Question: Is 11CrCb material a better fit for F class Exhaust Gas temperatures.
Answer: YES. 11CrCb has a much longer creep life that 409SS, but not quite as good as 304SS. HOWEVER, 304SS thermally grows almost twice as much as 11CrCb and 409SS so this drastically different thermal growth rate for 304SS induces additional stresses into the materials and welds through cycling. 11CrCb was specifically developed for the Gas Turbine and Automobile Exhaust Market.
The firing and exhaust temperature for these turbines have increased to a range to where higher alloy material should be considered for the manufacture of these silencer panels.
Comparison of 11 Cr-Cb and 409SS for Silencer Panels:
There are two different materials that are primarily used for silencer panels for high temperature applications. These are 409 stainless steel and 11CrCb. The 2 properties of interest when comparing 409SS and 11crcb are the fatigue and the creep properties at elevated temperatures. The fatigue properties determine the number of times the material can be subjected to a turbine start/shutdown cycle before failure occurs.
The creep properties determine the number of hours of continuous service at the elevated temperature the material can survive before the failure occurs. The 2 materials, 409SS and 11crcb have similar fatigue properties and will provide similar results for start/shutdown cycle life. The drawback for 409SS in turbines that operates above 1100º F is the creep properties. The creep strength of 409SS decreases significantly in comparison to 11crcb for service temperatures above 1100º F.