Tensile and impact specimens to two kinds of project steels were tested to determine the effect of rolled plate thickness on the mechanical properties and notch toughness. These steel plates, containing the thickness, 12, 20, 25, 35, 50, 65 and 80 mm, were rolled from two different charges. One of them has the chemical compositions of the mild steel, C class of ABS (tested in both as rolled and normalized conditions) and the auther has those of high tensile steel (fabricated after quenching and tempering process).
To estimate the effect of plate thickness on mechanical properties, the full thickness tension specimen of JIS classification and micro tension specimen were used, and also, to evaluate the notch toughness affected by thickness the standard and full thickness V notched Charpy specimens and Van der Veen specimens of full thickness were used.
As a result, the conclustions were summarized as follows;
(1) It was recognized that there was, at least, one "transition thickness" for the notch toughness of steel rolled out in the range of thickness from 12 mm to 80 mm. The "transition thickness" depended upon the kind of steel.
(2) In the case of mild steel, any significant effect of thickness was not obtained on the mechanical properties. On the contrary, the roll finish thickness has influence on the notch toughness. In the range of thickness exceeding 50 mm, the toughness was remarkably lowered, in consequence, in order to apply this range of steel plate to actual steel constructions, further devices would be needed in heat treatment and determing of steel compositions. However, the notch toughness of mild steel plate, 50 mm thick, corresponded to that of plate, . 35 mm thick, when the plate was normalized after rolling.
(3) In the quenched and tempered steel (high tensile steel) whose thickness exceeds 25 mm, the steel quality and heat tratment process should be determined very cautiously to improve their emechanical properties and notch toughness. The notch toughness of this quenched and temperfd high tensile steel, in spite of the decrease of the tohghess as the increase of thickness, whose thickness exceeds 35 mm, corresponded to that of the normalized mild steel.
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