cast iron or ductile cast iron?? how do you tell the difference ??

[sidesaddle queen]

hi,  

 

many times my sidesaddle  trees  need  the leaping head   (the part that goes over the thigh)   reshaped,  either to fit the new owner or because it is bent , either in a horse fall or mishandled thru the yrs,, 

most are easy to do and can be heated and shaped  like any mild steel but lately i have come across some that are cast.  

 sad to say the first cast one we ruined not realizing what it was  .. broke it in half because we spot heated it..  snapped like a popsicle stick!!  lol!

 now when i find a cast one i do not try to change it ..  if badly bent ,, i have to replace with a newly built one which is expensive ..    plus,  i like to keep them all original if i can,, 

 

 recently i read there was a ductile cast iron that could be heated and shaped..  is the true and if so how can i tell the difference,, 

[Ted Ewert]

If it isn't a very old saddle I would guess that you're looking at cast steel. Casting produces a different grain structure in steel than forging does, which makes it brittle. I would experiment with the broken one to figure out how to bend it, if possible, without breaking it. Probably lots of heat. 

[JHCC]

The brittleness in cast iron comes from its very high carbon content: there's too much carbon to remain dissolved in the iron crystal lattice, so as the molten metal cools, the carbon precipitates out into small flakes of graphite interspersed throughout the metal. These flakes have very low resistance to splitting, so cracks in cast iron tend to start easily and propagate easily.

Ductile cast iron is produced by a careful process of introducing a certain amount of silicon and controlled cooling. This forces the excess graphite to form spherical nodules rather than flakes. Since spheres disperse stress in multiple directions (think a basketball hitting a pile of sand rather than an axe splitting a log), even if a crack starts, it stops once it hits a nodule. This means that ductile iron has much more resistance to cracking -- especially in high-stress situations -- but it does NOT mean that it is malleable or can be forged.

With respect, Ted Ewert is incorrect about cast steel and its grain. The grain structure of steel is governed by its heat treatment, not by its original method of manufacture. One often sees "cast steel" stamped on older tools, but that was to indicate that it had been made by the new Bessemer process (which produced molten metal which was then cast into ingots for later forging) rather than by the older processes of carburizing solid wrought iron to produce blister steel or melting wrought iron with a carbon source in a sealed crucible and then allowing it to cool to produce a "puck" of crucible steel.

I don't know if leaping heads were made from cast iron, but from your description of how it broke, it does sound like that first one was. Were you trying to adjust it for a new owner? I would guess that if it's bent, it's probably not cast iron, as if it were, it probably would have broken before bending. 

Fortunately, it's possible to determine if a piece is cast iron or some variety of steel by spark testing. There are longer articles about this here on the forum, but the short version is that if you touch a corner of the piece to a grinding wheel, the size, color, and pattern of sparks will tell you a lot about the alloy content. Cast iron sparks tend to be shorter, redder, and with fewer bursting sparkles, while steel sparks are longer, whiter, and with more bursting sparkles. Comparing sparks of an unknown metal with the sparks of a known metal is very helpful.

Hope this helps.

[sidesaddle queen]

thy are very   very old saddles...  120 -150 yrs  

 

i understand what cast iron is,, i  just didn't expect it in a  sidesaddle part that is normally shaped to fit the rider..  so i blindly forged ahead..lol!! pun intended and asked a friend to heat it and rebend it,,  i told him to hea the whole thing but he decided he knew better  and just quickly tested the spot e was going to bend.. lol!! he was so surprised.. lol!! 

 

 some sidesaddle were cheaply made, like saddles now and they probably cast them because they were making them all the same shape and size rather than bespoke/custom

the one i broke was  very bent.. curled up . but it might have  been made that way to fit a thin thigh..  lol!!!

 

thank you so much , i knew there was a spark test but didn't have that in my info!!!! 

so, another question.. could the cast leaping heads be  mild steel  cast ??   rather than cast iron?  and the rough texture fooled me??   i will see if i can dig one up..

i had one made to place the one i broke,,     

[JHCC]

Always glad to help!

The cheaply made/mass produced thing makes a lot of sense. People often forget that there was a lot of poor quality stuff made in the past that simply didn't survive to the present day, and the notion that "everything was better quality and made to last back in the day" is not always correct!

(By the way, one thing about IFI is that we think of it not just as specific answers to specific questions, but as a resource for those who will come upon these discussions later. Longer explanations aren't intended to imply ignorance on your part, but to give context and understanding to the less-experienced.)

[ThomasPowers]

Early cast steels had lower strength in an "as cast" state due to the large grain structures formed by slow cooling.  Such materials needed to be forged to break down the grain size.   Modern steels may have alloying elements to help form a fine grain structure as they cool.  ("Cast Steel" tools were not cast to shape; but rather forged from cast steel bars.)  As the great expense was in the casting of steel in the first place it is rare to see items cast to shape and not forged to shape.

[sidesaddle queen]

lol!! got it..  i like the answer you gave , only stated i knew what it was to save you typing .. but your answer will be more helpful in the long run . i am not used to a blog situation where many people are talking a the same time on a subject,,     i am still thinking as a one one conversation,, lol!!  

montgomery wards. sears and other catalog companies  of the time carried all kinds of sidesaddles.. some very well made and were not..lol!!  

[JHCC]

The same goes for their blacksmithing equipment!

[sidesaddle queen]

i was very surpassed to see cast iron rather than forged.. i have handled or owned over 100 of the these saddles and only had 3 with cast pommels,,  i one here now that cast fork!! very interesting.  has an american patent on it,, 

surprised not surpassed,,  

 

lol!! yes .. contrary to old timers memories there was a lot of junk made in the 19 century,, lol!!

[ThomasPowers]

And we all have different opinions and different knowledge bases; when one person says "Old time smithing" they mean 19th century and if I say it; it might be 9th century.  People familiar with the materials we use today often assume that they were the same as what was used 150 years ago when they are not!

Have you checked the patent on it and read their description?

[sidesaddle queen]

yes i have the patent. interestingly , it does not state a method of production.. leaves to the maker.. just the engraving shows it is metal.. my fork doesn't have the pat # on it.. they didn't always do that back then.    this patent is  4 /3 / 1900.. 

 

[Ted Ewert]

5 hours ago, JHCC said:

With respect, Ted Ewert is incorrect about cast steel and its grain. The grain structure of steel is governed by its heat treatment, not by its original method of manufacture. 

 

Milwaukee Forge begs to differ: 

Forging is stronger than casting.

One of the main reason we choose to provide forging services is that it provides a stronger end product for our partners. According to a study performed by the Industrial & Manufacturing Engineering Department at the University of Toledo:

Forged parts had a 26% higher tensile strength than the same cast parts.

Forged parts had a 37% higher fatigue strength resulting in a much longer lifespan than cast parts.

Cast iron only had 66% of the yield strength of forged steel, a measurement that indicates the load amount metal can hold before deforming.

The forged parts had a 58% reduction in area when pulled to failure, compared to 6% reduction for cast parts. That means forge parts allow for much greater deformation before failure than cast parts.

Why is this?

When you melt metal, the grain size is free to expand. This creates a final product with a more random grain structure. A more random grain structure leads to deceased strength. The forging process keeps the grain structure tight and the product mechanically strong. There is also less need for expensive alloys to retain high strength.

https://www.forging.org/uploaded/tinymce/media/Fatigue.pdf

Edited June 9, 2021 by Mod34
Commercial link removed per TOS and replaced with academic link

[JHCC]

The study linked on that that page compares forged steel with ductile cast iron. Apples and oranges.

[Ted Ewert]

My father was a mechanical engineer and owned a gear manufacturing company. He explained to me at an early age the difference between casting and forging. I've read a lot about forging and casting since then and haven't seen anything that contradicts the theory that forging realigns the grain structure in steel to make it tougher and stronger than it's casted counterpart. If you have some new information I'm all ears. 

[JHCC]

Toughness and strength come (at least in part) from the number of dislocations in the crystalline structure. Forging does increase those dislocations — that is, creates a finer grain structure — but if the forged piece is then annealed, you get grain growth pretty much as coarse as a freshly cast piece. That coarse structure can be refined by normalizing, which forms new, smaller grains at the boundaries of the previous larger grains. 

In other words, while forging initially produces a finer grain structure, that structure can be destroyed by improper heat treatment or duplicated in a cast piece by proper heat treatment (assuming identical alloy compositions, of course). Also, since the grain of a forged piece tends to be finer towards the surface, at least some of that finer grain is removed if the piece is milled, while the grain in a cast piece tends to be more consistent throughout.

In short, there’s nothing intrinsic to a forging that guarantees a better grain structure and nothing intrinsic to a casting that guarantees a worse. Strictly speaking, my original statement should have been “The grain structure of steel is governed partly by its original method of manufacture, but much more by its heat treatment or the absence thereof.”

[ThomasPowers]

Note that normalizing to refine grain  size without previous/further deformation is a process that works a whole lot better in modern steel alloys and not so well in "historical" steels.

[JHCC]

Thomas, how are you defining “modern” and “historical” in this context?

[ThomasPowers]

It depends on the alloy really; but in general Modern steels are Post Bessemer process and historical are more pre Bessemer process.  However there are outliers in both directions.   Shallow hardening low alloy steels are more prone to grain growth and less prone to normalization refining grain size.   So if you work with tamahagane  that is modern made I would advise caution compared to a "high alloy" steel of the early 19th century.

[JHCC]

That's fair. Still, you wouldn't be dealing with that many steel castings pre-Bessemer, would you?

[ThomasPowers]

Well they tried when the Huntsman Process was first employed; learned better with experience.  We also know now that some of the characteristics of various steels are due to trace elements found in their ores; for one of the best examples: why making Wootz was rather specific to a narrow location and then the material was shipped all over.

[JHCC]

Historical metallurgy developments aside, would you agree with my assessment posted above?

[ThomasPowers]

if you add grain size is inversely proportional to Toughness and strength...

[JHCC]

Fair enough.

[sidesaddle queen]

wow!!! i just stepped into the deep end of the pool..     interesting discussion,, 

[ThomasPowers]

Slow day at work; folks are showing up with either pitchforks *or* torches when it's clearly stated that they must have *both*!