Prediction and control of geometric distortion and residual stresses in hot rolled and heat treated large rings

Abstract

Seamless rings are produced by hot rolling and heat treatment processes. The heat treatment is used to enhance the material properties of a wide range of mechanical steel components, according to their final application. Quenching is a common step in these heat treatments, involving the fast cooling of previously austenitized parts and leading to a phase transformation from austenite to hard martensite in the material. Quenching commonly causes a geometric distortion in the parts, associated with the thermal contraction and with the change in the mechanical and geometrical properties of the material phases. For the manufacturing of large thin-walled rings, the control of the distortion during the quench process is not possible. The high production rate, the range of rings sizes and all the quench conditions inside the tank represent a very complex system. It is of importance to predict these distortions, so that one can design corrective post-heat treatment shape corrections, leading to a final part with adequate shape and dimensions. This doctoral thesis develops a methodology to predict and correct the ring distortion so-called ovality. This methodology is based on finite element (FE) simulations of the heat treatment (normalizing and quenching) and straightening of an AISI 4140 steel hot rolled ring. The heat treatment simulation is validated using a Navy C-Ring Test. The straightening process uses a compressing machine with flat tools, and an experimental procedure is defined and performed through out simulation