Graininess variation research of steel 20 welding joints at deformation-thermal treatment

Abstract

It is known that the metal grains’ size affect on the metal physical-and-mechanical properties. At the fusion welding the metal grains irregular growth takes place, graininess is increasing. It affects negatively on physical-and-mechanical properties on the welding joint metal. For decreasing graininess variation thermal and thermoplastic treatment of welding joints (annealing, thermoplastic treatment) is used. In was carried out the comparative analysis of the results of steel 20 welding joints structure research after deformation at the temperature-rate regime of super plastic deformation and after annealing and after thermo cyclical treatment. At superplastic deformation during hot deformation, became possible processes of dislocation redistribution, including vacancy creeping, forming recrystallization nuclei and their growth, migration of the large angular boundaries. In this research a thermo mechanical treatment at super plasticity regime deformation is studied. In this case the effect of super plasticity deformation is not revealed in full, because for that there must present fine grain structure. The results of the research showed the positive effect of the thermoplastic treatment at super plasticity regime deformation. Slow rate of deformation in combination with definite temperature affects on the thermal activated processes of thermal loss of strength. Microstructure research was carried out on Neophot-30 microscope. For studying the graininess structure variation changing the parameters of grains dimensions distribution were calculated by using the industry system of images analysis SIAMS 600. It was determined that in the zone of the welding joint thermal effect the increasing of graininess variation in metal took place. After annealing of the welding joint the graininess variation in the zone of thermal effect almost had not changed. After isothermal rolling with heated rollers at the regime of super plastic deformation and thermo cyclical treatment the graininess variation in the zone of thermal effect decreased and approached to the value of the basic metal graininess variation.