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Something we all may not see every day


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During my last time I got to do some forging, I took a bunch of PW cut offs I had and forged them out into blade blanks. Over the winter I have been slowly finishing them. The latest one has presented a conundrum / question; do I continue with it? Heat treated yesterday afternoon and tempered once last night. This morning I took a look at it and saw there was a slight bend at the tip of the tang. It had been tempered once so I figured I'd just try bending it out in the vise. Nope. Snapped right off. Guess I need to temper a bit more.

 

But this was fortuitous? Found there is a weld flaw running right down the middle of the tang (and probably the whole knife)! So I went to my wife's stereo-microscope and got some pictures.

 

This was from an OLD billet I had laying around from about 5 years ago when I was using coal and first learning pattern welding. Not too fussed about loosing this knife but there are some lessons learned.

 

First, my heat treat is pretty spot on. Billet is 80CrV2 and 15N20. A couple of years ago I had tested this process and it had looked good. Nice to know I'm still getting it right.

Second, shows the importance of cleaning the mating surfaces before each round of welding. This billet I remember I was doing on the last day of class and I was rushing. Haste makes waste was never truer.

Last, it's some cool pictures (at least I think so) that most of us will never get to see (cause face it, how many of us have a stereo microscope with camera?)

 

The standard pic we can all get with the cell phone.

1_Cell Phone_IMG_2369.jpg

 

6.5 X.  Weld flaw clearly visible.

2_6.4X_ts_18_1.jpg

 

10 X

3_10x_ts_19_1.jpg

 

20X

4_20X_ts_20_1.jpg

 

30x. Looks like I trapped some flux (the black bright shiny stuff on the right) in the weld

5_30x_ts_21_1.jpg

 

40x

6_40x_ts_22_1.jpg

 

50x

7-50x_ts_23_1.jpg

 

50x without that nasty weld flaw.

8_50x just grain_ts_24_1.jpg

 

20x corner shot to see the flaw going right down the middle.

9_weld flaw corner 30x_ts_31_1.jpg

 

 

 

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Thanks for sharing this! I'm so new to this I haven't even fired up my forge yet, but truly enjoying the education I'm receiving through posts like this until spring. The ability to actually alter the structure of steel is fascinating to me, and I'm slowly learning how to work it to your advantage. Thx again for posting....does this mean I can send my 1st project to you for microscopic constructive criticism lol?

 

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8 hours ago, Alan Longmire said:

Cool shots, Bill!  

Too bad it's of something so undesirable. The good news is I snapped a little bit more off the tang and the weld flaw is gone. Looks like it may have only been at the tail of the tang!. Have a much shorter tang now but I think it will still work.

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It is an unfortunate thing that some of the coolest looking things are because something went wrong.  Stainless steel that leaks out of a broken mold can look amazing, like a piece of modern art; but in the foundry it looks like a production loss that is quite expensive.  Same with this weld flaw.  Unfortunate for the blade maker, but cool to look at none-the-less.  

 

Also, the scope I have on my desk at work doesn't get pictures that clean.  Very nice.  

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1 hour ago, Jerrod Miller said:

amazing, like a piece of modern art; but in the foundry it looks like a production loss


Have you tried auctioning them off? :D

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23 minutes ago, Charles dP said:

Have you tried auctioning them off? :D

It was suggested several times!  I have even seen it hanging on a lobby wall in a couple foundries.  It is kind of an in-joke with those that pour stainless.  Everyone knows it happens and that it can look quite cool.  It is often just too much of a mess to deal with.  It is usually a horribly awkward size/shape, with lots of sharp poky bits.  We never have that issue at the foundry I work at now.  Nope.  Never.  :ph34r:

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8 hours ago, Jerrod Miller said:

Also, the scope I have on my desk at work doesn't get pictures that clean.  Very nice.  

Thanks Jerrod. I was hoping you would chime in. Is there a way to get better pictures of grain? I remember seeing something about polishing and etching but I don't know if that would work at only 50X.

 

Also, (shameless question) what is your opinion on the size of grain in this piece. Looks good to me but I'm still learning. Thanks for any thoughts on the matter.

 

Yeah, I spent a lot of money when I bought the set up for my wife. She studies spiders and can count the hairs on the leg of a spider that is smaller than a pinhead. The fact I get to take cool pictures didn't have anything to do with the choice I made in the system :ph34r:.

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Generally speaking, for the grain sizes we want I would be inclined to put it on the metallographic microscope with 100X objective and 15X eye-piece (1500X total magnification).  To prep for that there would be lots of polishing down to a felt wheel with a 0.5 micron or smaller diamond powder slurry, then etch with 2-7% nitric acid in ethanol (aka: Nital).  It will look something like this (this is a look at a case hardened part):

image.png

 

Note the scale bar.  So really, a bit less magnification would be fine.  This is about what you need to measure the grain size for an actual classification.  For determining if you have your heat treat dialed in though, there is no need for any micro or macroscope.  As long as it looks pretty silky smooth, you're golden.  Ideally you shouldn't be able to make out individual grains with the naked eye.  Below are images of some super silky smooth tool steel fracture surface.  Same spot, different magnifications.  There is 10X, 50X, 150X, and 200X.  These were taken this morning with my desktop camera, just for you guys!  The sample is one I keep on my desk as a pretty sample (it took a LOT to break this part, even after it was pre-cracked in HT.  

 

10X (this camera is really bad at the lower mags)

CM40_fracture_10X.jpg

 

50X (slightly better at this level)

CM40_fracture_50X.jpg

 

150X (starting to do OK here)

CM40_fracture_150X.jpg

 

200X (Now we see problems with the sample not being flat, so not everything is in focus.  Excuse the lint, this happens.)

CM40_fracture_200X.jpg

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BTW, that was from a 1000 pound part that is an air hardening alloy.  This is why some modern cast anvils can be so much better than older anvils (we only produce the one tool steel here, at this time).  

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On 2/23/2021 at 12:51 PM, Jerrod Miller said:

150X (starting to do OK here)

CM40_fracture_150X.jpg

 

 

 

Great... Your pictures show me how unsatisfactory my heat treat actually is. To me, your 150x looks like my 50x. Back to the drawing board (heat treat forge...):lol:

 

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No, yours looks pretty good.  Mine is insanely fine, which is why it has been on my desk for a couple years now.  There is absolutely no need to get it like that.  And to be honest, I have no idea how it got that way.  When we first shake these out we hit the risers to break them off and the grains can be measured with a ruler!  I don't have a chunk of that at hand to get a picture of, but I will try later.  

 

If you need any magnification to see the grains you are doing good.  

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