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Equal HRC properly tempered comparison, through vs deferential

by Paul Soulsby
(Arkansas)

In a real world environment, if two swords of comparably properly tempered HRC ratings are matched, is there really any difference between swords made with through tempering vs differential tempering?

Would either have an advantage over the other if the wielders have comparable skills, and why?

Your thoughts?

Thank you.

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Tricky to Answer..
by: Paul

Hi Paul,

Thanks for your thought provoking question. It is actually a bit hard to answer as by its nature a differentially hardened sword has TWO HRC ratings, one at the edge and a lower rating at the back/spine (for those of you playing at home, HRC is a hardness rating used for steels).

The Katana and some Chinese swords were made this way to provide a very hard edge, but a softer spine to absorb impacts. So in theory, a through hardened sword of HRC 60 - which the what the idealized edge of a Katana is supposed to be at - would tend to be a little on the brittle side. So it would be sharp, and have a hard edge, but may break where the differentially hardened katana with a spine of 40 HRC would help prevent breakage.

Conversely, a sword that was HRC 40 may have an edge that is just a bit too soft to take a good edge or withstand serious impacts, but if well through hardened would flex where a Katana - with two different hardness ratings, is not designed to flex. You can see this pretty clearly in slow motion cutting videos - through hardened medieval swords often flex wildly when cutting and return to true, while a Katana barely seems to move at all..

At the end of the day, the "ideal" HRC of a differentially hardened Katana is 60 HRC on the edge and 40 HRC at the spine while a through hardened sword is best at around 50.

The steel type used and the tempering method may allow some monotempered swords to approach closer to HRC 60 without becoming overly brittle, but with all things, to gain in hardeness will trade of some durability and to gain durability will lose some hardeness. Differentially hardened swords are, in this way, the ultimate compromise.

Hope this helps - if I have missed the mark on your question just let me know.

- Paul

Follow-up to tempering question
by: Paul

Thank you.

It was my thought...assuming proper tempering in both cases...a through tempered blade with an HRC somewhere around 56 vs. a deferentially tempered blade with HRC around 60; assuming skill levels of the wielders was comparable; might give the through tempered blade less of a "bending" risk without compromising the blade too badly with risk of brittle breakage.

As I age, my skills seem to be off slightly...thus I thought I might transition towards a properly tempered through blade if this "theory" might possibly have some value.

Your thoughts?

I very much appreciate your dialog.

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