A two-dimensional mathematical model has been developed to predict stress generation in static-cast steel ingots during thermal processing with the objective of understanding the role of stress generation in the formation of defects such as panel cracks. In the first part of a two-part paper the formulation and application of a heat-flow model, necessary for the prediction of the temperature distribution which governs thermal stress generation in the ingot, are described. A transverse plane through the ingot and mold is considered and the model incorporates geometric features such as rounded corners and mold corrugations by the use of the finite-element method. The time of air gap formation between mold and solidifying ingot skin is input, based on reported measurements, as a function of position over the ingot/mold surface. The model has been verified with analytical solutions and by comparison of predictions to industrial measurements. Finally, the model has been applied to calculate temperature contours in a 760×1520 mm, corrugated, low-carbon steel ingot under processing conditions conducive to panel crack formation. The model predictions are input to an uncoupled stress model which is described in Part II.

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Mathematical Model of the Thermal Processing of Steel Ingots: Part I. Heat Flow Model

Shrinkage porosity criteria and optimized design of a 100-ton 30Cr2Ni4MoV forging ingot

Void closure studies have been conducted numerically and experimentally for open-die forging processes. The plane-strain FEM analysis was compared with bite forging experiments in order to determine how well the plane-strain approximation predicted the material flow in open-die forging. In addition physical modeling with plasticine was used to compare the measured and calculated deformation of the internal defect. The FEM analysis was in good agreement with the experimental results. Correlations for the computed effective strain and hydrostatic stress to the void closure were then calculated. Simulations of a solid cylinder side pressed with flat dies, V-shaped dies, and FML dies were done to determine the effectiveness of these dies at consolidating internal porosity based on the calculated strain and hydrostatic stress at the center of the billet. The V-shaped dies were found to be the most effective among those investigated. However, the press load for the V-shaped dies was also the highest.

Analysis of void closure in open-die forging

Influence of mould design on the solidification of heavy forging ingots of low alloy steels by numerical simulation

Efficient forging process to improve the closing effect of the inner void on an ultra-large ingot

Influence of hot top and mould design on the formation of central porosities and loose structure in heavy forging ingot was analysed by using finite element method. The results of the analysis were compared with those of sectioning investigation of 100 and 135t ingots and the influence of mould and hot top design on the internal defects has been made clear quantitatively.The result shows that the geometry of hot top and mould design plays most important role in the manufacture of sound heavy ingots. The central porosities and loose structure are liable to increase when the rate of vertical solidification at the centerline of ingot exceeds the value of about 10mm/min, and the defects are strengthened at the area where the rate of solidification is accelerated.For 0.25%C-3.5%Ni-Cr-Mo-V steel ingot, “A” segregation begins to form when the rate of transverse (horizontal) solidification decreases to the value of about 0.8mm/min.

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Influence of Mould Design on the Solidification and Soundness of Heavy Forging Ingots

For developing an optimum free forging process to close and consolidate internal cavities in heavy ingots by direct forging alone, internal deformation and internal stress were investigated with Plasticine models. First, a method to simulate the material behavior with the existence of a large temperature gradient was established. The forging processes used were the followings;1) the conventional process which uses symmetrical upper and lower anvils2) a process called the FM process in which the upper anvil is of the usual type but the lower anvil is flat and larger than the dimension of the material to be forged3) a process called the FML process-where the lower anvil is the same as that of the FM process and the upper anvil is smaller than the dimension of the material to be forged4) the so-called JTS forging process which uses the same combination of anvils as that of the FML process and is carried out with a large temperature gradient in the material.Among these processes, the conventional process can effectively cause a large deformation rate at the center and the use of wide anvils in any process is also effective for a large deformation even without a temperature gradient in the material. For attaining compressive stress, that is, a higher hydrostatic stress at the center, it is effective even without a temperature gradient to raise the value of the parameter w/h (w: width of anvil, h: height of, forging material) or to carry out unsymmetrical reductions such as that in the FM process and the FML process. A tri-axial compressive stress state is considered to be effective for closing and consolidating the central cavities.

Development of New Processes for Control of Internal Deformation and Internal Stress in Hot Free Forging of Heavy Ingots

PURPOSE:To produce a heat resisting steel having an excellent creep rupture resistance characteristic by subjecting a steel contg. a specific ratio each of C, Si, Mn, P, S, Ni, Cr, Mo, etc. to heating, hot working, accelerated cooling and tempering under specific conditions. CONSTITUTION:The steel contg., by weight 5, 0.02-0.25% C, =1050 deg.C. The steel is then subjected to hot working at 850-1000 deg.C and at least at 20% cumulative draft and is then subjected to accelerated cooling at the fastest possible point of the time. The steel is further tempered at 550-750 deg.C, by which the heat resisting steel is produced. The heat resisting steel having good creep rupture strength and excellent toughness is thus obtd.

Production of heat resisting steel having excellent creep rupture resistance characteristic

PURPOSE:To improve strength and toughness by specifying respective quantities of C, Si, Mn, P, Si, Ni, Cr, Mo, etc CONSTITUTION:This high-strength forged steel for nuclear pressure vessel has a composition consisting of, by weight, 018-023% C, =63kgf/mm tensile strength and 46kgf/mm 02% yield strength

Shiro Watanabe

Papers

Influence of Mould Design on the Solidification and Soundness of Heavy Forging Ingots

Development of New Processes for Control of Internal Deformation and Internal Stress in Hot Free Forging of Heavy Ingots

Influence of Mould Design on the Solidification and Soundness of Heavy Forging Ingots

Production of heat resisting steel having excellent creep rupture resistance characteristic

High-strength forged steel for nuclear pressure vessel