HCF Failure Modes and Mechanisms of Dissimilar Welds of Martensite/Austenite Metals at Elevated Temperature

Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, PR China

Corresponding author: lfg119@sjtu.edu.cn, lizg@sjtu.edu.cn

Abstract

In this paper, the high cycle fatigue (HCF) behavior and failure mechanism of welded joint for martensite/austenite dissimilar metals were systematically investigated at elevated temperature. The HCF tests were performed at different elevated temperatures of 550, 600 and 630°C with stress ratio of -1. Most tested specimens failed in the heat affected zone (HAZ) of martensite metal, while minor failure occurred on the weld metal (WM) with comparatively more scattered fatigue life. Fatigue crack in the WM initiated from welding defects like porosities and non-metallic inclusions. For failures in the 10Cr-HAZ, fatigue cracks nucleated from the interior matrix of HAZ, which possessed lower hardness. The initiation of cracks was divided into facet type crack origin (FTCO) and rough type crack origin (RTCO). FTCO was observed for specimens tested at high stress amplitude with fatigue life below 10⁷ cycles. Micro-cracks were observed at prior austenite grain boundaries (PAGBs) at high stress level. Micro-cracks preferred to form at martensite lath boundaries and coalesced into macro-crack leading to the formation of RTCO under the condition of lower stress.