Advice on forging PM steel failure

[HSC ///]

I forged some cpm cru wear
Annealed. Stress relieved. Hardened, cryo. Twice tempered

I had a failure where the tip broke off due to the pressure from Grinding. Not heavy pressure.

Any ideas on what might have caused this? suggestions or advice on the next one?

The spine thickness at that point is 1.89 mm

I have successfully made a forged cru wear petty before

Thanks

 

[lynx85]

Two color crack line suggests there was incomplete crack some time (darken oxide layer vs fresh metal) before grinding, when tip broke off. I would look into cryo step first - how fast do you immerse knife in liquid nitrogen, is knife fully immersed. Is there possibility crack line copies LN level in your dewar?

 

[HSC ///]

Two color crack line suggests there was incomplete crack some time (darken oxide layer vs fresh metal) before grinding, when tip broke off. I would look into cryo step first - how fast do you immerse knife in liquid nitrogen, is knife fully immersed. Is there possibility crack line copies LN level in your dewar?

Thanks for your input. I lower the blade into the dewar slowly as the LN boils off when you put the blade in. Same as always done many many times.

Measuring with a stick, there’s about 210 mm length of liquid nitrogen in the dewar. So doesn’t match the possible crack line point.

 

[Way-Barney]

Forging temperature a bit low and crack has been there all through process of annealing etc, look like an old crack even though no evidence of rust from that image.
Just guessing.

 

[HSC ///]

Forging temperature a bit low and crack has been there all through process of annealing etc, look like an old crack even though no evidence of rust from that image.
Just guessing.

I used a thermocouple to measure the heat through the forging process. I was very careful about this. I was always within range of 1980 - 2050F

 

[Joshua Fisher]

I’d clean the scale off the tip piece and the blade and etch both in acid. The acid may show if there’s any other cracks or spiderwebbing going on. Was the blade forged start to finish in one session and was it immediately annealed afterwards? Or were there any pauses in the forging process or afterwards before annealing.

 

[HSC ///]

I’d clean the scale off the tip piece and the blade and etch both in acid. The acid may show if there’s any other cracks or spiderwebbing going on. Was the blade forged start to finish in one session and was it immediately annealed afterwards? Or were there any pauses in the forging process or afterwards before annealing.

If I could fine the tip piece….

Forged in one session yes
Annealed right away yes

if I find the tip piece I will try what you said.

 

[HSC ///]

I’d clean the scale off the tip piece and the blade and etch both in acid. The acid may show if there’s any other cracks or spiderwebbing going on. Was the blade forged start to finish in one session and was it immediately annealed afterwards? Or were there any pauses in the forging process or afterwards before annealing.

I turned into a shorter wabacho
Here it is etched

 

[Way-Barney]

I turned into a shorter wabacho
Here it is etched

That is beautiful,

 

[HSC ///]

That is beautiful,

Thanks , I’ve been successful with forging cru wear just one time before when I tried

 

[Way-Barney]

Thanks , I’ve been successful with forging cru wear just one time before when I tried

Did you clay for the hamon or is it natural?

 

[HSC ///]

Did you clay for the hamon or is it natural?

There’s no hamon. It’s a powder metallurgy steel. The black is a kurochi finish. bladesmith forged finish

 

[Gilbert M]

A thought. I'm sure you were careful, but maybe one hit at the wrong temperature is all it would take to form a crack. Nice skill level to be able to forge CPM steel.

 

[HSC ///]

A thought. I'm sure you were careful, but maybe one hit at the wrong temperature is all it would take to form a crack. Nice skill level to be able to forge CPM steel.

This is a good point and perhaps the most plausible answer.
Indeed the tip area would get cooler faster

 

[Joshua Fisher]

This is a good point and perhaps the most plausible answer.
Indeed the tip area would get cooler faster

That was my thought, my suggestion would be if the purpose of forging the blade in this case is to achieve a kurochi finish I would cut the profile to the shape I want them basically texture/thin the blade while hot but not worry about forging the profile shape. I’d think that would be simpler to reduce the chance of cracks and still achieve the look that you are going for.