Botched backyard heat treat

[jcornell]

Before posting this I went back and re-read the stickies on HT - well done, Steve Sells.

I've done heat treating before, but it's my least favorite part of making a blade.  I have about 10 blades in various stages of completion right now, so I took time over the weekend to move some towards the finish line.

I did  a heat treat on three file knives (Nicholson) and a large blade made from a rail road clip (approximately 1055ish).

Took all the blades up past magnetic (I did them one at a time).  I use a propane forge.

Quenched the files in non-detergent motor oil (40 weight if memory serves correctly). (The other knife was quenched in water - it had already failed a HT in oil)

Dipped them up and down like I was taught in class.

After cooling and cleaning the oil off, I tested them all with a file - and the file bit into the knife edge.

Any clue on what I'm doing wrong?

At this point I'm tempted to cut the 40 weight oil with some ATF fluid and try again.

Suggestions, oh wise bladesmiths?

[ThomasPowers]

If these were forged then there is the possibility of a decarb layer try filing deeper and see if the file suddenly stops removing metal.  

Did you get to the quenchant fast enough?  Some simple steels have under a second to drop the first big chunk of their temperature.

Have you tried it another time making sure temp and speed are spot on?  

BTW did you normalize first?     And I would have gone with vegetable oil heated to about 140 degF

[jcornell]

The three file blades were all stock removal.  All normalized first.  Motor oil was heated before blades quenched.

I often wonder if I'm quick enough moving from forge to quench pail.

 

Normalize and trial again, I guess.

[SnailForge]

The three file blades were all stock removal.  All normalized first.  Motor oil was heated before blades quenched.

I often wonder if I'm quick enough moving from forge to quench pail.

 

Normalize and trial again, I guess.

​This is an issue I've had with razor blades, when I ground them too thin. A razors edge is basically very similar to a cooling fin. It has little thermal mass and a large surface. Trial and error have taught me how thin I can make it before it cools down too fast to quench it. This is fairly easy to judge though.

Take it out of the heat, and move it to the quench but stop right there and look at the steel. If it is still glowing, you would have been on time to quench it. Otoh, if the edge is already getting dark, you would not have been in time, and you were too slow. You can solve the problem either by being quicker, or by leaving a bit more mass near the edge, which would slow down the temperature loss.

By the same token, if you see it is glowing very bright, you could hold it right above the quench tank and let it cool down so that you can plunge it in when the steel has the exact right temperature.

Edited June 14, 2015 by SnailForge

[Steve Sells]

My tank is just behind my normal standing position.  No stepping needed, I just pull from the fire, turn, and dunk.  Having said that I have had to pour the quenchant into a 1 gal metal bucket, and place that 1 gal bucket on the forge table to get the from fire to quench fast enough for thin blades.

 

[SnailForge]

My tank is just behind my normal standing position.  No stepping needed, I just pull from the fire, turn, and dunk.  Having said that I have had to pour the quenchant into a 1 gal metal bucket, and place that 1 gal bucket on the forge table to get the from fire to quench fast enough for thin blades.

 

​Once I ground a razor so thin I couldn't get to the quench tank fast enough. I thought I'd be smart, and heat it in an iron pipe, then take out the pipe and upend it right above the quench tank. It hit the quench nice and orange, and then exploded when it hit the condensation layer at the bottom of the oil tank, a split second later. Cracked lengthwise down the middle over the entire length. Made an unholy noise I never hope to hear again coming out of a quench tank.

[Charles R. Stevens]

To be a fly on the wall for that!

[Frosty]

I've heard that sound, it's like a little demon squealing with joy and biting the steel with a snap. My slack tub has a screen on hangers just off the bottom. This is to make it reasonably easy to retrieve dropped pieces. So far I've only been hardening relatively heavy pieces for power hammer dies. However on the rare occasions I've hardened blades I laid a screen in the oil to keep dropped pieces a couple inches, say 5cm. off the bottom.

Frosty The Lucky.