Welding T1 Steel to 4130 Steel

[FldEngr]

Our fabrication shop typically welds a 1/2" thick T1 steel to a 3"thick x 11" wide 4130 steel "tire" (circular section). The 1/2" material is welded to the inside of the "tire" at approx. 26 places. The shop preheats the "tire" with propane rosebuds to 150 deg. F. at numerous positions while the "tire" rotates. While the tire is at the 150 deg. F., a man places the 1/2" T1 plate onto the inside of tire and a second man tacks the 1/2" plate to the tire using MIG. The weld wire is .035 and 100ksi. Once plate is tacked, the welder welds two oval shaped holes (approx. 2.5" wide x 3" tall) with approx. 3 or 4 complete circular passes - they do not fill the oval hole completely. They continue this process until all T1 plates have be welded to the tire. The assembly is then removed from the preheating/welding jig with no further postheat treatment except for cooling down at shop ambient temperature. This tire rotates with a load on it and the T1 plates (spokes) flex from tension to compression in its rotation - sort of like a bicycle tire.
We have experienced cracking on one side of the oval holes that runs square to the long axis of the ovals and the crack goes from one side to the opposite side of the T1 plate.
My concern is for our lack of "Welding Procedures" that address the preheat and postheat requirements. We do not employe a Welding Engineer or a Metallurgist to help with this problem.
Do you think our shop practice is correct?


Thanks very much,
First Time Inquirer, Long Time Reader

 

[bklauba]

This sounds like a rotating "mammoth".

When do the cracks appear? Do they appear soon after fab, after transport, after operation? Are the welds subjected to anything corrosive? The MIG wire, was it "baked-out" so as to remove any moisture?

BK

 

[metengr]

My concern is for our lack of "Welding Procedures" that address the preheat and postheat requirements. We do not employe a Welding Engineer or a Metallurgist to help with this problem.
Do you think our shop practice is correct?

No. You have lack of preheat, you mention nothing about interpass temperature to control the effects of heat input to the T1 material (do you understand that T1 is a high strength steel?) and based on what you described with the amount of weld build-up, you need to qualify your method - generate a weld procedure specification and qualify it. By the way, what is the function of this component??

 

[FldEngr]

bklauba:
There are two tires supporting a rotating steel drum (8'dia.) used in the asphalt hot mix industry. The drum serves as a dryer and a mixer to produce this hot mix and rotates on a daily basis.
The cracks typically show up sometime after the tires have been put into production. Some tires last a long time and others show cracks early on.
Typically, the welds are not subject to a corrosive atmosphere.
The weld wire is more than likely not kept in an oven. This industry does not require fabrication according to any codes accept for the structural supports.

mentengr:
The shop uses a temp. stick to determine when material is at desired preheat temp. Aside from that, I do not think they monitor any interpass temp's. And I do understand that the T1 is a high strength steel. I am not convinced that it is necessary for the spoke material to be T1 steel.
I agree the shop really needs to establish weld procedures.
Do you think the use of the 100k or 90k weld wire is correct? What sort of preheat or postheat treatment would you suggest?

Thanks again,

 

[metengr]

FldEngr;
Without knowing the loading on this component, I could not render an opinion as to which strength level you need to match. Also, you did not mention the heat treatment condition of the 4130 steel - is is normalized, quenched and tempered, what is the strength level? If you know this, you can match the filler metal strength to the 4130.

 

[FldEngr]

The loading issue is one we have had a hard time attempting to model. I do realize that not having a good handle on the loading puts us at a big disadvantage.
The 4130 is Q&T steel - 110k to 130k tensile strength.

 

[metengr]

FldEngr;
Most likely, T1 was selected to assure adequate strength of the spokes since they carry torsional and bending loads. Considering the amount of weld build-up, I would use a 100 Ksi filler metal. But more important, you should increase your preheat to 250 deg F and maintain the interpass temperature at or below 500 deg F. Also, make sure you use low hydrogen weld consumables. At this point, PWHT would effect the T1 material, and this is what you need in my opinion for strength. So, I would not PWHT.

 

[EdDanzer]

Your welding size variation 3 or 4 passes may be the reason some fail and some don’t. A FEA of the design may provide more details about weld size and its effects. The FEA work could also show if you could use a lower strength plate. The other possibility is where you start and stop the weld at. MIG welds frequently have cold laps on start. You may have better luck with flux cored or metal cored wire. The 150°F preheat should include the T1 plate.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[weldtek]

For some good info on welding this material try this website;

http://www.mittalsteel.com/documents/en/Inlandflats/Applications/HOW TO WELD.pdf