The influences of various conditions of quenching, annealing and preheating before annealing on the graphitization of dilatometric specimens and the influences of quenching and preheating before annealing on the grahitization and ultimate strength of link chain castings were investigatad.
The following results were obtained.
(1) The cracks which may be caused by the quenching from 800∼900°C are not detected in dilatometric specimens and in the link chain castings of 31∼66g in weight.
(2) The higher the quenching temperatures are, the shorter the time required for graphitization is.
(3) By preheating the quenched specimens and the non-quenched specimens up to 48 hours at the temperatures of 350∼550°C before annealing, the time for the first stage graphitization of the non-preheated specimens is shortened to about 1/4∼3/5 of the time for the non-quenched specimens and the time for the second stage graphitization is shortened to about 4/5.
(4) The number of graphite nodules is considerably increased by the quenching, and is exceedingly increased by the preheating before annealing, the number of graphite nodules of the quenched specimens increasing about ten times than that of the non-quenched specimens.
(5) The strength of the ferritic matrix link chain castings is not affected by those heat treatments carried out in this investigation and by the number of graphite nodules resulted from those treatments.
(6) It is possible to decrease the time for graphitization to half by the quenching before annealing without any fall of strength on manufacturing the black heart malleable iron castings.
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