Cast Iron vs Cast Steel

After studying the matter, I have now learned that there are many different receipes for cast iron. As one site put it, "saying 'cast iron' is like saying 'Sunday Dinner'...there are thousands of receipes that can fit that description. And after viewing other sites, I am pretty sure that state of the art for engine manufacturing includes cast iron and cast aluminum blocks. I do not find any reference to cast steel engine blocks.

At a website from the Univ of Washington, I found some description of the chemical analysis of cast iron and cast steel. They are both basically iron and small % of carbon. There are many different formulations that include small % of other metals such as Chromium, Molydebium (sp?), Tungsten, etc that give very different strength and machinability characteristics. Some of the specialty cast iron gives a superior friction wear property. This is probably a desirable property for engine blocks. Some of the additives to the receipe give a different grain structure to the casting. When working with a broken casting, you can see the grain structure in both cast steel and cast iron.

Now, in simple terms, what is the difference between cast steel and cast iron? My guess is that cast steel has less than 2% carbon, and cast iron is up in the 3% to 5% carbon content, and this affects the grain structure. (Where is Llamas when we really need him??).

Bottom line for all of us....the castings of the engine, transmission, and rear end of the N series tractors are good quality cast that is repairable by welding processes. There are many specialty welding companies and processes that have been developed to accomplish this task. One interesting website I found is www.muggyweld.com, having streaming video of the repair process.

Thanks to Bob for challenging my statement, and gently pushing me to learn some more about the metalurgy of our great machines. I hope that some others will add their knowledge to this discussion.

Paul in MN

Paul is spot-on; there are all sorts of 'cast iron'; it's a generic term. However there are two broad categories of cast irons: 'cast' iron and 'ductile' iron, delineated by the type of carbon found within. Both types of iron are cast, that is, molten metal is poured into a sand mold. 'Cast iron' has 'flakes' of carbon inside, while 'ductile' or 'nodular' cast iron has 'globs' of carbon inside. What's the diff? Well, flakes are not as strong as globs. Ductile iron is anywhere from 20-50% stronger than cast, and can withstand shock loading much better; cast iron parts can be broken with a sharp blow from a hammer, but ductile is more likely to bend or dent first. The only chemical difference between the two is a little manganese (?) added to the melt, which causes the free carbon to clump together into globs. The globs act like 'rebar' inside the iron, strengthening it and making it more ductile (flexible, in relative terms of course).

The interaction of iron and carbon is exceptionally complex. Throw in a few alloying elements like manganese, nickel, copper, whatever, and the combinations become endless. Here's a link to an introduction to iron and steel; interesting reading to a nerd like me, but deadly dull to normal folks.

Link

Happy Tractoring!

c.

You have both become Elders in my eyes today. That is the highest possible compliment I can pay anyone. I only hope you understand what it means. The reason I hope you do is so you understand how important your presence and your actions, even your words, are to everyone who visits or "lives on" this forum.

I am delighted to learn so much more today about cast iron and cast steel. But this is one of those times when I have learned far more important things on this forum. Thank you both.

Respectfully, Dawn

This is sure a great Forum, where information can be shared and critiqued in an intelligent manner, compared to some other Forums I frequent, with a lot of "hot shots".

You mention having trouble welding "crappy" cast iron. When I was growing up, my Uncle was good friends with a Swedish blacksmith who was known as being able to weld broken cast iron machinery parts others couldn't. He always told my Uncle the secret to welding some of the tough jobs was a LONG pre-heat, to burn off oil and other impurities that were present in the relatively porous cast iron, as well as a SLOW cooldown to prevent cracking. He would bury welded castings in hot ashes from a wood fire, which would then slowly cool, even over a period of a day or two. I have done the ash thing myself, and it seems to work well.

He welded the two pieces together and then welded a big steel plate to that for addtional strength. I always assumed those things to be cast iron but I'm certain now it must have been cast steel from the way he was welding it.