4340 for billet rods? March 04, 2009 09:33AM
Looking to make a set of steel billet rods for a pro stock application, was going to use 4340 and heat treat it 42-44 RC. I see alot of companys use 4340 for there rods, and I talked to a reputable heat treat shop and that is what they recommended. Was wondering what other people thought of 4340 for rods or if they recommended something different? Thanks.

Re: 4340 for billet rods? March 05, 2009 05:14AM
have you considered 4130

Re: 4340 for billet rods? March 05, 2009 09:29AM
I have looked into it some. I believe 4130 is alot cheaper, which would be nice. But the biggest difference is 4340 has some nickel content in it, which gives it toughness. 4130 doesn't have any nickel to speak of. Also the "40" number is the carbon content, I believe that is a percentage, so there is 40% carbon in 4340, and 30% carbon in 4130, which will allow for deeper hardness through the part. I would guess the nickel content is what makes it more expensive. Thanks for the suggestion.

Re: 4340 for billet rods? March 05, 2009 12:09PM
there are much better materials out there they are just a bit more expensive. New space age alloys come out all the time. just do some surfing online and look at the yield and ultimate you'll be surprised.

Re: 4340 for billet rods? March 05, 2009 12:42PM
4330 is generally the material of choice for a forged product...carrillo uses this for their cup rods....going billet i would stick with 4340....best bang for your buck

Re: 4340 for billet rods? March 05, 2009 01:09PM
I agree totally with both of you guys, I realize there are alot better materials, I looked at quite a few material data sheets, but I am looking for the most bang for my buck. Just wanted to hear some confirmation on what I was doing before I did it. I have 4340 priced at about 750 dollars for enough material to do 8 rods delivered at my door, does that sound like a reasonable price? If not, is there a better place I should look for 4340 that might be cheaper? Thanks for your help.

Re: 4340 for billet rods? March 05, 2009 01:25PM
I don't know much about machine work but it does fascinate me to learn about it. So bare with me if this is a simple question, but do you order your steel heat treated already or do that process after the rods are made? And is the heat treating process necessary?

Also what can a guy do or not do with stock crankshafts as far as heat treating and hardening them goes? Thanks.

Edited 1 time(s). Last edit at 03/05/2009 01:28PM by AV.

Re: 4340 for billet rods? March 05, 2009 03:02PM
If something needs to be hardened, usually rough machine work is performed while the material is soft, then it is heat treated to the desired hardness, and then the finish work is performed. Some materials like 4140 can be purchased prehard or annealed. The prehard is usually only about 30 rc, which is not real hard, but tougher than just using cold or hot rolled, and still pretty economical. As far as cranshafts, I have the same questions as you. I would be concerned with cracking heat treating a crank, but guys do a lot of welding on them and I guess they still hold up?? I'm not sure that maybe a crank shouldn't be a little soft to handle a little flexing without cracking or breaking? How hard are billet cranks usually made?

Re: 4340 for billet rods? March 05, 2009 04:14PM
We built some 3 -4 years ago exactly how you said 4340 and heat treated to 42-44rc. They worked great, ALOT of work though. Ran them on the Grand National Pro circuit with no issues! As for using different alloys we looked into that, along with the price, you have to figure out how to cut them - specialized tooling. How to heat treat them? Lots of questions on something you only want to do once! As for the heat treating after you "rough" the part, it is because steel will move when you take out a lot of it. So you rough it in, then heat treat then cut the last little bit off. So essentially you're cutting your part twice with a lot more attention to tolerance the second time thru!

Re: 4340 for billet rods? March 06, 2009 12:55AM
A good place to start would be the machinist handbook or the "bible of the machining world" as I like to call it. It can tell you a lot about different alloys and the heat treat of each. Metal will actually grow and distrort in heat treat. I am not sure about the above mentioned alloys, but S-7 is one of the most stable. Good luck!!!

Re: 4340 for billet rods? March 06, 2009 08:53AM
Check out Associated Steel Company

They have a product called Kromite #3. You can get by with out having to heat treat this material


Re: 4340 for billet rods? March 06, 2009 10:34AM
Manleys newer high dollar rods are 300M material. They are really nice and use a bolt better than arp. At $1200 for a SBC it better be.

Re: 4340 for billet rods? How about this? March 07, 2009 01:23AM
Over here we (Europe) we hear more and more about Toolox-steel. Check out the link:


Re: 4340 for billet rods? How about this? March 07, 2009 01:40AM
How about titanium? or 8620. Sorry I can't spell well, but would Incenel work for rods?

Re: 4340 for billet rods? March 07, 2009 01:47PM
We are using 4140 that will be heat treated and cryoed.

Re: 4340 for billet rods? October 15, 2020 07:21PM
4340 alloy steel round bar is a good material with good price. It is widely used in the industry. Its yield strength can up to 470 MPA

Re: 4340 for billet rods? October 16, 2020 12:55AM
Go with 4340. 4340 is generally thought of as an aircraft grade 4140. We've used it many times with no issues. Just make sure you leave enough material on the finished product so that your finish grinder for the pin bushings and bearing bore has enough material to do what he needs to do. Rc42-44 is a good level of heat treat. Just make sure after they heat treat them they also temper them so they don't get brittle. Most heat treat shops do this but it's always worth asking. And also need to be sure to cut your rods with the grain of the material. Sounds silly but its very important.


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