Development of Resistance Welding Process(VI)

Kono, Shusaku; Seki, Masayuki; Ishibashi, Fujio; Hirako, Kazuhiko*; Tsukada, Tatsuya*

The welding condition and the heat-treatment condition were optimized to evaluate welding properties of the martensitic ODS steel cladding tube. The test pieces for evaluation of strength properties of the welded zone were produced by the optimized welding condition. In order to evaluate the strength of the welded zone, the internal creep rapture test, the single axis creep rapture test, the burst test and the tensile test were conducted. Following results were obtained in these tests. (1) Weld ability. An excellent welding characteristic was observed. The micro cracks, etc. were not served at the joint starting point. The joint starting poonts were connected uniformly with errors less than 0.05mm. It is considered that an excellent welding characteristic was result of homogeneous micro structure of cladding material. (2) End plug material. In case of the material of end plug was martensitic ODS steel as same as that of cladding tube, the micro structure and the precipitation state carbide near the welded zone were found to be almost same as that of cladding tube. (3) Optimization of heat-treatment condition. The heat treatments of normalizing (10501C) and tempering (780C) were performed after welding and the micro structure near the welded zone was the isometric structure with low dislocation density, the precipitation state of carbide was uniform as same as that of cladding tube. These heat treatments can relax the residual stress accumulated when welding; it is considered that these heat treatments after welding are indispensable. (4) Strength of welded zone. The strength of the welded zone was found to be equal to that of cladding tube in all the strength tests. Therefore, it is concluded that the welding technology for the martensitic ODS steel is completed.