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H. S. Gadiyar - One of the best experts on this subject based on the ideXlab platform.

  • Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel
    Journal of Materials Engineering and Performance, 1996
    Co-Authors: K. M. Adhe, K Madangopal, Vivekanand Kain, H. S. Gadiyar
    Abstract:

    Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion Resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and Pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 °C for 30 min to 10 h. The heat-treated samples then undergo ASTM IGC and Pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr_23C_6 precipitation, σ-phase precipitates render this duplex stainless steel susceptible to IGC and Pitting corrosion. Even submicroscopic σ-phase precipitates are deleterious for IGC Resistance. Longer-duration heat treatments (at 750 to 850 °C) induce chromium diffusion to replenish the chromium-depleted regions around the σ-phase precipitates and improve IGC Resistance; Pitting Resistance, however, is not fully restored. Various mechanisms of σ-phase formation are discussed to show that regions adjacent to σ-phase are depleted of chromium and molybdenum. The effect of chemical composition (Pitting Resistance Equivalent) on the Pitting Resistance of various stainless steels is also noted.

  • Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel
    Journal of Materials Engineering and Performance, 1996
    Co-Authors: K. M. Adhe, K Madangopal, Vivekanand Kain, H. S. Gadiyar
    Abstract:

    Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion Resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and Pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 degrees C for 30 min to 10 h, Tbe heat-treated samples then undergo ASTM IGC and Pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr23C6 precipitation, sigma-phase precipitates render this duplex stainless steel susceptible to IGC and Pitting corrosion. Even submicroscopic sigma-phase precipitates are deleterious for IGC Resistance, Longer-duration heat treatments (at 750 to 850 degrees C) induce chromium diffusion to replenish the chromium-depleted regions around the sigma-phase precipitates and improve IGC Resistance; Pitting Resistance, however, is not fully restored. Various mechanisms of sigma-phase formation are discussed to show that regions adjacent to sigma-phase are depleted of chromium and molybdenum. The effect of chemical composition (Pitting Resistance Equivalent) on the Pitting Resistance of various stainless steels is also noted.

Yong-soo Park - One of the best experts on this subject based on the ideXlab platform.

  • Investigation of the localized corrosion associated with phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel in acidified chloride environments
    Corrosion Science, 2012
    Co-Authors: Seok-hwan Jang, Yong-soo Park
    Abstract:

    Abstract The localized corrosion associated with phase transformation of tube-to-tube sheet welds of hyper duplex stainless steel (HDSS) was investigated in acidified chloride environments. The localized corrosion Resistance of the HDSS tube-to-tube sheet welded with an Ar shielding gas supplemented with N 2 increased greatly due to a decrease in the α -phase fraction and Cr 2 N, and a decrease in the Pitting Resistance Equivalent number (PREN) difference between the α -phase and γ -phase in the weld metal and heat-affected zone. It was found that the HDSS tube-to-tube sheet welds showed significantly better localized corrosion Resistance than a costly super austenitic grade (S32050) welds.

  • Effects of shielding gases on the microstructure and localized corrosion of tube-to-tube sheet welds of super austenitic stainless steel for seawater cooled condenser
    Corrosion Science, 2011
    Co-Authors: Yong-soo Park, Min-chul Shin
    Abstract:

    Abstract The effects of shielding gas on the microstructure and localized corrosion of tube-to-tube sheet welds of SR-50A super austenitic stainless steel for seawater cooled condense were investigated in highly concentrated chloride environments. The localized corrosion Resistance of the weld metal after welding with an Ar shielding gas supplemented with N2 increased due to a decrease in the Pitting Resistance Equivalent number (PREN) difference between the PRENIR of interdendritic region and the PRENDC of dendrite core. The localized corrosion was selectively initiated at the dendrite core because the PREN of the dendrite core was smaller than that of the interdendritic region.

  • Effect of Shielding Gas Composition on Phase Transformation and Mechanism of Pitting Corrosion of Hyper Duplex Stainless Steel Welds
    Materials Transactions, 2011
    Co-Authors: Seok-hwan Jang, Yong-soo Park
    Abstract:

    The effect of shielding gas composition on the phase transformation and the mechanism of Pitting corrosion of hyper duplex stainless steel (HDSS) welds was investigated in highly concentrated chloride environments. The Resistance to Pitting corrosion of a HDSS tube after welding with Ar shielding gas supplemented with N2 was increased due to a decrease of the PREN (Pitting Resistance Equivalent Number) difference between the γ-phase and the α-phase in the weld metal and the heat affected zone. Cr nitrides (Cr2N) were precipitated in the weld metal and the heat affected zone due to a high α-phase content. Cr-depleted zone adjacent to Cr2N decreased the Resistance to Pitting corrosion.

  • Effects of solution heat-treatment and nitrogen in shielding gas on the Resistance to Pitting corrosion of hyper duplex stainless steel welds
    Corrosion Science, 2011
    Co-Authors: Seok-hwan Jang, Yong-soo Park
    Abstract:

    Abstract The effects of solution heat-treatment and shielding gas on the Pitting corrosion of hyper duplex stainless steel (HDSS) welds were investigated in highly concentrated chloride environments. The Pitting Resistance of a solution heat-treated HDSS after welding with an Ar shielding gas supplemented with N 2 was greatly increased due to the dissolution of Cr 2 N in α-phase, which followed the diffusion of N atoms from the α-phase to the γ-phase and an increase of the γ-phase in the weld metal and heat affected zone. It was also attributed to a decrease of the Pitting Resistance Equivalent number difference between the two phases.

  • effects of heat treatment on the phase ratio and corrosion Resistance of duplex stainless steel
    Materials Transactions, 2009
    Co-Authors: Heejoon Hwang, Yong-soo Park
    Abstract:

    The volume fraction of ferrite and austenite phase and corrosion Resistance of 26.2Cr-6.99Ni-2.37Mo-2.88W-0.35N duplex stainless steel have been studied by the use of optical microscopy, Feritscope, EBSD, SEM and Anodic polarization test after solution treatment at every 20°C at 1050°C∼1200°C for 30min. As the temperature of solution heat treatment increased, the content of ferrite that could be transformed to intermetallics such as σ and χ phase was higher, and besides, grain size increased and the number of grains decreased due to the growth of the phase and thus grain boundary and phase boundary that can be served as precipitation site of intermetallics were reduced, therefore the precipitation of intermetallics was suppressed. When PRE (Pitting Resistance Equivalent) values for the ferrite and austenite phases after solution heat treatment were calculated by weight percents of alloy elements using SEM-EDS, PRE value gap between the two phases was the smallest when heat treated at 1090°C. Because the increase over 1090°C of heat treatment temperature caused larger difference in PRE values between two phases, corrosion Resistance between the two phases was out of balance and thus corrosion Resistance was reduced when solution heat treated at the temperature over 1090°C.

Z. Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Effect of post-weld heat treatment on microstructure evolution and Pitting corrosion Resistance of electron beam-welded duplex stainless steel
    Corrosion Science, 2018
    Co-Authors: Z. Zhang, Hongyang Jing, Lianyong Xu, Lei Zhao, Xiaoqing Lv
    Abstract:

    Abstract The effects of electron beam welding and subsequent post-weld heat treatment at different temperatures on the microstructure evolution and Pitting corrosion Resistance of duplex stainless steel were investigated. The as-welded joint exhibited poor Pitting corrosion Resistance, and Pitting preferentially occurred at the ferrite grain in the weld. Heat treatment promoted austenite formation, Cr2N dissolution, and eliminated dendritic segregation, consequently improving the corrosion Resistance of the welded joint. The optimal solution temperature range was 1050–1110 °C. The austenite in the weld was prone to selective corrosion after heat treatment owing to its lower Pitting Resistance Equivalent number.

  • Influence of heat input in electron beam process on microstructure and properties of duplex stainless steel welded interface
    Applied Surface Science, 2018
    Co-Authors: Z. Zhang, Hongyang Jing, Lianyong Xu, Lei Zhao, Xiaoqing Lv, Jianyang Zhang
    Abstract:

    Abstract The influence of heat input in electron beam (EB) process on microstructure, mechanical properties, and Pitting corrosion Resistance of duplex stainless steel (DSS) welded interface was investigated. The rapid cooling in EB welding resulted in insufficient austenite formation. The austenite mainly consisted of grain boundary austenite and intragranular austenite, and there was abundant Cr2N precipitation in the ferrite. The Ni, Mo, and Si segregation indicated that the dendritic solidification was primarily ferrite in the weld. The weld exhibited higher hardness, lower toughness, and poorer Pitting corrosion Resistance than the base metal. The impact fractures of the welds were dominated by the transgranular cleavage failure of the ferrite. The ferrite was selectively attacked because of its lower Pitting Resistance Equivalent number than that of austenite. The Cr2N precipitation accelerated the Pitting corrosion. In summary, the optimised heat input slightly increased the austenite content, reduced the segregation degree and ferrite texture intensity, decreased the hardness, and improved the toughness and Pitting corrosion Resistance. However, the effects were limited. Furthermore, optimising the heat input could not suppress the Cr2N precipitation. Taking into full consideration the microstructure and properties, a heat input of 0.46 kJ/mm is recommended for the EB welding of DSS.

  • The influence of microstructural evolution on selective corrosion in duplex stainless steel flux-cored arc welded joints
    Corrosion Science, 2017
    Co-Authors: Z. Zhang, Hongyang Jing, Lianyong Xu, Lei Zhao
    Abstract:

    Abstract The influence of microstructural evolution on selective corrosion in duplex stainless steel flux-cored arc welding joint was investigated by the modified double loop electrochemical potentiokinetic reactivation in acidified chloride. Due to the lower Pitting Resistance Equivalent number, the secondary austenite was preferentially attacked over the ferrite and primary austenite phases, and inclusions acted as nucleation sites for micro-pits in the weld metal. Localised corrosion was generated in the secondary austenite and Cr-depleted zone around the Cr 2 N and sigma phases in the heat-affected zone. The weld metal exhibited the smallest susceptibility to localised corrosion because of the least weak phases.

  • Effects of nitrogen in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel welding joint
    Applied Surface Science, 2017
    Co-Authors: Z. Zhang, Hongyang Jing, Lianyong Xu, Lei Zhao, Chao Zhou
    Abstract:

    Abstract The effects of nitrogen addition in shielding gas on microstructure evolution and localized corrosion behavior of duplex stainless steel (DSS) welds were studied. N 2 -supplemented shielding gas facilitated the primary austenite formation, suppressed the Cr 2 N precipitation in weld root, and increased the microhardnesses of weld metal. Furthermore, N 2 -supplemented shielding gas increased Pitting Resistance Equivalent number (PREN) of austenite, but which decreased slightly PREN of ferrite. The modified double loop electrochemical potentiokinetic reactivation in 2 M H 2 SO 4  + 1 M HCl was an effective method to study the localized corrosion of the different zones in the DSS welds. The adding 2% N 2 to pure Ar shielding gas improved the localized corrosion Resistance in the DSS welds, which was due to compensation for nitrogen loss and promoting nitrogen further solution in the austenite phases, suppression of the Cr 2 N precipitation in the weld root, and increase of primary austenite content with higher PREN than the ferrite and secondary austenite. Secondary austenite are prone to selective corrosion because of lower PREN compared with ferrite and primary austenite. Cr 2 N precipitation in the pure Ar shielding weld root and heat affected zone caused the Pitting corrosion within the ferrite and the intergranular corrosion at the ferrite boundary. In addition, sigma and M 23 C 6 precipitation resulted in the intergranular corrosion at the ferrite boundary.

  • Influence of microstructure and elemental partitioning on Pitting corrosion Resistance of duplex stainless steel welding joints
    Applied Surface Science, 2017
    Co-Authors: Z. Zhang, Hongyang Jing, Lianyong Xu, Lei Zhao, Jianli Zhang
    Abstract:

    Abstract The influences of microstructure and elemental partitioning on Pitting corrosion Resistance of duplex stainless steel joints welded by gas tungsten arc welding (GTAW) and flux-cored arc welding (FCAW) with different shielding gas compositions were studied by optical microscopy, electron backscatter diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron probe microanalysis, and potentiostatic and potentiodynamic polarization methods The adding 2% N2 in shielding gas facilitated primary austenite formation in GTAW weld metal (WM) and suppressed Cr2N precipitation in GTAW weld root. In the HAZ, the banded microstructure disappeared while the coarse ferrite grains maintained same orientation as the banded ferrite in the BM. In the WM, the ferrite had one single orientation throughout a grain, whereas several families of austenite appeared. The austenite both in BM and WM enriched in Ni and nitro`gen, while Cr and Mo were concentrated in the ferrite and thus no element showed clear dendritic distribution in the WM (ER2209 and E2209T1). In addition, the secondary austenite had higher Ni content but lower Cr and Mo content than the primary austenite. The N2-supplemented shielding gas promoted nitrogen solid-solution in the primary and secondary austenite. Furthermore, the secondary austenite had relatively lower Pitting Resistance Equivalent number (PREN) than the ferrite and primary austenite, thereby resulting in its preferential corrosion. The Cr2N precipitation led to relatively poor Resistance to Pitting corrosion in three HAZs and pure Ar shielding GTAW weld root. The N2-supplemented shielding gas improved Pitting corrosion Resistance of GTAW joint by increasing PREN of secondary austenite and suppressing Cr2N precipitation. In addition, the FCAW WM had much poorer Resistance to Pitting corrosion than the GTAW WM due to many O-Ti-Si-Mn inclusions. In the BM, since the austenite with lower PREN compared to the ferrite, the Pitting corrosion occurred at the ferrite and austenite interface or within the austenite.

J. Li - One of the best experts on this subject based on the ideXlab platform.

  • Microstructure evolution and Pitting corrosion Resistance of the Gleeble-simulated heat-affected zone of a newly developed lean duplex stainless steel 2002
    Journal of Alloys and Compounds, 2016
    Co-Authors: Jincheng Hu, Y. Jiang, L. Jiang, J. Li
    Abstract:

    Abstract The effect of cooling rate on microstructure evolution and Pitting corrosion Resistance of the Gleeble-simulated heat-affected zone of a newly developed duplex stainless steel 2002 was investigated. The results showed that the content of austenite phase and the grain size of the austenite increased as the cooling rate decreased from 100 to 10 °C/s in the temperature range of 1350–800 °C. Meanwhile, the critical Pitting temperature (CPT) value increased from 31.2 to 43.6 °C and the Pitting potential (Epit) increased from 0.322 to 0.477 V, indicating that the Pitting corrosion Resistance increased with the cooling rate decreasing. With the cooling rate of 100 °C/s, the localized Pitting attack of the specimens occurred along the ferrite/austenite boundaries but preferentially inside the ferrite domains, which might be attributed to the fact that the precipitation of Cr2N led to the Cr-depleted region in the ferrite matrix. When the specimens were subjected to cooling rates of 50, 30 and 20 °C/s, the stable pits were all selectively located at the interior of the ferrite phase, suggesting that the ferrite phase was a weaker phase as compared to austenite phase. At 10 °C/s, the pits of specimens preferentially took place across ferrite/austenite phase boundaries, meaning that the Pitting Resistance of two phases almost achieved Equivalent. Moreover, with the decrease of cooling rate, the Pitting Resistance Equivalent number (PREN) of ferrite phase increased, while that of the austenite phase decreased. In addition, it was found that ferrite showed a lower Volta potential than austenite phase and the Volta potential differences between two phases grew smaller with the cooling rate decreasing. The relationship between PREN and Volta potential of specimens with respect to Pitting corrosion Resistance of steels was discussed.

  • Effect of Annealing Temperature on the Mechanical and Corrosion Behavior of a Newly Developed Novel Lean Duplex Stainless Steel
    Materials, 2014
    Co-Authors: Jincheng Hu, L. Jiang, J. Li, Yanping Wu
    Abstract:

    The effect of annealing temperature (1000–1150 °C) on the microstructure evolution, mechanical properties, and Pitting corrosion behavior of a newly developed novel lean duplex stainless steel with 20.53Cr-3.45Mn-2.08Ni-0.17N-0.31Mo was studied by means of optical metallographic microscopy (OMM), scanning electron microscopy (SEM), magnetic force microscopy (MFM), scanning Kelvin probe force microscopy (SKPFM), energy dispersive X-ray spectroscopy (EDS), uniaxial tensile tests (UTT), and potentiostatic critical Pitting temperature (CPT). The results showed that tensile and yield strength, as well as the Pitting corrosion Resistance, could be degraded with annealing temperature increasing from 1000 up to 1150 °C. Meanwhile, the elongation at break reached the maximum of 52.7% after annealing at 1050 °C due to the effect of martensite transformation induced plasticity (TRIP). The localized Pitting attack preferentially occurred at ferrite phase, indicating that the ferrite phase had inferior Pitting corrosion Resistance as compared to the austenite phase. With increasing annealing temperature, the Pitting Resistance Equivalent number (PREN) of ferrite phase dropped, while that of the austenite phase rose. Additionally, it was found that ferrite possessed a lower Volta potential than austenite phase. Moreover, the Volta potential difference between ferrite and austenite increased with the annealing temperature, which was well consistent with the difference of PREN.

  • Evaluation of Pitting Behavior on Solution Treated Duplex Stainless Steel UNS S31803
    Journal of Materials Science & Technology, 2014
    Co-Authors: Y. Jiang, J. Li, Jie Xu
    Abstract:

    The Pitting corrosion Resistance of duplex stainless steels UNS S31803 annealed at different temperatures ranging from 1050 °C to 1200 °C for 24 h has been investigated by means of potentiostatic critical Pitting temperature (CPT). The microstructural evolution and pit morphologies of the specimens were studied through optical microscopy and scanning electron microscopy. The potentiostatic CPT measurements show that the CPT was elevated with the annealing temperature increased from 1050 °C to 1150 °C and decreased as the temperature further increased to 1200 °C. The specimens annealed at 1150 °C exhibited the highest CPT and the best Pitting corrosion Resistance. The pit morphologies show that the pit initiation sites transfer from austenite phase to ferrite phase as the annealing temperature increases. The results were explained by the variation of Pitting Resistance Equivalent number (PREN) of ferrite and austenite phases as the annealing temperature was varied.

  • Influence of Cr-eq/Ni-eq on Pitting corrosion Resistance and mechanical properties of UNS S32304 duplex stainless steel welded joints
    Corrosion Science, 2013
    Co-Authors: Y. Jiang, L. Jiang, Zhiyu Wang, Jufeng Hong, J. Li
    Abstract:

    Abstract Pitting corrosion Resistance and mechanical properties of 2304 duplex stainless steel with different Creq/Nieq values after plasma-arc welding and welding thermal simulation were systematically studied. The results showed that the lower the Creq/Nieq value in the experimental range, the better the microstructure after welding or welding thermal cycle. High Pitting Resistance Equivalent number in the chemical composition brought in low weight loss rate and high critical Pitting temperature for base metal. Furthermore, as the Creq/Nieq value decreased, the degradation of Pitting corrosion Resistance after welding thermal cycle reduced.

  • Effect of Annealing Temperature on the Pitting Corrosion Behavior of UNS S82441 Duplex Stainless Steel
    Corrosion, 2013
    Co-Authors: Yanze Yang, Z. Zhang, Z.g. Wang, Y. Jiang, L. Jiang, J. Li
    Abstract:

    The Pitting corrosion behavior of UNS S82441 duplex stainless steel annealed at six different temperatures ranging from 1,000°C to 1,130°C for 1 h has been investigated by means of the potentiostatic critical Pitting temperature. The microstructure evolution and pit morphologies of the specimens were studied using optical/scanning electron microscopy. The results demonstrated that the volume fraction of the austenite phase decreased with the increasing annealing temperature. Lower critical Pitting temperature values were obtained after annealing at higher temperatures. Pitting was initiated preferentially inside the ferrite domains, indicating that the ferrite phase had inferior Pitting corrosion Resistance as compared to the austenite phase. The Pitting Resistance Equivalent number of the ferrite phase fell with the annealing temperature, while the values for the austenite phase rose. No equal Pitting Resistance Equivalent number of the ferrite and austenite phases was found for this steel in the range o...

K. M. Adhe - One of the best experts on this subject based on the ideXlab platform.

  • Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel
    Journal of Materials Engineering and Performance, 1996
    Co-Authors: K. M. Adhe, K Madangopal, Vivekanand Kain, H. S. Gadiyar
    Abstract:

    Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion Resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and Pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 °C for 30 min to 10 h. The heat-treated samples then undergo ASTM IGC and Pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr_23C_6 precipitation, σ-phase precipitates render this duplex stainless steel susceptible to IGC and Pitting corrosion. Even submicroscopic σ-phase precipitates are deleterious for IGC Resistance. Longer-duration heat treatments (at 750 to 850 °C) induce chromium diffusion to replenish the chromium-depleted regions around the σ-phase precipitates and improve IGC Resistance; Pitting Resistance, however, is not fully restored. Various mechanisms of σ-phase formation are discussed to show that regions adjacent to σ-phase are depleted of chromium and molybdenum. The effect of chemical composition (Pitting Resistance Equivalent) on the Pitting Resistance of various stainless steels is also noted.

  • Influence of sigma-phase formation on the localized corrosion behavior of a duplex stainless steel
    Journal of Materials Engineering and Performance, 1996
    Co-Authors: K. M. Adhe, K Madangopal, Vivekanand Kain, H. S. Gadiyar
    Abstract:

    Because of their austenitic-ferritic microstructures, duplex stainless steels offer a good combination of mechanical and corrosion Resistance properties. However, heat treatments can lower the mechanical strength of these stainless steels as well as render them susceptible to intergranular corrosion (IGC) and Pitting corrosion. In this study, a low-carbon (0.02%) duplex stainless steel is subjected to various heat treatments at 450 to 950 degrees C for 30 min to 10 h, Tbe heat-treated samples then undergo ASTM IGC and Pitting corrosion tests, and the results are correlated with the microstructures obtained after each heat treatment. In the absence of Cr23C6 precipitation, sigma-phase precipitates render this duplex stainless steel susceptible to IGC and Pitting corrosion. Even submicroscopic sigma-phase precipitates are deleterious for IGC Resistance, Longer-duration heat treatments (at 750 to 850 degrees C) induce chromium diffusion to replenish the chromium-depleted regions around the sigma-phase precipitates and improve IGC Resistance; Pitting Resistance, however, is not fully restored. Various mechanisms of sigma-phase formation are discussed to show that regions adjacent to sigma-phase are depleted of chromium and molybdenum. The effect of chemical composition (Pitting Resistance Equivalent) on the Pitting Resistance of various stainless steels is also noted.