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|標題:||The Study of the Influence of Fluoride on Shielded Metal Arc Welding
|關鍵字:||低氫系手銲條;Low-hydrogen Shielded Metal Arc Welding;CaF2;Na3AlF6;NaF;氫;氧;氮;銲道機械性質;CaF2;Na3AlF6;NaF;Hydrogen;Oxygen;Nitrogen;Weld mechanical property||出版社:||材料工程學系所||摘要:||
實驗結果發現，當銲藥氟化物添加量增加時，熔滴的表面張力、熔滴尺寸及比表面積會隨之增大。而銲藥中氟化物種類改變對上述熔滴性質影響不明顯。隨著銲藥中氟化物的增加，銲道氫、氧及氮含量減少。且銲藥中添加NaF時其銲道擴散氫、氧及氮含量最少，而添加CaF2時最多。由熔金成分分析可知，當銲藥中氟化物含量增加時，由於銲道氧含量減少，使銲道中碳、矽、錳及鉻的含量隨之增加。當銲藥中添加的氟化物種類改變時，銲道中碳、矽、錳及鉻含量在銲藥添加CaF2者為最少、Na3AlF6次之、NaF最多。由熔渣成分分析可知，銲藥中添加CaF2會增加渣中鈣與氟含量，添加Na3AlF6會增加渣中鈉、鋁與氟含量，添加NaF會增加渣中鈉與氟含量。經XRD測試，銲道主要為BCC結構的肥粒鐵，並無發現其他結構。由銲道結構分析可知，各組銲道中的針狀肥粒鐵比例隨著銲藥中氟化物的增加而增加，但銲藥中添加不同氟化物對針狀肥粒鐵含量影響不大。當銲藥中氟化物的添加量增加時，可增進銲道的強度與韌性。銲藥中添加不同氟化物使銲道金屬的強度不同，其順序由大至小為NaF > Na3AlF6 > CaF2。但銲藥中添加不同氟化物對銲道韌性影響不明顯。銲道硬度測試顯示，銲藥中氟化物含量與種類改變時，銲道的硬度沒有明顯改變。
During welding, harmful elements such as hydrogen, oxygen and nitrogen would enter the weld bead which cause defects in materials and make a lot of restrictions in using the materials. In order to remove harmful elements, low hydrogen electrode is often used during welding. Fluoride is a major component of the low hydrogen electrode. It can react with hydrogen during welding to produce hydrogen fluoride(HF), and decrease the hydrogen content of weld bead.
In this research, the content of fluorides, CaF2, Na3AlF6, and NaF, in the flux was changed to understand the effect of the content of every fluoride in welding flux on the harmful elements such as hydrogen, oxygen and nitrogen and the effect on weldment property. The first step of the experiment was to determine the kinds and variations of variables of flux and produce the shielded metal arc welding electrodes. Welding rods made from every set of flux had to test the surface tension and size of drplets, cooling rate of weld bead, weld metal diffusible hydrogen content, GDS analysis of weld pad, oxygen and nitrogen analysis of weld pad, XRF analysis of slag, tensile test, impact test, weld metal hardness, and weld metal microstructure.
From the experimental results, it was found that the surface tension, size, and surface area of droplets increased as the fluoride content in the welding flux increasing. The characters of droplets mentioned above have no obviously change when adding different fluoride in the flux.
It was found that the content of diffusible hydrogen, oxygen, and nitrogen of the weld bead is the lowest while adding NaF to the welding flux, and it was the maximum while adding CaF2. As the fluoride content of the welding flux increasing, the content of hydrogen, oxygen, and nitrogen of weld metal reduced.
When the content of fluorides in the flux increased, the content of carbon, silicon, manganese, and chromium in the weld bead would increase. The content of carbon, silicon, manganese, and chromium in the weld bead was the lowest while adding CaF2 to the flux ,and the maximum while adding NaF.
From the analysis of the content of slag, adding CaF2 to the flux would increase the content of calcium and fluorine in the slag. Adding Na3AlF6 to the flux would increase the content of sodium, alumium and fluorine in the slag. Adding NaF to the flux would increase the content of sodium and fluorine in the slag.
From the XRD, the weld metal was mainly ferrite with BCC structure. The content of acicular ferrite in the weld metal would increase as the content of fluoride in the welding flux increasing. Adding different fluoride didn't show obviously effect on the content of acicular ferrite.
When the content of the fluorides in the welding flux increase, it could improve the strength and toughness of the weld bead. Welding flux adding different fluorides would show different strength of weld metal. The order from large to small is NaF > Na3AlF6 > CaF2. Adding different fluoride didn't show obviously effect on toughness.
The results of weld bead hardness test showed that the hardness of welding bead has no obviously change.
|Appears in Collections:||材料科學與工程學系|
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