JPH07209220A - Quality control method for molten metal - Google Patents

Abstract

PURPOSE:To realize a highly accurate and effective quality control by prescribing temperature range where unsteady inflection state appears and effecting predictive control of fluctuation in various characteristics accompanying the solidified texture of molten metal or the fluctuation in texture. CONSTITUTION:Temperature of a predetermined quantity of molten allay 3 sampled by a casting mold 1 of a cooling curve measuring apparatus 10 is measured by means of a thermocouple 2. Electromotive force of the thermocouple 2 is expressed in terms of temperature by means of an operation analyzer 4 and presented on a temperature/analytic result display 6. On the other hand, a set value is inputted to a decision controller 5 where the temperature variable with time is calculated over a specified temperature range and the variation is compared with a set value to decide pass/fail of the molten metal and then the decision result is presented on a display 7. Consequently, erroneous decision due to measurement of temperature variation having no correlation with solidified texture caused by the disturbed measurement conditions or stability of measuring atmosphere, electric noise, etc., can be prevented and a slight fluctuation on a cooling curve caused by slight variation of texture can be decided accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quality control method for molten metal, in which a cooling curve due to temperature change of the molten metal is measured,
It is intended to appropriately improve the accuracy in a quality control method for predicting various characteristics such as solidification structure or castability or mechanical properties of the molten metal by an unsteady inflection state of the cooling curve due to temperature change.

[0002]

2. Description of the Related Art When a high-purity metal melt is cooled and solidified, its cooling curve is generally smooth by natural cooling except for the temperature change at the solidification point accompanying the phase change from liquid phase to solid phase. A steady curve showing various changes is shown. Especially at the freezing point, it shows complicated temperature changes with temperature drop, temperature rise or temperature stagnation, etc., which differ depending on purity, cooling conditions, etc., and is different from the above-mentioned smooth and stable temperature change associated with natural cooling, that is, a steady curve state. A non-steady inflection state is shown. In the case of the molten alloy, it becomes more complicated, and since a plurality of crystallized substances are crystallized in the cooling process, complicated solidification latent heat transfer occurs. As a result, the cooling curve shows a temperature change commensurate with the transfer of solidification latent heat. A curve having many non-steady inflection parts associated with crystallization of a plurality of crystallized substances is shown together with a steady curve state showing a smooth change in each part before solidification starts, during solidification, and after solidification is completed. In such a curve, it can be read that the latent heat of solidification was transferred from the non-steady inflection state of the curve, and the solidification composition of the molten alloy can be predicted. Based on such knowledge, the cooling curve of the molten alloy is measured to control the quality of the molten metal. That is, as a quality control method for a molten metal, a cooling curve due to a temperature change of the molten metal is measured, and a solidification structure, castability or mechanical property of the molten metal is measured according to an unsteady inflection state due to a temperature change of the cooling curve. Predictive management of any one or two or more of the above characteristics has been variously adopted. For example, it is known that the morphology of eutectic Si contained in an Al-Si alloy, that is, its size and shape, is greatly affected by the physical and mechanical properties of the alloy such as strength and ductility. The morphology of crystalline Si has the drawback that when the molten metal is cast without treatment, it forms a plate-like and largely developed eutectic Si, which reduces the physical properties such as strength and ductility. For this reason, it has been attempted to add a eutectic Si refining agent such as Na or Sr to the molten Al-Si alloy to obtain a desired eutectic Si.

In the above cases, however, Na, Sr, etc. may easily react with oxygen in the air, or may react with impurities in the molten metal to achieve the desired target characteristics. Therefore, after the treatment, a method of measuring the contents of Na, Sr, etc. by spectroscopic analysis that can be rapidly analyzed, and casting after confirming the contents is taken. Minute analysis time is required. Also,
Interaction of contained elements, or even the same amount of Na and Sr, may be influenced by other components, casting structures may differ, and mechanical and physical properties of the cast such as strength and ductility It has a great influence.

For these reasons, instead of analyzing the composition of the molten metal in recent years, or at the same time as the analysis, the correlation between the cooling curve of the molten metal and the morphology of the casting structure is grasped in advance, and these are used as the original data, and then separately melted. A part of the produced molten metal of the same composition is sampled and the cooling curve of this sample is measured,
Contrast this cooling curve with the original data that had the correlation between the cooling curve previously measured and the cast structure morphology,
A method for predicting the morphology of a cast structure when a separately melted molten metal to be measured is solidified has been developed and used. That is, this utilizes the fact that a slight deviation occurs in the cooling curve due to the morphology of the casting structure when the molten metal is solidified, and such a molten metal measuring device using thermal analysis during solidification of the molten metal has already been used. It is commercially available (cross meter AE meter).

An example of the measurement result by the above method is shown in FIG. 5, which shows an A356 alloy (Al-7% Si-0.3% Mg) which has not been subjected to eutectic Si refinement treatment. ) Shows the cooling curve near the eutectic and the morphology of eutectic Si, the eutectic temperature is about 571 ° C., and the supercooling temperature is 1 ° C. or less. Further, since the eutectic Si refining treatment is not applied, the morphology of eutectic Si is large and rough as shown in FIG. 6 shows the cooling curve and morphology of eutectic Si of the Sr-treated A356 alloy, the eutectic temperature is 568 ° C., the supercooling temperature is 1 ° C. or higher, and The morphology of crystalline Si is small and fine as also shown in FIG. That is, according to FIG. 6, eutectic Si
It can be seen that is sufficiently miniaturized. This cooling curve and the morphology of eutectic Si are based on the untreated alloy and eutectic as described above.
It is known that there is a correlation by repeatedly measuring the cooling curve of the Si refined alloy and the morphology of eutectic Si at that time.

Regarding the measurement using the above-mentioned principle, the temperature at which the first inflection point and the temperature at which the second inflection point of the cooling curve indicates are calculated using a computer (referred to as eutectic temperature). And the eutectic temperature are used to identify whether or not the eutectic Si refinement treatment of the alloy has been sufficiently performed, and to give an instruction to the measuring device. be able to.

[0007]

By the way, in the prediction of the solidification structure of the melt to be measured using such a cooling curve, the solidification structure can be discriminated in more detail by analyzing the cooling curve in detail. That is, for example, there are many kinds of elements contained in the alloy, and if the content of the element is the solid solution amount or more, the solidification structure contains various crystallized substances, and the cooling curve of the alloy is in the form of the solidification structure. It will comply. However, the change in the cooling curve that can be read by the morphology of the crystallized substance may be very small, and in this case, in order to read the slight deviation of the curve with the above-mentioned computer-based measuring device, it is necessary to continuously measure The gradient is calculated, the presence or absence of continuity of changes in the gradient is compared and judged, and the coagulated tissue is predicted.

However, the change in the gradient obtained by the above-mentioned method often varies depending on the measurement conditions at that time, the stability of the measurement atmosphere, electrical noise, and the like.
For example, a slight wind changes the cooling curve at the temperature position at that temperature, and as a result, a temperature change that does not correlate with the solidified tissue is read, resulting in an erroneous judgment. The same applies when the cooling curve changes due to electrical noise. Furthermore, depending on the composition of the alloy, different types of crystallized substances may crystallize at temperatures close to each other,
It may be difficult to determine which crystallized substance is due to the temperature change alone.

[0009]

The present invention has been studied to solve the problems in the prior art as described above, and by adopting a special method for measuring the change of the cooling curve, accurate and appropriate measurement can be performed. It succeeded in obtaining the result, and is as follows.

(1) A cooling curve of a sample taken from a molten metal is obtained on the basis of a temperature change of a cooling curve corresponding to each other and a solidification structure obtained in advance, and a non-steady inflection state due to a temperature change of the cooling curve is obtained. In predicting the solidification structure of the molten metal, the temperature range in which the unsteady inflection state appears is defined,
A method for quality control of molten metal, characterized by predicting and controlling changes in various characteristics associated with the solidification structure or structure change of the molten metal due to an unsteady inflection state manifested within the temperature range.

(2) The cooling curve of the sample taken from the molten metal is obtained based on the temperature changes of the cooling curves corresponding to each other and the solidification structure obtained in advance, and the cooling curve is subjected to the non-stationary inflection state due to the temperature change. In predicting the solidification structure of the molten metal, the temperature range and the time range in which the unsteady inflection state appears are defined, and the molten metal is defined by the unsteady inflection state revealed in those temperature range and time range. A method for quality control of molten metal, characterized by predicting and managing changes in various characteristics associated with solidification structure or structure change of steel.

[0012]

The cooling curve of the sample taken from the molten metal is obtained based on the temperature changes of the cooling curves corresponding to each other and the solidification structure obtained in advance, and the molten metal of the molten metal is changed according to the non-steady inflection state due to the temperature change of the cooling curve. In predicting the solidification structure, the temperature range in which the non-stationary inflection state appears is defined, and the various properties associated with the solidification structure or the tissue change of the molten metal due to the non-steady state inflection state developed in the temperature range. By predicting and managing the change of the temperature, it is possible to identify the change due to the measurement condition, the measurement atmosphere, the electrical noise, etc., and to accurately read the temperature change due to the target coagulation structure to perform the accurate quality control.

In predicting the solidification structure of the molten metal as described above, the temperature range and time range in which the unsteady inflection state appears are defined, and the unsteady state appearing in those temperature range and time range is defined. By appropriately managing the change of various characteristics due to the solidification structure or the structure change of the molten metal by the dynamic inflection state, even under varying conditions such as the measurement conditions, appropriately obtain the accuracy as described above,
Effectively carry out the desired high-precision quality control.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the accompanying drawings as needed. FIG. 1 shows a cooling curve measuring device 10 for carrying out the method of the present invention. The molten alloy 3 having a predetermined volume is held and used as a sample. However, 2 is a thermocouple, which measures the temperature of the molten metal sample 3 in the mold 1. A thermocouple electromotive force detection and calculation / analysis device 4 converts the electromotive force of the thermocouple 2 into a temperature by the electromotive force detection and calculation / analysis device 4. Further, 5 is a judgment control device, which inputs a set value to the judgment control device to calculate a temperature change which changes with time in a specified temperature range or a specified temperature range and time range, and compares the change with a set value. And passed,
The rejection is judged, and the result is sent to the pass / fail indicator 7 for displaying the pass / fail and displayed.

Reference numeral 6 in FIG. 1 denotes a temperature and analysis result display, which displays the value converted into temperature and the result of calculation analysis by the electromotive force detection and calculation analysis device 4 of the thermocouple 2. It is a recorder that records again. The mold 1 manages its heat capacity, or the measurement result obtained by combining the solidification rate of a fixed amount of the molten alloy 3 collected while heating with the solidification rate of the cast product to be the product from the measured molten metal is It is possible to accurately predict the solidification structure of the cast product.

FIG. 2 shows Al-15% Si- treated with P at 70 PPM by using the cooling curve measuring apparatus shown in FIG.
It is a cooling curve of a 0.7% Mg alloy. In this case, the temperature range designated in the judgment control device 5 is a range including the temperature where the cooling curve is measured in advance and the temperature change of the cooling curve and the correlation of the solidified tissue are confirmed. . By doing so, it is possible to prevent erroneous judgment due to measurement of temperature change that does not correlate with the coagulated tissue due to the result of being disturbed by the measurement conditions, the stability of the measurement atmosphere, the electrical noise, etc. It is possible to correctly judge the slight change on the cooling curve due to the change in the structure.

The case shown in FIG. 2 is a case in which the prediction purpose can be achieved almost appropriately by defining only the temperature range. However, Al-15 as shown in FIG.
If the cooling curve is measured for an alloy in which a compound such as Mg ₂ Si is crystallized in a eutectic composition of% Si-0.7% Mg alloy at a temperature close to the eutectic temperature, it is shown in FIG. The eutectic curve 11 and the eutectic curve 12 are generated. That is, in such a case, when only the temperature is within the specified range (a), the temperatures of the eutectic curve 11 and the eutectic curve 12 are both within the specified range (a) as shown in FIG.
There is a case in which it is not possible to determine which of the curved lines is caused by the detected inflection state because it is inside.

In the present invention, in such a case, the time range (b) is defined together with the temperature range (a), and the change state manifested in the temperature range (a) and the time range (b) is detected. However, each temperature change can be grasped and the judgment can be prevented from being mistaken. The time in which the temperature change occurs can be appropriately predicted by keeping the heat capacity of the mold 1, the amount of the molten metal sample, the temperature of the molten metal, the temperature of the sample jig, and the heating output of the mold 1 as necessary, almost constant.

A typical control measurement example according to the present invention will be described below.

Example 1 30 g of A390 alloy (Al-17% Si-5% Cu-0.5% Mg) melted at a temperature of 800 ° C. was sampled in a mold 1 of a measuring device 10 shown in FIG. The result of measuring the cooling curve of the molten metal 3 by inserting 2 into the molten metal 3 is as shown in FIG.

That is, the control device 5 of the measuring device 10
The crystallization temperature of primary Si obtained from experience in advance was 6
The temperature range of ± 15 ° C is specified with respect to 50 ° C, and it is read that the rate of change of the cooling curve gradient has changed in this temperature range. By designating the temperature range at which the changed position is read, it is possible to avoid misjudgment by reading the similar temperature gradient change rate 13 elsewhere, and improve the accuracy.

[0021]

Example 2 Measuring apparatus 1 shown in FIG. 1 for 30 g of A357 alloy (Al-7% Si-0.6% Mg) melted at a temperature of 800 ° C.
Sample No. 0 was cast in the mold 1, the thermocouple 2 was inserted into the melt 3, and the cooling curve of the melt 3 was measured. The resulting cooling curve is as shown in FIG.

That is, the control device 5 of the measuring device 10
The crystallization temperature of eutectic Si obtained from experience in advance was 5
The temperature range of 575 ° C to 525 ° C is specified for 60 ° C and the crystallization temperature of Mg2Si compound of 540 ° C, and the crystallization start time of crystallized Si is 3.5 ± with the melt temperature of the melt 3 being 750 ° C as the start time. Similarly, 1 minute and 9 ± 1 minute of the crystallization start time of the Mg 2 Si compound were designated, and it was read that the rate of change of the slope of the cooling curve changed in this composite of the temperature range and the time range.

That is, in any case, the change in the gradient change rate of the cooling curve due to the eutectic and the change in the Mg2Si compound are caused by the range designation of the position for reading the change in the gradient change rate of the cooling curve. It was possible to make a measurement with improved accuracy without making a mistake in reading the change in the rate of change of the gradient of the cooling curve due to the crystallization.

[0024]

According to the present invention as described above, the cooling curve due to the temperature change of such a molten metal is measured, and the solidification structure, castability, mechanical properties, etc. are obtained from the unsteady inflection state. In the quality control method, the accuracy can be appropriately improved, and effective quality control can be performed, so that the invention is industrially highly effective.

[Brief description of drawings]

FIG. 1 is an explanatory view of a cooling curve measuring device for carrying out the method of the present invention.

[FIG. 2] 70 PPM of P was treated by the apparatus of FIG.
It is a chart of the result of having obtained the cooling curve of Al-15% Si-0.7% Mg alloy.

FIG. 3 is a chart of the results of determining the non-steady inflection state of the cooling curve of the A390 alloy according to the present invention by defining the temperature range.

FIG. 4 is a chart showing the results of determining the non-steady inflection state of the cooling curve of the A357 alloy by defining the temperature range and the time range according to the present invention.

FIG. 5 is a table showing a cooling curve in the vicinity of a eutectic crystal of an A356 alloy that has not been subjected to eutectic Si refining treatment and a microscopic morphology of the eutectic Si.

FIG. 6: Cooling curve and eutectic of the above S356-treated A356 alloy
It is the chart which also showed the microscopic form of Si.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Thermocouple 3 Molten metal alloy 4 Electromotive force detection and calculation / analysis device 5 Judgment control device 6 Temperature and analysis result display 7 Pass / fail display 10 indicating pass / fail 10 Measuring device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kei Yamawaki 1-34-1, Kambara, Kambara-cho, Anbara-gun, Shizuoka Prefecture Nichiritsu Giken Co., Ltd. No. 34-1 Nikkei Information Systems Co., Ltd. Shizuoka Plant

Claims (2)

[Claims] 1. A cooling curve of a sample taken from a molten metal is obtained on the basis of a temperature change of a cooling curve corresponding to each other and a solidification structure obtained in advance, and the cooling curve is subjected to an unsteady inflection state due to a temperature change of the cooling curve. In predicting the solidification structure of molten metal,
The temperature range in which the unsteady inflection state appears is defined, and the change in various characteristics associated with the solidification structure or the structure change of the molten metal is predicted and controlled by the unsteady inflection state that appears in the temperature range. A characteristic method for quality control of molten metal. 2. A cooling curve of a sample taken from a molten metal is obtained on the basis of a temperature change of a cooling curve corresponding to each other and a solidification structure obtained in advance, and the cooling curve is subjected to an unsteady inflection state due to the temperature change of the cooling curve. In predicting the solidification structure of molten metal,
The temperature range and the time range in which the non-stationary inflection state appears are defined, and the characteristics associated with the solidification structure or the microstructure change of the molten metal are defined by the non-stationary inflection state that appears in the temperature range and the time range. A quality control method for molten metal, characterized by predicting and controlling changes.