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Thanks & Regards
J.Gerald Jayakumar
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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,
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Thanks & Regards
J.Gerald Jayakumar
Dear All,Below email is received from Mr.George Dilintas regarding the same matter on Tue, May 24, 2016
Thank You & RegardsWilliams P WilsonQA/QC EngineerWelding Inspector (CSWIP 3.1)Cell: (+968) 94600828P Please consider the environment before printing this message
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Thanks & Regards
J.Gerald Jayakumar
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below points to be verfied to analysie the hardeness issue1. Travel speed followed
Root | GTAW | ER80S-D2 | 2.4 | 200° C | 200 - 285 ° C | 102 | 10 | 101.45 | 0.603 | |
Hot Pass | GTAW | ER80S-D2 | 2.4 | - | 200 - 285 ° C | 175 | 11.4 | 130.20 | 0.919 | |
Fill | SMAW | E10018-D2 | 2.5 & 3.2 | - | 200 - 285 ° C | 111.1 | 22.8 | 84.10 | 1.807 | |
Cap | SMAW | E10018-D2 | 2.5 & 3.2 | - | 200 - 285 ° C | 84 | 22.70 | 106.20 | 1.077 |
2. How weld pass is deposited at different positions (what is the location of specimen 6 O clock or 12 clock or 3clock )
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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
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
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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