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Birger Karlsson - One of the best experts on this subject based on the ideXlab platform.
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cyclic deformation and fatigue behaviour of 7mo 0 5n Superaustenitic Stainless Steel slip characteristics and development of dislocation structures
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The present work concerns the development of dislocation structures and surface slip markings during cyclic straining of a Superaustenitic Stainless Steel. The composition of the tested material was Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%). Two total strain amplitudes, 2.7×10 −3 and 1.0×10 −2 , were employed and specimens were investigated at specific numbers of cycles corresponding to certain stages on the cyclic hardening/softening curve. For both strain amplitudes, the developed dislocation structures are strongly planar and with increasing strain amplitude, the slip mode gradually changes from single slip to multiple slip. The short range ordering between Mo and N, as indicated by an atom probe investigation, is broken down during strain cycling leading to increased slip planarity. Early stages of cycling show dislocation multiplication. With increasing number of cycles, the dislocations are gradually grouped together in planar bands with high dislocation density, surrounded by dislocation-poor areas. The evolution of such bands is associated with decreasing effective stresses, while the internal stresses are only slightly reduced. Macroscopic slip bands, similar to PSBs, are formed upon prolonged cycling at the high amplitude. The slip markings created on the specimen surface show strong similarities with the bands of localised slip observed in the dislocation structures of the bulk.
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cyclic deformation and fatigue behaviour of 7mo 0 5n Superaustenitic Stainless Steel stress strain relations and fatigue life
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The cyclic deformation characteristics and fatigue behaviour of a Superaustenitic Stainless Steel with composition Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%) have been investigated. Detailed studies were performed on cyclic hardening/softening behaviour, hysteresis loops, waveform, fatigue lifetime, and internal as well as effective stresses during cyclic straining in the total strain amplitude range 2.7·10−3–1.0·10−2. Special attention is paid to the role of nitrogen and the interaction between nitrogen and molybdenum. Immediate cyclic softening takes place at small strain amplitudes, whereas hardening occurs during the first few cycles at large strain amplitudes followed by softening. For all strain amplitudes a virtually stationary state develops after about 10% of the lifetime with only a weak decrease of the peak stresses. In the cyclic stress–strain curve the material hardens linearly during multi step testing, whereas single step testing leads to excessive hardening at the largest strain amplitudes. During strain cycling the internal stresses develop like the total stresses, while the effective stresses decrease with increasing number of cycles for all strain amplitudes and also diminish with increased strain amplitude. This behaviour is discussed in terms of developing dislocation structures, studied in an accompanying paper. A double slope behaviour in Coffin–Manson diagrams is observed. The fatigue lifetime resembles that of AISI 316 with 0.29 wt% nitrogen at high strain amplitudes but is shorter at lower strain amplitudes. However, in stress controlled situations the Superaustenitic material is superior.
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Cyclic deformation and fatigue behaviour of 7Mo–0.5N Superaustenitic Stainless Steel—slip characteristics and development of dislocation structures
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The present work concerns the development of dislocation structures and surface slip markings during cyclic straining of a Superaustenitic Stainless Steel. The composition of the tested material was Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%). Two total strain amplitudes, 2.7×10 −3 and 1.0×10 −2 , were employed and specimens were investigated at specific numbers of cycles corresponding to certain stages on the cyclic hardening/softening curve. For both strain amplitudes, the developed dislocation structures are strongly planar and with increasing strain amplitude, the slip mode gradually changes from single slip to multiple slip. The short range ordering between Mo and N, as indicated by an atom probe investigation, is broken down during strain cycling leading to increased slip planarity. Early stages of cycling show dislocation multiplication. With increasing number of cycles, the dislocations are gradually grouped together in planar bands with high dislocation density, surrounded by dislocation-poor areas. The evolution of such bands is associated with decreasing effective stresses, while the internal stresses are only slightly reduced. Macroscopic slip bands, similar to PSBs, are formed upon prolonged cycling at the high amplitude. The slip markings created on the specimen surface show strong similarities with the bands of localised slip observed in the dislocation structures of the bulk.
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Cyclic deformation and fatigue behaviour of 7Mo–0.5N Superaustenitic Stainless Steel—stress–strain relations and fatigue life
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The cyclic deformation characteristics and fatigue behaviour of a Superaustenitic Stainless Steel with composition Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%) have been investigated. Detailed studies were performed on cyclic hardening/softening behaviour, hysteresis loops, waveform, fatigue lifetime, and internal as well as effective stresses during cyclic straining in the total strain amplitude range 2.7·10−3–1.0·10−2. Special attention is paid to the role of nitrogen and the interaction between nitrogen and molybdenum. Immediate cyclic softening takes place at small strain amplitudes, whereas hardening occurs during the first few cycles at large strain amplitudes followed by softening. For all strain amplitudes a virtually stationary state develops after about 10% of the lifetime with only a weak decrease of the peak stresses. In the cyclic stress–strain curve the material hardens linearly during multi step testing, whereas single step testing leads to excessive hardening at the largest strain amplitudes. During strain cycling the internal stresses develop like the total stresses, while the effective stresses decrease with increasing number of cycles for all strain amplitudes and also diminish with increased strain amplitude. This behaviour is discussed in terms of developing dislocation structures, studied in an accompanying paper. A double slope behaviour in Coffin–Manson diagrams is observed. The fatigue lifetime resembles that of AISI 316 with 0.29 wt% nitrogen at high strain amplitudes but is shorter at lower strain amplitudes. However, in stress controlled situations the Superaustenitic material is superior.
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Precipitation behaviour in heat affected zone of welded Superaustenitic Stainless Steel
Materials Science and Technology, 1999Co-Authors: S. Heino, E.m. Knutson-wedel, Birger KarlssonAbstract:AbstractThe present work concerns the characterisation of intermetallic phases formed in the heat affected zone of a welded Superaustenitic Stainless Steel of composition Fe–0·02C–3Mn–24Cr–7·3Mo–22No–0·5Cu–0·5N (wt-%). Grain boundary precipitates at various distances from the fusion line have been investigated regarding crystal structures, compositions, and particle morphologies. A correlation of precipitation with the temperature history recorded in the heat affected zone was also performed. Two different precipitates, σ and R, were detected in the heat affected zone. These precipitates were evenly distributed along grain boundaries and had platelike shapes with typical lengths of 200–900 nm and 30–300 nm for σ and R, respectively. Near the fusion line, coexistence of R and σ phases was observed but, at larger distances, only R phase was found, indicating a lower temperature of formation for this phase.
S. Heino - One of the best experts on this subject based on the ideXlab platform.
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cyclic deformation and fatigue behaviour of 7mo 0 5n Superaustenitic Stainless Steel slip characteristics and development of dislocation structures
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The present work concerns the development of dislocation structures and surface slip markings during cyclic straining of a Superaustenitic Stainless Steel. The composition of the tested material was Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%). Two total strain amplitudes, 2.7×10 −3 and 1.0×10 −2 , were employed and specimens were investigated at specific numbers of cycles corresponding to certain stages on the cyclic hardening/softening curve. For both strain amplitudes, the developed dislocation structures are strongly planar and with increasing strain amplitude, the slip mode gradually changes from single slip to multiple slip. The short range ordering between Mo and N, as indicated by an atom probe investigation, is broken down during strain cycling leading to increased slip planarity. Early stages of cycling show dislocation multiplication. With increasing number of cycles, the dislocations are gradually grouped together in planar bands with high dislocation density, surrounded by dislocation-poor areas. The evolution of such bands is associated with decreasing effective stresses, while the internal stresses are only slightly reduced. Macroscopic slip bands, similar to PSBs, are formed upon prolonged cycling at the high amplitude. The slip markings created on the specimen surface show strong similarities with the bands of localised slip observed in the dislocation structures of the bulk.
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cyclic deformation and fatigue behaviour of 7mo 0 5n Superaustenitic Stainless Steel stress strain relations and fatigue life
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The cyclic deformation characteristics and fatigue behaviour of a Superaustenitic Stainless Steel with composition Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%) have been investigated. Detailed studies were performed on cyclic hardening/softening behaviour, hysteresis loops, waveform, fatigue lifetime, and internal as well as effective stresses during cyclic straining in the total strain amplitude range 2.7·10−3–1.0·10−2. Special attention is paid to the role of nitrogen and the interaction between nitrogen and molybdenum. Immediate cyclic softening takes place at small strain amplitudes, whereas hardening occurs during the first few cycles at large strain amplitudes followed by softening. For all strain amplitudes a virtually stationary state develops after about 10% of the lifetime with only a weak decrease of the peak stresses. In the cyclic stress–strain curve the material hardens linearly during multi step testing, whereas single step testing leads to excessive hardening at the largest strain amplitudes. During strain cycling the internal stresses develop like the total stresses, while the effective stresses decrease with increasing number of cycles for all strain amplitudes and also diminish with increased strain amplitude. This behaviour is discussed in terms of developing dislocation structures, studied in an accompanying paper. A double slope behaviour in Coffin–Manson diagrams is observed. The fatigue lifetime resembles that of AISI 316 with 0.29 wt% nitrogen at high strain amplitudes but is shorter at lower strain amplitudes. However, in stress controlled situations the Superaustenitic material is superior.
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Cyclic deformation and fatigue behaviour of 7Mo–0.5N Superaustenitic Stainless Steel—slip characteristics and development of dislocation structures
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The present work concerns the development of dislocation structures and surface slip markings during cyclic straining of a Superaustenitic Stainless Steel. The composition of the tested material was Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%). Two total strain amplitudes, 2.7×10 −3 and 1.0×10 −2 , were employed and specimens were investigated at specific numbers of cycles corresponding to certain stages on the cyclic hardening/softening curve. For both strain amplitudes, the developed dislocation structures are strongly planar and with increasing strain amplitude, the slip mode gradually changes from single slip to multiple slip. The short range ordering between Mo and N, as indicated by an atom probe investigation, is broken down during strain cycling leading to increased slip planarity. Early stages of cycling show dislocation multiplication. With increasing number of cycles, the dislocations are gradually grouped together in planar bands with high dislocation density, surrounded by dislocation-poor areas. The evolution of such bands is associated with decreasing effective stresses, while the internal stresses are only slightly reduced. Macroscopic slip bands, similar to PSBs, are formed upon prolonged cycling at the high amplitude. The slip markings created on the specimen surface show strong similarities with the bands of localised slip observed in the dislocation structures of the bulk.
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Cyclic deformation and fatigue behaviour of 7Mo–0.5N Superaustenitic Stainless Steel—stress–strain relations and fatigue life
Acta Materialia, 2001Co-Authors: S. Heino, Birger KarlssonAbstract:Abstract The cyclic deformation characteristics and fatigue behaviour of a Superaustenitic Stainless Steel with composition Fe–25Cr–22Ni–7.6Mo–3Mn–0.46N (wt%) have been investigated. Detailed studies were performed on cyclic hardening/softening behaviour, hysteresis loops, waveform, fatigue lifetime, and internal as well as effective stresses during cyclic straining in the total strain amplitude range 2.7·10−3–1.0·10−2. Special attention is paid to the role of nitrogen and the interaction between nitrogen and molybdenum. Immediate cyclic softening takes place at small strain amplitudes, whereas hardening occurs during the first few cycles at large strain amplitudes followed by softening. For all strain amplitudes a virtually stationary state develops after about 10% of the lifetime with only a weak decrease of the peak stresses. In the cyclic stress–strain curve the material hardens linearly during multi step testing, whereas single step testing leads to excessive hardening at the largest strain amplitudes. During strain cycling the internal stresses develop like the total stresses, while the effective stresses decrease with increasing number of cycles for all strain amplitudes and also diminish with increased strain amplitude. This behaviour is discussed in terms of developing dislocation structures, studied in an accompanying paper. A double slope behaviour in Coffin–Manson diagrams is observed. The fatigue lifetime resembles that of AISI 316 with 0.29 wt% nitrogen at high strain amplitudes but is shorter at lower strain amplitudes. However, in stress controlled situations the Superaustenitic material is superior.
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Precipitation behaviour in heat affected zone of welded Superaustenitic Stainless Steel
Materials Science and Technology, 1999Co-Authors: S. Heino, E.m. Knutson-wedel, Birger KarlssonAbstract:AbstractThe present work concerns the characterisation of intermetallic phases formed in the heat affected zone of a welded Superaustenitic Stainless Steel of composition Fe–0·02C–3Mn–24Cr–7·3Mo–22No–0·5Cu–0·5N (wt-%). Grain boundary precipitates at various distances from the fusion line have been investigated regarding crystal structures, compositions, and particle morphologies. A correlation of precipitation with the temperature history recorded in the heat affected zone was also performed. Two different precipitates, σ and R, were detected in the heat affected zone. These precipitates were evenly distributed along grain boundaries and had platelike shapes with typical lengths of 200–900 nm and 30–300 nm for σ and R, respectively. Near the fusion line, coexistence of R and σ phases was observed but, at larger distances, only R phase was found, indicating a lower temperature of formation for this phase.
Seunggab Hong - One of the best experts on this subject based on the ideXlab platform.
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Precipitation behavior of the sigma phase with Ni and Mn content variations in Superaustenitic Stainless Steel weld metal
Materials Characterization, 2018Co-Authors: Changmin Lee, Youngchai Lee, Changhee Lee, Seunggab HongAbstract:Abstract In this study, precipitation behavior of the sigma phase with variations of the Ni and Mn in Superaustenitic Stainless Steel weld metal was evaluated focused on microstructure and thermodynamic analysis. Experiments were conducted with variation of Ni and Mn based on a 23Cr-17Ni-6Mo Superaustenitic Stainless Steel weld. And GTAW welding was performed on the casted specimens for simulating the weld metal. The weld metal consisted of γ-dendrite and an amount of sigma phases at interdendritic boundaries. And the sigma phase fraction showed decreasing behavior inversely according to addition of the Ni and Mn in the weld metal. From the microstructural analysis, the Ni addition induced increase of Mo content in the sigma phase, which caused the Mo depletion zone around the sigma phase. Whereas, the Mn addition induced replacement of Mo in sigma phase by Mn, so that the Mo depletion zone was not formed. Also, from the Thermo-Calc analysis, it was revealed that Ni addition caused increase of Mo activity, which induced Mo clustering in the sigma phase, while the Mn addition showed opposite effect of the Mo activity.
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Possibility of Mn substitution of Ni through evaluation of mechanical properties and corrosion resistance in Superaustenitic Stainless Steel weld metal
Materials Science and Engineering: A, 2018Co-Authors: Changmin Lee, Youngchai Lee, Changhee Lee, Seunggab HongAbstract:Abstract In this study, the evaluation of the mechanical and corrosion properties of Ni, Mn and the possibility of Mn substitution of Ni in Superaustenitic Stainless Steel weld metal were researched. Axial tensile, polarization, and critical pitting temperature (CPT) tests were performed with variation of Ni and Mn to evaluate the mechanical and corrosion properties for the gas tungsten arc welding (GTAW)-fabricated weld metals. As a result, the weld metals mainly consisted of γ-dendrite and sigma (σ) phases at interdendritic boundaries, and a fraction of the sigma phases decreased due to the increase of both the Ni and Mn content at these boundaries. The Mo content in the sigma phase increased with Ni, resulting in aggravation of the Mo depletion zone. On the other hand, Mn prevented the Mo clustering in the sigma phase. The tensile test indicated that elongation and toughness were clearly improved by the decrease of only the sigma phase fraction regardless of difference in the Ni and Mn. From the results, reduction of the sigma phase induced variation of the fracture behavior from brittle to ductile. The polarization test showed that an amount of the sigma phase induced degradation of pitting potential (Epit), while Ecorr, icorr, and Epass varied as relatively uniform, despite of changes of the Ni and Mn content. Likewise, CPT values were found to be inversely related to the sigma phase fraction with variation of the Ni and Mn content.
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Influence of Si on sigma phase precipitation and pitting corrosion in Superaustenitic Stainless Steel weld metal
Materials Chemistry and Physics, 2018Co-Authors: Changmin Lee, Changhee Lee, Sungjoo Roh, Seunggab HongAbstract:Abstract In this study, we investigated the effect of Si on the precipitation of the sigma phase in super austenitic Stainless Steel welds. The Scheil module solidification, partition coefficient and activity were calculated using the thermo-calc software to study the thermodynamics of the precipitation behavior of the sigma phase during solidification of the weld metal. The fraction and average size of the sigma phases significantly increased with increasing Si content in the welds, which consisted of γ-dendrite and inter-dendritic sigma phases. Scheil solidification showed that the formation temperature range of the sigma phase increased with increasing Si content. Also, partition coefficient of Cr and especially Mo and Si substantially decreased under the L-γ solidification with addition of Si. And it resulted in increase of Cr, Mo and Si contents in the sigma phases. The activity of Mo rose sharply with increasing Si, which caused an increase in precipitation due to the fundamental elements of the sigma phase. Corrosion test results showed that pitting was sensitive to an increase in the Si assisted sigma phase precipitation.
Khaled Elleuch - One of the best experts on this subject based on the ideXlab platform.
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Failure mode analysis of SMAW welded UNS N08028 (Alloy28) Superaustenitic Stainless Steel under crack growth tests
Engineering Failure Analysis, 2019Co-Authors: Y. Kchaou, Veronique Pelosin, Nader Haddar, Gilbert Henaff, Khaled ElleuchAbstract:The Fatigue Crack Growth (FCG) behavior of welded UNS N08028 (Alloy28) Superaustenitic Stainless Steel was investigated in this paper. Alloy28 Superaustenitic Stainless Steel was welded using Shielded Metal Arc Welding process. The FCG behavior was studied under two load ratios (0.1 and 0.5) and for different specimen configuration: Base Metal (BM), Weld Metal (WM) and Welded Joint (WJ). The results indicated that FCG rates of WM specimen is lower than BM specimen at R = 0.1. Moreover, load ratio affects the FCG rate for BM and WM specimen. In addition, the observation of fatigue crack growth path of WM displayed that crack follows dendritic orientation giving a tortuous crack path, while it is less tortuous for BM specimens. Scanning Electron Microscope (SEM) observations of BM fractured surfaces showed that damage mechanism is intergranular for lower ΔK value, and transgranular for higher ΔK value. Moreover, SEM observations of WM fractured surface showed the presence of welding defects which can affect negatively fatigue crack growth resistance at R = 0.5.
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Low Cycle Fatigue behavior of SMAW welded Alloy28 Superaustenitic Stainless Steel at room temperature
Materials Science and Engineering: A, 2016Co-Authors: Y. Kchaou, Veronique Pelosin, Nader Haddar, Gilbert Henaff, Khaled ElleuchAbstract:Abstract This paper focused on the study of Low Cycle Fatigue of welded joints of Superaustenitic (Alloy28) Stainless Steels. Chemical composition and microstructure investigation of Base Metal (BM) and Weld Metal (WM) were identified. The results showed that both of composition is fully austenitic with a dendritic microstructure in the WM. Low cycle fatigue tests at different strain levels were performed on Base Metal (BM) and Welded Joint (WJ) specimens with a strain ratio Re=−1. The results indicated that the fatigue life of welded joints is lower than the base metal. This is mainly due to the low ductility of the Welded Metal (WM) and the presence of welding defects. Simultaneously, Scanning Electron Microscope (SEM) observations of fractured specimens show that WJ have brittle behavior compared to BM with the presence of several welding defects especially in the crack initiation site. An estimation of the crack growth rate during LCF tests of BM and WJ was performed using distance between striations. The results showed that the crack initiation stage is shorter in the case of WJ compared to BM because of the presence of welding defects in WJ specimens.
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Microstructural, compositional and mechanical investigation of Shielded Metal Arc Welding (SMAW) welded Superaustenitic UNS N08028 (Alloy 28) Stainless Steel
Materials & Design, 2014Co-Authors: Y. Kchaou, Veronique Pelosin, Nader Haddar, Gilbert Henaff, Khaled ElleuchAbstract:Abstract Shielded Metal Arc Welding (SMAW) was performed on UNS N08028 (Alloy 28) Superaustenitic Stainless Steel sheets. In the present work, the microstructure and the mechanical properties of base metal (BM), weld metal (WM), and welded joint (WJ) are investigated. Optical micrographs show that the base metal presents austenitic grains, and the weld metal exhibits a fully austenitic dendritic structure, confirming the Schaeffler diagram estimations. Microhardness measurements indicate that the hardness increases in the weld bead due to the rapid cooling and thermal cycle during welding procedure. The measured mechanical properties and the analysis of the fracture profiles show that the two materials are ductile but the ductility is less pronounced in the weld metal. Consistently the yield stress, the plastic strength and the impact toughness are lower than in the base metal. In addition, the BM presents a higher cyclic hardening and plastic strain compared to those of WM. Cyclic stress–strain hysteresis loops show that WM and WJ have almost the same cyclic behavior and especially at high imposed strain levels.
Changmin Lee - One of the best experts on this subject based on the ideXlab platform.
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Behavior of the sigma phase in Mn containing Superaustenitic Stainless Steel weld metals
???????????????, 2019Co-Authors: Changmin LeeAbstract:??? ??????????????? ??????????????????????????? ?????????????????? ????????? ?????? ???????????? ??????????????? ????????????, ???????????? ????????? ????????? ??????????????? ???????????? ?????? ????????? ????????? ???????????????. ??????????????????????????? ????????????????????? ???????????? ??????????????? ??????, ?????? ????????? Cr??? Mo??? ????????? ?????????, ??????????????? 6 wt% ????????? Mo??? ????????? ????????????????????? ????????????. ????????? ??????????????????????????? ????????????????????? ?????? ???????????? ???????????? ???????????????, ????????? ?????? ?????? ???????????? ?????????. ????????? ??????????????????????????? ????????????????????? ????????? ???, ????????? ?????? ??????????????? ??????????????????, ??????????????? ??? ???????????? ???????????? ????????? ???????????????. ????????? ??????????????? ?????? ????????? ??? ???????????? ????????? ????????? ??????????????? ??? ????????????. ??? ????????? ??????????????? ????????? ??????. 1) Si ????????? ?????? ??????????????????????????? ?????????????????? ???????????? ???????????? ???????????? ??? ????????? ?????? ??????, 2) Ni, Mn, N, W ??? ??? ?????? ????????? ?????? ??????????????????????????? ?????????????????? ???????????? ???????????? ?????? ???????????? ??????, 3) ????????? ?????? ??? ????????? ????????? ?????? ??????????????????????????? ?????????????????? ?????????????????? Mn??? Ni ?????? ????????? ?????? ??? ????????? ???????????? ??????, ????????? Mn??? Ni ?????? ????????? ?????? ????????? ??????????????? ???????????????. ????????????, ??? ??????????????? ????????? ??? ???????????? ????????? ????????? Si??? ??????????????? ????????? ????????? ???????????????. ??????, ???????????? ?????? scheil module ???????????? ??????, ???????????? ??? ????????? ????????? ?????? ????????? ?????? ?????? ??? ?????? ?????? ?????? ?????? ???????????????. ?????? ??????, ???????????? ??????????????? ?????????????????? ??????????????? ??????????????????, ????????? ?????? ????????? ????????? ??????????????? ???????????? ?????? ???????????????. ??? ???, ????????? ??????????????? Si??? ????????? ??????????????? ??? ????????? ????????? ??????????????? ???????????? ????????? ????????????. ?????? scheil ???????????? ????????????, Si??? ????????? ??????????????? ???????????? ???????????? (S.T.R)??? ????????? ??????????????????, ?????? ???????????? ?????? ?????? ?????? ??? ???????????? ????????????, ??????????????? ????????? ???????????? ?????????. ?????? ?????????, Cr, Mo, Si??? ???????????? (k-factor)??? Si??? ????????? ??????????????? ???????????? ????????? ??????????????????, ?????? ?????? Si??? ?????? ????????? ?????? ?????? Cr, Mo, Si ?????? ???????????? ??? ???????????????, ?????? ?????? ???????????? ????????? ??? ?????????????????? ?????? ????????? ??? ?????????. ???????????????, Si??? ?????? ????????? ?????? ????????? ?????? Mo??? ?????????(activity)??? ???????????? ???????????????. ?????????????????? ?????? Mo??? clustering ????????? ??????????????????, ?????? ?????? Mo??? ?????? ????????? ????????? ??????????????? ????????? ???????????????. ???????????????, ????????? ?????? ??????, ????????? Si ????????? ?????? ???????????? ????????? ?????? ???????????? ?????? ???????????? ?????? ????????? ???????????????, ???????????? ???????????? ????????? ?????? pitting??? ???????????????. ????????????, ??? ?????? ????????? ?????? ????????? ??????????????? ?????? ?????? ????????? ?????? ????????? ???????????????. ???????????? ??????????????? ????????? ??????, Ni, Mn, N, W ?????????. ??? ???, Ni??? Mn??? ????????? ?????? ???????????? ?????? ????????? ??????????????? ???????????????. ????????? Fe-23Cr-17Ni-6Mo ?????? ?????????????????? ????????????, ?????? ?????? ?????? GTAW??? ???????????? ???????????? ???????????????. ???????????? ?????????????????? dendrite??? ???????????? ????????? ????????? ??????????????? ???????????? ????????? ????????????. ????????? ?????? ???????????? ????????? Ni??? Mn??? ????????? ??????????????? ???????????? ???????????? ????????? ????????????. ?????????, Ni??? ????????? ???????????? ????????? ??????????????? ???????????? Mo??? ????????? ????????? ???????????? ????????? ???????????????, Mn??? ????????? ???????????? ?????? ???????????? ????????? Mo??? ?????? ?????? ?????? Mn??? ????????? ???????????? ????????? ????????????. Ni??? Mo clustering ????????? ????????? ??? ??????????????? Mo ????????? ????????? ??????????????????, ????????? Mn??? ????????? ????????? ??????????????????, ???????????? ?????? ???????????? ??? ????????? ????????? ?????????. ?????? N??? ????????? Ni, Mn??? ??????????????? ????????? ?????? ??????????????? ??????????????????, ?????? ?????? ????????? ???????????? ??????????????? ?????????????????? ????????? ?????? ????????? ????????? ????????? ???????????????. ?????? ?????????, N??? ????????? PREN ????????? ??????????????????, ??????????????? ??????????????? ????????? ?????? ???????????????. ?????????, W??? ????????? ????????? ?????? ??????????????? ??????????????? ??????, ??????-???????????? ??? ???????????? ????????? ??????????????? ????????? ????????????. ?????? ??????????????? ????????????????????? ?????? ??? ?????? ????????? ?????? ????????? ???????????? W??? ????????? ???????????? ??? ??????????????? ???????????????. ????????? ???????????? ????????? Mn??? N??? ????????? ???????????? ??????????????? ??????????????? ????????? ??????????????? ???????????? ????????? ??? ??? ??????. ?????????, Ni??? Mn ?????? ????????? ?????? ??????????????????????????? ?????????????????? ???????????? ????????? ?????? ??? ????????? ????????? ?????? Ni??? Mn ?????? ???????????? ?????? ????????????. ?????? ??????, ?????? ?????? ???, ????????? ????????????, ???????????????(CPT) ?????? ?????? ????????? ???????????????. ?????? ???????????? ?????? ?????? ?????? GTAW??? ???????????? ????????? ???????????????. ??????????????? ????????????????????? ???????????? ????????? ????????? ??????????????? ??????????????????, ?????? Ni??? Mn??? ????????? ??????????????? ???????????? ????????? ????????????. ?????? ??????????????? ????????????, Ni??? Mo ???????????? ??????????????? ??????, Mn??? ???????????? ??????, ?????? ???????????? ????????? ????????????. ???????????? ??????, Ni??? Mn??? ????????? ?????? ??????????????? ???????????? ??????, ???????????? ???????????? ???????????? ????????? ????????????. Nano-indenter??? ?????? ??????????????? ????????? ?????? brittle????????? ?????? ??????????????? ????????? ??????????????? ????????? ???????????? ????????? ???????????? ????????? ???????????????. ??????????????? ???????????? ???????????? ??????(ECO index)??? ???????????? ????????? ????????????. ????????? ???????????? ??????, Ni??? Mn ?????? ???????????? ???????????? ???????????? ????????? ????????????. ?????? ??????????????? ?????? ???????????????, Ni??? ?????? Mn??? ?????????, ?????????????????? ??? ?????? ????????? ????????????. ?????? Ni??? ?????? Mo ????????? ?????????, Mn??? ?????? ??????????????? ???????????? ????????? ??? ??????. ???????????? ????????? ?????? ??????, ????????? ?????????????????? Ni??? ????????? ?????? ?????? ??????????????? ??????, Mn??? ????????? ??????????????? ???????????? ?????????????????? ???????????? ????????? ????????????. ?????? DSC ?????? ??????, ???????????? ??????????????? Mn??? ?????? ????????? ?????? ??????????????? ??????????????????, ?????? ?????? Mn??? Ni ????????? ????????? ??????????????? ???????????? ?????? ????????? ???????????????. ?????? 12 wt% ????????? Mn ??????????????? ???????????? ???????????? ?????? ??????????????? ????????? ????????????. ??????????????? Mn??? ?????? ????????? ?????? ????????? ???????????? ?????????, ????????? Mn??? ????????? ??????????????? ???????????? ????????? ????????? ????????????. ????????? ??? ??????????????? 8 wt% ????????? ????????? ?????? ????????? ??????????????????, ????????? ??? ????????? Ni??? ???????????? Mn??? ????????? 8 wt% ????????? ?????? ?????? ????????? ????????? ??? ??????. ?????? ?????????, Si??? ????????? ???????????????, N??? ????????? ????????????, ??????????????? ????????? ??????????????? ?????????, ??????????????? ???????????? ???????????? ?????? ???????????? ?????? ???????????? ?????????????????? ??? ??? ??????.Superaustenitic Stainless Steels have been used for severe corrosion environments in various industrial uses such as offshore construction and power plants. Generally, these Stainless Steels have greater Cr, Ni, Mo, and N contents than other commercial Stainless Steels, and these Steels are characterized by superior mechanical and corrosion properties arising from the austenite microstructure. However, undesired formation of sigma phase, which is quite brittle, is directly generated along the dendritic boundaries in Superaustenitic Stainless-Steel weld metals. This worsens the mechanical and corrosion properties of the weld metals. Thus, suppression of sigma phase formation is desired to improve the overall properties. In this research, the behavior of the sigma phase formation in Mn-containing Superaustenitic Stainless-Steel weld metals was investigated, and a cost-effective filler metal was developed with Mn as a substitute for Ni. Specifically, the main purposes of this research included 1) observing the influence of Si upon sigma phase precipitation and corrosion resistance in Superaustenitic Stainless-Steel weld metal, 2) investigating the mechanism of sigma phase precipitation with various alloying element contents such as Ni, Mn, N, and W in the Superaustenitic Stainless-Steel welds using filler metal designs, and 3) demonstrating the possibility of Mn substitution of Ni through evaluation of the mechanical properties and corrosion resistance in Superaustenitic Stainless-Steel weld metals for the development of cost-effective filler metals. 1) The effect of Si on precipitation of the sigma phase in Superaustenitic Stainless-Steel weld metalsFor this study, microstructural analysis of weld metals having various Si contents was performed. Further, Scheil module solidification, partition coefficient, and elemental activity were calculated using the Thermo-Calc software to research the thermodynamics of the sigma phase precipitation behavior during solidification of the weld metal. Potentiodynamic polarization testing and solution treatment of the weld metals were also conducted. The fraction and average size of the sigma phases significantly increased with increasing Si content. The calculation results of Scheil module solidification showed that the temperature ranges of sigma phase formation increased with increasing Si content. Partition coefficients of Cr, and especially Mo and Si, substantially decreased under L?????? solidification with increasing Si content. And this resulted in increased Cr, Mo, and Si contents in the sigma phases. Additionally, the activity of Mo increased with increasing Si compared to other elements, which probably caused an increase of sigma phase precipitation. Corrosion test results showed that pitting corrosion behavior was sensitive to the increased sigma phase precipitation with Si addition. Finally, the solution treatments for sigma phase dissolution indicated that the sigma phases decreased proportionally to both temperature and exposure time. The dissolution rate of the sigma phases increased drastically at temperatures higher than 1150 ??C. 2) Precipitation of the sigma phase with variations of the Ni and Mn contents in Superaustenitic Stainless-Steel weld metalThe effects of N and W on the sigma phase in the weld metal were investigated. Experiments were conducted with variations of Ni, Mn, N, and W contents based on a 23Cr-17Ni-6Mo Superaustenitic-Stainless Steel weld. GTAW was performed on cast specimens to simulate the weld metals. Thermo-Calc simulations were conducted for thermodynamic analysis under elemental variations. The weld metal mainly consisted of ???-dendrite with sigma phases at interdendritic boundaries in 17Ni alloy. The sigma phase fractions decreased in increasing Ni and Mn contents in the weld metal. According to the microstructural analysis, increased Ni content induced increasing Mo content in the sigma phase, causing formation of an Mo depletion zone around the sigma phase, whereas increased Mn content suppressed Mo clustering in the sigma phase by means of substitution of Mo by Mn, preventing the formation of Mo depletion zones. Thermo-Calc analysis revealed that increasing Ni content increased Mo activity, which induced Mo clustering in the sigma phase, whereas increasing Mn content led to decrease of Mo activity. In the case of increasing N content, it decreased the sigma phases similar to Ni in the weld metal. And the addition of N likely increased the PREN and local corrosion resistance. However, the addition of W generated undesired phases such as ???-ferrite and chi phases instead of the sigma phases, and probably would degrade the weld metal properties. Therefore, W addition is not recommended. 3) The mechanical and corrosion properties with variation of Ni and MnThe possibility of substituting Mn for Ni in Superaustenitic Stainless Steel weld metals were also considered. Analysis of the Mn substitution limit was conducted. Axial tensile test, corrosion test (potentiodynamic polarization and critical pitting temperature tests) and varestraint test were performed using Superaustenitic Stainless-Steel weld metals with variation of Ni and Mn contents to evaluate their mechanical/corrosion properties and weldability. Tensile test clearly indicated that the mechanical properties (especially toughness) were proportionally improved by decreasing the sigma phase fraction with Ni and Mn addition. Also, reduction of the sigma phase changed the fracture mode from brittle to ductile. Polarization test showed that the sigma phase affected degradation of the pitting potential (Epit), regardless of variations in the Ni and Mn contents. Likewise, CPT values were found to be inversely related to the sigma phase fraction with variations in Ni and Mn content. From the varestraint test, Ni addition rarely affected the TCL and MCL, whereas Mn addition increased the MCL, regarded as a criterion of the solidification temperature range, and resulted in worsened crack susceptibility. DSC analysis revealed that Mn addition increased the solidification range. Also, the Mn penetrated the oxide film on the surface in cases of higher Mn content (>8 wt%). This degraded corrosion resistances, as evidenced by inferior passive film properties in cyclic polarization testing. Consequently, the sigma phase formation was effectively decreased by decreasing Si content and increasing Ni and Mn contents. Also, Mn suppressed the formation of a Mo depletion zone around the sigma phase, whereas Ni intensified the depletion zone. From this result, Mn addition improved local pitting resistance compared to Ni. However, Mn contents above 8 wt% probably degrade hot cracking and corrosion resistance.Docto
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Precipitation behavior of the sigma phase with Ni and Mn content variations in Superaustenitic Stainless Steel weld metal
Materials Characterization, 2018Co-Authors: Changmin Lee, Youngchai Lee, Changhee Lee, Seunggab HongAbstract:Abstract In this study, precipitation behavior of the sigma phase with variations of the Ni and Mn in Superaustenitic Stainless Steel weld metal was evaluated focused on microstructure and thermodynamic analysis. Experiments were conducted with variation of Ni and Mn based on a 23Cr-17Ni-6Mo Superaustenitic Stainless Steel weld. And GTAW welding was performed on the casted specimens for simulating the weld metal. The weld metal consisted of γ-dendrite and an amount of sigma phases at interdendritic boundaries. And the sigma phase fraction showed decreasing behavior inversely according to addition of the Ni and Mn in the weld metal. From the microstructural analysis, the Ni addition induced increase of Mo content in the sigma phase, which caused the Mo depletion zone around the sigma phase. Whereas, the Mn addition induced replacement of Mo in sigma phase by Mn, so that the Mo depletion zone was not formed. Also, from the Thermo-Calc analysis, it was revealed that Ni addition caused increase of Mo activity, which induced Mo clustering in the sigma phase, while the Mn addition showed opposite effect of the Mo activity.
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Possibility of Mn substitution of Ni through evaluation of mechanical properties and corrosion resistance in Superaustenitic Stainless Steel weld metal
Materials Science and Engineering: A, 2018Co-Authors: Changmin Lee, Youngchai Lee, Changhee Lee, Seunggab HongAbstract:Abstract In this study, the evaluation of the mechanical and corrosion properties of Ni, Mn and the possibility of Mn substitution of Ni in Superaustenitic Stainless Steel weld metal were researched. Axial tensile, polarization, and critical pitting temperature (CPT) tests were performed with variation of Ni and Mn to evaluate the mechanical and corrosion properties for the gas tungsten arc welding (GTAW)-fabricated weld metals. As a result, the weld metals mainly consisted of γ-dendrite and sigma (σ) phases at interdendritic boundaries, and a fraction of the sigma phases decreased due to the increase of both the Ni and Mn content at these boundaries. The Mo content in the sigma phase increased with Ni, resulting in aggravation of the Mo depletion zone. On the other hand, Mn prevented the Mo clustering in the sigma phase. The tensile test indicated that elongation and toughness were clearly improved by the decrease of only the sigma phase fraction regardless of difference in the Ni and Mn. From the results, reduction of the sigma phase induced variation of the fracture behavior from brittle to ductile. The polarization test showed that an amount of the sigma phase induced degradation of pitting potential (Epit), while Ecorr, icorr, and Epass varied as relatively uniform, despite of changes of the Ni and Mn content. Likewise, CPT values were found to be inversely related to the sigma phase fraction with variation of the Ni and Mn content.
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Influence of Si on sigma phase precipitation and pitting corrosion in Superaustenitic Stainless Steel weld metal
Materials Chemistry and Physics, 2018Co-Authors: Changmin Lee, Changhee Lee, Sungjoo Roh, Seunggab HongAbstract:Abstract In this study, we investigated the effect of Si on the precipitation of the sigma phase in super austenitic Stainless Steel welds. The Scheil module solidification, partition coefficient and activity were calculated using the thermo-calc software to study the thermodynamics of the precipitation behavior of the sigma phase during solidification of the weld metal. The fraction and average size of the sigma phases significantly increased with increasing Si content in the welds, which consisted of γ-dendrite and inter-dendritic sigma phases. Scheil solidification showed that the formation temperature range of the sigma phase increased with increasing Si content. Also, partition coefficient of Cr and especially Mo and Si substantially decreased under the L-γ solidification with addition of Si. And it resulted in increase of Cr, Mo and Si contents in the sigma phases. The activity of Mo rose sharply with increasing Si, which caused an increase in precipitation due to the fundamental elements of the sigma phase. Corrosion test results showed that pitting was sensitive to an increase in the Si assisted sigma phase precipitation.
