Welding 304SS to D6ac

[HardMetal]

I have an application in which I have to resistance spot weld a 304 stainless steel screen grid to the inside of a D6ac cylindrical section that is about 0.055 inch thick and 5 feet long. The stainless screen is about 0.030 inch thick. The spot weld diameter will be about 0.090 inch. The D6ac will be heat treated to 220 ksi tensile strength. The welding will be performed after heat treating the D6ac.

Does anyone have an ideas as to whether it is possible to weld the 304 to the heat treated D6ac? Will there be a heat affected zone through the entire thickness of the D6ac or will the HAZ be confined to just below the weld?

Thanks for your help.

Paul

 

[nousakmj]

You will be hard pressed not to have the HAZ extend through the D6AC, but anything is possible with fine control. In theory, you can spot weld heat treatable alloys such as D6AC, but you'll have to include a temper cycle in the weld programming to avoid cracking. Otherwise, you'll simply watch the spot welds come out whole and leave a crater behind. Is this 304 screening made up of wire? or just sheet with holes in it?

Matt Nosuak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com

 

[HardMetal]

The 304 SS screen is stamped from a sheet so that it has thin strip sections (~0.090) with square spaces (~1 inch) in between. This results in a criss-crossing pattern. The thin sections are then pressed to give them curvature. Several of the "nodes" are to be welded to the D6ac.

The problem is that the D6ac will already be heat treated before welding. Do you know how much strength (from the 220 ksi UTS) will be lost in the HAZ? Or do you think that weld cracking will be a more significant problem? Should I consider localized preheating the area of the spot weld?

Thanks.

 

[nousakmj]

D6AC was hardly developed for use in the as-welded condition. The composition is basically akin to that of a 4145 with a some nickel added for ductility and the molybdenum cranked up for thermal stability. The nominal composition is 0.46 C, 0.76 Mn, 0.22 Si, 1.10 Cr, 0.5 Ni, 1.0 Mo, 0.08 V. The original use for rocket motors.

I think weld cracking will be the problem unless you have a temper cycle built in. I think preheat would be useful, but difficult to apply without distorting the screen.
However, I think you can get it done since you will be able to run about 1/16" diameter spot welds -- as long as it doesn't crack, you shouldn't lose enough strength in the overall cross-section to matter.

You'll just have to try it and see.

Matt