Joints Of 316L Stainless Steel Research Articles

Microstructure, mechanical properties and corrosion behavior of austenitic stainless steel sheet joints welded by gas tungsten arc (GTA) and ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA)

Here, ultrasonic–wave–assisted gas tungsten pulsed arc (U–GTPA) welding is proposed as a new alternative welding process to gas tungsten arc (GTA) welding. To better understand the advantages of this new process, in this paper, the microstructure, mechanical properties and corrosion behavior of GTA- and U–GTPA-welded joints of 316L stainless steel are systematically compared. These results show that the weld zone (WZ) depth-to-width ratio of the U–GTPA-welded joint increased, and the area of the equiaxed grain zone was larger than that of the GTA-welded joint. This results in finally increasing the strength and hardness for U–GTPA-welded joints, and the ultimate tensile strength and elongation of the U–GTPA-welded joints were 7.1% and 26.2% greater than those of the GTA-welded joint, respectively. For the U–GTPA-welded joint, under the action of the pulsed arc, the grain distribution with high-angle boundaries (HABs) was different from that of the GTA-welded joint. The minimum of the HAB fraction corresponded to the fracture position for both joints in tensile tests. It shows that a large number of HABs were beneficial in improving joint tensile properties. However, for electrochemical corrosion experiments of two WZs in 3.5% NaCl solution, despite this GTA WZ having a higher HAB fraction, the corrosion current density and corrosion potential of U–GTA WZ were lower and higher than those of the GTA WZ, respectively. The corrosion rate and corrosion sensitivity of U–GTPA WZ indicated good corrosion resistance.

The Interfacial Microstructure and Mechanical Properties of Diffusion-Bonded Joints of 316L Stainless Steel and the 4J29 Kovar Alloy Using Nickel as an Interlayer

316L stainless steel (Fe–18Cr–11Ni) and a Kovar (Fe–29Ni–17Co or 4J29) alloy were diffusion-bonded via vacuum hot-pressing in a temperature range of 850–950 °C with an interval of 50 °C for 120 min and at 900 °C for 180 and 240 min, under a pressure of 34.66 MPa. Interfacial microstructures of diffusion-bonded joints were characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The inter-diffusion of the elements across the diffusion interface was revealed via electron probe microanalysis (EPMA). The mechanical properties of the joints were investigated via micro Vickers hardness and tensile strength. The results show that an Ni interlayer can serve as an effective diffusion barrier for the bonding of 316L stainless steel and the 4J29 Kovar alloy. The composition of the joints was 316L/Ni s.s (Fe–Cr–Ni)/remnant Ni/Ni s.s (Fe–Co–Ni)/4J29. The highest tensile strength of 504.91 MPa with an elongation of 38.75% was obtained at 900 °C for 240 min. After the width of nickel solid solution (Fe–Co–Ni) sufficiently increased, failure located at the 4J29 side and the fracture surface indicated a ductile nature.

Effect of Temperature on Microstructure and Mechanical Properties of 316L Stainless Steel Brazed Joints

The effects of brazing temperature on microstructure and mechanical properties of vacuum brazed joints of 316L stainless steel were studied. Choose three soldering temperature. After soldering, observed the microstructure, element distribution, microhardness and shear strength of welding clearance. The results show that the welding temperature for 940 °C, the brazing clearance organization mainly by Ni-Cr-P phase composition. Joint performance is poor, element can't get enough spread. P element does not spread easily, mainly in the brazing clearance; Cr element can spread along the grain boundary into mother material; the ability of spread of Ni elements is less than the Cr element. While welding temperature of 970 °C, the shear strength is the highest, and the comprehensive performance is the best.

Effect of Brazing Temperature and Clearance on Microstructure and Mechanical Properties of 316L Stainless Steel Brazed Joints

Vacuum brazing of 316L stainless steel with BNi-2 brazing filler metal.The effects of brazing temperature and brazing clearance on microstructure and mechanical properties of vacuum brazed joints of 316L stainless steel were studied. The results show that: As brazing temperature being 1 070 °C, with the increasing of the brazing clearance, the joint shear strength value become lower and lower. Brazing clearance compounds mainly contain intermetallic and solid solutions.

Fatigue life of AISI 316L stainless steel welded joints, obtained by GMAW

An investigation was conducted in order to determine the effect of both the metallic transfer mode (pulsed arc or short circuit) and the O2 content in the Ar/O2 gas mixture, of the gas-metal arc welding process (GMAW), on the fatigue life under uniaxial conditions of welded joints of 316L stainless steel. It was concluded that the mixture of the shielding gases employed in the process could have an important influence on the fatigue life of the welded joints of such steel in two different ways. Firstly, through the modification of the radius of curvature at the joint between the welding toe and the base metal and, secondly, through a more pronounced degree of oxidation of the alloying elements induced by a higher O2 content in the mixture. As far as the metallic transfer mode is concerned, it has been determined that the welded joints obtained under a pulsed arc mode show a greater fatigue life in comparison with the joints obtained under short circuit for both gas mixtures.

Mechanical Performances and Failure Modes of Direct Diffusion Bonding Joints of 316L Stainless Steel

Direct diffusion bonding of 316L stainless steel was performed at 850-1100°C for 1-3 h under a pressure of 10MPa in this study. The effect of bonding temperature and holding time on mechanical performances of the joints was investigated. Tensile tests were conducted to evaluate strength and elongation of the joints at room temperature and elevated temperature of 550°C. The microstructure and fracture surfaces of the joints were examined by optical microscope (OM) and scanning electronic microscope (SEM). The results indicated that the elongation of the joints increased with the increase of bonding temperature and holding time. However, overlong holding time had a side effect on the strength of the joint. Moreover, the change of the mechanical properties was closely related to the variation of the microstructure of the joints. The X-ray diffraction (XRD) analysis revealed that FeCr and Fe0.64Ni0.36 were formed at the DB6 joint during bonding process. It is suggested that FeCr should be detrimental to the improvement of high temperature strength of the joint.

Texture of welded joints of 316L stainless steel, multi-scale orientation analysis of a weld metal deposit

Weld material of type 316L is widely used in stainless steel X weldments in fast breeder reactors. As it is difficult to cut test specimens from an X weldment, the two-phase microstructure of 316L welds was simulated by manually filling a mould with longitudinally deposited weld beads. The material consists of γ columnar grains which form a matrix where δ-ferrite dendrites can be found. The crystallographic texture of the material was investigated on the basis of a multi-scale approach. Neutron diffraction analysis showed that on a macroscopic scale both phases had predominantly the same fibre texture with some reinforcements, {1 0 0} γ being parallel to {1 0 0} δ. Further analysis on an increasingly fine scale were then carried out by EBSD and by TEM, showing that the ferrite dendrites were nearly parallel to the neighbouring austenite columnar grains

Microstructural creep damage in welded joints of 316L stainless steel

The present work has been undertaken to study creep damage in welded joints. The complex dual phase microstructure of 316L welds are simulated by manually filling a mould with longitudinally deposited weld beads. Most of the moulded specimens were then aged for 2000 hours at 600°C. High resolution scanning electron microscopy was extensively used to examine the microstructure of the welded material before and after ageing. Columnar grains of austenite constitute a matrix in which thin dendrites of δ-ferrite can be found. The ageing generates the precipitation of carbides, resulting in less transformation in the material. Smooth and notched creep specimens were cut from the mould and tested at 600°C under different stress levels. The creep life of the simulated welded material is shown to be lower than that of the base material. Microstructural observations reveal that creep cavities are preferentially located along the austenite grain boundaries. This analysis of intergranular damage on test specimens is conducted to obtain a predictive damage law which could be used to calculate the lifetime of welded joints.