Race Engine - 4340 Steel Studs - Use HT or Heat Treat

[dalehays]

Hi Gang: I'm not a metallorgy engineer, so please bear with me! I'm building a blown racing motor (flathead ford) and a machine shop is going to make some custom main-bearing cap studs. He likes to use 4340 HT bar, 1/2" diameter, but this is very hard to find. If I was going to use standard 4340, what type of heat treating and (???) stress relieving procedure should I use for maximum strength in an engine application like this? I'll probably need to go the heat-treat route, so I need to know what to tell the heat treaters. Also, is there any special prep work or post heat-treat work that needs to be done? Thanks a bunch

 

[arunmrao]

4340 grade steel is used in oilquenched and tempered condition. As it is a standard grade the temperatures and soaking time will be known to heat treater. In the hardened and tempered condition you will be able to exploit the full potential of this alloy. Hope this helps.

 

[Metalguy]

Lot's of luck-you're going to need it! At least you can save some money on the steel since you only need 3 caps (for each engine). You can get almost the same strength etc. from 4140 in a 1/2" thick plate. 4340 is really for thicker stuff, over 1/1/2-2" thick. You'll probably rip the cast iron main webs out before a decent HT 4140 cap would break.

I'd keep the blower pressure REAL low if I wanted something like this to stay together. What crank are you using?

This is a hard way to get above ~300 HP!

 

[unclesyd]

We always used 4340 as we found it less prone to crack while heat treating. Temper two times at 1000°F. No matter which material you use have the studs Magnafluxed after heat treating.

Have you checked out the following website for your studs.

http://www.arp-bolts.com/

 

[Metalguy]

Unclesyd,
Your experience with 4340 vs. 4140 is a lot different from mine. Having heat treated many tons of both, I only cracked 4140 once, when I had to water quench a rough-machined part that had sudden thickness changes, and was so thick it should have been made from 4340 (about 3"+). The heat of 4140 was low in all the "good stuff", Mn, Mo and Cr, and it just wouldn't transform in oil. Rather than just scrap it, I tried a water quench until it went black, then lifted it out. Too late-BANG!

 

[unclesyd]

Dalehays,
Don't use either a 4140 or 4340 fastener above 150,000
psi TS for your application.

Here is a website you might find interesting.

http://www.auto-ware.com/shoptalkbody_index.htm

Metalguy,
We used to manufacture or have manufactured studs for use in a high pressure highly cyclic process (6250 psi) and we had trouble with cracking during heat treatment of 4140. We also experienced what would be a lower endurance with 4140 than literature would lead you to believe. This was in house or outside sources for heat treatment. This was especially true with the finer threads. We switched to 4340 and most of the problems went away.

We also had thousands of process parts made with 4140 that gave problems heat treating, but as you stated this was mainly due to complexity. We changed to 17/4 Ph which helped the heat treating problems but it had its problems too.

 

[funnelguy]

dalehays,
The link provided by unclesyd is a good one. You should definately see if ARP has something you can use.

Otherwise, please make sure the threads are rolled. You will fail studs with cut threads if there is any real loading involved. Rolled threads are the only way to go. Best if the threads are rolled after heat treat.

I believe CarTech makes some of the alloys used by SPS in their high end fasteners. You might want your shop to look there...

You have to torque those little 12 point SPS capscrews on Carillo rods to believe it!

I have made fasteners for unusual service out of S-7 tool steel with rolled threads. We galled a few and had to remove them from service. Still, my customer never failed one. Elevated temp service at 60 ft-lbs of torque on a 3/8-24 bolt.

 

[Metalguy]

Unclesyd,
I can easily understand the lower than expected fatigue data. Some heats of 4140 are near the low side of Cr, Mn and Mo, and those heats do not transform to "99%+" martensite during oil quenching unless the thickness is less than 1 or 1 1/2" thick.

But heats near the upper limits of those elements do fine. I also suspect that most 4340 is made cleaner than 4140 because it's intended for severe service. But clean 4140 is available.

I have no idea why you experienced so much HT cracking w/4140-I sure didn't. We made (mostly) turbine wheels for compressors, about 4-5' dia. I annealed them (usually isothermally at ~1,200 deg. F. IIRC), and then reheated and quenched them in Houghton oil-well circulated. I tried to temper them as soon as possible.

Not to nitpik, but I looked at a few "suggestions" given in your URL, and I don't agree with them-the site seems to be a little thin on some issues. Maybe I should check more of them. I don't agree with their advice on 350 Chevy front oil leaks or their "solid vs. hyd" cams stuff.

 

[dalehays]

Thanks a bunch for all the input, details, practical experience, etc.. I'm going to see if ARP has a standard product that I can use -- so I don't need to make custom studs. The machine shop that I was speaking with can only "cut" threads, not roll them . . . which is obviously not the best way to go. ARP has more advanced materials than 4340 HT and all their threads are rolled -- so this is the preferable way to go.


Rolled Threads - On-Off Jobs:

Does anybody know if it's possible to have somebody "roll" threads for just a small number of studs? I don't know the manufacturing process . . . is this only used for high production runs and not for one-off jobs?

 

[unclesyd]

At one time, if you were a good customer of fastener manufacture you could have few specials rolled by the lab. As every thing now is geared to production and profit small lots are a problem, cost and time. Fastener manufacturing is all based on scale, the high quantity the lower the price.

Some of the ARP products are rolled after heat treatment which is the very close to the best you can get. Some of the better speed shops sell ARP products.

 

[funnelguy]

I have a supplier who charges $35 for setup and $0.10/pc for small quantity jobs. I doubt he is the only one. I'm sure a web search or look through the Thomas Register will give you lots of options.

 

[arunmrao]

Dalehays,
if needed there are many facilities in India who can service small order quantities. Get the thread rolled ,heat treat,and air freight the lot.