Problems with precision Marshall steel, other sources

C

Cohutta

Joined
Feb 17, 2017
Messages
103
Has anyone else had issues with the A2 and O1 from them? On several occasions I’ve had A2 try to tear itself apart after a sub zero bath. Deep cracks running the length of the spine through the thickness of the materiel, not width. The finish on the precision ground leaves a lot to be desired as well.

The O1 just seems dirty. Using the exact same HT steps, one bar will come out of the quench as it should, mostly clean and a smooth dull grey, the next bar will be covered in scale with a funky speckled/textured look to the surface.

Before someone asks, yes I have a evenheat oven and I am preforming the same steps to prep for ht, same temps and soak times, and same oil temp etc.

Any help on a good source for those two steels would be much appreciated
 
I've seen high Mn. steels split as you described, if overheated....would suggest backing off 50deg, and re-trying.
The Precision Marshall O-1 I have is 12-15 yrs old. Descaled...not precision ground. Never had any split.
When you "cryo" , are you referring tp LN, or dry ice..?....quick or slow freezing..?
 
Russ Andrews said:
I've seen high Mn. steels split as you described, if overheated....would suggest backing off 50deg, and re-trying.
The Precision Marshall O-1 I have is 12-15 yrs old. Descaled...not precision ground. Never had any split.
When you "cryo" , are you referring tp LN, or dry ice..?....quick or slow freezing..?
Click to expand...

Sub zero meaning dry ice/alcohol after plate and air quench to room temperature. I don’t do this with the O1, just A2.

The O1 isn’t as much a problem as a complaint. It seems very inconsistent.
 
2PXtTpS.jpg

This is the cracking problem with A2. 3 out of 8 split down the thickness again. All made it through a full 2 hour temper at 450 with no issues. Cracks appeared after the second temper
 
Precision Marshall is an end processor and distributor. So they do things like surface grinding. They buy steel from someone else.
 
Larrin said:
Precision Marshall is an end processor and distributor. So they do things like surface grinding. They buy steel from someone else.
Click to expand...

Yes. Which leads back to my original question of another source. Seems most of the common suppliers carry steel that has been processed by them.
 
Cohutta said:
Yes. Which leads back to my original question of another source. Seems most of the common suppliers carry steel that has been processed by them.
Click to expand...
The Alpha Knife Supply website says their O1 and A2 come from an unnamed European mill with "very tight tolerances."
 
Niagara Specialty Metals has A-2 from Crucible and some old O-1 from Republic. (Very old)
 
Currently I'm testing/using O1 & A2 PG from SBSM (not NSM) also O1 from AKS and GFS (Ground Flat Stock from UK). Also have used A2 from AKS (not sure their source) before as well. So far, all test blades & coupons behave within range of normal (relative to my ht).

C Cohutta - from your A2 pic above, the center split might be due to dimensional stresses from combination of quench & temper. My interpretation: flat part of the blade was cooled way faster than the ground part, so martensite% increasing growth/transform from spine to edge. Incremental dimensional stress accumulating toward edge, thus lead to increase RA%. subzero+2nd temper convert big % of RA to mart = split center of edge lengthwise (pivoted by center area where split stopped).

If you are willing to try

*all ss foil wrapped

Coupon 1 (a full thickness piece of A2): full plate quench for 1 minute
Coupon 2 (a full thickness piece of A2): plate quench for 7 seconds, air cool (maybe for 10-15 minutes)
Blade 1 or coupon with primary ground similar dimension of the pre-ht ground blade: plate quench for 7 seconds, air cool (maybe for 10-15 minutes)

*all
remove ss foil
subzero
2x 450F temper

Break 3 samples. Looking for center split; cracks; grain size; fractured neutral axis (good brittleness indicator).

===
here are macros pic of my A2 (source from SBSM) chopper chopped (not batoned) 16D nail on hardwood backing
8dAu6c4.jpg
[/IMG]

O1, 8670, A8Mod bought from AKS
dM7jjVm.jpg
 
bluntcut said:
Currently I'm testing/using O1 & A2 PG from SBSM (not NSM) also O1 from AKS and GFS (Ground Flat Stock from UK). Also have used A2 from AKS (not sure their source) before as well. So far, all test blades & coupons behave within range of normal (relative to my ht).

C Cohutta - from your A2 pic above, the center split might be due to dimensional stresses from combination of quench & temper. My interpretation: flat part of the blade was cooled way faster than the ground part, so martensite% increasing growth/transform from spine to edge. Incremental dimensional stress accumulating toward edge, thus lead to increase RA%. subzero+2nd temper convert big % of RA to mart = split center of edge lengthwise (pivoted by center area where split stopped).

If you are willing to try

*all ss foil wrapped

Coupon 1 (a full thickness piece of A2): full plate quench for 1 minute
Coupon 2 (a full thickness piece of A2): plate quench for 7 seconds, air cool (maybe for 10-15 minutes)
Blade 1 or coupon with primary ground similar dimension of the pre-ht ground blade: plate quench for 7 seconds, air cool (maybe for 10-15 minutes)

*all
remove ss foil
subzero
2x 450F temper

Break 3 samples. Looking for center split; cracks; grain size; fractured neutral axis (good brittleness indicator).

===
here are macros pic of my A2 (source from SBSM) chopper chopped (not batoned) 16D nail on hardwood backing
8dAu6c4.jpg
[/IMG]

O1, 8670, A8Mod bought from AKS
dM7jjVm.jpg
Click to expand...
I will try to do some test samples as I get time.

As far as the stresses, that somewhat makes sense as the flats are in contact with the plates where the edge isn’t so naturally that will cool faster. But the blades from a while back that originally lead to this post were full thickness except a tiny 1/8” high 45 at the edge (scandi blades). They were cracked edge and spine nearly full length.

My heat treat is pretty standard for A2 and this has only become a problem over the last year or so and is sporadic. Ramp to 1425, equalize, ramp to 1775 for 25 min, plate quench, straight to sub zero after room temperature, temper when back to room temperature after sub zero
 
You can polish and etch the fractured surface - maybe that might provide clue whether material or ht defect.

Cohutta said:
I will try to do some test samples as I get time.

As far as the stresses, that somewhat makes sense as the flats are in contact with the plates where the edge isn’t so naturally that will cool faster. But the blades from a while back that originally lead to this post were full thickness except a tiny 1/8” high 45 at the edge (scandi blades). They were cracked edge and spine nearly full length.

My heat treat is pretty standard for A2 and this has only become a problem over the last year or so and is sporadic. Ramp to 1425, equalize, ramp to 1775 for 25 min, plate quench, straight to sub zero after room temperature, temper when back to room temperature after sub zero
Click to expand...
 
bluntcut said:
Currently I'm testing/using O1 & A2 PG from SBSM (not NSM) also O1 from AKS and GFS (Ground Flat Stock from UK). Also have used A2 from AKS (not sure their source) before as well. So far, all test blades & coupons behave within range of normal (relative to my ht).

C Cohutta - from your A2 pic above, the center split might be due to dimensional stresses from combination of quench & temper. My interpretation: flat part of the blade was cooled way faster than the ground part, so martensite% increasing growth/transform from spine to edge. Incremental dimensional stress accumulating toward edge, thus lead to increase RA%. subzero+2nd temper convert big % of RA to mart = split center of edge lengthwise (pivoted by center area where split stopped).

If you are willing to try

*all ss foil wrapped

Coupon 1 (a full thickness piece of A2): full plate quench for 1 minute
Coupon 2 (a full thickness piece of A2): plate quench for 7 seconds, air cool (maybe for 10-15 minutes)
Blade 1 or coupon with primary ground similar dimension of the pre-ht ground blade: plate quench for 7 seconds, air cool (maybe for 10-15 minutes)

*all
remove ss foil
subzero
2x 450F temper

Break 3 samples. Looking for center split; cracks; grain size; fractured neutral axis (good brittleness indicator).

===
here are macros pic of my A2 (source from SBSM) chopper chopped (not batoned) 16D nail on hardwood backing
8dAu6c4.jpg
[/IMG]

O1, 8670, A8Mod bought from AKS
dM7jjVm.jpg
Click to expand...

I apologize for going off topic, but between A8mod and 8670, wish one is the toughest, in your tests?
 
A8mod 60rc edge exhibited micro ductile but macro brittleness = poor overall toughness. Since result doesn't fall inline with a8mod tough reputation, hence keep in mind my test result is sample of 1.

8670 63rc is much tougher.

Both of these blades heat treated using standard/public protocol ... more details

hugofeynman said:
I apologize for going off topic, but between A8mod and 8670, wish one is the toughest, in your tests?
Click to expand...
 
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