SynopsisTellurium controls sulfide morphology in steel with a mechanism different from those of calcium, titanium and zirconium. The required tellurium content is proportional to the sulfur content.The resulfurized steels whose sulfides are controlled by tellurium addition have improved machinability, mechanical properties, fatigue strength and ductility in cold forging.

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Synopsis: Effects of heat-treated structures and cold working on machinability and tool life with high speed steel tools in drilling case hardening Cr steels containing sulfur up to 0.1% have been investigated. Lameller pearlite structures obtained by annealing or normalizing show the best drillability. As dispersion of cementite particles becomes uniform and spheridizing of carbide progresses drillability becomes worse remarkably. But machinability based on tool life is the best for spheroidized structures. Drillability seems not to be improved by cold working. The effect of cold working on tool life with high speed steel tools is understood as the result of both a favorable effect by decrease of ductility and an unfavorable effect of work hardening.

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