Synthesis of Nano‐Particle Dispersed Highly Substructured Strong and Ductile Low Carbon Steel Possessing Structural Hierarchy

Abstract

In this research work intercritical thermal cycling is adopted on a cost‐effective material (AISI 1010 steel) so as to attain a hierarchical structure at multiple length scales, from nanometer scale onwards. As a consequence, a considerably high strength (UTS = 1 GPa) along with a significant ductility (% Elongation = 15) is achieved. This is attributed to a novel microstructure that consists of nano‐sized cementite particle dispersed α‐ferrite islands in a matrix of nano‐sized cementite particle dispersed highly sub‐structured martensite (containing both “lath” and “plate” morphology). The substructure appears in the form of dislocations in lath martensite and nanoscale twins in plate martensite. The α‐ferrite islands provide intrinsic ductilization through microvoid coalescence; while extrinsic ductilization is attributed to crack arrest at dimples and crack deflection at hard plate martensite matrix. Such a high strength is obtained by virtue of martensitic strengthening (through generation of highly substructured martensite) and nano‐dispersion strengthening (due to presence of dispersed nano‐sized cementite particles).

Hardening of Steel Through High‐Voltage Low‐Current Energy Input

“…Most interestingly, the evolution of martensite in steel through atomic migration under HVLC-induced supersaturation of α-ferrite matrix is observed for the first time in the present research work. This novel observation has been substantiated with morphological appearance of "plate" shape in FESEM and HRTEM study, in particular for a treatment duration of 5 min for all three applied voltages (Figure 5e,f, 10e, and 15e), as also suggested in the standard literature [8,24] for preliminary prediction of martensite in terms of morphology. However, identification of martensite phase should also be done in terms of crystal structure and the well-known splitting of α-Fe peaks.…”

“…Altogether, the main three conventional heat treatment routes are annealing, normalizing, and quench hardening followed by tempering being applied for different purposes as per requirement. Other than these conventional heat treatment routes, incomplete austenitization based heat treatment of steel has been pioneered about a decade ago by the research group of Maity [2][3][4][5] and presently is a prime topic of investigation in the development of steel [6][7][8][9][10] so as to take simultaneous advantages of dispersion hardening (arising from the presence of dispersed submicroscopic hard cementite particles) and martensitic hardening (owing to austenite-tomartensite transformation). However, other than these thermal routes, hardening of steel has not been readily attempted with any other form of energy input, such as electrical energy.…”