What grade/alloy/heat-treat used for spring arms on weight distributing hitches?

[just_some_shmuck]

Does anyone know what alloy (and hopefully heat treat) is used on the spring arms used in weight distributing hitches?

 

[SwinnyGG]

That's a vague question - there are many manufacturers and designs.

Some sort of spring steel that's been through some sort of spring tempering process is the best you're going to get out of this forum.

 

[just_some_shmuck]

Thanks, Swinny. I thought it was a long shot, but one can always hope.

 

[TugboatEng]

It looks like SAE classifies 5 types of steel for springs.

https://www.engineersedge.com/materials/spring-steel.htm

One of these likely covers your application.

 

[SwinnyGG]

There are waaaaaaaay more than 5 alloys used for spring steel

For something like trailer hitches, I would assume from the start that of all possible spring steel alloys, the cheapest ones are going to be the most likely candidates

 

[TugboatEng]

SAE is Society of Automotive Engineers. They only list 5 alloys so it's a safe bet am automotive spring application would use one of those 5. Of course SAE is starting to evaluate composite springs now but that wasn't part of the question.

 

[SwinnyGG]

Note that the chart is titled 'common spring steel grades' not 'list of all spring steel grades'.

Trust me, there a lot more than 5.

 

[just_some_shmuck]

Equalizer is a very common hitch maker and they use springs arms that are a 1.5" square rod (3 feet long). I used a 3 point bend test to approximate their yield strength (because that was the handy equipment) and measured a yield strength of around 190ksi. This size, shape and strength put it way outside the realm of "normal" springs.

 

[mrfailure]

For what its worth, I most commonly encountered 5160 for my work both supporting spring manufacturers and from failure analysis. Of course, that is just anecdotal from one person's perspective...

 

[EdStainless]

If you go with a plain steel you are looking at 1080/1085 or similar.
In a low alloy steel you can reach 180-200ksi with steels like 4335V or 4340.
In all cases the correct Q&T process is critical.
You have to be super careful plating these steels because of hydrogen embrittlement.

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P.E. Metallurgy, consulting work welcomed