Heat Treating Results...

Well... how fortuitous that you ask...


Quenchant: For now, using baking soda and water. You must use what's correct for the metal. 1045 likes water cooling. What the books say about sinking potato peels -that's just a starting point. I test the solution by heating (with oxy/propane torch, simple mapp or propane torch is not hot enough) a 1/4" thick piece of metal until it's red/orange (color is important. Cherry red is cold. Orange, now you're talking) and dunking it until it does not boil with big bubbles but rather, fine "soda" or "carbinated water" bubbles. If the bubbles are too big, the hardness just won't be there in the finished piece. Add bi-carb soda until the desired bubbles are obtained when quenching a test part. Why bi-carb? It's a salt and it's cheap.

The water should start-out room temperature and there should be sufficient volume so the terminal temperature of the part and water is 150 degrees. I'm in the process now of writing the formulas to know how much water to start with to accomplish this. BTW: The books don't tell you this but it's easy inference if you see the picture of what's going on. At the very least, start-out with enough water and pull the part when it hits 150 (which is right at the threshold of being able to handle by hand). A rapid and smooth transition to 150 is the key. These little subtle points are what make a difference between something that comes out 30 RC when you intended 40 etc.


Pack Carburizing for low and mid carbon steel: So far, 95% crushed charcoal and 5% (by weight) potassium nitrate. Ground-up and crushed together. (Don't add any sulfur unless you plan to make gunpowder). I'm still tweaking this and may up the potassium to 10%. The potassium becomes solute with the charcoal at/around 500. The combination of the two produce a large amount of CO2 when temps hit 1300. This carries the carbon right into the metal as it starts to hit austentizing state. Of course, I'm wrapping in tool foil. The aftermath is not messy at all. Just some grey powder and scale afterward. It's all incenerated and the carbon is gone into the metal.


Ray


Hey Ray, tell us about the quenchant and what you concocted for pack carburizing.
 
Good afternoon - Hey, very interesting thread, would you mind sharing some info about your oven set up. Such as make, model, where did you get it or is it home made, is it inside your shop or outside ect. Any info would be helpful.

Thanks,
Woodrow
 
Hi Woodrow,

It's all documented here with the juicy stuff starting at post #26 of this thread: http://www.hobby-machinist.com/showthread.php/9929-Heat-Treat-Oven/page2?highlight=heat+treat+oven


Oh, BTW: It's inside my shop. When in operation it's only warm to the touch -and barely that. It's when you open the door things get hot.


Ray




Good afternoon - Hey, very interesting thread, would you mind sharing some info about your oven set up. Such as make, model, where did you get it or is it home made, is it inside your shop or outside ect. Any info would be helpful.

Thanks,
Woodrow
 
I have a paragon inside the shop and I have a co2 line with a regulated flow going in to keep from having to wrap my parts in stainless foil and I can polish the part up beforehand without much clean up. The shop has a hood vent do to the c02 but the flow is slight due to thermal expansion. It is a need trick that I picked up on a trip through mike bosses shop before he retired. The guy was a heat treat legend in the industry. Take care all.
 
I'd like to experiment with that some time. Good to know you've done it and get OK results so I at least know I'm not barking up the wrong tree.


Ray


I have a paragon inside the shop and I have a co2 line with a regulated flow going in to keep from having to wrap my parts in stainless foil and I can polish the part up beforehand without much clean up. The shop has a hood vent do to the c02 but the flow is slight due to thermal expansion. It is a need trick that I picked up on a trip through mike bosses shop before he retired. The guy was a heat treat legend in the industry. Take care all.
 
Made many more parts with weld build-up today so the oven was used to normalize them. They're all slow cooling now. While the oven was hot, I hardened a few pieces and tempered to a desired Rockwell of 40 RC. With the tester I'm using now reads 38 RC on the part. I've used the tester on some materials with know hardness of 60 and 62 and it gives results that are almost dead-on. I was shooting for 40 and got 38... For now, I'm OK with that.

Another ingredient (chromium oxide 1%) was added to the pack carburizing mix. I did one part with the chromium oxide and the other w/o it. Here's a few pics along the way. -Amazing how a few grams of a substances changes things so much. Both tested at the same rockwell but the finish felt different even though they were identical parts.

I use Caswell black oxide on a lot of things. The part that had the chromium did not accept the oxide treatment as well as the other part. To be expected I suppose; chromium does not oxidize very much -if any at all. Here are pictures of just the chromium treated part. The other is identical but has a darker tone.

First pic, right out of the oven, quenched and tempered.

OutOfOven.JPG

Second Pic, same piece after a few moments in the sandblaster. -Interesting to see sparks flying around in the sandblast box.

BrushedOff.JPG

Third pic, oxidized but not sealed yet. BTW: The Caswell treatment is a two-part chemistry. First step is to degrease the part and dunk it in the oxidizer then let it air dry. I find that performing that step a second time gives a better finish.

Caswell 1.JPG

Last pic, finished part after sealing and warm-air dried. The second Caswell step is to apply a sealer and let it air dry. It immediately turns black. The sealer smells just like linseed oil -although I don't know if that's what it really is. And for the record, the black oxide does not enhance the hardness of the part. It's just a surface treatment to retard rust. It works very well. A lot of the stuff I make is used on Yachts and most folks here navigate brackish and ocean routes. Nothing has rusted yet.

Caswell 2.JPG

... Looking forward to getting a Rockwell tester and I'd also like to get a Leeb unit as well. It's going to be a few more weeks before I turn enough jobs to get those.


Ray

BrushedOff.JPG Caswell 1.JPG Caswell 2.JPG OutOfOven.JPG
 
Ray, have you gotten to the point in your reading of studying TTT curves for various steels? They are widely available for simple heat treatable steels and most common tool steels. Once I understood the time and temperature factors concerned with hardening and crystal structure of the steel the procedures really started to make sense...and showed why it is so easy to fail the whole cycle with one tiny shortcut.

I was studying the many MANY conversations (arguments, fights, etc.) on the knifemaking forums and it got me curious enough to read up on it like you seem to be doing. I stick to commercial quench oils (after a brief experiment with ATF) to take that variable out of the equation.

WRT your case hardening, you are essentially changing the medium carbon surface to high carbon, so heat treat to the high carbon. For example:

http://www.cashenblades.com/steel/1080.html

Cracking is VERY common in water/brine quenching high carbon steels. The Japanese swordsmiths made an art out of interrupted quenching simple high carbon steel...another concept you may have read about.:thinking:
 
Hi...

Oh yes, doing lots of reading. All books so far cover TTT within the first section. This is really fascinating stuff and gives me the sense that metal is much more "alive" and has more "personality" (not anthropomorphically speaking) than I ever imagined. Anyhow, like you, I saw many conflicting techniques on the Internet covering the same topic. My uncle was a chemist turned metallurgist but, at the time he was still alive, I did not have the educational background to keep-up with his knowledge. My father was an old school T&D maker and he and my uncle shared lots of information at the family table but, my uncle's words went over my head at the time. In any event, I went straight to the professional publications from the AISI. Cost me a fortune but was cheaper than purchasing the individual chapters in PDF form... -And I have no desire to deal with knucle-headed arguments on Internet groups... What really bugs me is that I think my sister still has some of my uncles books -but she can't find them.


Right now, I'm slowly proceeding -mainly because it's a very time consuming process! I've noticed some things which I haven't been able to find information on... Maybe you know what's going on.

I've noticed that medium carbon steel tends to be slightly magnetic after heat treat quenching. Is this a good or bad sign?

Also, it seems (but I haven't systematically verified) that metal picks-up 1-2 Rockwell about 24 hours after the final treatment steps and cool down to room temperature.

I will look around for some quenching oil. I have seen some cracks here and there. Is it available in reasonable sized quantities? Also, would you mind making recommendations based on the kind of work I do? It's mostly machine parts of 1045 and some 41xx. I make a lot of shafts with flanges that are two-part welded (similar metals) so I need to normalize after weldin, bring to final dimension, then surface harden a little bit.

And finally, I didn't know about differential treating until it was mentioned on another post of yours several weeks ago and of course, I looked it up. LOL... At the moment, I'll just stick to getting uniform treatment...


Ray




Ray, have you gotten to the point in your reading of studying TTT curves for various steels? They are widely available for simple heat treatable steels and most common tool steels. Once I understood the time and temperature factors concerned with hardening and crystal structure of the steel the procedures really started to make sense...and showed why it is so easy to fail the whole cycle with one tiny shortcut.

I was studying the many MANY conversations (arguments, fights, etc.) on the knifemaking forums and it got me curious enough to read up on it like you seem to be doing. I stick to commercial quench oils (after a brief experiment with ATF) to take that variable out of the equation.

WRT your case hardening, you are essentially changing the medium carbon surface to high carbon, so heat treat to the high carbon. For example:

http://www.cashenblades.com/steel/1080.html

Cracking is VERY common in water/brine quenching high carbon steels. The Japanese swordsmiths made an art out of interrupted quenching simple high carbon steel...another concept you may have read about.:thinking:
 
Look at TTT curves for alloy steels and you will note that the transformation curve may extend to the hours+ range. Some high alloy steels literally do not fully transform at room temperature as well. This is where cryo quenching becomes real. It both speeds and drives to completion the martensite transformation. What I suspect you are seeing is the time factor coming in. It may take a day or so for alloy tool steels like O-1 or 40xx (and maybe even simple 10xx steels with some 'trash' alloying elements...nothing is pure any more) to fully transform and get that final point or 2 of hardness. For really wild steels like some of the particle metallurgy steels or some rare earth alloying elements the cryo quench adds 3-5 points of hardness that would otherwise never appear.

I bought quench oil in gallon quantities from McMaster. They have a fast and slow version, but I don't think their fast is 'fast enough' for 10xx series steels that need to go from 1500F+ down a few hundred degrees in under a second (hence the impossibility of fully hardening them to the core in larger cross sections) to miss the perlite nose of the TTT curve. They are great for 40xx and O1 class steels though. W1 is a water quench steel, hence the W designaiton. O series is oil quench. A series is air quench. (Yeah! Just let it cool in air! Easy!) Many suppliers don't want to mess with individuals and only sell in 55 gallon drum qty. Ugh. If you can find Parks quench oils in 5 gallon size they make a very fast oil (Parks #50 IIRC) supposedly 'water fast quench' but without the steam bubble insulation issues. Occasionally a knifemaking supply house would buy a lot and break it down, but I haven't looked for that in a few years.

http://www.mcmaster.com/#quenching-oil/=mv0r7t
http://heatbath.com/heat-treating-products-2/oil-based-quenchants/

It is a really fun topic that I wish I had time to fully investigate...but I already have too many hobbies! I have pretty much settled on stainless steel blades ground form barstock, so I send mine out for heat treating by professionals using either vacuum furnaces or molten salt baths. A guy's gotta know his limits!

- - - Updated - - -

As for your surface hardening, why not through harden? Start with higher carbon steel and just fully harden it. Is it a toughness issue where the full hard and tempered material is just too brittle?

I always think if rifle receivers in cases like this. As soon as good alloys were available for through hardening, case hardening virtually disappeared from the rifle making industry in the early 1900's...with good reason. Case hardening adds an extra step that is just not needed in most cases.
 
cdhknives...

Much thanks for the thoughtful reply and product links.

The stuff I work on is either for my own shop-made equipment (in which 1045 is just fine) or for adaptors of various sizes to convert pulleys, sheaves etc. and a handful fabrication parts for lawn mowers and tractors that do not really even need the surface hardening. This is all a lead-up to the bigger picture/plan I have in mind.


Ray
 
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