摘　　要

本研究係使用JIS SK85高碳鋼，探討鋼帶連續生產製程中，以雷射銲接取代傳統閃光銲接進行接合之可行性。銲後的顯微組織變化及機械性質之測試結果，皆為本研究評估之項目。
研究結果顯示，在室溫下進行雷射銲接會使SK85銲道生成硬脆的麻田散鐵組織，使銲道龜裂的發生機率提高，此現象可藉由200℃銲前預熱處理（使銲道轉變為波來鐵組織）獲得改善。在機械性質方面，預熱200℃之雷射銲件與母材相較下，抗拉強度雖大幅提升，但顯現出的衝擊韌性及延展性較差，需藉由700℃/10 min之銲後熱處理方可改善。
冷軋試驗的結果顯示，預熱200℃之雷射銲件經冷軋後，銲道內的波來鐵組織會隨冷軋程度的提高而變細緻。銲件經80% 冷軋後，抗拉強度較未經冷軋者高，延展性雖大幅下降，但仍在可承受冷軋的範圍內，並無裂紋生成。
此外，在SK85雷射銲接製程中添加鐵粉，可有效降低銲道生成麻田散鐵的趨勢，使其硬度下降，亦可填補對接間隙造成的銲道凹陷，唯熱影響區之性質仍需藉由預熱或銲後回火處理方等方式來改善。

Abstract

The emphasis of this study was on evaluating the feasibility of laser welding in continuous production line of JIS SK85 high carbon strip steel. The variations of microstructures and mechanical properties of laser welds were investigated.
After laser welding at room temperature (~ 25℃), the martensite was formed in the SK85 weld metal and accompanying cracks were easily found in the weld center line. By preheating specimens to 200℃ before welding, fine pearlite was formed and cracks could also be prevented in the weld metal. The 200℃ preheated SK85 laser welds showed greater tensile strength but lower impact toughness and ductility than the base metal. The deteriorated properties of the SK85 laser welds could be significantly improved by a 700℃/10 min-postweld heat treatment (PWHT).
According to the results of cold rolling test, the microstructure of the 200℃ preheated SK85 weld mteal showed much finer pearlite with larger cold reduction. Even 200℃ preheated welds after 80% showed much higher tensile strength but lower ductility than those without cold rolling, there is no crack found in the former.
The laser powder welding was also conducted in this research. The benefits of addition of pure iron powder include reducing the tendency of martensitic transformation and lowering the hardness in weld metal, and avoiding the underfill induced by specimen gap. The hardness of heat affected zone, however, could only be reduced by preheat or post-weld heat treatment.

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