of fra ⊂ tures ull cast steel SC49 us じd tls hvdraulic turbille rumer uged イ5 years , tension comp [ ・ esgiol 】 「 atigue tests were carr [ ed ⊂ )ut for the cast s 〔 cul cut 〔 lut frum the turbine rL 【 nner Eurfacc layer and illside 、 The resuits are svmmarized a $ follo " , s ; (1 )The S 一 ゴ Vcurve of aged SC49 has large scatter altht )ugh i し shows the tendcT 〕cy of th巳 right going d ' 」 wn . And also it is foulld that the fatiguc sLrengt1 ユ of inside pal ' t has larger scatter th cl ll tha し

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... f suriacc layer part 、 (2 ) From SEM ebservatien of 亡 he f1 ・ acture surfaccs , crack lnitiatlon s 正 tes were found to bc thc c [ 一 Lstillg defピct which colls { st of derldritic phase and pore 、 (3 )1匸 is possil〕le to evaluato し he fatigue life of aged SC ・ 19by using the casting defect sizc ( ar で a ) L3 and the k 】itial stress hltensityfactor ca ! cula しed by defeGt size . The va ] uc of Lhe thresh 〔 ) 1d stress intensity fac亡 or obtalned jn this study were 4 . 8MPa ・ m1 . 2 .(1 )The extreme statistics distribution of castiug defecl s〒 zo of surface luyer