Ce合金化下FAB法埋弧焊缝组织与性能研究
发布时间：2018-08-04 18:10
【摘要】：FAB(flux aided backing)法埋弧焊是一种利用背面陶质衬垫获得双面成形的单面焊接方法,具有生产效率高、装配简单、焊缝成形质量好等优点,广泛应用于船舶建造、海洋平台、大型储罐等领域钢结构的焊接制造中。在焊接过程中,FAB法埋弧焊的焊接热输入通常在50 kJ/cm以上,使得焊接熔池高温停留时间较长,焊缝中生成大量先共析铁素体和侧板条铁素体,从而降低焊缝金属强韧性,导致焊缝金属性能无法满足使用要求。由此,如何降低大热输入下FAB法埋弧焊缝中先共析铁素体和侧板条铁素体生成量,提高焊缝金属的强韧性成为亟需解决的问题。针对这一问题本文研究了Ce合金化下FAB焊缝金属的组织及性能,取得的研究成果如下:使用田口法设计正交试验,分析讨论了DH36低合金高强钢FAB法埋弧焊中焊接电流、焊接电压、焊接速度及焊丝干伸长四个工艺参数对焊缝成形质量的影响,建立了FAB法埋弧焊接工艺参数与焊缝成形质量的数学模型,优化得出了最优工艺参数组合。通过信噪比(S/N)分析和方差分析(ANOVA)得出,各因素对FAB焊缝成形质量影响程度排序为:焊接电流I干伸长L焊接速度v焊接电压U。FAB法焊接20mm厚DH36低合金高强钢时,最佳工艺参数组合为:焊接电流I=1010A,焊接电压U=32V,焊接速度v=23cm/min,干伸长L=35mm。对不同厚度DH36钢板进行FAB焊接工艺试验,分析了纯Fe粉条件下不同焊接热输入量对FAB法埋弧焊接接头微观组织及力学性能的影响。8mm、12mm、15mm和20mm厚的FAB焊接接头焊缝组织都主要由先共析铁素体(GBF)、侧板条铁素体(FSP)和针状铁素体(AF)构成。随着焊接热输入量增加,晶粒尺寸变大,焊缝中AF含量减少,GBF和FSP含量增加。粗晶热影响区组织是粗大的奥氏体晶粒,晶内有大量细小板条状的贝氏体铁素体,细晶热影响区组织为铁素体+珠光体,并有少量细小贝氏体铁素体。FAB法埋弧焊接20mm厚DH36钢板时,热输入量最大,焊接接头的室温拉伸性能、-20°C冲击功、弯曲性能均无法满足使用要求。试验测定的焊接热影响区不同区域的热循环曲线表明,随着热输入增大,高温停留时间和冷却速率均有较大幅度增加。研究了稀土Ce元素对FAB法埋弧焊缝金属的组织与性能的影响。在FAB埋弧焊剂中加入不同含量CeO2粉,稀土Ce能够过渡到焊缝金属中对夹杂物进行改性,使夹杂物由Al2O3、Si O2、Ti2O3和MnS的复合物转变为Al2O3、SiO2、Ti2O3、MnS、Ce2O2S及CeS的复合物。稀土Ce的加入使焊缝金属中直径小于1.0μm的夹杂物比例明显增加,细小的夹杂物增加了焊缝中诱导AF的形核质点。含Ce夹杂物表层的Ce2O2S和CeS与α-Fe的错配度小是诱导AF形核的主要机理。Ce元素提高了焊缝中AF比例,降低了GBF和FSP比例,显著提高了FAB焊缝金属的抗拉强度、延伸率和低温冲击性能。当焊剂中CeO2含量为3.0 wt.%时,夹杂物密度最大,AF比例高达76%,FAB焊缝金属的抗拉强度高达582 MPa,延伸率为24%,-20°C的V型缺口冲击功高达142J。对FAB焊接熔池中含Ce夹杂物的析出条件及存在形式进行热力学计算。在焊接熔池中,O、S元素同时存在时,Ce总是先进行脱氧反应,Ce的脱氧产物仅有Ce2O3。Ce与S元素生成CeS还是Ce2S3取决于S元素的活度大小。当a[O]0.13,a[S]/a2[O]97.72时,生成夹杂物是CeO2。a[O]0.13,a[S]/a[O]12.59时,生成夹杂物是Ce2O3;当a[O]0.13,12.59a[S]/a[O]263,或a[S]0.51,97.72a[S]/a2[O]134896时,夹杂物是Ce2O2S。当a[S]0.51,a[S]/a[O]263时,夹杂物是Ce2S3。而当a[S]0.51,a[S]/a2[O]134896时,夹杂物是CeS。根据热力学计算结果,对FAB法埋弧焊缝金属中含Ce夹杂物类型进行判定,判定结果与试验测定结果一致。
[Abstract]:FAB (flux aided backing) submerged arc welding is a single side welding method using the backside pottery liner to obtain double side forming. It has the advantages of high production efficiency, simple assembly and good weld forming quality. It is widely used in the welding of steel structures in shipbuilding, offshore platform, large storage tank and so on. In the welding process, the FAB method of submerged arc welding The welding heat input is usually more than 50 kJ/cm, which makes the welding pool stay at high temperature for a long time, producing a large number of pre eutectoid ferrite and side strip ferrite in the weld, thus reducing the strength and toughness of the weld metal, which leads to the failure of the weld metal properties to meet the requirements. Thus, how to reduce the first eutectoid ferrite in the FAB submerged arc weld under the high heat input is reduced. The formation of ferrite and side plate ferrite has become an urgent problem to improve the strength and toughness of weld metal. In this paper, the microstructure and properties of FAB weld metal under Ce alloying are studied. The results obtained are as follows: Using Taguchi method to design orthogonal experiments and analyze and discuss the welding electricity in FAB submerged arc welding of DH36 low alloy high strength steel. The influence of four technological parameters of flow, welding voltage, welding speed and welding wire elongation to weld forming quality, a mathematical model of FAB method for welding arc welding process parameters and weld forming quality was established, and the optimal process parameters were optimized. By means of S/N analysis and variance analysis (ANOVA), each factor was formed on the shape quality of the FAB weld. The influence degree of quantity is: welding current I dry elongation L welding speed V welding voltage U.FAB method to weld 20mm thick DH36 low alloy high strength steel, the optimum process parameters are as follows: welding current I=1010A, welding voltage U=32V, welding speed v=23cm/min, dry elongation L=35mm. to FAB welding process test of different thickness DH36 steel. The influence of different welding heat input on the microstructure and mechanical properties of FAB submerged arc welding joints.8mm, 12mm, 15mm and 20mm thick FAB welded joints are mainly composed of the eutectoid ferrite (GBF), the side plate ferrite (FSP) and the needle ferrite (AF). With the increase of the welding heat input, the grain size becomes larger and the AF content in the weld seam is contained. The content of GBF and FSP increases. The microstructure of the coarse grain heat affected zone is a coarse austenite grain, and there are a large number of fine bainite ferrite in the crystal. The microstructure of the fine crystal heat affected zone is ferrite and pearlite, and a small amount of fine bainite ferrite.FAB method is used to weld 20mm thick DH36 steel, and the heat input is the largest and the welding joint room temperature is the most. The tensile properties, -20 C impact power and bending performance can not meet the requirements of the use. The thermal cycle curves of different regions of the heat affected zone measured by the test show that the high temperature residence time and cooling rate are greatly increased with the increase of heat input. The effect of rare earth Ce elements on the microstructure and properties of the submerged arc weld metal by FAB method is studied. Adding different content of CeO2 powder to the FAB submerged arc welding flux, the rare earth Ce can be transferred to the weld metal to modify the inclusions, so that the inclusions from Al2O3, Si O2, Ti2O3 and MnS are converted to Al2O3, SiO2, Ti2O3, MnS, and the composite. Small inclusions increase the nucleation point of AF in the weld. The mismatch between Ce2O2S and CeS containing the surface of Ce inclusions is the main mechanism to induce AF nucleation, the main mechanism for inducing AF nucleation is.Ce element, which improves the proportion of AF in the weld, reduces the proportion of GBF and FSP, and significantly improves the tensile strength, elongation and low temperature impact properties of the FAB weld metal. When the content of CeO2 is 3 wt.%, the density of inclusions is the largest and the proportion of AF is up to 76%. The tensile strength of the FAB weld metal is 582 MPa, the elongation is 24%, the V type notch impact power of -20 degree C is as high as 142J. to the thermodynamic calculation of the precipitation conditions and the existence form of Ce inclusions in the weld pool of FAB. E always first deoxidize, Ce deoxidize product only Ce2O3.Ce and S element to produce CeS or Ce2S3 depends on the activity of S element. When a[O]0.13, a[S]/a2[O]97.72, the inclusion is CeO2.a[O]0.13, a[S]/a[O]12.59, the inclusion is Ce2O3. The inclusion is Ce2O2S. when a[S]0.51 and a[S]/a[O]263, the inclusion is Ce2S3. and when a[S]0.51, a[S]/a2[O]134896, the inclusion is CeS. according to the thermodynamic calculation result, it determines the type of Ce inclusions in the embedded arc weld metal of FAB method, and the result is in agreement with the test result.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG445
本文编号：2164688
[Abstract]:FAB (flux aided backing) submerged arc welding is a single side welding method using the backside pottery liner to obtain double side forming. It has the advantages of high production efficiency, simple assembly and good weld forming quality. It is widely used in the welding of steel structures in shipbuilding, offshore platform, large storage tank and so on. In the welding process, the FAB method of submerged arc welding The welding heat input is usually more than 50 kJ/cm, which makes the welding pool stay at high temperature for a long time, producing a large number of pre eutectoid ferrite and side strip ferrite in the weld, thus reducing the strength and toughness of the weld metal, which leads to the failure of the weld metal properties to meet the requirements. Thus, how to reduce the first eutectoid ferrite in the FAB submerged arc weld under the high heat input is reduced. The formation of ferrite and side plate ferrite has become an urgent problem to improve the strength and toughness of weld metal. In this paper, the microstructure and properties of FAB weld metal under Ce alloying are studied. The results obtained are as follows: Using Taguchi method to design orthogonal experiments and analyze and discuss the welding electricity in FAB submerged arc welding of DH36 low alloy high strength steel. The influence of four technological parameters of flow, welding voltage, welding speed and welding wire elongation to weld forming quality, a mathematical model of FAB method for welding arc welding process parameters and weld forming quality was established, and the optimal process parameters were optimized. By means of S/N analysis and variance analysis (ANOVA), each factor was formed on the shape quality of the FAB weld. The influence degree of quantity is: welding current I dry elongation L welding speed V welding voltage U.FAB method to weld 20mm thick DH36 low alloy high strength steel, the optimum process parameters are as follows: welding current I=1010A, welding voltage U=32V, welding speed v=23cm/min, dry elongation L=35mm. to FAB welding process test of different thickness DH36 steel. The influence of different welding heat input on the microstructure and mechanical properties of FAB submerged arc welding joints.8mm, 12mm, 15mm and 20mm thick FAB welded joints are mainly composed of the eutectoid ferrite (GBF), the side plate ferrite (FSP) and the needle ferrite (AF). With the increase of the welding heat input, the grain size becomes larger and the AF content in the weld seam is contained. The content of GBF and FSP increases. The microstructure of the coarse grain heat affected zone is a coarse austenite grain, and there are a large number of fine bainite ferrite in the crystal. The microstructure of the fine crystal heat affected zone is ferrite and pearlite, and a small amount of fine bainite ferrite.FAB method is used to weld 20mm thick DH36 steel, and the heat input is the largest and the welding joint room temperature is the most. The tensile properties, -20 C impact power and bending performance can not meet the requirements of the use. The thermal cycle curves of different regions of the heat affected zone measured by the test show that the high temperature residence time and cooling rate are greatly increased with the increase of heat input. The effect of rare earth Ce elements on the microstructure and properties of the submerged arc weld metal by FAB method is studied. Adding different content of CeO2 powder to the FAB submerged arc welding flux, the rare earth Ce can be transferred to the weld metal to modify the inclusions, so that the inclusions from Al2O3, Si O2, Ti2O3 and MnS are converted to Al2O3, SiO2, Ti2O3, MnS, and the composite. Small inclusions increase the nucleation point of AF in the weld. The mismatch between Ce2O2S and CeS containing the surface of Ce inclusions is the main mechanism to induce AF nucleation, the main mechanism for inducing AF nucleation is.Ce element, which improves the proportion of AF in the weld, reduces the proportion of GBF and FSP, and significantly improves the tensile strength, elongation and low temperature impact properties of the FAB weld metal. When the content of CeO2 is 3 wt.%, the density of inclusions is the largest and the proportion of AF is up to 76%. The tensile strength of the FAB weld metal is 582 MPa, the elongation is 24%, the V type notch impact power of -20 degree C is as high as 142J. to the thermodynamic calculation of the precipitation conditions and the existence form of Ce inclusions in the weld pool of FAB. E always first deoxidize, Ce deoxidize product only Ce2O3.Ce and S element to produce CeS or Ce2S3 depends on the activity of S element. When a[O]0.13, a[S]/a2[O]97.72, the inclusion is CeO2.a[O]0.13, a[S]/a[O]12.59, the inclusion is Ce2O3. The inclusion is Ce2O2S. when a[S]0.51 and a[S]/a[O]263, the inclusion is Ce2S3. and when a[S]0.51, a[S]/a2[O]134896, the inclusion is CeS. according to the thermodynamic calculation result, it determines the type of Ce inclusions in the embedded arc weld metal of FAB method, and the result is in agreement with the test result.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG445
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