Microstructure and mechanical properties of electron beam-welded AISI 409M-grade ferritic stainless steel

This paper deals with the microstructure and mechanical characterization of electron beam-welded AISI 409M-grade ferritic stainless steel joints. Single-pass autogenous welds free of volumetric defects were produced at a welding speed of 1,000?mm/min. The joints were subjected to optical microscopy, scanning electron fractography, microhardness, transverse and longitudinal tensile, bend and charpy impact toughness testing. The coarse ferrite grains in the base metal were changed into fine equiaxed axial grains and columnar grains as a result of characteristic rapid solidification of electron beam welds. Tensile testing indicates overmatching of the weld metal relative to the base metal. The joints exhibited acceptable impact toughness and bend strength properties.     

Microstructural and mechanical properties of dissimilar friction stir welds between AA6082-T6 and AA7075-T651

In the present work, similar and dissimilar friction stir welds have been produced on 6-mm-thick plates of AA6082-T6 and AA7075-T651. The microstructural characteristics and the mechanical response of both similar and dissimilar welds were investigated aiming to determine the major differences between them. Material mixing of the dissimilar weld nugget, which was created after the welding process, was studied in order to determine the produced different areas and their dominant alloying elements in this zone. Microstructural investigation was made in the welding zones of similar and dissimilar friction stir welds and indications of partial dynamic recrystallization were observed in the thermomechanically affected zone of the similar welds. Transverse and longitudinal microhardness distributions determined the heat affected zone as the weaker area in the welded specimen. After tensile testing, the fracture of the similar and the dissimilar welds at heat affected zone demonstrated the good bonding and weld quality of the similar and dissimilar weld nuggets.     

Study on microstructure and mechanical properties of dissimilar steel joint developed using friction stir welding

In the present study, microstructure and mechanical properties of dissimilar weld of structural steel and ferritic stainless steel (FSS) plates of thickness 3 mm were investigated. The plates were butt welded by friction stir welding and defect-free welds were produced at a traverse speed of 20 mm/min and rotational speed of 508 rpm using a tungsten carbide tool. The weld joint consisted of alternate bands of both steels resembling an onion ring pattern. In the weld joint, six distinct regions were found including both the base metals. The stir zone of structural steel revealed refined grain structure of ferrite, pearlite, and martensite whereas in ferritic stainless side, highly refined ferritic grains with grain boundary martensite was observed and also confirmed by x-ray diffraction (XRD). The hardness of the weld joint varies from 186 to 572 HV. This scatter of hardness in stir zone is due to the presence of metal from both sides. The ultimate tensile and yield strengths of the transverse weld specimens was higher than the structural steel base metal whereas lower than the ferritic stainless steel, having fracture from structural steel side.     

Effect of friction welding parameters on mechanical and metallurgical properties of ferritic stainless steel

Friction welding is one of the most economical and highly productive methods in joining similar and dissimilar metals. It is widely used in the automotive and aerospace industrial applications. Ferritic stainless steel (AISI430) is normally difficult to weld by fusion methods, due to the associated problems such as grain growth and retained austenite content. Such problems can be alleviated by the friction joining process. The present study utilized a continuous drive friction welding machine to join cylindrical specimens of ferritic stainless steel of similar composition and shape (equal diameter and length). The processing parameters such as friction pressure, friction time, upsetting pressure and upsetting time were changed in order to understand the role of parameters on the strength related aspects of friction processed joints. The joints were subjected to mechanical testing methods such as the uni-axial tension test, and charpy ‘v’ notch impact tests. The micro hardness variation across the joint zone was determined. Micro structural studies were also carried out. The characteristics such as tensile strength, toughness and microstructural aspects exhibited by friction processed joints were compared to parent materials.     

Microstructures and mechanical properties of friction stir welded dissimilar steel-copper joints

Welding dissimilar metals by fusion welding is challenging. It results in welding defects. Friction stir welding (FSW) as a solid-state joining method can overcome these problems. In this study, 304L stainless steel was joined to copper by FSW. The optimal values of the welding parameters traverse speed, rotational speed, and tilt angle were obtained through Response surface methodology (RSM). Under optimal welding conditions, the effects of welding pass number on the microstructures and mechanical properties of the welded joints were investigated. Results indicated that appropriate values of FSW parameters could be obtained by RSM and grain size refinement during FSW mainly affected the hardness in the weld regions. Furthermore, the heat from the FSW tool increased the grain size in the Heat-affected zones (HAZs), especially on the copper side. Therefore, the strength and ductility decreased as the welding pass number increased because of grain size enhancement in the HAZs as the welding pass number increased.     

Improvement of mechanical properties of Inconel 718 electron beam welds—influence of welding techniques and postweld heat treatment

Effects of electron beam oscillation techniques (sinusoidal, square, triangular, ramp, circle, and elliptical) in controlling Nb segregation, Laves formation, and tensile behavior of Inconel 718 electron beam welds were studied. Effects of various postweld heat treatments on tensile behavior were compared. Elliptical beam oscillation technique resulted in less Nb segregation and discontinuous finer Laves in the interdendritic regions compared to that of unoscillated beam weld. Response to aging was better for welds made with elliptical oscillated beam compared with welds made with unoscillated beam. Oscillated beam welds exhibited better mechanical properties than unoscillated beam welds in both solution-treated and aged and directly aged conditions.     

Mechanical and metallurgical properties of friction welded AISI 304 austenitic stainless steel

Owing to the superior properties, of stainless steel it is pertinent to make use of it in various automotive, aerospace, nuclear, chemical and cryogenic applications. It is observed that a wide range of dissimilar materials can be easily integrated by solid phase bonding techniques, such as friction welding and explosive bonding. This study mainly focuses on friction welding of AISI 304 austenitic stainless steel. The friction processed joints are evaluated for their integrity and quality aspects. Friction welding of austenitic stainless steel was carried out using a KUKA friction welding machine (Germany). As the friction time increased, the fully plastically deformed zone (region I) in the vicinity of the bond line becomes increased. In contrast, an increase in friction time will decrease the region (region II) where the grains are partly deformed and grown. Tensile test results indicated that, the joint strength is decreased with an increase of the friction time. The detailed fractographic observation confirmed that the rupture occurred mostly at the joint zone and partly through the base material.     

Mechanical and metallurgical properties of friction welded AISI 304 austenitic stainless steel

Owing to the superior properties, of stainless steel it is pertinent to make use of it in various automotive, aerospace, nuclear, chemical and cryogenic applications. It is observed that a wide range of dissimilar materials can be easily integrated by solid phase bonding techniques, such as friction welding and explosive bonding. This study mainly focuses on friction welding of AISI 304 austenitic stainless steel. The friction processed joints are evaluated for their integrity and quality aspects. Friction welding of austenitic stainless steel was carried out using a KUKA friction welding machine (Germany). As the friction time increased, the fully plastically deformed zone (region I) in the vicinity of the bond line becomes increased. In contrast, an increase in friction time will decrease the region (region II) where the grains are partly deformed and grown. Tensile test results indicated that, the joint strength is decreased with an increase of the friction time. The detailed fractographic observation confirmed that the rupture occurred mostly at the joint zone and partly through the base material.     

Fracture and mechanical properties of friction stir spot welds in 6063-T6 aluminum alloy

The influence of the tool dimensions and of the welding parameters on the fracture and lap shear properties of friction stir spot welds is investigated. Interrupted lap shear tests allow to follow the mechanisms leading to weld fracture. A triangular cavity opens at the hook during lap shear testing. The distance between this triangular cavity and the hole left by the pin is the main parameter controlling the type of fracture. A too short distance favors a fracture through the weld nugget and hence should be avoided. In particular, this happens when the tool pin diameter is too small and when the plunge rate is too large. Fracture initiating at the triangular cavity and following the thermomechanically affected zone, i.e., by the pullout of the weld nugget, is preferred. This fracture type leads to significant plastic deformation and generally favors a large ultimate force during lap shear testing. Large ultimate forces are observed when the welds are cooler (large plunge rates and low rotation speeds), but the welding conditions should be chosen so as not to lead to fracture trough the weld nugget.     

Wear and tribocorrosion behaviour of 304L stainless steel welds

The influence of the microstructures of the base metal and weld metals on the wear and tribocorrosion properties of 304L stainless steel (SS) welds prepared by Manual Gas Tungsten Arc Welding (M-GTAW) and Activated Flux Gas Tungsten Arc Welding (A-GTAW) processes are reported. Increase in sliding speed increased both friction forces as well as wear rate. Higher hardness in M-GTAW weld metal resulted in increased wear resistance than A-GTAW weld metal and base metal. The inferior wear resistance of the base metal was due to the strain hardening behaviour under sliding condition. The polarization curves showed increase in passive current density under sliding condition. The applied potential was found to influence the tribocorrosion resistance of the material. Under tribocorrosion condition, the total material loss was higher in base metal followed by A-GTAW weld metal and M-GTAW weld metal. Characterization of worn surface by SEM indicated a mixed wear mechanism of abrasive and adhesive wear. The worn surface appeared relatively smoother in nitric acid medium than in dry condition. The influence of microstructure affecting the hardness, wear and tribocorrosion resistance of the base metal and weld metals of 304L SS is discussed.     

不锈钢复合管的端部密封焊接

介绍了一种可实现不锈钢复合管可靠焊接的管端密封焊接技术。     

Finite element analysis of the residual stresses in T-joint fillet welds made of similar and dissimilar steels

In this paper, weld residual stress analyses are performed for T-joint fillet welds made of similar and dissimilar steels. Three-dimensional uncoupled thermo-mechanical finite element model which can accurately capture residual stresses in a weld piece is developed in order to predict the residual stress states in the fillet-welded T-joint. Results show that the maximum longitudinal residual stresses near the weld toes of the similar steel welds increase with increasing yield stress of the steel welded. For the dissimilar steel welds, the overall trend, shape and magnitude of the residual stress profiles in flange and web are similar to those of the corresponding similar steel welds despite the slight difference between the residual stresses in parts at which the flange and web come in contact with each other.