ASME Sec Viii Div 1 UCS-56 only mandates min. PWHT temperature and even that can be reduced
further a bit by compensating more time per UCS-56.1
Max. PWHT temperature shall never exceed lower transformation temperature for below reason:-
Guessing that thickness of component would be more than 32mm or above so heat treatment
condition would be either Normalizing or Quenching and Tempering:-
For Normalizing:- component heat treated above Ac3 (upper critical temperature and cooled under
control to form Ferrite + Pearlite microstructure, PWHT is carried out to reduce residual
stresses produced during thermal changes but must be below Lower critical temperature not to
change the microstructure.
For Quenching and Tempering:- component heat treated above Ac3 and cooled in water/oil forming
martensite to gain better strength but with excessive hardness then tempering at below Ac1
(lower critical temp) to temper the martensite thus reduce hardness and increase ductility and
toughness.
PWHT temperature is generally kept below 30deg C below tempering not to alter properties
maintained however there would be slight decrease in strength and toughness, is the reason
often client require to simulate with test coupons of same heat treatment that PWHT does not
reduce mechanical properties below required.
Regards
Manpreet Singh
On Sat, 11 Feb 2012 09:13:17 +0530 wrote
>Dear Friends,minimum PWHT Soaking temperature is given in ASME Sec VIII Div. 1 UCS-56, My
question is What is maximum temperature that we can use for PWHT with reference to some
applicable standards or metallurgical point of view point?ORCan we do PWHT for P.No.1 Gr.1 & 2
(e.g SA 516 Gr. 60 & 70) maximum up to lower critical temperature i.e. 723 Degree Centigrade?
Thanks in Advance for your valuable share.
--
>
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