Effect of the dendritic morphology on hot tearing of carbon steels

4th International Conference on Advances in Solidification Processes

材料科学;物理学

Ridolfi, M.R.^1

Centro Sviluppo Materiali S.p.A., Via di Castel Romano, Rome

100, Italy^1

关键词: Alloy compositions;    Columnar growth;    Dendritic morphology;    Hot tearing criteria;    Interdendritic space;    Peritectic steel;    Solid fraction;    Void formation;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/117/1/012063/pdf
DOI  :  10.1088/1757-899X/117/1/012063

学科分类：材料科学（综合）

来源: IOP

【 摘 要 】

Hot tears form during solidification in the brittle region of the dendritic front. Most hot tearing criteria are based on solid and fluid mechanics, being the phenomenon strictly depending on the solid resistance to applied strains and on the liquid capability of filling the void spaces. Modelling both mechanisms implies the precise description of the dendritic morphology. To this scope, the theory of coalescence of the dendritic arms at grain boundaries of Rappaz et al. has been applied, in this work, to the columnar growth of carbon steels by means of a simple mathematical model. Depending on the alloy composition, solid bridging starts at solid fractions down to about 0.8 and up to above 0.995 (very low carbon). The morphology of the brittle region changes drastically with increasing carbon and adding other solutes. In particular, ferritic dendrites, typical of low carbon steels, tend to offer short and wide interdendritic spaces to the surrounding liquid making possible their complete filling, and few solid bridges; peritectic steels show the rise of austenite growing and bridging rapidly in the interdendritic spaces, preventing void formation; austenitic dendrites form long and narrow interdendritic spaces difficult to reach for the liquid and with a lot of solid bridges. Sulphur addition mainly acts in delaying the coalescence end, more markedly in ferritic dendrites.