Gustav Schumacher

Investigation on oxygen controlled liquid lead corrosion of surface treated steels

Abstract A low alloyed martensitic steel Fe9Cr (OPTIFER IVc) and an austenitic steel 16Cr15Ni (1.4970) were exposed to liquid lead to examine their suitability as structural material for lead cooled accelerator driven subcritical actinide burners. The surface of part of the steel specimens was restructured and that of another part was alloyed with Al by treatment with high power pulsed electron beams. A corrosion test stand was constructed containing liquid lead under oxygen control at 550°C. Steel specimens were examined after 800, 1500 and 3000 h of exposure. For austenitic steel lower corrosion effects were observed especially when the surface was treated by the electron beam. No corrosion attack could be seen at all on both steels after alloying Al into a surface layer of 10 μm depth.

Results of steel corrosion tests in flowing liquid Pb/Bi at 420–600 °C after 2000 h

Abstract Corrosion tests were carried out on austenitic AISI 316L and 1.4970 steels and on MANET steel up to 2000 h of exposure to flowing (up to 2 m/s) Pb/Bi. The concentration of oxygen in the liquid alloy was controlled at 10 −6 wt%. Specimens consisted of tube and rod sections in original state and after alloying of Al into the surface. After 2000 h of exposure at 420 and 550 °C the specimen surfaces were covered with an intact oxide layer which provided a good protection against corrosion attack of the liquid Pb/Bi alloy. After the same time corrosion attack at 600 °C was severe at the original AISI 316L steel specimens. The alloyed specimens containing FeAl on the surface of the alloyed layer still maintained an intact oxide layer with good corrosion protection up to 600 °C.

Corrosion Behavior of FBR Candidate Materials in Stagnant Pb-Bi at Elevated Temperature

Three materials proposed for use in fast breeder reactors—FBR grade type 316ss, high chromium type martensitic steel and oxide dispersion strengthened martensitic type steel—were subjected to corrosion tests in stagnant lead-bismuth eutectic (LBE) containing 10-6 wt% of oxygen at 500–650—C for up to 5,000 h. After each test, the specimens were analyzed metallurgically using a scanning electron microscopy with energy dispersive X-ray analyzer and an X- ray diffractometer. It proved that, at temperatures not higher than 550°C, martensitic steels containing chromium to more than 9wt% presented good resistance against corrosion by the formation of spinel layer on the base metals, though outer porous oxide formed on the steels was detached and/or dissolved into LBE. At temperatures above 600°C, the oxide layer thickness diminished. This alteration in corrosion behavior seems to be ascribable to a change taking place at 570°C in the stable form of iron oxide from magnetite to wustite. At the temperatures, dissolution attack was observed at some portions. It was estimated that the oxide became to lose its adhesion to the base metal.

Application of pulsed electron beams for improvement of material surface properties

The pulsed electron beam facilities GESA I and GESA II were developed in cooperation between Efremov Institute St. Petersburg, Russia and the Research Center Karlsruhe (FZK), Germany for large area surface treatment with beam diameter of 4 – 10 cm. It melts the material surface down to a depth of 10–100 µm. Technological applications are improvement of high temperature oxidation resistance of MCrAlY and of its bonding properties to TBCs, prevention of liquid metal attack on steels, surface hardening and increase of wear resistance and lowering of sea water corrosion and high cycle fatigue of aircraft engine blades. An overview is given on the status of the current applications.

Oxide scale growth on MCrAlY coatings after pulsed electron beam treatment

The pulsed electron beam treatment method was applied to the surface of LPPS-MCrAlY coatings to improve the oxide scale behavior. Such protective coatings are used in advanced stationary and aero gas turbines to increase the corrosion resistance of air foils at high temperature. The electron beam generated by the GESA facility has a diameter of about 10 cm and sufficient power density to melt a surface layer of about 20 /spl mu/m of this area by just one electron beam pulse.