RESEARCH AND PRACTICE ON CRACKING OF 40CR BAR

The surface cracks of 40Cr bars produced by Henan Jiyuan Iron & Steel (GROUP) CO., LTD are investigated by sampling, examining and analyzing, and the reason for surface cracking in the bar is also verified. The results indicate that the contents of silicate nonmetallic inclusion exceed the allowable levels. Combining with productive process, it can be concluded that the silicate nonmetallic inclusion, carbon segregation as well as high drawing speed at the process of continuous casting are the reason for the surface cracking of 40Cr bar. The emergence of surface cracks can be controlled effectively with series measures, such as improving the quality of molten steel smelting, strengthening the test of the top slag and reforming the corresponding equipments, and so on, then the percent defective of steel could be decreased from 0.68% to 0.35%.