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Metals 2016,6, 218
acquiredfromsamples treatedaccordingtodifferentagingconditions,whilequantitativeevaluation
of theγ-Fephase fraction is reported inTable2. Amarked increase inaustenite content is induced
byaging. Furtherslightdecompositionofmartensitecouldbeachievedbyalso increasingtheaging
temperatureandbyextensivelyover-agingthesamples (e.g., aging8hat540 ◦C).
Figure8.XRDspectraof the18-Ni300steelasa functionofagingcondition.
Table2.Austenite (γ-Fe) fractionandcorrespondingtensilepropertiesasa functionofagingtemper.
Standarddeviationofdata isalsogiven inbrackets.
Condition γ-FeFraction(%) YS(MPa) UTS(MPa) Elongation(%)
asbuilt 11.38 (1.02) 914.9 (12.5) 1187.6 (10.4) 6.14 (1.33)
460 ◦C8h 15.55 (0.73) 1956.8 (43.3) 2017.1 (57.7) 1.51 (0.20)
490 ◦C4h 16.12 (0.57) 1793.3 (96.5) 1814.6 (95.1) 1.20 (0.13)
540 ◦C1h 17.17 (0.68) 1870.3 (53.8) 1956.9 (54.2) 2.07 (0.32)
540 ◦C8h 21.30 (0.77) 1545.9 (103.1) 1655.5 (87.5) 1.77 (0.05)
600 ◦C10min 17.15 (0.68) 1557.2 (140.4) 1659.1 (119.4) 1.60 (0.09)
Themeasuredmodificationsalsoreflectedintochangesoftheobservedmicrostructure. InFigure9,
acollectionofrepresentativeSEMmicrographs isgiven.Onaging,an increasedamountofaustenite
(brightconstituent inFigure9)decoratingcellboundariesbecamevisiblewhileover-agingadditionally
promotedprecipitationofausteniteat intragranularsites (Figure9d,f).
Table 2 also summarizes themain average data collected by room temperature tensile tests.
Low-temperatureagingpromotesadramatic increase instrengthover theasbuilt condition. Theyield
strength improvedfrom915MPaof theasbuilt steel to1957and1793MPafor samplespeak-aged
at460and490 ◦C,respectively.Conversely, fractureelongationunderwentadropfrom6.1%to1.5%
and1.2%for the samematerials. Theultimate tensile strength (UTS) and0.2%yield strength (YS)
given inTable2 forstandardpeakagingat490 ◦Caresubstantiallyconsistentwithspecifications for
wroughtproducts (e.g.,ASTMA538,AMS6514,andMIL-S-46850standards)andingoodagreement
with literaturedataonSLMed type300maraging steel [10]. Tensileductilityvaluesbetween1.2%
and2.1%wererecordedfromtests, irrespectiveofagingtemperatureandresultingaustenite fraction.
ThepoorfractureelongationofSLMedspecimensafterpeakagingisalsoconsistentwithliterature[10].
Figure10reports the tensilecurvesofsamplespeakagedat460 ◦Candofasbuilt samples tohighlight
thedramaticdifferences in tensilebehaviourbetweenthese twoconditions.
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book 3D Printing of Metals"
3D Printing of Metals
- Title
- 3D Printing of Metals
- Author
- Manoj Gupta
- Editor
- MDPI
- Location
- Basel
- Date
- 2017
- Language
- English
- License
- CC BY-NC-ND 4.0
- ISBN
- 978-3-03842-592-2
- Size
- 17.0 x 24.4 cm
- Pages
- 170
- Keywords
- 3D printing, additive manufacturing, electron beam melting, selective laser melting, laser metal deposition, aluminum, titanium, magnesium, composites
- Categories
- Naturwissenschaften Chemie