A cylindrical piece of steel 38 mm (1 1/2in.) in diameter is to be austenitized and quenched such that a microstructure consisting of at least 80% martensite will be produced throughout the entire piece. Of the alloys 4340, 4140, 8640, 5140, and 1040, which will qualify if the quenching medium is
(a) Moderately agitated oil and
(b) Moderately agitated water? Justify your choice(s).