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Zanatta A.M.,Aeronautical Institute of Technology ITA | De Oliveira Gomes J.,Aeronautical Institute of Technology ITA | Bressan J.D.,Santa Catarina State University | Barbosa C.A.,Villares Metals SA
Advanced Materials Research | Year: 2011

The aim of this study was to evaluate the influence of the amount and distribution of inclusions of titanium carbonitride and manganese sulfide on the machinability and polishability of Villares VP100 steel which is used in manufacturing polymer injection molds. By means of materials metallography, captured images were processed with image analysis software to characterize the inclusions. Tool life tests were performed in an open cavity in order to approach the real processes situation found in the toolmaking industry. The flank wear and chip formation were evaluated periodically. The cutting forces were also evaluated under the same conditions applied to the tool life test. The polishing tests were performed in a polishing equipment specially developed for this purpose, which allows adjustable rotation speed and pressure load. In the polishing process, abrasives with particle size of 1mm are applied and surface roughnesses of the samples were evaluated according to the polishing time. The results show that the amount of titanium and size of titanium carbonitride hard inclusions are fundamental for good machinability, while the soft sulfides of manganese do not take any effect in the presence of these hard particles. The polishability is worsened by the presence of large inclusions of manganese sulfides, forming pin holes. © (2011) Trans Tech Publication. Source

Goncalves C.S.,Villares Metals SA | Goncalves C.S.,University of Sao Paulo | Slaviero A.L.,University of Sao Paulo | Mesquita R.A.,University of Sao Paulo | And 2 more authors.
Journal of ASTM International | Year: 2011

High speed steels are usually employed in cutting tools and forming dies. Heat treatment is an important step during the tool manufacturing process, being responsible for most of the final properties, mainly hardness and toughness. In this context, an especial interest relies on the effect of hardening variables on mechanical properties and tool performance. The present paper aimed to study the effect of cooling rate during the quenching process of standard designation AISI M2 high speed steel, under typical industrial conditions. The experiments were carried out in an industrial vacuum furnace, with high pressure nitrogen quenching. Several cooling rates were obtained by variation of the nitrogen pressure and by the use of test specimens with different dimensions. Toughness results were mainly evaluated through static bend test. Low cooling rates were shown to decrease material toughness and large parts presented adecrease in mechanical properties from surface to core regions. Carbide precipitation on grain boundaries are pointed as the main explanation for all these effects. Copyright © 2011. Source

Barbosa C.A.,Villares Metals SA | Goldenstein H.,University of Sao Paulo
Journal of ASTM International | Year: 2011

Recent literature has shown several papers dealing with cryogenic treatments of tool steels. Most of them see an improvement in wear resistance supposedly due to microstructural modifications that occur at cryogenic temperatures. Cryogenic treatments are supposed to modify the way secondary carbides precipitate, obtaining a finer and more homogeneous distribution. Specimens of an AISI D2 tool steel were submitted to different thermal cycles, including cryogenic treatment, and the volumetric fraction of micrometric carbides was determined. The samples were analyzed by scanning electron microscopy and the image analysis was carried out with Image J software. The present work also discusses what is understood about secondary carbides and the modifications that occur with micrometric (from the austenite-carbide field) and nanometric (from the temper of martensite) secondary carbides. No difference was found between the micrometric carbide with and without cryogenic treatment, while some indications were found that the nanometric carbides are refined and more homogeneously distributed after cryogenic treatment. Copyright © 2011 by ASTM International. Source

Jaimes R.F.V.V.,University do Grande | Afonso M.L.C.d.A.,Technological and Nuclear Institute of Portugal | Rogero S.O.,Brazilian Nuclear Energy Research Institute (IPEN) | Agostinho S.M.L.,University of Sao Paulo | Barbosa C.A.,Villares Metals SA
Materials Letters | Year: 2010

Nickel, a component of stainless steels (SS) applied in orthopedic implants may cause allergic processes in human tissues. P558 nickel free SS was studied to verify its viability as a substitute for stainless steel containing nickel. Its performance is compared to ISO 5832-9 and F138 most used nowadays grades in implants fabrications, in minimum essential medium, MEM, at 37 °C. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and "in vitro" cytotoxicity were used as techniques. From the electrochemical point of view P558 SS is comparable to ISO 5832-9 SS in MEM. It remains passivated until the transpassivation potential, above which generalized corrosion occurs. F138 presents pitting corrosion at 370 mV/SCE. The cytotoxicity results showed that P558, ISO 5832-9 and F138 do not present cytotoxic character. Therefore, these results suggest that P558 SS can be applied in orthopedic implants. © 2010 Elsevier B.V. All rights reserved. Source

Mesquita R.A.,Nove de Julho University | Barbosa C.A.,Villares Metals SA | Morales E.V.,Santa Clara University | Kestenbach H.-J.,Federal University of Sao Carlos
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science | Year: 2011

The formation of secondary carbides during tempering of H11 hot work steels at 898 K (625 °C) was studied by transmission electron microscopy (TEM) and related to the previously established effects of Si content on mechanical properties. Lower Si contents (0.05 and 0.3 pct Si) and higher Si contents (1.0 and 2.0 pct Si) were observed to yield different carbide phases and different particle distributions. Cementite particles stabilized by Cr, Mo, and V in the lower Si steels were found to be responsible for similar precipitation hardening effects in comparison to the M2C alloy carbides in the higher Si steels. The much higher toughness of the lower Si steels was suggested to be due to a finer and more homogeneous distribution of Cr-rich M7C 3 carbides in the interlath and interpackage regions of the quenched and tempered martensite microstructure. The present effects of Si content on the formation of alloy carbides in H11 hot work steels were found to be the result of the retarding effect of Si on the initial formation of cementite, well known from the early tempering stages in low alloy steels. © 2010 The Minerals, Metals & Materials Society and ASM International. Source

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