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Flywheel Heat treat/Material

Flywheel Heat treat/Material

Flywheel Heat treat/Material

Hey everyone.  I'm having a custom flywheel machined, and I wanted to know what heat treat specs you all think I should be shooting for.  It'l be made of 4140, unless anyone can give me a reason I should step up and use 4340 ($).  I'm thinking I want a through heat treat, on the order of rc45, comments, suggestions?


RE: Flywheel Heat treat/Material

What are the dimensions esp. thickness of the flywheel. 4140 will only harden just so deep, anything thicker than like 1/2" wont harden through. 4340 will through harden to much larger section sizes than 4140.

Also 45 HRc is relatively hard for these alloys. 40 will give you higher impact strength and better resistance to scc etc...

RE: Flywheel Heat treat/Material

Sorry for the X-post, I wasn't in the forum I thought I was when I first posted.  Anyway, the section thickness is never more than about .4", being a lightweight flywheel, it changes a good bit.  I'm thinking it'l be treated, then the firction surface ground afterwards.....?

so mabye specify Rc 37-42, or something?

RE: Flywheel Heat treat/Material


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RE: Flywheel Heat treat/Material

What are you going to use it for ?
Are you revving it so high you need strength ?
If clutch heat is likely to happen, I'd be thinking the un-hardenability of mild steel might be an advantage.

RE: Flywheel Heat treat/Material


"If clutch heat is likely to happen, I'd be thinking the un-hardenability of mild steel might be an advantage."

Cept that 4130 is commonly tempered at 1000F, and the austenization temp is around 1600F, If his clutch sees these temperatures more than instantaneously it wont matter what his flywheel is made of.

I'm going to assume you are going to finish machine/grind after heat treating. I would ask the heat treater to harden to 35-40HRc. ( this could be done using an oil quench and then tempering at ~1000F for 2hrs or so.)

RE: Flywheel Heat treat/Material

It's a metallic racing clutch.  It will see VERY little slip=>  little heat.  It'l be revved quite high, though (~10k rpm), so I'm trying to get the burst strength up.  Also, yes, the friction face will be ground afterwards.  I decided to go with Rc-35 to 409 before reading your post, now I feel even more geinus-like than usual.  Thanks :)


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