Welding & Heat Treatment of 17-4
Welding & Heat Treatment of 17-4
(OP)
If a specification allows for welding after solution and before age, can anyone tell me what the microstructure of the weld-metal looks like (more or less)?
Also, one spec allows welding in the aged condition, and re-aging the part. But it limits this practice to 2 times. Does solution reset the part to zero (metallurgically speaking)? Thanks.
Also, one spec allows welding in the aged condition, and re-aging the part. But it limits this practice to 2 times. Does solution reset the part to zero (metallurgically speaking)? Thanks.





RE: Welding & Heat Treatment of 17-4
For 1st question, I'm sure more information is needed to give a precise answer. Please assume cooling-rate resulting from TIG weld-repair of .250 section casting, with copper-backing plate, and try to get me in the ball-park. Thanks.
RE: Welding & Heat Treatment of 17-4
What was the filler metal specification used for weld repair? If it was a matching chemical composition like AWS SFA 5.9 ER630, the weld metal microstructure will appear and respond just like the 17-4 base metal.
Yes, solution treatment after welding will allow the casting to be aged to the desired heat treatment condition.
RE: Welding & Heat Treatment of 17-4
2nd question - are you saying there is no cumulative deleterious effect of aging a part multiple times, so long as it is solution treated first every time?
RE: Welding & Heat Treatment of 17-4
As to the first, the weld nugget in 17-4PH sst looks like most weld nuggets in any base metal with dentrites and directional solidification. It does not look like the tempered martensitic base metal. You will have untempered martensite in the weld and in the base metal HAZ, which is why you need to perform PWHT. Post weld aging tempers the HAZ and weld marteniste. The weld metal will not look like the base metal after a post weld aging since you haven't caused recrystallation, only some homogenization and precipitation of phases in the weld. To get the weld to look like the base metal you have to solution anneal, and even then you can still find the weld with etching.
The reason for limiting the number of times a part can be given post weld aging treatment is you begin to overage the base metal and degrade the properties. Solution annealing restores the base metal.
The ASME Code requires the part be fully solution annealed after welding. However, you can successfully perform only aging, typically for 4 hrs at temmperature, after welding and get predictable properties.
RE: Welding & Heat Treatment of 17-4
Science and Technology of Welding and Joining, Vol 4, (5), 1999, pp 295-301
Ditto, Vol 11, (5), 2006, pp 502-508
They have some nice optical and electron micrographs
Steve Jones
Materials & Corrosion Engineer
http://www.linkedin.com/pub/8/83b/b04