Gray cast iron refers to the cast iron with flake graphite. The main components are iron, carbon, silicon, manganese, sulfur and phosphorus. It is the most widely used cast iron. Gray iron castings account for more than 80% of the total output of various iron castings. The casting performance, cutting performance, wear resistance and vibration absorption performance of gray cast iron are better than other types of cast iron, and the production is convenient, the yield is high and the cost is low. Therefore, since its inception, gray cast iron has been widely used in the machinery industry because of its excellent comprehensive performance, especially alloyed high-strength gray cast iron is mostly used in the engine cylinder block, cylinder head of gasoline engine and diesel engine, as well as machine tools and other places with special requirements.
With the continuous development of material science, gray cast iron, as a traditional industrial material, is facing more and more serious challenges. Due to some disadvantages of gray cast iron, such as low strength, poor toughness and weak fatigue resistance, it is greatly affected by new materials such as non-ferrous castings, steel castings, stamping parts and weldments, and the demand decreases slightly. According to the statistics of China Foundry Association in 2018, the output of gray iron castings in China is about 20.65 million tons, accounting for 41.8%.
The above statistics show that gray cast iron still plays a major role in castings. The release of the national six emission standards for automobile engines has taken the tensile compressive fatigue strength of high-strength gray cast iron as the inspection standard. Therefore, study the tensile compressive fatigue strength of high-strength gray cast iron, explore its fatigue fracture mechanism, fully develop its potential, and provide a reasonable basis for engine material selection, Making it play a greater role in production and construction has become a work of great significance.