Prediction of Geometric Distortion and Residual Stresses In Hot Rolled and Heat Treated Large Rings Through Finite Element Modeling
During quenching, hot rolled steel rings, especially those with a large outer diameter to wall thickness ratio, distort and develop undesired residual stresses. These phenomena are the result of three major mechanisms: metallurgical, mechanical and thermal. This paper presents the result of a comprehensive study on the heat treatment of rings by modeling via Finite Element Analysis. The simulation is carried out with coupled analysis of heat transfer, deformation mechanics and phase transformations. The material data required for the simulation of distortion during heat treatments, including TTT/CCT phase transformation diagrams, temperature dependent physical and thermophysical properties, as well as temperature and strain rate dependent mechanical properties are calculated by computer models.
A Numerical Procedure for Machining Distortions Simulation on a SAF 2507 Casting Workpiece
The workpiece distortion that occurs during machining, can lead to a large increase in the number of the scrap parts. Residual stresses are the main cause of these distortions and they are generally present in both forging and casting products. In order to obtain the desired microstructure and mechanical properties, the workpiece is subjected to heat treatment before being worked. Quenching produces residual stresses that exist throughout a large percentage of the casting or forging part. Distortion occurs as a result of removing stressed material from the workpiece. The component will re-equilibrate and distort as each layer of stressed material is machined away. This paper describes a procedure development for distortions numerical analysis on a SAF2507 casting bulk workpiece. A solubilization heat treatment has been simulated, in order to predict the bulk residual stresses distribution. Different metal cutting processes have been considered to measure the numerical distortions induced in the workpiece.
PREDICTION OF HEAT TREATMENT DISTORTION OF CAST STEEL C-RINGS
Navy C-Ring test parts were made of AISI 1022, 4320, 8625, and CF8M steels and heat treated in a designed experiment to evaluate the commercial heat treatment distortion simulation software DANTE. The parts were machined and then measured with a CMM for original dimensions. The parts were then heated and subsequently quenched in two different immersion orientations in agitated water. Temperature measurements were taken from the austenitic stainless steel parts to obtain heat transfer coefficients for the simulations. The part dimensions were re-measured and compared to pre-heat treatment values. The CF8M experiments show that the gap in the C-Ring closes due to thermal stresses. The cast carbon and low-alloy steel C-Rings resist the closure somewhat, though general trends toward closure are still apparent. This is in contrast to results shown in previous literature. The dimensional measurements for the different immersion directions and different alloys are compared and discussed. While the DANTE simulations are able to capture the general distortion trends seen in the experiments, they are not in complete agreement with the experimental results obtained here. Recommendations are made for future work.