Effect Of Heat Treatment On The Structure And Mechanical Properties Of Superaustenitic Stainless Steel_eti [efeito Do Tratamento Térmico Na Estrutura E Nas Propriedades Mecânicas De Um Aço Inoxidável Superaustenítico]

The austenitic stainless steel high alloyed (22Cr-25Ni-7Mo-0,3N), well known as superaustenitic, has as its main characteristic a high corrosion resistence to several environments, mainly in sea water. Furthermore the material shows good mechanical properties and thermal stability. To obtain the mentioned characteristics, the material must be thermically treated, taking into consideration the solubility of the alloy elements. Various heat treatments were performed in this research : solution heat treatment (from 1100 to 1250°C), stress relief (from 500 to 800°C) and sensitization (900°C, varing the time at 1,5h, 12h, 24h and 48h). Hardness and charpy tests were used to study the mechanical behaviour, and optical methalography was done to investigate the heat treatment influence in the material micro structure. It was observed that even with the solution at an extreamely high heat treatment temperature (1250°C), it was not possible to dissolve the precipitates formed during solidification scattering in the austenitic matrix. To maximize the energy absortion impact, the solution heat treatment must be performed between 1150°C and 1200°C and the stress relief until 500°C. In the 900°C temperature range, the material impact resistence (measured at environment temperature) decreasedfrom 25J to 7J when the heat treatment time was increased from 1,5h to 48 h.601155161ASTM A890/A890M - 91. Standard practice for castings, iron-chromium-nickel-molybdenum corrosion-resistant, duplex (Austenitic/ ferritic) for general application. American Society for Testing and Materials. Easton. v. 01.02. Ferrous Castings, Ferroalloys, p.556-569GRUBB, J.F., DEEMER, D.E., AL-6XN Alloy (2002) Allegheny Ludlum, pp. 2-7. , USA, pCURTIS, J.F., KOVACH, W., (2002) High performance stainless steel, p. 17. , USA: Níquel Development InstitutePADILHA, A.F., RIOS, P.R., Decomposition of austenite in uustenitic stainless steel (2002) USP: Departamento de Engenharia Metalúrgica e de Materials, pp. 325-337/ A744M. Standard specification for casting, Iron-chromium, iron-chromium-nickel, corrosion resistant, for general application (1998), pp. 1-6. , ASTM A744, American Society for Testing and Materials, U.S.A(1998) Corrosion-resistant steel casting, p. 8. , EUROPEAN STANDARD EN 10283, DIN Deutsches Institute fur Nourmung, Germany, BerlinNORSOK STANDARD M-630 MDS R16. Material data sheets for piping. Standards Norway, Norway, 2004Standard Test Methods and Definition for Mechanical Testing of Steel Products (1997), pp. 7-10. , ASTM A370, American Society for Testing and Materials, U.S.AStandard hardeness convertion tables for metals (2002), p. 893. , ASTM E 140, American Society for Testing and Materials, U.S.

Aging Heat Treatment Effect On The Microstructure And Impact Properties Of The Super-austenitic Stainless Steel Astm A 744 Gr. Cn3mn [efeito Do Tratamento Térmico De Solubilização Na Microestrutura E Nas Propriedades De Impacto Do Aço Inoxidável Superaustenítico Astm A 744 Gr. Cn3mn]

This research investigated the influence of solution heat treatments on the microstructure and properties of this type of material. These treatments were carried out at temperatures ranging from 1100 to 1250°C. Impact (Charpy) tests were conducted at room temperature and -46°C for all solution treated samples. The microstructural analyses were carried out by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. It was concluded that, to maximize the material's impact strength, the solution heat treatment should be done at 1200°C, at which temperature the volumetric fraction of precipitates is lower than at other solution heat treatment temperatures. The samples that were solution heat treated at 1200 and 1240°C presented sigma (σ) and M6C carbide phases.6311320(1990) Practice For Determining Volume Fraction By Systematic Manual Point Count.American Society For Testing and Materials, p. 15. , ASTM E-562-90, U.S.A(1998) Standard Specification For Casting, Iron-chromium-nickel, Corrosion Resistant, For Severe Service, pp. 1-5. , ASTM A744h/A744M, American Society for Testing and Materials, U.S.A(1997) Standard Test Methods and Definition For Mechanical Testing of Steel Products, pp. 7-10. , ASTM A370, American Society for Testing and Materials, U.S.AStandard Practice For Castings, Iron-chromium-nickel-molybdenum Corrosion- Resistant, Duplex (Austenitic/ferritic) For General Application, pp. 556-569. , ASTM A890/A890M - 91, American Society for Testing and Materials. Easton. V.01.02. Ferrous CastingsFerroalloys(1998) Corrosion- Resistant Steel Casting, p. 8. , EUROPEAN STANDARD EN 10283, Deutsche Institute fur Nourmung (DIN), Germany, BerlinGrubb, J.F., Deemer, D.E., (2002) AL-6XN Alloy, pp. 2-7. , Allegheny Ludlum, USAHeino, S., Knutson, M., Karlsson, B., (1999) Precipitation Behavior In Heat Affected Zone of Welded Superaustenitic Stainless Steel, p. 101. , Materials Science and Technology. Sweden, Chalmers University of TechnologyHeino, S., Knutson, M., Karlsson, B., (1999) Precipitation In a High Nitrogen Superaustenitic Stainless Steel, pp. 143-148. , Materials Science Forum, Sweden, Chalmers University of Technology(1982) Heat Treating. American Society For Metals, 4, pp. 1697-1705. , METALS HANDBOOK, Metals Park - Ohio U.S.A(2004) Material Data Sheets For Piping, p. 85. , NORSOK STANDARD M-630 MDS R16 Rev.3, Norway, Standards NorwayPadilha, A.F., Rios, P.R., (2002) Decomposition of Austenite In Austenitic Stainless Steel, pp. 325-337. , São Paulo: Departamento de Engenharia Metalúrgica e de Materiais - US

Phase Transformations On Astm A 744 Gr. Cn3mn Superaustenitic Stainless Steel After Heat Treatment

The superaustenitic stainless steel ASTM A 744 Gr. CN3MN (22Cr-25Ni-7Mo-0.2N) has as mainly characteristic high corrosion resistance in severe environment. As the corrosion resistance depends on the microstructure, it was investigated the phase transformations after a solution treatment at 1200°C. Thermocalc calculation for 53Fe-25Ni-22Cr alloy indicates austenitic phase between 1300 and 800°C and austenite + sigma phase below 800°C. The as-cast steel studied presented 2.7 % of precipitates volume fraction and the precipitates were located on the grain boundaries and inside the austenitic grains. X-ray diffraction confirmed the presence of sigma phase in as-cast sample. Scanning electron microscopy showed that the level of Cr and Mo was higher in the precipitates than in the austenitic matrix and the Ni content was higher in matrix compared to precipitates. After heating at 1200°C during 90 minutes, the precipitate volume fraction was reduced to 2.1 % and the grain boundaries precipitates were dissolved. The microstructural analyses made through transmission electron microscopy and X-ray diffraction showed the presence sigma phase and M6C carbide. © (2011) Trans Tech Publications.312-3155663Grubb, J.F., Deemer, D.E., (2002) AL-6XN Alloy, pp. 2-7. , Allegheny Ludlum, USAHeat treating (1982) Metals Handbook, 4, pp. 1697-1705. , American Society for Metals, Metals Park - Ohio U.S.A(1998) Standard Specification for Casting, Iron-chromium-nickel, Corrosion Resistant, for Severe Service, pp. 1-5. , American Society for Testing and Materials ASTM A744h/A744M, American Society for Testing and Materials, U.S.A(1998) Corrosion-Resistant Steel Casting, p. 8. , European Standard EN 10283, Deutsches Institut fur Normung (DIN), Germany, Berlin(2004) Material Data Sheets for Piping, p. 85. , Norsok Standard M-630 MDS R16 Rev.3, Standards Norway, Norway(1990) Practice for Determining Volume Fraction by Systematic Manual Point Count, p. 15. , American Society for Testing and Materials ASTM E-562-90, U.S.AStandard Practice for Castings, Iron-chromium-nickel-molybdenum Corrosion-resistant, Duplex (Austenitic/ferritic) for General Application, pp. 556-569. , ASTM A890/A890M - 91, American Society for Testing and Materials, Easton. V.01.02, Ferrous CastingsFerroalloys(1991) ASTM A800/A800M. Standard Practice for Steel Casting, Austenitic Alloy, Estimating Ferrite Content, p. 4. , American Society for Testing and Materials, U.S.ACasting (1988) Metals Handbook, 15, pp. 121-123. , American Society for Metals, Metals Park - Ohio - U.S.AAlloy phase diagrams (1994) Metals Handbook, 3, pp. 140-144. , American Society for Metals, Metals Park - Ohio - U.S.AHeino, S., Knutson, M., Karlsson, B., (1999) Materials Science Forum, 318-320, p. 143Lee, T.H., Kim, S.J., (1998) Scripta Materialia, 39, p. 95