Determine Ferrite Content in Metallic Materials

Ferrite measurement or delta ferrite measurement and the control of ferrite phase in both Austenitic and Duplex Stainless Steels is important to maximize the physical, mechanical and corrosion resistance of the material.

Ferrite is one of the metallurgical phases or components found in the microstructure of both austenitic and duplex stainless steels. Ferrite is an important constituent of stainless steel as it helps prevent hot cracking when the material is welded. In Austenitic Stainless Steels too much ferrite will lead to a reduction in the corrosion resistance properties of the material. The control of welding and ferrite measurement of components is important to ensure that zero or extremely low ferrite content is maintained.

Austenitic Stainless Steels are low strength materials so for more aggressive, higher temperature and structural applications Duplex Stainless Steels are used. These stainless steels contain a mixture of ferrite and austenitic phases. This increases the properties of Duplex Stainless Steels; toughness so it can be used at very low temperatures, strength so it can be used in structures such as bridges and its resistance to stress corrosion cracking which can be a serious problem in aggressive environments at elevated temperatures. Control of the ferrite content of components prior to and after welding is important to ensure that the material properties are maintained.

EILAB CAPABILITY FOR FERRIT CONTENT MEASUREMENT

Advanced NDT Solutions provide ferrite measurement and can assist in the control of welding to ensure that whatever properties are required, they are measured and controlled to ensure compliance.

Magnetic-Inductive Measurement: With the magnetic-inductive method, the ferrite content can be determined quickly and non-destructively in accordance with the ISO 17655. For example, weld seams on austenitic steel can be checked on site and repaired if necessary.

Optical Microscopic Method: This test method describes a systematic manual point counting procedure for statistically estimating the volume fraction of an identifiable constituent or phase from sections through the microstructure by means of a point grid.

Common ferrite measurement specifications are:

• ISO 17655 – Destructive tests on welds in metallic materials — Method for taking samples for delta ferrite measurement
• ASTM E407 – Standard Practice for Micro-etching Metals and Alloys.
• ASTM A923 – Standard Test Methods for Detecting Detrimental Intermetallic Phase in Duplex Austenitic/Ferritic Stainless Steels.
• ISO 945-1 – Microstructure of cast irons – Part 1: Graphite classification by visual analysis.