THE IMMUNIZATION OF FLAKES IN A MEDIUM CARBON MANGANESE STEEL BY HOT WORKING

42Mn2 steel cylinders processed by hot extrusion and drawing of flake-con-taining billets have been examined by SEM and by other methods to ascertain theimmunization of flakes in the final products. All internal flakes in the billets werecompletely healed after processing into cylinders, with the exception of those origi-nally exposed to the surface of the billet owing to oxidation. From practical appli-cation point of view, however, little difference in properties has been found betweencylinders completely or incompletely immunized from flakes. Thus, in the fatiguetest of the cylinders within cyclic stress ranges of 10?150 kg/cm~2, no signalsinduced by the formation and propagation of cracks were detected by acoustic emis-sion till 30,000-60,000 cycles. Likewise, the static bursting test of all cylindersalso met the standard set up by the users.