The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impac...The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature.The experimental results indicate that the nose temperature of precipitation is 920℃ and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2min.Prolonging aging duration the amount ofσ-phase increases and a dual structure with σ and γ is obtained when aging for 120min.The precipitation ofσ-phase leads to severe deterioration in impact toughness （longitudinal/transverse direction） and corrosion resistance of SDSS.展开更多
Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A...Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A8907 A has a unique composition and is expected to have a much better resistance to corrosion and erosion compared with the super-duplex grades 5 A and 6 A.This work is a comparative study of the mechanical properties,corrosion,and erosion-corrosion resistance of super-duplex grades 5 A and 6 A and the hyper-duplex grade 7 A.The three DSSs exhibited equiaxial austenite islands in the ferrite matrix and balanced phase ratios.The hardness of the grade 7 A was nearly 15%higher than those of the super-duplex grades,which is attributed to the effect of the higher contents of W and Mn in 7 A.The impact toughness of grade 7 A was found to be lower than those of the super-duplex grades due to the carbide precipitation resulting from the partial substitution of Mo with W.The oxide layer strengthening effect of rare earth elements and the higher pitting resistance equivalent number(PREN)of grade7 A resulted in higher corrosion resistance.The harder and more passive grade 7 A showed a 35%lower material loss during erosion-corrosion.展开更多
The main objective of this research is to better understand the correlation between the constituent phases presented in the super-duplex steel SAF 2507 when it is under welding process by arc shielding gas MIG-MAG (Me...The main objective of this research is to better understand the correlation between the constituent phases presented in the super-duplex steel SAF 2507 when it is under welding process by arc shielding gas MIG-MAG (Metal Inert Gas-Metal Active Gas). Conventional short circuit transfer and derivative STT (Surface Tension Transfer) using the 2594 welding wire as a filler metal and the effects on welding power in hardness, toughness and pitting corrosion are considered here. The results showed that the welding energy (Ew) changed the α/γ-phase’s balance and occasionally formed σ-phase in ferrite grain boundaries which led to changes in hardness, toughness and pitting corrosion resistance in molten zone (MZ), heat activated zone (HAZ) and metal base regions (MB). Furthermore, the increased amount of γ-phase improved the pitting corrosion resistance index (PRENγ) mainly in the MZ. This is due to decrease of α-phase fraction and formation of coarser grains, for higher welding energy. The toughness in the MZ decreased with less formation of γ-phase, coalescence of ferritic grains and localized formation of σ-phase, raising the hardness in the HAZ when the welding energy was lower.展开更多
采用响应面法的中心复合设计对双相不锈钢冷金属过渡与脉冲复合(cold metal transfer and pulse hybrid,CMT+P)电弧增材工艺进行优化,构建了送丝速度,移动速度及脉冲数量与增材件成形质量(沉积宽度、成形误差和奥氏体含量)之间的数学回...采用响应面法的中心复合设计对双相不锈钢冷金属过渡与脉冲复合(cold metal transfer and pulse hybrid,CMT+P)电弧增材工艺进行优化,构建了送丝速度,移动速度及脉冲数量与增材件成形质量(沉积宽度、成形误差和奥氏体含量)之间的数学回归模型。通过方差分析、摄动图以及响应曲面研究了不同工艺参数对成形质量的影响规律。结果表明:沉积宽度和奥氏体含量随移动速度增加而减小,随送丝速度和脉冲数量增加而增加;增加送丝速度或移动速度,成形误差先减小后增大,脉冲数量的影响不显著,得到优化的工艺参数为:送丝速度为3.9 m/min,移动速度为5.5 mm/s,脉冲数量12个。展开更多
基金Founded by the Special Project of Shaanxi Education Department(07JK309)Xi'an University of Architecture and Technology (JC0714)
文摘The nose temperature for σ-phase precipitation in super-duplex stainless steel （SDSS） UNS S32750 was evaluated by hardness method.Color-optical microscopy,scanning electron microscopy,energy spectrum analysis,impact and corrosion testing were carried out to investigate characteristics of microstructure and properties of the SDSS aged at the nose temperature.The experimental results indicate that the nose temperature of precipitation is 920℃ and aging at this temperature tiny σ phases can precipitate at phase interfaces or ferrite grain boundaries within 2min.Prolonging aging duration the amount ofσ-phase increases and a dual structure with σ and γ is obtained when aging for 120min.The precipitation ofσ-phase leads to severe deterioration in impact toughness （longitudinal/transverse direction） and corrosion resistance of SDSS.
文摘Duplex stainless steels(DSSs)used in subsea structures and desalination industries require high corrosion and erosion resistance as well as excellent mechanical properties.The newly introduced cast duplex grade ASTM A8907 A has a unique composition and is expected to have a much better resistance to corrosion and erosion compared with the super-duplex grades 5 A and 6 A.This work is a comparative study of the mechanical properties,corrosion,and erosion-corrosion resistance of super-duplex grades 5 A and 6 A and the hyper-duplex grade 7 A.The three DSSs exhibited equiaxial austenite islands in the ferrite matrix and balanced phase ratios.The hardness of the grade 7 A was nearly 15%higher than those of the super-duplex grades,which is attributed to the effect of the higher contents of W and Mn in 7 A.The impact toughness of grade 7 A was found to be lower than those of the super-duplex grades due to the carbide precipitation resulting from the partial substitution of Mo with W.The oxide layer strengthening effect of rare earth elements and the higher pitting resistance equivalent number(PREN)of grade7 A resulted in higher corrosion resistance.The harder and more passive grade 7 A showed a 35%lower material loss during erosion-corrosion.
文摘The main objective of this research is to better understand the correlation between the constituent phases presented in the super-duplex steel SAF 2507 when it is under welding process by arc shielding gas MIG-MAG (Metal Inert Gas-Metal Active Gas). Conventional short circuit transfer and derivative STT (Surface Tension Transfer) using the 2594 welding wire as a filler metal and the effects on welding power in hardness, toughness and pitting corrosion are considered here. The results showed that the welding energy (Ew) changed the α/γ-phase’s balance and occasionally formed σ-phase in ferrite grain boundaries which led to changes in hardness, toughness and pitting corrosion resistance in molten zone (MZ), heat activated zone (HAZ) and metal base regions (MB). Furthermore, the increased amount of γ-phase improved the pitting corrosion resistance index (PRENγ) mainly in the MZ. This is due to decrease of α-phase fraction and formation of coarser grains, for higher welding energy. The toughness in the MZ decreased with less formation of γ-phase, coalescence of ferritic grains and localized formation of σ-phase, raising the hardness in the HAZ when the welding energy was lower.
文摘采用响应面法的中心复合设计对双相不锈钢冷金属过渡与脉冲复合(cold metal transfer and pulse hybrid,CMT+P)电弧增材工艺进行优化,构建了送丝速度,移动速度及脉冲数量与增材件成形质量(沉积宽度、成形误差和奥氏体含量)之间的数学回归模型。通过方差分析、摄动图以及响应曲面研究了不同工艺参数对成形质量的影响规律。结果表明:沉积宽度和奥氏体含量随移动速度增加而减小,随送丝速度和脉冲数量增加而增加;增加送丝速度或移动速度,成形误差先减小后增大,脉冲数量的影响不显著,得到优化的工艺参数为:送丝速度为3.9 m/min,移动速度为5.5 mm/s,脉冲数量12个。
