Regular Article

Freckle formation and prevention in high strength low alloy steel ingots

State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, 100083, PR China

^* e-mail: weiyan@ustb.edu.cn

Received: 20 September 2019
Accepted: 7 May 2020

Abstract

Freckles considerably limit the development of larger electro-slag remelting (ESR) ingots. To simulate the freckling conditions in ESR ingots, high-strength low alloy (HSLA) steel was solidified with varying solidification front angles. Note that the freckling potential is enhanced and the orientation of freckle channel tends to be in the vertical direction with increase in solidification front angle. This is because the tilted solidification front contributes the available buoyancy and transports light (Si, Mn, Cr)-enriched liquid flows upwards toward the mush zone and then accumulates in the open segregation channel. For freckle formation in experimental HSLA steel ingots, a modified Rayleigh number (Ra) that considers the anisotropy of permeability and solidification front angle was evaluated and a threshold value of Ra that separates the freckled and freckle-free area was determined to be 0.79.