Procedure Qualification

Date 09-29-2011 11:41

Good morning;
We am trying to qualify a procedure and having a heck of a time. Material is 4140 80 ksi to same. The weld passes everytime but the hardness is what is killing us. What is required is 253 Vickers max. We are blowing by this by as much as 50 points in the HAZ and weld metal. We are using GTAW with 80s root and hot with 100s remainder. 700F interpass temp with a 450F preheat. PWHT is 1250F for one hour minimum. 14-19.5V. 95-195A. IPM is 3.5-7. Weld grade Argon at 40 cfm. Any analysis or suggestions would be greatly appreciated.

Have a good day:
Matt

By js55

Date 09-29-2011 11:55

First of all why 100s?
Second, you're going to have to kick up the PWHT a little and extend the time.
If you're getting 300 Vickers your heat treat ain't working.

By unclematt (***)

Date 09-29-2011 12:09

Good morning;
This test will be an amendment to a PQR that is already in use. The previous PQR used 10018 as a secondary filler metal. We are trying to stay inline with that PQR and include the stronger filler metal. The PWHT was done in the weld booth by wrapping the test with a portable machine. No furnace was available. The previous PQR called for 1250F/in for one hour minimum. The pipe wall was .500". I asked about quench and temper to obtain the hardness desired and was told that wasn't possible. Thank you for your response. I appreciate any and all suggestions and advice.

Matt

By js55

Date 09-29-2011 13:42

Keep in mind that if you do quench and temper you cannot use the procedure for stress relief production regimes. You have exceeded transformation temperature. A quench and temper is not a stress relief, although it will do that.

By unclematt (***)

Date 09-29-2011 14:04

Thanks js55. I suggested Q&T as a means to get us to the hardness we need. If it worked, every piece of tooling we did after would have to follow the same process. Manager said not feasible as we would have to destroy one part for each batch. He is going to send the PQR along with the lab results to the weld engineer and go from there. Thanks for taking the time to respond. There is a wealth of knowledge on this forum. I read it as often as I can. Have a good one.

Matt

By Superflux (****)

Date 09-29-2011 14:04

Matt,
Your hold time of one hour per inch sounds to be a standard rule of thumb. You might be having an issue with your fall rate. Are you able to monitor and Control how fast you are cooling down? Thermocouples in use, or are you just peeling back the insulation and using a gun or temp stix? An eternity of hold at temp is of little benefit if the zone gets a quench effect. Stuff the ends so there is no internal draft. Air blast can be just as detrimental as dunking in the bucket (well, not quite). 4140 tends to be some finiky stuff.

By unclematt (***)

Date 09-29-2011 14:08

Hello John;
There were thermocouples attached where the readings were sent to a chart recorder. The fall rate is monitored. The ends, however , were not closed off. Will try that on the next run. Thanks for the response. Hope you are doing well over there. Have a good day.

Matt

By TimGary (****)

Date 09-29-2011 14:27

As I'm no expert on stress releiving, instead of a response, I'll ask a clarification question to the experts...

In order to stress relieve and reduce hardness in high carbon steel, don't you have to post heat treat above the lower transformation temp of 1333 F?

Tim