As I describes this material and the welds are susceptible for embrittlement. To simulate this phenomenon there's a special PWHT, called step cooling. This PWHT is as follows :(example) warming up to 600°C at 50°C/hr, holding time 1 hr, followed by cooling steps : cooling down at 5.5°C/hr to 540°C, holding during 15 hr // cooling down at 5.5°C/hr to 525°C, holding during 24 hr // cooling down at 2.8°C/hr to 500°C, holding during 60 hr // cooling down at 2.8°C/hr to 470°C, holding during 100 hr // cooling down at 10°C/hr to 315°C, followed by air cooling.
After this cycle CVN values are measured.There's a shift in the 54 Joule transition temperature, compared to normal PWHT : example for normal PWHT there's 54 J at -40°C, but for PWHT with step cooling there's only 54 J at -20°C !!! The material is more brittle after step cooling. The acceptance criterium is formulated : transition temperature after PWHT + (1.5 x transition temperature after PWHT with step cooling) <= 38°C
Not every welding filler can give these results. If FCAW is used then step cooling results are very bad and the criterium fails. This is due to impurities (talking about ppm's P, As, Tn, Sb) in the flux. There are so called "embrittlement factors", describing the maximum amount of allowable impurities : Bruscato and Watanabe factors. There's no fabricator capable to produce flux cored wire with this low impurity level. Normal flux cored wires for this material of course exist but can not meet the requirements of step cooling !
For this reason there's only MMAW and SAW, step cooling tested, for most fabricators. Also GMAW should not be a problem ! So, I am looking for some field experience on thick plate !
If you want to read about this, look for "Science and Technology of Welding and Joining 2000 Vol.5 No.5" : good article.
Further : http:\\www.msm.cam.ac.uk/map/mapmain.html
Further : http:\\www.btwcan.com/html/ppf8.html