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This study investigated the resistance spot welding (RSW) parameters for an uncoated mild steel sample and two hot-dip galvanized steel samples with different zinc layer thicknesses. Two RSW schemes were considered: a one-step scheme with no pre-heating stage and a two-step scheme comprising a pre-heating stage followed by a main welding stage. The strengths and weldabilities of the weldments were evaluated by peeling tests, cross-tension tests and weld lobe diagrams with welding currents ranging from 5 to 12 kA and welding times of 8–24 cycles. The optimal welding time was found to be 16 cycles. The weldability window shifted to a higher welding current region as the zinc layer thickness increased. Compared to the one-step RSW scheme, the two-step scheme suppressed interfacial failure and achieved a higher peeling load at a lower welding current. For a given welding current, the weldments produced using the two-step scheme had a larger nugget diameter and higher cross-tension load. Overall, the two-step RSW scheme achieved a better welding quality than the one-step scheme irrespective of the zinc layer thickness.

The environmentally assisted cracking behavior of dissimilar metal (DM) welds, including Alloy 52-A 508 and Alloy 82-A508, under simulated BWR coolant conditions was studied. Effects of postweld heat treatment and sulfur content of the base metal on the corrosion fatigue and SCC growth rates of DM welds were evaluated. The crack growth rates for the DM weld heat-treated at 621 °C for 24 h were observed to be faster than those for the as-welded. But the DM weld heat-treated at 621 °C for 8 h + 400 °C for 200 h showed better SCC resistance than the as-welded. The longer the heat treatment at 621 °C, the higher the chromium carbides density along the grain boundary was observed. Sulfur could diffuse out of the base metal and segregate along the grain boundaries of the dilution zone, leading to weakening the grain boundary strength and the SCC resistance of the Alloy 52-A508 weld.

Corrosion fatigue behavior of the dissimilar metal weldment, Alloy 52-A508, under a simulated BWR coolant condition was studied. Corrosion fatigue crack growth rates of the dissimilar metal weldments were observed to increase with crack extension under the nominal constant ΔK loading mode. It could be accounted for by a decrease in the Cr and Ni contents and the crack closure effect with the weld depth. Finite element analysis on the welding residual stress was performed. The trend of analytical results agreed well with that of the residual stress measurements obtained by a hole-drilling strain gauge method.

The corrosion fatigue crack growth behavior of A533 and A508 low alloy steels under simulated boiling water reactor (BWR) coolant conditions was studied. Corrosion fatigue crack growth rates of A533B3 and A508 cl. 3 steels were significantly affected by the steel sulfur content, loading frequency and dissolved oxygen content of water environments. The data points outside the bound of Eason’s model could be attributed to the low frequency, higher steel sulfur content and high dissolved oxygen in water environments. The sulfur dissolved in the water environment from the higher-sulfur steels was sufficiently concentrated to acidify the crack tip chemistry even in the hydrogen water chemistry (HWC). Therefore, nitrogenated or HWC water showed little or no beneficiary effect on the high-sulfur steels. For the steel specimens of the same sulfur level, their corrosion fatigue crack growth rates were comparable in different orientations, which could be related to the exposure of fresh sulfides to the water environment. The percentages of sulfides per unit area, by quantitative metallography, were comparable for the steel specimens of both orientations. When the steel sulfur content was decreased to a critical sulfur content 0.005 wt.%, the crack growth rates decreased remarkably.

Fatigue tests under constant amplitude load were conducted on CT specimens of A533B3 steels with four levels of sulfur content at different temperatures in air and high-temperature water environments. A modified capacitance-type COD gauge was shown to be suitable for fatigue crack length measurement at high temperatures in air. The observation that the Young's moduli measured at a strain rate of 4 × 10 −3 s −1 for the A533B3 steels at 150 °C and 300 °C did not decrease with an increase in temperature seemed to be related to the presence of dynamic strain aging. The fatigue crack growth rates at 150 °C and 300 °C in air were about two and half times slower than those tested at 400 °C, because dynamic strain aging prevailed at 150 °C and 300 °C. Fractographic examination results suggested that inclusions embedded in secondary cracks enhanced the fatigue crack initiation rather than the fatigue crack growth. The fatigue crack growth rates taken in the oxygen-saturated water environment were one order of magnitude faster than those obtained in air.

A study of the microstructure and corrosion of dissimilar weldments of Alloy 690 and SUS 304L with various additions of niobium (Nb) (0.1, 1.03, 2.49, and 3.35% by weight) in the flux of coated electrodes is presented. With identical welding parameters and procedures, the weldments were butt-welded in three layers by shielding metal arc welding (SMAW), with each layer being deposited in a single pass. The results show that the dendritic microstructure in the fusion zone changed from a cellular to columnar dendrite and equiaxed dendrite with increasing Nb addition. Furthermore, the interdendritic phase increased in volume and changed in composition from an Al–Ti oxide to a mixture of Nb–Si phase and Nb-rich phase. Nevertheless, it was clearly observed that Cr 7 C 3 precipitated at the grain boundaries of the low Nb weldment root pass. Finally, the results revealed that corrosion occurs primarily at the grain boundaries and within the interdendritic regions of the weldements irrespective of the level of Nb addition. For the region of abundant formation of Nb-rich phase, the high-Nb weldment had a relatively low corrosion resistance.

A simple, uncontaminated method was described for graphite furnace atomic absorption spectrophotometry used for determination of Cd and Pb in milk serum prepared by spontaneous souring. Samples of raw milk were collected from the bulk holding tanks of 107 dairy farms in six counties in Taiwan. Raw milk samples were placed at room temperature (28 degrees C) for 48 h, to allow the pH to decrease below 4.6 and the casein and fat to precipitate. Milk serum was filtered and then directly injected into a graphite tube. The standard addition method was employed, and .1% phosphoric acid was the matrix modifier. During ashing, a 15-s oxygen influx prevented charcoal accumulation on the graphite tube. The mean recoveries of Cd and Pb from three added concentrations were 93.7% and 94.5%, respectively. The analyzed Cd and Pb concentrations in milk powder using this method were close to the certified values. The mean Cd and Pb contents obtained from 107 samples were .044 ng/ml, ranging from .021 to .173, and 2.03 ng/ml, ranging from .98 to 4.45, respectively. There were no significant differences among the six counties.