부산대학교 도서관

Using two kinds of coated metal molds preheated at about 150°C which had a form to restrict the contraction of castings, the tendency to hot tear formation of cast iron with varying composition was studied. Iron was melted in a high frequency induction furnace with alumina crucible at about 1,400°C and poured at about 1,300°C. The results obtained were as follows : (1) Free contraction was responsible for hot tear formation and chilling increased free contraction and promoted hot tearing. (2) Cast iron of lower Sc had more risk of hot tear formation. (3) The influence of various elements on hot tearing was : Si : Considerbly decreased hot tearing. Mn : Excessive Mn addition promoted both chilling and hot tearing. P : Promoted hot tear up to P 0.4%. Hot tear Remarkably decreased at P 0.6% but increased again above P 0.6%. S : Considerably promoted hot tearing. Cu : Contraction and hot tear formation tendency were slightly increased if Cu% was higher than 2.0. Sn : Promote both chilling and hot tearing if Sn content was above 0.2%. (4) Thick coating was effective not only on reducing cooling rate but on decreasing hot tear. (5) Inoculation was effective to reduce hot tear formation in low Sc iron castings. (6) It is considered that the temperature of hot tear formation is near to the solidus but the tearing temperature may be changed by chemical composition. When eutectic graphite structure is formed, hot tearing time is considerably late. When white iron structure is formed, hot tears form at comparatively high temperature. (7) It is effective to strip mold at early period to prevent hot tearing. In order to completely prevent hot tearing, it is necessary that the mold is stripped prior to finishing the eutectic solidification at the portion where tears tend to occur.