Influence of mould design on the solidification of heavy forging ingots of low alloy steels by numerical simulation A. Kermanpur a, * , M. Eskandari a , H. Purmohamad a , M.A. Soltani c , R. Shateri b a Department of Materials Engineering, Isfahan University of Technology, Isfahan 84156-83111, Iran b Iron and Steel Society of Iran, Isfahan 84156-83111, Iran c Department of Materials Engineering, Islamic Azad University Majlessi Branch, Isfahan, Iran article info Article history: Received 26 June 2009 Accepted 23 September 2009 Available online 26 September 2009 Keywords: (G) Numerical simulation (C) Ingot casting (A) Low alloy steel (C) Solidification (C) Hot forging abstract Ingot casting of a 6-ton, heat-treatable Cr–Mo low alloy steel was simulated using finite element method in three dimensions. Effects of casting parameters including bottom pouring rate, mould slenderness ratio, mould slope, and height and shape of the hot top isolate on solidification behaviour and crack sus- ceptibility during subsequent hot forging of the ingot were investigated. The simulation model was val- idated against experimental data of two different ingot mould designs. Influences of the casting parameters on the riser efficiency and possible crack formation in the intersection of hot top and ingot body during subsequent open-die forging of the cast steel ingots were discussed. Results showed that pouring the melt under a constant rate, reducing the mould slenderness ratio, and using a proper design for the hot top isolate would all improve the riser efficiency and thereby possibly reduce crack suscepti- bility during subsequent hot forging. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Today’s forging industry requires a wide range of raw materials, all of which must meet certain standards that limit the quality of the semi-finished products. In addition to imparting a certain shape and geometric dimensions, the forging process eliminates defects in the initial semi-finished product as it breaks up coarse-grained dendritic structures and nonmetallic inclusions [1]. Thus, the final product is characterized both by the inherited macrostructural nonuniformity of the ingot and by the nonunifor- mity which results from plastic deformation. However, cracking may occur during hot forging of steel ingots originating from the cast microstructure or unsuitable forging conditions. The intersec- tion between the hot top (riser) and ingot is a critical region in which circumferential cracks could form during the primary stages of forging. The crack then propagates into the ingot and leads to high crap formation. Fig. 1 shows a typical circumferential crack that is formed during the open-die forging of a low alloy steel ingot. The experimental investigation is not always possible and appropriate because it leads to experiments with a lot of parame- ters at complicated circumstances and as a result to great material expenditures. That is why a combination of mathematical model- ling and experimental investigations is nowadays acquiring greater significance. Attempts have been made by many researchers to understand temperature distribution and solidification of large in- gots through computer simulation of ingot casting process using the finite element method (FEM). Chernogorova and Vabishchevich [2] investigated the process of the solidification of a binary alloy in a cylindrical metal mould. Tashiro et al. [3] investigated the influ- ence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot (100 and 135 ton ingots) by FEM. Gu and Beckermann [4] numerically sim- ulated melt convection and macro-segregation in the casting of a large steel ingot. Their simulation was based on model for multi- component steel solidification with melt convection and involves the solution of fully coupled conservation equations for the trans- port phenomena in the liquid, mush, and solid. Radovic and Lalovic [5] developed two-dimensional (2D) numerical model of ingot solidification based on the Fourier’s differential equation as well as energy of lattice defects. On the basis of their numerical model results, they calculated temperature distribution, temperature gra- dient, distribution solid and liquid phase and increment of solid fraction. Recently, the casting and solidification processes of large, tool steel ingots were modelled numerically and the ingot shape was optimized with respect to the real solidification conditions, suppressing the ingot’s internal discontinuities and obtaining an acceptable level of structural and chemical homogeneousness [6]. Besides numerical modelling, artificial intelligence methods are also under development to design and study ingot manufacturing processes. A prediction model based on data mining roadmap including dynamic polynomial neural network and bootstrap method is recently developed by Bae et al. [7]. They collected trace 0261-3069/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2009.09.045 * Corresponding author. Tel.: +98 311 3915738; fax: +98 311 3912752. E-mail address: ahmad_k@cc.iut.ac.ir (A. Kermanpur). Materials and Design 31 (2010) 1096–1104 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes