Abstract
2.25Cr-1Mo steel with high strength at high temperatures and superior hydrogen resistance is widely used as power generation boiler material in high-temperature and high-pressure environments. Following the test evaluation of the ASME Boiler and Pressure Vessel Code, specimens from the base metal of a boiler pipe were found to have impact toughness values of 386 and 28J, which are drastically different values. The analysis of the fracture surface of the 28J test specimen revealed MnS inclusions and it was found that cracks were initiated at the inclusions. Observation of the cross-section of the crack propagation front revealed that cracks propagated along the ferrite regions and precipitate voids. Inclusions were also found in the 386J impact specimen. However, the volume fraction of the inclusions was significantly less than that of the 28J specimen. It was also found that the ferrite and carbide content of the 386J specimen was less than the 28J specimen. The reason that the inclusions, ferrite, and carbide content differed in the two adjacent impact test specimens was analyzed. The effects of micro-segregation such as MnS inclusions on ferrite and carbide were compared and analyzed.
Highlights
The 2.25Cr-1Mo Steel is widely used as a power plant boiler pipe material [1,2,3,4] due to its high temperature creep strength, good hydrogen resistance, high toughness at high temperatures, and the ability to withstand high pressure hydrogen atmospheres (12–21 MPa) and high temperatures (400 ◦ C to 450 ◦ C) and pressure use environments
The reason that the inclusions, ferrite, and carbide content differed in the two adjacent impact test specimens was analyzed
For the base metal of boiler tubes, the impact test should be tested under PWHT heat treatment conditions performed after the welding process
Summary
The 2.25Cr-1Mo Steel is widely used as a power plant boiler pipe material [1,2,3,4] due to its high temperature creep strength, good hydrogen resistance, high toughness at high temperatures, and the ability to withstand high pressure hydrogen atmospheres (12–21 MPa) and high temperatures (400 ◦ C to 450 ◦ C) and pressure use environments. The impact toughness of the material is affected by many parameters such duringasa microstructure, quality assurance inspection, it is necessary to analyze the cause and take measures to prevent phases fractions and distributions, test temperature, grain size, impact velocity, recurrence. Through these wetohave found that microsegregation is possibleaffects to prevent thetransformation recurrence by analyzing thestructure cause of the of the impact test and (MnS it inclusion) phase in mztrix andvariation this result is considered to be a it can be utilized as a basic data of the quality defect. Impact test results of 2.25Cr-1.0Mo steel in a power plant boiler pipe to better understand the cause of the variability
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