Thread: Thiers Issard grades

Originally Posted by superfly

I think the heating is done IN the lead...

Nenad

That's too low a temperature. Notice they heat it to 1300. Molton lead is only 850. I think they leave it at that lower temperature to change state slowly and harden.

Joe,
Although it melts at 850 deg. it can still be heated much higher than that. We use aluminum here for castings and although it melts at 1200 deg or so it can easily go far beyond that.

Tony

I love it when these threads take a turn into the realm of hard science of chemistry and physics. Whod'a thunk shaving could be so technical.

X

Originally Posted by Tony Miller

Joe,
Although it melts at 850 deg. it can still be heated much higher than that. We use aluminum here for castings and although it melts at 1200 deg or so it can easily go far beyond that.

Tony

My point was that it's not heating the steel. It's hardening it. In the video you can see an earlier heating step where the steel gets real hot. Then it goes into the lead.

So how exactly does this process work? Does it realign the structure of the metal?

Originally Posted by Joe Lerch

My point was that it's not heating the steel. It's hardening it. In the video you can see an earlier heating step where the steel gets real hot. Then it goes into the lead.

The lead is used to heat the steel, and as Randy said, it's purpose is to keep as much carbon as possible in it. In the video, the early stages of heating and making blade blanks from the blades is called hot forging, which is, in contrast to stamping, superior method of making blade blanks, because the steel structure gets altered in a way that improves edge holding and longevity.

After the blanks are formed, the blades are dipped in graphite oil, to prevent lead to stick to the blades, as mentioned before, and after that the blades are quenched in oil.

The video is showing cool blades dipped in graphite, and put in molten lead bath, which, as Tony mentioned, reach higher temperatures than 850C, which is the temperature the speaker mentioned as the "starting temperature"...

Nenad

But what exactly does the tempering process do to the steel? How does it make it harder?

Originally Posted by FiReSTaRT

But what exactly does the tempering process do to the steel? How does it make it harder?

http://www.anvilfire.com/FAQs/heat_faq_index.htm

Thanks. I'm looking into it.

Originally Posted by Joe Lerch

My point was that it's not heating the steel. It's hardening it. In the video you can see an earlier heating step where the steel gets real hot. Then it goes into the lead.

Joe,
In normal forging of blades the steel will be heated many times as it is shaped but it may not be at the initial solution temperature needed to start the real tempering process. Those first steps in the video look to me like othing more than the shaping and forging steps. I think the blade is then brought to the initial heat treating temperature in the lead bath as it provides a more stable atmosphere over heating in air. After the lead step the blade is likely quenched where it will have it's ultimate hardness. The temper is then drawn by heating to a lower temperature to add a little ductility to the steel which would otherwise be brittle.

I am sure Joe or Bill or Randy could chome in here with better details but this is it in a nutshell. Oddly though aluminum reacts exactly the opposite of steel. The freshly cast aluminum we make is soft. We solution heat treat it at 1000 deg for 12 hours, quench it in 180 deg water and it is dead soft and can be straightened (steel would now be at it's hardest). We then "artificially age" it in a 335 deg heated air oven for 3 hours after which it is harder and stronger, reaching it ultimate properties (on steel this would draw the temper and make it softer).

Tony