Transmission Electron Microscopic Observation and Microanalysis of Type 316L Weld Metal —Low Temperature Toughness of Austenitic Stainless Steel Weld Metal (Report 2)—

Hiroshi Tamura, Tadao Onzawa, Akito Takasaki

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Abstract

An authors’ previous paper which reported on the influence of delta-ferrite on low temperature toughness of Type 316L austenitic stainless steel weld metal, revealed that the toughness of as-welded specimen was dependent not only on the delta-ferrite content but also on the solidification mode. In this paper, various factors being affected on the toughness such as concentration difference, coherency, etc., were investigated in detail by using a transmission electron microscopy (TEM), an analytical electron microscopy (STEM/EDX) and a scanning electron microscopy equipped with an energy dispersive X-ray spectrometer (SEM/EDX). From an electron diffraction analysis, a crystallographic orientation of primary delta-ferrite was coherent with that of its adjacent austenite matrix but in the eutectic delta-ferrite, the relation was in-coherent. The amount of molybdenum contained in the eutectic delta-ferrite was 1.8 times as that in the primary delta-ferrite and moreover, a cell or a cellular dendrite boundary adjacent to the eutectic delta-ferrite, was enriched in molybdenum slightly. Probably, in these molybdenum-rich sites, a lattice strain was considered to be higher than that in the primary delta-ferrite. From the SEM/EDX analysis on the fractured surface of the Chirpy tested eutectic delta-ferrite specimen, the chromium and molybdenum rich zones were measured, where these compositions were equivalent to that of delta-ferrite or cellular dendrite. However, in the primary delta-ferrite specimen, such a zone could not be detected. From results above, when the eutectic delta-ferrite specimen was Charpy-tested, a crack initiation occurred at the delta-ferrite/austenite boundary or within the delta-ferrite and subsequently, the crack propagated preferentially along the cell or the cellular dendrite boundary or the delta-ferrite. In the specimen heat-treated at 923 K for 100 hrs, the concentration of the principal elements such as chromium, molybdenum and nickel within the prior delta-ferrite fluctuated widely, independent of its morphology, in which furthermore, the presence of carbide M23C6 and a phase were confirmed.

Original languageEnglish
Pages (from-to)256-262
Number of pages7
JournalQUARTERLY JOURNAL OF THE JAPAN WELDING SOCIETY
Volume5
Issue number2
DOIs
Publication statusPublished - 1987 Jan 1

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Keywords

  • Analytical electron microscopy
  • Austenitic stainless steel
  • Delta-ferrite
  • Low temperature toughness
  • Transmission electron microscopy
  • Weld metal

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Surfaces, Coatings and Films
  • Metals and Alloys

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