Abstract
In duplex stainless steels the ideally 1:1 ratio of austenite-to-ferrite phases ensures the outstanding mechanical and corrosion properties compared to other, conventional stainless steel grades. However, this phase balance can be easily shifted to a mostly austenitic or mostly ferritic microstructures, depending on the welding process and heat input. In order to determine the phase ratio, several methods are available to use, such as Feritscope measurements, ASTM E562 manual point count method (on metallographic images) or quantitative image analysis. From these methods, Feritscope measurements cannot be applied to determine phase quantification in the narrow heat affected zone of duplex stainless steel welds – because of the very limited heat input. The manual point count method is very dependent of the assessor and cannot be automated. In this paper a histogram-based image analyzing process was developed, using Beraha's etchant solution. The results were compared to Feritscope measurements and a very good correlation (R2 = 0.9995) was found. This method will give the ability to easily and automatically measure phase ratio in weld metal, heat affected zone or in subsurface regions of multi-pass welds.
Highlights
Duplex stainless steels (DSS’s) and advanced high strength steels are gaining more and more attention from industry, thanks to their excellent mechanical properties and corrosion resistance, compared to conventional stainless steels [1,2,3,4]
The heat affected zone (HAZ) of DSS welds are usually more ferritic, contrary to the weld metal (WM), which can be more austenitic in case of nitrogen-containing shielding gases, nickel over-alloyed filler metal and multi-pass welds [11,12,13,14,15]
In our research we investigated the effect of Beraha’s reagent’s etching time of 2205 duplex stainless steel (EN 1.4462) welds on the image quality
Summary
Duplex stainless steels (DSS’s) and advanced high strength steels are gaining more and more attention from industry, thanks to their excellent mechanical properties and corrosion resistance, compared to conventional stainless steels [1,2,3,4]. The unbalanced microstructure (more ferritic or more austenitic) after welding of a DSS can result in the loss of mechanical properties and corrosion resistance [16,17,18] This is the reason why measurement of the phase balance is mandatory after DSS welding. Magnetic induction based Feritscopes are mainly used for phase ratio quantification These instruments calculate the ferromagnetic phase ratio (ferrite in DSS) in a given volume. Fig. 1) – due to the maximum recommended heat input for DSS welding is 2.0 kJ · mm-1 This narrow region causes uncertainty at the positioning of the probe, and the excited volume is usually greater since the Feritscope is measuring either WM or BM as a part of the HAZ results [19]. The optimum etching process was determined, which gives the best correlation to Feritscope results in the weld metal and base metal
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