本文選題：5%Mn + 海洋平臺(tái)��； 參考：《昆明理工大學(xué)》2017年碩士論文

【摘要】：作為最新研制的690MPa級(jí)高強(qiáng)高韌海洋平臺(tái)用5%Mn鋼,Mn的大量加入,不利于該種鋼的焊接性能。因此,為了為5%Mn鋼的工程化應(yīng)用提供理論與試驗(yàn)依據(jù),對(duì)該種鋼的焊接材料及焊接工藝進(jìn)行研究就顯得尤為重要。為確定合適的氣體保護(hù)焊焊接材料,本文采用兩種Mn-Ni-Mo系列焊絲對(duì)20mm厚5%Mn鋼進(jìn)行混合氣體保護(hù)焊接,研究了不同C、Ni成分下焊接接頭組織與性能變化規(guī)律,并通過熱模擬技術(shù),對(duì)不同C、Ni成分下焊縫金屬組織連續(xù)冷卻轉(zhuǎn)變CCT圖進(jìn)行研究;通過斜Y抗裂性試驗(yàn)研究了工業(yè)試制30mm厚5%Mn鋼的冷裂紋敏感性,并研究了不同熱輸入和道間溫度對(duì)30mm厚5%Mn鋼接頭組織與性能的影響規(guī)律,結(jié)果如下:(1)通過兩種Mn-Ni-Mo焊絲對(duì)20mm厚5%Mn鋼進(jìn)行焊接,分析不同C、Ni成分下接頭焊縫金屬組織與性能變化規(guī)律,結(jié)果表明:高碳較低鎳焊縫金屬,末道焊縫組織由板條貝氏體和少量馬氏體構(gòu)成。受焊接熱循環(huán)的影響,焊道間再熱區(qū)熱影響區(qū)產(chǎn)生大量粒狀貝氏體,整個(gè)焊縫金屬強(qiáng)度高、韌性差、硬化明顯;而低碳較高鎳焊縫金屬,末道焊縫由先共析鐵素體和針狀鐵素體構(gòu)成,焊道間熱影響區(qū)先共析鐵素體略有增加,但仍以針狀鐵素體為主,整個(gè)焊縫金屬強(qiáng)度較低,但韌性優(yōu)異;同時(shí)焊縫金屬中M-A組元體積分?jǐn)?shù)的增加,大角度晶界所占比例減少以及夾雜物數(shù)量增加,也是導(dǎo)致高碳低鎳焊絲焊縫韌性低的原因。(2)通過對(duì)不同C、Ni成分焊縫金屬連續(xù)冷卻轉(zhuǎn)變CCT曲線進(jìn)行研究,結(jié)果表明:當(dāng)t8/3≤1800s時(shí),隨著t8β的增加,高碳較低鎳焊縫金屬顯微組織變化規(guī)律為:LM+LB-→LM+LB+GB→GB,而低碳較高鎳焊縫金屬顯微組織變化規(guī)律為:AF+GB→GB→GB+F+P。(3)采用低碳較高鎳焊絲,對(duì)30mm厚5%Mn鋼進(jìn)行斜Y抗裂性試驗(yàn),研究該種鋼冷裂紋敏感性,結(jié)果表明:預(yù)熱溫度為0℃、60℃和100℃時(shí),具有很高的根部和斷面裂紋率,且變化無規(guī)律;預(yù)熱溫度為120℃、150℃和200℃時(shí),隨著溫度升高,根部和斷面裂紋率降低,200℃時(shí)根部和斷面裂紋率分別降至4.47%和1%。裂紋起裂位置均為上半部分V型缺口根部,且容易沿?zé)嵊绊憛^(qū)粗品[區(qū)奧氏體晶界及馬氏體板條邊界擴(kuò)展,六種預(yù)熱溫度下均無表面裂紋產(chǎn)生。(4)采用低碳較高鎳焊絲,在熱輸入為12kJ/cm、15kJ/cm和18kJ/cm下對(duì)30mm厚5%Mn鋼接頭組織及性能進(jìn)行研究,結(jié)果表明:不同熱輸入下焊縫金屬顯微組織均由先共析鐵素體、針狀鐵素體和貝氏體構(gòu)成。隨著熱輸入增加,先共析鐵素體含量增加,針狀鐵素體尺寸增大,焊道熱影響區(qū)粒狀貝氏體含量增加,焊縫金屬中夾雜物數(shù)密度、所占面積百分比增加,可作為裂紋源的大尺寸夾雜物數(shù)密度增加,導(dǎo)致焊縫金屬抗拉強(qiáng)度和屈服強(qiáng)度、低溫韌性、硬度隨熱輸入的增加而降低。接頭熱影響區(qū)顯微組織由粗大的板條馬氏體構(gòu)成,粗晶區(qū)原始奧氏體晶粒嚴(yán)重長大,且存在與基體呈“脫離”狀態(tài)的氧化物夾雜,導(dǎo)致熱影響區(qū)低溫韌性較差。熱輸入為18kJ/cm時(shí),接頭熱影響區(qū)粗晶區(qū)奧氏體晶粒尺寸明顯增大,導(dǎo)致韌性較低。(5)采用低碳較高鎳焊絲,在100℃、120℃道間溫度下對(duì)30mm厚5%Mn鋼對(duì)接頭焊縫性能進(jìn)行研究,結(jié)果表明:隨著道間溫度升高,焊縫金屬顯微組織中先共析鐵素體含量,針狀鐵素體尺寸,焊道熱影響區(qū)粒狀貝氏體含量,夾雜物尺寸,均略有增加,從而導(dǎo)致焊縫金屬屈服強(qiáng)度和低溫韌性略有降低。接頭熱影響區(qū)低溫沖擊功分別為19J、47J,降低道間溫度惡化了接頭熱影響區(qū)韌性。
[Abstract]:As a newly developed 690MPa grade high strength and tough marine platform with 5%Mn steel, the addition of Mn is not conducive to the welding performance of this kind of steel. Therefore, in order to provide theoretical and experimental basis for the engineering application of 5%Mn steel, it is particularly important to study the welding material and welding process of this kind of steel. In this paper, two kinds of Mn-Ni-Mo series welding wire were used to protect 20mm thick 5%Mn steel with mixed gas protection welding. The changes of microstructure and properties of welded joints under different C and Ni components were studied. The continuous cooling and transformation of weld metal structure under different C and Ni components was studied by thermal simulation technology. The cold crack sensitivity of 30mm thick 5%Mn steel is tested by industrial trial, and the influence of different heat input and inter channel temperature on the microstructure and properties of 30mm thick 5%Mn steel joint is studied. The results are as follows: (1) welding the 20mm thick 5%Mn steel through two kinds of Mn-Ni-Mo wire, and analyzing the change law of the microstructure and properties of the weld metal under different C and Ni components, and the result table With the influence of the welding heat cycle, a large amount of granular bainite is produced in the heat affected zone between the weld and the weld metal is high, the toughness is poor, and the hardening is obvious, while the low carbon high nickel weld metal and the final weld are composed of the first eutectoid ferrite and the end weld. The formation of acicular ferrite, the first eutectoid ferrite in the heat affected zone between the welds is slightly increased, but it is still mainly with acicular ferrite. The strength of the whole weld metal is low, but the toughness is excellent. At the same time, the volume fraction of M-A component in the weld metal is increased, the proportion of the large angle grain boundary is reduced and the number of inclusions is increased. It is also the cause of high carbon low nickel welding wire welding. The reason of low fracture toughness. (2) through the continuous cooling of CCT curves of different C and Ni components, the results show that when t8/3 is less than 1800s, with the increase of T8 beta, the microstructure changes of high carbon and low nickel weld metal microstructure is LM+LB-, LM+LB+GB to GB, and the microstructure changes of low carbon and higher nickel weld metal are: AF+GB to G B / GB+F+P. (3) with low carbon and higher nickel welding wire, the anti crack resistance test of 30mm thick 5%Mn steel was carried out. The cold crack sensitivity of the steel was studied. The results showed that the crack rate of the root and section was high at the temperature of 0, 60 and 100, and the change was not regular, and the temperature was 120, 150 and 200. The crack rate of the section is reduced, and the crack rate of the root and section crack to 4.47% and the 1%. crack initiation at 200 c are both the upper part of the V type notch root, and it is easy to expand along the boundary of the austenite grain and martensitic slats in the area of the heat affected Zone, and there is no surface crack in the six preheating temperatures. (4) the low carbon and higher nickel welding wire is used in the heat transfer. The microstructure and properties of 30mm thick 5%Mn steel joint are studied under 12kJ/cm, 15kJ/cm and 18kJ/cm. The results show that the microstructure of weld metal under different heat input consists of the eutectoid ferrite, acicular ferrite and bainite. With the increase of heat input, the content of the eutectoid ferrite increases, the size of the acicular ferrite increases, and the heat affected zone of the weld channel is increased. As the content of granular bainite increases, the number density of inclusions in the weld metal increases and the number density of large size inclusions can be increased as the source of crack, which leads to the tensile strength and yield strength of the weld metal, low temperature toughness and hardness with the increase of heat input. The original austenite grain in the coarse grain region is seriously grown, and there is an oxide inclusion in the "detached" state of the matrix, which leads to the poor toughness at low temperature in the heat affected zone. When the heat input is 18kJ/cm, the austenite grain size of the coarse grain region of the joint heat affected zone is obviously increased, and the toughness is lower. (5) the low carbon and higher nickel welding wire is used at 100, 120 degrees C. The results show that the content of eutectoid ferrite, the size of acicular ferrite, the content of granular bainite and the size of inclusions in the heat affected zone of the weld metal are slightly increased with the increase of the inter channel temperature, which leads to the yield strength and low temperature toughness of the weld metal. The low temperature impact energy of the joint heat affected zone is 19J and 47J respectively, and the inter channel temperature reduces the toughness of the heat affected zone of the joint.

【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG457.11

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