15/15 Ti Stainless Steel Welding Process Optimization for GEN IV Nuclear Application in the GEMMA Project Frame

Abstract

This paper deals with activities carried out in the frame of GEMMA project on welded samples of 15/15 Ti stainless steel. The focus of GEMMA project has been on the investigation of material properties and associated welded joints for GEN IV nuclear plants. The RCC-MRx code uses the standard Base Metal Grade nomenclature (EN/ISO), but provides also additional specifications. Titanium stabilized “15-15Ti” stainless steel has been the primary choice for fuel cladding of current fast spectrum research reactor projects. The choice of cladding material is based on past experiences and the availability of material databases from similar steel grades proven in past sodium-cooled fast reactors programs [1-4]. On the basis of ENEA past experience, a strict specification has been written to realize a new heat treatment of this special stainless steel (SS). One of the main problems faced with this material is the high tendency to crack after the welding process. Several preliminary welding tests permitted to select TIG and laser welding processes for the 15/15 Ti SS. This fact because the main applications involve small thicknesses without filler material. The welding of the 15/15 Ti was performed using a fully automated TIG work station at ENEA CR-Casaccia. The base materials to evaluate the welding parameters were 15/15 Ti plates 100 X 170 X 3 mm welded under different shielding gas atmospheres and process parameters arrangements that permitted to obtain good quality joints avoiding catastrophic hot-cracking. The welded samples underwent a mechanical and metallographic characterization and the main results are here presented.