Sorry - Another heat treating question

amcardon

amcardon

Joined
Jun 29, 2009
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Hey guys, I just did my first heat treat in a home-made oven (following the british blades instructions) of some 3/16" 1080 steel that was heated to 1500F and then quenched in 130F canola oil... Checked with a file and it bit in, not hard but definitely bit. Besides my crappy choice of quenchant (yes, I know, I just can't afford Parks or AAA right now) what did I do wrong?

I put the blades in as the oven heated up and let it soak at 1500F for 5 minutes hoping that would be sufficient to heat the steel through, maybe I was wrong...

Any suggestions?
 
AAA would not be a good match for 1080 anyhow, when the time comes give Toughquench, MacMaster Carr, or one of the Houghton oils a try. As for your issues, this is a very common question on many forums and can be best handled with systematic trouble shooting. It is not too different than a small engine that won't start- check for fuel, check for spark, if you have both you are going to have to get more in depth with your investigation.

This is a simple steel so I will leave the steel for the more in-depth phase. Steel hardens by combining two factors - putting sufficient carbon in solution with heat and adequate super cooling to keep it in solution.

With this steel, sections under 1/8" should be able to be done with most oils, so your edge should have resisted the file even with the canola oil, but you could double check by running an identical test piece and quenching into water as a control. So unless that canola oil is really slow, your problem is more likely to be carbon in solution. This itself can be broken into two categories- lack of carbon to work with (decarb), or insufficient heat and time to put what is there into play.

1500F is certainly enough heat to put the carbon where you want it so we can narrow things down to decarb or soak time. Still air ovens take about the longest to bring things to temp of most heat sources so much of your time could have been used just trying to get the blade there. But before you go there, take the blade you do have, clean it up well and etch it in FeCl if you have some. If it comes out uniform gray, look harder at the time factor, if it comes out a patchwork of mottled gray and silver, you have decarb. You could also keep filing and see if the edge starts to skate under a soft skin. If decarb is the culprit, you may want to go the opposite direction on time and actually shorten it up a bit, or find some way of protecting the blade from the atmosphere during the soak.
 
Decarb had me scratching my head when I started out... I use an LP forge and even though my choke plate minimizes decarb... I get it every time. Work it down a bit, like Kevin said, there's probably a nicely HT'd blade under that soft stuff!

Rick
 
Thanks for the responses - Kevin, I don't know how much time I've spent reading your comments and stickies but probably as much time as I've spent reading everything else combined (and that's not a small amount of time I'm talking about!) and really appreciate your comment. I went back and re-read a bunch of stuff and was still scratching my head which is why I started this thread and I do think decarb is the culprit. I had normalized the blades and there was some decarb on the blade after that. Since this is my first time heat treating I figured this was normal and wouldn't hurt anything and I did not clean any of it off before heat treating so hopefully that's my problem. I will clean these up and normalize again and make sure they're pretty before I put them through heat treat #2.

Thanks again Kevin and Rick, I really appreciate it and will report back with my next attempts (though it might not be for a week or 2 - lots of exams coming up...).

-amcardon
 
Many of my first blades were made in 1080/1075. They regularly came out like yousr, seemingly not hard. A trip to the grinder started with dull or no sparks....then suddenly a shower of sparks came. Decarb was the problem. I learned that there will be a layer of decarb to some degree on any blade heated without oxygen exclusion. I started coating my carbon blades with Turco, and the decarb virtually disappeared.
 
Try to dig a deep notch with the file, if it sinks then you need to re-HT (file or grind out the notch first), if it is just a layer of soft decarb the file will eat a little ways in and stop abruptly. If the latter is the case there is no need to re-HT.
You should learn to expect a little of this, it can fool you if you are testing right out of HT, before finish grinding.
 
Also make sure that your quenchant is sitting close to your heat source. If you lose too much heat getting the blade from the oven to the quench I think that can do it do. Canola works well for me with 1080. I have never had that much decarb on a blade that I could not tell if it got hard or not, but then again I am doing stock removal. Try more than once to file it and listen for that "glassy" sound a really hard blade will make.
 
R.C. brings up a topic often made. It has some validity, but is mainly a wife's tale.

In still air, the speed at which a half pound of steel, heated to 1500F drops in temperature is not all that fast. You have plenty of time to safely and smoothly transfer the blade to the quench tank and immerse it evenly. More damage and injury has been done with super fast movements of hot blades, quench tank flare-ups due to being right under the forge, and blades going in at an angle due to haste.

It is the cooling rate after the blade enters the tank and drops below 1350F ( approx) when the clock starts. With 1080 ,you have about one second for the steel to cool from 1350F to 950F, thus the proper oil is critical. With 5160, you could walk the hot blade to your neighbors house, bring it back and quench it in last years lawn mower oil, and it would probably harden.

However, on simple steels, the surface may oxidize in the air if too much time is taken between forge and quench tank, resulting in a skin of scale with a martensitic core. A quick cleanup on the grinder will remove the skin ( also called "rind").

Placing the quench tank where you can turn 90 or 180 degrees and quench the blade without taking any steps is perfect. Directly under or next to the forge is an invitation to an accident.
With a large blade, or fast quench steel, I do a mock quench (dry run) when normalizing the blade before austenitization.I make sure the tank is in position, is large/deep enough, and that the oil has been pre-heated.If the blade is very long, I practice the hand turn to position it above the tank for a smooth quench.( rotating 3 feet or more of sword can be more of a trick than one would think). Often a set of steps or low platform is needed to stand on, just to get the tip high enough to enter the tank.
Once the blade is austenite and fully soaked, there should be no surprises.

Another thing amcardon may want to consider is the atmosphere in his forge chamber. Too much air in the fuel/gas ratio and he will surely get the results he has noticed. As Kevin said, a shorter soak may help, but adjusting the mix to create a slightly reducing atmosphere will allow any soak time needed.
 
I'm using an electric oven, sorry I wasn't clear about that earlier. Also, the quench tank is just in front of and to the side of the oven, less than 2 seconds from oven to oil... I think with the next run I will let my oven equalize at 1200F and then add the steel, ramp up, and soak for 5ish minutes to be sure the steel is up to temp. Does this sound reasonable?

Thanks guys!
 
bladsmth said:
Many of my first blades were made in 1080/1075. They regularly came out like yousr, seemingly not hard. A trip to the grinder started with dull or no sparks....then suddenly a shower of sparks came. Decarb was the problem. I learned that there will be a layer of decarb to some degree on any blade heated without oxygen exclusion. I started coating my carbon blades with Turco, and the decarb virtually disappeared.
Click to expand...

BTW... what is Turco? Thanks.
 
Turco and Turco II are a borax based protective coating that is great up to about 1550F.
Several of the suppliers used to sell it, but it has been hard to find lately. Brownell's sells some similar products. You just dip the blade in the Turco (or paint it on), let it dry for a bit, and put the blade in the forge/oven.
 
bladsmth said:
Turco and Turco II are a borax based protective coating that is great up to about 1550F.
Several of the suppliers used to sell it, but it has been hard to find lately. Brownell's sells some similar products. You just dip the blade in the Turco (or paint it on), let it dry for a bit, and put the blade in the forge/oven.
Click to expand...

Hmm. I use borax suspended in alcohol as flux in my silver work. Could I just paint the blade with that?

You also mentioned in a different thread using a thin coat of satanite to prevent pitting. What does the satanite or Turco do to the quenchant? Will the Quenchant degrade faster?


Doc
 
drdoc said:
Hmm. I use borax suspended in alcohol as flux in my silver work. Could I just paint the blade with that?

You also mentioned in a different thread using a thin coat of satanite to prevent pitting. What does the satanite or Turco do to the quenchant? Will the Quenchant degrade faster?


Doc
Click to expand...

I want to know this also.
 
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