Determination of creep and fracture properties of P91 steel by small punch testing


Thesis Type: Doctorate

Institution Of The Thesis: Uludağ Üniversitesi, Turkey

Approval Date: 2013

Thesis Language: Turkish

Student: BETÜL GÜLÇİMEN

Supervisor: ALİ DURMUŞ

Abstract:

Within the scope of this thesis creep and fracture mechanical properties of different zones of a P91 (9Cr-1Mo) steel weldment, namely weld metal, base metal, Heat Affected Zone-Fine Grained and Heat Affected Zone-Coarse Grained were determined by Small Punch (SP) Test which is a miniaturized testing technique. The obtained experimental results of the SP creep tests for the different zones of the P91 weldment were correlated with the conventional test results in accord with the guidelines of the CEN Code of Practice (CEN CoP) for SP testing. The evaluation of the SP creep test results was also performed according to a new approach originating from the membrane stretching theory and promising results were acquired validating the applicability of this approach. Ductile to Brittle Transition Temperatures were evaluated from SP fracture tests for all of the zones. The SP transition temperatures of base metal and weld metal were correlated with the transition temperatures obtained from Charpy V notch tests according to the Code of Practice and SP-Charpy transition temperature correlation coefficients were determined for P91 steel which weren?t available in the literature. As well as conventional SP specimens, a new type of SP specimen with a circular notch was used for SP fracture tests to investigate the notch effect on the SP transition temperature. The mechanical behaviour of P91 steel during SP creep and SP fracture tests was investigated by finite element models which were validated according to the experimental results. These models were also utilised in the optimization of the experimental equipment and understanding the mechanical behaviour of the notched SP discs. Optical microscopy was used for investigating the microstructure of the P91 weldment and scanning electron microscopy (SEM) was employed to study the fracture surfaces of the SP fracture discs.