Abstract
The strength of electron beam welded joint of the ultra high tensile steel was investigated. This steel has the chemical composition of 0.2%C-7.5%Ni-4%Co-2%Cr-2%Mo-0.1%V and tensile strength of 1470 MPa (150 kgf/mm2) lebel, made by cold rolling, hot rolling or forging.
The tension tests, impact tests and fracture toughness tests were made on each king of steels prepared by various processing: as for welding processes, EB welding and TIG wedling, and as for the procedure of welding and heat treatment, W-HT (Welding then Heat Treatment) and HT-W (Heat Treatment then Welding). Then various mechanical properties were compared to thoes examined on base metal.
Summerized results obtained from this investigation are as follows.
(1) For the tensile properties of welded joint;
They are almost similar to those of base metal in all cases tested.
(2) For the fracture toughness values of weld zone;
In the W-HT condition, weld metal and HAZ show alomst the same value of around 100 MPa √m as that of base metal. But in the HT-W condition, weld metal shows higher value of around 130 MPa √m and HAZ shows lower value of around 60 MPa √m than that of base metal.The lower value of fracture toughness of HAZ is probably due to the precipitation generated by welding heat.
