Abstract
The weld joints are characterized by microstructure inhomogeneity and defects due to non-uniform heating and cooling particularly at service while operating in extremely cold environment. Vickers micro hardness measurement was done on hard probes of welded samples of low-alloyed 14H2GMR and low-carbon St3sp steel. Experimental study was carried out to see the thermal cycling influence on the heat-affected zone properties. It was discovered that, welding at -40°C does not lead to a significant increase of steel micro hardness as compare to welding at +20°C despite the large difference in cooling rates. It was also discovered that, the crack grows mainly along the grain boundaries of martensite and bainite (as over chilled austenite), but in some cases passes through the grain body and cuts across it at 14H2GMR for pipe steel. For structural St2sp steel the inter granular cracks are revealed both in weld metal and in the heat affected zone nevertheless of milder test conditions against hard technological probes.
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