The effect of electroslag remelting on the cleanliness of CrNiMoWMnV ultrahigh-strength steels

Ali, Mohammed; Porter, David; Kömi, Jukka; Heikkinen, Eetu‐Pekka; Eissa, Mamdouh; Faramawy, Hoda El; Mattar, Taha

doi:10.2298/jmmb190211042a

Cited by 4 publications

(3 citation statements)

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“…Despite the large increase in the UTS, YS and hardness, the elongation and impact toughness have the same or slight increase and there is a slight increase in the percentage of ductile fracture from 30% to 34% as a result of ESR. This return to the high degree of refining with ESR as observed in our previously published work [19] in which the total impurity level reduced with ESR by 46%. Moreover, removal of most MnS, which has the most detrimental effects on toughness and ductility and some of them are nucleate and grow on some oxide or nitride inclusions leading to smaller size multiphase inclusions with an oxide or nitride core surrounded by sulfide, e.g., ( is the main reason to prevent deterioration of the impact toughness and elongation to fracture properties.…”

Section: Changes In the Mechanical Properties Of Uhss Isupporting

confidence: 80%

“…The fracture surfaces show the dimples characteristic of the microvoid coalescence associated with ductile fracture. Without ESR, Figure 11a-c reveals the presence of large voids, which are due to the presence of large NMIs with ECDs ranging from 8 to 10 µm, as observed in our previously published work [19]. However, after ESR, the frequency and sizes of the NMIs are reduced, which is seen as a lower incidence of large voids in the fracture surfaces in Figure 11d composition which leads to increase the bainite start temperature from 428 to 439 °C, as calculated using JMatPro software using the chemical composition without and with ESR.…”

Section: Changes In the Mechanical Properties Of Uhss IIIsupporting

confidence: 79%

“…The microstructural features considered are the phases formed, the prior austenite grains, effective grain, and lath sizes, numbers and sizes of precipitates, and the degree of microsegregation. This information, together with the information from previously published work on the NMI contents of the steels [19], is used to clarify the effect of ESR on the mechanical properties of the investigated UHSSs.…”

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confidence: 99%

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

Ali

Porter

Kömi

et al. 2020

Metals

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The effect of electroslag remelting (ESR) with CaF 2 -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.The prior austenite grains are divided into packets, which consist of blocks of laths with the same habit plane. These blocks contain sub-blocks in which the laths have similar crystal orientations. The boundaries between packets and blocks have high-angle misorientations while the boundaries between sub-blocks and laths have low-angle misorientations [8][9][10].Strength and toughness properties can be improved simultaneously by grain refining, which can be achieved, for example, by the pinning of the austenite grain boundaries by fine precipitates, which are stable at high temperatures [11]. A high number density of fine precipitates leads to enhanced pinning of the grain boundaries, which subsequently leads to a reduction of the final prior austenite grain, packet, and block sizes and a significant effect on the mechanical properties of the steel. It was observed by Wang et al. [12] that the yield strength of 17CrNiMo6 martensitic steel is increased by 235 MPa by reducing the prior austenite grain size (PAGS) by 33% and the Charpy U-notch impact energy at 77 K was enhanced more than eight-fold.In addition to the above strengthening factors, additional strengthening can be achieved through precipitation. In the case of dislocation bowing between precipitates, the Orowan relationship [13] shows that the yield strength increment from precipitation increases with increasing volume fraction and decreasing size of the precipitates. In the case of tempered martensite, the optimum combinati...