The quality and quantity of steel treated in an RH vessel can be enhanced through the optimization of the metallurgical reactions occurring during vacuum treatment and with an improvement in the equipment design and plant layout to reduce production-time losses. The enlargement of the diameter of the snorkel and vessel contribute to an accelerated reaction rate inside the vessel and to an increase in the overall productivity of an RH plant. With the introduction of twin-station RH plants in connection with a quick vesselexchange design, the loss of production time due to ladle transfer, vessel exchange and snorkel maintenance can be significantly reduced.

Considering the development of 56" line pipes, the barrel length of the work rolls of the DH finishing stand had been extended up to 4.8 m in 1981. This made it possible to roll plates with a maximum width of 4,700 mm. The 5.5 m roughing stand had been commissioned in 1985. With a view to further improve the rolling process, DH recently decided to revamp and modernize the existing finishing stand instead of ordering and commissioning a new stand. One and a half year experience with the revamped finishing mill confirm that this option is quite satisfactory and affords high productivity and availability.

Cementite decomposition leading to the formation of the white etching layer (WEL) on the surface of rail tracks was investigated by electron energy loss spectroscopy (EELS) in the TEM and by threedimensional atom probe (3D-AP). It is shown that the carbon concentration inside cementite laths undergoing severe plastic deformation in the transition zone between the pearlitic substrate and the WEL remains stoechiometric. However there exists a boundary layer at the ferrite/cementite interface where the carbon composition decreases, indicating that decomposition is an interfacial phenomenon. Carbon atoms diffuse into the ferrite and segregate along structural defects leading to a heterogeneous supersaturated composition in the white etching layer.

We propose a model for predicting the kinetics of cementite dissolution and austenite growth during heating and soaking. This model is applicable to multi component systems and a good agreement between the calculations and experimental data were obtained. This model is coupled with a mechanical module which allows taking into account the various effects of cold deformation on the kinetics of austenite formation during heating and soaking. A discussion is made from a 3D microstructural investigation.

As a result of the demand for increasing the operating life of aeronautic parts, it is sought in this work to optimize the mechanical characteristics of a bearing submitted to marine environment. Phase transformations during high speed austenizing have been studied together with the influence of thermal stresses due to induction heating. It is observed that there are two ways to obtain the best mechanical properties among which the shortest cycle could be used to reduce heat treatment time of highly alloyed cold work steels.