Need 100,000 psi yield steel than can be welded

ewlsey · May 13, 2016

I have a design for a spindle that needs to be welded to a piece of mild steel. In order to achieve the safety factor I want, I need at least 100,000 psi yield strength. Normally I would reach for 1144, but it can't be welded.

So, what steel can you recommend that has 100,000 psi yield strength, can be satisfactorily machined with conventional tooling, and can be welded to mild steel square tubing? I need something that does not require heat treatment.

Next, can you recommend the correct welding process? The spindle will be approximately 1.75 diameter. It will pass through a bored hole in the center of a piece of 2.5" 3/16 wall steel tubing. We will weld the spindle completely on both sides where it passes through the tubing. We are using MIG.

I assume that preheating the spindle will be required. If we need to stress relieve the assembly after welding, we can have that done. However, the spindle needs to have a tight sliding fit with a pair of tapered roller bearings, so I want to minimize any distortion of the machined surfaces.

So, what do you guys recommend?

johnoder · May 13, 2016

ASTM A514 "T1" plate is specifically that yield - less so where welded

4140/4142 is welded in great volumes in the oil tool biz. though I doubt the heat affected zones are 100K yield. This DOES require strict adherence to approved weld procedures and post weld heat treat

jscpm · May 13, 2016

This is not a machining question.

ewlsey · May 13, 2016

jscpm said:
This is not a machining question.

Thanks for your input.

mkd · May 13, 2016

PSI does not equal a safety factor.
<thank you for your input>

with that YP, signifcant carbon will be needed which will in turn need heat treat after, so it seems any CroMo should work.

ewlsey · May 13, 2016

The diameter is fixed by the bearing. The load is fixed by the application. To get the right safety factor, yield strength is the only variable left.

Milland · May 13, 2016

My first thought was 4130, but the way you talk about it, is the strength issue from static load or dynamic? If this assembly will be spinning at any significant speed I'd me more concerned about balance of the welded unit, and good transition radii wherever you've got a section change. Post-weld HT or SR is something to take seriously...

Can you tell us anything more about what this thing will do?

L Vanice · May 13, 2016

ewlsey said:
The diameter is fixed by the bearing. The load is fixed by the application. To get the right safety factor, yield strength is the only variable left.

Seems like not welding on the spindle and designing a different attachment method to the frame is a good path to investigate.

Larry

Monarchist · May 13, 2016

ewlsey said:
The diameter is fixed by the bearing. The load is fixed by the application. To get the right safety factor, yield strength is the only variable left.

KEEPING that strength is the harder part than just starting with the right alloy.

I'd call the welding and heat-treat not only the bigger variable, but also one that will not reliably remain solved, one part to the next.

'Safety' being cited, and limits being pushed, you'd have to factor-in funding for serious testing and a certain amount of rejects - reworkable, perhaps not at all.

And it IS a metal-mangling question, basically. 'Economics' apply to all such.

Bill

Heavey Metal · May 13, 2016

4140

600° pH

600° interpass

7018lh

ewlsey · May 13, 2016

It's a dynamic load, but very low speed. It's basically a type of crane arm. The weld diameter is 1.75. The bearing diameter is 1.25. So, the weld is larger than the critical diameter.

Further, the spindle is mechanically locked in the tubing. The only actual load on the weld in the shear load, not the bending load.

HuFlungDung · May 13, 2016

If you can, design it so that you weld a mild steel bushing into your tubing, bore it true after welding, then press fit your alloy steel spindle into that bushing, perhaps retaining it with a bolt and washer or some such.

I suppose you could assemble the spindle into the bushing, then weld only on the bushing. It will shrink even tighter on the spindle, and the spindle may not be removable afterwards without a bunch of scoring, etc.

ewlsey · May 13, 2016

Of course I could weld in a sleeve and use 1144 for the spindle with a jam nut to hold things together. It would be much cleaner and easier to just weld the spindle in.

We have made these before using 1045 for the spindle. The customer increased the load requirement and I'm trying to accommodate.

HuFlungDung · May 13, 2016

Scale it all up and use weldable materials. I don't think you can reliably vouch for the strength of the welded joint on alloy steel, or how the metal may have been affected.

ewlsey · May 13, 2016

I guess we could do that. I can actually get away with 88,000 psi.

People just can't leave well enough alone.

Milland · May 13, 2016

If this is a single-sided supported shaft, is there any possibility of increasing the shaft diameter for the outboard 1.25" bearing by going to a narrower section? It's a pretty big areal change going from the 1.75" tube mount to 1.25", if strength is the issue I'd wonder if a needle or roller bearing with a ~1.375 to 1.5" bore could be used. That might be a better way to get your strength then just a material change.

ewlsey · May 13, 2016

We use a pair of standard LM67048 tapered roller bearings. I use 1.75 material to get the right diameter for the seal we use.

We could go to a 1.375 diameter bearing, but I have to change every part of the assembly.

Milland · May 13, 2016

ewlsey said:
We use a pair of standard LM67048 tapered roller bearings. I use 1.75 material to get the right diameter for the seal we use.

We could go to a 1.375 diameter bearing, but I have to change every part of the assembly.

Yeah, PITB no doubt, but might be worth it. Biggest transition radius you can fit next to the bearing will help reliability too.

Monarchist · May 13, 2016

ewlsey said:
We use a pair of standard LM67048 tapered roller bearings. I use 1.75 material to get the right diameter for the seal we use.

We could go to a 1.375 diameter bearing, but I have to change every part of the assembly.

It makes for a 'visible' change after the paint goes on. The uber-alloy approach may look identical.

PITA, yes. But might also make it easier to show why you are due your price, and why your customer should have more money for the end-product as well. Hopefully reduces liability risk too.

Otherwise, how to differentiate light from heavy - other than a label or paint colour and some sales claim?

Bill

gbent · May 13, 2016

What is the loading frequency, and how much of the load is cyclic? Welding crosswise to a cyclic tensile stress is asking for trouble. Yes, it can be done successfully. But it has to be a well thought out procedure and properly executed every single time. My choice would be to rework the design for either slip fit or to put the weld in shear.

Need 100,000 psi yield steel than can be welded

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