SA533 B2合金鋼銲接熱模擬顯微組織之研究

Abstract

本次實驗用材料為SA533 B2合金鋼板。為了解鋼板在手工電弧銲接(Shielding Gas Metal-Arc Welding, SMAW)過程中的相變態行為及組織的演化情形，實驗分別模擬不同銲接入熱量(10、20、30 kJ/cm)、300℃下不同後熱持溫時間(10、30、60分鐘)，以及不同的590℃銲後熱處理時間(30、60、180分鐘)。實驗結果顯示，不同的銲接入熱量將會造成不同的變韌鐵生成溫度，在TEM觀察中也可以發現，SA533合金三種入熱量所得到的變韌鐵組織均為下變韌鐵型態。而10 kJ/cm與20 kJ/cm的試片中也觀察到麻田散鐵組織，此夾雜在變韌鐵束狀結構間的麻田散鐵則皆為板條狀的自動回火麻田散鐵(auto-tempered martensite)，其中又以10 kJ/cm模擬條件會得到較多的麻田散鐵組織。此外，由硬度量測與抗衝擊性質試驗結果發現，入熱量越小，硬度值越高，且材料直接冷卻後的抗衝擊性表現方面十分不理想，衝擊能吸收約只有母材鋼板的三分之一左右，但是分別依序經過後熱(300℃)以及銲後熱處理(590℃)後等步驟後，其硬度試驗結果均呈現大幅下降的趨勢，而在抗衝擊性質方面則可以獲得明顯的改善。綜合實驗結果得知，SA533 B2材料的衝擊值在經過30分鐘300℃的後熱處理之後，隨即升溫至590℃進行銲後熱處理並持溫60分鐘，可以達到此次實驗模擬條件中最佳的韌性(抗衝擊)狀態。

To investigate the phase transformation and the microstructural evolution of SA533 B2 steel plates during the SMAW (Shielding Gas Metal-Arc Welding) welding processes, simulations of the coarse grained region of heat affected zone (with heat inputs of 10, 20 and 30 kJ/cm) followed by inter-pass heating at 300℃ and post-weld heat treatments at 590℃ were carried out. The microstructural evolution and the toughness of the simulated specimens were studied after different soak time of heat treatments. With heat inputs of 10 and 20 kJ/cm, both of the simulated microstructures contain large amount of lower bainite with significant amounts of auto-tempered martensite. With the heat input of 30 kJ/cm, the simulated microstructure is composed mainly of lower bainite structure. Thus, the higher hardness of the specimens would be got under the smaller heat input condtions. Besides, the Charpy impact toughness property has been measured for the specimens treated by 20 kJ cm-1 heat input, followed by inter-pass heating at 300℃ and post-weld treatment at 590℃. The resaults of impact tests show that the impact energies would be meliorated after inter-pass heating and further improved by post-weld heat treatments. The highest impact energy was got in the specimen after 60 minutes of post-weld heat treatment following 30 minutes of inter-pass heating.