Remark; refer to above micro structure testing results, they are appeared structure of Cast Iron type Gray Cast iron (FC) with Type D and E pattern due to quite fast cooling (Thin shape) after pouring. So it contain of Pearlite, ferrite and Flake Graphite. When consideration on cracked side, the crack occurs from the outside to inside of the thread hole and still contain high Ferrite phase. At this point, the structure results are related and concern with hardness result. However, at the OK side, it looks the same structure but it has Ferrite less than cracked side and structure still smaller than cracked side which related with hardness result.
In short, the cracking has cracked from the outside come to inside which contain high Ferrite structure and get softer hardness. It means to easily to occur cracking when get the outside force or turning force during assemble with a bolt.
Suggestion, this metal part may develop by increase hardness and make more structure control in casting process to support the force
Remark; refer to above micro structure testing results, they are appeared structure of Cast Iron type Gray Cast iron (FC) with Type D and E pattern due to quite fast cooling (Thin shape) after pouring. So it contain of Pearlite, ferrite and Flake Graphite. When consideration on cracked side, the crack occurs from the outside to inside of the thread hole and still contain high Ferrite phase. At this point, the structure results are related and concern with hardness result. However, at the OK side, it looks the same structure but it has Ferrite less than cracked side and structure still smaller than cracked side which related with hardness result.In short, the cracking has cracked from the outside come to inside which contain high Ferrite structure and get softer hardness. It means to easily to occur cracking when get the outside force or turning force during assemble with a bolt.Suggestion, this metal part may develop by increase hardness and make more structure control in casting process to support the force
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