440C Problem/Question

D

dkemppai

Joined
Jun 13, 2008
Messages
11
Hi all,

I've been working on a blade made from 440C (First blade with 440C). I believe the MFR is Crucible (I am waiting for the supplier get back to me on that...)

Anyway, Heat treat was in foil, plate quench, tempered twice.

When I started grinding to 220 grit, I noticed the surface finish wasn't what I expected. Progressively finer grits showed a light 'frosting' of the blade. Eventually I worked down to 9 micron belt, and the finished appeared to be very small pits in the steel (Visible to the eye).

A quick check under a microscope, and lot a minute pits were immediately visible. They are on the order of .001 to .002 inches in dia, and spaced approximately .003 to .005 inches.

Now start the questions:

Is this normal for 440C?
Is it possible it is not normal, but caused by heat treat?
Could this just be an ‘off' of bad batch of 440C?

Any ideas?

Thanks!
Dan
 
Is this on the handle / ricasso area or on the primary grinds.

It is a common error to not adequately grind the mill scale off of mill finish stock.

If it is also happening in deep ground areas such as your primary bevels, then the problem lies elsewhere.

I have had complaints that mill finish is tough to get through. I have had no complaints about subsurface pitting or inclusions in Crucible steels.

What was your heat treat formula?

Rob!
 
Rob! said:
Is this on the handle / ricasso area or on the primary grinds.

It is a common error to not adequately grind the mill scale off of mill finish stock.

If it is also happening in deep ground areas such as your primary bevels, then the problem lies elsewhere.

I have had complaints that mill finish is tough to get through. I have had no complaints about subsurface pitting or inclusions in Crucible steels.

What was your heat treat formula?

Rob!
Click to expand...

Rob,

It's on the entire blade. Everywhere. It does look like mill scale, but it's all the way to the center of the stock, and much smaller pits. (I check very closely to ensure mill scale/finish is removed...)

I did notice it start become apparent before heat treat with a P220 belt. I didn't think much of if then. I took about .015 off of each side after heat treat, and it's still there. At this point there's no metal left to remove! It's well below the original surface of the sheet. It's Down to at least +-.009 from the center of a .152 inch sheet (Final grind on edge .018 right now!).

Just checked the log, and the heat treat was 1850F for 20 min, plate quench, and tempered for 2 hours 2 times at (Edit: was at 220 F, was tired last night, and typo'd 200F!). Kept the blade at approximately 140 to 150 between quench and first temper...

The previous knife was a CPM-154, and I saw similar issues, although much fewer of them (About 1 every 1.5 inches). Put a mirror finish on that one, and wanted to do the same to the 440C blade. The mirror finish brings them out the the point that I just see them when I'm looking for them. Only then when I look hard.

Tried to buff it down with green chrome, and it looks like mud! The chrome is extra agressive on the pits, and turns the thing to junk. Might have to finish this one with a scotch brite belt and call it good...

Loosing this knife isn't really an issue. What I after is an understanding of cause this issue so I can avoid it in the future.


Thanks!
Dan

How do I attach an image? I have one at about 75x...
 
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You can sign up for a free photobucket account (google it) and post the IMG code from there, or if you like, email it to me and I'll post it up.

--nathan
 
You have to go down to 'manage attachments' on the reply.

to post a photo.
200 F is not a temper !! Have you checked your temperatures ? You should be at 1850-1950 F to harden and a temper at about 375 F. Make sure your temperature is correct then get up to 1875 F and increase your time to 30 minutes.
 
Hmm,kinda odd. i had a real funky suface fnish on some 440c i used a while back,but this was only on the flats..,and stood out th higher grit i went!! no pits thogh just....this....

grain.jpg
 
LOts of flags here I think. 1850 is acceptable for 440C but at the low end and doesn't leave any room for oven temp variations or error. I use 1875 for 30-45 mintes depending on thickness. Plate quenching is great. I know the Crucible spec sheet shows 212F as the first temper level, but I think thats asking too much hardness of this steel. 325 should give you about RHC58 or 59+ with cryo.

My other concern is that you got some of this with CPM154 also. Is it possible that there is something corrosive or reactive in the air around your blades? That is just weird! Following this thread with interest.

Rob!
 
At this moment the Crucible 440C data is being revised ! Have they figured that 212 F doesn't temper ???
 
mete said:
At this moment the Crucible 440C data is being revised ! Have they figured that 212 F doesn't temper ???
Click to expand...

;) Yup.

It's been under revision for many years. I wonder why Crucible has so much problem with spec sheets?

It would be nice if they'd bring all of these into the 21st century by including things like plate quenching, revising older data sheets like 440C, and actually producing sheets on new products like CPM154 (I mean more than a copy of the 154CM sheet).

Rob!
 
Setting up a photobucket account now...I'm on dialup.

Note, Temper was at 220F. I typo'd 200F last night...

The Oven should be pretty close. But, I'll grab the thermocouple calibrator from work and check the TC cal on my controller... ...will re-cal if necesary.

Been thinking about using a TC Meter and spot welding TC leads to blade, maybe I'll try it next time....

As for the heat treat. I found it here. I checked a few other places, but couldn't manage to find much good informaton. The temper seemed a little low but this was the only 440C I had, and I was just trying to figure out if I liked working the steel or not...

Here's an image about 35x. Note, graduations on the ruler are 1/100th of an inch.

Thanks!
-Dan

This was reground with 800 grit, so scratches are a little larger in this pic...

440Cproblem-Smaller.jpg
 
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Some info at www.440c.com The picture to me indicates [unless the griding is don e with old belts ] that the matrix is soft .Higher temperature and/or soak time is not right. Soak time starts when the blade is at temperature .
 
mete said:
Some info at www.440c.com The picture to me indicates [unless the griding is don e with old belts ] that the matrix is soft .Higher temperature and/or soak time is not right. Soak time starts when the blade is at temperature .
Click to expand...


Grind was done with new belts. Soak time started after it hit 1850F.
The oven typically overshoots a few degrees (<5), then seems to be stable to within -3 to +2 degrees F. I'll check out that site, and see what I can find. Thanks!

I did a quick sharpening with a 15 micron polishing film, and then looked at it under the microscope. Maybe they are harder chunks in a softer matrix, but isn't that what the carbides are supposed be in steel? Just at a smaller scale.


I'm going to see how it holds an edge. Other than that, I wonder if it would be worth throwing the thing as is back into the furnace for a higher temp/longer soak, and seeing what happens?

-Dan

P.S. Oddly enough, I was just reading a post about how a guy would be trying to finish a grind, and his wife would be saying it was time to go to the hospital to deliver a baby... ...Um, I have to go now... ;) Depending on what happens, I may or may not be able to check back in the next day or two...


(Note dark chunks on the blade edge dirt...)
http://i280.photobucket.com/albums/kk193/dkemppai/440CProblem-Edge1.jpg
 
Wifey had a false alarm... ...no new baby tonight. 9 hours of contractions later, and she's really disappointed it's not here yet.

Anyway, back to the knife.

Put an edge on it, and I've been beating up on it for a while now. It seems to hold an edge, hair popping sharp. Nothing to complain about in that department. I've spent the last hour chopping wood, cutting wood, cutting paper, cutting cardboard. Everything seems to be fine. Will still cut hair after all of that (Not extremely well, but acceptably). For a stainless steel, No complaints.

Stabbed the tip into a pine 2x4, over half inch deep many times and bent it over sideways. Tore a large splinters of wood out, and the tip of the blade wouldn't bend or break. So, I think the heat treatment is OK.

Just for kicks, I blocked the knife up, and under a microscope pushed an exacto blade edge into this knife edge. The exacto blade chipped, bent, and literally was cut by the 440C. (A small wire would roll off the exacto in a little spiral). I couldn't get the 440C blade to chip, so it's not brittle. Only the very fine edge would deform, even then only slightly (So, it's not too soft...)

Weird... ...Maybe it's just this steel. I guess it could be carbides large enough to be visible... Or alloy distribution a little weird... Anyway, I'll have to think on this one some more.

Keep the input coming! I sure appreciate it!

Thanks!
Dan
 
Did a little more research and found out that 440C will normally produce chromium carbides the same size and spacing as I'm seeing on this knife. I did a little FeCl3 etch, and found that these spots are most likely carbides.

Turns out that 440C cannot be brought to a mirror finish after all.

Anyway, thanks for all the ideas!

-Dan
 
dkemppai said:
.......Turns out that 440C cannot be brought to a mirror finish after all.
....
Click to expand...

440C is one of the most readily mirror polished steels because of the excess chromium. There have been hundreds of thousands of beautifully mirror-polished 440C blades made over the years.

So, while I don't know exactly what you're problem is here, I can assure you it is not a generalized characteristic of the alloy.
 
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