銲接用於船舶，橋樑，壓力容器，工業機械，汽車，機車車輛等諸多領域。與銲接相關的問題，亦在這些領域中出現。鋼的可銲接性與銲接熱影響區（HAZ）的最大硬度和銲縫的冷裂紋敏感性有關。當鋼的銲接基材金屬在受銲接時的非均勻加熱和冷卻，會生成較硬的熱影響區（HAZ），此會有冷裂紋敏感性和殘餘應力存留在銲件中。減少上述困難最好的方法就是緩慢的加熱與冷卻母材及銲接熱影響區。然而有許多方法用於減少上述問題的影響，其中之一就是預熱與後熱，其已被廣泛應用在銲接操作中，用於防止冷裂紋。實驗技術是雙V溝槽設計以對接方式採用包藥銲線電弧銲(Gas shielded Flux Cored Arc Welding，FCAW-G)自動送線機器，搭配相當於美國銲接協會之AWS A5.20 E70T-1 規格之包藥銲條執行，銲條直徑1.2 mm，並輔以流率20Lmin-1遮蔽氣體CO2銲接而成。本研究主要探討預熱與銲後熱處理在JIS G3101 SS400 結構鋼與AISI 1045 中碳鋼兩種不同材質的異材銲接中顯微組織與機械性質上之影響，以消除S45C熱影響區的最高硬度並提高韌性，嘗試找出最佳化參數，將製程標準化後，確保不同的銲接機具與人員皆能達成相同的銲接品質，以符合工業上之需求。;Ships, bridges, pressure vessels, industrial machinery, automobile, rolling stock and many other fields are all produced by welding technology. The common problem in these fields is associated with welding process. The maximum hardness of the heat affected zone (HAZ) and the cold cracking susceptibility of welds are results in Weldability of steel. It would generate harder HAZ, cold crack susceptibility and residual stress in weldment, when steel is welded non uniform heating and cooling in weld metal and in base metal. To slow the heating and cooling rate of the base metal and weld heat affected zone is the best way to minimize difficulties above. However there are many methods to solve it and one of them is preheating and post weld heat treatment (PWHT). Preheating and PWHT have been widely employed in welding operation for preventing cold cracking and the maximum hardness in HAZ. The weldments with double V groove type were butt-welded by multiple passes as shown in Fig. 2. An automated Gas shielded Flux-Cored Arc Welding (FCAW-G) machine was used, with a welding wire of diameter 1.2 mm and CO2 shielding gas at 20 Lmin-1 flow rate, conforming to the American Welding Society standards AWS A5.20. In this study, it investigate the effects of preheating and PWHT on the microstructure, mechanical properties of JIS G3101 SS400 structural steel and AISI 1045 midium carbon steel dissimilar joints. It would eliminate the maximum hardness in the S45C HAZ and increase the toughness of the weldment. The welding process would be standardized which base on the obtained optimization parameters, in order to ensuring the welding quality from different workers that could reach the demands of industry.