Still air

[Natlek]

Often on many sites where was data about heat treating steel i read this ....cool in still air.
I understand definition for still air so my question is do we need some box which we will use it for this purpose .When i was doing grain refinement on this san mai blank I use channel in that brick to hold blank .Tip was inside but that chamber is short so butt of blank was out when cooling and it cool down much faster then part inside bricks .When I try to drill hole for pins , first two hole was not problem to drill but that last one on butt side HSS drill bits can not drill thru blank .Sims that somehow steel was hardened in that place .It start to drill easy try stainless till it come to core .I think that core was soft inside and that there was hardened stainless just where it was fused with carbon steel ?? I have very fine silica sand but that would be annealing steel ? So what do you think about this ? It will be easy to make some box ...........?

 

[Larrin]

Still air means you don't have a fan. So if you want still air just don't use a fan.

 

[fishface5]

maybe to prevent a breeze, rest it in a big bucket? but putting it part in and part out of a box that contains the radiated heat is the problem here, not the breeze per se

 

[Natlek]

Still air means you don't have a fan. So if you want still air just don't use a fan.

Thanks !
So air movement in my shop is not problem ? My shop/solid build/ is pretty big ..Lenght is 9m , wide 5m and 3.2m height .The front side is whole door/not good sealed / and i have other small door on one of side wall so there is plenty of airflow....like when you open a window and a door in room ,i don't remember at the moment the right word for that airflow .

 

[Natlek]

maybe to prevent a breeze, rest it in a big bucket? but putting it part in and part out of a box that contains the radiated heat is the problem here, not the breeze per se

Well , that make more sense.............What I wonder now is why it hardened ,there was visible /extremly shallow crack/ on butt , too ? So seems carbon core was hardened ....

 

[Natlek]

Guys , I understand that the outside will be the first to start cooling off in any case .... but more even cooling is good thing , I think ? So maybe that box make sense in my case ?

 

[Stacy E. Apelt - Bladesmith]

Air quenching methods are stated in:
"Still Air" - non-moving room air. No fan, air blast, etc. Normal room convection is fine.
"Forced Air" - Air form a strong fan or air compressor. Usually stated in a Bar pressure, eg. 2 Bar (30 PSI) or 4 Bar (60 PSI ).

 

[DAMNENG]

---- .It start to drill easy try stainless till it come to core .I think that core was soft inside and that there was hardened stainless just where it was fused with carbon steel ??

Natiek
After looking at your post I have the feeling this is a san mai blade with two stainless layers and a carbon steel core. If this is the case, which stainless steel did you use? If it was a martensitic stainless it is probably an air hardening steel.
Just a thought
Jim A.

 

[Natlek]

---- .It start to drill easy try stainless till it come to core .I think that core was soft inside and that there was hardened stainless just where it was fused with carbon steel ??

Natiek
After looking at your post I have the feeling this is a san mai blade with two stainless layers and a carbon steel core. If this is the case, which stainless steel did you use? If it was a martensitic stainless it is probably an air hardening steel.
Just a thought
Jim A.

It was 416 with 1.2519 as core ......

 

[tkroenlein]

Maybe the in house metallurgist can give a better answer, but it is my understanding that carbides can cause the hard spots without any hardening from martensite.

 

[DeadboxHero]

I think your drill bit is just dull

I like the cobalt drill bits best. The HSS black oxide and TiN coated ones go dull faster and the carbide bits break easy and cost a lot.

I like the steel choice here Natty.

Often on many sites where was data about heat treating steel i read this ....cool in still air.
I understand definition for still air so my question is do we need some box which we will use it for this purpose .When i was doing grain refinement on this san mai blank I use channel in that brick to hold blank .Tip was inside but that chamber is short so butt of blank was out when cooling and it cool down much faster then part inside bricks .When I try to drill hole for pins , first two hole was not problem to drill but that last one on butt side HSS drill bits can not drill thru blank .Sims that somehow steel was hardened in that place .It start to drill easy try stainless till it come to core .I think that core was soft inside and that there was hardened stainless just where it was fused with carbon steel ?? I have very fine silica sand but that would be annealing steel ? So what do you think about this ? It will be easy to make some box ...........?

 

[DeadboxHero]

Maybe the in house metallurgist can give a better answer, but it is my understanding that carbides can cause the hard spots without any hardening from martensite.

Nah, there are more carbides in the steel in annealed condition but that doesn't make it harder to drill/grind because the matrix that supports them is soft.

Also this is 416 and 1.2619, so not a carbide monster by any means.

 

[DAMNENG]

Natlek
I'm inclined to agree with DBH on the dull drill bit. I'm not familiar with tungststeels and don't know if they have a tendency to work harden easily. I do know that O1 will work harden when cutting or drilling to the point once you start cutting or drilling you want to finish before you let off the feed pressure. I would try a 3 or 4mm bit and see if I could drill through he unfinished hole. If this doesn't work, spot heat the unfinished hole with a torch until red and drill while hot. As a last resort use a TIG tip chucked up in a stick welder and push it through he hole or a cutting torch and blow it through. Cleanup with a carbide bit or counter sink.

Just out of curiosity, was the hole location at the same spot you grabbed the blade with the tongs when you removed it from the heat?
Jim A

 

[tkroenlein]

Nah, there are more carbides in the steel in annealed condition but that doesn't make it harder to drill/grind because the matrix that supports them is soft.

Also this is 416 and 1.2619, so not a carbide monster by any means.

Maybe. Forging can leave some pretty inconsistent steel behind, though, if it isn't corrected.

 

[Natlek]

I think your drill bit is just dull

I like the cobalt drill bits best. The HSS black oxide and TiN coated ones go dull faster and the carbide bits break easy and cost a lot.

I like the steel choice here Natty.

Well , that make ..............no sense Only best my friend ,only best HSS Co drill bits from Heller in my shop.Quite expensive but they worth every penny .

Seriously , I used sharp 3mm HSS cobalt drill bits , first two hole was drilled like in mild steel ..last one ................nada ?

 

[Natlek]

Natlek
I'm inclined to agree with DBH on the dull drill bit. I'm not familiar with tungststeels and don't know if they have a tendency to work harden easily. I do know that O1 will work harden when cutting or drilling to the point once you start cutting or drilling you want to finish before you let off the feed pressure. I would try a 3 or 4mm bit and see if I could drill through he unfinished hole. If this doesn't work, spot heat the unfinished hole with a torch until red and drill while hot. As a last resort use a TIG tip chucked up in a stick welder and push it through he hole or a cutting torch and blow it through. Cleanup with a carbide bit or counter sink.

Just out of curiosity, was the hole location at the same spot you grabbed the blade with the tongs when you removed it from the heat?
Jim A

I guess yes ? You think that that can be the reason of hardening ? Look , I try on several place to drill /close to butt/ same thing ,about an inch and a half from the end of the butt no problem......
PS . I drill that hole too , I used carbide drill bits . I want to know what happened . Last temperature was 800 Celsius ...If it is carbon migration in stainless and stainless harden on air ....Isn't 800 degree to low for stainless to get hard ?

 

[DAMNENG]

If you had a another piece of the same steel you could do a test. Heat it and grab it with the tongs in a location other than the end next to the oven door. Cool as before. Then try to drill through the tong grip area and the also the end next to the door and compare results.
If then door end won't drill, it might be the draft from opening the door that cools it enough to harden. If the grip area won't drill, this theory is starting to look plausable.
Things don't always go by the book LOL
Jim

 

[Natlek]

If you had a another piece of the same steel you could do a test. Heat it and grab it with the tongs in a location other than the end next to the oven door. Cool as before. Then try to drill through the tong grip area and the also the end next to the door and compare results.
If then door end won't drill, it might be the draft from opening the door that cools it enough to harden. If the grip area won't drill, this theory is starting to look plausable.
Things don't always go by the book LOL
Jim

I have , but they are to small for test like that .I will make another one this days ....What i test is toughness .... My opinion is that toughest steel in the world is san-mai without any doubt .I HT three small cut of pieces from this blank to see what my grain refinement done .It is almost impossible to break this thing ... You can bend it 180 degree if you want .And i don t understand why hard core don t crack ???? It take a lot of bending to finally break it ....crazy !