Enamel Kiln for hardening?

[Aled Dafis]

I think he means thickness.

The books I've read suggest that irons should be held at the hardening temp for a time equalling an hour per inch in thickness. So for a 6mm (1/4") thick iron it should be held at about 800C for 15 minutes.

Check out this book, it's quite detailed and some of the content goes above my head, but there's also a lot of good stuff in there.

http://www.amazon.co.uk/Hardening-T...=sr_1_1?ie=UTF8&s=books&qid=1267714265&sr=8-1

Cheers

Aled

 

[jimi43]

Righto Aled...excellent.

So say I have a 6" length...two inches wide and 6mm thick I still only heat it for 15 mins at 800C?

What about this pre-heat at 300C idea? Did you see that anywhere?

I wonder...should I put it in cold once the kiln has reached 800C or should I just put it in there from cold and when it reaches 800C leave it for 15 mins?

I guess it doesn't matter really do you think?

Jim

 

[Harbo]

Heating - the slower the better.

Rod

 

[jimi43]

Heating - the slower the better.

Rod

Do you mean start at room temperature with the blade cold in the kiln and bring them both up to 800C and leave for 15 mins Rod...do I read you correctly?

Jim

 

[Harbo]

Jim - yes

Rod

 

[jimi43]

Jim - yes

Rod

Magic! Just what I wanted to hear. It's bad enough having to try to hoik it out once when it is 800C and drop it into cold oil but putting it in is twice the risk...that thing is bleedin hot when you open the door!

I will get some forge tongs for that job...right tool...right job....always best maxim...

Jim

 

[Harbo]

Jim -the book Aled recommended is really worth it - about £4 from The Book Depository? (only £6.95 full price!)

Rod

 

[Racers]

Hi, Jim

You need to stir it around in the warmed oil to cool it don't just drop it in, do the blade end don't worry about the other end to much.
I do plane blades in a barbeque so I stick cold blades in the a hot place, I would be tempted to stick the blade in a hot furnace to minimise the time, you will be losing carbon from the surface of the metal when it gets up to temp, you don't want to have to grind lots of metal back to reach the good stuff.

Pete

 

[jimi43]

Jim -the book Aled recommended is really worth it - about £4 from The Book Depository? (only £6.95 full price!)

Rod

I've ordered it today...thanks for the tip guys.

So...to recap...I put the warm steel in the kiln preheated to 800C for 15 minutes (ish) then I take out and wave about in warm engine/vegetable oil (the latter I can get by the ton)...for a bit then I put in a preheated oven after lunch at 250C and let iron and oven cool together.

Is that about right?

Jim

 

[Chris Knight]

Trad advice is to dip it into the oil vertically. If done at an angle, differential cooling can cause a bend.

 

[jimi43]

Trad advice is to dip it into the oil vertically. If done at an angle, differential cooling can cause a bend.

Cheers Chris....great tips coming here...if these blades when made were to be valued on input from here alone they would be a couple of hundred quid each!!

Excellent tips!

Jim

 

[frugal]

Trad advice is to dip it into the oil vertically. If done at an angle, differential cooling can cause a bend.

Which is how they get the curve on japanses blades I am led to believe, they start with a straight piece of metal and quench same edge first every time.

 

[Harbo]

The book recommends you heat it up slowly - see page 28 when you get it.
You are rearranging the"little atoms" and have to give them time for the process. "Better to be too slow than too fast".

frugal - Japanese sword are forged curved. The blade is covered with varying thickness's of clay when hardening and quenched in water.
This results in varying hardness across the blades cross-section with the cutting edge being the hardest. On sharpening this shows as a "cloud effect " which is much desired.

Rod

 

[wizer]

Jim, are you bringing the kiln tomorrow? Would love to see it, along with your recent tools.

 

[jimi43]

Jim, are you bringing the kiln tomorrow? Would love to see it, along with your recent tools.

Sure thing mate...no problems.

Jim

 

[newt]

Jim - yes

Rod

Magic! Just what I wanted to hear. It's bad enough having to try to hoik it out once when it is 800C and drop it into cold oil but putting it in is twice the risk...that thing is bleedin hot when you open the door!

I will get some forge tongs for that job...right tool...right job....always best maxim...

Jim

Jim so glad you are not going to use your fingers. Jim forgot to mention make sure you plunge the blade fully covered into the oil, as partial submersion can cause the oil to ignite, DAMHIKT.

 

[jimi43]

Well...a couple of updates...

Firstly the book arrived...Hardening, Tempering and Heat Treatment by Tubal Cain...and I see what you mean about hard going.

But it is a very well written book and if you read the graph bits over a couple of times they make sense. I am really enjoying it.

Then the 01 steel arrived...500mmx50mmx3mm...nice pretty stuff!

I cut a slice out for the Galoot iron and now am approaching the hardening part of the project.

Reading a couple of previous posts on home hardening and have a couple of questions...some arising from the book.

Firstly...I am pretty sure I should grind the bevel first...the 01 now being pretty ductile and workable. My worry is that the bevel is a varying thickness (obviously) from sharp point to full thickness of 3mm. Will cutting the bevel pre-hardening not affect the quality of hardening/quenching/tempering...I have a feeling that it might?

Secondly...the hardening seems easy with the kiln...and it does recommend raising the temperature WITH the heating of the muffle (inside of the kiln) up to and beyond the "arrest point" where one can detect an apparent slowing down of colour change and then a sudden change as the arrest point is passed. I will then keep the steel at 800C or thereabouts (above the arrest point) for about 15-20mins and then quench.

Now...the quenching oil. Well it says definitely DO NOT use old engine oil as this is the wrong type of oil. Indeed it actually says in the book that this could prove quite dangerous, and I quote:

...but NOT motor oil which is blended for quite different service and characteristics and most emphatically NOT "used" motor oil. This is downright dangerous; it can contain up to 25% of the heavier fractions of petrol and can flash off into a furious fire if used for quenching hot metal.

Now I seem to remember elsewhere in the forum that I read someone was using motor oil...so I am now confused. It actually suggests "Quendila A22 or Quendila 19" quenching oil or "at a pinch", spindle oil of SAE10 or 20 would suffice.

I would like opinions on this point, particularly in light of the above safety warning!

So I ask for suggestions before I proceed further.

Cheers guys and gals

Jim

 

[9fingers]

I should start by saying I've not done any hardening of critical components!

1) When ever I make small tool items in my metalwork workshop that I will want to keep, I always blacken them. This is because they stand out against all metal swarf in the tray and so don't get thrown out in a clean up.
I do this by heating steel items to red heat and plunging into old engine oil.
Yes you get some fumes, and the odd puff of white smoke but I never in 30 odd years had anything ignite however briefly.

Provided you use a reasonable volume of oil - say 1/2 pint or more in a metal container (old saucepan?) no more than 1/2 full and have good ventilation then I consider it safe enough in the home workshop.

2) I can't see the harm in removing most of the metal for the bevel in the annealed state. I would expect to complete the bevel by a final grind post hardening plus honing using your favourite spells.

3) Following Tubal Cain's methods should see you right. There is little that man did not know about metalworking.

Good luck,

Bob

 

[Racers]

Hi,

I always use old engine oil without any problems, even did 6 blades in one go. I did get a little fire towards the end when the oil got hot :shock:

Grind the bevel first as it will be much harder to do after.

Here is old engine oil at Jims bash.

Pete

 

[Harbo]

As Pete said, best to get most of the shaping done beforehand - though my Norton 3X wheel makes short work of any grinding!

Rod