Nanostructured metals and alloys possess very high strength but exhibit limited plasticity. Enhancement of the strength/ductility balance is of prime importance to achieve wide industrial applications. However, postdeformation heat treatment, which is usually used to improve plasticity, can lead to a decrease in other properties. In the case of austenitic stainless steels, heat treatment in the range from 480 to 815°C can increase their susceptibility to intergranular corrosion. The aim of the work reported in this paper was to determine if nanostructured austenitic stainless steel is susceptible to intergranular corrosion if heat treated for 1 h at 700°C. Samples of 316LVM austenitic stainless steel were hydrostatically extruded, in a multi-step process with the total true strain of 1.84 to produce a uniform microstructure consisting of nanotwins. These nanotwins averaged 21 nm in width and 197 nm in length. Subsequent annealing at 700°C produced a recrystallised structure of 68-nm-diameter nanograins. The heat treatment improved the ductility from 7.8 to 9.2 % while maintaining the ultimate tensile strength at the high level of 1485 MPa. Corrosion tests were performed in an aqueous solution consisting of 450 ml concentrated HNO 3 and 9 g NaF/dm 3 (according to ASTM A262-77a). The evaluation of the corrosion resistance was based on transmission and scanning electron microscopic observation of the microstructure and chemical analyses. The results revealed that both the as-received and HE-processed samples are slightly susceptible to the intergranular corrosion after annealing at 700°C for 1 h.

No abstract

No abstract

Electrochemical measurements have shown that low Mn (-0.2% Mn) modified stainless steels with low (< 1.2% Mo) or no Mo exhibit a higher pitting resistance in NaCl aq (0.005 M up to 2 M NaCl) than the analoguous commercial steels with 1.4% Mn and -2.8% Mo. Microscopic examinations and X-ray microprobe analysis revealed a correlation between pitting resistance of the steels and the composition of the nonmetallic inclusions as well as of the adjacent matrix. They both differ considerably for the two groups of steels.Elektrochemische Messungen haben gezeigt , daB nichtrostende Stahle mit niedrigem Mangangehalt (etwa 0,2% Mn) mit Molybdangehalten unter 1,2% bzw. molybdanfrei in 0,005 m-2 m NaCl bestandiger gegen Lochkorrosion sind als die analogen handelsublichen Stahle mit 1,4% Mn und etwa 2,8% Mo. Mikroskopische Untersuchungen und Rontgenmikrosondenanalyse zeigen eine Beziehung zwischen der Widerstandsfahigkeit gegen Lochkorrosion und der Zusammensetzung der nichtmetallischen Einschliisse sowie der umgebenden Matrix der Stahle. Diese beiden GroRen sind bei den beiden Stahlgruppen sehr verschieden.

No abstract