Duplex Stainless Steels (DSS) possess improved mechanical and corrosion properties, if compared to other stainless steels grades. Moreover, DSS retain good impact fracture toughness even at low temperatures, and, if compared with ferritic stainless steels, the ductile-to-brittle transitions is more gradual. However, DSS are sensitive to secondary phase's precipitation during isothermal heat treatments, even for very short time, mainly in the temperature range 550-950°C, or during quenching treatments at insufficient cooling rates in the same temperature range. The aim of this work is to investigate, using a regression analysis of experimental data, the effect of the precipitation of a slight amount of secondary phases (more or less 1%) on the impact toughness behaviour in the ductile-to-brittle transition region in two DSS: the UNS S32205 and the Zeron-100 grades. In aged materials, small amounts (more or less 1%) were present: mainly chi-phase in Zeron-100 and sigma in UNS S32205. Materials were tested in wrought ("as received" and "sigma-free") and aged (isothermally heat-treated) states by means of Charpy-V impact tests, in a temperature range between 20 and-196°C. The results show that in the UNS S32205 grade the small amounts of secondary phases reduce the impact toughness at room temperature to over 70%. This difference increase with lowering the temperature also because the wrought material maintain a good impact toughness response to about-40°C, with a successive decrease to 100 KJ at-90°C. Instead the Zeron-100 retain a good impact toughness even at-100°C, but a slight amount of secondary phases affects the toughness behaviour by lowering the absorbed energy by about 80 J at room temperature, and this difference in toughness can be considered almost constant for all the experimental temperature range. The lateral expansion was evaluated in order to achieve a further parameter to characterize the plastic deformation in the transition region.
Influence of small amount of secondary phases on impact toughness of UNS S32205 and Zeron® 100 Duplex Stainless Steel
Gennari C.
;Breda M.;Brunelli K.;Ramous E.;Calliari I.
2017
Abstract
Duplex Stainless Steels (DSS) possess improved mechanical and corrosion properties, if compared to other stainless steels grades. Moreover, DSS retain good impact fracture toughness even at low temperatures, and, if compared with ferritic stainless steels, the ductile-to-brittle transitions is more gradual. However, DSS are sensitive to secondary phase's precipitation during isothermal heat treatments, even for very short time, mainly in the temperature range 550-950°C, or during quenching treatments at insufficient cooling rates in the same temperature range. The aim of this work is to investigate, using a regression analysis of experimental data, the effect of the precipitation of a slight amount of secondary phases (more or less 1%) on the impact toughness behaviour in the ductile-to-brittle transition region in two DSS: the UNS S32205 and the Zeron-100 grades. In aged materials, small amounts (more or less 1%) were present: mainly chi-phase in Zeron-100 and sigma in UNS S32205. Materials were tested in wrought ("as received" and "sigma-free") and aged (isothermally heat-treated) states by means of Charpy-V impact tests, in a temperature range between 20 and-196°C. The results show that in the UNS S32205 grade the small amounts of secondary phases reduce the impact toughness at room temperature to over 70%. This difference increase with lowering the temperature also because the wrought material maintain a good impact toughness response to about-40°C, with a successive decrease to 100 KJ at-90°C. Instead the Zeron-100 retain a good impact toughness even at-100°C, but a slight amount of secondary phases affects the toughness behaviour by lowering the absorbed energy by about 80 J at room temperature, and this difference in toughness can be considered almost constant for all the experimental temperature range. The lateral expansion was evaluated in order to achieve a further parameter to characterize the plastic deformation in the transition region.Pubblicazioni consigliate
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