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Sample prep for eutectoid steel lab

Sample prep for eutectoid steel lab - Change grinding paper...

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Processing, Structure, and Properties of a near eutectoid composition steel
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Fe – Fe 3 C phase diagram
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Terms Metastable Equilibrium Peritectic Eutectic Eutectoid δ – BCC γ – FCC – austenite α – BCC – ferrite Fe 3 C – cementite α’ – BCT – martensite Hypo & hyper Austenitize Quench Temper Spheroidize Normalize Time temperature transformation curves Continuous cooling curves
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Sample mounting schematic
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Optical microscopy Limited depth of field Samples must be polished Grain boundaries are areas of higher energy and are therefore attacked more aggressively by etchant We will perform microhardness testing on the samples Top and bottom surface must be parallel
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Polishing procedure Draw an arrow on the back of your sample to indicate direction Begin by mounting a 120 grit SiC grinding paper on the polishing wheel Polish until all scratches are in the same direction
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Unformatted text preview: Change grinding paper to 240 grit SiC and rotate your sample 90° • Polish until no scratches from the 120 grit are visible • Repeat procedure using subsequently finer grit paper, 120, 240, 320, 400, 600 • Change over to cloth and slurry polishing • Begin with 15µm Al 2 O 3 suspension and billiard cloth, polish until no scratches are visible from 600 grit • Change to fresh billiard cloth and polish with 5µm suspension • Change to velvet cloth and polish with 1µm suspension • Change to fresh velvet cloth and polish with 0.3µm suspension • Change to fresh velvet cloth and polish with 0.05µm suspension Etching procedure • Invert freshly polished sample in Nital solution (3% HNO 3 ) for 5 seconds • Rinse, dry, and examine for microstructure • Repeat as necessary to reveal grain boundaries in your sample. • Be careful not to over etch....
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