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Dan Hertzson

Thermocycle!

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So I finally got to really test the blower upgrade on my forge. Had been getting hot enough for welding HC, but struggling a bit with mild. Now I'm getting enough heat to reach yellow white temperatures and guess I need to watch more carefully. Was on my last pass at forging down a 3" tank turret bearing that I've struggled with in the past and at approaching 1/4" it got hot enough to crumble under the hammer when I got a little distracted. Before it wouldn't have been a problem since the forge never got hot enough to burn steel, but of course this was probably something like 52100 and needed extra care in any case.

 

Oh well,  so now I've forged out a 14" dirk instead of an 18" one.  Before going through all the grinding and heat treating I thought I'd check a piece of the worst of the crumbled portion to see if thermocycling would save it. Normalized my usual way with 3 decending cycles, heated to critical and quenched in parks 50.  Had to grind a groove to break it, but the cleavage shows lovely grain on the same steel that crumbled like cottage cheese earlier. Maybe a bit of surface decarb as well.  Hope the photo below of the results shows up.

 

20200606_234439.jpg

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You can certainly fix the grain, but when it turns to cheese there will be cracks that can't be fixed short of forge welding, and possibly not even then.

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Well I cut off the bad section, forged out the rest and no cracks yet.  Guess I'll find out when I quench, temper and final grind.  

 

The test coupon above was from the worst area that broke under the hammer.  I did no further forging and only thermocycled and quenched.  I had to cut a groove in it to be able to break it in my vise with a 3# hammer (it was a short and thick piece though..  Right now I'm more worried about surface decarb than cracks, but we shall see as things progress.

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