The working conditions of the crankshaft are extremely poor, and it is subjected to bending and shear stress caused by alternating loads during work, so it has extremely high requirements on the fatigue, wear resistance and strength of the crankshaft. With the development of trucks to high-power heavy-duty trucks, and the development of cars to speed and light weight, the performance requirements of the engine are getting higher and higher, and the cast crankshaft has to face severe tests. Because most of the crankshafts are damaged by bending fatigue due to the curved surface of the balance block, the greater advantage of forged steel crankshafts is that the steel has a higher bending fatigue strength, which is basically proportional to the tensile strength. The ductile iron crankshaft has low fatigue strength due to the existence of graphite pores, phosphide and grain boundary segregation of alloying elements, and is not proportional to the tensile strength. According to the test of Ford Motor Company in the United States, for the same width of crankshaft and connecting rod journal support surface, the life of cast crankshaft is only half of that of forged crankshaft.
With the requirements of high power, low fuel consumption and low emission, the explosion pressure of the engine has increased from 8MPa~9MPa to 12MPa, or even 14MPa. The ductile iron crankshaft cannot withstand such a high explosion pressure. Therefore, in recent years, the proportion of cast crankshafts at home and abroad has been declining. The proportion of forged crankshafts is increasing, and the trend of crankshaft casting and forging is becoming more and more obvious. For example, a domestic diesel engine factory has changed from using cast crankshafts to 70% of forged crankshafts.
Crankshaft casting and forging are becoming increasingly obvious
The working conditions of the crankshaft are extremely poor. The bending and shear stress caused by the alternating load during the work, so the fatigue wear resistance and strength of the crankshaft have extremely high requirements. With the development of trucks to high-power and heavy -duty trucks, and the development of cars to speed and light weight, the performance requirements of engines have become higher and higher. Casting crankshafts have to face severe tests. Because most of the crankshaft is damaged by bending fatigue due to the curved block split mold crankshaft, the biggest advantage of the forged steel crankshaft is that the steel has a higher bending fatigue strength, which is basically proportional to the tensile strength. Ductile iron crankshafts have low fatigue strength and are not proportional to tensile strength due to grain boundary segregation of graphite voids, phosphides, and alloying elements. According to the test of Ford Motor Company, for the same cranksha ft and connecting rod neck support surface width, the life of the cast crankshaft is only half of that of the forged crankshaft.
With the requirements of high power, low fuel consumption and low emissions, the explosion pressure of the engine has risen from 8MPa to 9MPa to 12MPa, or even 14MPa. Ductile iron crankshafts cannot withstand such high explosion pressures, so the proportion of cast crankshafts at home and abroad has declined in recent years. The proportion of forged crankshafts is increasing, and the trend of crankshaft casting to forging is becoming increasingly apparent. For example, a domestic diesel engine factory changed from cast crankshafts to 70% of forged crankshafts.
