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Metallography (Paper & Discussion)


Academic year: 2023

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As a micro study of metals involves an in-depth knowledge of the structure of the materials, an important study is to. This question goes into the structure of the crystal itself and is about the current limit of micro. First, the resistance pyrometer, where the increased electrical resistance of a wire (generally platinum) is measured; the wire's resistance increases with temperature, and is a direct measure of this.

The advantages of this type are (a) no part of the instrument must be in or near the furnace; (b) the range is greater as there is no metal to fuse as in the case of the resistance and thermo-fusion type. By plotting these on square paper, taking the temperature as the ordinate and the time as the abscissa, and adding the observed readings, the result will be a cooling curve of the sample. In the case of metals, the latent heat evolved at the moment of solidification often raises the temperature of the mass so much that it is visible to the eye as a distinct flash; this is especially noticeable in the accumulation of gold, the phenomenon being called Recalescence, and advantage is taken of it in some metallurgical operations.

Here we do not have an example of recalescence, but an undoubted example of a deep rearrangement of the molecules themselves in the solid and cold. It is proposed to consider only the examples of very simple alloys, but to understand them it is advisable to study the example of a simple solution such as common sea salt or sodium chloride in water.

It will be readily understood from what has been written that the study of alloys with many constituents, such as the iron alloys, with the possible allotropic modification of the iron and carbon, and the additional complexity due to such constituents as silicon, vanadium, tungsten, chromium, nickel, etc., which are found in some of the numerous varieties of steel, become exceedingly complex. The light is projected onto a transparent mirror, set at an angle of 45 degrees, in the tube of the microscope, reflected down onto the surface of the specimen, and reflected back up through the objective and eyepiece. In another arrangement, the transparent mirror is replaced by a right-angled or reflecting prism adjusted to cut off only a small portion of the field.

Therefore, it is desirable that when the exposure is properly adjusted, it is not necessary to move the tube. Finally, keep a complete record of the sample in every single case; it pays off when one comes back to it in maybe a year or so. We also know that the higher the temperature, as a rule, the more salt a solvent can dissolve, and when the temperature drops, the excess salt will crystallize.

The same goes for molten alloys; usually one finds practically a homogeneous mixture; but when cooling takes place, part of the solute is ejected by crystallization, and that substance may be a relatively pure metal or a relatively pure compound. I say relatively pure metal because when an alloy is cooled, the time for the complete separation of the metal is infinitely short compared to the crystallization of a salt. The importance of the cooling rate and the point at which the cooling started should be understood from what has been stated.

Hit-or-miss methods are now generally eliminated from the modern workshop, but soon this will also have to be the case for the physical processing of modern alloys produced for engineers. We all know such an example and use one every day of the week; but perhaps not all of us have yet realized the reason for this. Another example of the application of the same principle is Pattiuson's process of silvering argentiferous lead; it led.

The various liquidation processes are other examples of the two melting points of alloys used commercially. It shows the large crystals radiating from the sides of the mold and finer crystals in the center of the mass. In the case of pure gold, the structure of the crystal grains becomes visible by simply bending the sample, the slip bands due to the different orientation of the individual crystal grains reflect the light at different angles, the structure is macroscopic.

Silver is taken as the standard of electrical conductivity, and is regarded as such; copper comes next at 95, compared to silver, but an alloy of a mixture of the two does not equal the average of the constituents. This will surround the excess component, and the conductivity will depend on the conductivity of the eutectic, not to mention the thermoelectric effect of the (in this case three) dissimilar bodies in thermoelectric contact with all possibilities of counter E.M.


He could assure the members of that Institute of a very cordial reception at the meetings of the Society of Chemical Industry. ANKETELL HENDERSON, on behalf of the Photographic Society, thanked the Institute for the kind invitation. He had touched the outermost edge of the subject, and Major Law had awakened his interest.

Having been given a pure alloy, it had something of the character of the metal they were dealing with. Was not one of the main points of the alloys due to the separation of excess metal. He proposed to cross a good deal of the same ground which Major Law had taken.

When he discovered some problems at work, he was able to appreciate the success he had achieved. He looked forward to hearing Mr. and Steel" at a meeting of the Society of Chemical Industry. They were only useful when there was a small percentage of one and a large percentage of the other.

On behalf of the Institute he heartily thanked Mr. Fletcher for the invitation to attend the meetings of the Society of Chemical Industry. It was necessary to give the slag a certain time to rise to the surface of the molten steel. In the "acid open fire process", the ferromanganese was added to the steel while it was in the furnace, allowing plenty of time for the slag to rise to the surface of the metal before it was tapped.

The slag formed after the addition of ferromanganese did not have enough time to rise to the surface of the metal before the steel had to be poured into ingot molds. Such structures should be considered as shapes arising from the flow of material either in the mold or as it passes through the rolls. Such large sections could be prepared in the workshop by any of the usual working methods - machining, grinding, polishing with sandpaper, etc.

He also pointed out that when referring to the work with the crucible in the laboratory, the electric furnace was not mentioned. The subject was one of the most complex, and scientists were now only on the threshold of investigation.



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