臺灣博碩士論文加值系統

本研究使用氬銲以309L為銲料將低碳鋼及304不銹鋼進行異質銲接，銲接部位沉積2 mg/cm2 不同比例NaCl-Na2SO4混合鹽後，置於750 °C靜滯空氣爐中探討熱腐蝕之影響。鋼料銲接後在低碳鋼 HAZ與304 HAZ皆發生晶粒成長，且304之HAZ有發生敏化現象，低碳鋼與銲道之界面則有碳化物產生。
熱腐蝕實驗結果顯示，304與309L銲道均呈現典型內侵蝕，低碳鋼則為均勻腐蝕之型態，各區侵蝕深度皆隨持溫時間增加而增加；銲道因309L具高鉻含量使其金屬損失量最小。304之HAZ因敏化而具有大的金屬損失及總侵蝕深度；在有足量熔融鹽下，因加凡尼效應而導致在低碳鋼/309L界面之低碳鋼側發生嚴重侵蝕。

The purpose of this work was to study the hot-corrosion behavior of dissimilar weldments by gas tungsten arc welding applied to join 304 stainless steel and low carbon steel with consumable-309L stainless steel wires at 750 °C in static air with 2 mg/cm2 mixture of various NaCl-Na2SO4 deposits. It was found that both the weldments revealed the coarse grain structure in low carbon steel HAZ and 304 HAZ and the sensitization around 304 HAZ. Moreover, the carbon migrated from the low carbon steel base metal to the higher chromium weld metal side and formed chromium carbide adjacent to the low carbon steel HAZ/WM interface.
The results of hot corrosion showed that both 304 and 309L appeared subscale attack but low carbon steel was uniform corrosion. The depth of attack increased with increasing exposure duration of time. The weld metal had the smallest metal loss because of its high chromium content. Due to sensitized reaction the 304 HAZ had the most metal loss and the total depth of attack. The galvanic effect to the low carbon steel resulted in a serious corrosion with sufficient molten salt at low carbon steel HAZ/WM interface.

第一章　前言 1
第二章　文獻回顧 2
2.1　銲接 2
2.1.1　氬銲 2
2.1.2　銲接熱影響效應 4
2.2　異質金屬之銲接 6
2.2.1　碳鋼與沃斯田鐵系不銹鋼之異質銲接 8
2.2.1.1　碳鋼 8
2.2.1.2　沃斯田鐵系不銹鋼 9
2.2.1.3　碳擴散問題 10
2.2.1.4　硬度之變化 13
2.2.1.5　熱影響區之晶粒變化 13
2.3　熱腐蝕及熱力學 14
2.3.1　熱力學資料 14
2.3.2　NaCl之熱腐蝕 19
2.3.3　Na2SO4之熱腐蝕 21
2.3.3.1　硫化模式 21
2.3.3.2　熔鹽模式 22
2.3.4　NaCl-Na2SO4混合鹽之熱腐蝕 23
2.3.5　沉積鹽之熱腐蝕 25
2.4　加凡尼效應 30
第三章　實驗方法 32
3.1　實驗流程圖 32
3.2　試片準備 33
3.3　鋼料銲接試片 35
3.3.1　顯微組織 35
3.3.2　銲接試片受熱之影響 40
3.4　高溫腐蝕實驗 44
3.4.1　沉積鹽熱腐蝕 44
3.4.1.1　氯化鈉-硫酸鈉混合鹽噴覆作業 44
3.4.1.2　熱腐蝕試驗 44
3.4.2　浸泡熔鹽熱腐蝕 44
3.5　腐蝕實驗後分析設備與方法 47
3.5.1　分析設備 47
3.5.2　分析方法 49
第四章　實驗結果 51
4.1　沉積鹽熱腐蝕 51
4.1.1　100% NaCl熱腐蝕 53
4.1.2　Na2SO4熱腐蝕 62
4.1.3　NaCl-Na2SO4熱腐蝕 70
4.2　熔鹽腐蝕 92
第五章　討論 97
5.1　100% NaCl熱腐蝕 97
5.2　100% Na2SO4熱腐蝕 98
5.3　NaCl-Na2SO4混合鹽之熱腐蝕 99
5.4　熔鹽之熱腐蝕 100
第六章　結論 101
參考文獻 102

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