Abstract: The exhaust manifold is an important component of a car engine,and the material of the exhaust pipes for commercial vehicle engines is mostly made of silicon-molybdenum ductile iron castings.During engine hot running tests,the exhaust pipes are exposed to a high-temperature environment of about 700℃.After the tests,the inner cavity often shows red rust,and the rust spots can easily fall off,which may cause damage to the turbocharger blades,leading to customer complaints.Therefore,solving the problem of rust inside the exhaust pipes is crucial in actual production and supply.In order to solve the problem of rust in the inner cavity of QTRSi4Mo1 in the exhaust pipe of commercial automobile engine,a solution has been proposed for generating Fe₃O₄ protective film through high-temperature steam oxidation.Through comparative experiments,it is verified that the scheme can effectively improve the oxidation resistance of exhaust pipe castings and solve the problem of rust in the inner cavity.