Microstructurel characterisation of creep tested advanced austenitic stainless steel super 304H

Microstructural characterisation was performed on the gauge section of two creep rupture samples manufactured from Super 304H; an advanced austenitic stainless steel that is used as superheater and reheater tubes in power plants. The samples had been exposed to uniaxial creep tests (Sample A: 700 degrees C and 75Mpa, Sample B: 650 degrees C and 120Mpa) where both exhibited low creep ductility. Six phases were identified: MX (Nb-rich), sigma, Cu-rich, M23C6, modified Z phase and Fe (BCC). Quantification of Nb-rich and Cu-rich particles revealed similar to 10% and similar to 16% more Nb-rich and Cu-rich particles respectively in Sample A versus Sample B. The amount of sigma and the average particle size for the Nb and Cu-rich particles was similar for both samples. There appears to be an association between the sigma phase and creep cavities as shown in 2D microstructural characterisation which could have contributed to the low creep ductility exhibited by these two creep samples.

Automated summary

Microstructural characterization was conducted on two creep rupture samples made from Super 304H, an advanced austenitic stainless steel used in power plants. The results showed that Sample A had approximately 10% more Nb-rich particles and Sample B had approximately 16% more Cu-rich particles. The amount of sigma phase and the average particle size for Nb and Cu-rich particles were similar in both samples.