H. F. G. de Abreu

Publications (3)2.02 Total impact

• Article: Influence of heat treatments on toughness and sensitization of a Ti-alloyed supermartensitic stainless steel

  G. F. da Silva, S. S. M. Tavares, J. M. Pardal, M. R. Silva, H. F. G. de Abreu
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  ABSTRACT: Supermartensitic steels are a new class of martensitic stainless steels developed to obtain higher corrosion resistance and better toughness through the reduction of carbon content, and addition of Ni and Mo. They were developed to more critical applications or to improve the performance obtained with conventional grades AISI 410, 420, and 431. In this study, the influences of the tempering parameters on the microstructure, mechanical properties (hardness and toughness), and sensitization of a Ti-alloyed supermartensitc stainless steel were investigated. The material showed temper embrittlement in the 400–600°C range, as detected by low temperature (−46°C) impact tests. The degree of sensitization measured by double loop reactivation potentiodynamic tests increased continuously with the increase of tempering temperature above 400°C. Healing due to Cr diffusion at high tempering temperatures was not observed. Double tempered specimens showed high amounts (>20%) of reverse austenite but their toughness were similar to specimens single tempered at 625 and 650°C.
  Journal of Materials Science 05/2012; 46(24):7737-7744. · 2.02 Impact Factor
• Article: Influence of the grain size on deleterious phase precipitation in superduplex stainless steel UNS S32750

  J.M. Pardal, S.S.M. Tavares, M. Cindra Fonseca, J.A. de Souza, R.R.A. Côrte, H.F.G. de Abreu
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  ABSTRACT: In the present work, the effect of grain size on deleterious phase precipitation in a superduplex stainless steel was investigated. The materials studied were heat treated isothermally at 800 °C, 850 °C and 900 °C for times up to 120 min. Hardness tests, light optical microscopy, scanning electron microscopy and X-ray diffraction were carried out to detect sigma and other harmful precipitate phases. The ferritic and austenitic grain sizes in the solution treated condition of the two steels analyzed were measured by electron backscattered diffraction (EBSD). Cyclic polarization corrosion tests were performed to evaluate the effect of grain size on the corrosion resistance. The results presented show that the precipitation of deleterious phases such as χ, σ and γ2, which can occur during welding and forming operations, is retarded by grain growth.
  Materials Characterization. 60(3):165-172.
• Article: Microstructural, magnetic and mechanical property changes in an AISI 444 stainless steel aged in the 560 °C to 800 °C range

  S.S.M. Tavares, J.A. de Souza, L.F.G. Herculano, H.F.G. de Abreu, C.M. de Souza Jr
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  ABSTRACT: AISI 444 steel is an 18Cr–2Mo ferritic stainless steel, containing Ti and Nb as stabilizing elements. The effects of aging in the 560–800 °C range on the microstructure, mechanical and magnetic properties were investigated. The material was not susceptible to sigma phase formation until 100 h of exposure. Slight hardening at 560 °C and progressive softening in the 650 °C–800 °C range were observed. At these temperatures, Mo-rich phases such as Fe2Mo and FeMoSi precipitate. The increase of particle sizes with the increase of temperature above 650 °C is responsible for the decrease of hardness. Precipitation of the Mo-rich phases increases the coercive force.
  Materials Characterization. 59(2):112-116.