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Quantification of the dislocation density, size, and volume fraction of precipitates in deep cryogenically treated martensitic steels

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journal contribution
posted on 2020-11-01, 00:00 authored by Ajesh Antony, Natalya M Schmerl, Anna Sokolova, Reza Mahjoub, Daniel FabijanicDaniel Fabijanic, Nikki E Stanford
Two groups of martensitic alloys were examined for changes induced by deep cryogenic treatment (DCT). The first group was a range of binary and ternary compositions with 0.6 wt % carbon, and the second group was a commercial AISI D2 tool steel. X-ray diffraction showed that DCT made two changes to the microstructure: retained austenite was transformed to martensite, and the dislocation density of the martensite was increased. This increase in dislocation density was consistent for all alloys, including those that did not undergo phase transformation during DCT. It is suggested that the increase in dislocation density may be caused by local differences in thermal expansion within the heterogeneous martensitic structure. Then, samples were tempered, and the cementite size distribution was examined using small angle neutron scattering (SANS) and atom probe tomography. First principles calculations confirmed that all magnetic scattering originated in cementite and not carbon clusters. Quantitative SANS analysis showed a measurable change in cementite size distribution for all alloys as a result of prior DCT. It is proposed that the increase in dislocation density that results from DCT modifies the cementite precipitation through enhanced diffusion rates and increased cementite nucleation sites.

History

Journal

Metals

Volume

10

Issue

11

Publisher

MDPI AG

Location

Basel, Switzerland

eISSN

2075-4701

Language

eng

Notes

This article belongs to the Special Issue Heat Treatment and Mechanical Properties of Metals and Alloys

Publication classification

C1 Refereed article in a scholarly journal

Copyright notice

2020, The Authors