THE EFFECTS OF HEAT-TREATMENT ON AN IRON NAIL AS A MAGNETIC CORE FOR TEACHING AS ELECTROMAGNET MATERIAL - A STUDY WITH METALLURGICAL-MICROSCOPIC OBSERVATION -
1987 Volume 28 Issue 2 Pages 43-47
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1987 Volume 28 Issue 2 Pages 43-47
"The Electromagnet" is a first unit for the elementary school children to study about the interaction between electricity and magnetism. In the present study, it is described to investigate the effects of heat-treatment on the use of an iron nail as a magnetic core for teaching as electromagnet material in the unit. In order to observe the fine structure of an iron nail, a metallurgical microscope should be used. A heat-treated nail is embedded in the polyester resin, ground with sandpaper and polished with alumina to have a mirror face. The mirror face is etched with 3% nitric acid in methyl alcohol (Nital solution) and observed with a metallurgical microscope. As the results, it was proved that residual magnetic flux density (Br) of the iron nail was caused by internal strain and quenching structure (martensite). The internal strain can be eliminated with heat-treatment over the recrystallization temperature. The quenching st'lfucture can not be made at the temperature under the A1 magnetic transformation point.
