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Title: Effects of Mo on microstructure of as-cast 28 wt.% Cr–2.6 wt.% C–(0–10) wt.% Mo irons

Microstructures of as-cast 28 wt.% Cr–2.6 wt.% C irons containing (0–10) wt.% Mo with the Cr/C ratio of about 10 were studied and related to hardness. The experimental irons were cast into dry sand molds. Microstructural investigation was performed by light microscopy, X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. It was found that the iron with about 10 wt.% Mo was eutectic/peritectic, whereas the others with less Mo content were hypoeutectic. The matrix in all irons was austenite, partly transformed to martensite during cooling. Mo addition promoted the formation of M{sub 23}C{sub 6} and M{sub 6}C. At 1 wt.% Mo, multiple eutectic carbides including M{sub 7}C{sub 3}, M{sub 23}C{sub 6} and M{sub 6}C were observed. M{sub 23}C{sub 6} existed as a transition zone between eutectic M{sub 7}C{sub 3} and M{sub 6}C, indicating a carbide transition as M{sub 7}C{sub 3}(M{sub 2.3}C) → M{sub 23}C{sub 6}(M{sub 3.8}C) → M{sub 6}C. At 6 wt.% Mo, multiple eutectic carbides including M{sub 7}C{sub 3} and M{sub 23}C{sub 6} were observed together with fine cellular/lamellar M{sub 6}C aggregates. In the iron with 10 wt.% Mo, only eutectic/peritectic M{sub 23}C{sub 6} and M{sub 6}C were found without M{sub 7}C{sub 3}. Mo distributionmore » to all carbides has been determined to be increased from ca. 0.4 to 0.7 in mass fraction as the Mo content in the irons was increased. On the other hand, Cr distribution to all carbides is quite constant as ca. 0.6 in mass fraction. Mo addition increased Vickers macro-hardness of the irons from 495 up to 674 HV{sub 30}. High Mo content as solid-solution in the matrix and the formation of M{sub 6}C or M{sub 23}C{sub 6} aggregates were the main reasons for hardness increase, indicating potentially improved wear performance of the irons with Mo addition. - Highlights: • Mo promoted the formation of M{sub 23}C{sub 6} and M{sub 6}C in the irons with Cr/C ratio of about 10. • M{sub 23}C{sub 6} has higher Fe/Cr and Mo/Cr atm% ratios than M{sub 7}C{sub 3}. • Si content and high Mo content over about 9 atm% are characteristics of M{sub 6}C. • No M{sub 7}C{sub 3} was found at 10 wt.% Mo addition, only M{sub 23}C{sub 6} and M{sub 6}C presented. • High Mo matrices and M{sub 23}C{sub 6}/M{sub 6}C aggregates increased iron macro-hardness.« less
Authors:
 [1] ; ;  [2] ;  [3] ;  [4]
  1. Department of Physics and Materials Science, Chiang Mai University, Chiang Mai 50200 (Thailand)
  2. National Metal and Materials Technology Center, Pathumthani 12120 (Thailand)
  3. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai 980-8577 (Japan)
  4. Department of Industrial Chemistry, Chiang Mai University, Chiang Mai 50200 (Thailand)
Publication Date:
OSTI Identifier:
22340348
Resource Type:
Journal Article
Resource Relation:
Journal Name: Materials Characterization; Journal Volume: 90; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AUSTENITE; CARBIDES; CAST IRON; CHROMIUM; EUTECTICS; HARDNESS; IRON; MARTENSITE; MICROSTRUCTURE; MOLYBDENUM; SCANNING ELECTRON MICROSCOPY; SOLUTIONS; TRANSMISSION ELECTRON MICROSCOPY; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY