Study On The Sensitivity Of Welding Cold Crack Of X100 Pipeline Steels

In this paper,the cold cracking sensitivity and fracture characteristics of X 100 pipeline steel HAZ were studied by using submerged-arc welding with the measurements of Hydrogen diffusion ?the implant test?the testing method of maximum hardness in weld heat-affected zone(HAZ)?the optical microscopy and the fracture morphology.Through the use of deposited metal diffusible hydrogen measurement device unbaked electrode respectively,baked 200 ?× 1h,baked 400 ?× 1h when the diffusible hydrogen content.The results show that with the increasing of electrode drying temperature,the diffusible hydrogen content decreased,the critical fracture stress increases,which increasing the anti-cold cracking susceptibility.At the same time,establishing a hydrogen thermal diffusion factor M equation,according to the thermal diffusion factor M determined hydrogen diffusion welded residual hydrogen content HR,hw to calculate the average thickness of the weld is cooled to 50 residual amount of diffusible hydrogen HR50?,compared with welded measurement,it is more accurately.Under no preheating and 50 preheating with X100 pipeline steel,? at room temperature the critical fracture stress is740 MPa,preheated at 50 ?the critical fracture stress is 800 MPa,thus more than 0.75Rt0.5,that is X100 pipeline steel cold cracking has good performance at room temperature.By preheating can improve the ability of cold cracking.The Fracture morphology of X100 pipeline steel at room temperature shows the fracture of the cleavage and ductile fracture,when preheating at 50?,the fracture morphology is mixed fracture with quasi cleavage and dimple fracture.The maximum hardness used this function with the welding rod at no drying,drying at 200?×1h and 400?×1h,the maximum hardness in weld heat-affected zone of X 100 pipeline steel is322.1HV10,284.4HV10 and 281.0HV10,which less than 350HV10.So it can be avoided the cold cracking.Therefore,X100 pipeline steel in this welding process HAZ microstructure hardening tendency is low,anti cold cracking performance is good.