Abstract
Fracture failure caused by hydrogen embrittlement (HE) is a major concern for the system reliability and safety of hydrogen storage vessels, which are generally made of 2.25Cr1Mo0.25V steel. Thus, study of the influence of pre-charged hydrogen on fracture toughness of as-received 2.25Cr1Mo0.25V steel and weld is of significant importance. In the current work, the influence of hydrogen on fracture toughness of as-received 2.25Cr1Mo0.25V steel and weld was systematically studied. Base metal (BM) and weld metal (WM) specimens under both hydrogen-free and hydrogen-charged conditions were tested using three-point bending tests. Hydrogen was pre-charged inside specimens by the immersion charging method. The J-integral values were calculated for quantitatively evaluating the fracture toughness. In order to investigate the HE mechanisms, optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure of BM and WM specimens. The results revealed that the presence of pre-charged hydrogen caused a significant decrease of the fracture toughness for both BM and WM specimens. Moreover, the pre-charged hydrogen led to a remarkable transition of fracture mode from ductile to brittle pattern in 2.25Cr1Mo0.25V steel.
Highlights
In the view of good resistance to corrosion and hydrogen damage, the low alloy chromium-molybdenum (Cr-Mo) steel has been extensively applied in the fabrication of high-pressure vessels such as hydrogen storage vessels in the petrochemical industry
weld metal (WM) specimens were investigated by means of scanning electron microscopy (SEM) and optical microscopy (OM), respectively, to clarify the mechanisms of hydrogen embrittlement (HE)
An obvious two-stage characteristic process consisting of the elastic and plastic deformation stages is observed in the Base metal (BM) specimen, whereas only elastic deformation stage is shown for the WM specimen
Summary
In the view of good resistance to corrosion and hydrogen damage, the low alloy chromium-molybdenum (Cr-Mo) steel has been extensively applied in the fabrication of high-pressure vessels such as hydrogen storage vessels in the petrochemical industry. Hydrogen storage vessels suffer a severe hydrogen environment with high pressure during the operating process This may introduce hydrogen into the alloy steel, leading to a decrease in its mechanical properties, and this phenomenon is called hydrogen embrittlement (HE) [3]. These vessels usually operate under extreme work conditions (e.g., high pressure), which may lead to crack initiation, propagation, and even the fracture failure of welded joints. This can greatly compromise the safety of hydrogen storage vessels. To better understand the intrinsic hydrogen embrittlement (HE) properties, it is of great significance to investigate the influence of pre-charged hydrogen on the fracture toughness of 2.25Cr1Mo0.25V steel and weld without PWHT (as-received). The surface morphology of fracture and the microstructures of BM and WM specimens were investigated by means of scanning electron microscopy (SEM) and optical microscopy (OM), respectively, to clarify the mechanisms of HE
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