Inco 600 to Inco 600 Seal Attachment Weld Porosity Issue

Date 07-18-2011 13:27

Hi everyone,
We are trying to weld (AGTAW) a single J groove seal attachement weld with the following specifics:

- bm1=Inconel 600, Seal=Inconel 600
- bm1 root diameter=2.7"
- groove depth=approx .3"
- fm=EN82H (.031")
- gas=Argon,30CFH,7/16" cup
- electrode=2% thoriated, 3/32", 7/16 at bottom of groove, 3/8 when groove dimensions allow
- the groove takes 7 layers currently with oscillation starting on the fourth layer
- layers 1-3: 185A, 9V, 3 ipm
- layers 4-7: 185A, 9V, 3 ipm, .050" oscillation

The issue we are having is that every looks great up until the 6th layer, where we start getting tiny pores around the circumference of the weld. Its like clock work every 6th layer. We have been changing rpms to maintain consistant travel speed. We have tried using the lowest qualified travel speed in thought that it would provide a longer time for any pores to come to the surface. We have also tried lowering the flow rate in thought that there may be too much turbulance. We are currently throwing around ideas to figure out what to try next. Has anyone ran into anything similar to this or have any suggestions to try. Thanks

Brett

By Lawrence (*****)

Date 07-18-2011 14:21

Welcome to the forum!

That is a very hot and wide bead for a "superalloy" Gas coverage at the back of the pool becomes more critical, especially with oscellation added to the operation.

A custom gas shielding trail fixture (possibly built into the torch head) may provide superior gas coverage on the trailing edge of the weld as it solidifies...

The best exotic GTAW consultants on the face of the earth are at PWT
http://www.pwt-online.com/

These guys have made alot of people alot of money over the years. They give advice and also sell custom made trailing gas shields for GTAW, PAW and GMAW. They also do EB and Laser process control services.

Give them a contact.. Ask for Gregg.. and Tell him that Larry B from United sent you...

Your solution will be forthcomming.

By bjbercaw (*)

Date 07-22-2011 14:27

Hi Larry, thanks for your reply. We took your advice and tried a trailing shield with 3CFH argon. Everything looked great through the 6th layer, which is one layer better than we have seen previosly, but on the 7th layer indications popped up around the entire circumference as before. The 7th layer is a split cover layer (pass 7 and 8). I made a mistake in the first post with regards to the parameters used on layers 4-7. We are pulsing, syncing to the oscillation. The parameters used on layers 4-7 previously were as follows:

Primary Current: 195
Background Current: 160
Primary V: 9.4
Background V: 8.6
Primary WFS: 47 ipm
Background WFS: 30
Travel Speed: 3 ipm
Oscillation: .050"
Pulse mode: sync to oscillation

For this last part we ran (with the trailing shield), where we started seeing the indications on layer 7 instead of 6, we only made one change in the parameters when we welded layer 7. Because layer 7 is a split cover (pass 7 and 8) and we usually weld the first pass on the seal side and it gets very hot, we dropped the current down to 170 Pri/145 Bck and kept everything else the same. On the next part we plan to try keeping the current the same on layers 4-7 and on the cover layer starting pass 7 on the hub side instead of the seal side which will help keep from overheating the seal. We are also seeing some tiny black specs floating into the puddle from the seal which are likely contributing to the indications. Let me know if you have any further thoughts of changes we might try. Thanks again for the help.

Brett

By Lawrence (*****)

Date 07-22-2011 15:08

My money is still on gas issues

By Metarinka (****)

Date 07-23-2011 21:00

My bet is either a cumulative oxidation effect from bad trailing gas, or some type of contamination build up from filler etc. If you are controlling interpass to those temperatures it probably will hit 250 well before the 6th pass so that leaves out the idea of a interpass temperature issue.

Try the other way around, on a mockup or joint increase travel speed as high as possible. Higher speed = more efficient arc and in general less heat input. Which means a faster cooling rate and hopefully less oxidation.

By Lawrence (*****)

Date 07-23-2011 21:06

I would like (if it's possible) to see a pic of the trail gas setup... To my mind 3 CFH is next to nothing for a trailer.. Prolly doing little or nothing to aid your issue.

Increrased travel speed is not a bad idea for many reasons. (As long as you don't outrun your gas coverage) Which my money says is exactly the issue.

By Metarinka (****)

Date 07-23-2011 21:10

I would agree didn't catch the 3 CFH, which seems low i would start in the 7-15 range depending on the cup design, sounds like a rectangular narrow groove weld cup is needed or something similar.

I agree with the outrunning your trailing shield, however if you do the math you'll find usually a weld at double the travel speed will cool outside of the critical temperature range much much faster.

I've been doing a lot of tig welding in the 40+ IPM range and have fallen in love with it.

By petty4345 (**)

Date 07-19-2011 16:56

What are you using for minimum/maximum preheat/interpass temperature?

By bjbercaw (*)

Date 07-22-2011 14:06

min preheat is 60F, max interpass is 250F