gearbox shaft weld repair -4340

Date 03-08-2005 17:33

I need to weld build up damaged areas on the end of a mill drive gearbox pinion output shaft. Shaft coupling tangs (17" dia.) are damaged. Mat'l AISI 4340. Customer does not want to dis-assemble. Due to a babbit bearing (17" away) on same shaft post weld stress relieving unlikely. Tangs are heavily loaded. Any ideas on possible welding procedure?

By ajoy

Date 03-09-2005 07:36

Before finalising the welding procedure, it would be worthwhile to discuss on the following points :
1. What is the amount of build-up / what thickness ?
2. Considering the shaft being a Q/T material, what hardness are we looking at on the weld deposit ? It is known that the built-up surface cannot match the wear resistant property of the original material if it is done by carbon steel fillers.
2. Is distortion an issue considering the amount of build-up and the rigidity of the material.

If the amount of build-up/thickness is less, we can go for manual GTAW else SMAW.
A preheat of above 180 degres and a post heat of 300 degrees celcius is to be applied for carbon steel fillers of 90ksi or 100ksi strength. With this filler, the hardness will be in the order of 200 BHN only.

Another unconventional method of repair would by the use of 17 straight chrome or 17Cr/4Ni ferritic stainless steel with a buffer of 309 type stainless steel filler. This process is suitable for higher built-up thicknesses where the undiluted weld metal hardness on the surface can be as high as 300 BHN which almost matches the shaft hardness. Post heating can be avoided with such processes.

By Bill Mc (**)

Date 03-09-2005 13:38

I have not seen the work yet.
Discussions with the customer, I anticipate approx. 3/8" overlay required. He estimates a harness of 24Rc on the surface right now. The surface is fairly large -about 10" x 17" (x2 sides) so I anticipate applying a FCAW overlay process.

Distortion is not a big issue, the overlay will be machined.
But I have a big concern if the babbit bearing on the shaft will survive much post heat.
I do have a qualified procedure using E309LT-1 FCAW on 4140 without preheat, and will concider a material to apply over that.
Thank you for your input Mr. Bhattacharyya.