Had a cracked blade

[Chad J.]

So I broke it.   It didn't look bad.   I think it was while I was forging it.  I may have worked it too cold.

 

Any other opinions?  5160, I'll quenched with 2 cycles of 90 minutes at 425 for tempering.   I tried breaking it further up on the knife with no luck,  just moved my leg vice across the floor. 

[Irondragon Forge ClayWorks]

What did you quench it in?

[Frosty]

Good picture, very clear shot. May we see the rest of the broken end please?

Frosty The Lucky.

[Chad J.]

Quenched it in canola oil.  Frosty, I'll get both pieces side by side for a picture. 

[Frosty]

I just wanted to see the whole length of the break. I think I see a couple dark spots, one at the top corner and a longer one on the same side near the bottom of the pic. I THINK I see some elongated chevron marks in the more fine structure in the upper left. The grain transitions abruptly from more coarse to very fine with a sharp border that angles from lower right upwards to the left. 

The area with finer texture indicates it may have been more hard and brittle. The larger grain isn't so large I'd expect enlarged crystal embrittlement. There are also no fracture initiation nor direction indicators visible to me. 

The patterns I see in the fine grain appear to be chevron shaped indicating the fracture started on the upper right face about 1/3 of the way from the dark spot on the corner and the transition line between fine and coarse.  

Chevron patterns in torn or broken steel "point" to the initiation point. Envision the forces breaking a piece of steel starting at a POINT and spreading the tear as it travels. This is what forms the chevrons in torn and shattered steels. 

I'm not familiar with breaks in non ferrous or most exotic alloys so these cues may not apply to them.

Seeing both halves would be good but seeing the entire break might be enough to tell what happened.

Before you put too much stock in the two dark areas in the pic as shown they may simply be where it contacted the floor when it fell or you may have touched it with your grubby paws. 

If your blade snaps NEVER TOUCH THE BREAK! Get out your magnifying glass or take good pics like the one above just don't touch it. Even if your hands are clean your body oils are surprisingly corrosive and WILL discolor freshly exposed steel quickly, maybe within seconds.

Frosty The Lucky.

[Chad J.]

Thomas, the top right is where the original crack was.  That is what made me decide to finish it off.  I'll get the other half

[Frosty]

I see it, I'd estimate the crack's about the same length as the fine grain section. 

Frosty The Lucky.

[ThomasPowers]

Also was this a piece of new 5160; or did it come from what might have been a severely fatigued automotive spring? 

[Chad J.]

This was a used piece so it could very well have had micro fractures.   I wouldn't put it past a bad hammer blow or me working too cold, I'd been pushing that envelope a bit.   I think this is great for me learning,  either way.   Other than the crack, any issues on grain size?  

[anvil]

You have the right idea concerning microfractures. Altho it's important to know, I had far more failures like yours when first starting out than after gaining experience. Beginners need to look close at their technique and shy away from blaming their material.