Microstructural creep damage in welded joints of 316L stainless steel

Abstract

The present work has been undertaken to study creep damage in welded joints. The complex dual phase microstructure of 316L welds are simulated by manually filling a mould with longitudinally deposited weld beads. Most of the moulded specimens were then aged for 2000 hours at 600°C. High resolution scanning electron microscopy was extensively used to examine the microstructure of the welded material before and after ageing. Columnar grains of austenite constitute a matrix in which thin dendrites of 8-ferrite can be found. The ageing generates the precipitation of carbides, resulting in less transformation in the material. Smooth and notched creep specimens were cut from the mould and tested at 600°C under different stress levels. The creep life of the simulated welded material is shown to be lower than that of the base material. Microstructural observations reveal that creep cavities are preferentially located along the austenite grain boundaries. This analysis of intergranular damage on test specimens is conducted to obtain a predictive damage law which could be used to calculate the lifetime of welded joints.

Modelling creep damage in heat affected zone in 321 stainless steel. Part I: Quantitative study of intergranular damage

“…Three other materials are also included, i.e. : the base material AISI 321 [20], the weld material, OKR3U [21] and 316 L(N) material [7]. The two last materials are included because they were also studied using the same method as that one of the present study.…”

“…AISI 321 [20] ϫ ϫ OKR3U [21] ϫ ϫ ϫ 316L(N) [7] ϫ ϫ ϫ HAZ 1 ϫ ϫ HAZ 2 ϫ ϫ ϫ HAZ 3 ϫ ϫ ϫ of these materials was identified on tensile and creep tests on smooth bars tested at 600°C. Then creep tests were performed on notched bars in order to quantify the intergranular damage on these different materials.…”