Understanding Crankshaft journal hardness

[MikeK]

John, those cast aftermarket Model A cranks were cast nodular (spheroidal graphite) iron, not cast gray iron. They run extremely well at a lower hardness than a steel forging. In many ways cast nodular iron cranks are far superior to steel forgings. Nodular iron absorbs harmonics rather than ringing like a bell and is much more resistant to failure from stress-riser points than most heat-treated steel cranks. It cannot crack like cast gray iron or hardened steel, the microstructure is different. If they were available today I'd take one over a steel crank for an A.

[BlueSunoco]

MikeK I'm not an engineer but I'm following what you are saying about nodular crankshafts.

Ford I know for one, used nodular crankshafts in their hi-performance engines like the 428CJ and the 427 engines in racing applications, NASCAR, Drag Racing, etc. back in the 60's.

Maybe they still do today in modern NASCAR engines I'm sure they do...................

[johnneilson]

Originally Posted by MikeK

John, those cast aftermarket Model A cranks were cast nodular (spheroidal graphite) iron, not cast gray iron. They run extremely well at a lower hardness than a steel forging. In many ways cast nodular iron cranks are far superior to steel forgings. Nodular iron absorbs harmonics rather than ringing like a bell and is much more resistant to failure from stress-riser points than most heat-treated steel cranks. It cannot crack like cast gray iron or hardened steel, the microstructure is different. If they were available today I'd take one over a steel crank for an A.

Mike,

There was a guy making cast cranks a few years ago.
I have seen the remnants of a couple of them, you are right, they did not break. Both are bent over 1/8" on center main journal.

I am sure that done properly the nodular iron would be sufficient for a decent hotrod.

I will stick to the billet ones.

John

[Terry, NJ]

Greater heat transfer? We always wanted to slow down the heat transfer by using a thick brine (salt water) to prevent cracking. Parts of the crank are pretty massive and you can have quite a difference in outer temperature as opposed to the core temperature, which induces cracking. I'm assuming that oil and air hardening steels were not available in 1928.
Terry

Originally Posted by MikeK

Chris,
Thank you for the additions. I do disagree with your statement #1. Although quenching is also done in case hardening treatments, the Ford process as stated does not, in any way produce any case as it does not specify any previous treatment to diffuse carbon or nitrogen into the matrix surface. No type of quench can do that. The caustic is specified simply because it has a heat transfer rate much greater than plain water. 10% caustic potash (KOH) has a 1.38 rate, 10% sodium hydroxide (NaOH) has a 2.06 rate. This is done to ensure through hardening with the relatively low alloy steel Ford used. The quench function is to rapidly form Martensitic structure from austenite before excess carbon has time to diffuse out and form cementite (Fe3C).