For the given research on the "MMZ ISTIL" (UKRAINE)" samples from the AISI 8620 steel were selected (a 29 melting). On chemical composition this steel it is possible to identify how the steel 20HGNM. The statistical treatment was before conducted: equalizations of dependence of the basic controlled mechanical properties from maintenance of carbon and basic alloying elements in steel [2]. Statistical treatment was conducted by the "Statistica" program. Researches of macrostructure and microstructure of steel after the proper treatments produced: - 90 mm - billet after rolling; - the reforged billet on 30 mm; - 30 mm after annealing.

In the given work the influence of degree of deformation on a structure and properties of the AISI 8620 steel is considered. The present purveyances 30 was reforged on 25, 20, 15mm with the subsequent cooling in an oil and on air.

Forging was produced on an air-hammer with weight of the falling parts 400 kg.

A microstructure was studied on the models of etched in nitale, by the "Neophot 21" microscope the pictures of microstructure were done. With the use of the "ImageTool" program the correlation of structural constituents present in a structure after cooling on air is definite (ferrite, pearlite, bainite, martensite).