Sub zero quench issue.

Status
Not open for further replies.
waterstoneblades

waterstoneblades

Joined
Sep 17, 2013
Messages
551
I've been using the sub-zero quench method for a little while on stainless and tool steels. I can get the blades straight after the plate or air quench. I checked the blades before I put them in the dry ice acetone bath. I poured the acetone over the blades until covered and then added the dry ice slowly and evenly to gradually drop the temperature. I keep them in the mixture for about two hours and some of the blades were warped. I was able to correct them in the tempering process but I thought I would ask if anyone experienced this. I was thinking of a snap temper before sub-zero quenching but some steels are recommended right after the quench ? Any feedback would be appreciated!
 
Not sure if this is the reason or not, but I usually prep the acetone/dry ice slurry before dunking the blade in, so that I can make sure I put the blade in tip-down and evenly expose both sides of the blade to the same temperature slurry.
 
Thanks ted! I've tried the putting the blades into the pre-cooled slurry and had the same issues. I haven't put the blades nose down though, I'll try that next time! Thanks
 
Same here, I mix the slurry while the blades are in the soak at austenitization. It is fully cold when I place in the blades. I suspect you haven't really relieved the warp stress fully in straightening.
I would ask myself why you have warpage if using quench plates????
 
Stacy, the blades that warped in plates had some distal taper and the points were off center as a result. I also use air-stream quench in front of a fan. The tips cooled first and pulled as well as the handle area that was drilled out. When the blades went black , I quickly straightened them before they set up. They were room temperature and straight before the sub-zero quench and came out warped??
 
bladsmth said:
Same here, I mix the slurry while the blades are in the soak at austenitization. It is fully cold when I place in the blades. I suspect you haven't really relieved the warp stress fully in straightening.
I would ask myself why you have warpage if using quench plates????
Click to expand...

Stacy, would you mind explaining how to relieve warp stresses before the blade converts over to martensite?
 
What you did is the normal method. Straighten between 900F and 400F if possible. If not possible, wait until after the second temper.

What I usually do, unless the warp is major, is wait until after temper.
Another tip is to slightly overcorrect the warp, and then bring it back a tad to center. If there was a 1/8" left curve, I would correct it until it was 1/16" curved to the right. Then bring that back to center. You will notice that the second movement is much easier than the first, because there is usually still residual stress from the warp.

When taking out of the oven at 1950F, I immediately place the foil packet in the plates and clamp. I have occasionally had the tip walk off center, but rarely have a whole blade warp. I bring the tip back after tempering in most cases. Same for twist.

Since I send 95% of the stainless blades out now days, and most are ground post HT, the warp issue is moot for me.
 
Stress relieve at 1200F for 2 hours ,straighten if necessary .Then HT. Quench must always be edge or point down , agitate edge to spine . Quenching on the side will warp !
To correct warp after HT, heat to at least 400 F.
 
There are stainless and high alloy tool steel blades...no liquid quench.....just quench plates.

The 1400F step in the HT is to stress relieve them a bit before austenitization. After sitting at 1950F for 30 minutes, the stresses should be pretty much gone.
 
Last edited:
I preheated to 1400f soak for 5 min then ramped to 1955f. Soak at temperature for 30 min then quench. Air stream quench and checked blades for straightness when fully black. I corrected before blades set. .I think my problem is how the blades were placed in the dry ice acetone . Thanks mete I will try your method.
 
Rick, the extra 2 hour stress relief is not necessary if following the pre-heat temperatures and soak times IMO. My issue with warpage was pointed out by mete with the blade positioning into the sub-zero quench and I'm confident that will be resolve it.Stress Relieving
Annealed Parts: Heat to 1100-1300°F (595-705°C), hold 2
hours, then furnace cool or cool in still air.
 
Last edited:
Status
Not open for further replies.
Back
Top