Meanwhile, the fracture was accelerated due to the uneven surface hardness and the unreasonable distribution of the hardening layer on the crankshaft, and the bad lubrication condition in service.

• 同时轴左颈表面硬度不均匀、淬硬层分布不甚合理，工作过程中润滑条件差，加速了曲轴的断裂。