane University Faculty of Science and Engineering (56) References JP-A-6-77301 (JP, A) JP-A-10-116871 (JP, A) In-situ controlled plasma-based skin treatment process development, high-tech information, Japan, China Technology Promotion Center, November 30, 2000, No. 125, pp. 12-15 (58) Survey Field (Int.Cl. ⁷ , DB name) C23C 8/22 C23C 8/38 G01N 33/20 G01N 21/41 JICST file (JOIS) WPI (DIALOG) WPI / L (QUESTEL)

Claims (1)

(57) [Claims] Claims: 1. During carburizing, the material is treated during the carburizing process.
By irradiating polarized light to the material surface and measuring the reflected light,
The refractive index of the treated material surface was measured over time, it calculates the concentration of carbon absolute value than the treated material surface of the refractive index to calculate the carburizing rate Ri by the time change of the refractive index, immersion and the carbon concentration
Bending the carburizing control factor based on the calculation result of the coal velocity Fidoba <br/> click control, the treated material surface is corresponding to the target carbon concentration
A method of controlling a carburizing state during a carburizing process, wherein the carburizing process is performed until a state showing a folding ratio is reached .