Structure and Properties of Forged Steel with Regulated Austenite Transformation

Pressed steel with adjustable (regulated) austenitic transformation (RAT) is used for the hot deformation of a copper-nickel alloy at operating temperatures > 850°C (above the critical point A3 = 850°C). We recommend to extend the temperature range of forged steel with RAT (4Kh4N5М4F2 grade) and to use it in the martensitic state at operating temperatures < 630°С. For this purpose, we study the phase-structural state of this steel after optimized temperature modes of heat treatment (hardening and tempering). The relationship between the parameters of crystal structure and the mechanical properties of thermally hardened steel is established, as well as the temperature mode of hardening used for the process of primary recrystallization of steel with RAT. We compare the parameter of crystal structure and mechanical properties of the analyzed steel with the corresponding characteristics of two operated forged die steels, namely, steel for hot deformation of H13 grade (ASTM, USA; its analogs are the 4Kh5МF1S steel according to GOST 5950-2000, and SKD6 steel according to JIS, Japan) and 4Kh4N5M4F2 steel with RAT used to produce large-size wheels (extruders) for the hot deformation of copper. We justify the temperature mode of tempering for the process of softening of forged steel with RAT. Based on the established relationship between the parameters of crystal structure and hardness, it is shown that, at room temperature, the level of hardness should be lower than 40 HRC.