Nine pearlitic malleable irons, produced by commercial foundries and exhibiting wide differences in chemical composition, production practices, and microstructures have been investigated to determine the hardness and effective case depth with different surface-hardening heat-treatments. Flame- and induction- (3000, 9600, and 300,000 to 347,000 cycle) heating, followed by oil, water, or spray quenches have been used for the surface-hardening treatments. Case hardness and depth were determined by superficial Rockwell or Rockwell C measurements and metallographic examination of etched specimens. Of the structures investigated, one, a dense pattern of extremely small spheroids of cementite, was most responsive to all types of treatment. However, it was found in surface-hardening that at all frequencies an optimum power input existed which minimized the influence of microstructure to a pronounced degree.

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