Joint bar (fishplate) is an asymmetrical cross-section product with different mass elements - the web, the upper and lower bulbous heads. Technical standards specify the strict requirements on the joint bar mechanical properties and straightness. The microstructure after rolling (without heat treatment), after thermostrengthening according to the traditional technology - oil quenching, and accelerated water cooling technology has been studied by using optical and scanning electron microscope. The accelerated water cooling technology was the first implemented in industry for asymmetrical cross-section body. As a result, it was found that a high degree dispersion of the phases and the small grain size provided the best results in stable mechanical properties, which is typical for the sprayer system. The joint bar straightness is achieved in response to the cooling process controllability.