Influence of carbides precipitated by low-temperature tempering on roomtemperature mechanical properties of grade 91 steel

Kengo Watanabe, Shuntaro Ida, Kyosuke Yoshimi

Research output: Contribution to journalArticlepeer-review

Abstract

The precipitation behavior of carbides of modified 9Cr-1Mo steel (Grade 91) by low-temperature tempering and the influence of those carbides on the mechanical properties at room temperature were investigated. As-quenched sample (AQ) showed a small amount of MC carbide in the martensite microstructure. Three types of carbides were formed by low-temperature tempering at 300-500 C that were chosen for the purpose of suppressing recovery and growth of the dislocation substructure. These carbides were identified as Fe4 C, hP8 type Fe3 C, and oP16 type Fe3 C using replica samples for transmission electron microscopic and extracted residue analyses. Double low-temperature tempering at 500 C for 5 min followed by at 300 C for 1 h (DLTT) formed a large amount of carbide compared to AQ while AQ and DLTT had similar lath widths. The hardness of the DLTT sample was higher than that of the AQ sample, whereas the tensile strength of the DLTT sample was slightly lower than that of the AQ sample regardless of strain rate. The reason why the precipitation strengthening did not work for the improvement of tensile strength is considered to be the early formation of microvoids due to the delamination of carbide/matrix interfaces under tensile test.

Original languageEnglish
Pages (from-to)825-834
Number of pages10
JournalTetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan
Volume107
Issue number10
DOIs
Publication statusPublished - 2021 Oct

Keywords

  • Carbide
  • Grade 91 steel
  • Low-temperature tempering
  • Precipitation strengthening
  • Solid solution strengthening

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Metals and Alloys
  • Materials Chemistry

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