Quenching Methods

izafireman

Well-Known Member
I have been asking questions recently regarding heat treating my own steel as I normally have blanks heat treated in bulk in industrial kilns.

Now when I get round to doing my own heat treat I have noticed different methods, oil quenching, water, and air quenching between plates using compressed air. I would imagine certain steels react better to one or the other of the three methods but how do I know, obviously there will be heat treat profiles to follow but I am guessing all methods wont be covered on most instructions .So is there a method which is better overall and which steels like air quenching best.

The other question I have is once the steel is hardened do I have to temper the steel immediately or can It n done hrs or days later and would a normal house hold oven be sufficient ?
 
Yes to the house oven IF you use an oven thermometer to make sure the temp is correct. Ovens are notorious for being off a few degrees. As far as waiting to temper I would not. Though I have not tested the theory I was taught that the internal stresses from the quench could cause cracks if left for a long time. Plus that is just more time for you to drop the knife or break it in some other way.
 
Yes to the house oven IF you use an oven thermometer to make sure the temp is correct. Ovens are notorious for being off a few degrees. As far as waiting to temper I would not. Though I have not tested the theory I was taught that the internal stresses from the quench could cause cracks if left for a long time. Plus that is just more time for you to drop the knife or break it in some other way.


Thanks for the reply Chris.

I will be converting my toaster to a tempering oven which will be great as I use it at the moment when I stabilise wood and it is a nightmare to control the heat. But I did a quick search and saw a few conversions to control the heat using one of these https://www.amazon.co.uk/dp/B01MY2B6BR
absolute bargain as it has all the other components required. So that's my tempering and stabilising sorted ))
 
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The rate of quench will be determined by the alloying present. The more alloying, particularly things like Cr, and Mn, the slower the quench can be, eventually making air possible. Tempering absolutely should be done as soon as possible. If true full hardness is reached, immediate tempering is important. A larger kitchen oven will be superior to a toaster oven in heating for an even and accurate tempering . It is all about the thermal mass, something the size of a breadbox will spend all of its time overheating and underheating rather than holding the required steady temperature. Not to mention proximity to elements and amount of insulation.
 
The rate of quench will be determined by the alloying present. The more alloying, particularly things like Cr, and Mn, the slower the quench can be, eventually making air possible. Tempering absolutely should be done as soon as possible. If true full hardness is reached, immediate tempering is important. A larger kitchen oven will be superior to a toaster oven in heating for an even and accurate tempering . It is all about the thermal mass, something the size of a breadbox will spend all of its time overheating and underheating rather than holding the required steady temperature. Not to mention proximity to elements and amount of insulation.


Thanks for the reply Kevin and explaining about tempering.

With regards to the toaster oven, yes they are all over the place , over and under heating as I have exactly the same problem when I am curing my stabilised blocks in mine. I have taken readings with a digital thermometer probe and there was something like a 40 degree c variation over 30 minutes or so!

Earlier I was chatting to my father who is a retired electrician and he said its is due to the ovens being controlled by a simple cheap thermistor ?(think that's what he said ) and as you said no insulation.

I even built an external control unit using a variable resistor to control the power going in. This improved the situation slightly, around 5-10 degree variation but obviously still not what I wanted to achieve

What I am thinking of doing after doing a some reading up via searches is to rip apart my toaster oven, then remove, the temperature controls and thermistor. I will also shield the heating elements.

The oven will then be controlled via a new digital PID controller with a solid state relay and a dedicated temperature probe in the oven .The oven exterior will be insulated to keep the heat from escaping as much as possible. For thermal mass I will place a couple of inch thick fire bricks inside.

Hopefully it will work as my father tells me the PID controller is a type that controlled heated wrapping systems in the factory where he worked and is accurate to within 1 degree c. If it doesn't work it wont have cost me anything except for a temperature probe and a relay, both not expensive.

EDIT. I had several block to cure this eve and so tried two changes within the oven. Firstly I removed the cover from the bottom element (just a sheet that slides in and out) and put that so it covered the top element. Then I placed three fire bricks of around 10x4x1 over the bottom elelements and turned on the power. I was very surprised to find there was already a big difference in the heat up/ fluctuations as now the oven is heating up slowly as opposed to ridiculously fast before and the temperature climbing at a good slow rate, once it is up to temperature I will see how it holds but I have no doubt whatsoever that the firebricks have made the biggest difference here as the are very dense bricks for the base of my wood burning stove.

EDIT. Ok 40 mins later I checked the temperature, which was rising slowly but I turned the temp. down slightly and it seems to be holding at 114 which means by my reckoning the oven is out by 14 dec C...…..another 40 mins and it is holding at 103C so the bricks were retaining the heat....actually great for the stabilisation liquid I use so at least one result ))

I think I will check me main house oven later this week, which if ok is fine for steel but not the curing of the stabilising solution, did that once in the kitchen oven and never again lol.

Oh and I omitted to say Chris, I am going to buy the toasting oven with the biggest capacity I can find as the one I have now is tiny, that way I can get more volume.
 
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small toaster ovens are popular but something to consider. These usually have exposed elements and will be full on until the temp sensor says it's ok to shut off at the determined temp. The determined temp is usually a dial with numbers printed on it that don't match the actual temp. If you use one of these consider using a "muffle" which is nothing more than a length of pipe, tube, etc to put the blade inside of to slightly reduce the radiant heat from the blazing hot elements. Like Kevin says, a kitchen oven will generally work better. Just make sure the oil is all cleaned off or it smells pretty bad and your wife won't care for that. Ask me how I know.
 
I tried to use a toaster oven to temper but the one I bought will not achieve 400 degrees on my thermometer. Its either 380degrees or 430+ degrees no matter what you put the dial on. I now solely use the house oven to temper and the toaster oven for kydex, curing catus juice and gun kote. It does fine at those lower temps. Closer to 400 forget about it...
 
So is there a fairly inexpensive alternative to a toaster oven? I can use our kitchen oven, but my wife always grumps about it and that's why I got a toaster oven. I've seen some toaster ovens that have been modded with insulation etc. but I've always thought it was a lot of time and money put into something that still may not be all that accurate.
 
In honesty, if my shop had 220 I would find an old house oven at a yard sale and put it in or near my shop. I could temper in batches and no wife complaints. Its hot here in Georgia and running the house oven on 400 for two hours makes it much worse. She does not seem to mind as much during the two weeks of winter though.
 
I’ve heard convection oven’s work well because you don’t have the direct heat. They’re a little bit more than a toaster oven but not that much.
 
Thanks for the replies gents and valid points which is why I am looking at doing the conversion in the link below.
Basically toaster ovens , table ovens or caravan ovens , heard them called all those names are a heap of junk.

I bought one for curing my blanks when I stabilise and boy I had a few cursing moments as the dials lie like cheap Japanese watches. But after Kevin mentioned thermal mass I experimented last night with the dense fire bricks as my thread above.....a significant improvement.
This morning I was chatting with my dad and as stated the ovens do not achieve high temps nor are the temps accurate. But having share the like below with him I asked if an oven that was stated as 300 c for example , would the oven be able to achieve higher temperatures if the original controls were removed, it was insulated and controlled by a PID with a solid state relay...….' yes he said, I see no reason why as it will now be controlled by the PID'. ….There will be no cheap control turn it off when it reaches the limit set by the manufacture…..it will cut off at the temp the PID is set too.

There will be limited fluctuations in temperature as the oven will now be insulated and even better if you and fire bricks it has a good thermal mass.

This is the same principle as building your own kiln , a wire for an element , a PID and a relay....a decent thermocouple ......and thermal mass / insulation.

Obviously with electrics commons sense needs using.....don't insulate any wiring as you will change its rating, just insulate the oven itself and don't set the PID upper limits too high. Also bear in mind, the original toaster oven control will have been junk......a PID / relay / thermocouple will be taking countless readings per second, I think solid state relays can do over 100 actions per second!...….and this will be way more than a household cooker.

I will be buying a decent size toaster oven soon and I am going to have my father convert it and see how it goes, it will cost me $85 tops as I have some of the components, so has to be worth trying.



https://www.instructables.com/id/PI...&utm_source=pinterest.com&utm_campaign=buffer
 
I tried to use a toaster oven to temper but the one I bought will not achieve 400 degrees on my thermometer. Its either 380degrees or 430+ degrees no matter what you put the dial on. I now solely use the house oven to temper and the toaster oven for kydex, curing catus juice and gun kote. It does fine at those lower temps. Closer to 400 forget about it...


Yes same with mine, but it is limited due to the cheap controls in the oven. If replaced as in the link below it will heat up.

 
To piggy back on what Kevin said. No there is not one method of quenching that is better overall. It must match the alloy that you are using. You could use water or brine on steels like 1095, W1, or W2 if you have steady nerves. None of them will harden in air. A high speed oil would be best. 80CrV2, and 5160, 52100 will work well in a medium speed oil or canola oil. I don't care how steady your nerves are, don't quench in water or brine unless you have a lot of money to invest in steel. A lot of your stainless steels will air quench between aluminum plates. Some of the higher alloy tool and dye steels will do the same. The down side of going to high alloy steels is that you need to hold at a consistent high temperature to put carbon and carbides into solution and you my have to hold that austenizing temperature for 30-60 minutes plus a liquid nitrogen bath might be helpful in driving the retained austenite down.

So, yes, heat treating your own blades can open up the number of alloys that you can use but that may be dependent on what you are willing to invest in equipment.

Doug
 
To piggy back on what Kevin said. No there is not one method of quenching that is better overall. It must match the alloy that you are using. You could use water or brine on steels like 1095, W1, or W2 if you have steady nerves. None of them will harden in air. A high speed oil would be best. 80CrV2, and 5160, 52100 will work well in a medium speed oil or canola oil. I don't care how steady your nerves are, don't quench in water or brine unless you have a lot of money to invest in steel. A lot of your stainless steels will air quench between aluminum plates. Some of the higher alloy tool and dye steels will do the same. The down side of going to high alloy steels is that you need to hold at a consistent high temperature to put carbon and carbides into solution and you my have to hold that austenizing temperature for 30-60 minutes plus a liquid nitrogen bath might be helpful in driving the retained austenite down.

So, yes, heat treating your own blades can open up the number of alloys that you can use but that may be dependent on what you are willing to invest in equipment.

Doug


Hi Doug

Thanks for the answer, great advice as I would never use water for the reasons you state. When you say a high speed oil I take it that is an oil that kind of mimics water? If so can you give examples of such oils as will need to find one here in the UK. With regards to holding temperatures I am in the process of building my own HT kiln soon to the highest specs I can ie, brick types, thermocouple , PID controller and relay etc will all be the best I can source for my budget.

Regards

Pete
 
On the toaster oven - they work for tempering nicely as long as you don't need anything much over 400°F, and a PID is needed for control. I use a toaster oven for tempering as well as for powder coating cast bullets. By using a fire brick laying on rack (adds a bit of mass), then laying blades on top of fire brick. By using a PID controller the temp once stabilized is usually controlled to ±1°F with the tip of TC located just above center of blade.

A few folks have reworked toaster oven with extra insulation and got them to control closer to 500°F.
 
On the toaster oven - they work for tempering nicely as long as you don't need anything much over 400°F, and a PID is needed for control. I use a toaster oven for tempering as well as for powder coating cast bullets. By using a fire brick laying on rack (adds a bit of mass), then laying blades on top of fire brick. By using a PID controller the temp once stabilized is usually controlled to ±1°F with the tip of TC located just above center of blade.

A few folks have reworked toaster oven with extra insulation and got them to control closer to 500°F.
I'll have to try the PID and a fire brick. The last time I used my toaster oven I didn't use a fire brick but I stuck a PID in through the front which I think caused more heat chaos than it solved. I had one test piece come out spot on and the next one was way too soft.

Presumably you are drilling a hole for the PID controller some where in the body of the toaster oven rather than just sticking it in through the oven door?
 
Yep, a hole is drilled thru the rear of toaster oven with probe tip positioned about an inch above the brick. I'd NEVER put a blade in the oven until I've tested it a few times to be sure it's holding correct temp and not cycling too much. It doesn't take the expensive TC for a tempering oven, just the cheap $5 units seem to work just fine.

I built my PID controller in a box with a 120vac recept that is controlled by PID. The oven is plugged into recept and oven t'stat turned up to max, and timer set to "ON" (doesn't time out) and go from there. None of the work of removing oven controls and rebuilding.
 
This might be of concern to some?

I decided to check the accuracy of my main oven which is a Samsung, all singing all dancing which as a single guy I bought for my new kitchen I fitted. For the most part it is a nice piece of steel in the kitchen which my girlfriend cooks in when she visits.

So after the discussion above I thought, well I am single, have my man cave oven in my man cave kitchen I will use that to temper knives when I eventually build my HT oven. So I bought an external digital thermometer with a thermocouple that goes in the oven.

This evening I tested the oven three times and the results shocked me. No matter what configuration I tried as the oven can have lots of different settings and volume sizes due to a removable shelf, the results were worrying.

If I set the cooker to say 225C and left it to heat up the cooker temperature light would tell me it was up to that temperature...………..but when I looked on the external thermometer it was telling me there was maybe 30-40 c under what I had set (225)

So I left the oven on for two hrs and checked the results.....and the actual temperatures were way out.

If you look, the target temperature was 225 C....the oven indicated it was at this temps at about 206.....I then left the oven on 2 hrs.....there was a 19 degree difference in what the external thermometer was telling me. In reality.....not much difference in real terms than a cheap toaster oven.

The reason why?....well I am guessing they use cheap sensors in the ovens and how many times has your wife cooked a joint to the times it should be and then had to out it back in the oven for another 10 mins or so.....

To my way of thinking unless you have tested your oven I wouldn't us it for tempering, the only real way to be sure is with a PID controlled unit be it a toaster oven, main house oven.... PIDs will be accurate to .5 -1 degree ……...my Samsung oven which is an expensive so called flag ship model is not to be trusted for tempering...….check your ovens guys!!


EDIT....Well as the oven is hot I decided to crack open a bottle if red and cook some duck . Oven is now in the small oven configuration with the shelf fitted. I would expect that to be more accurate...nope ...Oven is set at 180c …..external thermometer is reading 154c...…..and its been on 20 mins , plus already hot from my tests. So a 26c difference this time....

As a matter of interest as I am new to tempering...or will be...what is an acceptable difference in temperature than the stated target temperature for excellent results?

I know I am most likely being a tad anal here but from my point of view if I am going to venture in HT / Tempering I should get it right not , sort of right..))
 

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