Modeling of microstructure and residual stress in cast iron calender rolls

A comprehensive mathematical model based on the commercial finite-element ( FE) code ABAQUS has been developed to predict the evolution of temperature, microstructure, and residual stresses in cast iron castings. The thermal c omponent of the model, applied in stage one of the analysis, is capable of simulating the formation of microstructure over a broad range of cooling co nditions, including the formation of columnar white iron as well as equiaxe d gray iron. To test the model, it has been evaluated against thermocouple and microstructural data collected from a reduced-scale calender roll test casting. The model has been demonstrated to be able to predict the transiti on from columnar white iron to equiaxed gray iron which occurs approximatel y 20 mm below the outside surface of the roll test casting. In addition, th e model is shown to be able to satisfactorily reproduce the evolution of te mperature recorded from thermocouples embedded at various locations in the test casting. An elastic-plastic stress analysis, applied in the second sta ge of the analysis, was performed using the temperature history and the vol ume fraction of white and gray iron obtained with the thermal/microstructur al model. The results were verified against residual stress measurements ma de at various locations along the outer-diameter (OD) surface of the roll. The elastic-plastic model accounts for the temperature-dependent plastic be havior of white and gray iron and the thermal dilatational behavior of whit e and gray iron, including volumetric expansion due to austenite decomposit ion and dilatational anisotropy in columnar white iron. The results of the mathematical analysis demonstrate that the residual stress distribution in full-scale calender thermorolls cannot be deduced simply from knowledge of the microstructural distribution and basic dilatometric considerations, as is currently the practice in industry.