Inclusion flotation-driven channel segregation in solidifying steels

Song

et al. 2018

Metall. Res. Technol.

In this research, super gravity field was introduced to investigate the macrosegregation behavior of solute Cu in Al-Cu alloys in super gravity field systematically. And the macrosegregation mechanism was also explored by well-designed experiments. When Al-Cu alloys were solidified in super gravity field, the macrosegregation of solute Cu was generated and the solute Cu increases along the direction of super gravity field. The macrosegregation becomes severer with the increasing gravity coefficient and the solute content. When the Al-4.5wt%Cu alloy was solidified in super gravity field of G = 800, the copper content at the bottom position increases up to 8.48 wt% and that at the up position decreases to only 2.58 wt%, resulting in the positive segregation at the bottom and the negative segregation at the top of the sample. The segregation mechanisms are that solute-rich regions, which have a larger density than the main liquid, sediment toward the bottom of the sample under the effect of super gravity, and at the final solidification stage, super gravity can drive the residual solute-rich liquid to flow toward the bottom of the sample along the dendrite space (channel), which formed the super gravity channel segregation.

Section: Gravity Segregation Mechanismmentioning

confidence: 99%

Macrosegregation behavior of solute Cu in the solidifying Al-Cu alloys in super-gravity field

Song

et al. 2018

Metall. Res. Technol.

“…At present, the research on FHRS mainly focuses on its microstructure, precipitates or mechanical properties after heat treatment or forging [7][8][9], but its solidification process has been paid little attention. In previous studies, the chemical distribution and solidification process were mainly investigated by dissecting the casting [10][11][12] or by numerical simulation [13][14][15], due to the large size of FHRS castings. Dissecting the heavy castings is not cost-effective and will cost a lot in human resources and time.…”

Section: Of 13mentioning

confidence: 99%

Thermal Simulation Study on the Solidification Structure and Segregation of a Heavy Heat-Resistant Steel Casting

Wang

Zhong

et al. 2019

Metals

The prediction and controlling of the solidification structure and macro-segregation in heavy steel casting, which is usually produced in limited quantities, was a conundrum in the foundry field. In this work, the cooling and solidification processes of a 16 t CB2 ferritic heat-resistant steel (FHRS) valve casting were reproduced by studying the solidification behavior of three typical units through a thermal simulation method. The results indicate that the types of casting without chilling have the most uneven distribution of solutes and hardness, while those types of casting in which parts are solidified by chilling are much more uniform. The macro-segregation degrees of B, C, Nb, P, Cr, Mo, Si, V and Mn decrease gradually during heavy casting of CB2 ferritic heat-resistant steel. Of them, B, C, Nb, and P are solutes prone to segregation, and the maximum macro-segregation index of B can even reach 15. The macro-segregation tendencies of Cr, Mo, Si, V, and Mn are relatively small. Further studies on the last solidification portion of samples taken by electron microprobe reveal that large-sized precipitates such as MnS and NbxC are easily formed due to solute enrichment, and the sizes of these precipitates were distributed from dozens to hundreds of micrometers.

“…The four simulation examples as shown in this article target only the most serious issues of steel ingots, such as shrinkage porosity/cavity, thermal stress and strain and the formation of inner cracks, and different types of macrosegregation. Note, that some other issues have also been tackled by different modeling researchers, for example, non-metallic inclusions and influence on the macrosegregation, [79,80] cellular automata simulation of as-cast structure with CAFE model, [81] interactions between thermal mechanics and fluid mechanics, [82][83][84] etc.…”

Section: Macrosegregationmentioning

confidence: 99%

Simulation of As‐Cast Steel Ingots

Ludwig²,

Kharicha

2017

steel research int.

Some of the most recent examples of simulations of as‐cast steel ingots are presented in this paper, focusing on discussions concerning available simulation/modeling tools and their capacities and limitations. Although, there has been some success from implementing criterion functions into commercial codes to predict shrinkage porosity and hot tearing, large‐scale ingot sectioning experiments, similar to what is done a century ago, are still needed to investigate other issues, such as macrosegregation, since models are currently unable to predict such issues well. Models with more sophisticated features for macrosegregation prediction that incorporate multiphase transport phenomena are already under development. A limiting factor in application of these models for simulating steel ingots is the demand on large computation resources. Following the recent development trend and the projection of Moore's law (computer hardware), in the foreseeable future, it is predicted that multiphase models will to a great extent reduce the need for the experimental pouring‐sectioning trials.