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Title: 特殊不鏽鋼之動態撞擊微觀組織演變
The microstructural evolution of the dynamic response of special stainless steels
Authors: Wuan-Yun Hsiao
Contributors: NTOU:Department of Mechanical and Mechatronic Engineering
Keywords: 雙相不鏽鋼;254 SMO;應變速率;雙晶;麻田散鐵;脈衝銲接;微觀組織;疊差能;Hopkinson pressure bar
duplex stainless steel;254 SMO;strain rate;twinning;martensite;weld;Hopkinson pressure bar;microstructure;stacking fault energy
Date: 2006
Issue Date: 2011-06-30T07:26:41Z
Abstract: 在動態應變速率8.5×102 s-1 與5×103 s-1 之下,雙相不鏽鋼SAF 2507與SAF 2205的微觀組織將產生變化。實驗結果顯示,材料的流應力-應變曲線與微觀組織的變化深受動態衝擊應變速率的影響。隨著應變速率增加,雙相不鏽鋼中的的肥粒鐵相可觀測出相互糾結差排之密度變化;在應變速率8.5×102 s-1下可於SAF 2205 DSS的沃斯田鐵相中發現相互交錯的持續滑移帶與雙晶,而在高應變速率5×103 s-1 時則有大量雙晶產生於雙相不鏽鋼的沃斯田鐵相中。超級沃斯田鐵不鏽鋼254 SMO擁有單一的沃斯田鐵相,在動態應變速率衝擊下所產生的微觀組織對流應力與硬度變化產生極大的影響。 □ 雙相不鏽鋼SAF 2507和SAF 2205與超級沃斯田鐵不鏽鋼254 SMO的銲件微觀組織變化與應變速率相關,在較低應變速率下,雙相鋼因受絕熱影響而形成雙晶。在高應變速率下,針狀及較厚的條狀雙晶在沃斯田鐵相成形。在254 SMO方面,較低應變速率下產生了差排迴圈;在高應變速率之下,大量的麻田散鐵成形。受化學份影響的疊差能與絕熱決定了在動態衝擊之下最終微觀組織的形成。
The microstructures of the duplex stainless steels (DSS) SAF 2507 and SAF 2205 were evaluated after dynamic impact tests with two strain rates: 8.5×102 s-1 and 5×103 s-1. Results indicate that the flow stress-strain curve and the microstructure are strongly affected by the impact loading rate. As the strain rate increases, the density of tangled dislocations were observed in the α phase for both duplex stainless steel. In contrast, the microstructure of SAF 2205 DSS in γ phase consists of persistent slip band intersected with twins at low strain rate of 8.5×102 s-1. Deformation twins occur only in the γ phase for dynamic impact at the relatively high strain rate of 5×103 s-1 for both duplex stainless steel. In the superaustenitic stainless steel 254 SMO, the unique γ phase exhibits a strain-induced martensite transformation. The impact flow stress behaviour and the hardness variation are associated with the transformed microstructure. The variations of weld metal microstructure after impact at different strain rates for three weld metals, SAF 2507 DSS, SAF 2205 DSS and 254 SMO steel, are addressed. The twin grain forms that appear inside the γ grain of duplex stainless steel at low impact strain rates may be caused by adiabatic heat. The needle-like or thick streak-like twins occur in the γ grain of duplex stainless steel, caused by shear stress at a high strain rate. The impact induces the dislocation loop formation in the γ phase of 254 SMO steel at low strain rate, but martensite is produced at a high strain rate. The chemical composition affects the stacking fault energy coupled with adiabatic heat to determine the final structure of the impact.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M94720001
Appears in Collections:[機械與機電工程學系] 博碩士論文

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