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Effect of heat treatment on the mechanical properties and microstructure of welded abrasion resistant steel AR200 Neykov, Vladimir P.Eng.


Fusion welding process is based on localized melting of materials of similar composition in order to form a permanent joint. Fusion welding is a cost efficient process widely used in the industry to join a variety of materials, weld geometries and weld characteristics. In this research, the effect of heat treatment on the microstructure, mechanical properties and residual stresses of welded abrasion resistant steel AR200 was investigated. Standardized testing as per ASTM regulations has been carried out and included the measurement of the tensile strength, impact strength, hardness and Jominy hardenability on welded and virgin AR200 steel samples. Then, Scanning Electron Microscopy (SEM) and light optical microscopy were carried out to characterize the alloy’s microstructure as a function of heat treatment temperature and time. Finally, residual stress was measured using a neutron diffraction technique, and the elastic residual stress was mapped in the vicinity of welds in AR200 C-sections. The tensile test results revealed a significant variation in the magnitude of yield and ultimate tensile strength between the virgin and heat treated welded AR200 samples, with the welded and heat treated samples exhibiting reduced ductility and strength. SEM microscopy revealed the entrapment of intermetallic compounds originating from weld slag, which acted as stress-concentrations and likely contributed to the initiation of fracture in the tensile specimens. The neutron diffraction results revealed the distribution of residual strain in three orthogonal directions in the virgin AR200 material, heat affected zone and the weld itself. The results suggest that although the heat treatment decreased and homogenized the residual strains, the duration of the heat treatment did not have a significant effect, and thus further optimization of the heat treatment parameters is required. These research findings confirm that successful welding of AR200 abrasion resistant steel must consider both the chemical composition of the steel as well as the heat treatment, part geometry and welding operator technique variability.

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