Metallurgical Examination of a Cast Armor Gun Shield Manufactured by General Steel Castings Corporation

摘要

Metallurgiocal examination was conducted on samples from the heaviest section (5.5-in - 6.3-in) of a cast armor gun shield, Serail No. 88, Heat No. 9035 produced from Pattern D7041960 at the Eddystone Plant of the General Steel Casting Corp. Coarse crystallinity throughout the section was observed in the samples fractured and the results obtained from V-notch Charpy impact tests were exceedingly low. Moreover, in view of the facct that the microstructure consisted of large bainite and martensite grains (ASTM grain size Nos. 4-6), it was apparent that this casting was improperly quenched and tempered. This fact was confirmed by the manufacturer who stated that this casting was one of two castings which was heat treated with regular production castings of thinner sections and, therefore, the quenching and tempering time was entirely too short for a heavy casting of this type.