The formation of the structure and mechanical properties of the structural steel during cold plastic deformation by radial forging

The laws of formation of the structure and properties of structural steel 35X during cold plastic deformation by radial forging (RF) are discussed. Tubular billets were subjected to toughening before cold radial forging. Methods of metallographic analysis, transmission electron microscopy, a uniaxial tension tests with determination of the strength and ductility, as well as the impact tests КСU and КСТ were used in the work. Methods of statistical analysis were used to quantitative evaluation the size of the elements of the subgrain structure of steel 35X. The studies found out that the cold RF of steel 35X tubular billets causes structure fragmentation, dissolution of the carbide phase formed by toughening and development of dynamic recrystallization. In this case the average size of α-phase subgrains reduced from 1500 nm to 730 nm after the first pass of cold RF and there is a further refinement of subgrain structure of investigated steel to the size of subgrains α-phase, 640 and 525 nm, after a second and third pass, respectively. The deformation of the structural steel 35X with deformation ratio 55 % results in incensing of the offset yield strenght (σ0,2) by almost 50%, and the ultimate tensile strength (σB) – 25 %, compared with the initial condition after the toughening. In this case, the reliability behavior (δ, ψ, KCU, KCT) of tubular billets of structural steel 35X are reduced insignificantly and remained at a high level.

radial forging, cold plastic deformation, subgrain structure, strength, yield point, impact toughness.