Screwdriver
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Lost my way with this one slightly!
That is now sanded to 1200 and is ready for heat treat. What is the wisdom on Normalising cycles? I now it is important if you are working with forged and hammered blanks. This is purely stock removal. Is it necessary?
That is now sanded to 1200 and is ready for heat treat. What is the wisdom on Normalising cycles? I now it is important if you are working with forged and hammered blanks. This is purely stock removal. Is it necessary?
Screwdriver
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If that's O1 for example then no, I think you'd be fine but it might help and certainly wouldn't do any harm.
You might want to jacket it for heat treating. That lovely 1200 grit finish is going to scale up like Gozilla.
O1 Tool Steel - Oil-Hardening Cold-Work Steel (UNS T31501)
Cold-work tool steels are high carbon steels that are further classified into three subgroups such as oil-hardening steels, high-carbon, high-chromium steels, and air-hardening steels.
www.azom.com
"Hot oil quenches faster".........sorry I dont see the logic there.........surely the colder the oil the faster the quench.........the aforementioned Martempering is effectively a quench into a hot bath (salt bath about 350oC) which holds it just above the transformation temperature and therefore reduces the shock when completing the quench.
h-dom
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I can't remember the logic, something to do with the temperature that the steel becomes fully hardened is around 400 degrees (not sure if F or C) and the warmer oil brings it down to that temperature faster. Doesn't make sense when I write it like that though.O1 Tool Steel - Oil-Hardening Cold-Work Steel (UNS T31501)
Cold-work tool steels are high carbon steels that are further classified into three subgroups such as oil-hardening steels, high-carbon, high-chromium steels, and air-hardening steels.
"Hot oil quenches faster".........sorry I dont see the logic there.........surely the colder the oil the faster the quench.........the aforementioned Martempering is effectively a quench into a hot bath (salt bath about 350oC) which holds it just above the transformation temperature and therefore reduces the shock when completing the quench.
My Old Landy
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This bit is the general thinking around heating the quenching media. Silver steel into cold water can crack it especially if you get the steel a bit too hot. O1 is the same (or in my trials and tribulations over the years!)
Theres another diagram here...... http://www.interlloy.com.au/our-products/tool-steel/o1-tool-steel-100mncrw4/?output=pdf
Look at the Ms line.......just above 200 oC.....thats the critical phase transformation......Martensite Start.........the longer it takes to cool through that line the softer it becomes.......but the 870 Hv line is quite a long time (for quenching) so these people recommend heating the oil to 180oc to 220 oC.
The other diagram appears to show that if youre tempering you do it from warm....
Look at the Ms line.......just above 200 oC.....thats the critical phase transformation......Martensite Start.........the longer it takes to cool through that line the softer it becomes.......but the 870 Hv line is quite a long time (for quenching) so these people recommend heating the oil to 180oc to 220 oC.
The other diagram appears to show that if youre tempering you do it from warm....
Screwdriver
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Yeah, it does seem odd but the reduced delta t is cancelled out by the increased thermal conductivity from the "thinner" lower viscosity oil. Cold goopy oil tends to vaporise and does not conduct heat away from the part so quickly.O1 Tool Steel - Oil-Hardening Cold-Work Steel (UNS T31501)
Cold-work tool steels are high carbon steels that are further classified into three subgroups such as oil-hardening steels, high-carbon, high-chromium steels, and air-hardening steels.
"Hot oil quenches faster".........sorry I dont see the logic there.........surely the colder the oil the faster the quench.........the aforementioned Martempering is effectively a quench into a hot bath (salt bath about 350oC) which holds it just above the transformation temperature and therefore reduces the shock when completing the quench.
Again no one can dispute the science behind professional heat treatment, least of all me but this is an old leaf spring of questionable alloy so whatever works, works...
Love the idea of salt tempering and liquid lead etc. but for me, I'd just want to get the thing 99% there. That last 1% (or whatever) would take a lot more effort. It would be fun to experiment and really get the very best out of these blades bit like chasing a few tenths of a thou on a clapped out lathe. At that point you'd also be looking at cryogenic heat treatment.
Incredibly, cryogenics "works" as part of the heat treating process an infinitely long period after it's all said and done. Graph of the phase change just goes infinite so you can increase the martensite in a hardened and tempered carbon steel years later. Apparently this is a well known trick which you can do to your HSS drill bits to toughen them up.
I think the hot oil is designed to soften the shock of the Austenite to Martensite transformation.....there is a volume change so if the piece is also stressed there is the possibility of cracks
I thought we had moved on from the old spring to O1 tool steel (diagrams are for that)
Yes, freezing can add a couple of points of hardness.........I worked for a hardfacing / reclamation outfit and it was part of the armoury should the test results just fail to meet the required hardness.........
I thought we had moved on from the old spring to O1 tool steel (diagrams are for that)
Yes, freezing can add a couple of points of hardness.........I worked for a hardfacing / reclamation outfit and it was part of the armoury should the test results just fail to meet the required hardness.........
Screwdriver
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Would you say a warm quench oil is better or worse for inducing stress cracking as shown in the OP?
Not a trick question, really would like to know. I assume it must help because it's all over the blade forums etc. but there is a fair bit of "seat of the pants" science going on.
Looking at the diagram it shows that for the 01 steel you can take about100 seconds the pass through the 200 / 220 oC (and maintain max hardness) area which for quenching is slow. As there is a volume change the stress induced will be high so the slower you can make it, the better........So a warm oil should results in less cracks........but remember shape etc will also have an effect....if youve got thick and thin sections the thin will quench quicker so you could get cracks because of that....
In some steels, eg plain high carbon, the quench through the Ms (maybe 300-400 oC) may need to happen in less than 10 seconds........so you dont have much choice if you want max hardness
Even the technical data published by the steel makers can vary a little.......plus small additions of Cr, Ni, Mo, V etc etc can have profound effects.....and some of those elements can be unintentional additions depending on how the steel is made.
h-dom
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Well, I've ground the bevels, heat treated, hand sanded and etched my latest attempt. This is from the billet I made and posted a photo of on Wednesday. Heat treat went perfectly, hardened up in oil and tempered in the oven for 2x2 hour cycles allowing to cool to room temp in between.
It was originally 7 layers, 4 layers of 01 and 3 layers of an old file but I have ground off the outer layers of 01 getting it straight and flat so really what you see is the 01 has etched darker than the file. I didn't expect any contrast so I'm pleased. Handle needs a little more shaping but apart from that it's ready for scales.
It was originally 7 layers, 4 layers of 01 and 3 layers of an old file but I have ground off the outer layers of 01 getting it straight and flat so really what you see is the 01 has etched darker than the file. I didn't expect any contrast so I'm pleased. Handle needs a little more shaping but apart from that it's ready for scales.
My Old Landy
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That looks really cool! A blue tinge will make it look like lightening (if such a thing is possible?)
My Old Landy
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That really does look sweet! Now all you have to do is pop it in a box and send it over 
