Monthly Archives: September 2019

Things to remember for heat treated armour

I’ve been cleaning up my heat treated and tempered knees, and thought that it would be useful to make a few notes to remember if you are doing this (or if I’m doing this after a long hiatus, which has been known to happen)

A bunch of this is obvious in retrospect, but my attempt to planish out some surface irregularities on tempered carbon steel was a hilarious (but not at the time) failure. Since I didn’t know how much “depth” I would be losing to firescale I figured that I should do all of my surface updates AFTER heat treating. Oops. This clean-up has taken a whole lot of time, hopefully the rough (150 grit) pass on the other knee will be considerably faster.
Knees partway through grinding with 150 grit to remove the last of the firescale and surface irregularities
So things to remember
Do all of the rough grinding / clean up of surface irregularities before heat treating because:

  • Planishing doesn’t work on hardened steel
  • abrasives are much less effective on tempered steel
  • If I have to clean up any surface irregularities, start with 120 grit instead of 150 grit
  • Do all edge bevels before heat treating (when it’s still easy)

More pictures when this gets finished…

Heat Treating 15th Century Knee Armour

I’ve been too busy building things to be doing regular updates, but it’s worth mentioning that I just heat treated a pair of early 15th century articulating knees (Poleyns). The basic treatment is simple enough – heat to between 1500 and 1600 degrees F and quench (I used an oil quench) followed by annealing at 400 degrees for 40 minutes (this was empirically tested). Note that I had a couple of lames (the pieces that articulate) that I had screwed up earlier and / or used to practice technique to test so that I could mess up and / or destroy representative pieces without destroying things I actually cared about!
Knee lame in furnace Knee Lame at heat
Part of the concern of heat treating is how much distortion you will get, particularly with hand formed pieces which will have a lot of uneven stresses. To alleviate this we initially heated below the critical range (to around 1200 degrees – still a cheerful orange) and held here for 15 minutes to stress relieve the metal. This did not have a significant impact on the shape (we traced before and after – again, pics below) and eliminating this step did not result in distortion more than a few millimeters (less than 1/16″) on lames. The Poleyns distorted more than this, since we did not have a sufficiently large furnace to play with and had to juggle the quench. This was offset by having very even heat in the furnaces we did use, and a change in our quench technique on the second poleyn led to a much easier quench with less distortion.
Lames showing distortion Lames showing distortion - offset pic
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