The design of cooling units for heat treatment is a multi-step research process that includes numerical simulations using transformation diagrams to describe and accurately determine the optimal cooling regime. The thermophysical properties of the heat-treated material and the knowledge of the heat transfer coefficient (HTC) between the cooled object and the cooling medium (mostly water) are inputs for numerical simulations that predict the temperature field in the heat-treated product. The design of an optimal cooling system and its testing are carried out using laboratory experiments in semi-operational conditions close to the product manufacturing process. The final mechanical properties of the heat-treated product are verified using metallographic study and analysis of mechanical properties such as hardness measurement, impact notch or tensile test, etc. Typical applications are heat treatment of pipes, rails, wheels, and flat products such as strips and plates.

Laboratory is equipped with unique experimental devices, allowing the complex study of cooling processes as close as possible to real processes. Laboratory equipment allows spraying on a moving sample of various shapes and dimensions (plate, tube, roll, rail, etc.), which are embedded by thermocouples. High-performance data logging (10 kHz for each channel), together with self-developed advanced inverse calculations software enables detailed determination of a heat transfer coefficient.

More detailed information could be found on: https://www.heatlab.cz/research/heat-treatment/

Cooling optimization to achieve better flatness of metal strips and plates during heat treatment

Heat treatment is often connected with undesirable thermal stresses and deformations. Knowledge of the heat transfer coefficient and material properties (thermal and mechanical) obtained by laboratory measurements allows the performing of conjugated thermal-stress numerical simulations in software such as Ansys or Comsol Multiphysics to predict and optimize residual stresses and deformations of the final product. The work on heat treatment of metals and alloys is a combination of practical experimentation, advanced simulation, and continuous optimization.

Laboratory recently developed software that predicts strip deformation after a complex cooling process (run-out table cooling followed by coiling, and finally, cooling of coils in a yard). This simulation uses advanced computational models (high plastic deformations, true stress-strain curves, TTT diagrams, etc.) to predict the reaction of different materials to the cooling process. It allows the forecast of the residual stresses and deformations in the final products, which are critical factors in determining the product's final quality and mechanical properties. The results are used to optimize the heat treatment process, adjusting variables such as the temperature, cooling rate, and coolant flow to achieve the best possible quality.

Simulation of steel strip deformation on run out table during heat treatment – formation of edge waves

Heat treatment of super alloys after 3D printing (Titanium, Inconel)

The laboratory focuses on heat treatment of super alloys, such as titanium and inconel alloys, produced by 3D printing. The goal is to optimize the microstructure and mechanical properties of these materials, which are critical for their application in the aerospace industry.

Heat treatment research of TiAl6V4 titanium alloy after 3D printing using SLM (Selective Laser Melting) includes several steps. Test specimens from TiAl6V4 titanium alloy using SLM are printed first. The mechanical and structural properties of these specimens are analyzed. Then, they are heat-treated. Mechanical and structural properties of the heat-treated specimens are compared with properties obtained from non-treated samples. The optimization of the heat treatment regime and the protective atmosphere minimizing the oxidation and material degradation follows. The goal is to find the ideal combination of solution annealing and aging to prepare a dual-phase α/β structure.

Heat treatment of Inconel alloy IN718 includes preparation of parts from IN718 Inconel alloy using additive manufacturing. These parts are heat-treated according to AMS 5664 standard, which includes two phases: Phase I: "annealing" in a protective atmosphere of argon or nitrogen and Phase II: "aging" under conditions defined by the standard. Heat-treated parts are mechanicaly tested to verify the achievement of the desired mechanical properties.