To properly model the cracking susceptibility during solidification under continuous casting conditions, it is essential to have accurate data. Such data for the mechanical properties of steel during solidification are scarce if not non-existent. An experimental tool called the Mold Cracking Simulator (MCS) has been used to simulate the initial shell formation under continuous casting conditions. As part of the test, the shell is mechanically subjected to deformation. A mathematical model has been developed to translate the force and elongation measured during the MCS trials into stress–strain components. To test the model and validate the assumptions, two steel grades were tested, a peritectic steel grade and a higher-alloyed grade. The results show that the reproducibility of the test is very good and the stress–strain curves are consistent with the steel composition. Moreover, the metallographic and fractographic analysis of the deformed MCS samples shows that the microstructure is comparable to that of a continuously cast product and the cracks generated are interdendritic, i.e., hot tears.