| Summary: | Mathematical models have been developed for the purpose of predicting the evolution of
microstructure and residual stress that develops during the manufacture of hypo-eutectic
cast iron rolls for the paper industry. These include, a finite element based heat flow
model to predict the evolution of temperature and microstructure, and a preliminary finite
element based stress model to estimate the evolution of residual stress. Both models have
been implemented in the commercial finite element code ABAQUS.
To characterize the evolution of solidified microstructure, specialized routines,
employing relationships describing nucleation and growth of equiaxed primary austenite,
gray iron and white iron, were formulated and incorporated into an ABAQUS thermal
model through user-defined subroutines. These relationships have been adapted and
extended from a number of investigations describing equiaxed cast iron solidification
presented in the literature. In addition, a preliminary columnar growth model was also
implemented and tested to describe white iron growth.
To describe the evolution of residual stress, a preliminary thermal stress model
was developed to describe the evolution of stress and strain throughout the casting
process. The preliminary stress model utilizes the temperature and microstructure
predictions of the thermal model as input and incorporates phase and temperature
dependent properties describing the elastic modulus, thermal dilatation, as well as, the
strain rate independent, Von Mises, plastic deformation of the various phases.
In order to validate the various components of the overall model, a series of
measurements involving two industrial castings - a Quik-cup casting and a reduced scale
roll casting - were undertaken to provide thermal, microstructural, and residual stress
data for use in 'fine-tuning' and validating the mathematical models. Comparison of the
predicted and measured temperatures show good overall agreement for both casting
geometries. Microstructure predictions for the Quik-cup casting agree with the observed
microstructure. However, in the reduced scale roll casting, key microstructure
phenomena were inaccurately predicted with the equiaxed microstructure model.
Improvements in the microstructure predictions were observed after the white iron
columnar growth model was implemented. Residual stress predictions for the reduced
scale roll casting show good overall agreement with the OD surface measurements. The
results of this analysis show the importance and usefulness of developing the ability to
predict residual stress and microstructure evolution in cast iron rolls.
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