Considerations to be taken when performing point counting of duplex stainless steels

摘要

Ferrite content is considered important for many reasons and the degree of relevance and optimal level is discussed in different forums. In order to even discuss different ferrite levels it is important to have accurate measurement methods. Recently some considerations that should be taken into account using a ferrite scope have been presented. In the present paper some considerations for measuring the ferrite content according to ASTM E562 are explored. The different areas that should be considered relevant when performing point counting are: 1.sample preparation, including both polishing and etching 1.1 Every step of a polishing procedure must remove the deformed volume from the previous step 1.2 A clear definition of location of phase boundary, decided and verified. Normally one should not choose the dark outline caused by an etchant. 2.Adequate sample types for measurements and relevance to final result. 2.1 Measure cross-sections 2.2 Consider only mean values as result and not distributions 3Measurement setup and helpful strategies 3.1 Use as low magnifications as possible still fulfilling recommendations in ASTM E562 for size of grid or other standards setting specific magnification. 3.2 Actively decide location of grid point, especially close to phase boundaries. Use zoom as a tool. Introduce rules for decisions for consistent results. 3.3 Verify procedure and strategy by reference measurements.