Effect of Intercritical Annealing and Austempering on the Microstructure and Mechanical Properties of a High Silicon Manganese Steel

Mattia Franceschi,Alberto Fabrizi,Manuele Dabalà,Claudio Gennari,Luca Pezzato,Katya Brunelli,Marina Polyakova,Dmitry Konstantinov

doi:10.3390/met10111448

Mattia Franceschi, Alberto Fabrizi + Show 6 more

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https://doi.org/10.3390/met10111448

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Abstract

High Silicon Austempered steels (AHSS) are materials of great interest due to their excellent combination of high strength, ductility, toughness, and limited costs. These steel grades are characterized by a microstructure consisting of ferrite and bainite, accompanied by a high quantity retained austenite (RA). The aim of this study is to analyze the effect of an innovative heat treatment, consisting of intercritical annealing at 780 °C and austempering at 400 °C for 30 min, on the microstructure and mechanical properties of a novel high silicon steel (0.43C-3.26Si-2.72Mn wt.%). The microstructure was characterized by optical and electron microscopy and XRD analysis. Hardness and tensile tests were performed. A multiphase ferritic-martensitic microstructure was obtained. A hardness of 426 HV and a tensile strength of 1650 MPa were measured, with an elongation of 4.5%. The results were compared with those ones obtained with annealing and Q&T treatments.

Highlights

Nowadays, one of the most important objectives of steel producers and researchers in metallurgy is to bring to the market materials with improved properties and performance, high strength-to-weight ratios, and low costs
From the SEM micrograph (Figure 4b,c) it can be further observed the presence of idiomorphic ferrite (FI ), nucleated inside the original austenite grains (GB), present before the quenching
This is the typical microstructure of a medium carbon steel after annealing treatment [28]

Summary

Introduction

One of the most important objectives of steel producers and researchers in metallurgy is to bring to the market materials with improved properties and performance, high strength-to-weight ratios, and low costs. High silicon austempered steels are attractive grades for their particular combination of mechanical properties and ausfererritic microstructure, which is a mixture of ferrite and high carbon enriched austenite [1,2]. This particular microstructure leads to better mechanical performance, in terms of strength, hardness, and impact toughness in comparison with austempered ductile irons [1]. A silicon weight percentage higher than 1% prevents cementite formation [1,2,3,4,5] and favors austenite carbon enrichment during austempering [6], permitting its retention at room temperature

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