Stainless San mai problems

D

Daffy69

Joined
May 27, 2014
Messages
7
I made a billet from 304 and 80crv2 by tig welding the pieces together and forging at around 2200-2300 degrees. The billet started out as 1/2 inch and i forged it down to just under a 1/4 cut a section off ground a small test blade and heated it to 1525degrees and quenched in aprox 100 degree canola oil and it cracked down the middle. What can i do to stop the steel from shearing? I have spent a while going through posts and haven't found the info I was looking for, do i need to clay the spine and ricasso area? I would try with some 4xx but cant find a source that wont break the bank and I am not sure the problem wouldn't still exist.
 
Last edited:
When you say "cracked down the middle" - do you mean delaminated? OR the billet cracked in half with crack thru both carbon and SS?

Either way, you need steels with similar rates of contraction/expansion when heating/quenching..... Any idea what the specs are on your two chosen steels?
 
Add nickel shim between layers, anneal and then cold forge, harden from the lower end of the HT range, and pull out of quench at ~ 400'f.

Hoss
 
so the nickel acts like a buffer? so keep the temps as low as possible and try to minimize stresses then. should I maybe lower the oil temp for slower cooling?
 
Daffy69 said:
so the nickel acts like a buffer? so keep the temps as low as possible and try to minimize stresses then. should I maybe lower the oil temp for slower cooling?
Click to expand...

don't forget the cold forging. and afterwards the blade then needs to go above critical but only long enough for new grain to nuecleate in the dislocations from the cold forging.
 
Another option should be to use a shallow hardening carbon steel core.
The edge will harden but if you do things right the inner core should have enough pearlite in the mix not to undergo the huge martensite expansion. Claying the sides and ricasso in this case should help.
The 300 ss serie won't expand in the quench and will try to pull the sides of the growing inner core. The nickel shims won't grow the same, i'm not sure why they can be of help since they don't differ much from the 300ss during ht.
I don't know how the nickel shims would behave, but the interrupted quench surely will help giving toughness in the very critical moment.
 
...i can't see why cold forging would help with the op problem other than creating the risk of unwanted brittleness from microfractures in the steel and carbide segregation.
The steel should be forged in its austenite state.
 
For someone who came into blades from blacksmithing, cold forging seems like heresy!
Would Bill or Devin be willing to briefly describe the process?

I'm guessing you hot weld (forge) the billet and draw it out some, anneal and power hammer it cold? How much is enough?
 
Cold forging stretches the out side layers and allows the core to catch up when it grows in quenching. Of course you can over do the cold forging if you're not careful.

Hoss
 
If you look cold forging is a common practice in Japanese style san mai bladesmithing.
 
Thanks for all the suggestions I made up another billet yesterday from 304 and w2 will cut coupons and try the suggestions,I don't have any nickel so didn't use any. I have discovered that the 304 is 3x harder to forge than carbon steel and has a much higher working temp, where 4xx is much closer to carbon steel for forging. I really need to make myself a power hammer.
 
The hall petch (read: grain refining) is pursued by heat and cooling alone, without ruining the steel, in an homogeneus fashion, that i prefer over banging cold steel, especially if i am experiencing inner layer splitting in half :)
stretching the shell as a pre deformation like Devin suggest is interesting, i bet it does require the proper experience.
The japanese kitchen san or ni mai blades have mild shells and the cold forging is performed after ht for straightening....it is a sort of peening that has the same effect used to curve the plates of the medieval armors over a flat anvil.
 
Just avoid the austenite/martensite conversion in the ricasso area, where the stainless is still mostly at full thickness.
The stresses result in the problem you have.
And remember that strength in steel comes from grain control.
Reducing heat thermal cycles post-forging activities are critical.
I have ripped a few.



 
Mr Anderson seeing your work was the inspiration to try the stainless san mai. Though I don't think I will ever make a knife to the high standards you have for your fit and finish but gives me something to shoot for. I do know I am going to need a power hammer if I keep making stainless san mai, hard on the arm reducing those billets.
 
stezann said:
The hall petch (read: grain refining) is pursued by heat and cooling alone, without ruining the steel, in an homogeneus fashion, that i prefer over banging cold steel, especially if i am experiencing inner layer splitting in half :)
stretching the shell as a pre deformation like Devin suggest is interesting, i bet it does require the proper experience.
The japanese kitchen san or ni mai blades have mild shells and the cold forging is performed after ht for straightening....it is a sort of peening that has the same effect used to curve the plates of the medieval armors over a flat anvil.
Click to expand...

Hall-Petch has to do with strengthening steel through deformation. It is also a proven method to grain refinement through dislocation and nucleation.

there are many videos on you tube showing Japanese smiths cold forging san mai and kasumi (2 layer) knives like this one

the cold forging here starts a 6:59
[video=youtube;qABAEcmPvyg]https://www.youtube.com/watch?v=qABAEcmPvyg[/video]
 
You must log in or register to reply here.
Back
Top