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Influence of Rolling on Microstructure and Mechanical Properties of Bronze-Steel Explosive Welded Sheets
Gh. Khalaj, E. Asadian,
Volume 8, Issue 2 (Journal OF Welding Science and Technology 2023)
Abstract

In this paper, the microstructure and mechanical properties of the plain carbon steel-bronze interface of explosive welding and rolling were investigated. Explosive connection was done at two stop distances and with two different thicknesses of explosive material. Rolling of the welded composite was done at both ambient and preheated temperatures of 300 °C and with a constant thickness reduction of 33.3%. The results showed that the wave interface of the steel-bronze connection includes different parts. By rolling, the connection interface was stretched and flattened and the vortex areas were compressed together and in some cases entered the steel field. The steel particles separated from the background along the wave crest and remained as isolated islands in the bronze background. On the other hand, in the areas near the vortex, a part of the bronze flying metal was caught under the wave and was observed as islands separated from the bronze background inside the steel. Porous areas were crushed and compressed as a result of rolling. The rolling force and temperature had partially removed the diffusion barriers and a metal bond had been formed between bronze and steel. During the connection, the voids and shrinkage pores were pressed together due to rolling and the separate borders were close to each other. Explosive joining and cold rolling had increased the hardness in the interface, and hot rolling has led to a decrease in the hardness in the interface. In the hardness test, the welding samples are arranged in the order of the highest impact energy. The effects of welding parameters remain after cold and hot rolling and the hardness rating does not change.


Investigation of the phase transformation and the structure of the simulated heat affected zone of double pass welding in X70 microalloyed steel
Gholamreza Khalaj,
Volume 8, Issue 2 (Journal OF Welding Science and Technology 2023)
Abstract
In multi-pass welding, the heat-affected zone formed in each pass is subjected to another thermal cycle by the next pass. This problem locally changes the microstructure of the heat-affected zone depending on the position of each area relative to the melting line of the next pass, and the overlapping of the heat-affected areas will lead to complex microstructures. In this research, based on the practical conditions of pipe production in the factory, including submerged arc welding with four electrodes in two passes from the inside and outside of the pipe, the thermal cycles of the heat-affected zone were first analyzed. Simulation of thermal cycles of heating and cooling up to the peak temperatures of 950, 1150 and 1350 °C was performed in a dilatometer and the transformation behavior and microscopic structure were studied. Simultaneous modeling of precipitation dissolution and austenite grain growth was done. It was observed that the grain growth reaches a limit in 300 seconds. The main cause of grain growth at temperatures below and above 1150 °C, is the dissolution of fine and coarse deposits of niobium carbonitride, respectively. Also, the modeling of austenite formation and decomposition was done using the classic JMAK equation. It was observed that the parameter n does not depend much on temperature; while parameter k strongly depends on temperature, transformation amount and austenite grain size.
 

Effect of post weld heat treatment on the structure and mechanical properties of explosive welding of austenitic steel 321 - aluminum 1050 - aluminum 5083
Gh. Khalaj, A. Fadaei,
Volume 9, Issue 1 (Journal OF Welding Science and Technology 2023)
Abstract
In this research, the effect of post weld heat treatment on the microstructure and mechanical properties of the three-layer explosion welding joint of austenitic steel 321-aluminum 1050-aluminum 5083 was investigated. The welded samples were heat treated at 250 and 350°C for 10000 seconds. The structure and properties were investigated using optical microscope, scanning electron microscope, microhardness measurement and shear-compressive strength. The results showed that in all conditions, the interface of aluminum 5083-aluminum 1050 was smooth and with complete continuity; However, the interface between stainless steel 321 and aluminum 1050 had a reaction layer with variable and discontinuous thickness. During the heat treatment, the thickness of the interface layer increases according to the diffusion kinetics and reaches 18.6 microns in the maximum value. With the increase of heat treatment temperature, the average concentration of aluminum in the reaction layer of the interface increased from 85% to more than 90%, but the concentration of iron decreased from 10% to less than 5%. Also, shear-compressive strength decreases from 94.6 to 56.7 MPa.

Investigation of the Joint Interface in Explosive Welding of Austenitic Stainless Steel 321 - Aluminum 1050 - Aluminum 5083 after Heat Treatment
Gh. Khalaj, J. Khalaj, F. Soleymani,
Volume 10, Issue 1 (Journal OF Welding Science and Technology 2024)
Abstract
In this study, the microstructure of the joint interface in three-layer explosive welding of austenitic stainless steel 321 - aluminum 1050 - aluminum 5083 was examined before and after heat treatment. The welded samples were subjected to heat treatment at temperatures of 250°C and 350°C for durations of 1000, 3000, and 10000 seconds. Microstructural analysis was performed using optical microscopy and scanning electron microscopy. The results revealed that under all conditions, the Joint Interface of aluminum 5083 - aluminum 1050 exhibited a flat and defect-free structure. With increasing standoff distance, the Joint Interface of stainless steel 321 - aluminum 1050 transitioned from a smooth to a wavy pattern, and the average layer thickness increased from 4.95 μm to 6.7 μm. During heat treatment, the layer thickness in the Joint Interface increased proportionally to the diffusion kinetics, reaching maximum values of 18.56 μm and 15.02 μm for samples with standoff distances of 6.75 mm and 6 mm, respectively. The activation energies for diffusion were calculated as 46.6 kJ/mol and 42.4 kJ/mol, and the diffusion constants were 142.2 ms-1  and 45.3 ms-1 for the same samples.


 
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