W2 blades keep cracking in water quench

[Bao nguyen]

I’ve run into a serious issue with water quenching my recent tantos, and I’m hoping to get some insight.
I’ve always water quenched and gotten beautiful hamons without problems but in my last four blades, every single one cracked.
Just about 10 minutes ago I quenched another, and it was the worst yet, there are hagire cracks spaced almost every 3/4" along the blade.
I believe i do everything perfectly but I did switch to a larger water container (a fish tank) and new supplier.
I’m starting to think either of those might be the cause or maybe something else entirely.
Before I waste more steel, I’ll list my full process and some potential causes I’m considering.
I’d really appreciate any feedback or advice.


My process:
1. forge or do a stock removal blade, I either leave a fresh finish with a file or a worn 60 grit belt finish so the clay sticks to the blade better
2. normalize then regrind
3.make sure that the entire edge is at least 1.5mm thick (to reduce fractures)
4. apply clay to the blade
5. heat the blade, until the steel is a little more than 1500 deg f making sure its equal throughout the whole blade (or atleast the visible parts excluding the tang)
6. immediately quench in water and hold for 5 seconds then out of the water for 5 seconds, then back into the water until its cooled completely
7. then i run to the oven where its already heated to 400 degrees f and do two 2 hour cycles with a room temp cool down in between


Possible problems:
1. ive switched to a 55 gallon fish tank coming from an old wooden troff, the fishtank is massive and may be why im experiencing problems.
2. i dont preheat the water which ive seen some smiths do but ive never had to in the past
3. i dont clay the entire blade first with a thin layer of clay.
4. i used to get my steel from old pueblo forge but for the past projects ive switched to NJSB so maybe the steel is better in different conditions.

thanks for any advice or considerations

 

[DevinT]

>1500 degrees is too hot.

You should be in the 1425- 1450 range.

You might need to anneal it also.

Normalize + >1500 is not good.

Hoss

 

[Alex Topfer]

Where are the cracks starting? On the edge or spine where there's a rough texture, or at the hamon? I've had them split at stress risers on rough edges, but also along the hamon
Also how are you heating the blade?

Depending where you are ambient temp could vary significantly, so you may want to look into preheating just to control that. My quench trashcan can be between ~8c and ~35c

 

[Bao nguyen]

Where are the cracks starting? On the edge or spine where there's a rough texture, or at the hamon? I've had them split at stress risers on rough edges, but also along the hamon
Also how are you heating the blade?

Depending where you are ambient temp could vary significantly, so you may want to look into preheating just to control that. My quench trashcan can be between ~8c and ~35c

theres a rough texture throughout the whole blade before i apply the clay so it adheres better and doesnt fall of during the heating, the cracks are only below the Hamon on directly on it (below the white line)

what temp should i preheat the water to?

 

[Alex Topfer]

Warm enough to be consistent. Hotter water is slower
Try smoothing out and rounding over the edge a bit. Also try doing it a little cooler if you can, as Devin suggested

 

[Stacy E. Apelt - Bladesmith]

You didn't tell us what size and type of blades you are quenching. That makes a difference.

Several red flags pop up for me:
1) The water bath should be brine. 7-10% is the normal range for the salt. While everyone calls it a "Water Quench" it is actually is brine.
2) The quench bath should be warmed to 100-120°F/50°C. This matters more than most folks think.
3) The surface is far too rough. A file groove or 60 grit groove can easily be a stress riser point the propagates a crack. I would suggest you go to 120 grit for the whole blade and the edge at 220 grit. This is the biggest red flag I see.
3) A water/brine quench should be at the lower end of the austenitization range. For W2, I suggest you heat the blade to 1425-1450°F/775-785°C. You only want the carbon in solution, not the carbides.
4) 5-seconds-IN, 5-seconds-OUT, 5-seconds IN is probably OK, but I do it in 3-seconds dips ... Quench -1-2-3-OUT1-2-3-IN-1-2-3-OUT Hold in still air till room temp and immediately temper.
5) I don't think that running to the tempering oven is part of your cracking problem, but the steel needs to drop below 100°F/38°C before temper. The conversion to martensite has not finished until then and the hamon may be affected as well as edge hardness. Also, cool to room temp in running water between tempers. You want the steel below 100°F/38°C before the second temper.

I doubt the tank size is the cause. How small was your old trough?
Having more thermal mass, the fish tank may be showing where the above inefficiencies are by faster cooling rates. Normally, the bigger the quench tank the better the quench.
As a rule, a proper tank should have at least 4" to 6" of quenchant in all directions from the blade. That means a round tank minimum would be 8" to 10" wide and 8" to 10" deeper than the blade is long.

Is this batch of steel te same as the previous blades. W2 is a general category. The amount of manganese and other alloys may be different.

All that said - in dong water/brine quenches there is always a high risk of cracked blades.

 

[Taz]

I would make sure to do a DET anneal or thermocycling after normalizing? Normalizing will grow the grain and a brine quench at a higher temp could lead to issues. You say normalize and regrind, not sure what that means?

 

[Stacy E. Apelt - Bladesmith]

Thanks , Taz. I didn't go too deep in the conditioning of the steel. You are absolutely correct that a water/brine quench blade needs the best structure before quench. I have pretty much stopped doing normalizing except for a quick one in the forge at the end of a days forging. a DET will restore all the properties needed prior to HT.

 

[Stuart Davenport Knives]

NJSB W2 is it's own animal. Last I heard if doing stock removal, 1900°F normalizing was necessary because it came so coarsely spheroidized from the mill. Not sure if that's still the case. If forging, no need for such a high normalizing heat, 1650°F will work after forging. I would do a cycle at 1500°F after normalizing, and then the DET anneal. Hardening temp should be 1450°F-1475°F.

For brine quench, I would make sure that the blade has at least a 220 finish, scratch pattern running lengthwise (tang to tip, never edge to spine). Leave meat on the edge, 1mm is fine, and round off the shoulders of that edge.

 

[Daniel Fairly Knives]

All of the above and it is good to add slip too. Water down some clay to nearly water thin and cover everything with that.