4340 tensile strenght 3

[Rollcages]

I am very new in this domain. We are in the motorsport business and recently we started to design and produce rollcages. I have a few questions for the people who really know about steel properties.
We are working on a very light rollcage from 4340 alloy but I discovered that it has lower impact strength than 4130 and a lot higher tensile strength. I want to ask you what should be the right alloy for this application, considering that the rollcage is only useful in case of an impact.
Thank you in advance.

 

[arunmrao]

It is rather difficult to make a specific recommendation between the 2 alloys based on the inputs provided by you. The material condition in which you have the property data is important. However,everything remaining same a higher carbon steel lowers the impact properties.


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[Wrenchbender]

The variables are rollcage geometry, material modulus, strain rate, operating temperature, heat treatment and physical metallurgy, but here’s the quick & dirty answer: Since toughness is a very useful property for a rollcage, a material having a large area under the curve in a uniaxial tensile test is desirable. Which of your two alloys wins this contest depends on their heat treatment, however lower carbon steels generally have better toughness. You may be able to find some published data for just comparison, but I suspect the better welding properties of 4130 would be an overriding factor in your application. (4130 normalized would be my first pick.)

 

[TVP]

Unless you plan to heat treat a welded 4340 roll cage after the welding operation, then don't bother using 4340. 4130 will perform better if it is to be used in the as-welded condition. Lincoln Electric and others have free information available for welding thin-wall steel tubes into roll cages, etc.

 

[Rollcages]

Thank you all for your replies. I decided to go with 4130 steel but they are still a lot of questions:
The supplier is telling me that his products comply with ASTM A519 and I must decide if I want the tube normalized or stress relieved.
As far as I know, normalizing can soften/harden/stress relieve the steel so I dont know what he means. The cage will be treated for stress relief after welding, anyway.
Any help would be appreciated.

 

[TVP]

ASTM A 519 is a standard that covers seamless steel tubes. Welded steel tubes (commonly called ERW for electric resistance welded) are covered by a different standard, ASTM A 513. You should probably purchase your tubes in the normalized condition unless you plan to do a lot of bending, in which case the stress relieved option may be better. The stress relief operation performed by a tube mill has nothing to do with the stress relief process performed after welding.

I suggest you download the following .pdf files and familiarize yourself with the different tube manufacturing processes:

http://www.smrw.de/downloads/Steel_tube_and_pipe.pdf

http://www.steeltubeinstitute.org/pdf/handbookofWCSMT/WCSMT_Sec1_Sec2.pdf

 

[Tmoose]

Some sanctioning bodies' rule books used to specify cage material, and some minimal design guidelines like minimum diameter, wall thickness and so on.

 

[Mr168]

Your sanctioning race body will dictate this the majority of the time, and you will find 4130 to be the norm where mild steel isn't specified. 4130 normalized is the most common for chassis work. Additional PWHT/stress relief after welding should not be necessary on tubing in the thickness ranges you'd be looking at.

 

[Robertmet]

I don't see any need for 4340.Rallies in the USA now have a 1.75" dia requirement .IIRC plain carbon or 41xx are used .Properly designed [very important] these roll cages hold up very well .The biggest problem is high speed impact with trees.