Abstract
The microstructural changes in the heat affected zone (HAZ) of 9% chromium ferritic steel for manufacturing fossil fired power plant components are investigated. The heat treatment region of 925°C in HAZ was tested as a potential location of Type IV cracks which occur during operation. For comparison of characteristics and material behaviour, the microstructural investigation of simulated specimens of HAZ was carried out at room temperature, i.e. 20°C and at an operating temperature of 600°C, using two Types of specimens: with postweld heat treatment (PWHT) and without PWHT. The test results revealed the presence of precipitates at the grain boundaries in specimens simulated at 925°C with subsequent PWHT. These results confirmed that PWHT is necessary for P91 steel to be integrated into components in service under creep condition.
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