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I Forge Iron

Stress Fracture in Railroad Anchor


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Hi All,

Recently I have been forging a handled slot punch from an old rusty railroad anchor. To my dismay as I was driving the handle into the eye, the tool split in half <_<. Surprisingly I was not terrible upset as it is better to have failed now and not when striking with an 8 pound sledge. From the short two years of forging I have done I have never had a tool fail from what I believe to be a stress fracture (kinda exciting). It appears the fracture was preexisting and not caused by poor heat management. As shown by the picture the crack seems to be symmetrical on both sides of the eye, I must have punched straight through the fracture. Further the fracture seems to be discolored looking life rust, is this typical? There also is a slight 'lip' between the fracture and the rest of the area.

Thought I might share.

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IMG_2130.thumb.JPG.7b4264e7c840bb0953bae73113401a51.JPG

 

 

-Mark

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Top piece in the top picture- 

Do you see the somewhat jagged pieces at the meeting of the 2 colors?

 

It looks like the grain structure had an internal inconsistency causing a stress riser. Notice how the other side has a fairly consistent appearance (color notwithstanding) across the fracture plane? 

Now, the lack of "beach marks" shows no real loading cycles, so my guess is that it let go the first bit, went through a heat, then failed through on the next run or 2. 

Without having it in my hand to see the grains and structure, a good failure analysis is harder. 

 

Always cool to see the origination of a fracture. You had a fatigue fracture of sorts with brittle final failure of sorts. 

 

Thanks for sharing, I know wiser minds will correct me if wrong.

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Very interesting. To clarify, ‘beach marks’ show cycles of stress? Interrupted use that propagates the crack in small increments. So then the final crack must have happened suddenly. 

No I do not see any jagged pieces, but on the top piece there seems to be areas that could be pried of with a fingernail, almost as if the crack persists farther into the steel.

 

-Mark

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I don't know much about railroads so I had to google "railroad anchor".  What I found doesn't look like it'd be good parent stock for what you have made.  Unless you welded a few of them together, it doesn't seem like they'd have enough steel in the right places to work.  Most of them are clip/bracket pieces that have bolt holes in them.  

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Did you punch the eye round, then form to oval, then drift? If so I would guess that the eye wall was too cold when formed back to oval. Otherwise, I cannot envision the failure mode, even then it’s oddly symmetrical. Just can’t see how that crack would have form on the inside wall otherwise.

I guess, if the hole was being stretched and the inside walls cooled by the drift, it could fail in that manner. Very interesting and thinking “out loud”...

If we can figure out what happened, it may help me avoid failures in the future. (I have a large number of these clip available!)

David

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What I think of as rail anchors: generally around 1050, no holes; 3 examples shown in the right hand of the picture linked below

http://www.rail-fastener.com/uploads/allimg/AGICO-high-quality-rail-anchor.jpg

Outside of the USA they often use Pandrol clips often of 5160

Were you thinking of items used to tie together joints in rails?  (Disappearing out where I am as they go to welded joints.)

Or tie plates?

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I would guess the eye was too hard at the final failure. No deformation at all and happened while driving the handle in. I’m really looking for the reason for the initial crack. Just can’t seem to get my head around that and can’t seem to let it go. 
The pictures below is the type of anchors I have readily available.

David

40C8EBB4-249E-4776-907F-006805D99CB7.jpeg

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Goods - yes, the eye was punched round, ovalized, and refined on a makeshift drift. It is entirely possible that an errant hammer blow hit the metal when it was to cold.  I did consciously place the steel back in the forge when it cooled below an orange or cherry red heat, but I could have defiantly had a miss wack. 

I do not believe the eye was to hard. I tempered the striking end and the eye of the tool twice after the heat treatment on the rest of the tool was finished.

The anchor I used was unusually thick compared to the ones I have seen before, the anchor second from the right.

The failure happened after forging was complete during the handling process.

lots of interesting thoughts here:lol:

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That’s one heck of a rail anchor. I wish all mine were that size!

Did you harden the whole tool? I just hardened the working end of the slitter shown below, and it held up quite good to a big striker with an eight pound sledge Saturday. 

David

(Really like the lines you had on yours.)

FC5F38BA-5C01-43B8-B22A-A37D9165227A.jpeg

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Agree looks like drifting too cold.  Even if bulk of stock looks hot, drift can locally suck a bunch of heat out of your billet.  Avoid quenching drift until it starts radiating in my experience,  and watch for black circle around drift in stock when hammering.  Did your drift ever get stuck during the process? 

Also making tools out of mystery metal can be problematic.  Grain at crack looks rather large.  Did you thermal cycle before hardening?  How long did you wait before tempering and what was your quench procedure?  Might have cracked during quench at thinnest part of eye if too fast a quench there.  I've had some success with struck tools in just quenching the working end in medium speed oil and running the colors, or full quench and torch tempering eye and struck end.

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That seems to be the most logical problem, at the time I was punching the eye the forge was running out of fuel and dropping in tempature, the drift must have cooled the eye to much. The picture exaggerates the grain of the metal, but it is larger then I was hoping. The steel was normalized 3 times at subsequently lower temperatures, unfortunately the eye was hotter then the working end throughout the process. Then, heated to non-magnetic and quenched the working end in water, waited 20 seconds and quenched the rest (in hindsight I could have used the residual heat from the eye to temper the rest instead). Beforehand, I tested a section of the anchor by quenching it in warmed oil, didn’t get as hard as I expected so opted for the water. As soon as the quench was complete I popped the tool into into a pre warmed toaster oven set at 425. I did one more tempering cycle a day later and used a torch to soften the striking an eye section.

it is quite the anchor, took a heavy beating to get it to move.

thanks for all the comments

- Mark

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Note that the broken surface shows 2 incidents: the first starting the crack which was then thermo cycled or left long enough to discolour the steel where it was and then the propagation of the crack leaving the shiny surface.  It definitely looks like the piece was too hard at the eye as it should be tempered "soft and gooey".

A lot of RR steel seems to be alloys that are tough under the hammer; good practice for when you move to the super alloys that may have extremely narrow forging ranges and *laugh* when you hammer them, (and require very strict high tech heat treats to get all you are paying for out of them.)

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Thank you to everyone who posted photos.  That's some big steel!

I ran across an interesting approach to punching an eye for a struck tool the other day.  The smith fullered opposing flats in the stock parallel to the eye.  Each flat was approximately half the narrow dimension of the drift.  Then they punched and drifted the narrowed section.  Once fully drifted, the eye cheeks were in plane with the original stock.  As far as I can tell, there are three advantages to this approach.

#1. The parent stock stays at forging temp longer for the fullering which gets things done faster.

#2. The drifting is easier because there's half as much stock resisting on either side of the drift.

#3. Any sort of rectangular shaped drift hole will likely be kept much more in line with the stock this way because the fullers reduce the resistance in plane with the parent stock.

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