Properties of fine-grained steels generated by displacive transformation

Abstract

It has been possible in recent times to make large quantities of steels in which the controlling scale is 20 nm or less, i.e., comparable to that of carbon nanotubes. The mechanical properties of such steels are abnormal. For example, in some cases the ductility vanishes as the strength increases, whereas in others the ductility almost entirely consists of uniform plastic strain. Some of the steels also can tolerate large fractions of brittle phases before fracture. These and other aspects of strong, nanostructured steels are critically assessed to arrive at a hypothesis which rationalises the odd observations.

Nanostructured bainite

“…it loses percolation (Bhadeshia 2008). Garboczi et al (1995) have modelled the percolation threshold for ellipsoidal objects placed in a matrix.…”

Carbide-Free Bainite: Compromise between Rate of Transformation and Properties

“…It has been suggested that with microstructures of the kind considered here, failure in a tensile test occurs when the retained austenite loses continuity [42] and that this percolation threshold is reached when the austenite fraction reaches about 0.1. The fraction of austenite present in the initial microstructure can be calculated from the fact that the bainite reaction, in the absence of cementite precipitation, obeys the incomplete reaction phenomenon.…”

The Comparative Study of the Microstructure and Phase Composition of Nanoausferritic Ductile Iron Alloy Using SEM, TEM, Magnetometer, and X-Ray Diffraction Methods

“…Electron diffraction patterns analysis revealed that the microstructure consisted of thin bainitic ferrite plates separated by thin layers of retained austenite. In case of steels this kind of microstructure is called nanobainite [13][14][15], while in ductile iron we can speak of nanoausferrite [6,7]. The average width of ferritic plates was similar for both samples and it was 126 ± 13 nm and 116 ± 7 nm in ADI-1 and ADI-2, respectively.…”