As for %Al allowed in CSEF materials I am basing the answer on grade 91.
The modifications that were made to the standard 9Cr-1Mo steel to create
Grade 91 included controlled additions of vanadium, columbium (niobium), and
nitrogen. The mechanism of enhanced creep strength for Grade 91 is the
precipitation of vanadium/columbium rich carbonitrides of type MX (where
M=Cb or V and X=C or N) at defect sites and lath boundaries in the martensitic
base structure. De-oxidizers, particularly aluminum, are commonly added during
the melting process to remove oxygen from the melt. Since Aluminum also has a
stronger tendency to combine with Nitrogen than do vanadium or columbium,
high levels of Aluminum will reduce the amount of free nitrogen available to
form the carbo-nitrides precipitates that support the long-term creep strength of
the alloy. Since it is difficult to increase the amount of nitrogen in the molten
alloy, the primary option to insure adequate free nitrogen is to limit the amount
of aluminum and other de-oxidizers that can be added to melt. The target ratio
for nitrogen-to-aluminum (N/Al) should be 4 or greater, and under no
circumstances should a ratio of less than 2.0 be accepted.
Michael J. Crichton
American Electric Power
Metallurgy, Welding & Standards (MWS)
| kannayeram gnanapandithan <kgpandithan@gmail.com> Sent by: materials-welding@googlegroups.com 04/26/2013 02:29 AM
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what is relation between Creep strength with grain size
How much %Al is allowed in CSEF steel and why, what is consequance if it is more than recommended
Pandithan
Welding Consultant
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