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Dong-Yih Lin,Chih-Chun Hsieh 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.3
The purpose of this study is to discuss the precipitation tendencies of δ, σ, and γ phases using a modified Cr/Ni equivalent ratio with 309L filler after welding dissimilar steels (SUS 304L and AISI 1017) while adding various Si contents of 0.25 wt.%, 0.45 wt.%, and 0.65 wt.% and hot rolling in AISI 309LSi stainless steels at 1200 °C for 2 h. The elemental compositions of δ, σ, and γ phases were performed by EDS in as-hotrolled AISI 309LSi as well as dissimilar welded samples, and the Creq/Nieq ratios were calculated by Hammer & Svensson’s equation. In this research, the Creq/Nieq of phase and matrix were presented as [Creq/Nieq]phase and [Creq/Nieq]matrix, respectively. The modified equation ([Creq/Nieq]modified) was equal to [Creq/Nieq]phase /[Creq/Nieq]matrix, and it was used to examine the effect of materials and processes in the δ, σ, and γ phases. The results indicated the Creq/Nieq ratios of the δ, σ, and γ phases were 2.557~1.304, over 3.143, and 1.229, respectively. The purpose of this study is to discuss the precipitation tendencies of δ, σ, and γ phases using a modified Cr/Ni equivalent ratio with 309L filler after welding dissimilar steels (SUS 304L and AISI 1017) while adding various Si contents of 0.25 wt.%, 0.45 wt.%, and 0.65 wt.% and hot rolling in AISI 309LSi stainless steels at 1200 °C for 2 h. The elemental compositions of δ, σ, and γ phases were performed by EDS in as-hotrolled AISI 309LSi as well as dissimilar welded samples, and the Creq/Nieq ratios were calculated by Hammer & Svensson’s equation. In this research, the Creq/Nieq of phase and matrix were presented as [Creq/Nieq]phase and [Creq/Nieq]matrix, respectively. The modified equation ([Creq/Nieq]modified) was equal to [Creq/Nieq]phase /[Creq/Nieq]matrix, and it was used to examine the effect of materials and processes in the δ, σ, and γ phases. The results indicated the Creq/Nieq ratios of the δ, σ, and γ phases were 2.557~1.304, over 3.143, and 1.229, respectively.
( Chih Chun Hsieh ),( Dong Yih Lin ),( Wei Te Wu ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 METALS AND MATERIALS International Vol.13 No.5
The dispersion strengthening behavior of the σ phase in 304 modified stainless steel as hot-rolled at 1073 K has been investigated in this study. The morphology, quantity and chemical composition of the σ phase were analyzed using optical microscopy (OM), X-ray diffractometry (XRD), ferritscope (FS), and image analysis (IA). The amounts of σ phase in the stainless steels increased gradually at 1073 K as the reduction ratio increased from 0% to 75%. The XRD analyses showed that a higher reduction ratio enhanced the conversion of δ-ferrite (110) to σ phase (542). The σ phase was precipitated homogeneously at the recrystallized ferrite grains when the reduction ratio was increased from 0% to 75%.
Phase Transformations of 24Cr-14Ni-0.7Si Stainless Steel under Different Aging Conditions
Chih-Chun Hsieh,Dong-Yih Lin 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.2
This study discusses the development of a phase transformation in 24Cr-14Ni-0.7Si stainless steel after aging under various aging temperatures, times, and N2/Air ratios. The observation of OM indicated that the initial state of δ-ferrite in the test material appeared as complete dendrite structures at short aging times and then exhibited lacy and dispersed structures when the aging time increased. This led to a gradual austenitization transformation as the nitrogen/air ratio increased, accelerating the δ/σ phase transformation and retarding the δ/γ phase transformation at the same time. The δ/σ phase transformation was dominant when the aging temperature was 800 °C. A line scanning analysis of the EPMA showed that the X-ray spectrum of Cr at the δ/γ interphase boundary was raised. In addition, Si showed lower X-ray spectrum energy after the δ/γ phase transformation. Clearly, Si had a stabilizing effect on the δ-ferrite and σ-phase. Furthermore, it had the fastest precipitation ratio for the δ/σ phase transformation at 800°C among all aging temperatures.
( Chih Chun Hsieh ),( Tao Chih Chang ),( Dong Yih Lin ),( Ming Che Chen ),( Wei Te Wu ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 METALS AND MATERIALS International Vol.13 No.5
The purpose of this study is to investigate the precipitation characteristics of σ phase in the fusion zone of stainless steel welds at various welding passes during a tungsten arc welding (GTAW) process. The morphology, quantity, and chemical composition of the δ-ferrite and σ phase were analyzed using optical microscopy (OM), a ferritscope (FS), a X-ray diffractometer (XRD), scanning electron microscopy (SEM), an electron probe micro-analyzer (EPMA), and a wavelength dispersive spectrometer (WDS), respectively. Massive δ-ferrite was observed in the fusion zone of the first pass welds during welding of dissimilar stainless steels. The σ phase precipitated at the inner δ-ferrite particles and decreased δ-ferrite content during the third pass welding. The σ and δ phases can be stabilized by Si element, which promoted the phase transformation of δ→σ + γ2 in the fusion zone of the third pass welds. It was found that the σ phase was a Fe-Cr-Si intermetallic compound found in the fusion zone of the third pass welds during multi-pass welding.