Re: [MW:33346] Hardness Issue on weld metal

Hi williamswilsonp 

After referring the welding parameter details in your mail please note my findings

1. Heat input followed during welding seems to be considerably low

2. Travel speed is little higher. 

3. bead width /bead overlap/ welding sequence followed to for PQR is to be checked for mail we cannot conclude for root causes          

based on parent material and consumable strength /metallurgy more heat input may require Say the range is 1.5 - 2.5kJ/mm for these sizes of electrodes to slow down the cooling during welding/ control of Cooling rate i.e. considerably Lower travel speeds are recommended for this material 

if base material heat treatment condition quenched and tempered, we cannot go PWHT temperature more than tempering temperature of material as strength may reduce considerably and may not meet the requirement of minimum strength. (for other material heat treatment conditions, we can go with PWHT soaking temperature 650-680°C for controlling the hardness as per some of the material/consumable suppliers. 

The stress relieving temperature is normally kept below (normally by about 30°C) the tempering temperature If the temperature exceeds this more metallurgical changes occur where by strength or hardness reduction is rapid. so the heat treatment is done below the known as tempering temperature.

In general higher the stress relieving temperature lower are the residual stresses and higher is the reduction in hardness. if the holding time kept higher there is a considerable reduction in hardness and residual stresses will be lower. the weld shall be allowed to cool slowly.
hardness reduction is depending on other factors like welding technique, parent metal and welding rod composition, preheat/inter-pass temperature, welding electrode or rod size, travel speed followed during welding. The hardness reduction after PWHT is dependent on its initial value as measured before PWHT. after PWHT the reduction in hardness is may not be same in all the three regions.

recommended to consider the below if you are going ahead with new PQR qualification:

1.       Minimum recommended Preheat temperature for welding is 200°C, increase this to 220- 230°C ensure inter- pass temperature is shall not cross more than -300-315°C

2.       Since PWHT temperature is lower cannot be increased further due material heat treatment for this material it is recommended to increase the Soaking time to achieve required hardness

3.       Heat input range: 1.5 to 2.5Kj/mm or considerably with lower travel speed to keep heat input in control

4.       Temper bead technique or ensure minimum 40-% bead overlapping during welding to get proper tempering effect

5.       Weld interruption shall be avoided, during unavoidable situation, the weld shall be wrapped by thermal insulating blanket for slow cooling.

6.       To avoid hardening peaks, last filler pass should be flush with the pipe surface so that the edges of the joint preparation are melted.

7.       Before last capping pass apply minim 270-280°C Preheat

Experts , correct me if any changes required in above undestding .

Thanks & Regards 

Srinivas Rao

welding Engineer 

On Tuesday, August 2, 2022 at 7:17:20 AM UTC+4 williamswilsonp wrote:

Dear Sir,

Thanks for your email.

Consider my reply marked in "Blue"

On Thu, Jul 28, 2022 at 7:25 AM Sudhakar Kuppuswamy <sudhak...@gmail.com> wrote:

Hi, 

With 600 Deg C as holding temp and one hour holding time is not adequate to bring down the hardness . Increasing  the holding time to 2 hours minimum will definitely help. 

Otherwise , holding temp of about 650 Deg C will greatly help in reducing the hardness. - This material tempering done at 630°C

    That's why we decided to conduct the PWHT at 600 °C (lower than the tempering temp.)

To have a good control on the cap side hardness (I.e the  last layer hardness) please try to slightly increase the pre-heat temp to the maximum possible extent. let say, in your case above 220 degrees C but less than 260 degree C. Also deposit the cap pass with temper bead technique. By doing so, the layer underneath the cap pass gets well annealed, so the hardness limit will fall within the acceptable limits. - We will start doing this method  

Hope this helps!

Regards,

Sudhakar K 

On Wed, 13 Jul 2022 at 3:22 PM williams p wilson <william...@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

P Please consider the environment before printing this message

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Regards,

Sudhakar K CEng MWeldI,IWE.

Welding & Metallurgical Engineer,

Email: sudhak...@gmail.com.

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