A robust and reliable test for the recipe of welding products for stainless steels

The austenitic stainless steel AISI 316L(N) (X2CrNiMo17-12-2) with controlled nitrogen content is widely used for manufacture of vessel and primary circuit structures of the 4. Generation sodium-cooled fast reactors. Multi-pass welds with an appropriate filler metal is used to assemble thick components. Solidification cracks may occur in the mushy zone near the melting weld poor during solidification when a liquid film is distributed along grains boundaries and inter dendritic regions and the shrinkage strains across the boundaries cannot be accommodated. It is therefore necessary to prevent this defect using a hot cracking criterion. The approach used in this study is to initiate experimentally a hot crack by a weldability test, and then to simulate these tests to identify a critical strain using a hot crack criterion for the prediction of solidification cracking. Therefore, a hot cracking test (Controlled Restraint Weldability (CRW) test) is proposed in the present study to analyze the susceptibility to hot cracking for base metal 316L(N) and its filler metal 19-15H Thermanit grade. This test is designed to initiate a hot crack in thermal steady state, and then to stop the crack once the local thermomechanical conditions are met. The initiation and stop of the crack depend on external mechanical preload. The material constitutive equations chosen for the material is a visco-plastic model with isotropic and kinematic hardening. The Gleeble thermomechanical tests have been performed at high temperature in order to identify material parameters. The increase of the grain size in the thermally affected zone was modeled and integrated into constitutive equations. The temperature range of melting and solidification of 316L(N) were determine by using the Differential Thermal Analysis (DTA). The analysis of the solidification microstructures were also carried out in order to better understand the phenomenon of hot cracking. Some CRW tests were then simulated by finite element method using the Cast3M and Abaqus software in order to valid the hot cracking criterion and to determine a thermomechanical criterion of hot cracking for 316L(N). (author)