Heat Treatment

[MachineTom]

What began as a way to HT a couple of parts, has grown into a small HT oven and stuff to go along with it.

Seems the HT companies all have a minimum charge $120 or so to HT up to 80-100 lbs.

If you would like a couple pieces HT give me a note, and we can work it out.
Limited by size 6" wide 8" long 4" high. Materials will only be steel, 4140, 4130, O-1 D-2 other tool steels.

After Heat Treating, The work will be black, I use decarbonizing coatings, Depending on material, the coatings will be easy to difficult to remove. Media blasting works great. Depending on shape the is sometimes movement of the piece, Resulting in Slight warping, in a 8"long bar of O-1 it moved about .002, final grinding took care of that. Parts can be remachined with Carbide tools, But tapping is near impossible. Turning hardened parts need shallow DOC and fine feed, but the finish is brilliant.

 

[PeperPan88]

I'll take note of that mate. Seems you got quality specs there to offer

 

[petertha]

MachineTom, nice gesture, this could be valuable. Beyond my Neanderthal experimental torch techniques, I do not envision myself getting a $$ HT oven soon. Maybe one day with sufficient justification. But for now, enough challenge just making the bits & pieces.

 

[rklopp]

Be careful you don't ruin your furnace, especially the element if electric, with fumes from the anti-scaling compound. Been there done that on my old TECO oven. My new Paragon oven instructions say using compounds will void the warranty. Apparently the elements develop a protective oxide skin that slows further oxidation, but the compound kills it. I use foil wrap instead.

 

[MachineTom]

I am aware of the coating issue, The compounds manufacturer claims no ill effects to the coils from the coatings. I tried the SS wrap with torn up paper added. First piece was quenched with the wrap in place, a very uneven hardening resulted. The others were done by cutting open the wrap, and dropping into the quench oil. The results of the hardening were good, but the metal had quite a bit more decarboning erosion than the pieces coated with the mud. So for these I will stick with the mud.

 

[petertha]

After Heat Treating, The work will be black, I use decarbonizing coatings, Depending on material, the coatings will be easy to difficult to remove. Media blasting works great.

I was wondering if you could expand on this. When you say 'after heat treating', I assume you mean the completed (hardened quenched) part will have a coating. How is O1 for difficulty/ease to remove?

Reason I ask is, I was talking to a local knife maker guy recently & mentioned I'd like to have a HT oven one day for model parts. His opinion on smallish O1 parts was there are ways of keeping the oxygen off during heat-up phase (coatings, SS bags, inert gas etc.) but the issue is more-so quenching. ie these protection materials then become kind of thermal insulators & the oil cant get at it to take the temp down properly (fast enough?). I recognize there are probably differences in hardness levels, alloys & desired end result between knife making & model parts. But does this sound right to you?

Sorry, I don't want your offer to turn into a HT discussion & I'm happy to create a new post. I just thought I'd ask because you mentioned your process & I don't know what I don't know

 

[MachineTom]

The issue is in the Heating before Quench, The tempering is not hot enough to have the O2 react with the carbon in the steel. Which is the scale that comes off the part after quench. The coatings for the most part fall off at quench. I doubt they slow hardening at all. My results have been very good with the coatings.The SS bags I've used are something else. If the part is something that can be tightly wrapped then the hardening is uniform, the material came out well. if it is odd shaped and can't be wrapped well, I have had uneven hardening, as the areas of voids cooled slower, then oil came in and boiled rather than drew heat away as in liquid form it should.


I will later post a couple photos.

 

[MachineTom]

Here are some photos from the process.

First is the parts coated in mud.

Next is in the oven
And now out of the quench
Final ground

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[lohring]

Another approach to heat treating tool steels from Jim Allen:

There is no inert gas of any kind used inside the sealed, high chromium stainless steel, bags. "The lightweight Sen/Pak container heats more rapidly than the work piece. As a result, the undesirable elements in the entrapped atmosphere react with the Sen/Pak container long before the work piece is hot enough to be damaged by them. In addition, the Sen/Pak container acts as a protective barrier throughout the hardening & quenching operation." A preheating soak of the piece in it's bag at 1350*F to 1375*F is done first. Then the piece is raised to the hardening austenitizing temperature of 1770*F to 1780*F & allowed to soak again. The entire bag is submerged in heated (90*F) standard hardening oil & holes are immediately punched in, which prevents the heated piece from ever being exposed to the atmosphere. After the piece has cooled to approximately 150*F, I use a double tempering operation at 400*F to bring the piece to it's final temper. At this point the piece is not clamped between the heavy steel pieces. The double tempering operation is only necessary for sections greater than 1.000" thickness. However, I have always, after cooling the piece to room temperature, tempered a second time at the 400*F temperature.

I use a Lucifer heat treating oven, with a digital temperature control, capable of holding the temperature at + or - 5 *F up to 2300*F. I use a Paragon High Fire Kiln with a Staco Energy Variable Auto-Transformer & an Omega HH-99A-K thermo-couple digital thermometer for tempering operations. I can hold the tempering temper at + or - 2* F with the variable transformer controlling the voltage to the ovens heating elements.

Jim Allen

 

[petertha]

The entire bag is submerged in heated (90*F) standard hardening oil & holes are immediately punched in, which prevents the heated piece from ever being exposed to the atmosphere.

Ha! we travel the same forums!
I mentioned this bag punching/snipping technique to the HT knife maker fellow. He seemed somewhat apprehensive & I can kind of visualize why. A block of red hot steel, a vat of hot oil, getting the part quickly exposed while submerged using tongs or tools & trying not to splash... Jim is obviously top notch metal man. Just not sure I'm as keen or capable.

Tom in your 'out of quench' pic, would that scale come off relatively easily if it was O1? Would most of these issues go away if you were sent parts from Air hardening steel & just left in foil, or does it not quite work that way? Only reason I was going down the OHS path was better machinability (I think).

 

[MachineTom]

The coating used on that 4140 comes off easily, To clean it further I submerge it in a bath of muiriatic acid cut 50% with water. The black is pretty much gone at that point. On O1 The MUD stuff seals much better, so the surface is in much better shape, but it needs blasting or machining to take it off. I have not yet tried the first material on o, as it is listed to do so. But i soon will.