I am working on developing fully pearlitic steels with fine interlamellar spacing. I am going to heat up samples to austenization temperature (1000 degC) at a heating rate of 10 degC per second and hold/soak it at austenization temperature for 10 min and cool it down to room temperature at 0.2 degC/sec. This is possible for lab scale samples. I would like to know if there are heat treatment methods for decreasing austenization holding time for thick and heavy samples around 500-800 kg to obtain fully pearlitic microstructure.
Transformation of the pearlitic regions at temperatures occurs by the same processes for the lamellar pearlite Upon heating, the pearlite regions, which contain about 0.8 wt. % C, become unstable above the eutectoid temperature and transform to austenite. Nucleation takes place predominantly on the pearlite-ferrite grain boundaries. The pearlite phase is the first one that transforms to austenite. After the pearlite-to-austenite transformation is completed, the structure consists of regions of austenite, replacing the original areas of pearlite, and regions of unaffected pro-eutectoid ferrite. The pro-eutectoid ferrite is continuously reduced with increasing austenitizing temperature.
Simultaneously, carbon in the austenite regions (formed from pearlite colonies) is
diffusing to the austenite formed from the ferrite regions. It is adopted that solution of pro-eutectoid ferrite is a diffusion-controlled process, for which the rate-controlling factor is the diffusion of carbon in austenite.
at low heating rates the formation of austenite is controlled by the long-range diffusion of carbon. However, at higher heating rates under certain conditions the growth rate increased drastically and the interface-controlled reaction growth mechanism was claimed to be responsible for the transformation. Thus, results appear to suggest that assuming long-range diffusion of carbon to be determining for different heating conditions might not be accurate and a change from diffusion-controlled to interface-controlled transformation can be expected during austenitization of steels with a pearlite-ferrite microstructure.
The spheroidization is only observed at rather low heating rates (like 0.05 °C/s) and was detected during experiments for all the studied alloys. No spheroidization was observed at higher heating rates. The movement of the interface in a lamellar structure is quite different from the spheroidized one. In the first case, the interface moves rather quickly due to the short carbon diffusion distances (carbon is already present at the reaction point). In the second case, the spheroidized cementite particles will serve as a pinning factor for the propagation of the interface. In addition, carbon will have to diffuse though the austenite phase, thus the pearlite-to-austenite transformation will be retarded.
One thousand drgrees is too high for pearlitic steel .Max.800 is enough
Depending on your geometry, induction heating may work but at the end the core of the steel piece has to heat up to a certain temperature (say 800C ) for some time (3-5 min) to allow austenitization.
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