A STUDY OF ELECTROCHEMICAL BEHAVIOUR OF VARIOUS THERMAL HISTORY ZONES AND DIFFERENT PHASE STRUCTURES ON THE WELDMENT FOR LOW ALLOY STEEL 16Mn IN NITRAfE SOLUTION

The electrochemical behaviour, including free corrosion potential, free corrosion current density and polarization curve, of various thermal history zones on the weldment was measured in this paper. The weldment consisted of matrix, tempering zone. incomplete normalized zone, normalized zone, overtemperature zone, fusion line zone and weld metal zone. The electrochemical behaviour of the ferrite, pearlite and mixed structure in various zones have successfully measured. The results showed that there was a difference of free corrosion potential which is smaller than ca. 200mV between various zones and about 20-150mV potential difference between ferrite and pearlite in every zone. The free cormsion potential of fusion line zone was the most negative between various zones. The free corrosion potential of pearlite was some dozens mV more negative than ferrite. The corrosion course of various zones and of different phase structures on the weldment and their effect on corrosion attack of weldment were discussed.

Defect detection in brazed weldment with lattice structure using ultrasonic Lamb wave technique

In this paper, defects detection in brazed weldment with lattice structure is studied using ultrasonic Lamb wave. Based on the ultrasonic guided wave theory, the frequency dispersion curves for phase and group velocity of I Cr18Ni9Ti are obtained by solving the Rayleigh-Lamb equation. The incident angles of different modes are determined through theoretical calculation and experimental analyses. Artificial defects of through-wall slots with different dimensions are made and tested. Experimental scattering effects of the fundamental symmetric mode S2 and asymmetric modes A1 and A0 are analysed and compared. The results show that mode Ao is suitable for detecting artificial defect, and the amplitude of the received signals are in good agreement with the defect size. Brazed weldment specimen containing lack of brazing with certain dimensions is made. Using the same methodology, scattering effects produced by weld defects are measured. The results show that the clutter wave brought about by the filler metal will certainly disturbs the identification of defect signal. But, when the defect is 3.0 mm in width, the presented mode Ao could be used potentially.

Simulation and experiments of ultrasonic propagation in nickel-based alloy weldments

In order to obtain good understanding of complicated beam propagation behaviors in nickel-based alloy weldments , ray tracing simulation is established to predict the ultrasonic beam path in a special welded structure of dissimilar steels. Also experimental examinations are carried out to measure the ultrasonic beam paths in the weldment. Then comparisons of the modeling predictions with experimental results are presented to reveal the complicated beam propagation behaviors.

Locating flaws in anisotropic and inhomogeneous weldments using ray tracing method

Ultrasonic inspections on nickel-based alloy weldments meets some difficulties due to the curvilinear propagating paths will appear in both anisotropic and inhomogeneons welded joints. Thus, it is difficult to determine the exact location of flaws using the traditional ultrasonic testing method which is based on the assumption that the sound beam will propagate in straight lines. In order to overcome this problem, we provide a new model-based inspection approach to locate the flaws in the nickel-based alloy weldments. Furthermore, some experimental examinations are carried out to compare the locating accuracy between the traditional and the modeled-based approach. It shows that the provided model-based inspection method is more accurate than the traditional method in inspection of the nickel-based alloy weldments.

Improvement in hot corrosion resistance of dissimilar alloy 825 and AISI 321 CO2-laser weldment by HVOF coating in aggressive salt environment at 900℃

This study investigated the hot corrosion performance of a dissimilar weldment of Ni-based superalloy and stainless steel joined by CO2-laser welding and improved by high-velocity oxy-fuel(HVOF)coating in a Na2SO4-60wt%V2O5 environment at 900℃.A dissimilar butt joint of AISI 321 and alloy 825 was fabricated by CO2-laser welding with low heat input after obtaining the optimum welding parameters by bead-on-plate trials.The metallurgical and mechanical properties of the laser weldment were evaluated.The tensile test results indicated the occurrence of fracture in the base metal AISI 321 side.The HVOF process was employed to coat Ni-20wt%Cr on the weldment.To evaluate the surface morphology of the corrosion products formed on the uncoated and Ni-20wt%Cr-coated weldments,scanning electron microscopy(SEM)analysis was performed.Energy-dispersive spectroscopy(EDS)was used to determine the different elements present on the surface scales.The existence of oxide phases on the weldments was determined by X-ray diffraction(XRD).The cross sections of the weldments were characterized by SEM with EDS line mapping analysis.The results indicated that the Ni-20wt%Cr-coated weldment exhibited superior hot corrosion resistance due to the development of Cr2O3 and NiCr2O4 protective oxide scales.

Models for Assessment and Computational Analysis of Hardness of the Heat Affected Zone in Water Cooled Aluminum Weldment

Models have been derived for assessment and computational analysis of the hardness of the heat affected zone (HAZ) in aluminum weldment. The general model;γ = 1.2714[(αβ/α + β)] was found to predict the HAZ hardness of aluminum weldment cooled in water as a function of the HAZ hardness of both mild steel and cast iron welded and cooled under the same conditions. The maximum deviations of the model-predicted HAZ hardness values γ, α and β from the corresponding experimental values γexp, αexp and βexp were less than 0.02% respectively.

Defect detection in brazed weldment with lattice structure using acoustic shadow technique

Brazed weldment with lattice structure has been widely used in aerospace industry. The non-destructive testing is often difficult because of the poor inspection accessibility. The present paper illustrates how the plane-like defect lack of brazing can be detected rapidly in this kind of structure by using ultrasonic Lamb wave. Experimental weldments are prepared and weld defect are tested using S2 mode Lamb wave. Acoustic shadow technique is employed based on Lamb wave testing method. The character of the tested D-scan image and A-scan signal is studied. The experimental results show that acoustic shadow based Lamb wave testing method is effective in detecting through-wall lack of brazing. Meanwhile, the D-scan tested data can be rapidly collected and easily interpreted compared with pulse echo bused Lamb wave testing method.

Focusing behaviors of ultrasonic phased arrays in anisotropic and inhomogeneous weldments

It meets some difficulties in the case of ultrasonic phased arrays testing for the nickel-based alloy welded joint, since the ultrasound will propagate with curvilinear paths in this kind anisotropic joint. Thus, it is hard to calculate the phased array time delays properly according to the traditional focusing approach, which is based on the assumption that the sound beam will propagate in straight lines. In order to focus the phased arrays beam in this kind anisotropic joint, we provide a modified focusing approach by combining the ray tracing method and the bisectional searching optimization. With the help of this focusing approach, the curved ray path connecting each element position in phased arrays to the expected focus point in weldments can be determined, so that it can be used to calculate the proper time delay and control the beam focusing in the anisotropic weldment. Furthermore, some experimental examinations are carried out to compare the focusing behaviors between the traditional and the modified focusing approach. It shows that the provided focusing approach is more accurate than the traditional method in the case of inspection on the nickel-based alloy weldments.

Distribution of Inherent Strains and Residual Stressesin Medium Thickness Plate Weldment

A fundamental theory for the analysis of residual welding stresses and deformation based on the inherent strain distribution along the welded joint is introduced. Distribution of inherent strains and longitudinal residual stresses in medium thickness plate weldment is calculated and analyzed. A new method of calculating inherent strains and longitudinal residual stresses is proposed.

Predictability of Hardness of the Heat Affect Zone in Aluminum Weldments Cooled in Palm Oil Based on Hardness of Similarly Cooled Mild Steel and Cast Iron Weldments

The predictability of hardness of the heat affected zone (HAZ) in aluminum weldments cooled in palm oil, based on hardness of similarly cooled mild steel and cast iron weldments has been ascertained. The general model: α = 1.2769? indicates that HAZ hardness of aluminium weldment is dependant on the ratio of product to sum of HAZ hardness of mild steel and cast iron weldments cooled in palm oil under the same conditions. The maximum deviations of the model-predicted HAZ hardness values α, μ and β from the corresponding experimental values αexp, μexp and βexp were less than 0.04% indicating the reliability and validity of the model.

Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was deter- mined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treated steel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested materials. This was manifested mainly as a considerable loss in the ductility of tensile specimens and a decrease in the time to failure and threshold stress of constant load specimens. The 308L weld metal exhibited the highest, and the 304L solution treated steel the lowest, resistance to hydrogen embrittlement. Hydrogen embrittlement was associated with the formation of strain induced martensite as well as a transition from brittle to ductile fracture morphology onwards the centre of the specimens.

Pitting and stress corrosion cracking studies on AISI type 316N stainless steel weldments

Pitting and stress corrosion cracking(SCC) studies on the 316 N stainless steel(SS) weldments in aswelded(AW) and thermally aged(solution annealing(SA), 550C/4 h and 750C/1 h) conditions were carried out in acidic and acidic chloride media. Pitting corrosion and SCC resistance was the highest for SA weldment, which was attributed to homogenization of microstructural and microchemical heterogeneities during solution annealing. SA specimen showed the most stable passive film as compared to AW weldment because of higher amount of delta-ferrite in AW weld metal, which resulted in an increased heterogeneity and inferior SCC resistance in AW. Stability of passive film was found to be adversely affected due to heat treatments(at 550C/4 h and 750C/1 h) because of the precipitation of carbide and sigma phases.

Cavitation erosion behavior of nickel-aluminum bronze weldment

Cavitation erosion behavior of nickel-aluminum bronze(NAB) weldment in 3.5% NaCl aqueous solution was studied by magnetostrictive vibratory device for cavitation erosion. The results show that cavitation erosion resistance of the weld zone(WZ) of the weldment is superior to that of the base metal. SEM observation of eroded specimens reveals that the phases undergoing selective attack by the stress of cavitation erosion at the early stage of cavitation erosion are: martensite in the WZ, α phase in the heat-affected zone(HAZ) and eutectoidal phase in the base metal; the microcracks causing cavitation damage initiate at the phase boundaries.

Development of Fuzzy Logic System to Predict the SAW Weldment Shape Profiles

一个模糊模型被介绍预言包括热的形状的沉没的弧焊接(锯) 的焊接形状侧面影响了地区(HAZ ) 。锯 bead-on-plates 被跟随一个完整的因素的设计矩阵焊接。设计矩阵由焊接进程参数的输入的三个层次组成了。焊接是 cross-sectioned 并且蚀刻，并且地区被测量。一种印射的技术被用来测量焊接地区的各种各样的片断。这些印射的地区被用来造一个模糊逻辑模型。模糊模型的会员功能为焊接地区的精确预言被选择。模糊模型进一步为一套测试用例数据被测试。模糊逻辑模型预言的焊接地区与试验性地获得的形状侧面和靠近的同意在之间相比二被注意。为焊接地区和模糊逻辑模型开发的印射的技术能被用于 SAW 过程的联机控制。从 SAW 模糊逻辑模型熔化和 HAZ 罐头的一个评价也被开发。

Characterization of the Type IV crack in high Cr steel weldments

The weldments for several types of high Cr ferritic steels were investigated to understand the fracture mechanism of the Type IV crack. The creep testing shows that the Type IV cracking is more likely to occur at the lower stress level, whereas at the higher stress level the crack shifts towards parent metal. The microstructures observed in the HAZ for all the materials are mostly tempered lath martensites. There was no δ ferrites found in all creep specimens.

不同蠕变条件下耐热钢焊接件的空洞损伤演化

针对两种马氏体耐热钢焊接接头(F92/Co3W2和Co3W2/Co3W2)在105~250 MPa和873~948 K条件下开展蠕变拉伸测试,利用Larson-Miller参数法外推不同温度下焊接接头服役100000 h寿命对应的蠕变断裂许用应力,研究其在不同蠕变条件下的空洞损伤规律.随着外加应力的降低,两种焊件的断裂位置、断裂模式及断裂机制均发生了转变,从位于母材的穿晶塑性断裂变为细晶热影响区的沿晶脆性断裂(即Ⅳ型断裂).针对断口区域的空洞损伤变化规律的研究表明:(1)当断裂模式由塑性断裂转变为脆性断裂时,断口附近空洞会出现突变,塑性断口空洞“个头大数量少”而脆性断口空洞“个头小数量多”;(2)在相同断裂模式下,随蠕变应力的减小,空洞按照“尺寸变大、数量密度增大及面积分数增大”的规律变化;(3)Ⅳ型断口处空洞存在合并链接现象,其方向与应力方向垂直.

Creep Behavior and Life Assessment of a Novel Heat-Resistant Austenite Steel and Its Weldment

In the present study, creep activation energy for rupture was obtained as 221-348 kJ/mol for 22Cr15Ni3.5 CuNbN due to the precipitation-hardening mechanism. The extrapolation strength of creep rupture time of 10~5 h at 923 K for22 Cr15 Ni3.5 CuNbN is more valid(83.71 MPa) predicted by the Manson-Haferd method, which is superior to other commercial heat-resistant steels. The tensile creep tests ranging from 180 to 240 MPa at 923 K were conducted to investigate creep deformation behavior of welded joint between a novel heat-resistant austenite steel 22Cr15Ni3.5 CuNbN and ERNiCrCoMo-1 weld metal. Apparent stress exponent value of 6.54 was obtained, which indicated that the ratecontrolled creep occurred in weldment during creep. A damage tolerance factor of 6.4 in the weldment illustrates that the microstructural degradation is the dominant creep damaging mechanism in the alloy. Meanwhile, the welded joints perform two types of deformation behavior with the variation in applied stress, which resulted from the different parts that govern the creep processing. Also, the morphology evolution of the fracture surfaces confirms the effects of stress level and stress state.

某产品大型铝焊接件防变形控制

本文对承制的某项目配套大型焊接件,在实际生产研究过程中焊接工艺设计的依据、工艺技术的实施过程和焊接方法进行了探究,通过制定一系列的措施,控制了该产品的焊接收缩、变形,实现了设计功能,完成了生产任务,为之后同类产品的焊接工艺改进提升提供了一定的理论和操作依据。

对接接头焊件缺陷空间定位及分布特征研究

为实现对接接头激光焊件缺陷的空间定位及可视化,添加辅助块将其转换为T形接头焊件.基于无标识旋转视差法获取了焊件X线检测图像,建立了缺陷空间定位的数学模型.实现了焊件缺陷的深度、偏移量、沿焊缝纵向分布、缺陷大小等空间位置数据的自动提取,并对缺陷空间定位模型进行了无损伤验证.试验结果表明:80个预设空间位置气孔缺陷的深度平均相对误差为0.21%,偏移量平均相对误差为0.71%,沿焊缝纵向分布无误差.创建的焊件三维模型实现了批量气孔缺陷的空间再现.通过统计分析获得了批量气孔缺陷的空间分布特征,可为该类焊件的焊接工艺修订、连接质量判定及结构完整性评价等奠定良好基础.