Ductility of Bulk Nanocrystalline and Ultrafine Grain Iron and Steel

Abstract

This paper reviews the ductility of nanostructured and ultrafine iron obtained using a variety of methods. Mechanical milling of powder and subsequent hot consolidation, one of the most popular methods offer high mechanical strength but poor ductility. Improvements made in the consolidation processes and the introduction of final heat treatments, in addition to new approaches such as spark plasma sintering and high pressure torsion, have increased the total plastic strain of nanostructured iron. The development of bimodal structures enables the existence of strain hardening and more uniform deformation. The paper also includes a steel study, which finds that the hardness of milled powder and the role of carbon atoms inside ferrite grains make it more difficult to improve the ductility of nanostructured samples.

How the Thermomechanical Processing Can Modify the High Strain Rate Mechanical Response of a Microalloyed Steel

“…The increase in impact toughness was observed in the case of the sample rolled according to the scheme 3A and it should be noted that this increase is the greatest among all tested samples. Observing the image of the microstructure for this sample 3A, it should be assumed that high toughness value in this case is a direct result of the bimodal distribution of significantly refined and large grains [6][7][8][9]13]. The rolling pattern B (two hot passes), in turn, in each case shows an increase in the fracture energy for air-cooled samples, and the obtained results are very similar to each other.…”

“…metals whose strain rate sensitivity is high. Recently published works have suggested several ideas to improve the ductility of modern steels by using dispersed oxide, cementite or martensite [10][11][12], the use of a bimodal microstructure or distribution of grain size [13]. It is also possible to apply deformation of the ultrafine grained (UFG) material at a very low temperature and/or high strain rate, thereby increasing the high strain rate sensitivity or introducing heavy twinning into the material during processing [14].…”