The Ford Barn - View Single Post - Understanding Crankshaft journal hardness

Chris in CT · 06-09-2015, 08:03 AM

Hi Guys,

First of all, let me say that Mike K's explanation above is excellent and very much to the point. I'd like to add a couple of observations to his remarks and to address Brent's initial question above.
1. Quenching in a caustic solution (sometimes arsenic!!) is part of a case-hardening process. Brent's recitation of the Ford process does indicate some level of case-hardening in the manufacturing process.
2. Nitridization is a modern form of case hardening. In vacuum nitridization, it is not necessary to exceed about 950 degrees Fahrenheit, not enough to warp a piece of forged steel unless there are captured stresses in the forging. Therefore, a reground crankshaft can safely be re-nitrided. There will be a light surface film on the journals and mains which will need to be carefully removed with crocus cloth. Ask the performance engine guys about this - they do it more than a little frequently...
3. In modern heat treating practice, it is common to do more than one level of body, or web hardening. Heat treat practice will often harden the outer section of the workpiece for stiffness and ridgidity, while leaving a core thickness much softer for toughness and resilience.
4. It is difficult to compare the hardness specifications for a modern crankshaft against the heat-treat process for an antique crankshaft. The best practice would be to hardness-test the antique crank and compare the specs with the specs for the modern crank. This would have to include core-samples from the antique crank. And yes, I get it, the best way to be sure about the modern crank would be to hardness-test it as well... Happy Motoring!

06-09-2015, 08:03 AM	#7
Chris in CT Senior Member Join Date: May 2010 Location: Connecticut Posts: 272	Re: Understanding Crankshaft journal hardness Hi Guys, First of all, let me say that Mike K's explanation above is excellent and very much to the point. I'd like to add a couple of observations to his remarks and to address Brent's initial question above. 1. Quenching in a caustic solution (sometimes arsenic!!) is part of a case-hardening process. Brent's recitation of the Ford process does indicate some level of case-hardening in the manufacturing process. 2. Nitridization is a modern form of case hardening. In vacuum nitridization, it is not necessary to exceed about 950 degrees Fahrenheit, not enough to warp a piece of forged steel unless there are captured stresses in the forging. Therefore, a reground crankshaft can safely be re-nitrided. There will be a light surface film on the journals and mains which will need to be carefully removed with crocus cloth. Ask the performance engine guys about this - they do it more than a little frequently... 3. In modern heat treating practice, it is common to do more than one level of body, or web hardening. Heat treat practice will often harden the outer section of the workpiece for stiffness and ridgidity, while leaving a core thickness much softer for toughness and resilience. 4. It is difficult to compare the hardness specifications for a modern crankshaft against the heat-treat process for an antique crankshaft. The best practice would be to hardness-test the antique crank and compare the specs with the specs for the modern crank. This would have to include core-samples from the antique crank. And yes, I get it, the best way to be sure about the modern crank would be to hardness-test it as well... Happy Motoring!