本研究的目的在探討沃斯田鐵系304不銹鋼管線之對銲(butt-welding)接點，在歷經數次反覆銲接、切除、再銲接後，其熱影響區(heat-affected zone)硬度、金相組織、衝擊性質及最大抗拉強度之變化，並藉以了解多次重複銲接(以下簡稱為修銲- - -repeated weld-repairs)對於AISI 304材料強度、韌性、延展性及其他機械性質之影響。
實驗的背景、方法及參數均模擬國際上石化、煉油及發電廠業界實際施工的狀況，本研究第一道銲接以氬焊(GTAW)打底，第二層以上的銲接以遮護金屬電弧銲(SMAW)施銲。每次修銲均取樣分析，直至5次修銲，比對每次修銲的機械性質差異及變化，並進行綜合分析研究。
實驗結果顯示: 修銲後熱影響區域材料硬度並未明顯下降，晶粒組織未顯著成長。將修銲HAZ試片和未經銲接的試片比較，抗拉強度略為下降，但仍高於規範要求，且最大抗拉強度並未隨著修銲次數增加而降低。檢視低溫衝擊值及側膨脹量，發現多次修銲後材料並未明顯轉脆，且延展性仍符合規範之要求。

The effect of multiple thermal cycles related with repeated weld-repairs on the variation of hardness, microstructure and mechanical properties in the HAZ of AISI 304 stainless steel welds was investigated in this study. The welding procedures and parameters used in this work were designed to approach to the practical applications in the field. The first pass of welding was conducted by gas tungsten arc welding (GTAW) process and the remained passes were completed by shield metal arc welding (SMAW) process. After the final pass was finished, the weld metal was removed by grinding. Repeated procedures were conducted and lasted for five times.
The results indicate that the low energy input of SMAW process had less influence on varying the grain size and hardness in the HAZ of 304 stainless steel weld. For the repaired welds, the tensile strength was less than that of the un-welded base metal, but still met the requirement of ASME code. In regarding to impact tests at low temperature down to -40℃, the impact values and lateral expansion of repeated weld-repairs specimens were not deteriorated by the multiple thermal cycles in comparison with un-welded base metal. Besides, the lateral expansions of repeated weld-repairs specimens were higher than ASME B31.3 code requirement. It shows the impact toughness and ductility of AISI 304 were not affected by repeated weld-repairs.

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