Volume 47, Issue 8

Mechanical properties of ferrochrome based hardfacing layers coated on AISI 1020 steel obtained by the aid of Plasma Transfer Arc (PTA) was experimentally studied. Ferrochrome powders were mixed with sodium silicate gel to avoid spreading. The mixture was laid to 1.5 × 8 × 100 mm slots machined on AISI 1020 steel. Hardfacing layer was performed by PTA process under pure Argon as protective gas with 130 A/20 V power supply. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), micro hardness and abrasive tests were employed for the evaluation of ferrochrome alloyed coating. Hardfacing was successfully performed under given conditions. Microstructural changes and formations (phases) significantly improved hardness, abrasive wear resistance and integrity of hardfacing layer.

CO 2 laser welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy, using different welding speeds (3 m/min, 4 m/min and 5 m/min). The microstructure and composition analysis of weld metal was examined using optical and scanning electron microscopy (HR-SEM, EPMA and EDS/X). Room temperature hardness and tensile properties of the weldments in the as-welded condition were studied and correlated with the microstructure. The microstructure of fusion zone consists of two parts: the equiaxed zone in the middle part and the columnar zone adjacent to fusion boundary. It has been shown that the average width of columnar grains in the fusion zone is increased with decreasing the welding speed. Microstructural examination showed that the equiaxed grain size in the fusion zone was the least in the welds made using 5 m/min welding speed. It has been shown that welds prepared with 5 m/min welding speed exhibited increase in hardness, yield strength and ductility when compared with other welds.

The failure took place on a welded elbow pipe which exhibited a catastrophic transverse rupture. The failure was located on the welding HAZ region, parallel to the welding path. Branching cracks were detected at the edge of the rupture area. Deposits of corrosion products were also spotted. The optical microscope analysis showed the presence of transgranular failures which were related to the stress corrosion cracking (SCC) and were predominantly caused by the welding residual stress. The significant difference in hardness between the welded area and the pipe confirmed the findings. Moreover, the failure was also caused by the low Mo content in the stainless steel pipe which was detected by means of spark emission spectrometer.