Study On The Precipitation Mechanism Of Cementite In Low-carbon Aluminium Killed Steel During Controlled Rolling And Cooling Process

As a kind of typical Stamping steel, low-carbon aluminium killed steel are widely used in automobile manufacturing industry, construction industry and packaging industry and other fields. It is one of the products having high yield and better economic benefit in metallurgical industry.Aiming at solving the cracking phenomena of low-carbon aluminium killed steel(LACK) occurred in the stamping process in a certain steel company, cracking mechanism was studied. The main factor that results in the crack of the stamping was found. The field production was simulated through laboratory, process parameters were adjusted, and the occurance of cracking was controlled. The ideal process was implied in the field production to solve the problems that stamping performance does not meet the requirements of products.Cup drawing test was adopted to study the cause of cracking resulted by the lack of deep drawing performance. The results show that the toughness of steel is better, fracture is dimple, but thick carbide precipitate in ferrite grain boundary. Micro cracks grow at in the carbide. A sheet of carbide is the main reason that results in the crack of the steel plate, and extension direction of steel plate crack is consistent with carbide precipitation location.Gleeble test was adopted to adjust production process to study the infiltration law and precipitation mechanism of cementite in different process conditions. The results show that finishing temperature and temperature drop speed have great influence on cementite precipitation in the organization. Ferrite grain has a tendency to grow up with the increase of finishing temperature, and cementite precipitate volume also increased significantly. When at a certain finishing temperature, ferrite grain size remains the same, the amount of cementite precipitation increase, the same as net cementite with the drop of the temperature. The deep drawing performance of steel sheet will be affected by the precipitation amount and precipitation location of cementite, and less affected by less precipitation and dispersion distribution of cementite. The best finishing temperature of 850℃ is selected, and the temperature drop speed is 200℃/min. Optimum production process is as follow. Melt temperature is 1250℃, the range of roughing temperature is 1100℃~1050℃, the temperature before finishing is 1010℃±30℃, finishing temperature is 850℃±20℃, and coiling temperature is 650℃±10℃. The optimal technology is applied in the field, and the result is in conformity with the laboratory study. cementite is scattered, which have a minimal impact on deep drawing performance.