Cracked Gyuto

[jawilder]

My brother had asked me to make him a set of kitchen knives rather than buying them at a store and I accepted his challenge. My first thought was to buy some blanks, put handles on them and call it a day but I wanted to give him more than that so I began forging one out of 1084, which is the only steel I have used so far outside of stainless, which has been sent out for HT.

I started with a 3/16 x 1.5" bar and cut the profile out. I knew it would be a difficult grind as I wanted both a distil taper and tapered tang with bolster.

I started by cutting out the profile, drilled the holes, then forged the blade out to 2". I normalized it 3 times in the forge first a bit above nonmagnetic, then at nonmagnetic, then just below nonmagnetic. Then I brought it back up to nonmagnetic and set in pearlite to cool overnight. In the morning it was warped pretty bad but I wasn't too concerned because I was able to straighten it out with a 3 point jig and light taps on the anvil.

I cut off the excess length that was created by forging and was very happy with it. I cleaned it up a bit and started the tapered tang as well as a bit more of a distil taper. I din't start on the bevels just yet because it was already at 3/32 so I figured I'd go ahead and heat treat it.

Today I put clay on the blade hoping to get a temper line and heated it to 815c (1499f). During the 10 minute soak, or rather while the blade was coming up to temp, the kiln fluctuated between 815c and 818c (1499f-1504f) then quenched it in 120 degree P50. I did not pull the blade out of the quench until it was pretty cool. I may have gone wrong there.

While I was cleaning the oil off the blade and getting it ready to temper I heard that dreadful *TINK* and sure enough it cracked.

If you look at the pics you can see that it cracked where I went a bit too far while forging. I was trying to draw it from 1.5" to 2" and may have gotten too thin or uneven on the heel of the blade.

Aside from forging it too thin, where did I go wrong?

I have not broken it apart yet to look at the grain. I was wondering if I should temper it first or look at the grain pre-temper.

Thanks.
Jason

 

[Rick Marchand]

Did you forge in that upward curve because it seems to have cracked right where it is the deepest? What is that mark at the crack site of pic 2?

I think things went wrong in a couple areas...

1. I am surprised to hear that it came out of the pearlite more warped than when it went in. (something odd about that)
2. Light taps on the anvil with cold thin steel is never a good thing. Try straightening on a wood block with a wooden mallet.

Essentially, you added the stress of a differential HT to a blade that was already stressed and possibly fractured.

Rick

 

[Carl_First_Timer]

Darn shame too, it looked like it would have had a nice feel to it.

 

[woodwrkr221]

Would it still be possible to salvage it, make it a boning/utility knife?

 

[jawilder]

Rick,
I think you are on the money. I need to get a wooden block and wooden malot. That would help a lot. Lesson learned there. The spot in picture two is where I forgd deeper than I intended. The crack is right in the middle of that divot. I was planning to just grind it out. I should have run another normalizing cycle before HT but I din't heat the blade up very much while cleaning up the scale.

The blade was profiled at first and kept its shape while forging, it just grew.

Carl, I was very proud of it (and still am) it feels great in the hand and very light.

Woody, I'll take another look at it when I get home. A boning knife might be a good idea. I would have to re HT it as the uncracked section was clay quenched. I might just break it into pieces and learn what I can about it.
Jason