不同C、Ni成分焊丝及工艺参数对5%Mn钢焊接性的影响

发布时间：2018-05-11 07:32

本文选题：5%Mn + 海洋平台　；参考：《昆明理工大学》2017年硕士论文

【摘要】：作为最新研制的690MPa级高强高韧海洋平台用5%Mn钢,Mn的大量加入,不利于该种钢的焊接性能。因此,为了为5%Mn钢的工程化应用提供理论与试验依据,对该种钢的焊接材料及焊接工艺进行研究就显得尤为重要。为确定合适的气体保护焊焊接材料,本文采用两种Mn-Ni-Mo系列焊丝对20mm厚5%Mn钢进行混合气体保护焊接,研究了不同C、Ni成分下焊接接头组织与性能变化规律,并通过热模拟技术,对不同C、Ni成分下焊缝金属组织连续冷却转变CCT图进行研究;通过斜Y抗裂性试验研究了工业试制30mm厚5%Mn钢的冷裂纹敏感性,并研究了不同热输入和道间温度对30mm厚5%Mn钢接头组织与性能的影响规律,结果如下:(1)通过两种Mn-Ni-Mo焊丝对20mm厚5%Mn钢进行焊接,分析不同C、Ni成分下接头焊缝金属组织与性能变化规律,结果表明:高碳较低镍焊缝金属,末道焊缝组织由板条贝氏体和少量马氏体构成。受焊接热循环的影响,焊道间再热区热影响区产生大量粒状贝氏体,整个焊缝金属强度高、韧性差、硬化明显;而低碳较高镍焊缝金属,末道焊缝由先共析铁素体和针状铁素体构成,焊道间热影响区先共析铁素体略有增加,但仍以针状铁素体为主,整个焊缝金属强度较低,但韧性优异;同时焊缝金属中M-A组元体积分数的增加,大角度晶界所占比例减少以及夹杂物数量增加,也是导致高碳低镍焊丝焊缝韧性低的原因。(2)通过对不同C、Ni成分焊缝金属连续冷却转变CCT曲线进行研究,结果表明:当t8/3≤1800s时,随着t8β的增加,高碳较低镍焊缝金属显微组织变化规律为:LM+LB-→LM+LB+GB→GB,而低碳较高镍焊缝金属显微组织变化规律为:AF+GB→GB→GB+F+P。(3)采用低碳较高镍焊丝,对30mm厚5%Mn钢进行斜Y抗裂性试验,研究该种钢冷裂纹敏感性,结果表明:预热温度为0℃、60℃和100℃时,具有很高的根部和断面裂纹率,且变化无规律;预热温度为120℃、150℃和200℃时,随着温度升高,根部和断面裂纹率降低,200℃时根部和断面裂纹率分别降至4.47%和1%。裂纹起裂位置均为上半部分V型缺口根部,且容易沿热影响区粗品[区奥氏体晶界及马氏体板条边界扩展,六种预热温度下均无表面裂纹产生。(4)采用低碳较高镍焊丝,在热输入为12kJ/cm、15kJ/cm和18kJ/cm下对30mm厚5%Mn钢接头组织及性能进行研究,结果表明:不同热输入下焊缝金属显微组织均由先共析铁素体、针状铁素体和贝氏体构成。随着热输入增加,先共析铁素体含量增加,针状铁素体尺寸增大,焊道热影响区粒状贝氏体含量增加,焊缝金属中夹杂物数密度、所占面积百分比增加,可作为裂纹源的大尺寸夹杂物数密度增加,导致焊缝金属抗拉强度和屈服强度、低温韧性、硬度随热输入的增加而降低。接头热影响区显微组织由粗大的板条马氏体构成,粗晶区原始奥氏体晶粒严重长大,且存在与基体呈“脱离”状态的氧化物夹杂,导致热影响区低温韧性较差。热输入为18kJ/cm时,接头热影响区粗晶区奥氏体晶粒尺寸明显增大,导致韧性较低。(5)采用低碳较高镍焊丝,在100℃、120℃道间温度下对30mm厚5%Mn钢对接头焊缝性能进行研究,结果表明:随着道间温度升高,焊缝金属显微组织中先共析铁素体含量,针状铁素体尺寸,焊道热影响区粒状贝氏体含量,夹杂物尺寸,均略有增加,从而导致焊缝金属屈服强度和低温韧性略有降低。接头热影响区低温冲击功分别为19J、47J,降低道间温度恶化了接头热影响区韧性。
[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.

【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.11

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