Re: [MW:33233] Hardness Issue on weld metal

Please Experts can anyone explain the effect of strain Hardening due to residual stresses and how PWHT reduces Hardness by reducing the dislocation density.

Thanks & Regards

J.Gerald Jayakumar

On Thursday, 14 July, 2022 at 08:46:59 am IST, srinivas rao <engr.srini@gmail.com> wrote:

Hi Williams P Wilson,.

Increase in hardness & strength after a heat treatment is due to Secondary Hardening effect. This phenomenon happens in steels that contains strong carbide forming elements mainly Cr, Mo, Ti, W and V Mostly, normal carbon steels are very less susceptible to such phenomenon and this is very common in Cr-Mo steels, unless there is an excess carbide forming elements present in the steel or supplied thru filler metal. In your case the increase in hardness is seen only on the weld metal. /hardness of base metal hardness to be verified to confirm.

Nowadays most of the clients asked for three cycle PWHT requirements, hence consumable manufacturers left with no other options rather than increasing these micro- alloying elements to the possible extent within the acceptable as per codes. In order to achieve the required mechanical properties after extended hours of PWHT, check with your manufacturer about received a lot/batch containing for the same, kindly check the batch test certificate

you have to report this problem to the consumable manufacturer and seek further advice on consumable selection, it is highly recommended to go with reputed manufacturer for welding consumables procurement for better control on welding

specify the technical requirements to consumable supplies through TDC prior to the obtaining of consumables.

 

 Best Regards,

Srinivas Rao 

Welding Engineer

On Wed, Jul 13, 2022 at 4:27 PM srinivas rao <engr.srini@gmail.com> wrote:

Hi Williams P Wilson,

following points to be verified before going to further details for investigation 

1. Have you checked for consumable mechanical properties with heat treatment conditions before using it PQR qualification ..? 

2. Have you verified Harness on base metal ? 

3. What is the tempering temperature of base material? 

4. Have you Checked Consumable certificates  before welding?  Are your consumables are guaranteed for PWHT applications? 

5. Have you tried other hardness methods for cross verification??

In general PHWT will not increase/affect the hardness, it is just for relieving the stresses only ,On the other hand, PWHT is usually in the same temperature range as the tempering heat treatment operates. Therefore, you should expect the same effects & results which include an increase in hardness. In such cases some of the codes and standards are recommending to control the PWHT temperatures just below 25-30 deg C below the tempering temperatures to control the mechanical properties.

you should check the filler metal certificates and data sheets for better understanding of weld metal mechanical properties before & after PWHT ,  check PMI of weld metal which will give some clarity to easily spot elements  which cause high hardness. 

Regards,

Srinivas Rao 

Welding Engineer

On Wed, Jul 13, 2022 at 3:22 PM williams p wilson <williamswilsonp@gmail.com> wrote:

Dear Experts,

During the PQR qualification of ASTM A 519, Grade 4130 , Pipe 3" x Sch XXS material hardness value in SMAW weld metal area observed in b/w 247 to 283 HV.

The required value is in blw 201 to 241 HV, Base metal hardness also is in the same range.

Preheat temperature : 200 ° C

Interpass temperature : 300 ° C (Max)

Stress relieving details as follows,

600 ° C ± 10  ° C, Holding Time : 01 Hour

Cooling Rate : 150 ° C / Hour
Heating rate : 150 ° C / Hour
Unrestricted heating up to 300 ° C
Controlled cooling upto to 300 ° C

Please reply with your valuable comments to reduce the high hardness observed in the weld metal.

Thank You & Regards

Williams P Wilson

QA/QC Engineer

Welding Inspector (CSWIP 3.1)

Cell: (+968) 94600828

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