Évolution des aciers spéciaux

Evolution of special steels

Directeur scientifique de L'IRSID

Abstract

The metallurgy of spécial steels lias evolved significantly over the past 15 years. The development in the techniques of vaccum ladle metallurgy lias liad several important consequences. Firstly hy enahling the composition ranges to he tiglitened, this technology has led to the development of new produi ts with more uniform and more reliahle service properties. Moreover the progress in ladle metallurgy lias enahled tlie impurity content of the steels to he markedly reduced with a conséquent improvement in toughness, fatigue lifc, corrosion résistance and susceptibility to hydrogen emhrittlement. Finally the resulting improvements in the control of the nature, size andform of inclusions has permitted the development of new grades with improved machinahility.

Prealloyed powder metallurgy constitutes a second line of development with new industrial applications in the fields of high speed steels and aeronautical super-alloys.

The third area of development concerns the so called "multi materials" which involve the association of several materials, for example metal/metal or more recently metal/polymer. The products which have already heen developped or which are in the course of industrialization demonstrate the importance of these new materials.

The three above-mentioned development areas in which the principal evolution and mutations of special steels have taken place, are not specific to these steels but concern, to a greater or lesser extent, the majority of metallic materials.