Alloy systems developed for pressing and sintering in the ferrous field

Abstract

Development during the last decade regarding production methods and processing conditions used in the manufacture of sintered low-alloy steel components is reviewed. The nature of the powder metallurgical (PM) manufacturing process leads to a choice of alloying elements and alloying techniques which deviate considerably from those prevailing in wrought steel technology. Maintaining close tolerances forms the justification of the PM technique. Alloying additions, in order to improve the mechanical properties of the sintered material, must therefore be of such a kind and made in such a manner that this dimensional precision is not lost. The factors of importance in this respect are segregation phenomena during the handling of the powder and dimensional variations occurring during sintering. There are principally three types of powder used in the manufacturing of low-alloy PM components, i.e. plain mixes of an iron powder and powders of the alloying elements, partially prealloyed powders, and finally, fully prealloyed powders produced by atomizing. These different types of powder are discussed with respect to their ability to meet the demands described above, and examples of commercially used powders and attainable mechanical properties are given. The specific, and for the wrought steel metallurgist, unusual microstructure and its relation to the properties of sintered low-alloy steels is also discussed.