Effect of interfacial oxidation occurring during the duplex process combining surface nanocrystallisation and co-rolling

Abstract

This paper presents an investigation of the interface quality of nanocristallised 316L stainless steel multilayer structures. They were produced by a duplex process, combining the Surface Mechanical Attrition Treatment (SMAT) and the co-rolling process at two different annealing temperatures (550°C and 650°C). Oxide layers were observed at the interfaces between the sheets and their morphology was characterised by optical microscopy. Their chemical composition was determined by Energy Dispersive X-ray spectrometry. The microstructure near the interfaces was analysed by Transmission Electron Microscopy (TEM). In the laminate co-rolled at 550°C, the presence of ultrafine grains was demonstrated. Additional tensile tests have shown an influence of the annealing temperature on the yield strength, as well as on the resistance of the interfaces of the co-rolled multilayer structures.

Numerical analysis of highly reactive interfaces in processing of nanocrystallised multilayered metallic materials by using duplex technique

“…The shape of the predicted strain contours are in good agreement with the shape of deformation bands observed experimentally by Waltz et al [15] in the microstructure of the co-rolled stainless steel sheets composing the laminate (Fig. 5b).…”

“…TEM investigations combined with X-ray study of 316L austenitic stainless steel, which is material characterised by low SFE, subjected to SMAT revealed the chain of micro events leading to the formation of nanoscale grains at the surface layer [14,15,28]. The strain generated in the surface layer during such treatment is non-uniform exhibiting gradient distribution.…”

“…At some points metal from the neighbouring steel sheets came into contact creating a good bonding while gaps have been observed in other areas [15,35]. The gaps were filled with oxide clusters primarily composed of hematite, magnetite and other complex oxides.…”

“…Numerical simulation of the hot rolling process was undertaken for the assembly of two nanocrystallised fcc 316L austenitic stainless steel plates, each of 1 mm thick and 120 mm long, under the parameters similar to those applied in the co-rolling trials described elsewhere [14,15]. For the initial temperature of 550°C and 55% rolling reduction, the distribution of the equivalent strain predicted in the area of the oxidised interface around the separate oxide islets exhibits clearly visible strain localisations (Fig.…”

“…It has been shown that the interfacial oxidation can lead to the formation of discontinuous oxides or a continuous oxide layer at the interfaces ( Fig. 1) [15].…”