What did I do wrong

[Kylemakesstuff]

Hi guys, first time post and I’m looking to find out what I did wrong, this is only the 3rd blade I have made and when I tried a quick chop test is snapped in half, it looks like there was a stress fracture in the blade but I could be wrong, could it have been an error with the heat treat or temper?

[ThomasPowers]

Definitely a crack in the blade; as to what you did wrong it could be: alloy, forging too hot or too cold, pre-existing crack in used steel, wrong quench temperature or quenchant, wrong tempering temperature.  The Devil is in the details!

[Kylemakesstuff]

Sedona looks like there was a crack in the blade, the temper seemed strange as different parts came out different colours (most parts were straw but patches were purple)

[ThomasPowers]

ALLOY? QUENCHANT?  WORKING/QUENCHING TEMPERATURE?  How even was the temperature in what you were drawing the temper in?   All make a difference in making blades.

And don't use the "at" symbol here---that came with Johnny come lately Social Media stuff----did you read the "Read This FIrst"  thread yet?

[Jobtiel1]

Indeed we need some more information to define the problem you have. The alloy, where you got it from (scrapped/new), and quench medium would go a long way. What you're asking right now is like asking: "my car broke down, what part do I need" without any additional information.

~ Jobtiel

[Kylemakesstuff]

Sorry the tagging was force of habit, it was a reclaimed (scrap) file, normalised it 3 times, the temp was an even bright orange across the blade (don’t have anything to test temp with) quenched in canola oil, and tempered at 200c for around 2 hours, when the steel was spark tested it did show high carbon but to be honest I am unsure of what steel it was. Also never forged it cold (below red in colour)

[Jobtiel1]

Looking at the grain I think your normalizing temps may have been a bit high, but more experienced metallurgists may chime in on that one. Concerning the crack, if you didn't forge it too cold it makes me believe it is due to high temp during quenching. Have you used a magnet to better estimate the quenching temp? with files I don't really need to go higher than red to get the steel non-magnetic and harden properly.

~Jobtiel

[Kylemakesstuff]

I magnet tested it but it was a more orange than red so that could be one of the reasons

[Randy Griffin]

I second high temp at quench. That grain is huge. Try normalizing at a lower temp and quench just above non mag.

[JHCC]

The change in color on the crack surface means that there was already a microcrack when you did your quench and temper. The large grain size is bad, but it only hastened the inevitable.

[Jobtiel1]

Is it possible this change in color happened during tempering? 

~Jobtiel

[ThomasPowers]

Do you know what the scrap was used for previously?  Might give some idea about alloy.

[Kylemakesstuff]

It was an old file tool originally. 

[ThomasPowers]

Files are generally good steel for blades, but a bit picky in forging and quenching temps.  They also tend not to have fatigue cracks in them!

How thick was the edge when it was  quenched?

[Kylemakesstuff]

The edge was around 1-1.5mm thick when quenched. I’ve attached a photo of how it looked after the temper just in case that could shed some light on it.

[ThomasPowers]

I'd advise a thicker edge at quench, especially for file steel; as quenching puts a lot of stress on it and file steel tends to be brittle.  You did draw temper on it immediately after quenching, right?

[Kylemakesstuff]

I did, as soon as it quenched it was in the tempering oven with 2 or 3 minutes if not quicker

[ThomasPowers]

Good.

[JHCC]

1 hour ago, Jobtiel1 said:

Is it possible this change in color happened during tempering? 

~Jobtiel

The color changed when the inside surface of the crack was first exposed to oxygen; that happened between when the crack first formed and when the blade broke. That might have been in hardening and tempering, or it might have been before.

In your photo above, I can see two dark lines radiating back from the inside curve; either of those might be the crack that initiated the break. Can you give us a photo of the two pieces aligned as they were before breaking?

[Kylemakesstuff]

Here is the last photo I have of it before the brake and after. I noticed a dark line on my photo of the temper and it seems to be where it broke.

[velegski]

Glad you picked up on that. I was trying to type about that flaw as you posted. I guessing but I'd bet that crack developed when you forged that curve into the blade. 

The other comments about grain size and temps are spot on. I'd suggest that you darken your forge area before doing any part of the hardening process. Doing it in daylight makes it hard to judge steel colors and you have a tendency, at least in my case to be to hot,  daylight washes out colors I see. 

 

[Frosty]

Low red heat is pretty low for forging high carbon. Were someone doing it in my shop I'd tell them to stop and take it to the fire. 

Frosty The Lucky.

[Buzzkill]

Leaving the teeth of the file intact is also a risky move.  Every place there is a defined tooth with a sharp transition in the steel is another potential failure point.  

Another trick to use for determining quenching temperature is to put some table salt on the blade while it's heating in the forge.  When you see the salt melt it should be at a good quenching temperature.

As was already stated, based on the grain size you quenched at a much higher temperature than is ideal, and one way or another you had a small crack in the blade either from the forging process or from heat treating.  It was definitely there before you tested the knife.

[Kylemakesstuff]

Thanks all, I will take the tips and run with them in my next project. I like the idea about the salt.