Change in thermal energy and particle arrangement of molten steel after becoming completely solid:
Due to the rise in the temperature, the particles start moving speedily. Because of the achieving the kinetic energy, which helps in the higher collision rate and makes the diffusion rate high. In case of the solids the particles are strongly bound in sequential order. Even though we can’t see it, but the vibrations can be felt. During heating the internal energy increases and helps the particle to move faster.
