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A Cause Analysis of Fatigue Failure of Fuel Pump Block Material(CK35) for Marine Engine

선박 엔진용 Fuel Pump Block 소재(CK35)의 피로파손 원인규명

  • 최성종 (경일대학교 기계자동차학부) ;
  • 강창원 (밀양대학교 대학원) ;
  • 김태규 (밀양대학교 신소재공학과)
  • Published : 2005.05.01

Abstract

DIN CK35 (JIS S35CK) steels have been used as a material in fuel pump blocks for marine engines. Failures in the inner surface of a drilling hole, due to the initiation of fatigue cracks have been frequently reported. However, the mechanism initiating these cracks and growths has not been clearly diagnosed yet. This study was conducted using a scraped fuel pump block, containing an initiated fatigue crack in the inner surface of a drilling hole. Initially, the cracks and fractured surfaces inside the block were investigated using an optical microscope and a SEM (Scanning Electron Microscope). In addition, microstructure observation, fatigue life test and fatigue crack growth test were performed using a specimen, which was taken from the same block. Results from these tests are summarized as follows; (1) The early crack in the block was supposed to occur inside the inner surface of the drilling hole. (2) The fatigue endurance of this material was about 330 Mpa. (3) The early crack was generated in the cavitations created by the breakdown of a big inclusion, or separation between the big inclusion and the base metal, in which the fundamental ingredients of the inclusion were C, 5, and Mn. (4) In order to prevent these types of failures, the suppression of inclusions inflow by improving the casting process, formation of fine inclusions by applying a heat treatment process, and coating of the surface of the drilling hole were required.

Keywords

Fuel Pump Block;Marine Engine;Inclusions;Fatigue Fracture;Fatigue Crack;Cavitations

References

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