【摘要】：雙相不銹鋼具有優(yōu)良的力學性能和腐蝕性能,被廣泛應用于石油化工、海洋結構和船舶行業(yè)。雙相不銹鋼的優(yōu)異性能是建立在合理的雙相比基礎上,然而焊接后接頭雙相比例失衡嚴重,造成接頭性能顯著降低。在實際應用中手工焊條電弧焊(SMAW)的使用最為普及,所以研究手工焊條電弧焊焊后接頭組織及性能很有必要。本文采用三層三道焊,使用兩種焊條(焊條E2209-16、焊條309MoL)對6mm厚2205雙相不銹鋼進行平板對接試驗,每種焊條分別進行不同焊接位置、不同熱輸入的焊接試驗。重點研究了不同焊接位置、不同熱輸入對接頭微觀組織、力學性能的影響,以及不同工藝參數(shù)對接頭殘余應力的影響。研究表明,焊后接頭沒有出現(xiàn)宏觀缺陷,焊縫成形良好。接頭焊縫區(qū)鐵奧兩相含量差距明顯,焊縫區(qū)奧氏體含量最高,熱影響區(qū)奧氏體含量最低,由于焊條309MoL中Ni元素含量遠遠高于母材和焊條E2209-16,使焊后獲得接頭焊縫區(qū)奧氏體含量比焊條E2209-16獲得接頭高。XRD分析表明所有接頭焊縫區(qū)沒有出現(xiàn)有害次生相。掃描電鏡和能譜分析表明接頭合金元素在熱作用下發(fā)生了擴散遷移,使得冷卻時鐵素體晶界優(yōu)先析出奧氏體,后續(xù)的熱循環(huán)使鐵素體晶內析出大量細小奧氏體。三層三道焊得到的接頭每層焊道之間的奧氏體組織形態(tài)和含量存在差異。接頭力學性能測試表明,焊條309MoL焊接試樣抗拉強度低于焊條E2209-16焊接試樣,且試樣全部斷裂在焊縫。平焊剛性固定試樣延伸率最小,這與接頭較大。彎曲試驗中所有接頭面彎和背彎都沒有出現(xiàn)裂紋,表明接頭塑韌性良好。沖擊測試中熱影響區(qū)沖擊值高于焊縫,但都低于母材,焊縫沖擊斷口斷口存在大量韌窩且全部為韌性斷裂,而熱影響區(qū)斷口存在較大范圍的平齊的解理面或準解理面以及少量韌窩,所以斷裂方式為脆性為主的韌脆混合斷裂機制。接頭硬度值和所在區(qū)域的奧氏體含量相關,熱影響區(qū)硬度值最高,焊縫中蓋面層的硬度值最小。利用ANSYS有限元軟件對焊接過程進行溫度場和應力場模擬計算,結果表明三層三道焊中第二層焊道焊接熱循環(huán)曲線的最高溫度高于其他兩層焊道,達到了2800°C,對接頭冷卻時間產生很大影響,從而影響接頭組織析出含量。接頭下層熱影響區(qū)受到三次熱循環(huán)作用,每次熱循環(huán)最高溫度都超過母材相變溫度。應力場測試表明接頭焊縫區(qū)縱向和橫向殘余應力相反,橫向表現(xiàn)為拉應力,縱向表現(xiàn)為壓應力,橫向殘余應力在遠離焊縫的區(qū)域拉應力逐漸過渡為壓應力最后趨為零,小孔法測試應力與模擬值較吻合。對變形嚴重的板材進行機械矯正,拉伸測試結果顯示矯正后板材抗拉強度略升高,應力應變曲線中屈服階段不明顯,且試樣斷裂于焊縫,斷口存在細小的韌窩,韌性降低。
[Abstract]:Duplex stainless steel has been widely used in petrochemical industry, marine structure and ship industry because of its excellent mechanical and corrosion properties. The excellent properties of duplex stainless steel are based on reasonable double comparison. However, the imbalance of the two phase ratio of welded joints is serious, which results in a significant decrease of joint properties. The use of (SMAW) in manual electrode arc welding is the most popular in practical application, so it is necessary to study the microstructure and properties of welding joint after manual electrode arc welding. In this paper, three layers and three pass welding are used, and two kinds of electrode (electrode E2209-16, 309MoL) are used to test 6mm thick 2205 duplex stainless steel. Each electrode has different welding position and different heat input. The effects of different welding positions and heat input on the microstructure and mechanical properties of the joints and the effects of different process parameters on the residual stress of the joints were studied. The results show that there is no macroscopic defect in the welded joint and the weld is well formed. The difference of iron and oxygen content in weld zone is obvious. The content of austenite in weld zone is the highest, and the content of austenite in heat affected zone is the lowest. The content of Ni element in 309MoL of welding rod is much higher than that of base metal and electrode E2209-16. The austenite content of weld zone obtained after welding is higher than that obtained by electrode E2209-16. XRD analysis shows that no harmful secondary phase appears in all weld areas. SEM and EDS analysis show that the alloy elements in the joints are diffused and migrated under thermal action, which makes the ferrite grain boundary precipitate first during cooling, and the subsequent thermal cycling results in the precipitation of a large amount of fine austenite in the ferrite crystal. The microstructure and content of austenite are different between three layers and three pass welded joints. The mechanical properties of the joint show that the tensile strength of the 309MoL welding specimen is lower than that of the electrode E2209-16 welding specimen, and all the specimens are broken in the weld. The elongation of flat welded rigid fixed specimen is the smallest, which is larger than that of joint. No cracks were found in the bending and back bending of the joints in the bending test, which indicated that the joints had good ductility and toughness. In the impact test, the impact value of the HAZ is higher than that of the weld, but lower than that of the base metal. There are a lot of dimples on the impact fracture surface of the weld and all of them are ductile fracture. However, there are a wide range of flat or quasi cleavage surfaces and a few dimples on the fracture surface of the HAZ, so the fracture mode is ductile-brittle mixed fracture mechanism. The hardness value of the joint is related to the content of austenite in the zone, the hardness value of the heat affected zone is the highest, and the hardness value of the cover layer in the weld is the smallest. The temperature field and stress field of the welding process were simulated by ANSYS finite element software. The results show that the maximum temperature of the thermal cycle curve of the second layer welding pass is 2800 擄C higher than that of the other two layers. It has a great influence on the cooling time of the joint, thus affecting the precipitation content of the joint structure. The heat affected zone of the lower layer of the joint is subjected to three thermal cycles, and the maximum temperature of each thermal cycle is higher than the phase transition temperature of the base metal. The stress field test shows that the longitudinal and transverse residual stresses in the weld zone of the joint are opposite, the transverse stress is tensile stress, the longitudinal stress is compressive stress, the transverse residual stress is gradually transferred to zero compressive stress in the area far away from the weld seam. The stress measured by the small hole method is in good agreement with the simulated value. The tensile test results show that the tensile strength of the plate is slightly increased, the yield stage of the stress-strain curve is not obvious, and the specimen is broken in the weld, there is a small dimple on the fracture surface, and the toughness decreases.
【學位授予單位】：江蘇科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG457.11

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