Special features of heat treatment of welded joints in large systems in the construction of nuclear power stations

Special features of heat treatment of zones of welded joints in welding of systems of nuclear power stations in the assembling conditions are described. Design features of the equipment for heating the zones of the welded joints and special features of the heat treatment conditions are outlined.     

Effect of welding technology on the mechanical properties of welded joints in pipes for deep water offshore gas pipelines

Results of investigations into the dependence of mechanical properties of welded joints of pipes for offshore pipelines on welding conditions are presented. In particular, the results show that the mechanical properties of pipes of the strength categories K60 (X70) and K56 (X65) are influenced mainly by the heat input, the fracture toughness of welded joints, and pipes of a high strength category are lower by 30–35% than in the case of the K56 (X65) pipes. The hardness of the weld metal in the upper layers is 15–17% higher for automatic submerged arc welding and in the lower layers for gas-shielded automatic arc welding. In inspecting the mechanical properties of the welded joints, special attention must be given to the longitudinal welded joints in the pipes.     

Special features of metallurgical processes in plasma welding of chromium bronze

The metallurgical processes taking place in the weld pool in plasma welding of chromium bronze are investigated. The reasons for the formation of defects, hot cracks, and pores are determined, and measures that should be taken to prevent the formation of these defects are indicated.     

Special features of the formation of welded joints in vertical laser-arc welding of low-alloy steels

ABSTRACT

Investigations were carried out into the special features of the technology of vertical laser-arc welding of large structures made of high-strength and low-alloy steels with a variable welding gap and a large root face.

The parameters of the conditions of vertical laser-arc welding of root passes in the low-alloy steel 30–40 mm thick with a root face of 10 mm (welding speed, the amplitude and frequency of transverse oscillations, the intensity of welding current, arc voltage, laser radiation power) resulting in the formation of high-quality welded joints are determined. The experimental results show that the laser radiation power, required for producing continuous penetration of the root face, depends on the thickness of the parent metal: for the metal thickness of 14–30 mm the sufficient laser radiation power is 3.8 kW, for a thickness of 40 mm it is no less than 4.6 kW to penetrate a depth of 5 mm.

The welded joints have a fine-dispersed acicular structure of the martensitic – bainitic type. The experimental results were used to develop a technology of welding of low-alloy steels of different thickness using robotic equipment.     

Effect of the energy parameters of the welding process on the structure and properties of welded joints in low-alloy steels

The results of investigations of the effect of the pulsed welding process on the structure and mechanical properties of welded joints in low-alloy steels are presented. It is shown that the pulsed welding conditions improve the homogeneity of the structure and reduce the grain size of the metal of the welded joint and the heat-affected zone (HAZ). Changes in the structure increase the ductility of the welded joint.     

Effect of vibroimpact treatment on the physical and mechanical properties of the surface layer of welded joints in rails

The formation of the hardened layer on the surface of the welded joint in the railhead by the method of vibroimpact hardening in an electromagnetic impact action machine is discussed. The procedure and results of investigations of the effect of vibroimpact hardening on the physical and mechanical properties of the welded joints in rails are described.     

热矫形温度对6N01铝合金接头组织与性能的影响

对6N01-T5铝合金焊接接头进行了不同温度的热矫形,研究了矫形温度对接头微观组织及力学性能的影响规律。结果表明,250℃内加热时接头强度和焊缝区硬度有微量上升,HAZ和母材区硬度逐渐变大;高于250℃时强度和硬度开始下降,软化区范围加宽,分别向母材和淬火区方向延伸,高温下性能恶化严重;150℃~200℃加热时易发生弯断,且弯断角随温度升高而减小。室温时,接头母材区析出相为GP区和β″,硬度值较低,热影响区软化区晶内在只有粗大析出相;250℃加热时,母材区开始析出β′相,在β″和β'的析出转变期接头硬度与强度出现峰值,软化区因重新析出β'/β″相得到强化,拉伸断于焊缝;450℃加热时,接头处于严重过时效状态,无弥散析出相,硬度和强度降低。     

Effect of friction welding parameters and heat treatment on the quality of welded joints in creep-resisting deformable nickel alloys

Methods of friction welding creep-resisting deformable nickel alloys and heat treatment are investigated. Welding conditions are selected. The results of mechanical tests and the determination of short- and long-term strength and impact bending resistance are presented, and the data obtained in metallographic and fractographic studies of the welded joints are described.     

Special features of the formation of the structure of rotational friction welded joints in VZh175 creep-resisting wrought nickel alloy

ABSTRACT

The finite element method is used to construct the model for the determination of the temperature fields and strains in the welded joint zones. The effect of the welding conditions in the structure and mechanical properties of the welded joints is investigated. The mechanism of formation of the welded joint in the rotational friction welding of VZh175 nickel alloy is described.     

Effect of interpass temperature on microstructure,impact toughness and fatigue crack propagation in joints welded using the GTAW process on steel ASTM A743-CA6NM

Mainly due to their great toughness, martensitic stainless steels are used for manufacturing hydraulic turbines. However, these steels have some restrictions regarding regions recovered by welding, mainly due to the formation of non-quenched martensite, which causes a reduction in toughness. Considering repair of hydraulic turbines, there is a great interest in developing welding procedures that increase impact toughness and avoid post-welding heat treatment (TTPS). This study aims to analyse the influence of interpass temperature on microstructure, impact toughness and fatigue crack propagation in multipass welded joints on martensitic stainless steel CA6NM, using AWS410NiMo filler metal and the gas tungsten arc welding (GTAW) process. In the sample with interpass temperature of 80°C, influence of the interpass temperature on the formation of ferrite δ, with intragranular formation in the two-phase δ field, was observed, while in the sample welded at 150°C, the formation of ferrite δδ occurred mainly in the single-phase field. The change in the formation of ferrite δ, with the low interpass temperature, promoted an increase in impact toughness and a decrease in the fatigue crack propagation when compared with the sample welded with a higher interpass temperature. The results obtained indicate that the TIG process is an excellent alternative for the repair of CA6NM steel, with a significant influence from the interpass temperature.     

Effect of welding methods on the structure and mechanical properties of welded joints in creep-resisting titanium alloys with different initial structural conditions

Problems of welding rotor components made of creep-resisting titanium alloys are investigated. Comparative tests of the effects of fusion welding and rotational friction welding (FW) on the structure and properties of welded joints in titanium alloys are carried out. The experimental results show that welded joints produced by rotational FW have a structure identical to the structure of the parent metal, and the heat-affected zone does not form at all. The optimum conditions of FW of creep-resisting titanium alloys are determined. Irrespective of the initial type of structure, these conditions result in the mechanical properties of the welded joint at a level of 0.9 of the properties of the parent metal.     

Effect of the electron beam welding conditions on the structure and mechanical properties of welded joints in an austenitic steel with bronzes in the manufacture of power engineering structures

Investigations were carried out into the production of combined welded joints in 316L(N) austenitic steel and BrKh1Tsr (CuCrZr) and CuAl10Ni5Fe4 bronzes 30 mm thick by electron beam welding (EBW). The formation of the welded joints in dissimilar materials is investigated and the EBW conditions determined. The microstructure, mechanic properties and chemical composition of the welded joints are also determined. It is shown possible to obtain the mechanical properties of welded joints similar to the properties of the parent bronze by weldbrazing. It is therefore necessary to increase the accuracy and stability of the electron beam parameters as a technological tool.