A Comparison of Corrosion Behavior of a Super Duplex Stainless Steel and an Austenitic Stainless Steel in a Molten Sn–3.0Ag–0.5Cu Lead-Free Solder

Abstract

To determine the endurance of a super duplex stainless steel (SDSS) used for wave soldering bath materials, the corrosion behaviors of a SDSS, SAF2507, and a comparative austenitic stainless steel, SUS304L (conventional material for tin-lead soldering container) in a Sn–3.0Ag–0.5Cu molten lead-free solder were investigated. After testing, the samples were analyzed by optical microscopy (OM), scanning electron microscopy (SEM), and semi-quantitative phase identification under an energy dispersive spectrometer (EDS) to evaluate the effects of the composition of test materials and immersion conditions on their microstructure evolution and corrosion behaviors.
As results show, when compared to the SUS304L, SAF2507 has better corrosion resistance to lead-free solder after immersion at the assigned temperatures (350, 450, and 550°C) and times (from 250 up to 1500 h). When the test temperatures of 350 and 450°C were employed, no obvious dissolution occurred for SAF2507, whereas SUS304L exhibited severe dissolution. However, if the immersion temperature of 550°C was used, the dissolution rates of SAF2507 increased significantly. It was found that the failure type of both materials was related to atom diffusion, formation of the reaction layer (RL), and finally dissolution, which is a typical failure type of Liquid Metal Corrosion. Moreover, SEM and EDS results reveal that the major intermetallic phases in the RL for both stainless steels are Fe/Sn and Cr/Sn compounds.