Papers by Author: Rejane A. Nogueira

Abstract: The purpose of this study is to evaluate the effect of the stages and tempering temperatures in the microstructure, tenacity and hardness of the vacuum sintered high speed steel AISI T15. The material was uniaxial pressing at 700 MPa and sintered in a vacuum furnace at 1275°C. After that, different samples of the materials were submitted to the annealing treatment at 870°C, quenching at 1235°C and tempering (single, double and triple) at 540, 550 and 560°C. Concluded the treatments, Rockwell C measurements of hardness were accomplished and, to evaluate the toughness of the material, TRS (Transverse Rupture Strength) tests were done. Later on, the materials were submitted to the metallographic preparation for microstructure analysis in optical microscopy, SEM, EDX and X-ray diffraction. Finally, each property analyzed was evaluated and correlated with the different tempering stages and temperatures accomplished.

Abstract: The heat treatment of high speed steel tools consists of austenitizing, quenching and tempering. The size of austenite grains formed during the hardening treatment is an important factor in the final microstructure of the steel, and it also affects properties such as wear resistance and toughness. This paper presents the austenite grain size, matrix composition and hardness of commercial AISI M2, AISI T15, VWM3C and Sinter 23 high speed steels that were austenitized and quenched from five distinct temperatures. This study shows that increase in quenching temperature results in grain growth of steels such as AISI M2 and VWM3C, obtained by the conventional method (cast to ingot and worked). The P/M Sinter 23 high speed steel showed a slight grain growth (about 10%). This effect was not observed in AISI T15 obtained by the powder metallurgy process.

Abstract: Low-pressure powder injection molding was used to obtain AISI T15 high speed steel parts. The binders used were based on paraffin wax, low density polyethylene and stearic acid. The metals powders were characterized in terms of morphology, particle size distribution. The mixture was injected in the shape of square bar specimens to evaluate the performance of the injection in the green state, and then sintered. The samples were injected under the pressures of 0.4, 0.5 and 0.7MPa and at temperatures varying from 110 to 150°C aiming the optimization of the process. The results of the variation of injection pressure were evaluated by measuring the density of the green parts. Debinding was carried out in two steps: first, the molded part was immersed in heptane to remove the major component of the binder and then heated to remove the remaining binder. A second step debinding and sintering were performed in a single step. This procedure shortened considerably the debinding and sintering time.

Abstract: The effect of quenching heat treatments on the microstructure of cast and worked commercial steel AISI M2 and hot isostatically pressed as well as IPEN vacuum sintered AISI T15 have been studied. The quenching treatments were carried out from 1160, 1185, 1210 and 1235°C. The average grain size, volume fraction and average size of the primary carbides M6C and MC were determined by scanning electron microscopy and by using the digital image analysis method "Quantikov". An increase in average austenite grain size with increase in quenching temperature was observed for the AISI M2 commercial steel and vacuum sintered specimens. In the case of the AISI T15 steel specimens, increase in quenching temperature did not result in an increase in average grain size, both for the commercial and the vacuum sintered steels. The average size and volume fraction of M6C and MC carbides remained unaltered with increase in quenching temperature.