International Journal of Automotive Technology

The Korean Society of Automotive Engineers (한국자동차공학회)
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EFFECT OF HARDNESS CHANGES AND MICROSTRUCTURAL DEGRADATION ON CREEP BEHAVIOR OF A Mod.9Cr-1Mo STEEL

  • PARK K. S. (Department of Mechnical Engineering and Materials Science, Yokohama National University) ;
  • CHUNG H. S. (School of Mechanical and Aerospace Engineering, Gyeongsang National University) ;
  • LEE K. J. (Division of Information Commmunication, Yangsan College) ;
  • JUNG Y. G. (School of Mechnical Engineering, Kumoh National Institute of Technology) ;
  • KANG C. Y. (Division of Materials Science and Engineering, Bukyung National University) ;
  • ENDO T. (Department of Mechnical Engineering and Materials Science, Yokohama National University)
  • Published : 2005.02.01
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Abstract

Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

Keywords

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