Welding 4340 forging to 4130 pipe

By ronourse Date 08-27-2004 18:21

We are having a problem with post weld cracking in the HAZ of the 4340 forging:

Conditions are:

4340 forging: annealed / normalized, weight 10 - 12#, 4.5" diameter
4130 pipe: annealed / normalized, 4.5" OD, .25" wall, 69" long
Process:
1) Preheat forgings to 450 deg F in electric oven
2) Place pipe in allignment fixture
3) Pull forging from oven, allign and tack only, put on weld positioner
4) Flame heat weld prep area and 3" each side to 800 - 900 deg F, check with temp stick
5) TIG root pass
6) GMAW until fully welded using E4130 weld wire
7) Flame heat the same area back to 800 - 900 deg F
8) Wrap in mineral wool insulation and stack weldments in a covered steel box to facilitate slow cool.
9) Part is sent out for harden and temper to Rc 39 - 44
10) Sent out for Mag Part. inspection. Last lot had 33% fallout for cracks in HAZ of forging.

Any ideas or experience with these materials?

By ajoy

Date 08-29-2004 07:54

could you please check the AWS classification of the GTAW / GMAW filler wire as the wire you have specified does not seem to be of a suitable carbon steel type.

Also, I would suggest to you to inspect the weld just after welding and make sure you dont have any sharp notches on the toes. HAZ cracks generally pick up notches at weld toes to originate.

By ronourse Date 08-30-2004 18:41

Weld wire is NOT to an AWS specification. Weld wire purchased and certified to SAE 4130. This is the same chemistry as the pipe material.

Thanks for your input.

Ray

By ajoy

Date 08-31-2004 05:51

I am afraid this wire wont work and you may continue having cracking problems in your welds.

The right choice for this application would be any 80 ksi AWS classified solid wire of 0.8 or 1.2 mm.

By ronourse Date 08-31-2004 11:25

Thanks. We will take a serious look at this. Why 0.8 - 1.2 mm wire? This is a fairly large weld. Also, what is your opinion of our preheat and post heat process? Any more detailed specifics?

Thanks again.

Ray

By ajoy

Date 08-31-2004 13:11

You may use a higher size filler, lets say 2.4 for GTAW and 1.6 for GMAW.

I would increase the preheat to 250 deg. c ( min.) and probably reduce the post heat to 350 deg. c. Further, dressing of the weld needs to be done just after the welding to remove all notches.

From QA point of view please keep in mind that when using a suitable filler wire for the weld, you will not get a hardness of 39 to 44 RC on the weld surface after hardening. This is because, all the filler wires for carbon steels have less than 0.1 % carbon and thus do not respond to heat treatment.

By GRoberts (***)

Date 08-31-2004 14:55

If you want a hardened weld, you are using the right wire, but if you don't need it, the 4130 wire is making it a bit more difficult. A lower strength wire if allowable would place less stress on the HAZ of the base metal.
There are some other questions that might be pertinant. How much do the parts cool off during the welding process? At what point does the HAZ crack? Before or during/after heat treatment? How clean are the parts? Are there any machining oil or other contamination that might be contributing hydrogen?

Here are some other ideas you might want to look at:
Can you go right to PWHT without cooling down all the way, even an intermediate stress relief , say at 1200F or similar?
Can you keep them above approx 450F for several hours after welding to aid hydrogen removal? (Not a substitute for proper cleaning though)

By ronourse Date 08-31-2004 19:13

To both you and ajoy,

A little more research has been done uncovered the following:

The 4130 weld wire was a requested deviation from the drawing requirement by the previous manufacturer to the customer. The original weld wire callout on the drawing is ER-140S-1 (we are not familiar with this wire). I can find no reason for the request. The contract documents do not specifically require the weld itself to meet any post heat treat hardness requirements. Post heat treat hardness requirements are specifically called out for the 4340 forging and the 4130 pipe.

Unfortunately, we cannot go directly into a 1200 deg F oven right after weld. The best we can do is re-heat after weld and wrap with mineral wool to facilitate a slow cool. Quite possible that we are not holding it at the necessary temperature long enough.

I have taken note of all the other suggestions, especially the post weld prep of the "toe". The cracks do appear to start at the weld toe. We do a Mag Particle inspection after heat treat. That is where the cracks are seen. Visually, they are almost impossible to see. We have had one weldment sent out for lab testing and the results indicated the defect was a result of the weld process (or lack thereof). We will start doing a visible dye penetrant test before thae part is sent out for heat treat. Also, the parts are "ground" clean before welding. The pre heat should be burning off any organics thay may be present.

Thanks for your help.