What material is the crankshaft made of?

The stress on the crankshaft is extremely complex, and it works under the combined action of periodically varying gas pressure, reciprocating inertial force, and torque, and bears enormous bending and torsional alternating loads. At the same time, it is also a slender high-speed rotating part, so strict dynamic balancing is required. Bending and twisting are not allowed to exceed a certain value.

Therefore, the crankshaft needs to be made of very high-quality materials and undergo strict surface treatment processes. Generally, medium carbon steel and medium carbon alloy steel such as 45, 40Cr, and 35Mn2 are used for forging. In recent years, more ductile iron is used.

After forging or casting, in order to improve the fatigue strength of the crankshaft and eliminate stress concentration, it is also necessary to conduct shot peening on the surface of the journal, and the fillet must be subjected to rolling treatment; In order to improve the surface hardness of the journal, it is also necessary to perform high-frequency quenching or nitriding treatment on the surface of the journal, followed by finishing.

After this treatment, the crankshaft has sufficient fatigue strength and stiffness to resist bending and torsion, while the journal has sufficient pressure bearing surface and wear resistance.

On the crankshaft, there are oil passages running through the main journal, crank, and connecting rod journal. From this passage, pressure oil from the main oil passage of the lubrication system enters the main journal and connecting rod journal to lubricate the two friction pairs, namely, the main journal and main bearing shells, and the connecting rod journal and connecting rod bearing shells.

However, due to the huge stress on these two parts, there will inevitably be a certain degree of wear in use; Other types of damage can occur if the lubrication is poor or the engine is overloaded.