Results in Materials (Sep 2020)

Microstructural modification of a static and dynamically solidified high chromium white cast iron alloyed with vanadium

  • A. Sánchez-Cruz,
  • A. Bedolla-Jacuinde,
  • F.V. Guerra,
  • I. Mejía

Journal volume & issue
Vol. 7
p. 100114

Abstract

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The objective of this study is to analyze the effect of dynamic solidification and vanadium additions in a range from zero to 6.42 ​wt% to a high chromium white iron with the purpose of refining the microstructure and to improve hardness. The alloys were characterized by optical and electron microscopy, EDS and X-ray diffraction and complemented with phase quantification undertaken by image analysis and XRD data. Bulk hardness was measured for different casting thicknesses in both as-cast and after a destabilization heat treatment at 900 ​°C for 45 ​min. The results show that V addition produces a refining effect on the M7C3 carbide as well as the VC carbide formation which can nucleate as primary carbide for V contents higher than 4.75 ​wt%. Dynamic solidification of the experimental irons produced a notable decrease in the size of the carbide phase and increased its volume fraction. This solidification technique also produced a transformation of the iron matrix of the base alloy from predominantly austenitic to a fully pearlitic matrix, while for the 6.42 ​wt% V alloyed iron a notably smaller, slightly elongated and isolated VC carbides embedded in a highly martensitic matrix were observed. This microstructural modification resulted in the maximum harness values obtained in the as-cast conditions. After the destabilization heat treatment, a softening of the microstructure of the V alloyed irons was observed due to the C depletion of the matrix inhibiting the martensitic transformation; conversely, the base alloy experienced a considerably increase in hardness as a result of the high amount of precipitated carbides embedded in a highly martensitic matrix. The results of the present study show that, V alloying and the dynamic solidification technique can be used as effective ways to refine the carbide phase obtaining high hardness levels in the as-cast condition, avoiding this way heat treatments.

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