Stainless Steel In Mercury Research Articles

Cavitation-erosion resistance of 316LN stainless steel in mercury containing metallic solutes

Room temperature cavitation tests of vacuum annealed type 316LN stainless steel were performed in pure mercury and in mercury with various amounts of metallic solute to evaluate potential mitigation of erosion/wastage. Tests were performed using an ultrasonic vibratory horn with specimens attached at the tip. All of the solutes examined, which included 5 wt% In, 10 wt% In, 4.4 wt% Cd, 2 wt% Ga, and a mixture that included 1 wt% each of Pb, Sn, and Zn, were found to increase cavitation-erosion as measured by increased weight loss and/or surface profile development compared to exposures for the same conditions in pure mercury. Qualitatively, each solute appeared to increase the tenacity of the post-test wetting of the Hg solutions and render the Hg mixture susceptible to manipulation of droplet shape.

Erosion damage of laser alloyed stainless steel in mercury

The effect of laser surface alloying of type 316 stainless steel on the erosion resistance in mercury has been investigated. The alloying was produced by melting predeposited Al–Si powder and a portion of underlying substrate with a pulsed Nd:YAG laser beam. The microhardness of the modified layer was found to be 2.5 times higher than that of untreated steel. The erosion test of laser alloyed surface and steel in mercury was carried out by using the electromagnetic impact testing machine. The laser alloyed surface was found to be less damaged after 10 5 cycles of impacts compared to untreated stainless steel. However, after 10 6 cycles the erosion resistance of the modified layer is much lower than that of untreated steel. Liquid metal embrittlement in contact with mercury and residual stresses were considered as factors impairing the erosion resistance of the laser alloyed surface.

Assessment of cavitation–erosion resistance of 316LN stainless steel in mercury as a function of surface treatment

A vibratory horn apparatus was used to assess the cavitation–erosion resistance in mercury of annealed type 316LN stainless steel as a function of surface treatment. The modifications examined included cold-working, welding, laser-alloying of the surface, and two low-temperature carburization treatments. Based on general wastage (measured by weight loss) and depth of surface relief/pitting, the best cavitation–erosion resistance in Hg was achieved with one of the carburization processes for which the substrate material was oriented such that inclusion stringers were parallel to the test surface. The most successful carburization process was found to be similarly effective for both wrought and welded 316LN.

316 Erosion Damage of Laser Alloyed Stainless Steel in Mercury

316 Erosion Damage of Laser Alloyed Stainless Steel in Mercury

Influence of mercury velocity on compatibility with type 316L/316LN stainless steel in a flow loop

Previous experiments to examine corrosion resulting from thermal gradient mass transfer of type 316L stainless steel in mercury were conducted in thermal convection loops (TCLs) with an Hg velocity of about 1 m/min. These tests have now been supplemented with a series of experiments designed to examine the influence of increased flow velocity and possible cavitation conditions on compatibility. In one experiment, the standard TCL design was modified to include a reduced section in the hot leg that provided a concomitant increase in the local velocity by a factor of five. In addition, a pumped-loop experiment was operated with a flow velocity of about 1 m/s. Finally, a TCL was modified to include an ultrasonic transducer at the top of the hot leg in an attempt to generate cavitation conditions with corresponding extreme local velocity associated with collapsing bubbles. The results indicate that compatibility of type 316L/316LN stainless steel does not depend significantly on liquid metal velocity in the range of 1 m/min to 1 m/s. Benchtop cavitation experiments revealed susceptibility of 316L coupons to significant weight losses and increases in surface roughness as a result of 24 h exposure to 1.5 MPa pressure waves in Hg generated ultrasonically at 20 kHz. However, attempts to generate cavitation conditions on coupons inside the TCL with the ultrasonic transducer proved largely unsuccessful.

Preliminary evaluation of cavitation resistance of type 316LN stainless steel in mercury using a vibratory horn

Type 316LN stainless steel in a variety of conditions (annealed, cold-worked, surface-modified) was exposed to cavitation conditions in stagnant mercury using a vibratory horn. The test conditions included peak-to-peak displacement of the specimen surface of 25 μm at a frequency of 20 kHz and a mercury temperature in the range −5 to 80 °C. Following a brief incubation period in which little or no damage was observed, specimens of annealed 316LN exhibited increasing weight loss and surface roughening with increasing exposure times. Examination of test surfaces with the scanning electron microscope revealed primarily general/uniform wastage in all cases but, for long exposure times, a few randomly oriented ‘pits’ were also observed. Type 316LN that was 50% cold-worked was considerably more resistant to cavitation erosion damage than annealed material, but the surface modifications (CrN coating, metallic glass coating, laser treatment to form a diamond-like surface) provided little or no protection for the substrate. In addition, the cavitation erosion resistance of other materials – Inconel 718, Nitronic 60, and Stellite 3 – was also compared with that of 316LN for identical screening test conditions.

Nonlinear cavitation erosion of stainless steel in mercury versus applied power

The cavitation erosion rate for 316 stainless steel in mercury was found to increase in a nonlinear fashion with the maximum applied power. In addition, the incremental increase in erosion was observed to decrease with increased power in water, yet increased six to seven times when mercury was used as the cavitating fluid.