Analysis of Causes for Transversal Crack of 4130X Steel Pipe for Making Large-volume Gas Cylinder

In order to find out the causes for the transversal crack of the 4130X steel pipe for making of the largevolume gas cylinder,the fracture surface is analyzed by means of both the macro and micro analyses,while the specimen is tested in terms of chemical composition,mechanical property and metallurgical structure.As a result,it is identified that the crack is a quenching-crack which is caused by the residual stress during quenching of the cylinder.When the pipe is being quenched,the milling scratch of it gets the stress concentrated,which acts as the incentive for the quench crack.Accordingly the steel pipe manufacture process is optimized with measures such as descaling the pipe with the pickling process and reduction drawing so as to avoid the re-occurrence of the problem.