Failure analysis of a diesel engine transmission shaft crack

42crmoh steel belongs to medium carbon alloy structural steel, which has high strength and toughness, good hardenability, no obvious temper brittleness, high fatigue limit and multiple impact resistance after quenching and tempering treatment, and good low temperature impact toughness. Therefore, 42crmoh steel is designed for diesel engine transmission shaft.

(1) Through the analysis of the subcutaneous blowhole defects in the production of a certain type of cylinder head, the causes of the defects are as follows: the gas generated in the molten iron is blocked on the surface of the molten metal and can not overflow; the poor exhaust of the sand core of the water jacket causes part of the gas to invade the surface of the casting.

(2) In view of the causes of the defects, the corresponding solutions were formulated, including controlling metallurgical quality, appropriately reducing the amount of spheroidizing agent, strengthening the coating coating process control, enhancing the core exhaust and controlling the carbon equivalent at 4.55% – 4.70%.

(3) The results show that the defects of subcutaneous blowholes are effectively avoided and qualified cylinder head castings are obtained.