Some bearing-cap bolts of the diesel engine were found fractured on the intersection between the hexagon head and the pole,after the diesel engines ran 30000~70000km.The fractured bearing-cap bolt was analyzed by fractography,chemical composition analysis,mechanical properties testing,metallographic examinations and hardness testing.The results show that the bearing-cap bolt is hydrogen embrittlement.Hydrogen-content inspection on the bolts shows hydrogen-content is excessive.Some improvements are proposed ...