Is there a steel alloy that is stronger than 1018 and can be welded to A36 plate? 2

[JST Fab]

Is there a steel alloy that is stronger than 1018 and can be welded to A36 plate?

By stronger, I mean a higher tensile strength.

The material needs to be machined before welding.

The application is a shaft that a hub assembly with bearings bolts on to (similar to a weld-on trailer axle stub shaft).

 

[gtaw]

The choice of a heat treatable alloy steel is probably not the best decision if one is going to weld it and then have no intention of a post weld heat treatment.

I can see the back-room discussion; "Let's pick a stronger steel so it won't break again."
"Why did it break?"
"I don't know."
"Was it fatigue? Did it happen immediately or after several years of use?"
"I don't know, but if we use a stronger steel, it won't happen again. We can order the steel annealed or hardened. The annealed stuff doesn't have the strength the hardened stuff has, so let's order it in the hardened condition!"

You haven't really told us much about the failure. You didn't include any history of the failure or past failures. What was the mode of failure?
You haven't told us what the calculated loads are, the application, etc. What are the details of the welded connection? What are the dimensions? What is the degree of restraint during welding?

Please, please tell me this is for a homemade trailer that will be pulled by a tractor in the field and not intended for highway use.




Best regards - Al

 

[TugboatEng]

The bearing obviously sets the diameter where the shaft is currently failing but the diameter at the weld joint is uncontrolled. Control of the size of the HAZ can limit the softening to the larger diameter where the reduction in strength won't be an issue.

 

Please, please tell me this is for a homemade trailer that will be pulled by a tractor in the field and not intended for highway use.

Unless highways are heavily potholed in your neck of the woods, pulling a trailer through a field would impart some seriously higher fatigue loads. Just saying!

Control of the size of the HAZ can limit the softening to the larger diameter where the reduction in strength won't be an issue.

Not sure how that works. A smaller HAZ is made by lower heat input and it could end up harder than you would like.

Folks, we are seriously overthinking this. I suggest the OP do some simple benchmarking or even reverse engineer the design from a competitor's part. This configuration has been made millions of times before and the vast majority never fail.
It is not very big, so there is no need to go to a heavily alloyed steel. And in general, follow the K.I.S.S. principle by going to minimum alloy and minimum manufacturing complexity.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[gtaw]

I figured if it failed in the back hay lot, fewer people would be endangered.

Best regards - Al

 

[TugboatEng]

Ironic, I'm just trying to say that there are ways to keep the HAZ in the low stress areas through design, not just perform a "cold weld". For example, one could press fit the spindle in the plate and weld only the back side.

 

[ATSE]

Did anyone mention ASTM A572-65?
65ksi yield / 80 ksi tensile. Easy to machine, bend... Very weldable (unlike chromoly).
After that, A516.

 

[BrianE22]

If you get really desperate, you might consider bolting the shaft to the plate. Buy some 4130 tubing heat treated to a medium strength, machine it and bolt it on. A long center bolt would provide a favorable compressive pre-stress.

Disadvantages would be the higher cost (bolting versus welding) and the possibility that the bolt would come loose.

 

[tbuelna]

Might also consider reducing the shaft diameter between the bearing shoulder and the fillet weld edge. This might reduce the stress concentration at the bearing shoulder fillet.

 

[Tmoose]

I would be most reluctant to modify the "design" or even change materials before examining the fracture and reviewing a big chunk of reliable history.

Like some Old Time Radio cop (pre Dragnet) said - "my business is facts ma'am. Do you know any?"

===========

One of our suppliers made shafts to drawings of a mature and successful product.
A couple of the shafts broke pretty quickly,

It turned out that the new-ish shop foreman interpreted one of our admittedly under-dimensioned drawings from the (19)60s as having a relatively deep, sharp cornered groove as transition at the end of some threads on the shaft in between the keyed drive end and the high inertial built up rotor.
Basically they machined the thread transition groove to the full depth of a nearby "keyway" for a large tabbed bearing lockwasher, and with amazingly sharp corners.

In our case Maybe obviously, maybe not, the correct "solution" was to add some dimensions to the drawing that had sufficed to create reliable shafts for 2 score years.
NOT to change the material.
Not to even change the shaft "design."

 

Folks, we are seriously overthinking this.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."