What the heck is going on?!?!?!

okzj

okzj

Joined
Aug 16, 2008
Messages
222
I just got this one forged and heat treated. After heat treat, it was taken to 400 grit and vinegar etched. Looked great before, and in my opinion it looks great now, but I'm afraid not everyone will appreciate it. It's a very busy hardening line. Not at all what I expected. I like it, but I wanted to present it to you guys. It looks grainy and platey, almost like I left scale or decarb on it. I didn't. There was a lot of stock removal after forging and a nominal amount after HT, and the hardness checked out with a file right after HT.

Here's my procedure for scrutiny;

It's HR1095. I forged in the as received condition.

Forged to as good a finish as I could muster. Left the edge at least 3/32". Took about 10 heats on the blade. Not a terrible amount of scaling.

Normalized x3

Process annealed. Got to normalizing heat, shut off the forge, closed both ends, threw Kaowool blanket over whole forge, then covered with moving blanket and an old coat. After 9 hours it was still very hot to the touch.

Ground bevels flat, took edge to 1/16" and did file work. Drilled holes in tang. Ended grinding at 400 grit, which is as far as I ever go on a working blade, although I do hand rub the 220 and 400 after HT.

Clayed blade with soupy potter's clay. Dried in front of forge. Very dark area is where it was clayed. It followed the outline fairly faithfully.

HT was a shade above non-magnetic. No soak. Interrupted water quench; in, out, in, out, in. After the third dunk, I left it until cool.

Tempered at 400 for 2 hours.

Back on grinder for finishing. Took little metal off. Only used 220 and 400 belts.

Vinegar etched in almost boiling white vinegar with some soap in it for surface adhesion. Total etch time was ~10 minutes. Rubbed clean with 400grit every 30 seconds - 1 minute.

Pay no mind to the edge. It is the start of a convex grind, and was done right before final etch. I stopped working on the edge after the character started coming out, as I was trying to figure out what was going on.

Did I etch too long? Did I not take it up to a high enough finish before HT or after? Did I muck up the HT? What caused this look?

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I agree with mete. I've had this happen, but another hefty sanding and re-etch and the problem went away.

However, you might want to dull up that blade before you rub it again! :)
 
Does it really decarburize that much in HT? I took a lot off after forging, so if it really decarbed that much in forging, I might as well just do stock removal. Hmmm.

I'll try it. BRB...
 
It is kinda hard to say Okzj. If you had a pic before etch that would help a ton. Depending on the atmoshpere when heat treating there can be alot of decarb.

What did the surface of the blade look like after it was hardend?
How clean was it before you etched?

I bet what you have is an uneven/partially removed decarb layer. This layer may have been just from your heat treat.

I would advice you to take more off and re etch. Make sure the blade is clean before you etch.
 
When you buy HR that's got a decarb layer. Forging adds to the decarb layer.HT adds to decarb but not as much as forging. The higher the temp the more decarb, more time at temp more decarb, the more oxidizing the atmosphere the more decarb.
 
Well, I took some thickness off and it helped, but not too much. It looks like I'm just going to have to use this HR for stock removal and get some CRA for forging. No big loss. Thanks guys.
 
If you run a hot enough slightly oxidizing atmosphere that you get significant scaling when you forge you will actually scale off metal faster than you decarb it. it's a sacrificial loss. I will get probably run out of town as a heretic for suggesting this but it works well when I do it. The other approach is to run a reducing atmosphere, or forge at lower temperatures. If I'm stuck forging hot rolled I like to start by pickling it in Sodium Bisulfate which removes a lot of the scale (PHdown at the pool/hottub supply store) it is a buffered sulfuric acid, so treat it with appropriate caution, and don't breathe the fumes! then rinse thoroughly, then hotscale off the mill scale.

your mileage will vary

-Page
 
I need to get a proper burner for my forge. As it is, I can't control air, so my atmosphere is directly related to how hard I'm firing. I can slide the front and rear doors closed some to choke the burn a little, but only marginally. I normally run slightly reducing, and I get hardly any scale. None in the forge, but it does scale when I pull it out. I haven't even tried to get an oxidizing atmosphere. I probably can't get the forge hot enough if I turn the burner down that low.
 
sunshadow said:
If you run a hot enough slightly oxidizing atmosphere that you get significant scaling when you forge you will actually scale off metal faster than you decarb it. it's a sacrificial loss. I will get probably run out of town as a heretic for suggesting this but it works well when I do it. The other approach is to run a reducing atmosphere, or forge at lower temperatures. If I'm stuck forging hot rolled I like to start by pickling it in Sodium Bisulfate which removes a lot of the scale (PHdown at the pool/hottub supply store) it is a buffered sulfuric acid, so treat it with appropriate caution, and don't breathe the fumes! then rinse thoroughly, then hotscale off the mill scale.

your mileage will vary

-Page
Click to expand...

Page,

Would you tell me the mixture of sodium bisulfate to water you use, please? Do you warm it, boil it, leave it how long? And I don't get... "then hotscale off the mill scale."

Mike
 
I agree that it will be hard to tell much until the surface is sanded smooth and the hamon is etched. I had an almost identical request for information this morning and made this reply:

(The blade was 1095, and the hamon had gone way below the clay line, all the way into the edge in places)

It appears that the blade was too hot and the hamon went all the way into the edge.This means that there is pearlite down into the edge and the blade won't hold and edge or cut right. The hamon line is caused by the steel under the clay staying hotter, and cooling slower, thus not converting to martensite. The line is usually somewhere a little below the clay, due to the fact that the heat retained in the covered area leaches down the blade during the quench. If the spine is thick and heavy, this is even more so. The exact ending spot of the hamon is always a bit of a surprise, as there are so many variables. Even the best Japanese smiths never know exactly what it will come out like. The blade has to be at the proper temperature. How did you do the HT? If it was by eye, I would bet the temperature was much higher than you thought. The final piece of the puzzle (and most probable) is the quench medium and procedure. It needs to be fast. Water/brine or a fast oil are necessary.The interruption also needs to be timed right. I always say to start with in for 1-2-3, out for 1-2-3, in to cool. This is a start timing. You have to try it and develop the times that work for your forge/quench setup. It is a bit different for everybody.

There is no loss on this blade. Just re-do it. Re-do the clay the same,don't go above 1450-1475F and hold for about 5 minutes , quench in a fast medium, allow enough time for the edge to convert to martensite, and the blade to cool back to the clay (about 2-4 seconds), interrupt long enough for the hot steel to run a high temper to just beyond the clay (this is the heat leaching back out. It takes from 1 to 3 seconds), put back in to the quench until cool.

The blade shape and thicknesses make all this happen. The thinner the edge, the more tricky the quench. Most folks leave a pretty thick edge when doing a hamon quench.

Hope this helps. Let me know how it comes out.
Stacy
 
Look to your annealing operations for answers as well. One thing that I can tell from your image for certain is that you have plenty of banding going on, so your carbide got segregated pretty well in at least one of your operations. The anneal you describe is very bad for hypereutectoid (above .8%) steels it results in heavy segregation and carbide in the grain boundaries, which will lead to embrittlement even under the best of conditions. To this I would add the diagnosis of decarb that others have pointed out as is evident by some of the patterns in the hamon. It is interesting to note the banding patterns in the hamon and how they are faded considerably, this is what happens to the stuff when you actually put things into solution, much of the contrast is also lost due to a martensitic background as opposed to stark banding within dark pearlite.

Decarb is VERY ubiquitous, much more so that the majority of bladesmiths want to believe, the safest route is to assume that it is there and plan to remove a few thousands to be rid of it. Forging gets you decarb, there are many self deluded smiths who believe that you can use the atmosphere of the forge to totally eliminate it or even add carbon, however our anvils do not rest in a vacuum and neither do we while we hammer on hot steel. What Page suggested is not really that far out there, it is just much more advanced than most smiths can get with control and observation, and there is testing, research and practice in industry to support it. Under proper conditions with controlled atmosphere ovens tool steels can actually concentrate carbon on the surface due to a higher rate of iron loss in an highly oxidizing atmosphere.

Thus your forging with low scaling probably removed a lot of carbon from a steel that already has a decarb skin from the mill unless it was debarked before shipping. Normalizing can be a very decaburizing operation under many conditions. The anneal used almost certainly sucked another share of carbon out of the steel. Heat treating, or the hardening part, also grabbed whatever carbon it could, and here many folks working with clay ignore the possible chemical complications to decarb that this foreign material applied to the steel could introduce at high temperatures, simple silica is not a problem at all but any number of carbon loving elements could be introduced to the mix.
 
So I should do something more like this, huh Kevin? You might recognize the response:

Milt, the ideas of overnight cooling all work fine with 1084, 1080 and other steels with less carbon, but will give you no end of troubles with a hypereutectoid steel like 1095, and is exactly why you found it less than pleasant trying to drill your holes. Heating to above critical (or even non-magnetic) and allowing the steel to slow cool is called a lamellar anneal and it forms coarse pearlite within the metal. This state is made up of extremely hard carbide segregated out into sheets between areas of soft iron, so such a blade will bend and seem soft but will rip drill bits up! No amount of reheating (tempering type) short of a full normalization will have any effect on these sheets. But of even more concern is that leaving hypereutectoid steel that is in solution to slow cool will allow all the carbon in excess of .8% to fill the grain boundaries and cause a very weak an brittle condition that would be rather bad for a knife.

Hypereutectoid steels, and forgive me for not explaining the term which simply means steel that has more carbon than the eutectoid or .8%, really should be spheroidized if you are going to be doing any machining with them. It is best done with well controlled heat treating equipment but it can be approximated in a simpler shop as well. To accomplish this with just a forge you should heat the steel up and normalize it well to homogenize things and get any carbide our of the grain boundaries that may be there. Next reheat it a couple of times at lower temperatures to refine the grain and on the last cycle heat it to just above non-magnet and then quench it in any oil you may have.

Now for the anneal- reheat the hardened blade to red but never allowing it to lose magnetism, do this several times and it will ball all that extra carbon that you trapped in the quench up into little spheres suspended in a soft iron matrix. The steel will be soft and bendable and when a drill or mill hits those little spheres they will just move out of the way and allow you to keep cutting
Click to expand...

mad0235.gif' alt='sick smileys' border='0'
 
Mike Krall said:
Page,

Would you tell me the mixture of sodium bisulfate to water you use, please? Do you warm it, boil it, leave it how long? And I don't get... "then hotscale off the mill scale."

Mike
Click to expand...

I use either a saturated solution or a saturated solution diluted to 50/50 depending on what seems to be addressing the problem at hand
by hot scaling I mean scaling off iron in a slightly oxidizing atmosphere at high forging temperature to stay ahead of decarb.
I leave a lot of scale behind, but my decarb layer is extremely thin and the metal moves FAST! (think fewer heats)


-Page
 
Well, I made a few changes... I did a stock removal blade from some of the 1/8'' HR1095. I used Kevin's spheroidizing procedure and it turned the steel to butter. Thanks Kevin!

I switched my quench to oil. Not sure about this yet. I need to get some faster oil. Right now I'm using motor oil/atf and I don't know that it's fast enough to give me a good quench. The hardening line did not follow the clay that well. That said, I did get some good definition. I may try some wilder patterns on the clay to see if I can get some more activity that way. Here is the result:

out of HT, cleaned up with some steel wool:

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And the finished product:

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I was going to mention that it looked like you had some banding on that first blade, but Kevin beat me to it. Banding can look cool, but after having Kevin point it out on a bowie that I shoed him a couple fo years ago at Blade and having the risks explained to me, I do the sphereoid anneal using HT foil and the 15 minute soak in the oven on every blade now. I have had nary a sign of banding, etc. on any of my W2 blades since I started doing this.
 
Hey now.. that looks better! Just a note atf is faster than motor oil. Of course something like parks #50 is better. One thing I would like to point out is, as you go through what went wrong with the first knife it may be a good idea to change one thing at a time and do some experimenting. I would think though that we have at least narowed down what went wrong with the first one.
 
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