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.
The Calculation of TTT and CCT diagrams for General Steels
Knowledge of the TTT or CCT diagrams of steels is an important factor in the thermomechanical processing of steels. Much experimental work has been undertaken to determine such diagrams. However, the combination of wide alloy specification ranges, coupled with sharp sensitivity to composition changes plus a dependency on grain size, means that it is impossible to produce enough diagrams for generalised use. To this end significant work has been undertaken over recent decades to develop models that can calculate TTT and CCT diagrams for steels. Almost without exception, these models have been shown to be limited in applicability to carbon and low alloy steels. The aim of the present work is to develop a model that can provide accurate TTT and CCT diagrams for general steels, including medium to high alloy types, tool steels, 13%Cr steels etc., for inclusion in the software programme JMatPro. This aim has been achieved and the present paper provides a background to the calculation method and present results of an extensive validation of the model against experiment.
Analysis and Prevention of Quenching Failures and Proper Selection of Quenching Media: An Overview
Quenching is an essential part of the thermal process used for the manufacture of metallic parts. Quenching involves rapid cooling of a metal from an austenitizing temperature to a lower temperature; usually, but not necessarily, room temperature. The quenching process is typically accompanied by thermal and transformational stresses, which are the main causes for most quenching failures. Any failures or defects during the quenching process result in excessive waste and an often unacceptable increase in the overall production cost. Prevention and elimination of quenching failures are of great significance especially with respect to the rational utilization of energy and resources and the reduction of carbon emissions. Therefore, the quenching method and quenching medium are among the most important factors to be considered in the design of the manufacturing process. The objective of this paper is to discuss quenching failures and to analyze their causes. Counter-measures for prevention of quenching failures and a new criterion for quenchant selection are also suggested.