A cylindrical piece of steel 75 mm (3 in.) in diameter is to be austenitized and quenched such that a minimum hardness of 40 HRC is to be produced throughout the entire piece. Of the alloys 8660, 8640, 8630, and 8620, which will qualify if the quenching medium is (a) moderately agitated water and (b) moderately agitated oil

a) 8660 and 8640 alloys

b)  8660 alloy

Explanation:

Diameter of a cylindrical piece of steel = 75 mm ( 3 in )

Equivalent distance from quenched end for the center position is about 17 mm

a) If the quenching medium is moderately agitated water the alloys that will qualify are : 8660 and 8640 alloys  because these are the two alloys that would have a minimum of 40 HRC at the center and also throughout the cylinder

b) if the quenching medium is a moderately agitated oil the alloy that will qualify is : 8660 alloy . because it is the only alloy that will maintain a minimum of 40 HRC at the center and also throughout the entire cylinder.