One of my guilty pleasures is watching "Forged in Fire." While I wish they'd put a lot less energy into attempting to create drama & tension and more into teaching the craft, there's enough in there to keep it at least marginally interesting.
One thing, though - I have repeatedly seen them quenching W-1 steel in oil. While it gives that satisfying and dramatic plume of flame and smoke, I thought W-1 is supposed to be quenched in water.
So, what's the deal here? Obviously, I have no skills in this area, but why would they do that?
slow quench . Which leads me to a question for any knife makers hangin'
out here . What kind of oil do you use ? I have a blade I forged that
needs heat treat (4140 type AFAICT) . I also have a whole shitload of
that same steel , so figuring out the proper heat treat will make a
difference in what i use it for . BTW , one of the FIF guys lives here ,
I've met Shawn Ellis and he's a pretty nice guy . SHAAZZZAAAAMMMMM!
One of the FIF guys lives here as well. He will remain nameless. He
contacted me about cutting profile blanks for knives out of stock, but
didn't seem to want to pay anything for it. Maybe I just misunderstood.
I made some replacement pipe cutter wheels from EN24T (4340 a low alloy
steel common in the UK), similar to 4140, and treated them like carbon
steel for quench and temper and when tested they crumbled as still
brittle. When I looked up the heat treatment for the alloy online, took
awhile, the quench may have been similar but the tempering for what I
was aiming at was up around 500C + and held for a longer period than
basic carbon steel so the temper temperature for the alloy was some 300C
- 350C higher than a basic carbon steel for the same hardness. Does make
me wonder when I watch FIF how they manage with unknown steels as the
heat treatment requirements can vary widely depending on alloy composition.
So does that pretty much call the whole show "just a show?" Their "tests" s
ubject the knives to some pretty harsh stuff - the Marines' KA-BAR replicas
chopping away at a rifle barrel and still holding their edge (though one g
ot a pretty good chunk busted out) - how could that and the other nasties t
hey do work if the heat treat is all wrong?
Again, I wish they'd spend more time on the craft and less on the show. Som
e of these guys are really talented, but it gets lost in the high drama the
y are attempting to create.
Likewise. I don't disagree that the tests are tough and real and the
process of tempering is frequently mentioned on the show but I don't
recall ever seeing a blade bulk tempered after quenching to bring the
hardness of the whole blade down, especially the edge. All I can
remember is them showing localised tempering of the back of the blade
and tang to increase toughness of those areas. Regarding material maybe
they just make sure the source materials are going to be simple carbon
steels and so behave as expected. IIRC 5160 is used a number of times
and having just looked up the tempering data for that it was given as
being between 426C(800F) and 704C(1300F) so somewhat higher than a
simple carbon steel.
You may have gotten enough of the picture from the other posts, and I
don't want to add confusion, but maybe a different description will
flesh it out.
"Water hardening" and "oil hardening" are just names that refer to the
necessary quench rates of different steels. It doesn't mean that you
have to quench it in water or oil. In fact, you may need to quench
thick oil-hardening in water, and thin water-hardening in oil.
The terms refer to the *quench rate* required for a *typical
thickness* of each steel, to convert it to the hard, martensitic
phase. A thin piece of W-1, like many knife blades, will be quenched
with adequate speed in oil. Preferably, you don't quench it any faster
than necessary, but you have to quench it quickly enough to get a
complete, or near-complete, conversion of the austenetic phase to a
martensitic (hard) phase. Plain carbon steels (W-1) require a faster
rate than oil-hardening alloys, which, in turn, require a faster rate
than A-1 air-hardening. The higher-alloy, slower-quenching steels
don't get any harder. W-1 will get as hard as the others. But it may
not harden as deep, if it's a thick piece.
You want a complete conversion with *maximum safety*. That means you
want to minimize the chance of cracking. The thicker steel is, the
more likely it is to crack from an excessive quench rate, both from
differential thermal shrinkage and from something I'll explain below.
Once you've reached the necessary quench rate, quenching it faster
won't make it any harder -- or not enough harder to be worth the risk.
The hardness of the finished piece depends on the percentage of the
steel that was converted to maretnsite. We'll put tempering aside for
now -- that confuses the picture a bit. But be aware that the
different steel phases (ferrite, austenite, martensite and the
mixtures, like pearlite) have different densities. When you convert
ferrite to austenite by heating it above its critical temperature, it
expands from the heat. When you quench it, it shrinks. But, say,
you've quenched a thick piece of W-1 in water, and the inner part of
the piece doesn't quench quickly enough to get a high conversion to
martensite. That's common. So now you have a martensitic outer, say
1/4 inch, and then the slower conversion of the inside returns it to
ferrite. Ferrite is *denser than martensite*. That's the other thing
that leads to cracking. So you have high stress where the outer,
martensitic layer transitions to the inner ferritic layer. It will
shear at the transition point, and it can be enough shear stress to
crack the martensitic layer right off of the piece.
Hmm. I'm getting a little windy. Steel is very complicated. I
studied it for years when I was materials editor at _American
Machinist_. It kept me busy. But you don't need all of that detail to
get the baisic idea. If you need more explanation, let me know.
I've ever watched and only because he's a friend of my neighbor the
blacksmith . I do know that Shawn's knives are selling for some serious
money . Pretty nice stuff , definitely worth what he's charging .
Keep in mind that recommended tempering temperatures often are based
on *expected uses* of the steel. If it's expected to be used for a
straight razor, the tempering temperature will be low. If 4140, it's
expected to be used in a structural application and it will need to be
less brittle. If it's 5160, it's expected that it will be used for a
spring, and it will need to be tough and even somewhat ductile at high
And so on. d8-)
I forged and hardened a froe (shingle or kindling splitter) from 5160
and was advised to temper it at around 180-200C for half an hour or
so, which gave a faint yellow color. A file barely scratches it.
ey'd put a lot less energy into attempting to create drama & tension and mo
re into teaching the craft, there's enough in there to keep it at least mar
il. While it gives that satisfying and dramatic plume of flame and smoke, I
thought W-1 is supposed to be quenched in water.
why would they do that?
"Steel is very complicated." An understatement of majestic proportions. It
is just these complications that made me question the whole FIF thing in th
e first place.
They never show any sort of tempering, just heat the piss out of it (for wh
atever value of "it" they have chosen that day) and plunge it into oil and
hope for the best. Then they slash a pig carcass, pound the blade through s
teel plate, chop up bricks, bend the blade 40 degrees, and rarely have any
of the blades sustain damage or fail the tests. Methinks there's a whole lo
t they don't show.
Thanks to all you guys for your input. Especially Ed for an excellent level
of detail. I will continue to watch FIF, but with a more relaxed hope of l
The 5160 froe is intended to be driven by a wooden club (beetle) and
thus could be tempered hard and possibly brittle. The instructor
suggested a temperature that a toaster oven can reach, though I
completed an old heat treating oven project to do it.
Actually since I posted last I do remember a recent FIF episode on UK
Freeview TV where towards the end of the show one of the guys making a
sword at his home forge was shown quenching it and then placing it in a
heat treatment oven for tempering but it seems very unusual to show that
tempering step on the show.
Do you know a good non-destructive test for proper temper?
My bouncing-ball scleroscope reads low on thin or light stock like
lathe bits, even when clamped in a heavy vise. It did read a heavy
hammer head known to be RC58 correctly.
If they start quenching in the blood of a virgin goat, you can safely
discount their technical accuracy. d8-)
BTW, somebody asked about quenching oil. That one is easy -- buy
quenching oil. A bucket of it will last a lifetime. Quench in used
motor oil only if you wnat a surface mottled with hard and soft spots.
There is quite a bit of variation in tempering recommendations, and in
practice. It's a case of "use what works." But steel is versatile
enough, and forgiving enough, that the "experts" often don't know what
The major tool-steel companies do extensive testing and provide a
wealth of information. But when you're using some hunk you got off of
a scrap heap, good luck, and may the angels be with you. d8-)
No I don't. The question is, what is "proper" temper? For what
application? The big tradeoffs are hardness, impact strengh (notched
or unnotched?), elongation (ductility, more or less), and local
hardness vs. toughness (a softer temper for the back of a knife blade
or a saw blade). Then you get into fatigue strength, "timbre" (don't
ask), thermal tolerance (high-speed steel) and more. I don't know of a
multi-purpose non-destructive test. There may be one; I just don't
know what it would be.
Those tests will tell you hardness, but with a grain of salt.
Thickness of the piece; differential hardening *within* the piece;
backing; etc. all require some interpretation.
I'm no expert on testing methods, but I enjoyed working for Mitutoyo
years ago and learning from the experts there. My takeaway is that you
have to know exactly *why* you're testing for some property, or
combination of properties, because you can only test for one or two
things at a time.
To me, it's part of what makes metalworking so interesting. And
My go-to for carbon and alloy steels. This appears to be the same
edition as my print copy issued by Bethlehem Steel ca. 1980. Some of
the older editions are also available as scans online. The only real
difference I've noticed is some editions include Rockwell in addition
to Brinell hardnesses in the tempering graphs, which I sometimes find
I wouldn't expect 4140 to make a very good knife, not compared to tool
given several rounds varying from 2 1/4 to 3 3/8 diameter and all around
6 feet long . Any knives I make will be just for me , practice ,
whatever . Should I ever decide to make knives for sale , they will be
made from new stock purchased for the purpose . Until then , I still
have a couple hundred pounds of this stuff left to experiment with . I
will say that it does forge nicely - once I got the heat up where it
needed to be . The one piece I'm having problems with is big enough to
really need a power hammer , my puny little arm isn't makin' much
headway with a 4 pound hammer . When that piece is finally beat into
shape it will be machined into the body of a screwless vise for my mill
. In fact , the vise project is what induced me to buy an anvil and
build a forge .