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.
Reduced Cylindricity on Outer Diameter when Grinding Rings on Inner Diameter
A problem in the manufacturing of precision bearing rings is reduced outer diameter (OD) cylindricity when grinding inner diameter (ID). Shot blasting is used to remove surface scale from hardened rings prior to grinding. The basic hypothesis is that ID grinding releases residual surface stresses from blasting resulting in reduced OD cylindricity. In this study shot blasted rings are found to exhibit 300% reduced OD cylindricity after ID grinding. Moreover, outer diameters show a pronounced 2-point eccentricity after ID grinding. Sand blasting rings, while just as efficient at removing scale, imparts 40% lower residual surface stresses. No changes in cylindricity or eccentricity are found after ID grinding. Experimental data does not contradict the conclusion when residual surface stresses are high ID grinding imparts sufficient thermo-mechanical loading to release stresses resulting in reduced OD cylindricity.
Explanation of the Origin of Distortion and Residual Stress in Carburized Ring Using Computer Simulation
Case carburizing is recognized as a suitable process for realizing low distortion and high compressive stresses near the surfaces under optimal conditions. Patterns of distortion and residual stresses in carburized cylinders and rings under different conditions have been identified from measurements performed for many years. Some pioneers of the heat treatment simulation compared their simulated results of carburized and quenched parts with experimental data for verifying their programs. However, these early researchers did not sufficiently explain their distortion and stress generation mechanism using their simulated results. Although one of the authors tried to illuminate their mechanism of a carburized and quenched ring, the work has not been finished because the purpose was limited in examining the role of transformation plasticity in the process. In this paper, the same simulated results were analyzed more comprehensively for explaining the origin of distortion and residual stress in the ring based on a concrete strategy newly developed.