Papers by Author: Rafael Agnelli Mesquita

Abstract: A reduction from 1.0 to 0.3%Si has recently been shown to improve mechanical properties of H11-type hot work tool steels. The present paper shows that an important improvement in toughness can be explained by the effect of Si content on the precipitation sequence of secondary carbides during tempering after quenching. Carbide particle distributions were observed and identified by electron microscopy, allowing to relate the effect of Si on mechanical properties directly to its effect on cementite and subsequent alloy carbide formation during high temperature tempering.

Abstract: Powder metallurgy (PM) and spray forming (SF) have been reported as important alternative routes for tool steel production. The ability to promote refined and more uniform microstructures is their main advantages, leading to improved properties and larger isotropy. While PM application is a completely established technology, the SF process may be considered as a not totally explored field. Therefore, the present work aimed to study the potential of both processes, focusing at high-speed steel (HSS) production. AISI M3:2 highspeed steel was produced by conventional casting, spray forming and powder metallurgy. Conventional ingots and a 400 mm diameter SF billet were rolled to small diameter bars, with cross section around 110 mm. The PM material was evaluated in the as-HIPed condition, in comparative diameters. Large diameter HSS bars are used mainly in cutting tools, but are also applied in cold work tooling when high wear resistance is required. In the present characterisation, microstructures and bend test analysis were used, both in transverse and longitudinal directions. The results show that the as-HIPed PM material presents finer and more uniform carbide distribution, leading to a complete isotropy and higher toughness than conventional steel. In the SF material, carbides are also finer, have good distribution and the isotropy is considerably higher than that for conventional HSS.