Re: [MW:29863] HIGH HARDNESS AFTER PWHT

Dear Karthikeyan,

Further to Mr. Ramin's comments, I would like to add few more points.

The phenomenon of increase in hardness & strength after a heat treatment is termed as Secondary Hardening. This phenomenon occurs in steels that contains strong carbide forming elements mainly Cr, Mo, V, W and Ti. Usually, Cr- Mo steels are highly susceptible to secondary hardening during PWHT, whereas carbon steels are very less susceptible to such phenomenon, unless there is an excess carbide forming elements present in the steel or supplied thru filler metal.  

From the given data, we can see the increases in hardness is seen only on the weld metal. So, the below could be the possible reason for high hardness only in the weld metal.

• Widely these days If PWHT is applicable, most of the reputed clients mandated 3 cycle PWHT requirements. Hence, in order to achieve the required mechanical properties after extended hours of PWHT, consumable manufacturers left with no other options rather than increasing these micro- alloying elements to the possible extent within the acceptable as per ASME Section 02 Part C.  (You may be received a lot/batch containing increased microalloying elements, please check the batch test certificate and if possible, carry out a weld metal chemical analysis)

In this situation, you must report your observations/concerns to the concerned consumable manufacturer and seek further advice.

It is always recommended to stipulate the technical requirements in terms of Technical Delivery Condition (TDC) prior to the procurement of consumables.

 

Regards,

Sudhakar K

Welding Engineer. 

On Wed, Jul 10, 2019 at 1:41 PM Karthikeyan Muthuvel <m.karthick2020@gmail.com> wrote:

Dear Experts,

Good day.

We had used the consumables (ER70S-2) / OK TIG ROD 12.62, Size : 2.4mm Dia. for our Production weld joints (Pipe materials : Carbon Steel ASTM A 106 Gr. B; Size : 3" X Sch 40). further to inform you that we had checked the Hardness of Base material , HAZ & on weld Metal before & after PWHT (below hardness readings were observed).

HARDNESS VALUES BEFORE PWHT

1. Base material : 130 to 150 HB
2. Heat Affected Zone : 140 to 160 HB
3. Weld Metal : 170 to 190 HB

HARDNESS VALUES AFTER PWHT 

1. Base material : 120 to 140 HB
2. Heat Affected Zone : 130 to 150 HB
3. Weld Metal : 210 to 250 HB

After performing PWHT the hardness value of Base material & Heat Affected Zone has been reduced. whereas the Hardness value of Weld Deposition has been increased (which is beyond the acceptable limit). 

So, I would like to know from you that what might be the technical reason/root cause for increase in hardness only on the weld joint after PWHT. 

Below are the PWHT parameters fyi.

Soaking Temp. : 620 Deg C

Soaking Time : 1 hr.

Rate of Heating : 100 Deg C per Hour (from 100 Deg C)

Rate of Cooling : 100 Deg C per Hour (Upto 100 Deg C)

Note:

1. We had performed nearly 30Nos. of Production joints & we had face the problem of Hardness on all the weld joints. 
2. Hardness was tested using Mic 10 tester method ( even cross verified with Equotip method & Tele brinell Method)

Thank you for your support.

Warm Regards,

KARTHIKEYAN  M.

QA/QC Inspector

Saudiarabia

Mobile:+966-501176985,

E-mail: m.karthick2020@gmail.com

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