Welding 8620 (ASTM A732 Grade 13Q) investment casting

[grayseal]

A current supplier is requesting they substitute an 8620 investment casting instead of the specified 1020(A732 Grade 1A). The part is welded to low carbon steel tubing having .125 wall thickness. The part is not highly stressed. My concern is with weld cracking. I do not want to pre or post heat the weld. Should I be concerned? The reason they want to substitute is that they are having porosity issues with the 1A grade. Is this common?

grayseal

 

[GRoberts]

Having not made investment castings, I cannot comment with regards to the porosity, but I would say that you are definately taking more welding risk if you allow the switch to 8620. The pre/post heat requirements would greatly depend on your application and casting configuration, but there would probably be few applications where no pre/post weld heat treating would not be advised. (i.e. no low temperatures, no high stress, no cyclic loading, no thick sections, etc.) Is there any other weldable grades they can pour without porosity problems, such as A216 Gr. WCA, WCB, or WCC, or A352 Gr. LCA, LCB or LCC.

On the other hand, if your weld is not critical, could your supplier provide welability tesing, such as a Batelle underbead cracking test, or a Controlled thermal severity test?

 

[grayseal]

GRoberts,

Thanks for the reply. Weldability testing sounds like a good start.

grayseal

 

[GraySyracuse]

I recommend heat treatment after welding: Normalize and Temper (see ASTM A487 - 9. Repaire by welding, para 9.3). It works more like a stress releve. (You may have cracking problems if you do not do it.)I am doing as a general rule: Normalize: 1600°F ± 25°F, one hour per inch of maximum section, 45 minutes minimum, air or liquid quench below 500°F. Temper: 1265°F ± 25°F for one hour.
If the amount of welding is minimal (really "cosmetic" repairs) and the part is for a commercial application, you maybe go without PWHT, depends on the heat affected zone

 

[awol]

If porosity is a concern, be careful with A216. I am having trouble with a thin-wall casting of A216. I am looking at changing to A352 for the lack of a better option.
My part is threaded so I am avoiding Stainless alloys.
-awol