Calibration Tests for Microstructure Models

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Holger Brüggemann

Academic Staff

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+49 241 80-95950

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Final product properties are mainly determined by the microstructure of the material after forming and, if necessary, a subsequent heat treatment. In order to consider the microstructure evolution in forming simulations, the IBF offers several tests to characterize individual aspects of microstructure changes. Static recrystallization is investigated via stress relaxation experiments on the institute's forming dilatometer. Dynamic recrystallization is characterized by isothermal cylinder compression tests on the servohydraulic testing machine - Servotest. Finally, various furnaces with a maximum temperature of up to 1,500° C are available for grain growth experiments.

Calibration Tests for Microstructure Models

  • Dynamic recrystallization (cylindrical compression test)
  • Static recrystallization (stress relaxation test, annealing tests)
  • Grain growth (annealing tests)

 
 

Dynamic Recrystallization

Conduction of compression test using the servo-hydraulic testing machine Copyright: © IBF Conduction of compression test using the servo-hydraulic testing machine

To determine the dynamic recrystallization kinetics, compression tests are carried out at characteristic points along the flow curve. For this purpose, the servo-hydraulic testing machine - Servotest, as well as the forming dilatometer are available at the IBF. On the Servotest, strain rates between 0.001 and 100 s-1 at temperatures up to 1200°C can be realized. The forming dilatometer offers strain rates between 0.001 and 20 s-1 at temperatures up to 1500°C. Typical final strains are between 0.8 to 1.2. The samples can then be prepared metallographically and the recrystallized fraction validated in the optical microscope for the parameterization of microstructure models, e.g. JMAK models, StrucSim or DIGIMU®.

 
 

Static Recrystallization

Conduction of stress relaxation test using the forming dilatometer Copyright: © IBF Conduction of stress relaxation test using the forming dilatometer

Static recrystallization is characterized by means of stress relaxation tests. For this, compression tests are carried out up to strains of 0.05 to 0.1 and then the stress drop is measured while maintaining the temperature. The stress drop can then be used to calculate the recrystallization kinetics of static recrystallization. The forming dilatometer is available for carrying out the stress relaxation tests. Here, strain rates between 0.001 and 20 s-1 at temperatures up to 1500°C can be realized. The kinetics can be validated by metallography and optical microscopy.

 
 

Grain Growth

Conduction of annealing test using the dilatometer Copyright: © IBF Conduction of annealing test using the dilatometer

For the characterization of the grain growth, annealing tests are carried out at different temperatures and holding times. Various furnaces, as well as the dilatometer with a maximum temperature of up to 1500°C are available for this purpose. The grain sizes can then be determined by metallographic sample preparation and optical microscopy.