Hydrogen induced cold cracking in steel HAZ

Date 10-30-2015 13:27

Hi all, i was reading one of the articles on hydrogen induced cold cracking in steels.it was written there that it mostly occurs in HAZ of C-Mn steels and are transgranular but can occur in weld bead of low alloy steel. Can any please explain any metallurgical reasons behind this?

Thanks to all in advance.

By Jarhead1 (**)

Date 11-02-2015 14:23

Read this - Good article (AWS)

https://app.aws.org/wj/supplement/WJ_1976_09_s276.pdf

By waqasmalik (**)

Date 10-30-2015 13:36

It says HAZ of C Mn steels are more susceptible to brittle microstructures than weld bead but in case of low alloy steel the weld bead is more susceptible brittle microstructure

By 803056

Date 10-30-2015 14:51 Edited 10-30-2015 14:54

The HAZ usually experiences a high (faster) cooling than the weld, thus more likely to have a martensitic microstructure. Another reason the weld is less likely to become as hard as the HAZ is the weld filler metal is formulated with a lower carbon content than the base metal.

The high hardness can be mitigated by using sufficient preheat and maintaining sufficient interpass temperature to prevent rapid cooling. By ensuring the weld and the HAZ are "soft", the probability of hydrogen assisted cracking is greatly reduced.

Best regards - Al

By waqasmalik (**)

Date 10-30-2015 17:42

HAZ experiences high cooling rate than weld because it is in direct contact with relatively colder base metal?

By Beh Date 10-30-2015 18:02

Hello everyone.
Would you pleas tell me how many time can we do PWHT on one joint ?
And pleas tell the reference ?
Thank you so much ......

By 803056

Date 10-30-2015 18:07

What code? What material? What form of PWHT?

Al

By WeldinFool (**)

Date 10-30-2015 18:26

Dude, learn how to start your own thread!!

By waqasmalik (**)

Date 10-31-2015 12:03

For hydrogen induced cracking to occur four factors must occur simultaneously.
1: temperature less than 300 degrees celcius.
2: residual tensile stress greater than 0.5 of yield stress.
3: hydrogen level greater than 15ml per 100gm of weld metal.
4: susceptible microstructure( cooling rate influence) .

HAZ experiences faster cooling rates than weld bead and also hydrogen likes to go to HAZ mostly? All four conditions find room simultaneously mostly in HAZ?

By Tyrone

Date 11-02-2015 11:51

Hydrogen cracking is black magic.

In some situations one of the factors may dominate. For instance under conditions of ery high stress, cracking may occur in apparently nonsusceptible microstructures or with extremely low hydrogen contents, or under conditions of high hydrogen and a high susceptibility microstructure cracking may occur with no apparent external stress. - Graville

As others have stated, cracking usually occur in the HAZ because:
it cools quicker (heat flow into the base metal), creating martensite (susceptible microstructure), hydrogen migrates to high stress areas.

Tyrone