Analysis and Discussion of Reason for Cracking of Automobile Axle Pipe as Developed during Quenching& Tempering Process

Cracking is found with a certain batch of automobile axle pipes as quenched and tempered.Accordingly the cracking material is overall analyzed in terms of mechanical property, non-metallic inclusion, metallographic structure and SEM morphology,etc.The test results reveal that the reason for the cracking is that the local(Fe,Mn)S composite inclusions aggregate,and extend along the rolling direction in the subsequent rolling process;the dense inclusions destroy the continuity of the structure,and deteriorate the transverse performance of the structure,leading to the cracking of the material at the outer corner with the largest transverse deformation,and the expansion under the effect by the structural stress during the quenching-tempering process.Accordingly it is suggested to reduce Scontent in the steel during the melting process,and improve the size,shape and distribution of the sulfide,and eliminate the entrapped slag,so as to reduce the quantity and local aggregation of the inclusions in the steel.