As forged 4340 .... EN24

[youngdylan]

Most of my tooling is made from 4340 (EN24) with the odd bit off H13. Heat treating is a black art to me and my usual way is forge, cool slowly in a swithed off gas forge (or air) heat to slightly above magnetic, quench in oil, temper at purple. Works well for my purposes and is just about grindable, machinable with carbide tooling etc

What I have noticed is that the "as forged" often seem seems harder than my "heat treated stuff" . It wont cut with a bimetal saw blade and can be a pig to grind. Kinda assuming that with small pieces it air hardens because the rate of cooling is quick enough.

What I'd like to know is how "usable" it "as forged", if not tempered is it a bit brittle, should I just temper it or go through the full heat treating hoo haa. It would be real handy to just "forge and play" cos the heat treating can often disrupt the flow, especially when being experimental.

Photo show the scale of things I'm talking about, they're tools for the treadle hammer forged from 1". ... I'm talking stuff forged from say 1" up to 3" round, hammers punches etc not industrial sized behemouths

[Fe-Wood]

I'm going to take a stab at this one more to see if my understanding is correct....

Heat treat is important for 2 reasons;
Taking the steel to non magnetic or critical heat ( not always the same? ) helps relieve the stress caused from forging-Normalising. This can be done with the heat from forging as you suggest, allowing it to cool slowly in the shut off forge or Vermiculite, etc.

The taking the steel to critical again and quenching is making the steel as hard as it can be, or close to it. Taking it back to Purple is softening it a bit but not as much as taking it to straw?

My assumption is that you are using these tools in a press- I would want the end that goes into the press to be softer than the ram of the press so the wear would be in the tooling and not the machine.

I may be wrong but it seems to me that you are hardening your tools to much. If and when they fail, they will shatter sending sharp bits flying.

[bigfootnampa]

Straw temper is much harder than purple... so these should be reasonably suited to their tasks. Purple tends to be a bit harder than I usually temper my hammers (light blue). I've not much experience with 4340 but regularly use 4140 and find it usually works well as forged. As regards tooling for power hammering though, I would tend to want it more carefully heat treated. I have found that "as forged" tools will sometimes have slightly uneven hardness which also means slightly unpredictable hardness and both these things seem somewhat dangerous in tooling which sees the extreme stresses of power hammer usage. I wouldn't be afraid of it for hand tooling but for power hammer use I would take the time to be more careful and safer. Just my personal judgement.

[bigfootnampa]

There ARE several types of shortcuts for heat treating though. One that I have personally liked and had success with is to heat to past critical and oil quench and then to flame off the oil in the forge. I will redip in the quenching oil and flame off several times (about 5x) and after a final quench I air cool. This has the advantage of being very fast and allows the tempering to follow the quenching almost immediately. I do NOT think this method is as accurate or reliable as oven or kiln tempering but it is very quick and helps to prevent cracking and warpage (because the temper takes place before the metal cools from the quenching) and it has worked quite acceptably for me.

[John B]

EN24 Heat treating details from http://www.westyorkssteel.com/en24.html

Hardening:
Heat uniformly to 823/850°C until heated through. Quench in oil.


Tempering:
Heat uniformly and thoroughly at the selected tempering temperature, up to 660°C and hold at heat for two hours per inch of
total thickness. Tempering between 250-375°C in not recommended as this can seriously reduce the steels impact value.

Stress Relieving:
Heat slowly to 650-670°C, soak well before cooling the EN24 tool in a furnace or in air.

[youngdylan]

Fe, As bigfoot points out purple is softer than straw. I've made a whole heap of tooling over the years including power hammer dies and it's all stood pretty well so far, nothing shattered ...... yet! ...Kinda curious about how "as forged" stands up with none or little post forging heat treatment.

John, thanks for that. It's not a million miles away from what I do, as mentioned its the "as forged" condition I'm curious about. I don't want top spend a lot of time doing some fancy tooling and leave it as forged if it wont stand up. I kinda suspect it will take some abuse.

Bigfoot, good to know that you find "as forged" is usable. Things like power hammer dies I would go through the whole heat treating hoo haa (as best I can with a gas forge). but its the experimental or stuff that is only likely to be use a few times as part of a job I'd like to leave as forged. It does seem that 4340 can take a lot of abuse in a wide range of DIY heat treated conditions. Anyone else have any experiences/ observations?

[Fe-Wood]

Ok, I guess I need to pay more attention.... I knew I would learn something with this thread. Now that my LG hammer is up and running- I'm going to making lots of tooling. So far I've only used mild steel.

[Nakedanvil - Grant Sarver]

Well, i guess the longer you been around and the more injuries and near misses you've seen the more cautious you get. I also hate to see a bunch of work on a tool disappear in a few seconds. Personally, I think it's foolish to use un-heat treated tools, and often downright dangerous. There's all kinds of things you can "get away with", until you don't. We all smack mushroomed tools that we know we should dress, but we "get away with it"...........most of the time! And I got the scars to prove it! Well, I'll just say this; "most of the time" ain't good enough for me any more!

Kinda like predator and prey. Everything around you is predator and you are prey. In the battle of predator vs prey, prey have to win EVERY time, the predator only needs to win once!

[youngdylan]

Point noted and taken.

Guess I was more concerned that not treating the "as forged" could damage the forgings in use , guess I should be more concerned that the forging could damage me :)

[youngdylan]

EN24 Heat treating details from http://www.westyorks...l.com/en24.html

Tempering between 250-375°C in not recommended as this can seriously reduce the steels impact value.

I guess I should really be tempering above purple then, though from memory 375 C is above the colour range .... a bit difficult to do at this temp without a kiln, salt bath etc

As yet I haven't had any trouble with with doing it at purple, occassionally blue. One pair of power hammer dies in particular has stood up .... so far... to years of quite brutal treatment including a lot of cold work. That said, Grant's point about being the prey is making me think again.

[John B]

One of the main problems here is the perception of colour to temperature ratio, and oven tempering gives different colours for heats than heat and quench techniques, it can also depend on what charts you are looking at to use as a datum.

Tempering range seems to be generally in the region of 210 to 345 degrees Celsius so I would interpret the statement

Tempering between 250-375°C in not recommended as this can seriously reduce the steels impact value.

to mean that it is usable as forged.



Anything tempered below 254 Celsius is suitable for penknives (Not larger ones), scissors, lancets, hoes, cold chisels etc. so would not be applicable in this situation.

Personally I would use them as forged, ideal for under the power hammer or fly press where the tool is held secured in use and not impact struck,

If using it hand/tong held, then ensure the struck end is dressed regularly and don't allow cracking to develop.

After recently seeing someone ignore this, and a piece breaking off, entering the back of their hand and severing an artery, narrowly missing the nerve, which then required extensive surgery to remove the offending piece, it tends to focus the self preservation trait somewhat. Thank goodness for the NHS, it still cost him 3 weeks lost time minimum.

It may be time to consider investing in a pyrometer/thermometer thingy wotsit

[forgemaster]

4340 when heat treating is recomended by the book "tempering in the range between 200 degC to 450 degC should be avoided. Tempering in this range shows a decrease in its impact properties and increase in the brittleness of the steel as evidenced by the downward trend in IZOD values in this range.
What this means is it is not a good idea to temper 4340 between 200 to 450 degC if you want to use it as a tool subjected to impact or sudden stress. Using the colour method of heat treat will give you a temper range smack bang in the middle of these temperatures.

We have used 4340 in the normalised or as forged as forging tools but not as punches etc but as stamping tools under the hammer. It seems to hold up OK so long as you quench the tool after each time it is used or at least at the end of each heat, depending on how long the job stays in the tool and how hot the tool is getting.

We prefer to use EN36 for tooling under the hammer, from punches to stamping dies, to heat treat it we take it to orange, chuck it into the water, let it cool out get it out and weld the handle onto it and use it.
It costs about the same as 4340 but is easier to heat treat, and stands up to impact longer in my opinion so long as it is kept cool.

cheers
Phil

[JNewman]

4340 when heat treating is recomended by the book "tempering in the range between 200 degC to 450 degC should be avoided. Tempering in this range shows a decrease in its impact properties and increase in the brittleness of the steel as evidenced by the downward trend in IZOD values in this range.
What this means is it is not a good idea to temper 4340 between 200 to 450 degC if you want to use it as a tool subjected to impact or sudden stress.

What I find confusing about this is that range is the range that you use to achieve a good hardness for forging tools. The oil flashing temperature is in this range and getting dies in the high 40s to 50rc is in this range as well. According to the ASM heating to 450C will take 4340 to around 43rc http://www.asminternational.org/pdf/HTSRefCharts/OMM061908.pdf. This seems a LITTLE soft to me?

Unfortunately EN36 does not seem to be a common alloy here in North America. But I will ask next time I am calling EMJ I will be asking them about it.

[monstermetal]

I think we would consider EN36 to be 8620 which should be available the same place you would buy your 300M/4340/EN24

Not a common alloy but not unheard of... The Nimba anvils are made from 8640 which is a pretty close cousin I think

[JNewman]

I just looked up the metallurgy the EN36 has more chromium and 3 times the amount of Nickel. It actually seems very close to 4340 but with only 15 points of carbon rather than 40 and less moly. According to a chart I looked up it is equivalent to AISI 3310 which I have never seen around.

[youngdylan]

We have used 4340 in the normalised or as forged as forging tools but not as punches etc but as stamping tools under the hammer. It seems to hold up OK so long as you quench the tool after each time it is used or at least at the end of each heat, depending on how long the job stays in the tool and how hot the tool is getting.


Phil

Phil what do you guys refer to as stamping and what is punching?

I am right in taking what you and John B say as meaning it's generally okay under the hammer/press but not when struck with a hand hammer?

[youngdylan]

What this means is it is not a good idea to temper 4340 between 200 to 450 degC if you want to use it as a tool subjected to impact or sudden stress. Using the colour method of heat treat will give you a temper range smack bang in the middle of these temperatures.

Kinda wondering If I might have a few time bombs (Grant's predators) lurking around my workshop. Photo shows some hammer dies machine from a 4340 billet (supplied as "black" or annealed). Heat to orange red, quench in oil and from memory tempered at light blue ...... could this be a severe case of oops at sometime in the future. I must say in their defence they have stood up to a few years of abuse including a fair bit of cold work.

I've ended up using 4340 for most of my tooling cos I got a "lifetimes" (1) supply from an auction a few years back. To date is has proved pretty tough. Just about the only problem I've had is drilling some of the as forged stuff. Annealing seems the hard part.

Already started looking one ebay for a pottery kiln.


(1)said lifetimes supply seemed a mountain when I got it , few hundred kg, only thought I use a few bits of it, few years down the line and I'm starting to top it up

[youngdylan]

The oil flashing temperature is in this range and getting dies in the high 40s to 50rc is in this range as well. According to the ASM heating to 450C will take 4340 to around 43rc http://www.asmintern.../OMM061908.pdf. This seems a LITTLE soft to me?

Scuse my ignorance, whats oil flashing?

[Mainely,Bob]

Can we for clarity`s sake refer to "quenching" as being a part of a planned, deliberate heat treating process and keeping any tool cooled while working as "cooling" whether you are using water,grease,air or any other medium?
I,for one,would find it a whole lot easier to follow what exactly is happening here and in other threads and what the desired results would be if those two processes were more clearly defined and people who were trying to cool something while working would stop using the word quench in a non-heat treating context during a tooling/heat treating discussion.
Thanks in advance for your consideration.

Oil flashing to me means after you have quenched a tool in oil to the point where it is cool enough for the oil to remain on it`s surface you then return it to the heat till the residual oil is burnt off.
Any differing experiences?
Now that folks are using a wide variety of oils with sometimes big differences in flash points to quench tools I am seeing this used a lot less.If you know and understand the temperature your particular oil is burning off at then it still would be a viable indicator I would think,along the same lines as the "greasy stick" temp indications.

Most of the heat treating info I use comes from sites like Crucible and others.They give very detailed information as to things like times and temps.Tempil Sticks and paints are a more accurate method of keeping track of what`s happening during heating and after seeing Phil`s(Forgemaster) post about the damage done to him by an exploding punch I personally would like to see us slow down and take the time to make reasonably durable tools rather than taking shortcuts that may produce shrapnel instead(sometimes further down the road when we least expect it and have become complacent enough to trust it too much).
I enjoy reading posts like this but really fear that somebody I consider a friend,who works alone,could potentially get badly hurt and bleed out in his shoebox sized shop because he was in a hurry and used either less than optimum steel or hurried heat treating.

In short,I hope you and others play it safe and keep all your parts intact,Cap`n.

[JNewman]

I agree with Bobs point that we should use the term quenching as a heat treating term rather than to mean cooling especially when steel is not raised to the Curie point. Phil mentioned flashing the oil off as the way he quickly heat treated shop tools before he got a tempering oven. The way I do it is to quench the item in oil then heat it to the point where the quench oil flashes off when away from an ignition source. This often involves pulling the work out of the forge dripping some oil on the tool or dipping a corner, because on heavier stock the oil burns off in my gas forge long before the steel is hot. I often turn the forge off and let the residual heat in the forge do the heating so the outside doesn't get hot while the inside is still cold. After the oil flashes I let the work air cool so that it has some time at temperature. I tend to use this shortcut only for chunky stuff, not punches or cut off tools.

I just ordered the ASM heat treaters guide and a heat treating oven or salt pot is something I feel I should buy or build soon so that I can do things a lot more accurately.

[Nakedanvil - Grant Sarver]

In the area of advise I can only offer best practices. The things I "get away with" are not properly shared. Exactly what I do and how I do it can be subject to misinterpretations with disastrous results. One mans "as forged" is not the same as another's. Just as one mans "cherry red" is not the same as another's. I've worked out of temperature controlled furnaces and am a little better able to judge by eye. Even so, I needed frequent "calibration" from the furnace to stay in tune.

4340 is very tough and forgiving and seems to give acceptable results over a wide range of treatments (or mis-treatments!). You can't get creative on a musical instrument until you first learn the discipline of playing it. Do things "by the book" as close as you can until you have acquired the knowledge base to do thing differently. Doing thing by the seat of my pants I have on occasion gotten sterling result that I have been at a loss to reproduce. So if I can't reproduce the result, how in the world can you expect to?

Take all advise with a grain of salt and endeavor to understand "why" as much as "what". In the end only you are responsible for any consequences.

[bigfootnampa]

Okay, I think I'll take Grant's advice as it seems better than mine. This has been a good thread! Thanks Grant!

[youngdylan]

In short,I hope you and others play it safe and keep all your parts intact,Cap`n.

Thanks Bob!

How does skipping the oil quench and simply tempering to "a bit above" blue sound for those quick and experimental "as forged" tooling. Quick to do, maybe not optimally treated but hopefully safe to use???Though that said, some of those quickies end up being used for years.

On a related note I've been using used motor oil for a quench. This one habit I'm gonna loose cos those fume just simply smell TOXIC. I generally do it outside but the smell still seems to linger around the door for days afterwards. From my little knowlege, it seems (all) about the rate of cooling, viscosity etc. How would vegetable oil do? Maybe I could even collect the bacon fat from my grill and add some to the pot?

I just ordered the ASM heat treaters guide and a heat treating oven or salt pot is something I feel I should buy or build soon so that I can do things a lot more accurately.

Looking on ebay smallish (5-10KW) pottery kilns seem to go for a few hundred quid or less. I kinda assume these will do as heat treating oven ? Is there any about a heat treating kiln that makes it different than a potters kiln? Maybe with a more accurate (programable?) temperature controller.

Take all advise with a grain of salt and endeavor to understand "why" as much as "what". In the end only you are responsible for any consequences.

I keep trying to gen up on heat treating via books etc to get to grips with the WHY but it doesn't seem to sink in to much. Even for someone like me with an "academic" background all those graphs and terms get abit abstract. Guess advice on what works from seasoned pro's is just as invaluable. Despite the manufactuers advice about not tempering at purple, it does seem to work for me ... or have I just being "getting away with it" for to long

In my early days my (limited) tooling was made from coil or leaf springs (what ever steel they maybe) and it was just a few minutes to bang a shape on the end, dip in oil, let the residual heat take it to purple. That's still really as far as my heat treating knowledge goes. That said I find I'm spend a lot more time doing quite complicated tooling and this thread has pretty much convinced by to get a kiln ........... yipeee, new toy.

[Mainely,Bob]

That said I find I'm spend a lot more time doing quite complicated tooling and this thread has pretty much convinced by to get a kiln ........... yipeee, new toy.

Where in the overhead are you gonna put it?
Pretty soon you`ll have cornered the market on beam clamps,snatch blocks and rigging in order to store all your toys "at the next level". ;)

[forgemaster]

EN36 subsitutes can be 4317 17CnM06, 8620 will do at a pinch, its the nickel that gives it its properties, normally used as a case hardening gear steel.
The punch that we made that took off, was made from what we call Kroball, normally a high carbon silicon manganese steel specially made for grinding ball applications (Grades 5190 5080H) We heat treated that punch by normalising it all over then heating the face to a depth of say 1/2" and only that face that does the punching, to a high orange and dropping it into the quenching oil. After each time the hammer drives it through the tool the striker tosses it into the water tub to cool it out, that punch had probably punched maybe 500 slots and these slots are about 2 1/2" deep x 1" wide x 4" long and was getting pretty fatigued. It was my fault that it broke I should have known better, I should have renormalised it, or inspected it and retired it before it broke, but as I said in the thread it did'nt do much damage to anyone only me and then it was only a soft tissue cut, but it could have had dire consequences if it had hit someone in the head had they been sitting down.

One thing I am pretty strict on is warming of hammer tools before they are used under hammers, especially in winter, and winters here are not like they are for some of you. Using a cold tool under a hammer is a sure invitation for a breakage. Depending on the configuration of the hammer we will also put heating blocks between the dies of hammers before we start our first heat of the day to take the chill off them so as to prevent fracture.

Phil