臺灣博碩士論文加值系統

ASTM A533 合金鋼為核電廠之壓?容器之主要鋼材。異材銲接多使用在壓力容器、壓縮機及蒸氣機上以降低成本。相較於遮蔽金屬棒電弧銲（SMAW）及惰性氣體鎢棒電弧銲(GTAW)等傳統銲接，雷射銲接具有更多優點。因其具有高強度熱源，可以克服異種材料間熱傳導差異之問題。雷射銲接穿透模透式可以形成相當窄的銲道及熱影響區並減少熱扭曲、有效的減低殘留應力及改善銲接料的冶金性質。
本研究選用ASTM A533 TypeB Class2 與A572 Grade 65鋼板，板材厚度為3mm，並採用Nd-YAG雷射銲接製程對兩種材進行?材對接。並觀察不同雷射銲接參數對銲件的微結構組職、機械性質及殘?應?值的影響。實驗結果顯示當熱影響區的冷卻速率在115℃及170 ℃間，重融區、粗晶及細晶區的組職皆有麻田散鐵形成。拉伸試驗的結果則斷裂處產生在A572母材處，拉伸強度為83.76 ksi。此結果顯示藉由雷射銲接，其銲接處之強度高於A572母材強度。雷射銲接也形成較窄之熱影響區，其寬度約在1.4mm，此區域形成殘留應力雖高於傳統銲接製程，但銲道並無因殘留應力而導致拉生斷口發生在銲道處，仍符合使用上的安全需求。

The A533 and A572 low alloy steels are key materials which have been used in nuclear reactor facilities, such as pressure vessel, compressor, and stream generator where dissimilar welding is commonly employed with an aim to save cost. Meanwhile Laser Beam Welding (LBW) has many advantages in comparison with conventional welding techniques such as Shield Metal Arc Welding (SMAW) and Gas Tungsten Arc Welding (GTAW). With its high intensity heat source, LBW is able to overcome differences in thermal conductivity problems between different materials. Penetration mode of laser beam welding can produce a narrow weld bead with a narrow Heat Affected Zone (HAZ) which limits thermal distortion, reduce effectively residual stress and improve metallurgical properties of welded metal.
In this study, dissimilar welding of ASTM A533 Type B Class 2 to A572 Grade 65 was carried out with Nd – YAG Laser Beam Welding. Microstructure, mechanical properties as well as residual stress adjacent to the weld were studied after butt welding. Experimental results show that with the cooling rate of 115 0C/s-170 0C/s in HAZ, martensite is formed in the fusion zone, coarse and fine grains in Heat Affected Zone. The welded structure fabricated by LBW has a much higher hardness than that done by conventional welding. Hardness increases rapidly from base metal to Heat Affected Zone. Tensile tests revealed that fracture occurred at base metal of A572 by 83.76 Ksi. It demonstrated that strength of dissimilar weld joint is higher than the base metal and satisfied the safety requirement during operating. Meanwhile Laser beam welding makes a narrow Heat Affected Zone which is about 1.4 mm in comparison with 2 to 2.5 mm HAZ done by Shield Metal Arc Welding. And the residual stress in this area was formed.

摘要 I
Abstract II
Acknowledgement III
List of figures VII
List of tables X
Chapter 1: Introduction. 1
Chapter 2: Theories and Literature review. 6
2.1. Welding [18, 19, 9, 12] 6
2.2. Advantages of Laser beam welding. 9
2.3. Welding heat affected zone 13
2.3.1. Weld 13
2.3.2. Heat affected zone. 14
2.4. Residual stress formed in single pass weld [6, 16, 17, 19] 17
2.5 Hole-Drilling Strain-Gage Method 20
2.5.1 Theoretical description [6, 25] 20
2.5.2. ASTM Standard E837 [21] 26
Chapter 3: Welding materials and experimental procedure 34
3.1. Experimental planning 34
3.2. Experimental workflow 35
3.2.1 Materials’ composition and specification 35
3.2.2. Laser beam welding. 38
3.2.3. Metallography preparation. 42
3.2.4. Microscopic analysis 42
3.2.5. Thermal history. 42
3.2.6. High speed drilling strain gage [21] 43
3.2.7. Vickers hardness test 43
3.2.8. Tensile test 44
3.2.9. Fracture analysis 44
3.3. Instruments and equipments 45
Chapter 4: Experimental results and Discussion 54
4.1 A533 and A572 base metal 54
4.2 Bead on plate result 57
4.2.1. BOP with A533 low alloy steel 58
4.2.2 BOP with High strength low alloy steel A572 60
4.3. Microstructure of dissimilar weld A533 to A572 61
4.3.1. A533 and A572’s continuous cooling transformation 61
4.3.2. Dissimilar weld A533 to A572 heat affected zone 63
4.3.3. Cooling rate and thermal history 70
4.4. Hardness 72
4.5. Residual stress 75
4.6. Tensile tests 79
4.7. Fracture surface analysis 81
Chapter 5: Conclusions 83
Chapter 6: Suggestions and future works 84
References: 85

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