SU1558875A1 - Specimen for study of phase transformations in cast metal - Google Patents

Abstract

The invention relates to metallurgy and can be used to study phase transformations in a cast metal by the method of electrical resistivity. The purpose of the invention is the expansion of technological capabilities and carrying out rapid studies. The natural combined sample is made by pouring liquid steel into a mold in the form of a truncated cone with an angle between the generator and the axis 10-15 °. Before pouring into the working cavity of the mold, a protective quartz cap is installed under the thermocouple and the working ends of the measuring and compensating electrical circuits. In this case, the slave ends of the electrical circuits are located from the protective cap at a distance of no more than 0.085 of the smallest diameter of the sample. The proposed sample allows to expand the technological capabilities and conduct rapid studies of phase transformations. 1 il.

Description

The invention relates to metallurgy and can be used to study phase transformations in a cast metal by measuring electrical resistivity.

The purpose of the invention is the expansion of technological capabilities and carrying out rapid studies.

Example. The natural composite sample is made by pouring liquid steel into a steel mold in the form of a truncated cone with an angle between the generator and the axis 10-15.

The protective quartz cap and the working ends of the electrical circuits are inserted into the working cavity of the mold before pouring the liquid metal.

The proposed sample is designed to estimate the kinetics of phase transformations, as well as their onset and end temperatures using a complex thermal analysis method to obtain an electrical characteristic curve. A specific feature of the sample is the use of a small millimeter diameter (for example, 5-12 mm) in the quality of the investigated volume of the alloy, located in the immediate vicinity of the working thermocouple thermocouple, which is located in the thermal center of the sample, where the temperatures and the cross section differential are small compared with the periphery.

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When studying phase transformations, a known sample has the following disadvantages: it is impossible to estimate the temperature range during melting and crystallization; it is not possible to make express determinations under production conditions.

The known sample is used in a dilatometer to study phase transformations only in the solid state. The proposed sample is obtained by pouring the molten metal into the chill form, so it allows to obtain the electrical resistance curve in the melting-crystallization intervals and determine the critical points of these transitions. In particular, it is possible to solve a practical problem of assessing the chemical composition and a number of properties of the alloy. As a result, the technological capabilities of the resistivity measurement method are expanded.

A major disadvantage of the known sample is the inability to make express determinations of the temperature ranges of phase transformations in the solid and transition states in production. One of the reasons for this is the long cycle of sample production, which ranges from several hours to several days. After the production of metal products by pressure treatment, it is necessary to cut test bars and then use the latter as blanks to obtain dilatometric samples by means of mechanical processing.

It takes several minutes to obtain t of the proposed sample by pouring the liquid metal into the chill mold.

The second reason for the lack of possibility of express-determination when using a known sample is the incorrectness of measurements in a dynamic mode. Samples used in dilatometers often have considerable dimensions, so a significant temperature difference occurs in the sample during dynamic measurements.

(The usual speed for dilatometric measurements is 1-3 ° C / min. Analyzing the signs of known and proposed samples, it was found that

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Finding the contact pads of the electrodes of the measuring circuit in the immediate vicinity of the working thermocouple spa allows to obtain information on changes in the electrical resistance of the alloy element located between the contact pads of the electrodes and at the same time in the immediate vicinity of the working thermocouple spa. This element of the alloy, according to the example, has dimensions of 10.5x2.4x7.0 mm and, being practically in the thermal center of the sample, has a minimum temperature difference across the cross section. The small dimensions of the alloy element between the contact areas of the electrodes make it possible to measure, at elevated cooling rates, since the occurrence of a significant temperature difference over the specified volume of the alloy element is unlikely. The average cooling rate of the example is 9.2 ° C / min. It may be more. Therefore, the proposed sample has a positive effect when measured in the area of increased cooling rates (tens of degrees per minute), when a known sample cannot be used. Thus, the positive effect of the invention is associated with the expansion of technological capabilities by the method of research and the conduct of rapid definitions.

Claims (1)

 Invention Formula A sample for studying phase transformations in a cast metal, having the shape of a body of revolution with a thermocouple opening in it and containing elements of measuring and compensating electrical circuits, is characterized in that, in order to expand technological capabilities and enable rapid studies, the sample molded in the shape of a truncated cone with an angle between the generator and the axis 10-15 °, with the hole provided with a protective cap, and the elements of the measuring and compensating electrical circuits p placed inside the sample at a distance from the opening under the thermocouple no more than 0.085 of the smallest diameter of the sample.