Hand Tools Archive

Voids in steel

Patrick Chase
Referring back to David's scope shots showing voids in some of his chisels, particularly the AIs IIRC.

I'm kicking myself for not having recognized or remembered this at the time. Those voids almost certainly formed in the inter-dendritic regions during casting/solidification. See Ch 15 (starts on p.159) in the Verhoeven book, and particularly figure 15.2 which shows "micropore" formation, and p.167 which describes the mechanism in the long para in the middle: http://www.hybridburners.com/documents/verhoeven.pdf.

Basically all conventionally solidified (read: non-PM) steels have those in their "as cast" states. One of the purposes of hot-working by forging or rolling is to eliminate such microvoids via compression. The fact that they're present in your AIs may point to a less thorough than ideal manufacturing process.

You would not expect to find those in PM-V11 or any other PM steel, for the simple reason that they shouldn't have a chance to form in the first place. Such casting-induced defects are why PM exists, and why it doesn't need conventional forging to achieve very high performance. Similar reasoning applies to the primary carbides that form during conventional casting.

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