Abstract
(1) In broad sense, the defenition of inclusions in steel must be extended to gaseons substances such as hydrides or nitrides, not only for solids.
(2) One of the main causes of flakes or white spots in forged steels is considered to be the destructive force of free hydrogen arrested by doxidiging agents, which evolves suddenly at Ar3 point in the case of cooling.
(3) In order to obtain clean steels free of gaseous inclusions in the melting, it is necessary to have.
a) long vigorous boil, owing to the quality of furnace charges, and b) minimum use of reducing agents.
(4) Ni-Cr-Mo steels are suitable manufactural clean steels with toughness in large ingots, as main additional elements such as nickel and molybdenum have little effect to kill the bath and are easy to get quality steel free of gaseous defects. It is advisable, however, to select 0·3% molybdenum steel in stead of usual 0·6% one in view of the diffusibility of gases for avoiding hair cracks.
