Whey Normalize After Welding? 1

[tc7]

I have a weldment that specifically calls for "normalizing and stress relief" after welding. The material is 4130 purchased in the normalized or annealed condition. AWS D1.1 is the applicable Code. This sequence is different than my typical welds and weld procedures call for, i.e., typical (for us) is to weld on normalized or annealed material then perform a simple PWHT (stress relief/HAZ conditioning) operation for the typical 1150 degrees at 1-hour per inch.

Since this job is requiring a complete post weld normalizing "and" stress relief, am I bound to qualify a new WPS?

As an aside, what would be the logic or advantage in completely re-normalizing after weld as opposed to just post weld stress relieving?

 

[metengr]

tc7;
Normalizing and stress relief are two different concepts; if a normalizing heat treatment is performed on a completed weld, stress relief is accomplished as well as eliminating the weld heat affected zone, and tempering of the weld and surrounding base metal heat affected zone structures. Stress relieving, via PWHT, can be done w/o normalizing. Tempering is accomplished, however, the base metal heat affected zone still remains.

So, if you intend to normalize in lieu of PWHT, you would need to re-qualify the PQR's for this thermal heat treatment.

 

[tc7]

Thanks Met-
You confirmed much of what I suspected, however when you state that "Stress relieving, via PWHT, .... Tempering is accomplished, however, the base metal heat affected zone still remains", does this mean that the hardened HAZ will indeed become annealed but we will be left with an inconsistent grain structure? If so, what affect will this have on strength and toughness?

 

[metengr]

tc7;
I appreciate your questions - this statement reflects the following, the base metal HAZ structure will remain, the hardness and residual stress will be reduced from tempering. As with most carbon and low alloy steel responses to tempering, as the hardness decreases, the strength will decrease but the ductility and toughness will increase.

Normalizing results in the elimination of the HAZ structure because the base metal and weld metal are austenitized and air cooled.

 

[tc7]

Have you ever seen a need to perform the low (relative) temperature stress relieve prior to normalizing the weldment so as to possibly minimize distortion concerns?

 

[metengr]

tc7;
No, because I would revise the ramp up rate for heating in the furnace during the normalization heat treatment.

 

[tc7]

Excellent information Metengr, as always.
Thankyou for your help.

 

[GRoberts]

TC7,
If you do end up having to qualify a WPS with a normalizing PWHT, be carefull about your consumable selection. The normal filler metals used to weld this type of material (depending on the materials strength), such as 7018-12018 or equivalent wires, will generally not have enough alloy content to match the strength of the 4130 after normalizing. You will need to use a filler metal that is closer to the base metal in chemistry. ESAB makes some SMAW electrodes for this purpose. (They make FCAW electrodes as well, but they have excessive spatter and smoke)