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Title: Effect of heat treatment on microstructure and hardness of Grade 91 steel

The modified 9Cr-1Mo steel (Grade 91) is a material of choice in fossil-fuel-fired power plants with increased efficiency, service life, and reduction in emission of greenhouse gases. It is also considered a prospective material for the Next Generation Nuclear Power Plant for application in reactor pressure vessels at temperatures up to 650°C. In this paper, heat treatment of the modified 9Cr-1Mo steel was studied by normalizing and tempering the steel at various temperatures and times, with the ultimate goal of improving its creep resistance and optimizing material hardness. The microstructural evolution of the heat treated steels was correlated with the differential scanning calorimetric results. Optical microscopy, scanning and transmission electron microscopy in conjunction with microhardness profiles and calorimetric plots were used to understand the evolution of microstructure including precipitate structures in modified 9Cr-1Mo steel and relate it to the mechanical behavior of the steel. Thermo-CalcTM calculations were used to support experimental work and provide guidance in terms of the precipitate stability and microstructural evolution. Furthermore, the carbon isopleth and temperature dependencies of the volume fraction of different precipitates were constructed. The predicted and experimentally observed results were found to be in good agreement.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3]
  1. Univ. of Idaho, Moscow, ID (United States). Dept. of Chemical and Materials Engineering.
  2. Univ. of Idaho, Moscow, ID (United States). Dept. of Mechanicial Engineering.
  3. Idaho National Lab. (INL), Idaho Falls, ID (United States). Energy Systems Integration.
Publication Date:
OSTI Identifier:
1178075
Report Number(s):
INL/JOU--15-34939
Journal ID: ISSN 2075-4701; MBSEC7; PII: met5010131
Grant/Contract Number:
AC07-05ID14517
Type:
Accepted Manuscript
Journal Name:
Metals
Additional Journal Information:
Journal Volume: 5; Journal Issue: 1; Journal ID: ISSN 2075-4701
Publisher:
MDPI
Research Org:
Idaho National Lab. (INL), Idaho Falls, ID (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
99 GENERAL AND MISCELLANEOUS; 20 FOSSIL-FUELED POWER PLANTS; 42 ENGINEERING modified 9Cr-1Mo steel; Grade 91 steel; heat treatment; microstructure; differential scanning calorimetry; Thermo-Calc; precipitates