The Effect of Electroslag Remelting on the Microstructure and Mechanical Properties of CrNiMoWMnV Ultrahigh-Strength Steels

Mohammed Ali,David Porter,Jukka Kömi,Hoda El Faramawy,Mamdouh Eissa,Taha Mattar

doi:10.3390/met10020262

Mohammed Ali, David Porter + Show 4 more

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https://doi.org/10.3390/met10020262

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Abstract

The effect of electroslag remelting (ESR) with CaF2-based synthetic slag on the microstructure and mechanical properties of three as-quenched martensitic/martensitic-bainitic ultrahigh-strength steels with tensile strengths in the range of 1250–2000 MPa was investigated. Ingots were produced both without ESR, using induction furnace melting and casting, and with subsequent ESR. The cast ingots were forged at temperatures between 1100 and 950 °C and air cooled. Final microstructures were investigated using laser scanning confocal microscopy, field emission scanning electron microscopy, electron backscatter diffraction, electron probe microanalysis, X-ray diffraction, color etching, and micro-hardness measurements. Mechanical properties were investigated through measurement of hardness, tensile properties and Charpy-V impact toughness. The microstructures of the investigated steels were mainly auto-tempered martensite in addition to small fractions of retained austenite and bainite. Due to the consequences of subtle modifications in chemical composition, ESR had a considerable impact on the final microstructural features: Prior austenite grain, effective martensite grain, and lath sizes were refined by up to 52%, 38%, and 28%, respectively. Moreover, the 95th percentiles in the cumulative size distribution of the precipitates decreased by up to 18%. However, ESR had little, if any, the effect on microsegregation. The variable effects of ESR on mechanical properties and how they depend on the initial steel composition are discussed.

Highlights

In steels, ultrahigh strength can be achieved through a combination of several mechanisms like grain refinement, precipitation strengthening, solid solution strengthening, dislocation strengthening, and texture strengthening
This study aims at evaluating the effect of electroslag remelting on the mainly martensitic microstructures of three novel ultrahigh-strength steels (UHSSs)
The microstructures of UHSS I, II, and III without and with electroslag remelting (ESR) are shown in Figures 2–4, The microstructures

Summary

Introduction

Ultrahigh strength can be achieved through a combination of several mechanisms like grain refinement, precipitation strengthening, solid solution strengthening, dislocation strengthening, and texture strengthening. Many of these mechanisms are enhanced through the use of thermomechanical treatments [1,2,3,4]. Bainitic and lath martensitic microstructures are commonly used to achieve good combinations of ultrahigh strength, high ductility, and high impact toughness. The microstructure of martensitic or bainitic steels is subdivided into the following units: Prior austenite grains, packets, blocks, sub-blocks, and laths, with unit size decreasing from left to right. High-carbon nanoscale carbide-free bainite and with retained austenite (RA) gives high ductility through transformation-induced plasticity (TRIP) [5,6,7], but at the expense of the weldability that is desired for structural steels.

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