Uvođenje novog termina - Gustina feritnog broja (FND) za merenje feritnog broja zavarenih spojeva na tankim limovima od nerđajućeg čelika serije 300

Abstract

Delta-ferrite content in austenitic steel welds is a crucial parameter to control, since a number of properties depend on this. A FeritScope® is commonly used commercially to measure the Ferrite Number (FN) of the welds which takes advantage of the fact that the retained delta-ferrite phase at room temperature is magnetic whereas austenite is not. However, the readings obtained from the FeritScope® are influenced by a number of constraints such as sheet thickness, weld clad thickness, etc. Although some correction factors have been introduced by the FeritScope® manufacturer to account for these influential conditions, some other geometrical features of the welds were also found to influence the measured FN; for example, despite being a major influential parameter, there is no factor introduced to correct the measurement inconsistencies associated with smaller weld crown widths. In addition, the results obtained on measuring the FN using a FeritScope® contradicted the trends that were expected considering the literature. This research introduces a term called Ferrite Number Density (FND) to represent the ferrite content, in which the measured FN is further proportioned with the cross-sectional area of the weld bead, thus eliminating its dependency on the geometrical size of the weld. It has been established from this research that for welds completed on sheets thicker than 2.4 mm, the FN can be directly used as an indicator of the ferrite content in the weld; however, for thinner sheets, the FND must be used to indicate the ferrite content of the weld, if a FeritScope® with an apportioned size probe is used, e.g. in this case an FGAB1.3-Fe probe. Use of FND eliminated all the contradictions obtained between experimental data and literature for thin sheet welds.