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Snapped M390 Artifex

Mon Feb 18, 2013 1:54 am

First and foremost I posting this out of curiosity and would like more knowledge of what I'm looking at....

Ok, so I thinned the Artifex 2-3weeks ago from 2.3mm to 2.0 and took the edge from .025in to .012 using a 100grit blaze and following up with a 220grit Norax. I dipped the blade in water after every pass and made sure to move the blade quickly when grinding.
Today I tried handing sanding with diamond pads and the blade snapped when sanding the tip. For reference I had the blade on an old cutting board, my left hand sanding and my right hand holding the handle (5lbs max downward force). I started getting more aggressive with sanding near the tip and POP goes the Gyuto.
My biggest question are why did it happen, how do I prevent it from happening again, and what's with the grain growth near the spine?

Thanks for any insight available!
Pics for reference:

Image

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Re: Snapped M390 Artifex

Mon Feb 18, 2013 3:40 am

holy shit!!!!!

Re: Snapped M390 Artifex

Mon Feb 18, 2013 4:47 am

wow....just wow.....

Re: Snapped M390 Artifex

Mon Feb 18, 2013 5:24 am

Looking at the pic with the rust spot, it looked like there was a crack in the blade prior to it snapping. Even stainless steel can rust, especially if it hasn't been heat treated yet. The rust makes me think it had a crack prior to or during the heat treating cycle. It looks like the blade may have had a flaw/crack/void in it before or during Heat Treating with the rust being on the inside of the break like that. There is also an odd splotch down near the bottom of the tang section going towards the edge, too. The picture does look like the grain is larger at the rust spot, which could mean that spot was over heated (which can cause grain growth and/or cracks), or it may be an illusion with the rust? It's hard to tell if it was a flaw from the heat treating cycle or the steel itself had a flaw in it, but it looks like there was some sort of flaw in it. The shape of the crack is interesting, too, with one part being rusted on one side of the blade, but not the other (rust didn't go all the way thru the blade on one part, so the void was only partial there prior to the crack).

I would send it back to Mark so he can check it out in person and find out what happened. I've worked on numerous M390 blades from CKTG (handles and convexing/thinning) and never had any issues with them cracking like that.

Re: Snapped M390 Artifex

Mon Feb 18, 2013 5:27 am

Looking at the pics, is there a dark streak in the middle of the crack going from the shiny part inside the break to the spine area?

Re: Snapped M390 Artifex

Mon Feb 18, 2013 9:17 am

taz575 wrote:.................................

I would send it back to Mark so he can check it out in person and find out what happened. I've worked on numerous M390 blades from CKTG (handles and convexing/thinning) and never had any issues with them cracking like that.



+1

Re: Snapped M390 Artifex

Mon Feb 18, 2013 11:45 am

Taz,

Thank you for the insight. I planned on sending it to Mark so he can have a look at it. I was thinking it was decarb from the HT or rust prior to HT. I'm half way tempted to snap the blade in sections to see if I affected the grain growth from thinning.

Re: Snapped M390 Artifex

Mon Feb 18, 2013 11:53 am

As long as the steel didn't change colors on you when you were grinding it, it shouldn't be affecting the heat treating at all. If it turned a dark gold, it may have reduced the hardness slightly, and blue/purple colors mean the steel may have gotten way too hot and burned. It would have to be over 400 degrees to affect the temper; grain growth generally occurs when the steel gets hot during the part of the heat treating cycle or forging process when the steel is up to it's critical temperature prior to quenching, like 2100 degrees for m390 IIRC from the spec sheets I have seen.

Re: Snapped M390 Artifex

Mon Feb 18, 2013 12:06 pm

Yeah, it didn't change colors or get to hot. My passes took about 3sec per side and if anything I spent less time at the heel due to the proximity of the handle.

Re: Snapped M390 Artifex

Mon Feb 18, 2013 12:07 pm

Yeah, that shouldn't have affected the temper then. The rust in the crack shows the crack has been there for a while.
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