Keywords
thermokinetic modeling
OpenCalphad
Scheil’s rule
bainite transformation
TRIP effect
fatigue strength
How to Cite
Abstract
This work presents a comprehensive study of the evolution of the microstructure and mechanical properties of large-scale shaft gears during heat treatment. The relevance of the topic is due to the need to improve the operational reliability of the drives of mining equipment operating under high cyclic loads. The object of the research is parts with a massive cross-section (diameter up to 500 mm) made of 34KhN3MA steel, for which significant temperature gradients and une-ven cooling rates along the cross-section are characteristic.
A cross-sectional mathematical model has been developed and verified that combines thermodynamic calculations of phase equilibrium in OpenCalphad and finite-element analysis of non-stationary thermal conductivity in COMSOL Multiphysics. The kinetics of overcooling austenite decomposition during continuous cooling were described using the modified JMAK equation and Sheil's additivity principle.
The model takes into account the thermal effect of the phase transition (recalescence) and the transformation-induced plasticity effect (TRIP), which made it
possible to predict the critical points of decay with high accuracy.
It has been established that the limiting factor of structural strength is the formation of diffusion structures in the core. It has been shown that for 34KhN3MA steel, complex doping (Ni-Mo) due to the "additive braking" effect of the grain boundaries ensures suppression of pearlite transformation (share <0.5%) even in the thermal center of the shaft. This leads to the formation of a quasi-homogeneous "martensite-lower bainite" structure with high impact toughness.
Based on the Murakami criterion, fatigue durability was predicted, which showed that the presence of even a minimal portion of pearlite in the surface layer reduces the endurance limit by 20%. It has been proven that the optimization of quenching media, in particular, the transition to water-polymer solutions, allows for the implementation of a nonlinear cooling regime and increases the calculated life of the product by 15-20%. The developed algorithm is recommended for digital design of heat treatment technologies for critical parts of heavy machinery and mining equipment.
Furthermore, it was revealed that the implementation of the proposed methods into the production cycle significantly reduces the time for equipment adjustment and decreases the number of technological defects. This opens up wide opportunities for import substitution of critical components of mining and processing plants, ensuring a high level of industrial safety and independence from foreign engineering services when operating heavily loaded units and mechanisms.
References
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This work is licensed under a Creative Commons Attribution 4.0 International License.
Copyright (c) 2026 Saibov, M.F., Ulug‘ov, G'.D., Ashurov, X.X. (Muallif)