The influence of the heating rate of cemented constructional steels on the growth of austenitic grain in the process of high-temperature holding

The influence of the heating mode of samples of constructional cemented steels 20ХН3А, 20ХГНР and 15ХГН2ТА on the value of austenite grain after high-temperature isothermal aging at 1000 °С is studied. It is shown that the heating of steels at a rate of 1.2–3.0 °C / min in the phase-transformation interval stabilizes the grain structure of the steels and leads to a slowing down of the kinetics of the growth of austenite grains during prolonged high-temperature aging, which makes it possible to increase the temperature of the chemical-thermal treatment of steels. It is concluded that the stabilization of the grain structure of steels is associated with the formation of segregation of impurity atoms and particles at grain boundaries with high-angle disorientation during slow heating, which prevents migration of grain boundaries in the process of prolonged high-temperature aging. A high-temperature chemical-thermal treatment of a batch of billets from steel 20ХН3А under experimental conditions with stepwise heating in the phase-transformation interval provided a qualitative fine-grained structure of the cemented layer.

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Matematical modeling of the process of enlarging the austenitic grain during high-temperature heating of alloy structural steel

Litiyo i Metallurgiya (FOUNDRY PRODUCTION AND METALLURGY) ◽

10.21122/1683-6065-2019-3-74-84 ◽

2019 ◽

pp. 74-84

Author(s):

V. A. Kukareko ◽

B. M. Gatsuro ◽

A. N. Grigorchik ◽

A. N. Chichin

Keyword(s):

High Temperature ◽

Heating Rate ◽

Grain Structure ◽

Slow Heating ◽

Case Hardening ◽

Regression Equations ◽

Impurity Atoms ◽

Average Size ◽

Case Hardening Steel

The influence of the heating rate of a typical case hardening steel 15KHGN2TA and 25KHGT on the growth of austenitic grain during long-term isothermal exposures at the high-temperature chemical-heat treatment was studied. It is shown that the change in the rate of heating case hardening steels in the temperature interval a®g transformations during chemical-thermal treatment has a significant impact on the process of growth of austenitic grains in them.Regression equations describing the dependence of the average size of austenitic grain on the heating rate, pre-annealing temperature and cementation temperature are obtained, which allow selecting the cementation modes of various steels. A phenomenological model describing the mechanism of formation and growth of austenitic grains in steels under heating at different speeds is developed.It is concluded that the slow heating of steels in the interval of phase a®g transformation contributes to the formation of a complex of small austenite grains separated by high angle boundaries with adsorbed on them by impurity atoms, which ensures higher resistance grain structure to coalescence and reduce the rate of migration of the boundaries during prolonged hightemperature austenization.

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