Blotchy Etch in 1084 (With Pics)

J

jawilder

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Jun 27, 2006
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My Observations: Very cloudy and splotchy etch on 1084. Possible bad heat treat?

My Process:
Last night I heat treated a fairly thin (too thin) 2" wide 1084 blade with the following process:
1. Blade was forged, then normalized three times at reduced temps (by eye)
2. Profiled and beveled
3. Heat home built kiln to 1200 and hold for 20 minutes, then ramp to 1600
a. Insert blade, wait for temp to come back to 1600 and hold for 10 minutes.​
b. Remove blade and cool in still air until black​
4. Ramp oven to 1499
a. Insert blade, wait for temp to come back to 1500 and hold for 10 minutes​
b. Remove blade and cool in still air until black​
5. Reinsert blade into 1499 oven, allow to come to temp, and hold for 5 minutes
a. Remove blade and quench in P50 for 3 seconds, remove to inspect, then back in oil until cool (Blade was moved up and down to agitate oil)​
b. I first noticed a very uneven color on the blade. Very cloudy, but i wasn't too concerned.​
6. Clean off oil, put blade between straightening jig during 425 temper. First temper was one hour, second temper was 2 hours
7. Grind blade to 400 grit, wash blade, and etch in FCL
a. After a quick etch I noticed that the areas that were previously hazy were still that way after etch (see 5b)​
b. After a longer 5 minute etch I noticed more of the blade was turning dark but the spots were still there​

This isn't the first time I've had this problem. It pretty much happens with every blade I heat treat and am wondering if it is common or if my process or even equipment is off somewhere.

Possible Solution: Should I raise the temp on my oven incase 1499 isn't really 1499? Should I let the blade soak longer?

The splotchy area is in the middle of the blade. It etches much lighter than the spine or edge. Does that mean that it didn't get as hard as the spine/edge?

Aside from the large lighter area after etch, there are also spots in the etch. It looks a bit freckled.
Any ideas or suggestions?

Here are 1000 words:
20120926_104447.jpg


20120926_104515.jpg
 
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decarb

you have spent a lot of time hot. FeCl responds to hardened carbon steel, if the carbon has diffused from the steel the FeCl doesn't etch the same. My guess is that you have areas where you haven't gotten below your decarb layer with your grinding. You can reduce but not eliminate the decarb in your kiln by putting a chunk of lump charcoal in the kiln to generate a reducing atmosphere (convert free oxygen to carbon monoxide don't do this in a poorly ventilated area since as soon as you open your kiln you will let out a puff of carbon monoxide) my guess is that if you grind more you will get under it

-Page
 
Page, I hope that's all it is, but let me tell you the rest of the story.

I have been working on 3/32 O1 kitchen knives before this and HT the 8" Chef blades with only a profile. No grinding. After I grind them down (of course keeping them cool) and etching, I notice the same thing happening. Surely, there wouldn't be any decarb left on the blade after grinding a 3/32 blade down to .007

I like the idea of charcoal. Thanks for the tip but not sure decarb is the problem here.
 
I'm not sure why you're going through all these steps with 1084 since it's one of the most simple heat treat steels out there. After doing a good normalizing process, heat the steel to 1475 and then quench in oil at 130deg. Pick your favorite quench oil, don't worry about soak times, just get to the right temp and quench. The reason for hazy transition lines may be the steel itself. Aldo's improved 1084 is a great blade steel, but the transition lines will not show up as distinct and crisp as older 1084.
 
I'm with Rick on this. Don't worry about soaking 1084. Normalize at 1600F, 1500F and quench at 1475F. 1084 doesn't need added encouragment, it's superior eutectoid properties take care of itself.:thumbup:

Are the blotchy areas coming up in the same pattern?
What is your prep prior to the etch(do you wipe the blade with anything after degreasing?)
 
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Could it be a chemical contaminant in either your cleaning process or the quenchant or the etchant itself? It seems odd that would happen the same way with two different steels and two different grinding styles. I'm just thinking out loud.
 
Are you doing multiple short etches and rubbing the oxides off in between? One dip can be splotchy.

I'm with the others here. Too much time at high temps!
 
To clean the blade I use dawn and kitchen sponge (don't tell the wife) and just rinse under tap water without drying.

The time and temps came from K. Cashen but I can drop the 10 minute soak. How long do you wait to pull the blade after the oven comes back to temp? I just ordered some tempisticks to verify my oven temps.

I just took more steel off tonight and am wondering if page is right on decarb. I'll etch again tomorrow and try to take pics of the results.
 
I had a prob etching a 1084 Damascus blade recently my self. I dipped it and pulled it out at 5 min to see what kind of pattern I was getting and there was a large spot on both sides of the blade that didn't etch. I pulled it out cleaned it off and hand sanded the areas that didn't etch, then cleaned with dawn and water. I heated the blade up by running hot water on it right out of the sink and immediately re dipped it. Etched just fine after that. So I'd say maybe you havnt gotten past your carb scale possibly to long at to high a temp as contributing factor as well.
 
jawilder said:
I just ordered some tempisticks to verify my oven temps.
Click to expand...
Make sure you are using them correctly. Tempilstiks are not made to verify cavity temperatures and pulling steel out of the kiln to check is not very accurate. I ran a long experiment on kiln temperature spiking and had to get creative. The best way I found was to cut a few small tabs from several T-stiks and place them in an enclosed "box" of steel or refractory to shield from radiant heat. Then you can set a temperature, run a cycle and see which tabs melted.

BUT.... even then, you are testing in 50F increments. My suggestion is to purchase a second thermocouple and install it into your kiln. I bought an analog with a probe for $30 online.
 
In my experience, unhardened or not-fully hardened spots in a blade will usually show the same (or similar) pattern on both sides of the blade. Decarb will usually create a unique pattern on each side.
This might help you pin down the problem.
I have quenched a few 1084 blades recently in Parks AAA and it hits a nice hardness in thin areas but thicker sections do not harden fully, this is not a huge surprise considering that the AAA really isn't fast enough for this steel but if you're getting this kind of activity using P50 then there is something else at work in your case.
 
OK, looks like I was wrong and Page was right. I'm now thinking decarb after hand sanding and noticing that many of the areas have gone away.

Here are 1000 words:
20120926_104447.jpg


20120926_104515.jpg


But that still wouldn't explain why it happens on my O1 kitchen knives
 
O-1 will have de-carb with the best of them. Because O-1 requires slightly higher temps and longer soaks than say, 1084, de-carb can tend to be a problem at times. (especially if you grind too thin pre-heat treat.) My best experiences with O-1 come from leaving things a tad bit thick, then handling the de-carb during post H/T grinding/sanding.
 
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Like Ken Andersen said

"It is like burnt toast and you have to get down to the good part"

:)
 
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