JPH052003A - Measuring method for specific heat of metal - Google Patents

Abstract

PURPOSE:To obtain a considerably reliable method for measuring the specific heat of a metal inexpensively and easily in the wide temperature range. CONSTITUTION:Ends of a thermocouple 3 are welded to a small piece of metallic sample 2. The sample 2 is placed in a radiant heating furnace 1. The curve of the temperature rise when the sample 2 is heated in the furnace is recorded by a temperature recorder 5. The total heat absorption ratio thetaCG1 of a first approximate value C1 (known specific heat value of a metal close to the metallic sample 2 is obtained by the inverse calculation using a radiation conduction formula from the temperature rise curve and the known specific heat value C1. Then, the total heat, absorption ratio thetaCG2 of a second approximate value is obtained from the obtained value and the specific heat value of two points as the first approximate value. A specific heat value C2 as the more reliable second approximate value is obtained from the above value and the temperature rise curve using the radiation conduction formula.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the specific heat of metal.

[0002]

2. Description of the Related Art In the industry for heat treating a wide variety of steels, such as the iron and steel industry, it is very important to understand the specific heat value as a control parameter for heat treatment. By the way, as a conventional specific heat measuring method, an adiabatic continuous method or a laser flash method is widely known.

As an adiabatic continuous method, for example, an adiabatic calorimeter as shown in FIG. 4 is generally used. That is, a heat insulating container 12 having a good conductor of heat and having no singular point of specific heat is stored in the center of the vacuum container 11, and a sample 13 is arranged in the center thereof. A heater 14 is electrically insulated and embedded in the sample 13, and a DC voltage is externally applied via a wiring 15. A heater 16 that heats the heat insulating container 12 is provided outside the heat insulating container 12, and a heat reflection plate 17 that prevents the heat of the heater 16 from radiating to the outside is attached to the outside of the heater 16. Then, the sample 13 and the heat insulating container 12 are respectively heated via both the heaters 14 and 16, and the temperature difference between them is measured by the differential thermocouple 18, and the temperature difference is eliminated and the temperature is kept the same from the outside. The specific heat value is measured by applying a constant heat input to the sample 13 in a state where the heat input to and from the sample 13 is cut off, that is, in a heat-insulated state, and comparing the time of the temperature rise with a standard value. There is (for example, Industrial Measurement Handbook (edited by the Society of Precision Instruments and Society of Instrument and Control Engineers, published by S57.1, P.612-613)
)reference).

On the other hand, the principle of the laser flash method is, for example, as shown in FIG. 5, the surface of a disk-shaped sample 21 is uniformly and instantaneously irradiated with the pulsed light of the ruby laser device 22, and the back surface of the sample 21. The temperature is detected by the infrared sensor 23, and the temperature rise is observed by, for example, the high speed memory recorder 24. Then, the thermal diffusivity is calculated from the obtained characteristic curve of the backside temperature rise, and the specific heat is further calculated (for example, the paper “New Material AlN and High Thermal Conductivity Measurement (Metal, April 1988, P.25. ~ 26))).

[0005]

However, the above-mentioned conventional adiabatic continuous method or laser flash method is disadvantageous in that the measuring apparatus is expensive and the measuring temperature range is limited. Further, the measurement sample is also required to have a size and shape according to the measuring device, and a nonstandard sample has a problem that it needs to be once melted in a vacuum furnace or the like and then shaped. Further, the specific heat value of metals can be found in many documents, but in the case of alloys, the specific heat fluctuates depending on the component ratio, and in the case of Cr-based stainless steel, the transformation point changes depending on the Cr content. Since the peak point of the specific heat and its peak value change in various ways, the literature values near the transformation point are often referred to only as the first-order approximation values.

The present invention has been made in order to solve the problems of the prior art as described above. If the specific heat value of a representative steel grade is available, the specific heat value of a similar sub-steel grade can be obtained inexpensively and easily, It is an object of the present invention to provide a method for measuring the specific heat of a metal, which has a wide measurement temperature range and is somewhat inferior in accuracy, but fairly reliable.

[0007]

According to the present invention, in a method for measuring a specific heat of a metal, a step of heating a small metal sample having a thermocouple end welded in a radiant heating furnace to record a temperature rising curve, Calculating a total heat absorption coefficient as a first-order approximation value by using a radiation heat transfer equation from the temperature rising curve and a specific heat value as a first-order approximation value close to the specific heat value of the metal sample; By using two more reliable points of the overall heat absorption rate as the first approximation value and the specific heat value as the first approximation value, a more reliable overall heat absorption rate as the second approximation value is obtained. And a step of back-calculating a more reliable specific heat value as a second approximate value from the overall heat absorption coefficient as the second approximate value and the temperature rise curve by using the radiation heat transfer equation. Is a method for measuring the specific heat of a metal.

[0008]

[Operation] The operation of the present invention will be described below.
The structure of the specific heat measuring device used in the present invention is shown in FIG.
That is, a small piece of metal sample 2 having the end portion of the thermocouple 3 welded is loaded into the radiant heating furnace 1 and radiantly heated by the heater 4 fed from the heater power source 5, and detected by the thermocouple 3 at that time. The temperature of the metal sample 2 is recorded on the chart of the temperature recorder 6 as a temperature rising curve.

[0009] Now, when the thin metal piece 2 having a plate thickness D is used as the small metal piece 2 for radiant heating, the temperature rise curve of the obtained metal sample 2 is generally represented by the following equation (Equation 1). It is known to follow the heat equation.

[0010]

[Equation 1]

Where T _S is the temperature of the metal sample 2 and T _F
Is the atmospheric temperature in the radiant heating furnace 1, t is the heating time, c is the specific heat, ρ is the specific gravity, φ _CG is the overall heat absorption rate, and σ is the Stefan Boltzmann constant. Therefore, first, the temperature T _S of the metal sample 2 is obtained from the chart of the temperature recorder 6. The furnace atmosphere temperature T _F is the same as that of the metal sample 2 when the temperature T _S of the metal sample 2 when the metal sample 2 is held in the radiant heating furnace 1 for a certain time and the furnace atmosphere temperature T _F substantially match. Temperature T _S
To choose. Then, since the unknowns in the equation (Equation 1) are only the specific heat c and the overall heat absorption coefficient φ _CG , if one of the unknowns is determined, the other can be uniquely obtained. Although the specific heat c and the total heat absorption coefficient φ _CG can be considered as a function of the metal sample temperature T _S , the total heat absorption coefficient φ
_CG mainly depends on the surface condition of the metal sample 2, whereas the specific heat c depends on the physical properties inside the metal sample 2, and the plate thickness D
When the temperature rises rapidly by decreasing
It can be considered that _CG changes only slowly over a wide range of metal sample temperatures.

On the other hand, the specific heat c depends on the physical properties of the metal as described above, and has a sharp peak value especially around the transformation point. In the case of alloys, the transformation point moves and the peak value also changes depending on the content of the added metal, but in the low temperature region and high temperature region far from the transformation point, the specific heat near the transformation point has less variation and the metal with a similar composition Can be considered to be almost equal to the measured value or the literature value.

The present invention is realized by applying such a fact, and the principle of the present invention will be described below with reference to FIG. The specific heat c ₁ of a metal having a material close to that of the metal sample 2 to be measured and having a known specific heat is checked in advance over the required measurement temperature range. The metal sample 2 is heated in the radiant heating furnace 1, and the temperature rising curve is recorded on the chart of the temperature recorder 6.
Temperature rising curve obtained in step (see, for example, Fig. 3)
Using the specific heat c ₁ as the first approximation value from the step and back calculation using the equation (Equation 1), the overall heat absorption rate φ for each temperature in the temperature increase curve measurement range as the first approximation value
_{Get CG1} . Since the specific heat c ₁ as the first approximate value of the step is fairly reliable in the low temperature _and high temperature regions distant from the transformation point, the summary as the first approximate value in the step obtained by back calculation with the specific heat of the region The heat absorption rate φ _{CG1 is} also reliable. Since this total heat absorption coefficient φ _CG1 changes only slowly over a wide temperature range, the total heat absorption coefficients φ _CGL and φ _CGH in the low temperature region and the high temperature region sandwiching the above transformation point are used, and The overall heat absorption coefficient φ for each measured temperature of the temperature rise curve as the second approximate value
_{Get CG2} . This total heat absorption coefficient φ _CG2 is more reliable than the total heat absorption coefficient φ _CG1 as the first approximate value obtained in the step. From the overall heat absorption coefficient φ _CG2 as the second approximate value obtained in the step and the temperature increase curve obtained in the step, the equation (Equation 1) is back-calculated to obtain the temperature increase curve within the measurement range as the second approximate value. The specific heat c ₂ for each temperature is obtained. The specific heat c ₂ as the second approximate value can be more reliable than the specific heat c ₁ as the first approximate value, and the behavior of the specific heat c near the transformation point becomes more accurate and clear.

[0014]

EXAMPLES Examples of the present invention will be described below. As a metal sample, for example, the component is C: 0.04 wt%, Si: 0.40
wt%, Cr: 16.30 wt%, Mn: 0.55 wt%, N: 0.010 wt%,
P: 0.025 wt%, S: 0.07 wt%, Ni: 0.20 wt%, Al:
The specific measurement procedure for measuring the specific heat of JIS SUS430 stainless steel consisting of 0.11 wt% and the balance Fe will be described.

First, a known iron alloy close to the specific heat of JIS SUS430 stainless steel as a metal sample is JIS SUS410 stainless steel, and the specific heat at a plate thickness of 1 mm has the characteristic values shown in FIG. Can be seen from literature values. This is SUS430
Specific heat value c as a first approximation close to the specific heat of stainless steel
_Set to ₁ . On the other hand, one example of the chart of the temperature rising curve obtained by heating the metal sample SUS430 stainless steel in the radiant heating furnace is as shown in FIG. 5, so that the temperature rising curve of FIG. 5 and the specific heat value c of FIG. the overall heat absorption rate phi _CG1 as a first approximation of the metal sample from the ₁ shows the results obtained by back calculation equation (equation 1) in FIG. 6.

Here, the transformation point of SUS430 stainless steel is 50.
Since it is 0 to 900 ℃, the overall heat absorption rate φ _CGL at the plate temperature 300 ℃ which is lower than that of Fig. 6 is 0.30, and the total heat absorption rate φ at the plate temperature 1000 ℃ as the high temperature range φ _It can be seen that _CGH is 0.34. Therefore, as a result of smoothly interpolating these total heat absorption coefficients φ _CGL and φ _CGH , the total heat absorption coefficient φ _CG2 as the second approximate value in the temperature range of 500 to 900 ° C. is obtained as shown in FIG. I was able to get it.

Finally, the specific heat value c ₂ as the second approximate value of the metal sample was back calculated from the new total heat absorption coefficient φ _CG2 and the temperature rising curve by using the formula (Equation 1) again.
The results shown in were obtained. This specific heat value c ₂ has a clear difference between the specific heat value of the conventional literature and 500 to 900 ° C. between the transformation point temperatures, and it can be seen that a value that can be practically used is obtained within this range.

[0018]

As described above, according to the present invention, the specific heat can be easily measured only by the equipment such as the radiant heating furnace, the thermocouple, and the temperature recorder, and the special and expensive equipment dedicated to the specific heat measurement. Is also unnecessary, and there is an effect that there are few constraint conditions such as processing a metal sample to be measured into a special shape and size for a specific heat measuring device. Further, the present invention can measure the specific heat in the entire temperature range heated by the radiant heating furnace, and has an effect that there are less restrictions on the measurement temperature range than the conventional method.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a configuration of an embodiment of a specific heat measuring device used in the present invention.

FIG. 2 is a flow chart showing the procedure of the present invention.

FIG. 3 is a characteristic diagram showing a temperature rising curve.

FIG. 4 is a characteristic diagram showing the relationship between the plate temperature of SUS410 stainless steel and the specific heat ratio c ₁ as a first approximation.

FIG. 5 is a characteristic diagram showing changes in plate temperature of SUS430 stainless steel.

FIG. 6 is a characteristic diagram showing the relationship between the plate temperature of SUS430 stainless steel and the overall heat absorption coefficient φ _CG1 as a first approximation value.

FIG. 7 is a characteristic diagram showing the relationship between the plate temperature of SUS430 stainless steel and the overall heat absorption coefficient φ _CG2 as a second approximation value.

FIG. 8 is a characteristic diagram showing the relationship between the plate temperature of SUS430 stainless steel and the specific heat ratio c ₂ as a second approximate value.

FIG. 9 is a side sectional view showing a configuration example of a conventional adiabatic calorimeter.

FIG. 10 is a perspective view showing the principle of a conventional laser flash method.

[Explanation of symbols]

 1 Radiant heating furnace 2 Metal sample 3 Thermocouple 4 Heater 5 Temperature recorder

Claims (1)

Claim: What is claimed is: 1. A method for measuring a specific heat of a metal, comprising:
A step of heating a small metal sample whose thermocouple ends are welded in a radiant heating furnace to record a temperature rise curve; a specific heat value as a first approximation value close to the specific heat values of the temperature rise curve and the metal sample. From the above, the step of back-calculating the total heat absorption rate as the first approximation value using the radiation heat transfer equation, and the total heat absorption rate as the first approximation value and the specific heat value as the first approximation value Using the more reliable two points of the above, a step of obtaining a more reliable total heat absorption rate as the second approximate value, and a total heat absorption rate as the second approximate value and the temperature rising curve A method for measuring a specific heat of a metal, comprising a step of calculating a more reliable specific heat value as a second approximate value by using a radiation heat transfer equation.