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Secondary Ferrite Number Reference Materials: Gage Calibration and Assignment of Values



Christopher N. McCowan, Thomas A. Siewert, D P. Vigliotti, C M. Wang


Ferrite Numbers (FN) were assigned to blocks of stainless steel that serve as secondary ferrite reference materials (RM 8480 and 8481), and these specimens were placed in our Reference Materials inventory. These reference materials are used to calibrate several types of instruments used to measure the FN, which is proportional to the ferrite content in stainless steel welds. The ferrite content influences the physical and mechanical properties of stainless steel welds. This report documents the procedures used to measure the reference materials and the results of our measurements. Appendices are included to document our primary gage calibrations (Appendix A), the measurements made on the FN reference materials (Appendices B and C), and other supporting measurements made for the study (Appendix D). Our initial effort was devoted to finding and reducing sources of uncertainty in the gages (instruments for measuring FN) and in the calibration procedures. After improving our gages and procedures, we found that our calibration lines were nearly linear over the range of 0 to 100 FN and that the gages compare well to gages used by The Welding Institute (TWI), which had assigned the certified FN values to secondary specimens produced in the past. The measurements on the reference materials showed that the standard deviations in FN for the secondary specimens were typically less than 0.5 FN for the 0 to 30 FN range, and less than 3 FN for the 30 to 100 FN range. The microstructure was found to be a finely dispersed and homogeneous mixture of ferritic and austenitic phases, with a percent ferrite area fraction that was nearly equivalent to the FN assigned to the reference materials (up to about 60 FN).
Special Publication (NIST SP) - 260-141
Report Number
No. 260
Part 141


feritscope, ferrite, ferrite content, ferrite detector, ferrite number, inspector gage, Magne-Gage, reference material, stainless steel


McCowan, C. , Siewert, T. , Vigliotti, D. and Wang, C. (2000), Secondary Ferrite Number Reference Materials: Gage Calibration and Assignment of Values, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed July 15, 2024)


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Created February 1, 2000, Updated November 10, 2018