The influence of deformation on the structural phase state of heat-affected zone in the welded seam of 12Х18Н10Т steel

Structural phase state of heat-affected zone of a welded seam made by manual arc welding from austenitic steel 12Х18Н10Т and further subjected to plastic deformation was investigated by transmission electron microscopy on thin foils. A universal testing machine Instron 1185 was applied for mechanical tests on quasi-static active strain under room temperature, with velocity of 1.7´10^-4 s^-1 up to strain degrees of 5 and 37%. The focus of the study was on the heat-affected zone at the distance of 1 mm from the weld line towards the base metal, i.e. base metal zone; and also at the distance of 0.5 mm towards weld metal, i.e. weld metal zone. It was revealed that welding leads to the formation of e-martensite both in base metal and weld metal zones; and g ® e conversion occurs more intensively in weld metal zone. Plastic deformation within the range of e = 0-5% along the whole heat-affected zone results in further g ® e-phase change. In the weld metal zone this change also occurs more intensively. Further increase of plastic deformation within the range of e = 5-37% results in g ® e ® a-phase change and elasto-plastic distortion of a-phase crystalline lattice. Apart from that, g-phase crystalline lattice still has plastic bending. Overall, two conditions are fulfilled within the whole volume of material in heat-affected zone: scalar density of dislocations is higher than excess density and internal shear stresses are higher than those of long-distance ones.

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