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.
Highlights
For economic considerations, different materials are usually used in industrial components to maximize their properties
When the temperature increased to 630 °C, fatigue life of the specimen failed in weld metal (WM) was much lower than that of the failures in 10CrHAZ
During the high cycle fatigue (HCF) testing at elevated temperatures, the austenite microstructure of the WM is more sensitive to welding defects
Summary
Different materials are usually used in industrial components to maximize their properties. For high cycle fatigue (HCF), cracks usually nucleate from small defects, which are mainly porosities and non-metallic inclusions in the weld seams. Such defects usually act as a stress raiser and induce highly localized irreversible slip deformations for crack formation. Unlike the dual-phase steel, microstructure in the HAZ is high-gradient distributed due to welding heat effect. Both the proportion between microstructure phases and their mechanical properties vary greatly. INFCO in the HAZ is reported for welded joint at elevated temperatures in our previous study [5], but the mechanism was not fully clarified. The purpose of this investigation aims on getting a better understanding on the formation mechanism of INFCO in the HAZ at high temperature
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