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).

 

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

Almost any steel is stronger than 1018. By which I presume you mean SAE 1018.
Personally I substitute A516-70 for A36 plate wherever possible. It is just as available (i.e., same cost) and will give you a good bump in tensile properties while having excellent weldability.

The material needs to be machined before welding.

All carbon steels have good machinability. Since you are welding you should avoid the resulphurized and/or leaded grades, whose only claim to fame is enhanced machinability, but at the expense of everything else.

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

 

[TugboatEng]

4130 seems like the obvious choice.

 

[mrfailure]

Whatever you pick, check carbon equivalency to see if you need to preheat before welding and if post-weld heat treatment is indicated.

 

[kingnero]

Planning welding on high-strength steels is more than checking CEq.
But that is indeed a good place to start.
Some others are:
avoidance of cold cracking (directly related to CEq), delamination on the plate, weld geometry/fatigue design, weld process control (eg. spray arc, penetration depth, choice of filler material)...

 

4130 is not such an obvious choice; nobody has said how strong it needs to be;

and

'carbon equivalency' is not a thing

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

 

[weldstan]

1030 to 1035 would provide higher tensile properties and easy weldability without preheat or PWHT.

 

[EdStainless]

And do you really need the whole thing stronger or do you need some areas harder?
Is it just the pin or the plate as well?
How strong do you need it? 50ksi, 70ksi, 200ksi? Give us a clue.

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P.E. Metallurgy, consulting work welcomed

 

[mrfailure]

Carbon equivalency is of course a thing, at least according to AWS. It provides a good guideline for pre/post weld heat treatment and if they are needed. Agree with kingnero on the other the other parameters as well.

 

I understand the concept perfectly well, but what is wrong here is the colloquialization (I know, probably not a word) of a technical term. Even google knows it.

Maybe I am being overly touchy here, but most of my days now are spent at war with overpaid semi-literates at giant EPCs. In code space, precision in communication still matters.

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

 

[JST Fab]

We are leaning towards 4130 or 8620.

The failure point is where the inner bearing seats. See diagram below. The shaft snaps completely at this point.

Note: when used as directed, the shaft works great. It is when the product is used incorrectly (ie: extreme offset wheel used off road) where there is a failure.

Ideally we would like to avoid heat treating processes. We do not have the equipment for this in house.

The ideal choice would be easy to machine, materials cost not too high, can be mig welded (preferably with ER70s-6 wire using spray arc transfer), no post heat treat, as strong as possible without adding extra cost or complexity to the job (ie: we simply have the machinist switch the material).

 

[kingnero]

8620 is a case hardening steel, meaning especially made for heat treatments. For your application,this doesn't seem a logical choice.
Also requires a carefully selected welding process.

Does the failure originates from the radiused step ? If so, can't you make the radius bigger?

 

[JST Fab]

Hi Kingnero,

Yes the failure is in the radius step. Originally it did not have a radius. We added the largest radius possible in that area (that the bearing would allow). Still needs to be stronger.

I think we are leaning more towards 4130.

 

[kingnero]

I've had good results using a peening process introducing compressive stresses in the surface, in a similar application.
There are many variants on this process. Might be worth exploring...

 

[EdStainless]

4130 could be pre-hardened, but the welding will be more demanding. There will be weld pre-heating and PWHT needed.
Any higher strength alloy will be more hardenable and will require similar treatment.
Peening may help, but this will likely require more.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[mrfailure]

Components fail at the weakest point so the radius adjacent to the bearing seat surface would be the expected point of failure due to higher stresses and geometry. I think it is most likely the shaft fractured under fatigue during service during time as opposed to a one time event that broke it - I mention this because the term "snapped" implies a one-time event, which would really require further investigation. You are on the right track looking for higher strength steel (which also means higher fatigue strength) and looking at actions outlined above including shot peening. Changing the radius may help, but the main factor here is the increase in stress under loading that results from the reduction in shaft diameter at this critical point.

 

4130 could be pre-hardened, but the welding will be more demanding.

Welding would destroy the temper at the critical location where fatigue initiates.

Geometry; i.e., stress concentration factor and surface condition (finish, compressive stress) carry more weight than other factors like material strength. Not that strength is unimportant, but high strength is wasted if the design is not good.

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

 

[bobjustbob]

First off, have you determined what strength you need? Also, what are the toughness requirements?

If you only need to get up to 85/40 ksi (tensile/yield) you can do that with a modified 1018. A little more Mn and maybe Mo along with a quench and temper can give you those strengths with decent toughness that is easily weldable. We would cast a modified LCC material like this that was welded into the truck of passenger rail cars.

If you need more strength, I like an 8620 material. It is not just a carburizing grade. However, you will need a bit of preheat and probably a draw after welding depending on the toughness that you need in the HAZ. We would use a bit higher carbon grade of 8625 to go from 90/60 ksi up to 120/100 ksi.

4130 seems to be overkill, especially if you plan to weld it with ER70S-6 wire. It is a good way to get good strength without paying for the Ni in 8620. carbon and Cr are cheaper ways to go, however you will have a more difficult time welding it. You will need preheat and a draw after welding.

I think you need to better understand the strength and toughness that is actually required before just swapping out materials.

Bob

 

[EdStainless]

Hot finished bar or cold finished? ASTM specs or SAE specs?
Either way you don't want to order by chemistry only, you need a spec that has required strength properties (ASTM A663 or SAE J410 for example).
If fatigue is an issue do you need some cleanliness limits? Some NDT requirements?
You should be able to find steels with 70ksi min UTS and C<0.26% (maybe with Mn and or Si higher) that will be plenty weldable.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Tmoose]

By inspection I'm kind of surprised that the plate-to-axle weld toes have not shown to be a fatigue problem.
Perhaps the original non-radius was quite sharp indeed.

IN the picture it appears there may also be a joint or seam in the axle ~ .5" to the left of the alleged "failure point".
What's up with that ?
Was the axle portion machined from one piece or was it two pieces welded together, or a sleeve added to form the bearing abutment or ???