What Steel? Rear Upright Lower Clevis Bolt

[Hawke]

After 43 years, the clevis bolt is in need of replacement. What's the current thought of the steel to use?

[Steve Demeter]

4130 if you have someone who can weld it without making it brittle. It will last another 43 years.

I just looked at the picture again. Is that a single piece?

[Hawke]

Steve, it is one piece.

[R. Pare]

4130, 4140, 4150, 4340, 8620, ETD150

All will work, and are in about the same area for annealed or narmalized condition bar stock ( except the ETD150)

All can be heat treated easily to a Grade 5 bolt strength ( around 150 kpsi tensile strength), and you can go much higher with all but the 8620. The ETD150 is already heat treated to about that.

If you want to go stainless, 17-4 H900 will be in the 210 kpsi tensile area.

[Hawke]

Richard, thanks for that. I was just going to machine it myself, but the heat treatment bit is beyond my capability. Would you say it is really needed? Bear in mind, that when Mr Lazenby made these Hawkes in the 70's, it would surprise me if he did so.

[R. Pare]

Take what you have there to any good machine shop or heat treating facility to have the hardness checked. From the hardness number, you can look up the approximate strength here:

http://www.carbidedepot.com/formulas-hardness.htm

Most likely, it was made from something like 4130 in either the normalised or annealed condition simply because of cost - and they thought that mild steel might have been too weak.

The biggest issue on "soft" steels will be ruining the threads over time if they are either over-torqued (leading to thread stripping) or if "displaced thread" lock nuts are used instead of nyloc nuts - the displaced thread nuts will over-stress the bolt threads, causing them to fail rapidly.

If you have a good machine shop nearby, see if they can roll-thread it for you instead of making the threads by cutting - you will have much better threads.

If you want something that is harder and stronger than normalised or annealed, make it from the ETD150 if you can get it over there. If not, my choice would be to make it from 8620 and use a torch to heat it cherry red, hold for a couple minutes to allow at least partial crystal formation, then quench in oil. That will bring the hardness up to around RC28-32 most likely. Used to make T-type sway bars this way when doing one-offs and didn't have the time (days) to go through a heat treating facility ( or were just too cheap to pay their price! )

You can do the same with 4130 with usually good results, but the others will harden up too much because of the extra carbon and could easily get brittle if you don't know how to to-draw it back to the hardness you want.

The most critical area I can see in machining this piece is the transition from the bolt shank to the clevis - you want as big and smooth a radius as you can get and still have it seat on the adjoining upright surface correctly.

[Hawke]

Richard, many thanks. I've realised that I should have taken more notice in my Strength of Materials lectures, and they were over 40 years ago.

[john f]

Make it out of 4140 pre-hard. It's around 30 Rc and machines great. Just my $0.02

john f

dirt cheap, too

[DanW]

http://www.speedymetals.com/s-67-heat-treated.aspx

[patman]

Your local machine shop will probably hardness test it for you if you bring them a box of donuts.

Once you know the hardness, you can order pre-hard steel that is in the same hardness range, then machine it from there.

IMO, home heat treating of critical parts is not a good idea, especially if you have no way to verify final hardness.