The quality and quantity of steel treated in an RH vessel can beenhanced through the optimization of the metallurgical reactionsoccurring during vacuum treatment and with an improvement in theequipment design and plant layout to reduce production-time losses.The enlargement of the diameter of the snorkel and vesselcontribute to an accelerated reaction rate inside the vessel and to anincrease in the overall productivity of an RH plant. With the introductionof twin-station RH plants in connection with a quick vesselexchangedesign, 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 ofthe work rolls of the DH finishing stand had been extended up to4.8 m in 1981. This made it possible to roll plates with a maximumwidth of 4,700 mm. The 5.5 m roughing stand had been commissionedin 1985. With a view to further improve the rolling process, DHrecently decided to revamp and modernize the existing finishingstand instead of ordering and commissioning a new stand. One anda half year experience with the revamped finishing mill confirm thatthis option is quite satisfactory and affords high productivity andavailability.

Cementite decomposition leading to the formation of the whiteetching layer (WEL) on the surface of rail tracks was investigated byelectron energy loss spectroscopy (EELS) in the TEM and by threedimensionalatom probe (3D-AP). It is shown that the carbonconcentration inside cementite laths undergoing severe plasticdeformation in the transition zone between the pearlitic substrateand the WEL remains stoechiometric. However there exists a boundarylayer at the ferrite/cementite interface where the carbon compositiondecreases, indicating that decomposition is an interfacialphenomenon. Carbon atoms diffuse into the ferrite and segregatealong structural defects leading to a heterogeneous supersaturatedcomposition in the white etching layer.

We propose a model for predicting the kinetics of cementite dissolutionand austenite growth during heating and soaking. This modelis applicable to multi component systems and a good agreementbetween the calculations and experimental data were obtained. Thismodel is coupled with a mechanical module which allows taking intoaccount the various effects of cold deformation on the kinetics ofaustenite formation during heating and soaking. A discussion ismade from a 3D microstructural investigation.

As a result of the demand for increasing the operating life of aeronauticparts, it is sought in this work to optimize the mechanical characteristicsof a bearing submitted to marine environment.Phase transformations during high speed austenizing have beenstudied together with the influence of thermal stresses due to inductionheating. It is observed that there are two ways to obtain the bestmechanical properties among which the shortest cycle could beused to reduce heat treatment time of highly alloyed cold worksteels.