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Characteristics and Formation Tendency of Freckle Segregation in Electroslag Remelted Bearing Steel

State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, China
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Metals 2020, 10(2), 246; https://doi.org/10.3390/met10020246
Received: 2 January 2020 / Revised: 1 February 2020 / Accepted: 7 February 2020 / Published: 12 February 2020
(This article belongs to the Special Issue Advances in Metal Casting Technology)
Undesirable macro segregation defects, freckles, restrict the commercial production of large-sized electroslag remelting (ESR) bearing steel ingots through degradation of the mechanical properties and service lifetime. In order to clarify the freckle characteristics and formation tendency as well as the formation mechanism, freckles from an industrial large-sized GCr15SiMn ESR ingot were investigated through structural and compositional analysis, along with simulation calculation. The results show that freckles consist of (Si, Mn, Cr)-enriched equiaxed grains and occur in about the 1/2 radius region at the middle-upper part of the ESR ingot, where the secondary dendritic arm spacing (SDAS) and solidification front angle are large but cooling rate is small. The absolute value of relative Rayleigh number, Ra, also reaches its maximum in the 1/2 radius region, with a liquid fraction of 0.3–0.5, corresponding to the region where freckles form. Based on the experimental and simulation results, to evaluate the freckle formation in industrial-scale GCr15SiMn ESR ingots, the threshold value of relative Ra, a freckle criterion considering the compositional and thermal effects, was determined to be about −0.023.
Keywords: electroslag remelting; bearing steel; freckle segregation; relative Ra criterion electroslag remelting; bearing steel; freckle segregation; relative Ra criterion
MDPI and ACS Style

Yan, W.; Zhang, Y.; Chen, W.; Li, J. Characteristics and Formation Tendency of Freckle Segregation in Electroslag Remelted Bearing Steel. Metals 2020, 10, 246.

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