SPA Pribor named after S. S. Golembiovsky (St. Petersburg, Russia)
Yu. A. Nabokov, Cand. Eng., General Director
E. Yu. Alimova, Head of the Central Plant Laboratory
BSTU VOENMEKH named after D. F. Ustinov (St. Petersburg, Russia)
A. I. Olekver, Cand. Eng., Associate Prof, Dept. E4, leshicher@mail.ru
E. Yu. Remshev, Dr. Eng., Prof., Head of Dept. A2
G. A. Vorobyeva, Cand. Eng., Associate Prof, Dept. A2
E. D. Antipin, Postgraduate Student
The aim of this work was to experimentally study the possibility of forming a functionally gradient structure in high-quality low-carbon steel during cold stamping. Three processing modes were developed: medium deformation mode, maximum deformation mode, and minimum deformation mode. The obtained mechanical tests showed that as plastic deformation increases, the tensile strength and hardness of the samples increase significantly, while relative ductility and impact toughness decrease. Thus, at maximum deformation, the tensile strength reached approximately 670 MPa, and at minimum deformation with the relief of residual stresses, it was approximately 400–410 MPa. Similarly, the hardness increased to 96 HRB in the maximum stamping stretch mode, while in the minimum deformation mode it decreased to ~ 60 HRB, while impact toughness, conversely, increased to ~112 KCV. Microstructural images revealed a clear gradient across the wall thickness: at medium and maximum deformation conditions, grains and fragments of ferrite subgrains on the outer surface are oriented and elongated along the pearlite direction, while in the middle part of the wall, ferrite grains are significantly deformed and highly refined. In contrast, with minimal deformation and final annealing, the steel structure was virtually uniform across the thickness: grains are equiaxed on both the outer and inner walls. Thus, a direct relationship was established between the plastic processing conditions, microstructure development, and the material’s performance properties: increasing the forging intensity leads to significant grain fragmentation, an increase in defect density, and, consequently, to steel hardening.
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