Let’s see if addressing this step by step may be able to clear up some of the questions both here and in other posts within this thread.
My Observations: Very cloudy and splotchy etch on 1084. Possible bad heat treat?
First let’s establish the expected outcome in order to ascertain our goals and how the current outcome is falling short of that. Is that a blade that is intended to have a decorative hardening line of sorts, and is the purpose of the etch to reveal that feature?
Assuming that is the case we will address the following:
1. Blade was forged, then normalized three times at reduced temps (by eye)
If you are following this up with full controlled normalization one cycle to get started is more than enough. The fewer times a blade sees heat, under uncontrolled (atmosphere and temperature) circumstances, the better; i.e. less opportunity for something bad to happen.
I would seriously consider swapping steps 2. and 3. There is no need for a full normalization after simple grinding operations and normalizing, particularly with soaks, can be a very decarburizing operation. Grinding afterwards would allow you to remove decarb. If a post grinding heat treatment is indicated I would go with a simple stress relieving cycle of heating to 1200F and then air cooling.
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
First, if the kiln is home built double check the calibration, if you have not yet done so, to assure that the heating is even and accurate throughout. This is 1084 so you will have full solution at the lowest possible temperature and time of any steel common blademaking steel. A soak is beneficial to almost any steel but for 1084 it is not critical, I don’t think 10 minutes is too much at all considering time also needed for blade to fully assume temp. 1600F is a very good true normalizing temperature, the idea of which is to even out all internal components of the steel. Steels with carbon content greater than .85% benefit from the dissolving of the extra carbon and distributing it evenly throughout, but beware of slow cooling which will allow it to pool back up, so no slower than still air. 1084 will have little in the way of leftover carbon to deal with so it will quickly be dealt with at this temp and the grain size may very well increase, but that may even be a good thing on this first heat in order to homogenize it. Even grain size is of even more benefit than the size itself.
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
Very good second thermal cycle to reduce grain size, it could even be followed with a third at 1450F. but be aware that the finer the grain size the shallower hardening the steel will be, thus moving your hardening line closer to the edge.
A note about soak times and grain growth:
Time equals temperature but not proportionally, temp always trumps time. The lower you go in temperature the longer your soaks can be. Almost all modern steels are what could be termed “fine grained” due to aluminum killing procedures, thus they will resist grain growth through most of the normal heat treating temperatures, almost regardless of time, but once the grain coarsening temperature is exceeded growth will be VERY rapid. Thus you can go from ASTM size 9 to ASTM size 3 in one heat if that heat is out of control. If, however your heat is tightly controlled and held under that given coarsening temperature the grains can be stable even in hours of soak times (this is especially true if you have an alloy steel). This is due to aluminum nitride particles contributing to grain boundary stabilization even beyond what carbide contributes. I am confident that upwards of 90% of all grain growth episodes that bladesmiths tell horror stories about were solely a matter of loss of temperature control, even if only for an instant.
5. Reinsert blade into 1499 oven, allow to come to temp, and hold for 5 minutes
If your goal is a hardening line, a temperature between 1450F and 1475F will give you more definition. Do be aware that as temp drops soak times can increase.
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)
3 seconds is way too short a count, you are flirting with upper bainite there, and even if you feel knives are for beating on things rather than cutting, lower bainite would be better, the upper feathery stuff sucks for just about everything. I am surprised you are not flashing the oil at that temp. There is no need to return to the oil if you get as close to Ms as possible, and the lower temp will be safer. If you have clay on the blade you will want a 10 count or better. If the blade is bare, a seven count will get you to just at the top of Ms and then you will be approximating a marquench, if that is your goal.
6. Clean off oil, put blade between straightening jig during 425 temper. First temper was one hour, second temper was 2 hours
What size blade is this? For a small cutter you could start out at 400F instead, for a larger chopper, go for it. Be aware the higher tempering temps will somewhat fade really vibrant hardening lines.
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.
For hardening lines FeCl is not the ideal etchant, if you nail the process the lines should pop all on their own without the need for etching, but something like apple cider vinegar will work better. The idea is to have a very weak etchant that will take a long time to attack the microstructures at the top of the line differentially, more aggressive reagents tend to attack more evenly.
Possible Solution: Should I raise the temp on my oven incase 1499 isn't really 1499? Should I let the blade soak longer?
Possibly longer but first let’s examine the answer to the next question more…
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. Sorry I didn't get pictures, I know that would have helped. Any ideas or suggestions?
Without pictures it is very hard to say, but what you describe sound a lot like decarb. I have found several areas in you procedures that would result in decarb and allow it to survive to the etch. You don’t need more and a few microns of decarb to throw the etch off. Splotches and light “freckles” are classic decarb descriptions. Try to move all of your normalizing to before the grind so that you are removing any decarb it causes, and then watch your atmospheres during your hardening, especially with extended soaks in a kiln. Anti-scale compounds or foil envelopes will help.
Do not confuse scale with decarb, they are two different things but do result from many of the same factors. If you helps, I would be willing to say that most makers would see the same splotches if they dipped all of their blades in FeCl , decarb is very perniciously ubiquitous.
A final note:
Since an etch will show what's happening inside the blade, I think this is more of a heat treat issue than poor etch.
This is a very erroneous concept that unfortunately is perpetuated in places like knife magazines, by folks who want you to think they have a clue about what goes on inside of the steel but most often reveal that they don't. To actually know what is going on inside the blade requires a bit more processing than a dip in FeCl for the entire blade. Logic would dictate that in order to see inside the blade you need to actually reveal the inside of the blade. This is done by proper cross sectioning and the use of special reagents (none of which resemble FeCl) designed specifically to reveal particular microstructures. As you are experiencing, the slightest issue on the outside of the blade will throw a wrench in the concept of seeing into the blade from the outside. You may get an idea of zones of hardness or different microstructures in a very general way, but actual hardness, grain size or exact microstructure are not revealed by the FeCl etch despite all the deceptive marketing claiming otherwise, and a little decarb will rob you even of that.