Test specimen consisting of several, esp. 5-10, steel disc plates, each separated from th other by a layer of material with heat-conductivity lower than that of steel, e.g. of metal oxide, esp. 0.2-1.2 mm mica layers, is used in head quenching test on a cylindrical steel test specimen (Jominy test) in which specimen is heated and quenched from its frontal face, following which structural and hardness investigations may be undertaken along length of specimen to extend testing process to steels cooling slowly from case-hardening temps. and to air-tempered heavy plate 150 mm thick, and reduce heat flow in axial direction to front face. Pref. steel plates and intermediate layers have an axial drill-hole for a headed screw bolt which can be screwed into the threaded hole of the bottom plate of the vertical specimen until its head is drawn tightly against a flange of the top plate.
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