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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52162

Title: 正常化處理對銲接熱模擬T91、T92抗潛變合金高溫應力斷裂性能影響
The Effect of Normalizing Temperature and Thermal Simulation on the Stress Rupture of T91 and T92 Steels at Elevated Temperature
Authors: Wu, Hao-Wei
吳浩偉
Contributors: NTOU:Institute of Materials Engineering
國立臺灣海洋大學:材料工程研究所
Keywords: 臨界熱影響區;高溫定負載;晶界角度
ICHAZ;T91;T92;EBSD
Date: 2018
Issue Date: 2019-05-23T06:19:35Z
Abstract: 本實驗使用臺灣電力公司所提供超臨界鍋爐使用的鉻鉬鋼管材,為T91及T92抗潛變合金鋼,使用高真空熱處理爐對材料進行一小時正常化處理及回火,正常化處理後進行紅外線熱模擬爐實驗,模擬材料銲接後的過度回火區及臨界熱影響區,再次進行銲後回火處理。高溫定負載實驗將試片負載持續進行1000小時,觀察在1000小時內斷裂的試片。本實驗條件溫度及壓力皆高於超臨界鍋爐所使用條件,以比較T91及T92經過不同正常化處理及熱模擬試片,在高溫時抗潛變強度的差異。 高溫定負載實驗結果顯示,T92試片的抗潛變強度明顯優於T91試片,相同試片下經過較高溫的正常化處理有較良好的抗潛變性質,試片熱模擬至臨界熱影響區後,材料組織已產生大量肥粒鐵次晶界,明顯降低合金鋼抗潛變的強度,在較高溫定負載條件下,會使試片內部析出物(M23C6)明顯粗大化。硬度量測結果顯示經過熱模擬後回火試片硬度值皆較原來材料低。在高溫定負載斷裂試片中,位於斷裂端的硬度值最低。從SEM顯微組織觀察,T92試片與T91試片相比有較大的晶粒尺寸,而熱模擬至臨界熱影響區有明顯析出物缺乏區及眾多的次晶生成。使用EBSD分析T91及T92合金鋼,在正常化處理試片及熱模擬至過度回火區試片,其與正常化處理材料的組織相似。在過度回火條件試片,可發現部分新生成肥粒鐵次晶界,但主要組織以低角度晶界(麻田散鐵)及高角度晶界(先前沃斯田鐵晶界)為主。在臨界熱影響區中,T91試片存在著大量生新成肥粒鐵次晶界,在900°C熱模擬會明顯改變材料結構特徵,使高角度晶界與低角度晶界長度皆減少。在試片的斷裂端顯示眾多細小晶粒的高角度晶界,為高溫定負載情況下,使材料發生再結晶現象。觀察負載後的破斷面,可發現窩穴組織破裂特徵,為材料延性破壞的特徵。
In this work, gas-tungsten arc welding in multi-passes was used for the welding of T91 and T92 creep-resistant steel tubes. Moreover, microstructures similar to those found in the heat-affected zone (HAZ) of T91 and T92 steel welds were simulated to evaluate their stress-rupture-life at elevated temperatures. An infrared heating system with the heating rates as high as 60°C/sec was applied for heating the samples to 900°C and 860°C for 1 min, followed by cooling to room temperature. The simulated specimens were then subjected to conventional post-weld heat treatment (PWHT) at 760°C/2hr. The detailed microstructures of distinct samples were inspected by transmission electron microscope (TEM). The stress-rupture life of the investigated samples was correlated with the inherent microstructures of the specific sample. The results indicated that the 900°C as-simulated specimen (ICHAZ) had fine-grained microstructures and showed short term stress-life, regardless of prior normalizing temperature. The 860°C simulated specimen (STOT) with over-tempered microstructures were also inferior creep resistance to the original substrate. Under the same material preparation and testing condition, the samples normalized at 1060°C were more resistant to creep rupture than the ones normalized at 940°C.
URI: http://ethesys.lib.ntou.edu.tw/cgi-bin/gs32/gsweb.cgi?o=dstdcdr&s=G0010555004.id
http://ntour.ntou.edu.tw:8080/ir/handle/987654321/52162
Appears in Collections:[材料工程研究所] 博碩士論文

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