FERRITE DETERMINATION IN STAINLESS-STEEL WELDS - ADVANCES SINCE 1974

Since the Comfort A. Adams Lecture of W.T. DeLong in 1974, significant advances in the determination of ferrite content in stainless steel w elds have taken place. These art reviewed in the present Comfort A. Ad ams Lecture. Examination of MagneGage Number 3 Magnet strengths led to a concept for extending, by extrapolation, the calibration range of A WS A4.2-74 to ferrite levels above 28 FN. Ferrite Numbers could then b e assigned to thinner coating thickness standards for primary calibrat ion of MagneGages over the extended range. Round robin studies were co nducted to establish the reproducibility of measurement of Ferrite Num bers in duplex stainless steel welds. The method was incorporated into ANSI/AWS A4.3-91. Calibration using primary standards (coating thickn ess standards) is limited to a very few instruments, due to the differ ence in distribution of ferromagnetic material in costing thickness st andards vs. that in stainless steel weld metal. Secondary standards, c overing the range from near zero to about 100 FN, became available for calibrating additional instruments at the beginning of 1995. A round robin of tests established that the interlaboratory reproducibility of measurement after calibration by the secondary standards is similar t o that observed with MagneGages calibrated by use of primary standards . Excessive ferrite in duplex stainless steel weld metals has adverse effects on weld properties. The utility of the Ferrite Number measurem ent system for duplex stainless steels is thus established. Developmen t of a solid link between Ferrite Number and ferrite percent, determin ation of ferrite in the heat-affected zone (HAZ) of duplex stainless s teel weldments, and further development of predicting diagrams remain for the future.