Influence of several annealing procedures on the mechanical properties of semi-finished products of the material P91/92
Components of P91/P92 in 540-600°C power plants have shown reduced mechanical properties below specified limits after the post weld heat treat-ment (PWHT) procedure.
The quality assurance of PWHT applied on the martensitic steel grades P91 and P92 needs for avoidance of the prior described effect a valid hardness measurement database. This database is currently not available The hardness measurement is a simple method to estimate overtempering effects on mechanical properties in the workshop and on site. It opens the possibility to specify the limits of annealing in respect to mechanical properties of the component.
The database to be established in the project will allow answers on the following questions:
- How often is it possible to repair a weld without a significant negative effect on mechanical properties?
- Is it possible to repair an already repaired component through weld and PWHT without affecting the creep strength?
- How does an over tempering influence the hardness in comparison to an extended tempering time?
The hardness investigation will be based on a test matrix covering six tem-peratures between 710 and 800°C and total tempering durations between 2 and 14h (84 samples). The tests will be completed with toughness measurements, hot tensile tests and some structural analysis.
In case of successful project implementation a better understanding of the results of hardness measurements during quality assurance will be avail-able.
The project is supported by the VGB-Technical Committee “Materials and Quality Supervision".