Features of heat treatment of a new steel for the manufacture of hot deformation dies

The influence of heat treatment parameters on the structure and properties of the promising 70Cr3Mn2WTiB die steel, which is offered for the manufacture of mold parts for aluminum alloy injection molding machines, is revealed. A rational mode of thermal hardening is recommended for the developed steel, including spheroidizing annealing at a temperature of 780 °C with combined cooling; quenching at 1000 °C with oil cooling; high-temperature tempering at 550–600 °C with cooling in calm air. The structure formation and behavior of carbide phases in microalloyed steels at various stages of heat treatment are evaluated. The features of phase transformations and the mechanism of dispersion hardening during high-temperature tempering that provide the required set of mechanical and technological properties are determined. The influence of heat treatment modes on mechanical and operational properties under cyclic loading and heat exposure at normal and elevated temperatures is evaluated. Fractographic studies of zones of cyclic and static crack growth in fractures of samples after testing for crack resistance under cyclic and static loading were performed. The main regularities of changes in the thermal structural stability of chromium steels under cyclic temperature and force influences, depending on the nature of alloying and heat treatment modes, are substantiated, which made it possible to reasonably recommend the developed 70Cr3Mn2WTiB steel for implementation.

Mechanism of Cementite Spheroidization from Different Initial Microstructures in Fe-0.65C-2.33Mn Alloy

The spheroidization mechanism from different initial microstructures during spheroidizing heat treatment was studied in Fe-0.68C-2.33Mn alloy. Two types of initial microstructures, i.e. pearlite and martensite, were obtained by varying the cooling rate. The microstructure and property evolution during spheroidizing annealing was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The DICTRA software, assuming local equilibrium conditions, was used to simulate the carburizing process of different initial microstructures through different cooling rate. The results indicate that the spheroidization mechanism of cementite was related to the initial microstructures and the smaller lamellar spacing of pearlite inhibited the coarsening of cementite, resulting in the size of cementite smaller than that of martensite as the initial structure.

The effect of structure and properties of steel 30KhGSA on the shaping of round blanks using plastic bending

The influence of the structure and properties of 30KhGSA steel on the shaping of round-shaped blanks using the method of plastic bending is studied. Bending of the initial steel rod sample results in the sample fracture. Methods of mechanical tests and metallographic analysis used in the study showed that the steel sample in the initial satate has a structure of lamellar perlite. A comparative evaluation of the structure and properties of the steel samples prior to and after additional heat treatment (spheroidizing annealing) revealed that annealing enhanced the plastic properties of the sample and changed the sample structure from lamellar to globular perlite. Formation of the granular perlite structure indicates to the devision of the plates into smaller particles and their further spheroidization due to transferring carbon through the surrounding solid solution. Thus, additional cyclic heat treatment of steel in the state of delivery, allowed us to solve the problem of the rod fracture upon subsequent plastic bending. As a result of the research, the values of the mechanical properties of steel were obtained experimentally, which ensure the process of bending the rod into a round shaped blank without destroying it. The proposed mode of cyclic heat treatment (spheroidizing annealing) can be used to improve the plasticity characteristics of the metal upon shaping by the method of plastic bending.