本研究之目的在於探討D6AC超高強度合金鋼以惰氣鎢極電弧銲接與電漿電弧銲接兩種不同能量密度之實用高品質銲接製程進行3mm厚D6AC板材對銲，並搭配不同之銲前、銲後熱處理組合；以金相顯微組織觀察、銲道截面微硬度分佈量測與拉伸試驗了解基本機械性質，以缺口拉伸試驗針對銲道缺口破裂韌性分析，利用疲勞裂縫成長試驗探討疲勞特性，再輔以各試片破斷面之SEM微觀分析做更進一步判斷。
　　實驗結果顯示，電漿電弧銲件可獲得較佳之硬度、拉伸延性表現；於硬度、拉伸強度、拉伸延伸性及缺口韌性上，母材直接施銲搭配銲後淬火及兩小時450℃回火之試片，可消除回火軟化並使銲件整體組織均質化，擁有最佳的綜合表現；就疲勞裂縫成長特性上，電漿電弧銲件試片之過度回火區有最出色之延遲裂縫成長能力，單就熔融區來比較，也於各參數試驗試片中有最佳抵抗疲勞裂縫成長能力。

In this research, the mechanical properties, notch fracture toughness and fatigue properties of the D6AC ultrahigh-strength low alloy steel (HSLA) gas tungsten arc weldment and plasma arc weldment, which undergone various heat treatment were investigated by microhardness test, tensile test, notch tensile test, fatigue crack propagation test; also carried off metallographic by optical microscope (OM), the nature of fracture surface by scanning electron microscope (SEM).
Results revealed that the plasma arc weldment, showed the better hardness and tensile ductility than gas tungsten weldment. The specimen, welded on as-received plate undergone quenching and 450℃ tempering for 2 hours, by eliminating the overtempering soft zone, performed the best comprehensive properties except the ability for resist fatigue crack propagation. The portion of the overtempering zone of plasma arc weldment has the best fatigue crack propagation resistant ability of all fatigue specimens.

目　錄
中文摘要………………………………………………………………..I
英文摘要…………………………………………………………….…II
誌謝…………………………………………………………………....III
目錄………………………………………………………………...…..V
圖索引………………………………………………………………....IX
表索引……………………………………………………………....XVII
第一章 前言………………………………………………..……..….1
第二章 文獻回顧…………………………………………………....3
2-1 D6AC簡介……………………………………………..….3
2-1-1 超高強度鋼…………………………………….…...…..3
2-1-2 D6AC超高強度鋼………………………………….……4
2-1-3 D6AC銲接特性………………………………….…..…..7
2-1-4 D6AC熱處理特性……………………………….…....…9
2-1-5 氫脆對材料機械性質的影響…………………..….......11
2-2 惰氣鎢極電弧銲與電漿銲接…………………………..…15
2-2-1惰氣鎢極電弧銲……………………………..…....……15
2-2-2 電漿電弧銲接…………………………………..….......15
2-3 疲勞裂縫成長試驗……………………………………...…......18
2-3-1 顯微結構對疲勞裂縫成長的影響………………….....22
第三章 實驗方法………………………………...…….……….…..24
3-1實驗材料………………………………………………….….…25
3-2銲接製程……………………………………………....…….….26
3-2-1惰氣鎢極電弧銲接…………………………….…...…..27
3-2-2電漿電弧銲接……………………………………….….29
3-3熱處理程序……………………………………………....……..30
3-4機械性質測試……………………………………………….….32
3-4-1硬度量測………………………………………………..32
3-4-2拉伸試驗…………………………………………...…...32
3-4-3缺口拉伸試驗…………………………………………..32
3-4-4疲勞裂縫成長試驗………………………………...…...33
3-5金相顯微組織觀察……………………………………………..39
3-6 SEM破斷面觀察………………………………………………..39
第四章 結果與討論…………………………………….....…40
4-1 金相組織…………………………………………………….....40
4-1-1 母材經熱處理之金相組織…………………………….40
4-1-2 母材直接施銲之銲件金相組織……………………….40
4-1-3 銲後回火銲件之金相組織…………………………….41
4-1-4 銲後淬火及450℃兩小時回火銲件之金相組織…......42
4-2 硬度試驗……………………………………………………….54
4-2-1 銲前熱處理對硬度的影響…………………………….56
4-2-2 銲後熱處理對硬度的影響…………………………….57
4-3 拉伸試驗……………………………………………………….64
4-4 缺口拉伸試驗………………………………………………….78
4-4-1 母材直接施銲之銲件缺口拉伸破斷面……………….79
4-4-2 銲後450℃兩小時回火對銲件缺口拉伸破斷面之
影響…………………………………………………….80
4-4-3 不同銲後回火溫度對銲件缺口拉伸破斷面之影響….80
4-4-4 銲後淬火及450℃兩小時回火對銲件缺口拉伸
破斷面之影響…………………………………...……..81
4-5 疲勞裂縫成長試驗…………………………………………….98
4-5-1 母材經惰氣鎢極電弧銲接之疲勞破斷面…………....100
4-5-2 母材經電漿電弧銲接之疲勞破斷面…………………102
4-5-3 銲件經銲後淬火及450℃兩小時回火之疲勞破斷面.103
4-6 四種銲接製程的比較……………………………………...….121
4-6-1硬度比較……………………………………………….121
4-6-2拉伸強度比較…………………………….……………122
第五章 結論………………………………………..………..127
第六章 未來研究方向………………………………………………129
參考文獻………………………………………………..……………..130

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