Substitute for 17-4PH H900 1

[JHurley32]

Disclaimer: I'm a fireman with access to a machine shop. I have a good general understanding of materials but I'm far from an engineer.

I have been manufacturing pickets (or stakes) that get driven into the ground via a striking cap and sledge hammer. The ends of the pickets are machined (one end to a point and the other turned with threads to accept the striking cap.) I'm running into issues with the cost of 17-4PH H900 and was wondering if there was a similar metal that would take the impacts of striking without breaking the bank. I've experimented with 4140 before, but the pickets are 42" long and we had issues with the stock warping during the heat treat process. Any help would be greatly appreciated.

 

[tbuelna]

The obvious difference between 17-4PH and 4140 is that 17-4PH is corrosion resistant and 4140 is not.

If a non-corrosion resistant alloy steel like 4140 is acceptable, then take a look at ETD 150. It is a 41XX alloy steel that develops its strength (150ksi uts) during the drawing process, so it does not require secondary heat treatment. It machines well and the as-drawn bar stock has good straightness. As for whether it has adequate strength for your application, I can't say based on the limited information provided in your OP. Definitely lower strength than 17-4PH H900 (190ksi uts).

 

[WKTaylor]

What diameter or cross-section/size are Your 'pickets'?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[JHurley32]

I do need some corrosion resistance as it is an exterior application. The pickets are 1” outside diameter and they pass through a 1.5” thick anodized aluminum plate with three 1.007 bores (one picket in each hole) in it and go into the ground for a short amount of time (<2hrs.) This creates an anchor anywhere the pickets can be driven. A load of up to 10,000 lbs is imparted to the plate as long as the soil will hold.

 

[tbuelna]

JHurley32,

From your last post it doesn't appear that the working stress levels in your pickets are that high. However, it would be helpful if you could provide a simple sketch of your picket, and also a diagram of how loads are applied from the plate to the pickets. The only exception I can think of is high local stresses in the threaded connection between the picket body and striking cap produced by sledge hammer impacts. But this condition can likely be resolved by modifying the joint design.

You noted that a corrosion resistant material is required for the pickets, and since it appears the service stress levels may not be that high, you might consider using a more economical grade of stainless steel such as cold drawn 303S/303Se Gr. B (115ksi uts) round bar. It will have the diameter/straightness tolerance you require in the as-drawn condition, it machines easily, and will resist galling at the striker cap thread connection.

Hope that helps.
Terry

 

[EdStainless]

Cold drawn Nitronic bar is available also as Aquamet 22 (145ksi UTS) or cold drawn modified 304 as Aquamet 19 (130ksi UTS).
These are used for prop shafts on boats so people actually stock them.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[JHurley32]

The stresses on the picket are two-fold and very different. Initially the striking cap is threaded onto the picket (the picket has 1"-8 threads on the top 6" which aren't shown on the pictures here) and the picket, which is 42" long, is driven ~36" into the ground. All three pickets are driven through the plate and are in line. The load is applied to the plate, in-line with the pickets. The three pickets immediately engage with the plate due to the tight tolerance.

 

[JHurley32]

 

[DAVIDSTECKER]

https://www.gettent.com/tents/42-x-1-double-head-tent-stake.asp

Have you looked commercial tent stakes?

 

[DAVIDSTECKER]

The more I looked at the web site the more I saw that I think you might want to look at in the way stake drivers and pullers.
They have a gas (Honda Engine) stake driver.
I've used the jack hammer version years ago and it makes quick work of driving a stake.

 

[Compositepro]

Having to drive and remove three stakes at once causes a number of problems. I think a more robust design would be stakes with a double head design that can be driven one at a time though holes in your plate, as DAVIDSTECKER suggests. You cannot compete with the cost and availability of commercial, off-the-shelf stakes. Keeping carbon steel stakes oiled can prevent most of the rust issue.

 

[JHurley32]

The stakes are driven in one at a time and removed one at a time.

For fire/rescue operations or wilderness rope rescue, gas powered units are a little too cumbersome to carry with this setup.

The stake pullers that you normally see sold with tent stakes tend to burr the sides of the pickets which makes the tight tolerance not fit the next time you go to use it. I will follow up with that company to see what they’re using and if I can turn down the OD to meet my specs but I imagine if they’re saying the stakes are 1” that they’re probably a bit undersized (0.990)

The operation (driving, pulling, removing) is set in stone. I really just wanted to know if there was a similar metal to 17-4 that wasn’t as expensive or had some minor differences from 17-4.

Thanks for all of the replies so far.

 

[DAVIDSTECKER]

The more I browse the tent site the more useful information I find.
Excellent video how to library.
This one is of multiple stakes and plate arrangements.

https://www.youtube.com/watch?v=-3KsAKm7qYU&t=0s&list=PL3DF0C5FE58C9F72F&index=17

http://WWW.matweb.com

is a site where you can enter material properties and see what materials meet them.
Also you can contact the larger steel suppliers across the country and use their knowledge base, ask if they have any Applications Engineers or Metallurgists.
Reach out past your local supplier.

Ok, here's the engineering side of things.
First, if your need for corrosion resistance is due to the very tight hole clearance's then you can get to a point of diminishing returns.
That is the point where the extra precision and expense no longer adds to the performance of the product.
There are many steels as strong out there for less, there are Weathering steels that the coating of rust is their protective coating.
Blacksmiths use Bees wax as a rust preventive if you want to be environmentally minded.
I will say it is a very good looking product you have, but is it really any better than the carnival stuff?
I also think that you have a very useful product but are you limiting it's use by having a product to is not in range of more departments budgets?
What is your main objective for this product.
I encourage you to continue making your product as you see fit but also make changes as you see fit to best meet your goal of have the equipment available to save as many life's as possible.
Best regards, David