304不銹鋼覆銲熱影響區及308L銲道金屬之顯微組織研究

• Main Author: 郭建奕
• Other Authors: J. R. Yang
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/64709150061713624100

碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 90 === The 304 stainless steel is most frequently used in nuclear power stations for water recycling pipes. Multi-pass welding is a necessary process during fabrication of the pipes. As a consequence of the severe thermal cycle during multi-pass welding, the original microstructure of the base material in the region close to the weld is changed; this microstructure is referred to as the heat-affected zone （HAZ）. It appears that the existence of the HAZ causes a significant deterioration in properties. To meet the stringent safety requirements for service, the development and control of the microstructure of the weldment in the 304 stainless steel pipes should be carefully monitored. It is useful to be able to simulate the weld thermal cycle under laboratory conditions for the purpose of obtaining information about microstructural and property changes. In this study, the research work is concerned with multi-pass welding simulation in 304 stainless steel. The microstructural constituents of each sub-critical region in the HAZ have been identified quantitatively through the thermal simulations in a dilatometer. The microstructural details of multi-pass weld deposits will be characterized. Furthermore, if the welding heat input is high（e.g. 80kJ/cm）, the HAZ microstructure will contain some carbides which precipitate at γ-γorγ-δ boundaries. However, at the low-peak temperature area（peak temperature ≈ 600℃） in HAZ carbides only precipitate at γ-δ boundaries. In this work, the solidification structure of weld metal has also been investigated. The microstructural details have been explained as well. It is hoped that some information can provide for industrial application.