Bainite P91
Bainite P91
(OP)
Would someone explain to me how P-91, welded to F-91 with 91 filler could turn into bainite. I have never seen any studies, or CCT diagrams saying it could be anything but martensite (possibly with retained austenite), even after PWHT. It was reported bainite microstructure. All I could think was possibly one piece of the equation was not 91, but that has been checked.





RE: Bainite P91
The tungsten /wolfram modified alloys P92, T23, and P911 are deliberately formulated to form bainite, but they use a different formulation than P91- they substitute W wolfram for molubdenum. They also need to be cooled extra fast in order to have the code required creep properties associated with bainite.
RE: Bainite P91
RE: Bainite P91
RE: Bainite P91
The alloy composition will not permit bainite to form, instead it will be either ferrite and carbides (held or slow cooled for 2 hours between 650 deg C and 800 deg C)or martensite + ferrite + carbides (cooled between 450 deg C and 650 deg F over a 2 hour period).
RE: Bainite P91
Speaking of ORNL, do you know whatever happened to the alloy that Dr. Jawad and ORNL were developing to overcome a lot the problems with welding and PWHT for this this family of alloys?
RE: Bainite P91
RE: Bainite P91
Was the reported bainite in the base metal, weld metal or HAZ; through thickness or OD surface? How was preheating and dehydrogenation performed; with resistance elements or oxy-acetylene? I have seen some highly unusual microstructures in P91 recently - associated with suspect normalizing and tempering and preheating/dehydrogenation.
The reported bainite may have been coarse martensite + ferrite.
RE: Bainite P91
I presume you are referring to the Fe-3Cr-W(V) bainitic alloys, called 315, 315T? Do you have a copy of the following Technical Report-"Development of a Fe-3Cr-W(V) Ferritic Steels for Industrial Applications" by Dr Jawad (Nooter) and Dr Sikka (ORNL)?
Information is still being reviewed thru our ASME B&PV Code Subgroup on Materials. The report mentioned above is one of the most comprehensive status reports on these alloys.
RE: Bainite P91
through thickness or OD surface? --- od
How was preheating and dehydrogenation performed; with resistance elements or oxy-acetylene? --- resistance
Thermal history : Preheat to 400F, Weld, Post heat @ 625F for 2 hr, cool rate @ 175/hr to 100F, PWHT 1300F 2 hr, cool rate 200/hr. According to charts provided
RE: Bainite P91
RE: Bainite P91
Lowest - 127 BHN
Highest - 223 BHN
Most between 150 and 190
I can't figure it out. The PWHT chart they supplied looks reasonable - if it is the right one. The hardnesses are ridiculous for the material and PWHT described - if they took them correctly. The microstructure reported shouldn't be, although I have two reports on material ID - all 91.
RE: Bainite P91