Thread: Now here is something you don't see every day :)

I was working on a suminagashi blade that hadn't hardened properly along the edge. The reason was I had ground it too thin, and even with the oil tank right next to the forge, I could not get the blade in the tank quickly enough before the air cooled the edge to below critical.

So I thought I would be smart and instead of taking out the blade, I'd take the iron pipe itself out of the fire, and upend it above the quench tank. That way the blade would hit the oil instantly. However, this is the result



I spent yesterday trying to think what had happened, talked it over with a friend of mine who is a master bladesmith, and we came to the following conclusion: The blade fell out of the pipe, immediately hardening the edge. The blade hit the bottom of the tank a split second later, where it made an unholy noise, like water falling into a potato chip fryer. What my friend suggested was that there is likely a thin film of icecold condensation water at the bottom of my quench tank.

When the blade hit the bottom, the side that hit the bottom got a thermal shock that was so bad that it literally tore one side of the razor apart from the other side. The crack goes right through the middle of the core steel because it has less 'give' in it than the mild steel sides. The reason it doesn't fall apart is that thehollow ground part is whole, as well as the tail.

Apart from this minor detail the blade came out pretty nicely and I am going to finish it and make scales. Probably use it as a personal blade for a while. Sure it is not perfect but there is no reason to just throw it away either. If anything, it should shave me just fine

Anyway, this illustrates perfectly the raw violence of a blade quench. Any force strong enough to rip an entire blade in half, lengthwise has to be respected.

Ouch!!!!! That sucks!!!!!

You have me curious, how deep is your oil in your quench tank? I am just amazed that the temps stayed high enough to cause this reaction. May end up being one of your best personal blades with a "2-n-1" quench!

I am interested to hear if the spine is of equal hardness when you hone it up.

It won't be the same hardness in any case, since suminagashi steel has sides of mild steel with thin contrast layers.

Now, let's say that the razor started to drop from 50 cm above the surface.
this means it was going about 3 m per second when it hit the surface. The oil was preheated, so let's assume that the resistance was just enough to stop it from accelerating further. With a 40 cm tank depth, that is less than 150 ms to the bottom of the tank. Enough for an edge to harden, but the spine would still be glowing red in the middle.

That is really interesting. I hope you still plan to post pics when it is done.

Originally Posted by Bruno

I could not get the blade in the tank quickly enough before the air cooled the edge to below critical
.

I grind pretty thin before heat treating and had this same issue with the edge cooling as soon as it was removed from the heat. Then it was pointed out to me that that cooling was all part of the quench and as long as I was staying left of the nose on the TTT diagram, there should be no problems.
http://straightrazorpalace.com/attac...40927small.jpg

Originally Posted by bluesman7

I grind pretty thin before heat treating and had this same issue with the edge cooling as soon as it was removed from the heat. Then it was pointed out to me that that cooling was all part of the quench and as long as I was staying left of the nose on the TTT diagram, there should be no problems.
http://straightrazorpalace.com/attac...40927small.jpg

The edge was thinner than that
For steel like this, oil quenching is already borderline not fast enough, so if the edge gets dark before you hit the quench, there is no hope of getting a hardened edge.

Here is the blade as it turned out.
http://straightrazorpalace.com/custo...hite-blue.html

All in all I am pretty happy with how it turned out, ignoring for the moment the minor fact that the blade is essentially unsellable

Originally Posted by Bruno

The edge was thinner than that
For steel like this, oil quenching is already borderline not fast enough.

Ah, right. I'm used to thinking about 01 times which are quite slow.

Я ещё такого не видел. Видел трещины разные, но вдоль... How many degrees was liquid? Thanks for the info, I'll know for the future.