不□鋼TIG-Flux銲接技術之研究

Abstract

本研究目的主要在探討活性助銲劑對沃斯田鐵不□鋼銲道特性之影響。實驗材料選用AISI 304沃斯田鐵型不□鋼，活性助銲劑選用氧化物、氟化物、硫化物與碳酸鹽基等粉末，銲接方法採用不加填料金屬的氬氣保護鎢極電弧銲來進行Bead-on-plate實驗，銲接過程中利用影像擷取系統，並採訊號同步接收方式來拍攝銲接電弧動態影像與紀錄電弧電壓變化。以金相實驗來觀察銲道形態與微觀組織；以肥粒相測定儀來量測銲道殘留肥粒相含量；利用微硬度測定機與拉伸試驗機來瞭解銲道機械性質；以EDS來分析銲道合金元素成份之變化；以Spot-Varestraint test來評估熱裂敏感性；以平均垂直位移法來量測銲件角變形。實驗結果顯示添加氧化物所組成之活性助銲劑將可有效提高銲接金屬熔融效率與銲接熱源能量密度，而得到窄而深的銲道截面與較小的銲接熱影響區，亦可有效降低銲件變形。然有效提高銲道穿深能力是由電漿電弧收縮及熔融銲池緊縮現象為其主要作用機制。此外，TIG-Flux銲接製程將會使銲接金屬在銲後會殘留有較多的肥粒相含量，可有效降低金屬熱裂敏感性的效果；然而其銲道機械性質雖略比傳統佳，但差異不大。評估自行研發出之80%MnO2-20%ZnO為不□鋼TIG-Flux活性助銲添加劑後，在實際工程應用上應可大幅提高生產效率與降低生產成本。

This study aims to investigate the effect of activating flux on the characteristics in austenitic stainless steel welds. Autogenous TIG welding process through a layer of the flux was applied on the AISI 304 stainless steels to produce a bead-on-plate welded joint. Oxide, fluoride, sulfide and carbonate powders were used as the activating fluxes. During welding, a CCD camera system was used to observe and record images of the arc profiles and voltage data. The microstructure and morphology of the welds obtained were examined by means of an optical microscope. The retained ferrite content of welds was measured by using the Ferritscope. Transverse tensile and Vickers hardness test were used to determined for the mechanical properties of weldments. EDS were employed for studying the elemental analysis of the welds. The hot cracking susceptibility was evaluated by the Spot-Varestraint test. The mean vertical displacement method was utilized for calculating the welding angular distortion. The experimental results indicate that higher penetration depth and narrower HAZ range are characteristics of the increased energy density of the welding heat source, and therefore the angular distortion of austenitic stainless steel weldments can be reduced, while working with certain oxide flux. Physically constricting the plasma column and reducing the anode spot are the possible mechanisms for the main contribution to the augmented weld penetration capability. TIG-Flux welding process can increase the measured ferrite number in welds, and tends to reduce hot cracking susceptibility in as welded structures. The welds with activating flux exhibit equal or better mechanical properties than conventional TIG welds deposited without using the flux. Of the different additives considered, the 80%MnO2-20%ZnO mixture can bring about large benefits in terms of productivity, cost and achieve practical use.