Change of oxide film in nodular graphite cast pipe during heating
The consequence of ductile iron pipe is that at every moment, some atoms'energy exceeds the uniform energy of atoms, while some atoms' energy is far less than the uniform energy. This energy nonuniformity is called energy fluctuation. However, in the rolling process, the friction coefficient between the practical surfaces is far less than that between the pure l surfaces. Because of the change of the appearance and state of practice, the friction condition also changes. If the friction is changed from adhesion friction to sliding friction, the friction coefficient will drop. Even with the same data, when the chemical composition changes, there are differences in the friction coefficients. The strength of ductile iron pipe is higher, such as with the increase of carbon content in steel, the friction coefficient decreases. The friction coefficients of ductile iron pipe tie rod material and surface state of cast iron roll are lower than those of steel roll. The friction coefficients of ductile iron pipe and unquenched steel are higher than those of quenched steel. In addition, the friction coefficient of cemented carbide roll is 10% to 20% lower than that of alloy steel, and the friction coefficient of cermet roll is 10% to 20% lower than that of cemented carbide roll. In individual states, the higher the hardness of rolls, the smaller the friction coefficient. Similarly, with the increase of carbon content in steel, the hardness of steel increases correspondingly, and the friction coefficient decreases significantly.
