Abstract
There is a continuous quest for discovery of a steel grade which has better properties and lower production cost. To design steel with superior properties for industrial application, it is essential to understand the effect of microstructure and engineer it to fit the purpose. In this study, a counter intuitive strategy has used to reveal the mechanism of high carbon steel with ultrahard structure. High compact force has been used to produce a structure which has ceramic-like hardness without compensating the toughness significantly. The behaviour of high carbon low-alloy steel as the starting material under different stages of deformation has been studied to differentiate various deformation paths and microstructural transformation processes. Microscopy investigation by secondary electron microscopy, high-resolution electron backscattered diffraction (HR-EBSD) analysis and Transmission electron microscopy (TEM) showed that the key point to achieve ~75% increased hardness in this steel is through generation of nano-structured martensite of less than 50 nm grains size which can be formed due to high impact force. In this paper, we reveal a nano grained steel structure with excellent mechanical properties resulting from phase transformation, uniform dislocation distribution, grain refinement and recrystallization.
Highlights
There is a continuous quest for discovery of a steel grade which has better properties and lower production cost
To investigate the new microstructures achieved by impact deformation and the associated mechanical behaviours at different load we have used secondary electron microscope (SEM), nano indentation, high resolution Electron backscattering diffraction (HR EBSD), Transmission Kikuchi Diffraction (TKD), Transmission electron microscope (TEM) and Focused ion beam (FIB) sectioning
The microstructure of the deformed sample was observed using a Transmission electron microscopy (TEM) equipped with a field emission gun (Philips CM 200, Netherlands) after preparing by using a dual beam FIB (FEI xT Nova Nanolab 200, USA), and the thickness of the specimens was estimated to be ~100 nm.The cross-sectional morphology of the deformed sample has demonstrated phase transformation and grain refinement as a phenomenon of plastic deformation
Summary
There is a continuous quest for discovery of a steel grade which has better properties and lower production cost. The toughness and abrasion resistance of low-alloyed high carbon steel can be enhanced by microstructural engineering to have martensite and retained austenite structure at the same time[1]. Three main deformation mechanism of steel which include, transformation-induced plasticity (TRIP), twinning–induced plasticity (TWIP) and dislocation plasticity[9,10,11], was incorporated in this study in combination of recrystallization which helped to achieve high hardness, but the mechanism did not reduce the toughness significantly. The aim of this study is to reveal the micro mechanisms in low alloyed the high carbon steel associated to generate a new grade of steel with ceramic-like hardness and metal-like toughness by activating different deformation mechanism at high impact force and at the same time by successfully producing ultra-fine grains with low dislocation density through recrystallization due to generated heat. Identifying the behaviour of this grade of steel, phase transformation as well as microstructural evolution of deformed phases down to the nanometre level is a vital aspect to characterising the low cost low alloyed high carbon steel as a potential new grade of steel for extreme operational conditions
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