Modelling descaling during hot rolling of steel

A computer model was developed to study the stresses that develop within the oxide formed on the surface of reheated steel slabs. The model considers that the crust grows during reheating following temperature dependent parabolic rates, and, as result of its thickness and growth rate, it will be stressed. Removal of this crust takes place by the impingement of water from high pressure jets installed in descaling units, which are located prior to deformation to avoid oxide imprint on the steel surface. Removal of the oxide layer depends on the velocity and amount of the water, as well as the force of the impact. A criterion based on these parameters can be established to determine the feasibility for oxide removal

Aging of a cast 35Cr-45Ni heat resistant alloy

International audienceThe microstructural evolution during aging and its effect on the mechanical properties of a centrifugally cast 35Cr-45Ni heat resistant alloy was studied by means of optical and electron microscopy, and by mechanical testing in samples aged in air at 750 ◦C for a period of time of up to 1000 h. The as-cast microstructure consisted of an austenitic matrix and a network of two types of primary carbides that were identified as NbC and M7C3 by their light and dark tones when viewed in backscattered electron mode in a scanning electron microscope. Aging promoted the occurrence of different phenomena such as the transformation of primary M7C3 to M23C6 carbides, precipitation of secondary M23C6 carbides and the transformation of NbC to Nb3Ni2Si. It was found that aging promoted an increase in Vickers microhardness of more than 50%, the increment in tensile strength of around 20% and the reduction in ductility of close to 70%