4130 and 4140 comparison 1

[steve37]

I am machining a set of steering tie rods out 4140 for a customer. He wanted 4130 but I was out, I recommended 4140 and he agreed. How do these two metals compare ??? These tie rods are for a Off-road desert racing truck, extreme duty, should I just order some 4130 ?

 

[israelkk]

4130 is better for welding but, for heat treating 4140 is even better because you can heat treat heavier sections for through hardness compared to 4130.

 

[CoryPad]

Steering tie rods made from 4140 can be suitable for your proposed end use. You must process them in the appropriate manner - raw material, forming, machining, heat treating, and surface finishing.

 

[Wrenchbender]

What heat treatment are you specifying? What is the industry precident or standard?

My seat of the pants feeling is that either alloy would suffice for automotive tie rods, even as-rolled or in a normalized condition. For severe applications maybe consider a tempered martensite structure with a generous tempering temperature for the higher toughness. Check crankshaft con rod material for comparisons.

For a 1-inch diameter rod, 4140 should almost give a thru hardness; 4130 about halfway(ref ASM Hdbk Vol 1), but I would rate toughness more important that strength. A failure would probably be due to a fatigue crack nucleating at the surface from maybe a thread root or a corrosion pit. In theory the lower carbon steels are tougher because they contain fewer brittle carbides. Whichever you pick, go for toughness.

 

[tbuelna]

steve37,

As the other posters have implied, the only reason to use 4130 instead of 4140 is if there is fusion welding required. If no welding is required and your tie rod is more than about 1/2 inch in diameter, use 4140. There's no real cost difference, and 4140 will give at least 30 percent higher tensile properties in a normalized condition, while still having good elongation properties.

Regards,
Terry

 

[steve37]

Thanks for the help guys. The O.D. of the tie rods will be .875". When I thread on the lathe, I usually cut in a relief at the end for the end of the threadcutting. But for this application, I think I will not cut in a relief (possible cracking).4140 it is!!!

 

[ornerynorsk]

We had this issue once for wheelchair axle components. 4130 is specified in a lot of aircraft applications, so many people assume it is "better" material. There were some material shortage problems years ago which caused us to investigate alternate choices, as you are doing. I have come to love 4140 as my "general purpose" material, the stuff is nice to work with, easy machining, heat treatable, and tough as nails.

 

[Tmoose]

How do tie rods fail in this service?
- Direct bending from side loads ( drive over large rock and tie rod is asked to support weight of vehicle for a moment)?
- Bending from buckling when the tires try to auto-steer in response to whacking things, or when tires are jammed against rocks and the drive must exert maximum effort to the steering wheel?
- breaking after many hours of service?

I'd say upgraded materials would only be useful for maybe doubling resistance to 2 of the failure modes, and might even limit the options for trail repairs, whereas improved geometry of a basic material would offer immensely improved resistance to all three.

Dan T

 

[monkeydog]

Steve,

Please don't take this as a personal attack; but -

Lesson for everyone, the OP's customer wanted a specific material, the OP recommended another for reasons not specified, my guess the recommended was "on-hand", but when the OP made the recommendation, he did not know what the differences were.

When your supplier/vendor makes an alternate material/process change, know what the differences are!

 

[steve37]

You are right! I began "roughing out" the material then stopped, thought about it and figured I better get some answers before I go any further. Thanks

 

[steve37]

Tmoose, Usually the problem is hitting a boulder. They are covered with Nevada silt and hard to spot. Also, they like to hide behind a bush. Braking is another issue, where the driver see's a huge ditch and slams on the brakes as he drops into it, which wears and fatigues parts quickly. The right way is to slam on the brakes before the ditch then tap the gas to get the front end up and let it ride! K back to topic, sorry guys