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Title: Crystallography of lath martensite and stabilization of retained austenite

Abstract

TEM was used to study the morphology and crystallography of lath martensite in low and medium carbon steels in the as-quenched and 200/sup 0/C tempered conditions. The steels have microduplex structures of dislocated lath martensite and continuous thin films of retained austenite at the lath interfaces. Stacks of laths form the packets which are derived from different (111) variants of the same austenite grain. The residual parent austenite enables microdiffraction experiments with small electron beam spot sizes for the orientation relationships (OR) between austenite and martensite. All three most commonly observed ORs, namely Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano, operate within the same sample.

Authors:
Publication Date:
Research Org.:
Lawrence Berkeley Lab., CA (USA)
OSTI Identifier:
6620798
Alternate Identifier(s):
OSTI ID: 6620798; Legacy ID: DE83003714
Report Number(s):
LBL-15111
ON: DE83003714
DOE Contract Number:
AC03-76SF00098
Resource Type:
Technical Report
Resource Relation:
Other Information: Thesis. Portions of document are illegible
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CARBON STEELS; CRYSTALLOGRAPHY; MICROSTRUCTURE; AUSTENITE; ELECTRON DIFFRACTION; HEAT TREATMENTS; LATTICE PARAMETERS; MARTENSITE; MORPHOLOGY; TRANSMISSION ELECTRON MICROSCOPY; ALLOYS; CARBON ADDITIONS; COHERENT SCATTERING; CRYSTAL STRUCTURE; DIFFRACTION; ELECTRON MICROSCOPY; IRON ALLOYS; IRON BASE ALLOYS; MICROSCOPY; SCATTERING; STEELS 360102* -- Metals & Alloys-- Structure & Phase Studies

Citation Formats

Sarikaya. M.. Crystallography of lath martensite and stabilization of retained austenite. United States: N. p., 1982. Web. doi:10.2172/6620798.
Sarikaya. M.. Crystallography of lath martensite and stabilization of retained austenite. United States. doi:10.2172/6620798.
Sarikaya. M.. Fri . "Crystallography of lath martensite and stabilization of retained austenite". United States. doi:10.2172/6620798. https://www.osti.gov/servlets/purl/6620798.
@article{osti_6620798,
title = {Crystallography of lath martensite and stabilization of retained austenite},
author = {Sarikaya. M.},
abstractNote = {TEM was used to study the morphology and crystallography of lath martensite in low and medium carbon steels in the as-quenched and 200/sup 0/C tempered conditions. The steels have microduplex structures of dislocated lath martensite and continuous thin films of retained austenite at the lath interfaces. Stacks of laths form the packets which are derived from different (111) variants of the same austenite grain. The residual parent austenite enables microdiffraction experiments with small electron beam spot sizes for the orientation relationships (OR) between austenite and martensite. All three most commonly observed ORs, namely Kurdjumov-Sachs, Nishiyama-Wassermann, and Greninger-Troiano, operate within the same sample.},
doi = {10.2172/6620798},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Oct 01 00:00:00 EDT 1982},
month = {Fri Oct 01 00:00:00 EDT 1982}
}

Technical Report:

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  • Some observations made on the orientation relationships of the austenite ..-->.. lath martensite transformation are reported.
  • The orientation relationships between retained austenite and lath marteniste transformation are reported. Direct crystallographic analysis using retained austenite ceveals that the dominant austenite-martensite (lath) orientation relation in medium carbon experimental steels corresponds to either Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) relationships depending on the composition.
  • The purpose of this work was to assess the effects of the amount of retained austenite content on the ductile-to-brittle transition temperature of martensitic precipitation strengthened stainless steels for four different precipitation strengthening systems, one utilizing NiTi strengthening and three utilizing R-phase strengthening. The retained austenite contents in the four systems were varied by varying composition. The austenite content in the NiTi strengthened system was varied by varying the chromium content and the austenite content in the R-phase strengthened Systems was varied by varying the nickel content. The room temperature toughness levels of the NiTi strengthened system were quite lowmore » and it was decided not to pursue this system further. The three R-phase strengthened systems had sufficient room temperature toughness and strength to be of further interest. Of these three systems the primary focus was on the 12Cr/12Co/5Mo system. In this system four alloys, identical except for variations in nickel content, were the primary focus of the work. These alloys achieved, on tempering at 5250 C for 3.16 hours, yield strengths on the order of 210 ksi and ultimate tensile strengths of 235 ksi. The effect of test temperature on the Charpy impact energy was investigated for two tempering temperatures for these four alloys. It was found for both tempering conditions that lower ductile-to-brittle transition temperatures were favored by increasing amounts of austenite in the structure. In fact, the ductile-to-brittle transition temperature was quite low, about -750 C, for the tempered at 5250 C for 3.16 hours microstructure of the alloy in this series which contained the highest nickel and the highest amount of retained austenite after quenching. At this point it is believed the austenite content is an important contributor to the low ductile-to-brittle transition temperature of this microstructure.« less